Determining the Suitable Sediment extraction Locations of Existing Sand and Gravel Mines on Boshar River in Iran using HEC-RAS Modeling

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1 ICSE6-134 Determining the Suitable Sediment extraction Locations of Existing Sand and Gravel Mines on Boshar River in Iran using HEC-RAS Modeling Mohammad GHARESIFARD 1, Ali JAHEDAN 2, Bahar MOLAZEM 3 1 Civil Engineering Expert/Asmari Consultant Engineers No.44 Sarv-e-naz St. Eram Blvd. Shiraz-Iran - Gharesifard@yahoo.co.uk 2 Water Resource Management/Shiraz Azad University Pardis Complex, Sadra, Shiraz-Iran - Jahedan.ali@gmail.com 3 GIS Expert/ Asmari Consultant Engineers No.44 Sarv-e-naz St. Eram Blvd. Shiraz-Iran - Bhr_ml@yahoo.com ABSTRACT In recent years, rapid development of Construction Projects has led to an increased demand for river sand and gravel as a source of construction material. In Iran, like many other countries, the main source of sand and gravel is from in-stream mining. In-stream sand mining can damage private and public properties as well as aquatic habitats. Excessive removal of sand may significantly distort the natural equilibrium of a stream channel. The magnitude of the impact basically depends on the Time, Location and magnitudes of the extraction relative to bed load sediment supply and transport through the reach. The main Idea of this paper is to apply HEC- RAS River modeling on a selected river in order to identify the suitable locations for sand and gravel mining along the river reach and compare the results with the actual Location of three existing mines which have been identified based on local knowledge of the aggradation or scour rate. The selected river is Boshar River, a main upstream prong of Khersan River in Karoon Catchment which is located in Kohkeloyeh and Boyerahmad Province-Iran. There are several in-stream sand and gravel mines along this river and these mines extract a large volume of sediments from this river each year. The selected model portion is an 8.9Km part of Boshar River which has 3 active sand and gravel mines. The geometric input data were derived from 1/2000 surveyed topographic maps and the DEM files were developed using GIS. Applying HEC-GEORAS extension the geometric data were imported in to HEC- RAS. In the next step the boundary conditions obtained from the nearest hydrometric station where inputted in to HEC-RAS. Analyzing the model output sediment spatial plots, Time series plots and bed change plots, Parts of the river reaches that experience deposition or aggradation were identified along the river length. Based on these output results, there are three main zones which experience the most deposition along the river length. Comparing these potential deposition locations to the actual extraction areas of the 3 existing mines shows quite a good match, although a 100 to 250 meters change in location of extraction areas is recommended in order to find the best location for excavation and minimize the aggradation or scour problems. KEYWORDS Sediment Modeling, HEC-RAS, River, Sand and gravel mines. I INTRODUCTION The earliest attempts in sediment modelling originated from relating soil loss from field plots to slope and steepness (Zingg, 1940). This work extended by several researchers (Smith, 1941; Browning et al, 1947) 477

2 ICSE6 Paris - August 27-31, 2012 which led to the development of the famous universal soil loss equation (USLE) (Wischmeier and Smith, 1958, 1965, 1078). Early models were based on simple one-dimensional, steady-state conditions. Advances in the theory of flow and transport phenomena and in computer technology elevated the art of sediment transport and water quality modelling as time constraint was not a factor anymore. Development of fully dynamic steady state and three dimensional water quality models became feasible. The computational capability allowed the coupling of water quality models with watershed and hydrodynamic models. As results, varieties of models have become available. HEC-RAS is an integrated package of hydraulic analysis programs in which the user interacts with the system through the use of a graphical user interface (GUI). The current system is capable of performing steady and unsteady flow water surface profile calculations, and sediment transport. In HEC-RAS terminology, a project is a set of data files associated with a particular river system. The modeler can perform any or all of the various types of analyses included in the HEC-RAS package as part of the project. The sediment transport potential is computed by grain size fraction, thereby allowing the simulation of hydraulic sorting and armoring. Major features include the ability to model a full network of streams, channel dredging, various levee and encroachment alternatives and the use of different equations for the computation of sediment transport. The data files for a project are categorized as follows: plan data, geometric data, steady flow data, unsteady flow data, sediment data, and hydraulic design data. In this study, HEC-RAS will be utilized as one of the mathematical models to simulate the Sediment transport in Boshar River and suitable locations for sediment extraction will be determined using this hydraulic modelling program. II PROJECT SITE DESCRIPTIONS The selected river is Boshar River, a main upstream prong of Khersan River in Karoon Catchment which is located in Kohkeloyeh and Boyerahmad Province-Iran. This river is 150 kilometres long and its catchment area is 3600 square kilometres. Boshar River's catchment mainly consists of mountains and highlands and includes lowlands with poor vegetation in a small area. There are several in-stream sand and gravel mines along this river and these mines extract a large volume of sediments from this river each year. The selected model portion is an 8.9Km part of Boshar River which has 3 active sand and gravel mines as shown in Figure1. Figure 1: Aerial view of Selected mines on Boshar River. 478

3 III HEC-RAS MODEL INPUT DATA A HEC-RAS sediment model requires geometric data, cross sections, roughness coefficient, flow boundary conditions and sediment data. These input data have been derived from site surveyed maps, hydrometric station data and other collected field data. Detailed descriptions on each Parameter are as follows: III.1 Geometric data and cross sections HEC-RAS has the ability to import three-dimensional (3D) river schematic and cross section data created in GIS system. The geometric input for the model was derived from the 2008 surveyed plan in CAD format. Selected surveyed map has 1/2000 scale in order to have enough accuracy. Then the DEM file was developed from CAD topographic plan using GIS. The next step was to create cross sections in GIS which was created with an average distance of 50 meters from each other as shown in Figure2. Study site stretch is approximately 8.9 km. HEC-RAS modeler has the ability to develop the geometric data by importing it from GIS. HEC-GEORAS extension was employed In order to import the data. III.2 Figure 2: Developed cross sections in GIS Estimating Manning's roughness coefficient In order to determine Manning's roughness coefficient, four different cross sections where surveyed along the river length and there water level were measured on site. Table 1 illustrates the measured data for each cross section. These data were collected on 4 August 2009, measured discharge on this date at SHAHMOKHTAR hydrometric station was 2.73m 3 /s. Using manning equation water level was determined for different manning roughness coefficients and Standard Error of Estimate (SEE) was calculated for each n value. The smallest SEE relates to n=0.037 which was selected as the calibrated manning roughness coefficient for the model. Table 2 illustrates the calibration procedure of n value. Section Hydr-Radius(m) Area (m2) Slope Water level (m) a b c d Table 1: Surveyed cross sections and related water levels. 479

4 Section Measured Determined water level using manning equation (m) water level on site n=0.025 n=0.028 n=0.031 n=0.034 n=0.037 n=0.040 (m) a b c d SEE III.3 Table 2: Manning roughness coefficients calibration using SEE method. Flow boundary conditions Flow boundary conditions for the model were collected from SHAHMOKHTAR Hydrometric station which is located approximately 5 Kilometers upstream of the selected mine location. Table 3 represents Boshar River s average discharge of different months of The average annual discharge recorded in SHAHMOKHTAR Hydrometric station is 23.68m 3 /s. JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEP. OCT. NOV. DEC. ANNUAL III.4 Table 3: Average monthly and annual discharge in m3/s of Boshar river. Sediment data Sediment data employed to perform the HEC-RAS sediment transport analyses are as follows: - Bed material gradation Four Bed material samples have been selected from Boshar River, in order to determine river's bed material gradation. Figures 3 and 4 represent Sieve analyses test results of the selected samples. 480

5 Figure 3: Bed material sample gradation curves (Samples No.1 & No.2) 481

6 Figure 4: Bed material sample gradation curves (Samples No.3 & No.4 ) Sediment samples were collected from different locations across the length of the river in order to represent the intermediate grading of the aggregates. HEC-RAS has the ability to interpolate bed material gradations. Using this Ability Three medium gradation curves from the selected samples were developed. 482

7 - Sediment transport function There are numerous sediment transport equations, each of which was developed for specific types of conditions and purposes, since sediment transport is sensitive to so many variables, the potentials computed by the different equations can vary by order of magnitude, depending on how the actual material and hydrodynamics compare to the parameters over which the transport function was developed. Therefore the sediment transport function which has been developed for similar bed form, gradation and hydraulic parameters should be selected in order to achieve the best results. There are seven sediment transport functions in HEC-RAS 4.0 and table 4 illustrates slope, data source, bed properties, sediment size and other conditions for which they were developed. Table 4: HEC-RAS available Sediment transport functions and there descriptions Acker and white equation is based on flume experiments and has Froude number limitations. England Hansen equation should be restricted to sand bed systems with bed material size restrictions that do not match the study site. Laursen Copeland equation has been developed for a specific slope range that does not match our channel slope. Meyer- Peter Muller is also based on flume experiments and is strictly a bed load function. Toffaleti is best suited for sand bed large rivers and finally Wilcock is a bed load equation which is very sensitive to sand content parameter. Yang equation was selected as the best suited sediment transport function for the study site, because it has been developed from both flume data and field data, it's applicable for graded beds containing both sand and gravel and has been successfully tested for both flume data and field data (Chang 1988). - Bed sorting method In most of the river systems, the full bed gradation is covered by a layer of coarse material called an armor layer. This layer can be formed by static armoring or the differential transport of the finer 483

8 materials. In order to model this armor layer, two algorithms have been included in HEC-RAS to simulate bed sorting and armoring. Both methods are based on dividing the bed material into an active layer and an inactive layer. Exner 5: A three layer active bed model (see Figure 5) that includes the capability of forming a course surface layer that will limit erosion of deeper material thereby simulating bed armoring (Tomas 1982). Active layer method: This is a simplified two layer active bed approach (see Figure 5). The active layer thickness is set equal to the d90 of the layer. This assumption is only appropriate for gravel beds and is intended to use with the Wilcock transport method in particular. Based on the existing conditions and chosen sediment transport equation, Exner 5 method has been selected for the model. Figure 5: Schematic of the mixing layers in HEC-RAS sorting methods - Fall velocity method There are currently four methods for computing fall velocity in HEC-RAS, Ruby, Toffaleti, Van Rijn and Report 12. The employed method is Van Rijn, who used Ruby as an initial guess and then computed a new fall velocity from experimental curves based on Reynolds's number computed from the initial guess. IV HEC-RAS MODEL OUTPUT GRAPHS AND TABLES There are a wide range of variables which can be accessed either in graph or tabular format from Sediment Spatial Plot menu in HEC-RAS. These include: thalweg elevation, water surface elevation, velocity, bed change, and an array of weights and volumes tracked by layer and grain size. Figure 6 illustrates a number of Boshar River s output graphs. Monitoring bed changes along the river length during different time periods will help us to locate the potential deposition areas. h:\3-hec-ras on jahedan-gharibi (Pourab14)\model2.sed04 h:\3-hec-ras on jahedan-gharibi (Pourab14)\model2.sed booshar-1 Legend 0.8 booshar-1 Legend 02JAN :00:00-Ch Invert El (m) 02JAN :00:00-Invert Change (m) 30DEC :00:00-Ch Invert El (m) 30DEC :00:00-Invert Chang e (m) Ch Invert El (m) 1680 Invert Change (m) Main Channel Distance (m) booshar h:\3-hec-ras on jahedan-gharibi (Pourab14)\model2.sed Main Channel Distance (m) Legend 02JAN :00:00-Mass Bed Change Cum: Al l (tons) 30DEC :00:00-Mas s Bed Change C um: All (tons) Mass Bed Change Cum: All (tons) Main Channel Distance (m) Figure 6: HEC-RAS Spatial Plot output graphs 484

9 V RESULTS Analysing the model output sediment spatial plots, Time series plots and bed change plots, Parts of the river reaches that experience deposition or aggradation were identified along the river length. Based on these output results, there are three main zones which experience the most deposition along the river length. Comparing these potential deposition locations to the actual extraction areas of the 3 existing mines shows quite a good match, although a 100 to 250 meters change in location of extraction areas is recommended in order to find the best location for excavation and minimize the aggradation or scour problems. Figure 7: Invert change spatial plot & suitable extraction locations VI CONCLUSIONS This modelling procedure may be used in order to determine best suited sediment extraction locations and spot the potential deposition zones along the river length. Combination of this simulation output results with the local knowledge of the river morphology can be applied to achieve the best results and minimize aggradation or scour problems caused by in-stream mining. VII REFERENCES Chang, H. H. (1988). Fluvial Processes in River Engineering. John Wiley and Sons, New York. Gary W.Brunner (2008). HEC-RAS 4.0 River Analysis Hydraulic Reference Manual. Gharesifard, M. (2010). Karoon Catchment Sand and Gravel report, Regional Water Department of Isfahan, Iran. Yang, C.T. (1996). Sediment Transport Theory and Practice. The McGraw-Hill Companies, Inc., New York 485