SESAM Sediment Export from large Semi-Arid Catchments: Measurement and Modelling

Transcription

1 SESAM - Sediment Export from large Semi-Arid Catchments: Measurement and Modelling SESAM Sediment Export from large Semi-Arid Catchments: Measurement and Modelling Interim Report /12/2006 E. N. Müller 1, T. Francke 1, G. Mamede 1,5, R. J. Batalla 3,4, J.C. de Araujo 5, A. Güntner 2, A. Bronstert 1 1 University of Potsdam, Germany 2 GeoForschungsZentrum Potsdam, Germany 3 Universitat de Lleida, Spain 4 Forestry Institute of Catalonia, Solsona, Spain 5 Universidade Federal do Ceará, Fortaleza, Brazil

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3 TABLE OF CONTENTS 1 Introduction 6 2 Status of the monitoring campaigns Overview Monitoring at the Ribera Salada Catchment Monitoring at the Isabena Catchment Monitoring at the Aiuaba and Bengue Catchments Fieldwork campaigns in Fieldwork campaigns in Status of the modelling development Overview Landscape unit mapping program for the Isabena Catchment Bedload modelling for the Ribera Salada River Small lake modelling option 25 4 SESAM Publications Overview Abstract collection 31 5 SESAM Poster Presentations Overview Poster collection 38 6 Theses and student projects within the SESAM project 48 7 Conclusion and future tasks 50 REFERENCES APPENDIX 1: SESAM Study Areas Appendix 1-A: Study areas in Spain Appendix 1-B: Study areas in Brazil APPENDIX 2: WASA Modelling Approach Appendix 2-A: Hillslope modules Appendix 2-B: River modules Appendix 2-C: Reservoir modules 2

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5 PARTNERS OF THE SESAM PROJECT The SESAM project is funded by Deutsche Forschungsgemeinschaft DFG. The following partners are involved: Institute of Geoecology University of Potsdam Postfach Potsdam Germany Website GeoForschungsZentrum Potsdam Telegrafenberg Potsdam Germany Website Department of Environment and Soil Sciences University of Lleida Lleida, Catalonia Spain Website Forest Technology Centre of Catalonia Pujada del Seminari Solsona (Lleida) Spain Website Department of Hydraulic and Environmental Engineering Federal University of Ceara, Fortaleza Campus do Pici Fortaleza, Ceara Brazil Website 4

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7 1 Introduction In dryland environments, water availability for human, agricultural and industrial usage often relies on the retention of surface waters in artificial reservoirs. Erosion of the land surface and deposition of the eroded material in such reservoirs threatens the reliability of reservoirs as a source of water supply and often has adverse effects on the local population. The SESAM project (Sediment Export from Semi- Arid Regions: Measurement and Modelling) deals with severe soil-erosion problems and resulting sedimentation of reservoirs that commonly occur in dryland regions of Spain and NE Brazil. The SESAM project is a DFG (Deutsche Forschungsgemeinschaft) funded, joint research project of institutions in Germany (University of Potsdam, GeoForschungsZentrum Potsdam), Spain (University of Lleida, Forest Technology Centre of Catalonia) and Brazil (University of Ceara, Fortaleza). The SESAM project objectives are first, the monitoring of water and sediment fluxes within meso-scale dryland catchments and second, the development of the WASA model system (Güntner 2002 and Güntner and Bronstert 2003, 2004), that enables the assessment of sediment production at the hillslope scale, the sediment transport in river systems and sediment retention in reservoirs for catchments in semi-arid and sub-humid regions. The necessary data for model development and application are being derived from extensive field data collection programs within experimental catchments, dryland rivers and reservoirs of Spain and NE Brazil. This interim project report provides a comprehensive summary of the work that has been carried within the SEAM project during the first two project years since December 2004 and is an extension of the Annual Report 2005 (Mueller et al. 2005). Chapter 2 in combination with Appendix 1 gives a detailed description on the study sites and reports on the current status of the monitoring campaigns on water, suspended sediment and bedload fluxes at the study locations in the Isabena / Esera and Ribera Salada Catchments in the Pre-Pyrenees of Spain and the Aiuaba and Bengue Catchments in NE Brazil. In addition, it summarises the field campaigns to the Spanish and Brazilian study catchments that were carried out in 2005 and 2006 to investigate specific hydrological and sediment-transport processes related to reservoir sedimentation, the assessment of high-intensity erosion rates on so-called badland regions (during a three-months field campaign in Spain), the importance of temporary sediment storage in the river system and other geomorphological, hydrological and vegetation parameters that were required for describing sediment export processes at the meso-scale. Chapter 3 in combination with Appendix 2 describes the WASA modelling approaches that are employed to simulate the transport of water and sediment on the hillslopes and in the river and to model the sedimentation in large reservoirs as well as the latest amendments to the modelling framework. This chapter contains current research foci on the implementation of a landscape unit mapping program for the semiautomated parameterisation of meso-scale hillslopes (Francke et al. in revision), a bedload modelling study of small flood events in the Ribera Salada River (Mueller et al. submitted) and a new small lake options to account for the trapping capacity of numerous micro-reservoirs in the Brazilian dryland catchments. Chapter 4 contains a list of peer-reviewed publications on SESAM research and the corresponding abstracts followed by Chapter 5 with poster presentations at international conferences. Chapter 6 comprises a summary on current PhD and student projects are directly linked to the scope of the SESAM project. Chapter 7 gives an outlook on future work for

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9 2 Status of the monitoring campaigns 2.1 Overview The SESAM project concentrates on the monitoring of soil-erosion and sedimentation processes at the hillslope, river and reservoir scale in the Isabena/Esera and the Ribera Salada Catchments in the subhumid Pre-Pyrenees of northeast Spain and the Aiuaba and the Bengue Catchments in the semiarid regions of north-east Brazil. Appendix 1 contains detailed descriptions of the study areas including information on topography, climate, vegetation, geology and the installed monitoring equipment for the continuous measurement of water and sediment fluxes. Newly installed monitoring equipments of the SESAM project are the bedload trap in the Ribera Salada River for the continuous monitoring of bedload transport rates, the turbiditymeter probe and ISCO sampler in the Isabena River for the continuous monitoring of suspended sediments, and automatic sediment samplers within the Aiuaba and Bengue Catchments for the measurement of suspended sediments in the ephemeral river network. This chapter comprises a summary account on the on-going collection of monitoring data and the field campaigns that were carried out in 2005 and 2006 to investigate specific hydrological and sediment-transport processes and geomorphological, hydrological and vegetation parameters required for model parameterisation. 2.2 Monitoring at the Ribera Salada Catchment The objective of the monitoring campaign in the Ribera Salada River is the analysis and modelling of the sediment yield, sediment transport, and related fluvial processes in a gravel-bed river draining a forested catchment. Continuous measurement and recording of sediment transport process, including both suspended sediment and bedload are available since July Key hydraulic parameters (i.e. water depth) and complementary variables (i.e. water temperature) are also recorded (Table 1). Table 1 Monitored variables at the Ribera Salada control sections Variables Equipment Cogulers a Canalda a Inglabaga b (2.6 km 2 ) (65 km 2 ) (110 km 2 ) Water stage 1 Pressure sensor Turbidimeter 2 1 Suspended sediment Automatic sampler Water-stage sampler 3 1 Bedload Pit-traps 2,4 3 Water temperature Thermal-probe as surrogate for discharge continuous record was done. However data exists also for small floods during Spring water and sediment sampling during floods 4 bedload sampling during floods a in operation since 1998 b station constructed in July 2005, water stage and suspended sediment measured since November 2005; bedload fully measured since July 2006 after successful calibration of the traps 8

10 Besides the installation of the sediment transport station at the Ribera Salada River for the continuous measurement of water and sediment transport, river channel-related measurements are routinely taken, such as grain-size samplings (surface, subsurface and patches). Precipitation is continuously measured at three different locations in the catchment. Recording hydrological and sedimentary data is of essential use to understand sediment transport process and to estimate sediment yield of the catchment, as well as for modelling purposes. As an example, water depth, and suspended sediment and bedload transport at the Inglabaga monitoring section during summer 2006 floods are shown in Figure 1. Water depth (m) July 16th Flood August 15th Flood Bedload transport rate (dry weight in g/ms) SA SB SC :40:00 16:45:00 16:50:00 16:55:00 17:00:00 17:05:00 16/07/ /07/ /07/ /07/ /07/ /07/ Turbidity (NTU) Time (5 minutes steps) Time (5 minutes steps) Figure 1 Water depth (left), suspended sediment (right bottom) and bedload transport (right top) recorded at the Inglabaga monitoring section during Summer 2006 floods. 2.3 Monitoring at the Isabena Catchment The objective of the measurement program at the Isabena River is the monitoring of the sediment transport from a mountainous catchment on highly erosive sediments, and the estimation of the sediment yield to the Barasona Reservoir. Continuous measurement and recording of suspended sediment transport, both during baseflows and floods are taken since May Key hydraulic parameters (i.e. water depth, rainfall intensity) are also recorded (Table 2). Table 2 Monitored variables at the Isábena river control sections Capella a Variables Equipment (420 km 2 ) Water stage 1 Water-stage recorder 2 1 Capacity sensor 2,5 Turbidimeter 2 1 Automatic sampler 3 1 x Suspended sediment US59 Depth Integrated Sampler 4 Manual Sampling 4,5 Metal bars 6 Cabecera b (146 km 2 ) Villacarli c (42 km 2 ) 1 1 Rainfall Rainfall 5 1 x x

11 1 as surrogate for discharge 2 continuous record 3 water and sediment sampling during floods 4 bedload sampling during floods 5 in operation since September temporal storage of sediment in the riverchannel a gauging station operated by the Ebro Water Authorities since 1951 b including a rain-gauge at les Paúles c rain-gauge at Villacarli Measuring hydrological variables and sediment transport at the Isabena control section is of fundamental importance to estimate the amount and frequency of fine sediment deposition in the Barasona Reservoir. Figure 2 shows the turbidity record of the period May 2005 May 2006, together with the statistically significant (p<0.01) rating curve between discharge and suspended sediment concentration for Spring 2006, and the seasonal sediment yield of the basin. Turbidity Terbolesa (NTU) Turbidity record May May Time Temps (days) (dies) Concentració (g/l) SSc (g/l) 100,0 SSc= Q C = 0,0086 Q ,0611 r R 2 = 2 =0.61 0,6142. Significatiu p <0,01 10,0 1,0 0,1 0,0 0,0 Annual Runoff and Sediment Load (%) 0,01 0, Discharge Cabal (m3/s) (m 3 /s) A (m3) SS (t) Css (g/l) Suspended Sediment Concentration (g/l) Figure 2 Turbidity record May 2005-May 2006, rating curve Q-SSc and seasonal sediment yield in the Isabena River 0 Spring Summer Autumn Winter Mean Monitoring at the Aiuaba and Bengue Catchments An extensive database has been compiled on climate and hydrological data such as rainfall intensities, evaporation rates, interception rates and reservoir level data for the Boqueirao reservoir at the outlet of the Aiuaba Catchment for the time period Suspended sediment concentration was collected during six rainstorm events for the rainy season of 2006, as summarized exemplarily in Table 3. The hydrograph of a corresponding rainstorm event is depicted in Table 3. Table 3 Suspended sediment concentration at the outlet of the Aiuaba Catchment, Brazil Date Sediment conc. [mg/l] 20/03/ /03/ /04/ /04/ /04/ /05/

12 Figure 3 Rainfall and Boqueirao reservoir level for the rainstorm event on the 09/04/06, Aiuaba Catchment A three-month field campaign is planned for the rainy season in 2007 to complement the continuous monitoring equipment with field data on suspended sediment concentration in runoff at the outlet of the Aiuaba Catchment and data on the sediment and water discharge dynamics in the ephemeral river system of the Bengue Catchment during individual rainstorm events. 2.5 Fieldwork campaigns in 2005 Extensive fieldwork campaigns have been carried out to collect data for the parameterization and testing of the water and sediment transport models within the WASA modelling framework. The campaigns in 2005 were already described in detail in the Annual Report of the SESAM project (Mueller et al. available at workingpapers/annual_report_sesam.pdf). Processes and properties under investigation included: Measurement of hillslope parameters related to water- and sediment export in the Esera Watershed, NE Spain (publication under revision by Francke et al. 2006); Remote-sensing-based characterization of land-cover and terrain properties of the Bengue watershed in semi-arid northeast of Brazil (diploma thesis by Benjamin Creutzfeldt); Derivation of representative river stretches: A field survey of a mountain river in the Pyrenees, the Isabena River in NE Spain (published by Mueller et al. 2006a); Sedimentological characterization of the Barasona Reservoir, NE Spain (published by Mamede et al. 2006); Characterisation of the Bengue Reservoir in the semi-arid north-eastern part of Brazil; Classification of badlands regarding their morphological characteristics in the Isabena Catchment (diploma thesis by Katharina Appel). The information in the brackets refers to the corresponding publication or MSc diploma thesis for which the field data have been collected. 11

13 2.6 Fieldwork campaigns in 2006 Several large fieldwork campaigns were carried out at the study sites in Spain and Brazil during The field studies investigated missing links for the monitoring and modelling analysis such as: (1) dynamics of sediment-transport on badlands for individual rain-storm events in the Isabena Catchment over a time period of 3.5 months, (2) estimation of the spatial distribution of the temporary sediment storage in the Isabena River, (3) measurement of land-cover properties for the Bengue Catchment, (4) characterization of micro-reservoirs in the Bengue Catchment and (5) a new bathymetrical survey and analysis of the depositional history of the Barasona Reservoir Evaluation of erosion hotspot dynamics on badlands in the Villacarli Basin, Isabena, Spain by Till Francke Time: Location: Villacarli Valley, Isabena Catchment, Huesca, Aragon, Spain (ca. 80 km north of Lleida) Motivation: Studies of various authors (e.g. Fargas et al., 1997; Martínez-Casasnovas and Poch, 1997) indicated that the major amount of sediments reaching the Barasona reservoir at the outlet of the Esera/Isabena Catchments originate from the Internal Ranges and the Intermediate Depression, namely from badland formations. A major part of the badlands is concentrated in the sub-basin called Villacarli. No monitoring data are currently available for water and sediment fluxes from both individual badland hillslopes and from the entire badland valley. In order to obtain calibration and testing data for the runoff and suspended sediment concentrations as required for model parameterisation, the following objectives were pursued: 1. Evaluation of sub-catchment event response (water and sediment export) at several spatial scales within the Villacarli Badland Valley; 2. Assessment of long- and medium-term sediment yield of an individual badland source areas. Methods: Hydrological and sediment response of the Villacarli and the adjacent Cabecera sub-catchments were monitored in 2006 for individual rainstorm events over a time period of 3.5 months with automatic equipment and by manual sampling. For this purpose, water stage loggers were installed at the outlet of a small hillslope catchment and at the outlets of the Villacarli and the Cabecera catchments (A, B, C in Figure 4). For all rainstorm events from the end of August until the middle of December 2006, the hydrographs were recorded continuously and the suspended sediment content was sampled by taking manual water samples with a time resolution of ca minutes. In addition, an automatic pluviograph was newly installed within the Villacarli Valley to provide high-resolution rainfall intensity data (R in Figure 4). 12

14 C R A B Figure 4 Location of instruments in the Villacarli sub-basin Figure 5 Raingauge Villacarli (R), gauge B1 (C), gauge Villacarli (A), gauge Cabecera (B) A medium-term erosion budget for an elementary badland was assessed at the hillslope scale by exploiting a sediment trap formed during the construction of a road in the 1980s. A drilling campaign of the trapped sediment in which the depth of deposited sediments was assessed at about 60 locations (Figure 6) yielded the total deposited sediment volume over a time period of ca. 20 years. Figure 6 Drilling scheme to assess volume of sediment in trap at the outlet of a badland hillslope 13

15 Complementing this data with the readings of the erosion and deposition pins installed in the previous year (see Annual Report 2005, Chapter 4) and the event-based water and sediment monitoring data for the badland will allow the computation of the mean annual sediment yield of this badland hillslope. Results: For all sub-tasks, data analysis is still being carried out and complemented by on-going measurements. Monitoring of runoff and suspending sediment showed that high temporal variability in discharge and sediment concentration exist (Table 4). No simple relation between discharge and sediment concentration exists. The relation to multiple auxiliary datasets (erosivity of rain, rate of change, etc.) is currently being analysed. Preliminary calculations for the sediment trap result in approx m 3 of sediment accumulated within roughly 20 years. This figure compares well to the increase of volume by 70 m 3 from 09/05 untill 09/06. Heavy rainstorms during September 2006 resulted in m 3 of sediments deposited in the trap. Assuming a trapping efficiency of 10 % (based on pin data) this equals to a sediment yield of 6 kg m -2 a -1 or 6000 t m -2 a -1 for badland areas within the Isabena Catchment. Table 4 Range of discharge and suspended sediment concentration for the monitoring sites B1, Villacarli, Capella Monitoring site Discharge [m 3 /s] Sediment concentration [g/l] B Villacarli Cabecera Estimation of the spatial distribution of temporary sediment storage in the Isabena River, Spain by Eva Nora Müller Time: Location: Isabena River, Huesca, Aragon, Spain (ca. 80 km north of Lleida) Motivation: This study investigates the sediment transfer and storage processes in the Isabena River by quantifying the total amount and its spatial distribution of fine sediments stored in the riverbed. The fine sediments originate from the badland areas of the Villacarli Valley and are transported via the river to the Barasona Reservoir causing severe sedimentation. Figure 7 shows as an example an ephemeral river stretch in which sediment from badland areas was deposited after a large rainstorm event. The outcome of the study will enable to determine the role and the order of magnitude of in-channel storage in the annual sediment budget of the catchment. The total storage volume should also allow estimating the residence time of fine sediments in the river system. In addition, the study will enable a numerical quantification of sediments that are deposited in the floodplains by relating the riverbed form for bankful stage to the annual discharge dynamics as measured at the gauging station at Capella. The study thus attempts to contribute to the currently limited knowledge of the role of temporary sediment storage in watersheds that experience extreme soil-erosion stress. 14

16 Figure 7 Temporary sediment storage in ephemeral riverbed in the Isabena Catchment Methods: The Isabena River is characterised by a very heterogeneous distribution of riverbed parameters such as bankful depth, widths and riverbed particle size distribution. Sampling was therefore carried out with intervals of 100- to 500-metres from the outlet of the Villacarli Valley to the confluence of the Isabena River with the Esera River over a total river length of ca. 33 km. For measuring the fraction of a river transect filled with fine badland sediments, the sampling procedure after Hilton and Lisle (1993) was employed as depicted in Figure 8. Figure 8 Spatial sampling procedure of temporary river storage (after Hilton and Lisle 1993) The high spatial resolution data on riverbed storage volume are currently be related to estimates of riverbed slope, geology and cross-sectional characteristics to study geospatial units and pattern formation of the river system Measurement of land-cover properties for the estimation of hydrological and erosionrelevant model parameters for the Bengue Catchment, Brazil by Till Francke Time: Location: Bengue Catchment, Municipal Aiuaba, Ceara, Brazil (ca. 450 km west of Fortaleza) Motivation: The erosion routine of the hillslope module of the WASA model employs the USLE crop/cover factor (C-factor) for the parameterisation of erosion properties, either used as the (M)USLE-factor or 15

17 additionally for an estimate of a sediment delivery parameter Kv. Considering the prevalent importance of the C-factor and the scarcity of literature values for the specific quasi-natural vegetation typical for the Bengue study area, a fieldwork campaign was carried out to collect data on land-cover properties to improve model parameterisation. Measurements were conducted for each of the nine dominant land use classes of the Bengue Catchment, as was previously defined by Creutzfeld (2006). The transect locations were chosen to be typical and representative for their class and to show a reasonable degree of homogeneity. Along the transects, data were collected at constant intervals to allow the estimation of the C factor for USLE (Wischmeier, 1978; Dissmeyer & Foster, 1980) and RUSLE (Renard et al., 1997). The following parameters were measured: vertical canopy distribution (average canopy height, mean minimum drip height, etc.), fraction and type of ground cover, thickness of organic layer, estimate of depression storage, root mass density and random roughness. The data was collected following the LCTA-line-transect scheme (Tazik, 1992), supplemented by surface roughness measurements with a profile meter, skyward looking images for the determination of canopy cover and the assessment of the MRZ-class (Morphological Runoff Zone) according to Bracken (2005) as a qualitative indicator of soil erosion. Results: With the exception of vertical canopy distribution and random roughness, all parameters show a high degree of variability within the same land-use class. The parameters were used to compute C-factor values and Manning s roughness coefficient. The resulting values are summarized in the table below. Table 5: Values for C-factor and Manning s derived for the different land-use classes Land-cover class C-factors (calculated) Manning s n Agriculture Agropecuaria Caatinga arbustiva-arbórea conservada Caatinga arbustiva-arbórea pertuba Floresta seca Vegetacao de tabuleiro regeneracao The difficulty of capturing temporal and spatial variability of the investigated parameters was identified as a major challenge in the described campaign. The latter is currently tried to be addressed with the help of remote sensing data based on the ground truth collected during the fieldwork. The suitability of the results for a publication is currently being evaluated Characterization of micro-reservoirs for the analysis of their effects on the water and sediment balance of the Bengue Catchment, Brazil by George Mamede Period of time: Location: Bengue Catchment, Municipal Aiuaba, Ceara, Brazil (ca. 450 km west of Fortaleza) 16

18 Motivation: A preliminary survey of small micro-reservoirs was carried out in the Bengue Catchment to enable an assessment of their sediment trapping capacity during rainstorm events. The employed methodology consisted of analysing the geometric properties of six micro-reservoirs and giving a description of the physical properties of the deposited sediment and suspended sediments. Methods: In order to obtain the geometric characteristics of the reservoirs, the following methodology was adopted: firstly, measurement of the contour of the lake using a GPS; second, determination of the difference between the current water level and the maximum water level at the emergency spillway; and third, estimation of the current water depth at the deepest point of the reservoir, provided either by the reservoir s owner or by locals. For the Riacho Verde Reservoir, the geometry was survey in detail by using a theodolite during very low reservoir level. Sediment samples were collected at the open-air exposed area and immediately downstream of each studied reservoir to determine their physical properties such as grain size distribution, soil permeability, wet and dry bulk density, dry bulk density of compacted sediment, and real density. Measurements of suspended sediment concentration in the studied reservoirs were carried out by sampling the water-sediment mixture by using a Van Dorn bottle. Results: Table 6 shows the geometrical characteristics of the surveyed micro-reservoirs, the detailed geometry of the Riacho Verde reservoir is presented in Figure 9. Figure 9 Topography of the Riacho Verde Reservoir, Bengue Catchment, Brazil 17

19 Table 6 Geometrical characteristics of the surveyed micro-reservoirs Name Current depth (m) Maximum depth (m) Perimeter (m) Area (m 2 ) Year of dam construction Gameleira* not informed Mulungu Malhada* not informed Chico Mancambira not informed Retiro before 1968 Riacho Verde not informed Sao Benedito * data provided by Marjella de Vries In Figure 10, the results on grain size distribution of the sediment deposited upstream the small reservoirs are presented. A strong variability of grain size distribution was observed. The sediment deposited in the Riacho Verde and Retiro reservoirs is predominantly clay, with percentages of 55% and 35%, respectively. In the Sao Benedito reservoir and the Chico reservoir, a predominant presence of silt was observed (52% and 44%, respectively). For the other reservoirs, a higher percentage of sand was obtained varying between 70% and 93%. Concerning the sediment collected downstream of the reservoirs, the results indicate that the material is composed mainly of sand (70% to 93%). It can be concluded that the sediment deposited immediately downstream of the reservoirs is not characterized by the material transported in suspension out of the reservoir when spillway overflow occurs. The main sediment source in that case is the lateral sediment contributing during surface runoff. Percent finer (%) S 01 S 02 S 03 S 04 S 05 S 06 S 07 S 08 S 09 S 10 S 11 S Grain size (mm) Figure 10 Grain size distribution of the sediment collected upstream and downstream of the microreservoirs Table 7 summarises the results on suspended sediment concentrations in the micro-reservoirs. The overall low sediment concentrations can be explained by the fact that no sediment fluxes into the reservoir existed at the time of measurements. Therefore, it is fundamental to measure not only the suspended sediment concentration of the sediment input and output in the reservoir, but also the size distribution of sediment inflow and effluent size distribution in order to enable the assessment of the impact of the impoundment on the sediment transport. 18

20 Table 7 Suspended sediment concentration of the water samples of the micro-reservoirs Samples Fixed solids (mg/l) Volatile solids (mg/l) Total solids (mg/l) A A A A A A Bathymetrical survey of the Barasona Reservoir, Spain by George Mamede, Ramon Batalla, Damia Vericat Time: May 2006 Location: Barasona Reservoir, Huesca, Aragon, Spain (ca. 80 km north of Lleida) Motivation: A bathymetric survey of the entire Barasona Reservoir was carried out in may 2006 to evaluate the changes of depositional and degradation patterns and amounts in the reservoir in comparison to the previous bathymetrical surveys from the years 1998, 1993 and A Thales Navigation GPS (double frequency, 1cm-resolution) and an Echo-sounder Lowrance LCX-15CI (200 khz frequency, during the sounding) were used to record a total number of 1420 data points within the reservoir area. Figure 11 Bathymetric survey 2006 of the Barasona reservoir (UTM Zone 31, European Datum 1950): (a) two navigation routes, (b) bed elevation change map produced by comparison of elevation values of reservoir bed obtained from the 2006 survey to the 1998 survey and (c) bathymetric survey. Results: A procedure was adopted to supplement elevation data from the bathymetrical survey from 1998 to those locations of the 2006 survey where no information were available, particularly at the upper part of the Barasona reservoir. Figure 11 presents a) the navigation routes along the Barasona Reservoir, b) 19

21 the height difference map between the survey from 2006 and 1998 and c) the derived digital elevation model for the Barasona. Topographic maps of the Barasona reservoir derived from the bathymetric surveys of 1998, 1993, 1986 and 2006 are depicted in Figure 12. Major changes of the reservoir geometry can be observed at the downstream part of the reservoir near the dam, where deposition of fine sediment takes place, particularly during flood events. Deposition of coarse material can be found mostly at the upstream part of the reservoir, in the deepest points on the bed (thalweg), following the path of the original river. However, at the most upstream part of the Barasona reservoir, the reservoir bed elevation does not change significantly. There, the coarse sediment is temporarily deposited during low water discharges, but it is immediately transported into the reservoir, whenever flood events occur. Figure 12 Bathymetric surveys of the Barasona reservoir (UTM Zone 31, European Datum 1950 EP): (a) in 1986; (b) in 1993; (c) in 1998; and (d) in 2006 The 2006 bathymetric survey indicates a storage capacity reduction of 26 Mm 3 caused by sediment deposition in the Barasona reservoir since According to Table 8, a sedimentation rate of 0.24 Mm 3.year -1 was observed in the Barasona reservoir for the period For the period , the overall sedimentation rate decreased strongly to values below 0.03 Mm 3.year -1 due to reservoir management actions when sediment deposited in the reservoir was released during flushing 20

22 in The highest sedimentation rate occurred in the period , which may be explained by the fact that no sediment control measures were applied to flush the incoming sediment out because the bottom outlets were completely obstructed by sediment previously deposited. After 8 years of sediment deposition in the Barasona reservoir without using the bottom outlets ( ), the Spanish authorities decided to dredge the sediment deposited near the dam in order to ensure the operation of the bottom outlets and, at the same time, flushing out as much sediment as possible. This procedure was performed after the irrigation season in three consecutive years ( ). About 4,2 Mm 3 of sediment was flushed out during these three years. Finally, almost the same amount of sediment (4,3 Mm 3 ) was deposited again in the Barasona reservoir in the time period between 1998 and Table 8 Storage capacity reduction and sedimentation rate Year Storage capacity (10 6 Mm 3 Storage capacity reduction ) (10 6 Mm 3 ) Sedimentation rate (Mm 3 /year) * (-4.18)** (-0.84)** * a maximum storage capacity of 59,59 Mm 3 corresponding to the initial maximum reservoir level in 1932 ( m) was used ** negative values indicate that the sediment release is greater than the sediment deposition in the period 21

23 3 Status of the modelling development 3.1 Overview The modelling objective of the SESAM project is to set up and validate the WASA model for the quantitative assessment of sediment production on hillslopes, sediment transport in the river system, and sediment retention in reservoirs. The focus is laid on meso-scale river basins (several hundreds to thousands of square kilometres in size) in dryland regions, particular for the Isabena/Esera and Ribera Salada Catchments in Spain and the Aiuaba and Bengue Catchments in Brazil. For this purpose, the hydrological WASA model (Model for Water Availability in Semi-Arid environments) developed by Güntner (2002) and Güntner and Bronstert (2003, 2004), which has been adapted to specific environmental characteristics of semi-arid areas, was extended with components representing erosion and sediment transport processes at the hillslope, river and reservoir scales. The hillslope component was extended to include sediment-transport processes using the MUSLE approach. The existing river routine of the WASA model of water flow was modified to include a spatially distributed, semiprocess-based modelling approach for the modelling of water and sediment transport through the river network. Furthermore, the WASA model was extended to include a reservoir module that deals with the transport of water and sediment as well as sedimentation processes in reservoirs. A full account of the implemented routines and sub-modules was given in the Annual Report 2005 of the SESAM project (Mueller et al. 2005) and is reproduced in an updated version in Appendix 2. A manual for the WASA model is available to facilitate model parameterisation (Mueller et al. 2006b). Currently, preliminary model parameterisations are available for all study catchments of the SESAM project. Testing and modelling studies considering climate change and land-use scenarios are planned for the third project year. Recently developed modelling tools within the WASA modelling framework include a landscape unit mapping program for hillslope delineation (LUMP), a package of bedload transport modelling routines and a small lake modelling option to include the trapping effects of micro-reservoirs and are described in the following sections. 3.2 Landscape unit mapping program for the Isabena Catchment In hydrological and soil erosion modelling at large spatial scales such as the Isabena/Esera and the Bengue Catchments, semi-distributed approaches may use representative hillslope profiles to reproduce landscape variability. Until now, the process of delineating landscape units as homogeneous parts of the landscape with regard to their terrain, vegetation and soil properties required expert knowledge and familiarity with the study area. In addition, the delineation procedure was often highly time-consuming and included a high degree of subjectivity. To overcome the related uncertainties of spatial parameter space representation, a semi-automated approach for the delineation of landscape units, the derivation of representative toposequences and their partitioning into terrain components called LUMP (Landscape Unit Mapping Program) was developed by Francke et al. (submitted) to 22

24 facilitate the parameterisation process of the WASA model. The LUMP tool incorporates an algorithm to retrieve representative catenas and their attributes for elementary hillslope areas based on elevation and other key spatial data frequently required as environmental model input, e.g. vegetation and soil data. The derived data is processed in a way that allows easy portability to a database system facilitating the storage and modification of the data and the generation of the WASA input files. In 2006, LUMP was extended with a method that computes representative catenas on an areal extent of elementary hillslope areas. Furthermore, an option for successive classification for each included attribute was added. A complete documentation of LUMP and its capabilities has been submitted for publication (Francke et al., submitted, see Section 4.2 for SESAM publication abstract). The improved LUMP-version was used in the parameterisations of the Ribera Salada and the Isabena/Esera catchments. Outside the SESAM project, LUMP was applied to research catchments in Peru and India. 3.3 Bedload modelling for the Ribera Salada River The WASA model has been extended to include routines for the modelling of bedload transport rates in the river system. Bedload transport is a key process for sediment mass movement in the Ribera Salada River, however, it is less relevant for the sediment fluxes of the Isabena/Esera and the Bengue Catchments which are dominated by suspended sediment transport. Bedload transport formulae have been developed for streams in different geographic and climatic settings, the magnitude of water discharge ranging between < 1 to > 3500 m 3 /s, differing riverbed slopes and different riverbed compositions, which are commonly divided into gravel-bed and sand-bed rivers with different particle size distributions typically characterised by the median D 50 (Reid and Dunne 1996). The following five bedload transport formulae have been selected for the implementation into the WASA modelling framework as their boundary conditions - such as the appropriate range of water discharge, riverbed texture and slope - resembled closest the conditions of a small, mountainous, gravel-bed stream like the Ribera Salada River. 1. Meyer-Peter and Müller (1948) q s 8 ( τ τ = g ρ 1.5 crit ) with: τ = ρ g d S and τ = ( ρ ρ) g D50 Equation 1 crit s where q s is sediment discharge in submerged weight (g/ms), τ and τ crit are the local boundary shear stress and critical shear stress for sediment entrainment (kg/m*s 2 ), g is the acceleration due to gravity (m/s 2 ), ρ s and ρ are the sediment (2650 kg/m 3 ) and fluid (1000 kg/m 3 ) densities, D 50 is the median sediment particle size (m), d is the mean water flow depth (m) and S is the slope given (m/m). The formula was developed for both uniform and non-uniform sediment, grain sizes ranging from 0.4 to 29 mm and river slopes of up to Schoklitsch (1950) q ρs ρ = ) 1000 ρ 1.5 s 2500 S ( q q crit s 23

25 with: q crit ρs ρ = 0.26 ( ) ρ D50 7 S 6 Equation 2 where q and q crit is the unit water and critical water discharge (m 2 /s) and all other variables as stated above. The equation is applicable for non-uniform sediment mixtures with D 50 values larger than 6 mm and riverbed slopes varying between and 0.1 m/m. 3. Smart and Jaeggi (1983) q s * 1.6 τ crit ρs = 4.2 q S (1 ) /( 1) 1000 ( ρ ρ) * s τ ρ * d S * dcrit S with: τ = and τ crit = Equation 3 ρs ρ s ( 1) D50 ( 1) D50 ρ ρ where τ * and τ * crit are the dimensionless local and critical shear stress (-), d crit is the critical flow depth for initiation of motion (m), and all other variables as stated above. According to Batalla et al. (2005, p. 507), bedload transport at the Ribera Salada commences at a critical discharge of 2 m 3 /s, which corresponds to a critical flow depth of 0.3 m. Smart and Jaeggi (1983) developed the formula by using the data of Meyer-Peter and Müller and additional laboratory experiments as an extension to steep stream slopes for riverbed slopes varying between m/m with D 50 values comparable to the ones of the Meyer-Peter and Müller equation. 4. Bagnold (1956) * * * ρ s q s = τ ( τ τ crit ) (( 1) g D50 ) 1000 ( ρ s ρ) Equation 4 ρ reshaped by Yalin (1977), where all variables are as stated above and applicable for sand and fine gravel and moderate riverbed slopes. 5. Rickenmann (1991, 2001) q s D90 = 3.1 ( ) D τ *0.5 ( τ * τ * crit ) Fr 1.1 ρ s ( 1) ρ 0.5 ρ s (( 1) g D50 ρ 3 ) ( ρ s ρ) with: Fr v 0.5 = ( ) Equation 5 g d where Fr is the Froude number of the flow (-), D 30 and D 90 are the grain sizes at which 30 and 90 % by weight of the sediment is finer (m), and v is the water flow velocity (m/s). The equation was developed for gravel-bed rivers and torrents with bed slopes between 0.03 and 0.2 m/m and for D 50 values comparable to the ones of the Meyer-Peter and Müller equation in the lower slope range with an average D 50 of 10 mm in the higher slope ranges. The newly implemented bedload transport routines of the WASA model were used to model and reproduce measured bedload rates for five storm events at the Ribera Salada Watershed. The resulting 24

26 publication by Mueller et al. (submitted) investigated the influence of the spatial scaling of the D 50 parameter on the model outcome (see Section 4.2 for SESAM publication abstract). 3.4 Small lake modelling option The presence of micro-reservoirs has a large impact on the water and sediment balance of meso-scale watersheds as they act as a potential sediment trap and a storage space of water and sediment fluxes between rainstorm events. For the Bengue Catchment, for example, about 160 small micro-reservoirs were identified through satellite imagery analysis by Creutzfeld (2006) (Figure 13). The original WASA model did not account for sediment storage in small micro-reservoirs. Therefore, a small lake modelling option was implemented into the WASA modelling framework to account for the storage and trapping capacity of water and sediment fluxes in small micro-reservoirs. The following paragraphs give a short description of the newly implemented water and sediment routing schemes of the small lake modelling option. Figure 13 Location of the small reservoirs in the Bengue Catchment Water routing In order to represent an aggregate description of water balance in the small reservoirs, a storage approach respecting different reservoir size classes and their interaction via river network is applied, as proposed by Güntner (2002). The water balance of small reservoirs is performed using a cascade routing scheme after some assumptions. For each class, the water balance is calculated for one hypothetical representative reservoir of mean characteristics as follow: V t,rm = V t 1,rm + (Q in,r U ) / n Q r out,rm + (P E pot ).A rm I rm Equation 6 where V t,rm is the storage volume of the representative reservoir rm in class r at timestep t; Q in,r is the inflow discharge into the reservoir class r; U r is the withdrawal water use from class r; Q,out,rm is the outflow discharge from the representative reservoir, provided by spillway overflow whenever its maximum storage capacity is surpassed; P is the sub-basin precipitation; E pot is the potential evapotranspiration; A rm is the reservoir area surface, computed as a function of storage volume, 25

27 according to Molle (1989); and I rm is the infiltration losses to bedrock. According to Molle (1989), infiltration losses is in average 34% of evaporation losses. The total actual storage volume V t,r is then given by the multiplication of the storage volume of the representative reservoir V t,rm and the total number of reservoir from class n. Water inflow into the small reservoirs is provided only by runoff generated within the sub-basin itself where the reservoirs are located. The micro-reservoirs are not georeferenced within the modelling framework. The generated runoff (Q w gen) is equally distributed among the reservoir classes. To each of the five reservoir classes, one-sixth of the water yield is attributed as direct inflow. Another sixth part of the water yield is directly attributed to the water discharge at the outlet point of the sub-basin without retention. Finally, smaller reservoirs are assumed to be located upstream of larger-sized reservoirs. Therefore, additional water inflow to the larger size classes may be provided by the smaller ones, whenever their storage capacity is surpassed: Q r 1 (Q.n ) gen out, xm x Q = + Equation 7 in, r 6 x = 1 6 x where Q w out,xm is the additional water inflow into the reservoir class r provided by spillway overflow from the smaller representative reservoir xm located upstream; and n x is the total number of reservoirs from that class. A detailed explanation of the water inflow equation is illustrated in Figure 14. Q gen 6 1 Q Q 2 Q Q Q 3 gen out,1 gen out,1 out, Q gen 6 Q Q Q out,1 out,2 out, Q Q Q Q Q gen out,1 out,2 out,3 out, Figure 14 Water inflow scheme for each reservoir class After the passage of the cascade routing scheme, the total water discharges at the outlet point of subbasin (Q sub,r ) is then given by the sum of generated runoff not intercepted by small reservoirs and outflow discharges from the small reservoirs: Q 5 (Q.n ) gen out, rm r Q = + Equation 8 sub, r 6 r = 1 6 r Sediment balance Small reservoirs are assumed to serve as sediment detention basins, considering their small structure without bottom outlets and intake devices. According to Haan et al. (1994), a pond performance modelling approach can be applied to determine the trapping efficiency and effluent size distribution. It consists of using the overflow rate concept for a rectangular reservoir with steady-state inflows and outflows without re-suspension of sediment. In Figure 15, sediment flow trajectories in an ideal rectangular reservoir are depicted. The critical settling velocity is defined as the minimum settling velocity that allows a particle to settle to the bottom in its trajectory through the reservoir. Particles with settling velocity (V s ) greater than the critical settling velocity will be trapped. The critical settling 26

28 velocity is given by the ratio of reservoir depth and flow through time. After some rearrangements, the equation can be expressed as the overflow rate equation: Q out, rm V = Equation 9 c A rm where all variables are stated above. Completely mixed inlet zone Completely mixed outlet zone V s < V c V s = V c V s > V c Figure 15 Sediment flow trajectories in an ideal rectangular sediment pond (Haan et al., 1994) The total trapping efficiency (TE) considering the grain size distribution can be computed using the overflow rate concept as presented below: X n V c V s, i TE = (1 X ) + s.dx = (1 X ) +. X Equation 10 c V c i 1 V i 0 c = c where X c is the fraction of particles with settling velocity less than V c ; and n is the number of intervals X used to calculate the integral of the previous equation. The effluent size distribution can be estimated with the overflow rate concept, expressed by following equation: F = j F Equation 11 1 i i = i where F i is the fraction of effluent smaller than particle size i; j is the number of particles size smaller than i; and F i is the fraction of effluent for each particle size i, as follow: (1 V V ). X s, i c i i = (1 V V ). X s, i c i F Equation 12 Given the trapping efficiency and the effluent size distribution of each reservoir class, the sediment balance of small reservoirs at the sub-basin scale is performed using the same cascade routing scheme. Erosion and deposition processes at tributaries are assumed negligible. Sediment inflow into the reservoir class r is given by Equation 13, whereas Equation 14 calculates the sediment discharges at the outlet point of sub-basin after the passage of the cascade routing scheme. The index s refers to sediment discharges. 27

29 Q s r 1 (Q s.n ) Q s gen out, xm x = + in, r 6 x = 1 6 x Equation 13 Q s 5 (Q s.n ) s gen out, rm r Q = + Equation 14 sub 6 r = 1 6 r The size distribution of incoming sediment into the reservoir class r (%P k,in,r ) and that related to water discharges at the outlet point of sub-basin (%P k,sub ) can be calculated using the equations 15 and 16 derived from equations 13 and 14, respectively. %P k,in,r %P k,sub Q s r 1 (Q s.n ) gen out, xm x %P. + %P. k, gen 6 k, out, x x = 1 6 x = Equation 15 Q s in, r Q s 5 (Q s.n ) gen out, rm r %P. + %P. k, gen 6 k, out, r r = 1 6 r = Equation 16 Q s sub where %P k,gen is the percentage of grain size k in the generated runoff; %P k,out,x is the percentage of grain size k released by the smaller reservoir class x located upstream; and %P k,out,r is the percentage of grain size k released by the reservoir class r. %P k,out,r is obtained from the pond performance modelling presented previously by interpolation of the effluent size distribution of each class r. The small lake modelling option is thought to be a valuable improvement for the within-catchment water and sediment balance of the WASA model. It is currently being parameterised for the Bengue Catchment. Following a field campaign on morphologic characteristics of micro-reservoirs in the beginning of 2007, the here-proposed model framework for sediment trapping processes in microreservoirs within semi-arid meso-scale watersheds is planned to put forward for a scientific publication. 28

30 29

31 4 SESAM Publications 4.1 Overview Several academic papers have been published in or are in the revision process of peer-reviewed, international journals. The following list summarises the key publications followed by a section that contains the corresponding abstracts. Published: A. Bronstert, A. Güntner, J.C. de Araujo, A. Jaeger, M. S. Krol (2005) Possible climate change impacts on water resources availability in a large semi-arid catchment in Northeast Brazil. IAHS- Publications 295, Wallingford (GB), pp J.C. de Araujo, A. Güntner, A. Bronstert. (2006) Loss of reservoir volume by sediment deposition and its impact on water availability in semiarid Brazil. Hydrological Sciences Journal, 51, J. C. de Araujo, A. Bronstert, A. Güntner. (2005) Influence of reservoir sedimentation on water yield in Brazilian semiarid region. IAHS-Publications. 292, Wallingford (GB), pp A. Güntner, M. S. Krol, J. C. de Araujo, A. Bronstert. (2004) Simple water balance modelling of surface reservoir systems in a large data-scarce semi-arid region. Hydrological Sciences Journal, 49 (5), M. S. Krol, A. Jaeger, A. Bronstert, A. Güntner. (2006) Integrated modelling of climate, water, soil, agricultural and socio-economic processes: a general introduction of the methodology and some exemplary results from the semi-arid Northeast of Brazil. Journal of Hydrology, 328, doi: /j.jhydrol G. L. Mamede, A. Bronstert, T. Francke, E. Müller, J. C. de Araújo, R. J. Batalla, A. Güntner. (2006) 1D Process-based modelling of reservoir sedimentation: a case study for the Barasona Reservoir in Spain. Conference Proceeding River Flow International Conference on Fluvial Hydraulics. Lisbon September 06 08, 2006 P. H. A. Medeiros and J. C. de Araujo (2005) Modelagem da interceptacao no semi-arido brasileiro: aplicacao do modelo de Gash na Bacia Experimental de Aiuaba CE IN: Conference Proceeding of the XVI Simpósio Brasileiro de Recursos Hídricos (XVI Water Resources Brazilian Simposium), Water Resources Brazilian Association E. N. Müller, R. J. Batalla, A. Bronstert. (2006) Dryland river modelling of water and sediment fluxes using a representative river stretch approach. Book chapter IN: Natural Systems and Global Change, 30

32 Eds: Z. W. Kundzewicz and F. F. Hattermann, Potsdam Institute for Climate Impact Research, German-Polish Yer, Turew, Poznan, p In review / in press: A. Bronstert, R. J. Batalla, J. C. de Araújo, T. Francke, A. Güntner, G. Mamede, E. Müller. (2007, in press) Investigating erosion and sediment transport from headwaters to catchments to reduce reservoir siltation in drylands. Book chapter IN: IAHS-Publications No. xxx, Wallingford (GB) T. Francke, A. Güntner, A. Bronstert, G. Mamede, E. N. Müller. (2006, in revision) Automated Catena-based Discretisation of Landscapes for Semi-distributed Hydrological Modelling. International Journal of Geographical Information Science G. Mamede, J. C. de Araujo, A. Bronstert. (2007, in press) Global change scenarios in the prediction of reservoir sedimentation and water availability. Book chapter IN: IAHS-Publications No. xxx, Wallingford (GB) E. N. Müller, R. J. Batalla, C. Garcia, A. Bronstert. (submitted) Modelling bedload transport during small floods in a gravel-bed river. submitted to Journal of Hydraulic Engineering 4.2 Abstract collection A. Bronstert, A. Güntner, J.C. de Araujo, A. Jaeger, M. S. Krol (2005) Possible climate change impacts on water resources availability in a large semi-arid catchment in Northeast Brazil. IAHS- Publications 295, Wallingford (GB), pp Abstract: The semiarid region of Northeast Brazil is characterized by water scarcity, vulnerability of natural resources, and pronounced climatic variability. An integrated model has been developed to simulate this complex situation with an emphasis on a large-scale representation of hydrological processes and on the sensitivity to climate change. Regional climate change scenarios were obtained by empirical downscaling with large-scale climate information from different GCMs which differ strongly in their projections for future precipitation. The results show that due to these differences, it is still impossible to give quantitative values of the water availability in a forecast sense, i.e. to assign probabilities to the simulated results. However, it becomes clear that efficient and ecologically sound water management is a key question for further development. The results show that, independent of the climate change, agriculture is more vulnerable to drought impacts in the case of rainfed compared to irrigated farming. However, the capacity of irrigation and water infrastructure to enhance resilience with respect to climatic fluctuations is significantly constrained in the case of a negative precipitation trend. 31

33 A. Bronstert, R. J. Batalla, J. C. de Araújo, T. Francke, A. Güntner, G. Mamede, E. Müller. (2007, in press) Investigating erosion and sediment transport from headwaters to catchments to reduce reservoir siltation in drylands. Book chapter IN: IAHS-Publications No. xxx, Wallingford (GB) Abstract: Deposition in reservoirs threatens their reliability for water supply in dryland regions. We present a modelling scheme for the quantitative assessment of sediment mobilisation in catchments, transport in the river system, and retention in reservoirs with a focus on meso-scale semi-arid catchments. An existing hydrological model tailored for specific semi-arid features is extended to represent erosion and sediment transport. Data sets from dryland catchments, rivers, and reservoirs in NE-Spain and NE-Brazil are used and expanded by own measurements. First results concerning a representation of erosion-prone landscape units, the role of sediment transport in the river system, and the sedimentation in reservoirs are presented. J.C. de Araujo, A. Güntner, A. Bronstert. (2006) Loss of reservoir volume by sediment deposition and its impact on water availability in semiarid Brazil Hydrological Sciences Journal, 51, Abstract: A methodology is presented to assess the impact of reservoir silting oil water availability for semiarid environments, applied to seven representative watersheds in the state of Ceara, Brazil. Water yield is computed using stochastic modelling for several reliability levels and water yield reduction is quantified for the focus areas. The yield-volume elasticity concept, which indicates the relative yield reduction in terms of relative storage capacity of the reservoirs, is presented and applied. Results chow that storage capacity was reduced by 0.2% year(-1) due to silting, that the risk of water shortage almost doubled in less than 50 years for the most critical reservoir, and that reduction of storage capacity had three times more impact oil yield reduction than the increase in evaporation. Average 90% reliable yield-volume elasticity was 0.8, which means that the global water yield (Q(90)) in Ceara is expected to diminish yearly by 388 L s(-1) due to reservoir silting. J. C. de Araujo, A. Bronstert, A. Güntner. (2005) Influence of reservoir sedimentation on water yield in Brazilian semiarid region. IAHS-Publications. 292, Wallingford (GB), pp Abstract: The semiarid region of Brazil (10[6] km[2]) is densely populated and highly vulnerable to droughts. Governmental water policy has long been oriented towards the construction of reservoirs to reduce the impacts of droughts. Nonetheless, continuous reservoir sedimentation not only affects water quality, but also reservoir morphology, thus reducing water yield for a given reliability level. This research assesses the effect of reservoir silting on water availability in the State of Ceará. Yieldreliability curves were calculated for selected reservoirs, using a stochastic approach, in two different morphologic states. The methodology was applied to four impoundments in Ceará, where long-term (an average of seven decades) sedimentation rates were determined. The results indicate that basin management, rather than only reservoir management, is necessary to avoid substantial reductions in water-yield reliability due to regional reservoir siltation. 32

34 T. Francke, A. Güntner, A. Bronstert, G. Mamede, E. N. Müller. (2006, in revision) Automated Catena-based Discretisation of Landscapes for Semi-distributed Hydrological Modelling. International Journal of Geographical Information Science Abstract: In hydrological and soil erosion modelling at the meso- and large scale, semi-distributed GIS approaches may use representative hillslope profiles to capture and reproduce landscape variability. Until now, the upscaling process of delineating landscape units as homogeneous parts of the landscape in regard to their terrain, vegetation and soil properties required expert knowledge and familiarity with the study area. In addition, the delineation procedure was often highly timeconsuming and included a high degree of subjectivity. This paper presents a novel, semi-automated approach for the delineation of landscape units, the derivation of representative toposequences and their partitioning into terrain components. It incorporates an algorithm to retrieve representative catenas and their attributes for elementary hillslope areas based on elevation and other key supplemental spatial data as frequently required as input parameters for environmental models, e.g. data on vegetation and soil types An example application illustrates how characteristic catenas of a landscape are derived with the semi-automated approach. Thus, upscaling of hillslope properties becomes feasible for meso-scale modelling while ensuring reproducible results. A. Güntner, M. S. Krol, J. C. de Araujo, A. Bronstert. (2004) Simple water balance modelling of surface reservoir systems in a large data-scarce semi-arid region. Hydrological Sciences Journal, 49 (5), Abstract: Water resources in dryland areas are often provided by numerous surface reservoirs. As a basis for securing future water supply, the dynamics of reservoir systems need to be simulated for large river basins, accounting for environmental change and an increasing water demand. For the State of Ceara in semiarid Northeast Brazil, with several thousands of reservoirs, a simple deterministic water balance model is presented. Within a cascade-type approach, the reservoirs are grouped into six classes according to storage capacity, rules for flow routing between reservoirs of different size are defined, and water withdrawal and return flow due to human water use is accounted for. While large uncertainties in model applications exist, particularly in terms of reservoir operation rules, model validation against observed reservoir storage volumes shows that the approach is a reasonable simplification to assess surface water availability in large river basins. The results demonstrate the large impact of reservoir storage on downstream flow and stress the need for a coupled simulation of runoff generation, network redistribution and water use. M. S. Krol, A. Jaeger, A. Bronstert, A. Güntner. (2006) Integrated modelling of climate, water, soil, agricultural and socio-economic processes: a general introduction of the methodology and some exemplary results from the semi-arid Northeast of Brazil. Journal of Hydrology, 328, doi: /j.jhydrol Abstract: Many semi-arid regions are characterised by water scarcity and vulnerability of natural resources, pronounced climatic variability and social stress. Integrated studies including climatotogy, hydrology, and socio-econornic studies are required both for analysing the dynamic natural conditions and to assess possible strategies to make semi-arid regions Less vulnerable to the present and changing 33

35 climate. The model introduced here dynamically describes the retationships between climate forcing, water availability, agriculture and selected societal processes. The model has been tailored to simulate the rather complex situation in the semi-and north-eastern Brazil in a quantitative manner including the sensitivity to external forcing, such as climate change. The selected results presented show the general functioning of the integrated model, with a primary focus on climate change impacts. It becomes evident that due to Large differences in regional climate scenarios, it is still impossible to give quantitative values for the most probable development, e.g., to assign probabilities to the simulated results. However, it becomes clear that water is a very crucial factor, and that an efficient and ecologically sound water management is a key question for the further development of that semi-arid region. The simulation results show that, independent of the differences in climate change scenarios, rain-fed farming is more vulnerable to drought impacts compared to irrigated farming. However, the capacity of irrigation and other water infrastructure systems to enhance resilience in respect to climatic fluctuations is significantly constrained given a significant negative precipitation trend. G. L. Mamede, A. Bronstert, T. Francke, E. Müller, J. C. de Araújo, R. J. Batalla, A. Güntner. (2006) 1D Process-based modelling of reservoir sedimentation: a case study for the Barasona Reservoir in Spain. Conference Proceeding River Flow International Conference on Fluvial Hydraulics. Lisbon September 06 08, 2006 Abstract: In order to simulate reservoir sedimentation processes and to enhance sediment management strategies, a process-based one-dimensional modelling approach has been developed within the framework of an international research consortium. The reservoir sedimentation module simulates the sediment transport along the longitudinal profile of a reservoir. The sediment transport component is calculated using a non-uniform sediment transport approach based on the concept of sediment carrying capacity. Up to four different sediment-transport equations can be selected for the simulations. The reservoir sedimentation model was applied to the 92.2 Mm 3 Barasona Reservoir, located in Aragon (Spain). This research presents, tests and discusses the simulation results of the computed sediment deposition and the bed elevation changes of the Barasona reservoir along a longitudinal profile using the different transport equations, a varying number of sediment size classes, and a varying number of cross-sections for the representation of the complex reservoir characteristics. G. Mamede, J. C. de Araujo, A. Bronstert. (2007, in press) Global change scenarios in the prediction of reservoir sedimentation and water availability. Book chapter IN: IAHS-Publications No. xxx, Wallingford (GB) Abstract: The goal of this research is to analyze sedimentation and resulting water availability reduction in reservoirs from tropical sub-humid environment, using the case study of the Acarape do Meio Reservoir, located in Ceará (Brazil). The simulation considers four reference scenarios: two climatic and two macroeconomic. The lumped HIDROSED model was applied to the Km 2 Acarape catchment for a simulation period of 50 years ( ) to quantify sediment yield and deposition in the reservoir. The results show that reservoir sedimentation varies from 4.17 to 9.58 million tons, depending on the scenario. This implies a reduction of water availability (with 90% 34

36 reliability level) ranging from 5.6 Mm 3 year -1 to 0.4 Mm 3 year -1 (38% to 3%, respectively) in five decades. The research concludes that the reservoir sedimentation processes are more strongly affected by soil use than by climatic changes. P. H. A. Medeiros and J. C. de Araujo (2005) Modelagem da interceptacao no semi-arido brasileiro: aplicacao do modelo de Gash na Bacia Experimental de Aiuaba CE IN: Conference Proceeding of the XVI Simpósio Brasileiro de Recursos Hídricos (XVI Water Resources Brazilian Simposium), Water Resources Brazilian Association Abstract: The performance of the Gash model of interception losses was assessed for the Aiuaba Experimental Watershed, located in the Ecological Station of Aiuaba, State of Ceará, Brazil, where the vegetation of caatinga is well preserved. The Gash model was used, once it is physically based and uses daily registers of precipitation to calculate the losses, besides being largely used with good results. Two groups of parameters were simulated: calculated according to the literature and another with the calibration of the parameters. The group of parameters calculated according to the literature simulated the losses in Aiuaba with an error of +19%. Aiming to establish a group of parameters to the model to reproduce the measured losses, the mean rate of evaporation during rain events was calibrated, being reduced in 19%. The sensitivity analysis of the Gash model indicates that it is little sensitive to the vegetation parameters, but is very sensitive to the climatic parameters. E. N. Müller, R. J. Batalla, A. Bronstert. (2006) Dryland river modelling of water and sediment fluxes using a representative river stretch approach. Book chapter IN: Natural Systems and Global Change, German-Polish Seminar Turew, Poznan Abstract: The study investigates the process-based modelling of sediment transport in dryland rivers within a meso-scale watershed in the Pre-Pyrenean region of NE Spain. The modelling study is carried out to enable the quantification of sediment fluxes that erode mainly from local badland areas during high-intensity rainstorm events, resulting in sediment torrents in the river system and severe sedimentation of a down-stream large reservoir thus threatening future water supply. To enable model parameterisation, representative river stretches were derived from the results of a field campaign that investigated central model parameters such as the cross-sectional profile, slope, roughness and the gradation of the riverbed material. The sediment load from the badland areas and the sediment transport in the river s main stem was modelled for a hypothetical sediment-input scenario using a composition of representative river stretches. The proposed modelling framework enabled a detailed spatial and temporal examination of complex deposition and river bed degradation patterns as well as an insight into the temporary sediment storage behaviour of the riverbed and of its floodplain along the entire river flow path. E. N. Müller, R. J. Batalla, A. Bronstert. (submitted) Modelling bedload transport during small floods in a gravel-bed river. to be submitted to Journal of Hydraulic Engineering Abstract: This study investigates the applicability of five bedload-transport formulae (after Meyer- Peter & Müller 1948, Schoklitsch 1950, Smart & Jaeggi 1983, Bagnold 1956 and Rickenmann 2001) 35

37 to reproduce bedload transport rates of frequent, low-magnitude flood events (maximal bankful discharge) for a mountainous, gravel-bed river. For model parameterisation, special emphasis was placed on the spatial scaling of the riverbed gradation to evaluate the impact of a bimodal particle size distribution. Three parameterisation approaches were tested for the D 50 value that considered the apparent bimodality of the riverbed gradation to a varying degree. The modelling study demonstrated that the spatial scaling of the riverbed gradation to include its bimodal character has an important impact on model performance - a unimodal parameterisation approach failed to reproduce measured bedload rates for all tested bedload formulae; the bimodal parameterisation approach that considered only fine sediments from the small patches as bedload source material in combination with the Schoklitsch and Rickenmann equations yielded the best results, whereas the Meyer-Peter and Mueller and the Bagnold equations overpredicted bedload rates for all scenarios. The modelling study thus showed that the bedload formulae are sensitive towards the spatial structure of the riverbed gradation which should not be treated as a continuum of sediment size fractions but rather as composition of fine sediment areas to enable an adequate reproduction of measured bedload data of the gravel-bed river. 36

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39 5 SESAM Poster Presentations 5.1 Overview The following posters have been presented at international conferences: E. N. Mueller, R. J. Batalla, A. Bronstert. (2006a) Dryland River Modelling of Water and Sediment Fluxes using a representative River Stretch Approach Presented at the European Geosciences Union 2006 General Assembly, Vienna, 2 7 April 2006 T. Francke, B. Creutzfeldt, A. Güntner, M. Maerker, G. Mamede, E.N. Mueller. (2006) Spatial Discretisation in semi-distributed hydrological Modelling using the Landscape Unit Mapping Program (LUMP) Presented at the European Geosciences Union 2006 General Assembly, Vienna, 2 7 April 2006 K. Appel, E.N. Mueller, T. Francke, C. Opp. (2006) Soil-Erosion Modelling along Badland Hillslopes in a Dryland Environment of NE Spain Presented at the European Geosciences Union 2006 General Assembly, Vienna, 2 7 April 2006 G. Mamede, A. Bronstert, E. N. Müller (2005) Sedimentation modelling of reservoirs for dryland environments in Spain and Brazil Presented at the 8 th International Conference on Fluvial Sedimentology, 7-12 August 2005, Delft, The Netherlands 5.2 Poster collection The following pages present the abstracts and corresponding posters. 38

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41 Dryland River Modelling of Water and Sediment Fluxes using a representative River Stretch Approach E. N. Mueller (1), R. J. Batalla (2, 3), A. Bronstert (1) (1) Institute of Geoecology, University of Potsdam, Postfach , Potsdam, Germany, (2) Department of Environmental and Soil Sciences, University of Lleida, Lleida, Catalonia, Spain, (3) Forest Technology Centre of Catalonia, Pujada del Seminari, Solsona, Spain (enmue@unipotsdam.de / Phone: ) The study investigates process-based modelling of sediment transport in dryland rivers within a mesoscale watershed of the Pre-Pyrenean region in NE Spain. The modelling study is carried out to enable the quantification of sediment fluxes that erode mainly from local badland areas during high-intensity rainstorm events, resulting in sediment torrents in the river system and severe sedimentation of a down-stream large reservoir thus threatening future water supply. The study reach is characterised by a heterogeneous spatial distribution of river forms and properties, which makes the parameterisation of state-of-the-art river models a difficult task. Steep, narrow, deep incised mountain torrents with rocky, gravely riverbeds in the upper parts of the catchment alternate with shallow, plain and very wide riverbeds and large floodplains with silty riverbed materials in the lower catchment area, with parts of the river system having an ephemeral flow regime. To enable model parameterisation, representative river stretches were derived from the results of a field campaign that investigated central model parameters such as the cross-sectional profile, slope, roughness and the gradation of the riverbed material. The flow regimes of the representative river stretches were then assessed for different high and low flow conditions and a thorough sensitivity analysis was carried out to investigate model parameter uncertainty. Subsequently, the sediment load from the badland areas and the sediment transport in the river s main stem was modelled using a composition of representative river stretches. The modelling framework thus enabled a detailed spatial and temporal examination of complex deposition and erosion patterns in the riverbed and their floodplains along the entire river flow path. Presented at the European Geosciences Union 2006 General Assembly, Vienna, 2 7 April

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43 Spatial Discretisation in semi-distributed hydrological Modelling using the Landscape Unit Mapping Program (LUMP) T. Francke (1), B. Creutzfeldt (1, 2), A. Güntner (2), M. Maerker (1), G. Mamede (1), E.N. Mueller (1) Institute for Geoecology, Germany, University of Potsdam, P.O. Box , Potsdam, Germany (2) GeoForschungsZentrum Potsdam (GFZ), Telegrafenberg, Potsdam, Germany / Phone: ) In hydrological and soil-erosion modelling, spatial discretisation of the model domain is usually accomplished in a fully distributed, semi-distributed or lumped scheme. For meso- and large scale modelling, semi-distributed approaches commonly describe the properties of a landscape unit using a representative catena or toposequence which is modelled in detail, with results then being extrapolated onto the represented model domain. The manual delineation of the landscape units and the derivation of a representative toposequence is a time consuming task because of a lacking automated procedure. Objective results cannot be obtained because of the high degree of subjectivity involved. The necessary detailed expert knowledge and familiarity with the study area is not always available. This poster presents an approach for semi-automated delineation of landscape units and their further partitioning into terrain components using the Landscape Unit Mapping Program (LUMP). LUMP incorporates an algorithm of retrieving catenas and their attributes based on a DEM and supplemental spatial data like vegetation or soil classes. By including user-specifiable weighting factors, the catenas are classified using cluster analysis. A representative toposequence and its attributes are computed for each class to provide the parameters for the resulting landscape unit. Spatial extent of the landscape units result from interpolation between the classified catenas. In the next step, each toposequence is further sub-divided into homogeneous elements called terrain components by considering multiple attributes following the spatial concept of the WASA-model. The results show the capability of LUMP to derive characteristic toposequences of a landscape. Open questions remain concerning the proper choice of relevant terrain attributes and their respective weighting factors in the classification scheme. Presented at the European Geosciences Union 2006 General Assembly, Vienna, 2 7 April

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45 Soil-Erosion Modelling along Badland Hillslopes in a Dryland Environment of NE Spain K. Appel (1,2), E.N. Mueller (1), T. Francke (1), C. Opp (2) (1) Institut für Geoökologie, Universität Potsdam, Postfach , Potsdam, Germany (2) Fachbereich Geographie, Philipps-Universität Marburg, Deutschhausstraße 10, Marburg (kajoap@gmx.de / Phone ) Badlands are hillslopes of unconsolidated sediments with no or little vegetation that cannot be used for agriculture and are characterised by their desert like appearance and their very high soil erosion rates. This study assesses the feasibility of modelling soil erosion rates from badlands of the Isabena Watershed in the Pre-Pyrenees, NE Spain using a field-work integrated, process-based, semidistributed modelling approach. For this purpose, a field campaign was carried out recently to collect model parameterisation data on slope, vegetation cover, aspect, infiltration and particle size distribution as well as testing data on water and sediment fluxes. Four typical badland formations were selected in the field as a function of form, extent and internal gully system to enable a comparative study of badland processes. The four badland types were then modelled using a soil-erosion routine based on the MUSLE (Modified Universal Soil Loss Equation) approach coupled with a hydrological model. The fieldwork results as well as the modelling results and a sensitivity analysis for different spatial representations of the badland types are presented. The poster discusses the limitations but also the advantages of the MUSLE approach for the modelling of extreme soil-erosion rates from badlands, specifically in regard to the scaling of sediment budgets towards the regional scale. Presented at the European Geosciences Union 2006 General Assembly, Vienna, 2 7 April

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47 Sedimentation modelling of reservoirs for dryland environments in Spain and Brazil G. Mamede, A. Bronstert, E. N. Müller (1) Institut für Geoökologie, Universität Potsdam, Postfach , Potsdam, Germany / Phone: ) Dryland environments are often exposed to the hazard that the available freshwater resources fail to meet the water demand in the domestic, agricultural and industrial sectors. Water availability often relies on the retention of river runoff in reservoirs. However, the water storage in reservoirs is often adversely affected by sedimentation as a result of severe soil erosion. To guarantee future water supply, a quantification of the sedimentation processes becomes indispensable. Therefore, a modelling approach is being developed to enable the assessment of reservoir sedimentation specifically for dryland settings taking into account the processes that occur along the longitudinal deposition profile of a reservoir. The modelling approach will enable the calculation of reservoir life expectancy, the trapping efficiency of the reservoir, the amount of released sediments downstream the reservoir and the simulation of various reservoir sediment management scenarios. The poster summarises the temporal and spatial components of the model approach that will be used to calculate sediment balances and the spatial sedimentation distribution for a daily time step. In addition, it presents the results of field studies at the Barasona Reservoir, NE Spain and the Bengue Reservoir, Brazil that are required for model parameterization. Parameters under investigation included data on sediment discharges, suspended flow, sediment compositions and sediment compaction. This research is performed within the framework of the SESAM-Project (Sediment Export from large Semi-Arid catchments: Measurement and Modelling), a joint research project of institutions in Germany (University of Potsdam, Geoforschungszentrum Potsdam), Spain (University of Lleida, Forest Technology Centre of Catalonia) and Brazil (University of Ceara, Fortaleza). Presented at the 8 th International Conference on Fluvial Sedimentology, 7-12 August 2005, Delft, The Netherlands 46

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49 6 Theses and student projects within the SESAM project The following PhD research, MSc theses, final year student projects, internships have been carried out within the SESAM project until the year PhD / Doctoral thesis: Till Francke 1 Sediment-transport modelling at the hillslope scale in semi-arid regions Vanda Teresa Malveira 2 Hydro-sedimentological assessment implacts in the Oros Watershed, Ceara, Brazil Pedro Henrique Augusto Medeiros 2 Connectivity of sediment transport transfer routes at the Aiuaba and Bengue Catchments, Brazil George Mamede 1,2 Sedimentation modelling and sediment management in reservoirs of semi-arid catchments MSc thesis: Katharina Appel 1 (submitted October 06) Characterisation and sediment-transport modelling of badlands in the Isabena Watershed, NE Spain Alexandre Cunha Costa 2 (submitted January 06) Compilation of a data-base on hydrological data and its application for the study of evaporation processes for the Aiuaba Experimental Basin, Ceara, Brazil Benjamin Creutzfeldt 1,3 (submitted April 2006) Remote sensing based characterisation of land-cover and terrain properties for hydrological modelling in the semi-arid Northeast of Brazil Jose A. López 4 (submitted November 06) Suspended sediment transport in the Isabena River (Ebro Basin) Student projects: Anita Becker 1,4 Evaluation of the temporal variations in sediment storage in the Isabena River, Pre-Pyrenees, NE Spain Niko Bornemann 1 48

50 Quantification of the spatial pattern of sediment storage along a 33 km long stretch of the Isabena River, Pre-Pyrenees, NE Spain Björn Guse 1 (submitted April 2005) Statistical analysis and comparison of rainfall characteristics from the semi-arid Bengue Catchment, NE Brazil and the Isabena Catchment, NE Spain Florian Hacker 1 (submitted August 2005) Estimation of transmission losses by infiltration at rivers in the semi-arid Federal State of Ceara (Brazil) Conrad Jackisch 1 (submitted January 2006) Estimation of the water balance of the Aiuaba Experimental Catchment, Ceara, Brazil Steffi Schuchort 1,5 Monitoring of bed-material dynamics and bedload transport in the gravel-bed, mountainous Ribera Salada River, Pre-Pyrenees, NE Spain Eric Sommerer 1 Regionalisation of geomorphological and land-use data of a valley dominated by badland processes Internships: Daniela Brucher 1,6 ( ) WASA model parameterisation of the Ribera Salada Catchment, NE Spain Jan Holtkamp 1,6 ( ) Spatial derivation of the event dependency of the runoff coefficient and of the MUSLE C-Factor for the Bengue Catchment, NE Spain 1 University of Potsdam, Germany, 2 Federal University of Ceara, Fortaleza, Brazil 3 GeoForschungsZentrum Potsdam, Germany 4 University of Lleida, Spain 5 Forest Technology Centre of Catalonia, Spain 6 University of Freiburg, Germany 49

51 7 Conclusion and future tasks This interim report gave a full account on the study areas in the Pre-Pyrenees of Spain and the NE of Brazil of the SESAM project, previous and on-going monitoring campaigns and fieldwork studies of the last two years, a record of current publications and research foci as well as a complete overview on the employed modelling approaches and conceptual models. Future work of the SESAM project will continue to focus on the two main aspects of the research consortium: the monitoring program on water and sediment fluxes at the hillslope, river and reservoir scale and the development of the modelling framework for the assessment of sediment export from meso-scale dryland catchments. The installed monitoring schemes at the study catchments of Isabena/Esera, Ribera Salada and Bengue will enable a unique insight into hydrological and sediment-transport processes in meso-scale dryland catchments and are expected to provide valuable testing data for the WASA modelling framework. The measured data sets already supply novel information on sediment transport for different seasons of the year. A continuation of data collection in the third SESAM project year is going to provide the database for hydrological data, suspended sediment and bedload rates that can then be used for comparison of transport behaviour of different annual rainfall patterns. The analysis of the data collected during the latest three-month fieldwork campaign to the Spanish catchments is going to provide valuable information on rainfall-runoff relations and suspended sediment generation from badlands at the hillslope and small catchment scales for up to twelve individual rainstorm events. For 2007, a fieldwork campaign is planned at the Aiuaba and Bengue Catchments in Brazil for a time period of three months to cover the entire rainy season and thus enable data collection during each individual rainstorm event. Parameters under investigation will include water and sediment fluxes in the ephemeral river system and the sediment trapping capacity of micro-reservoirs. Currently, testing studies of the hillslope, river and reservoir modules are carried out for the model parameterisations of the Esera-Isabena and Ribera Salada catchments in Spain and the Aiuaba and Bengue catchments in Brazil. The testing phase includes the validation of model results with measured time series for individual rainstorm events as well as for longer time periods extending over several years of water discharge, suspended sediment, bedload and reservoir sedimentation rates. For all study catchments, a nested testing scheme will be applied to enable the separate testing of the simulation results of the hillslope, river and reservoir modelling modules. In parallel, uncertainty analysis will be carried out as a means of evaluating the appropriateness of the employed spatial discretisation, the mathematical process descriptions and model parameterisations. Once the model components have been tested sufficiently, the WASA model will be employed for scenario calculations, such as the simulation of the effects of erosion control management, of various sedimentation management options in reservoirs and of possible future and past land-use change climate change scenarios. The ultimate outcome of the SESAM project after the third and final project year (2007) is expected to markedly improve the knowledge and modelling capabilities of sediment export processes from mesoscale dryland catchments. It provides an indispensable step towards future studies on open questions related to sediment-transport processes such as connectivity issues of sediment transfer routes and the upscaling of process knowledge to the macro and regional scales. 50

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53 REFERENCES Abrahart, R. J. and S. M. White, Modelling sediment transfer in Malawi: comparing backpropagation neural network solutions against a multiple linear regression benchmark using small data sets. Physics and Chemistry of the Earth, Part B: Hydrology, Oceans and Atmosphere 26 (2001): Ackers, P. and White, W.R. (1973). Sediment transport: a new approach and analysis, Proc. ASCE, Journal of the Hydraulics Division, Vol. 99, HY11, pp de Araújo, J.C.de, Fernandes, L., Machado Júnior, J.C, Oliveira, M.L.R. and Sousa, T.C. (2003): Sedimentation of reservoirs in semiarid Brazil. In: Gaiser, T., Krol, M.S., Frischkorn, H. and Araújo, J.C.de: Global change and regional impacts: Water availability and vulnerability of ecosystems and society in the semi-arid Northeast of Brazil. Springer-Verlag, Berlin Heidelberg, Germany, de Araújo, J.C. (2005, submitted): Entropy-based equation to assess hillslope sediment production de Araujo, J. C.,Güntner, A., Bronstert, A. (2006) Impact of reservoir silting on water availability in a semiarid region. Hydrological Sciences Journal, 51, de Araujo, J. C., Bronstert, A. Güntner, A. (2005) Influence of reservoir sedimentation on water yield in Brazilian semiarid region. IAHS-Publications. 292, Wallingford (GB), pp Ashida, K. and Michiue, M. (1973). Studies on bed load transport rate in alluvial streams, Trans. Japan Society of Civil Engineers, Vol. 4. Bracken, L. and Kirkby, M. (2005) Difference in hilllsope runoff and sediment transport rates within two semi-arid catchments in southeast Spain. Geomorphology, 68, Bronstert, A. Güntner, A., de Araujo, J. C., Jaeger, A., Krol, M. S. (2005) Possible climate change impacts on water resources availability in a large semi-arid catchment in Northeast Brazil. IAHS- Publications 295, Wallingford (GB), pp Bronstert, A., Batalla, R. J., de Araújo, J. C., Francke, T., Güntner, A., Mamede, G. L., Müller, E.N. (2007, in press) Investigating erosion and sediment transport from headwaters to catchments to reduce reservoir siltation in drylands. Book chapter IN: IAHS-Publications No. xxx, Wallingford (GB) Chow, V. T., D. R. Maidment, L.W. Mays (1988) Applied Hydrology. McGraw-Hill International Editions. Civil Engineering Series. Singapore Creutzfeld, B.N.A. (2006). Remote sensing based characterisation of land cover and terrain properties for hydrological modelling in the semi-arid Northeast of Brazil. MSc-Thesis, Universität Potsdam, Germany. Dissmeyer, G.E. and Foster, G.R. (1980). Predicting Sheet and Rill Erosion on Forest Land.. Agriculture Handbook 537, Washington: U.S. Gov. Print. Off. Fargas, D., Martínez-Casasnovas, J. and Poch, R. (1997) Identification of Critical Sedmient Source Areas at Regional Level. Phys. Chem. Earth., 22, Francke, T., Güntner, A., Bronstert, A., Mamede, G. L., Müller, E. N. (2006, in revision) Automated Catena-based Discretisation of Landscapes for Semi-distributed Hydrological Modelling. International Journal of Geographical Information Science 52

54 Garcia, C., Laronne, J. B., and Sala, M., 2000, Continuous monitoring of bedload flux in a mountain gravel-bed river: Geomorphology, v. 34, p Govers, G. (1987) Empirical relationships on the transport capacity of overland flow, Proceedings of the Jerusalem Workshop, Erosion, Transport and Deposition Processes, March April 1987, 25 IAHS Publ. No. 189, 45 63, Graf, W.H. and Altinakar, M.S. (1998). Fluvial Hydraulics Flow and transport processes in channels of simple geometry. John Wiley & Sons LTDA. ISBN Güntner, A. (2002). Large-scale hydrological modelling in the semi-arid North-East of Brazil. PIK- Report, Potsdam Institute for Climate Research, Germany. No. 77. Güntner,A. and Bronstert,A. (2003). Large-scale hydrological modelling in the semiarid Northeast of Brazil: aspects of model sensitivity and uncertainty, In E.Servat, W.Najem, C.Leduc, and A.Shakeel, editors, Hydrology of the Mediterranean and Semi-Arid Regions. IAHS-Publication 278 Güntner,A. and Bronstert,A. (2004). Representation of landscape variability and lateral redistribution processes for large-scale hydrological modelling in semi-arid areas, Journal of Hydrology 297: Güntner, A., Krol, M.S., de Araujo, J.C., Bronstert, A. (2004) Simple water balance modelling of surface reservoir systems in a large data-scarce semi-arid region. Hydrological Sciences Journal, 49 (5), Haan, C.T., Barfield, B.J., and J.C. Hayes. (1994) Design hydrology and sedimentology for small catchments. New York: Academic Press. Hilton, S., Lisle, T. E. (1993) Measuring the fraction of pool volume filled with fine sediment. Research Note PSW-RN-414-WEB. United States Department of Agriculture, Forest Service IRTCES (1985). Lecture notes of the training course on reservoir sedimentation. International Research of Training Center on Erosion and Sedimentation, Sediment Research Laboratory of Tsinghua University, Beijing, China. Krol, M. S., Jaeger, A., Bronstert, A., Güntner, A. (2006) Integrated modelling of climate, water, soil, agricultural and socio-economic processes: a general introduction of the methodology and some exemplary results from the semi-arid Northeast of Brazil. Journal of Hydrology, 328, doi: /j.jhydrol Krysanova,V., F. Wechsung (2000) SWIM (Soil and Water Integrated Model) User Manual, Version: SWIM-8. Internet resource (accessed on ): Martínez-Casasnovas, J. and Poch, R. (1998) Estado de conservación de los suelos de la cuenca del embalse de Joaquín Costa. Limnetica, 14, Mamede, G. L., Bronstert, A., Francke, T., Müller, E. N., de Araújo, J. C., Batalla, R. J., Güntner, A. (2006) 1D Process-based modelling of reservoir sedimentation: a case study for the Barasona Reservoir in Spain. Conference Proceeding River Flow International Conference on Fluvial Hydraulics. Lisbon September 06 08, 2006 Mamede, G., de Araujo, J. C., Bronstert, A. (2007, in press) Global change scenarios in the prediction of reservoir sedimentation and water availability. Book chapter IN: IAHS-Publications No. xxx, Wallingford (GB) 53

55 Medeiros, P. H. A. and de Araujo, J. C. (2005) Modelagem da interceptacao no semi-arido brasileiro: aplicacao do modelo de Gash na Bacia Experimental de Aiuaba CE IN: Conference Proceeding of the XVI Simpósio Brasileiro de Recursos Hídricos (XVI Water Resources Brazilian Simposium), Water Resources Brazilian Association Morgan, R. P. C., Quinton, J. N., Smith, R. E., Govers, G., Poesen, J. W. A., Auerswald, K., Chisci, G., Torri, D., Styczen, M. E., Folly, A. J. V. (1998): The European Soil Erosion Model (EUROSEM) Documentation and user guide, Cranfield University Morgan, R.P.C, Quinton, J.N., Smith, R.E., Govers, G., Poesen, J.W.A., Auerswald, K., Chisci, G., Torri, D. & Styczen, M.E. (1998): the European Soil Erosion Model (EUROSEM): a dynamic approach for predicting sediment transport from fields and small catchments. Earth Surface Processes and Landforms, 23, Mueller, E. N., Mamede, G., Francke, T., Batalla, R. J., de Araujo, J. C., Güntner, A., Bronstert, A. (2005) Annual report 2005 SESAM: Sediment Export from large Semi-Arid Catchments: Measurement and Modelling. Available online at: Müller, E. N., Batalla, R. J., Bronstert, A. (2006a) Dryland river modelling of water and sediment fluxes using a representative river stretch approach. Book chapter IN: Natural Systems and Global Change, German-Polish Seminar Turew, Poznan Mueller, E.N., Francke, T., Mamede, G., Güntner, A. (2006b) WASA Model Documentation. Available online at: Wasa_Documentation.pdf Müller, E. N., Batalla, R. J., Bronstert, A. (in review) Modelling bedload transport rates during small floods in a gravel-bed river. submitted to Journal of Hydraulic Engineering Neitsch, S.L., J.G. Arnold, J.R. Kiniry, J.R. Williams, K.W. King (2002): Soil and Water Assessment Tool. Theoretical Documentation, Version Published by Texas Water Resources Institute, TWRI Report TR-191 Rius, J., Batalla, R. J., and Poch, R. M., 2001, Monitoring water and sediment yield in Mediterranean mountainous watersheds: preliminary results, in Mohtar, R. H. and Steinhardt, G. C., editors, Sustaining the global farm. Selected papers from the 10th International Soil Conservation Organisation Meeting, Purde University and USDA-ARS National Soil Erosion Research Laboratory: p Sanz Montero, M. E., Cobo Rayan, R., Avendano Salas, C., and Gomez Mantana, J. L., 1996, Influence of the drainage basin area on the sediment yield to Spanish reservoirs.: Proceeding of the First European Conference and Trace Exposition on Control Erosion Schmidt, J. (1991): A mathematical model to simulate rainfall erosion. Catena Suppl., 19, Tazik, D.J., Warren, S.D., Diersing, V.E., Shaw, R.B., Brozka, R.J., Bagley, C.F. and Whitworth, C.F. (1992). U.S. Army Land Condition-Trend Analysis (LCTA) Plot Inventory Field Methods.. Vericat, D. and Batalla, R. J., (2005). Sediment transport in a highly regulated fluvial system during two consecutive floods (lower Ebro River, NE Iberian Peninsula): Earth Surface Processes and Landforms, v. 30, p

56 Valero-Garces, B. L., Navas, A., Machin, J., and Walling, D. E., 1999, Sediment sources and siltation in mountain reservoirs: a case study from the Central Spanish Pyrenees: Geomorphology, v. 28, p Verdú, J.M., Batalla, R.J., Poch, R.M. (2000): Dinámica erosiva y aplicabilidad de modelos físicos de erosión en una cuenca de montaña Mediterránea (Ribera Salada, cuenca del Segre). Pirineos, 155, Verdu, J. M., 2003, Analysis and modelling of the hydrological and fluvial response of a large mountainous Mediterranean catchment (Isabena River, Pre-Pyrenees): University of Lleida. Wischmeier, W. and Smith, D. (1978). Predicting rainfall erosion losses. Agriculture Handbook 537; Washington: U.S. Gov. Print. Off. Williams, J.R. (1995). Chapter 25. The EPIC Model. p In Computer Models of Watershed Hydrology. Water Resources Publications. Highlands Ranch, CO. Wu, W., Wang, S.S.Y. and Jia, Y. (2000), Nonuniform sediment transport in alluvial rivers, Journal of Hydraulic Research, Vol. 38, No. 6, pp Yang, T.C. and Simoes, F.J.M. (2002) User s Manual for GSTARS3 (Generalized Sediment Transport model for Alluvial River Simulation version 3.0). U.S. Department of the Interior, Bureau of Reclamation, Technical Service Center, Denver, Colorado Yitian, L. and R. R. Gu. Modeling flow and sediment transport in a river system using an artificial neural network. Environmental Management 31 (2003):

57 APPENDIX 1: SESAM Study Areas Appendix 1-A: Spain Two study sites have been selected in the north-eastern part of Spain as depicted in Figure 16: the Esera-Isabena catchments in Aragon, and the Ribera Salada catchment in Catalonia. The catchment sites are within the Ebro watershed as shown in Figure 16. The field monitoring program of the study areas is carried out by the University of Lleida and the Forestry Centre of Catalonia. Climatic, vegetation, geological and topographical characteristics of the two study areas are described in the two following sections, each section being followed by information concerning the existing and newly installed monitoring equipment for the measurement of water and sediment fluxes. Figure 16 Location of the study sites in NE Spain (Left: Ebro Catchment, Right: Isabena Catchment in dark green) Esera Catchment in light green and Ribera Salada Catchment in red) Isabena Esera Catchments Figure 17 displays a map of the Esera and Isabena Catchments and their confluence into the Barasona Reservoir. The Esera Catchment covers an area of 906 km 2, the neighbouring Isabena Catchment an area of 435 km 2. The climate of the Esera and the Isabena Catchments is a typical Mediterranean mountainous type with a mean annual precipitation rates of 600 to 1200 mm and an average potential evaporation rate of 550 to 750 mm. Both rates show a strong south-north gradient, which can be related to the strong topographical difference of altitude within the watersheds ranging from 430 m to 2970 m over MSL (data excluding the snow-driven parts in the uppermost northern part of the Esera Catchment). The major rivers in the catchment never dry up, although flows are low during the summer and some of the tributaries of the Isabena and Esera Rivers exhibit ephemeral behaviour with no flow at the end of the dry season. Most floods occur due to the passing of cold fronts in spring and to local thunderstorms in autumn and winter. The vegetation includes evergreen oaks and pines in the valley bottoms and deciduous oaks in the upper areas. 56

58 Figure 17 Map of the Esera and Isabena Catchments (Projection: UTM 30N) Figure 18 displays a map of the lithology for both catchments. The lower parts of the two catchments are mainly dominated by Miocene continental sediments, the middle part by carbonate rocks and marls, and the upper part by Paleozoic rocks. Figure 18 Lithology of the Esera and Isabena Catchments (Valero-Garces et al. 1999) Erosion processes are very intense in many parts of the basin even under normal precipitation conditions. A significant part of the erosion processes occur on badlands. Badlands are a typical landform of this region within the upper middle part of the catchments, dominated by Mesozoic carbonate rocks and marls. Badlands are heavily dissected barren terrain that is composed of poorly cemented debris and marls lacking any vegetation cover. Badlands are vulnerable to flash flood erosion and produce large amounts of eroded material, that are then transported downstream as suspended sediments in the Esera and Rivers. The large amount of suspended sediments in the river system creates severe problems of reservoir sedimentation at the outlet of the Esera River. The Isabena River confluences into the Esera River, which then flows into the Barasona Reservoir. The Barasona Reservoir was built in 1932 with an initial water capacity of 71 x 10 6 m 3 mainly for irrigation purposes 57

59 and power generation. The crest elevation of the dam was increased in 1972 which resulted in an augmented storage capacity of 92 x 10 6 m 3 (Valero-Garces et al. 1999). The Barasona Reservoir is heavily affected by the sedimentation of suspended sediments that reach the reservoir via the Esera and Isabena River. The badlands are thought to be the major cause for the sedimentation of the Barasona Reservoir (Fargas et al. 1996,. According to Sanz Montero et al. (1996), the reservoir had lost about one third of its initial water storage capacity. They report that the volume of accumulated sediment in the reservoir was about x 10 6 m 3 with a maximum thickness of m near the dam wall (in 1995). Most of the sediments are delivered to the Barasona Reservoir during flood events (Valero-Garces et al. 1999). The sedimentation of the reservoir is a severe problem for the region as it is a long-lasting threat for the water outlets to the canal of Aragon and Catalunya. Part of the sediment accumulated in the reservoir was sluiced between 1995 and 1997 after intense engineering works to make the sediment fluid enough to move through the dam bottom gates. Existing monitoring scheme A two-year database with hydrological data for precipitation and flood runoff is available for the Isabena Catchment (Verdú, 2003). Furthermore, there is a gauging station with a record of 60 years of discharges at the Isabena basin outlet, and three gauging stations along the Esera River with a record of 55 years; their locations are depicted in the map in Figure 17. In total nine rainfall gauges are available within the catchment areas that provide information on daily rainfall and temperature with a record of at least 15 years, four of them with a record of 55 years. New monitoring scheme within the SESAM project In July 2005, a turbidity meter was installed at the outlet of the Isabena Catchment (at the gauging station number 47 if the Ebro Water Authorities), as depicted in Figure 19, which enables the continuous measurement of turbidity with a temporal resolution of 15 minutes. The device is a NEP- 390-CBL Turbidity probe NTU (-2.5 v to * 2.5 v dc). The turbidity measurements are going to be used as a measure for the content of suspended sediment concentration mostly during baseflows and small floods in the Isabena River. Data is collected by means of Campbell CR10X data-logger. Figure 19 Turbidimeter probe and ISCO-3700 sampler water intake at the gauging station 47, Isabena River At the same location, an ISCO-3700 Sampler with water level actuator was installed that takes up to 24 1-litre water samples for a single flood event (Figure 20). Direct water samples are regularly taken 58

60 to support the calibration of the turbidity and automatic sampler measurements. The water samples are collected and the data processed by the Spanish partners of the SESAM project. Figure 20 ISCO-3700 Sampler at the gauging station 47 during a small flood in the Isabena River (18/08/2005) Ribera Salada Watershed Ribera Salada is a 225 km 2 catchment in Catalonia that includes two nested experimental catchments: the Canalda Watershed with an area of 65 km 2 and the Cogulers Watershed with an area of 2.5 km 2 as depicted in Figure 21. The smaller watershed is thought to be controlled mostly by slope-driven processes, whereas the larger one possesses a fully developed fluvial system. Figure 21 Schematic drawing of the nested watersheds at the Ribera Salada The climate is a typical Mediterranean mountainous climate, where rivers never dry up, although flows are very low during the summer. Mean annual precipitation is around 700 to 800 mm, mean annual evaporation varies between 700 and 750 mm. Snow melt plays a secondary role, and most floods are due to autumn and winter thunderstorms. The catchment is mostly on conglomerate supporting sandy-loamy soils, the erosion processes being rather limited under normal precipitation. The vegetation includes evergreen oaks and pines in the valley bottoms and deciduous oaks in the upper areas. The mean altitude of the catchment is 700 m MSL ranging between 460 m in the southwest and 2200 m in the northeast. Erosion processes on the headwater slopes were monitored and 59

61 subsequently modelled by means of the EROSION 2D (Schmidt, 1992) and the EUROSEM (Morgan et al. 1998) models. Results published in Verdú et al. (2000) suggested a predominance of non- Hortonian processes and a limited sediment supply to the fluvial system. Suspended load transport is thought to be the dominant sediment transport process, although in a much lower proportion than in the Isabena River, whereas bedload sediment transport is considered to be lower (Batalla et al. 2005, sediment transport data for the period ), but much more relevant than in the Isabena. Under present climatic and land-use conditions, colluvium on the footslopes and the drainage network itself are probably the main sediment sources. Table 9 Existing water and sediment instrumentation in the Ribera Salada experimental watersheds (Rius et al. 2001) Nested catchments Instrumentation Cogulers Canalda Ribera Salada * (2.6 km 2 ) (65.2 km 2 ) (110 km 2 ) Meteorological station 1 Rain-gauges 3 8 (5+3) 9 (1+5+3) Water level sensors Automatic water and sediment sampling 1 1 Manual water and sediment sampling 1 1 Bedload traps 6 * This section was operating between 2000 and 2002 Existing monitoring data A five-year database containing precise hydrological and sediment transport data is available within the two nested watersheds Cogulers and Canalda. Table 9 summarises the existing instrumentation including a meteorological station, several rain gauges, water level sensors, automatic and manual water and sediment samplers and bedload traps that were already installed prior to the start of the SESAM project. New monitoring scheme within the SESAM project In July 2005, the SESAM partners from the University of Lleida and from the Forestry Centre of Catalonia started the installation works of a total sediment transport station in the middle reaches of the catchment (with a contributing area of around 100 km 2 ). The station is composed of three automatic bedload pit traps, a NEP-390-CBL Turbidity probe, an ISCO-3700 automatic sampler with 24 1-litre sample bottles and a water level actuator, and a water level sensor. The bedload trap was installed to enable a continuous measurement of bedload flux for single rainstorm events with a sampling period of at least five hours. The bedload trap consists of a concrete structure which contains a metal box with a capacity of 0.22 m 3 supported on top of a water pillow (MSC Survival), which records the increase by weight of the entering bedload and transmits it by a means of a pressure sensor (PTX-1730) to a Campbell CR1000 data-logger. Sediment capacity of each trap is around 330 kg (submerged weight). Recording interval is 5 minutes. Pit traps have been preliminary calibrated and fully operate since mid-november 2005, together with the rest of the instrumentation. A water temperature sensor will be installed during December

62 Figure 22 displays photographs of the installation of the sediment transport station, with particular attention to the bedload pit trap. The specific design of the bedload trap was based on previous works done by Garcia et al. (2000). Besides permanent instrumentation, sediment transport devices will be deployed from the bridge above the station during floods to complement the automatic sediment transport records. Bedload will be measured by means of a 76 kg 152 mm-intake Helley-Smith Sampler and suspended sediment by means of a US DH-74 depth integrated sampler (for details see Vericat and Batalla 2005). Figure 22 Installation of the bedload trap at the Ribera Salada Watershed 61

63 Appendix 1-B: Brazil The field monitoring program of the study areas in Brazil is carried out by the Federal University of Ceara, Brazil. Three nested experimental catchments have been selected in the north-eastern part of Brazil, as depicted in Figure 23: the Oros catchment and nested inside the Bengue Representative Basin and the Aiuaba Experimental Basin, all located within the Federal State of Ceara. Figure 23 Location of study sites in Brazil (Picture supplied by Benjamin Creutzfeldt) Aiuaba Experimental Basin The Aiuaba Experimental Basin has a size of 11.5 km² and is controlled by a reservoir with a present storage capacity of about 100,000 m 3. The climate in the watershed is typical of the Brazilian semiarid zone, with a mean annual precipitation of 430 mm, accompanied by a high interannual (as well as intra-annual) rainfall variability and a potential annual evaporation rate of 2,200 mm. The rainfall occurs in the rainy season between January and June. The mean annual temperature in the area is approximately 25 C. The natural vegetation of the basin is called caatinga. It is woodland with a mixture of trees and shrubs with a height of 3 to 7 m and a density which can vary from very high dense dry forests to almost desert sites, where bushes are isolated. Thorn-bearing species and xerophytes are frequent in the drier parts of the area. In most areas, farmers use the land for cattle breeding and for corn and beans crops, the most important economic activities in the region. The main geological unit is the Precambrian and Proterozoic crystalline basement. Soils on the crystalline basement tend to be shallow, clays and often contain a significant amount of rock fragments. Existing monitoring data Within the Aiuaba Experimental Basin, three automatic rainfall gauges are installed. Each station is composed of one automatic pluviometer with resolution of mm, which computes rainfall every 5 min and 6 h, one soil humidity sensor (installed at a depth of 15 cm), which measures soil humidity every hour and one data-logger. Close to one of the rain gauge, a class A pan is installed as depicted in Figure 24 for the measurement of the potential evaporation rate. This pan has an automatic ultra-sound level sensor, which measures hourly and a micrometer for manual measurements which are carried out once a day. 62

64 Figure 24 Rain gauge (left) and class A pan (right) in the Aiuaba Experimental Basin An experimental site (10x10 m 2 ) was constructed to study rainfall interception of vegetation (dense dry forest caatinga), close to one of the automatic rain gauge (50 m). Eleven Ville de Paris pluviometers (ten underneath the vegetation with random relocation every two weeks and one in an open spot) and sample bottoms for the collection of stemflow were installed to compute daily interception losses. Figure 25 shows the instruments within the experimental plot. Figure 25 Ville de Paris pluviometers (left) and stemflow measurement (right) as part of the interception study A Parshall flume, connected to a pressure transducer and a data-logger, has been installed at the main river of the watershed, controlling a catchment area of about 9 km 2 (Figure 26). Figure 26 Parshal flume within the Aiuaba Experimental Basin The change or water table level at the reservoir at the outlet of the Aiuaba Experimental Basin is measured twofold, as shown in Figure 27: first, an OTT Thalimedes Shaft Encoder Water Sensor 63

65 connected to a data-logger is installed close to the outlet of the reservoir and measures the water level on an hourly basis. Second, four limnimetric rulers are installed at different locations within the reservoir and readings are taken by a technician once a day. Figure 27: Automatic sensor support structure (left) and limnimetric rulers inside the reservoir (right) at the outlet of the Aiuaba Experimental Basin New monitoring scheme within the SESAM project A water-stage sediment sampler was installed in the summer 2005 inside the main stream of the basin, ca. 5 m downstream of the Parshall flume. The sampler enables the measurement of suspended sediments in the river water with sediment concentration being measured at different depths of water flow inside the river. Figure 28 shows photographs with, from left to right, the metal sampler holder in the dry, ephemeral riverbed, the box containing 15 sampling bottles, and the installed sediment sampler. Two similar samplers are under installation in the main rivers upstream the Bengue reservoir. Figure 28 Automatic sediment sampler, left: dry riverbed, middle: sampling box, right: installation Bengue Representative Basin The Bengue Watershed has a size of ca. 933 km 2 and contains the Aiuaba Experimental Watershed. The main river of the watershed is the Umbuzeiro River which disembogues into the Bengue Reservoir. The Bengue Reservoir has a storage capacity of 19.6 million m 3 and floods an area of ca. 350 ha. The average inflow into the reservoir is about 30 million m 3 water per year, but since evaporation (2100 mm per year) and yearly inflow coefficient of variation (Cv = 1.2) are very high, the reservoir yields only 6.5 million m 3 /yr (with 90% guarantee level). According to Araújo et al. (2003), the sedimentation rate in Ceará for similar watersheds varies from 130 ton.km -2.yr -1 to 690 ton.km -2.yr -1, depending on land use, so that sedimentation expectation for the Bengue dam ranges from 1.4 to 7.3 million tons per decade, or from 1.2 to 5.6 million m 3 storage capacity reduction per decade. This means that, if erosion is not controlled, the dam could be lost in less than 40 years due to 64