&21&(37,21$1',03/(0(17$7,212)$1+<'52*(20$7,&02'8/()25 :$7(56+('$1$/<6,6 )UDQFR54XHQWLQ(DQG'tD]'HOJDGR& &HQWUR,QWHUDPHULFDQRGH5HFXUVRVGHO$JXD&,5$8QLYHUVLGDG$XWyQRPDGHO(VWDGRGH0p[LFR8$(0 &37ROXFD(VWDGRGH0p[LFRHPDLOUIS#XDHPH[P[ $%675$&7 Since the last sixties, the rapid progress of geomatics, associating geosciences with informatics, gives to decision manager of natural resources as water, tools indispensable for an integrated analysis of spatially related problems. Nevertheless, most Geographic Information Systems (GIS) presents basic operations for general purpose as distances and areas calculation, reclassification, overlay, map algebra, and very few advanced specific functions. Regarding hydrologic modeling, the algorithms integrated in GIS concern mainly the extraction from a Digital Elevation Model (DEM) of the flow direction, the flow accumulation, the flow length and the delimitation of subwatersheds and flow paths. The present work is aimed to the conception and implementation of an user-friendly hydrologic interface including existing operations adequately presented for a water-professional end user, like the computation of the principal physiographic and hydrographic characteristics of a watershed, as well as other fundamental but more complex hydrologic procedures such as network ordering (Strahler or Shreve) and hydrologic balance. As most of hydrologic algorithms are already developed, the challenges consists in their adaptation to the vector, raster and attribute GIS structures, and to help the user validating the data entries that must be conformed according to the result requested..(<:25'6 GIS, Hydrology, Management, Watershed,1752'8&7,21 Since the beginning of the establishment of human settlements, the importance of water and its availability in quantity and quality is no more to prove. But the persisting problems affecting this vital element demonstrate that the management of the water resources is lacking adequate methodologies. The concept of watershed and its uses in the elaboration of water management plans reveals to be adequate to solve in particular superficial water related questions, as the watershed of an outlet or river is the region providing water to this point or segment by superficial flow. It is important to outline that this concept allows a spatial division of a study region to various hierarchical levels depending of the scale desired. Moreover, the flow process is controlled by various factors that are variable over the watershed extent, the principal one being the altitude. These characteristics implies the necessity of the use of a geographic system for spatial analysis and integration of various parameters. This correspond to the definition of a Geographic Information System (GIS), it is to say a software for the creation, manipulation and analysis of a geo-database, making possible modeling and simulations of hydrologic processes by the way of a geomatics algorithms (Burrough and McDonnell, 1998). In the actual GIS software, basic functions of general use as area and distance calculations can be convenient for watershed analysis. And recently, they also include elemental functions deriving watershed and flow from a Digital Elevation Model, it is to say an altitudes matrix, called also raster, grid or image. An interesting approach for the design of a GIS menu concerns the software "Idrisi" (Eastman, 2003) where the organization of the modules considers two point of view : the toolset type Franco, R. HWDO 18
(database query, mathematical operators, distance operators, context operators or the application type (statistics, decision support, change/time series, surface analysis). That is why the water related modules can be find in various submenus: the Context Operators Submenu (neighborhood, local operators) or the Feature Extraction Submenu. The Idrisi hydrologic related functions comprise the following ones. PIT REMOVAL creates an adjusted "depressionless" DEM in which the cells contained in depressions are raised to the lowest elevation value on the rim of the depression. This is an important preparation step in many flow models. FLOW calculates the flow direction from each pixel into its next downhill neighbor. Unlike ASPECT, which gives a continuous output of directions, the output of FLOW is restricted to the eight neighboring cells for each pixel. This output is useful in many flow and hydrological applications. RUNOFF calculates the accumulation of rainfall units per pixel as if one unit of rainfall was dropped on every location. Using the RECLASS module, a threshold can be applied to the output to produce drainage networks. WATERSHED identifies areas that contribute flow to a part of the drainage network. The user either indicates the minimum size of watershed desired and the module breaks the entire image into watersheds of this size or larger or the user indicates one or more seed features for which to identify watersheds. RUSLE evaluates farmland and rangeland non channelized soil loss by water. It is an implementation of the Revised Universal Soil Loss Equation (RUSLE) described in the USDA Agricultural Handbook, Number 703. Arc View includes an hydrology extension for the ArcView Spatial Analyst version 1.1 further extends the Spatial Analyst user interface for creating input data for hydrologic models. This extension provides functionality to create watersheds and stream networks from a DEM (a grid data source representing elevation), calculate physical and geometric properties of the watersheds, and aggregate these properties into a single attribute table that can be attached to a grid or shapefile. The functionalities available are: Hydrologic Modeling - launches a custom dialog for the creation of watersheds and their characteristics Flow Direction - computes the direction of flow for each cell in a DEM. Identify Sinks - creates a grid showing the location of sinks or areas of internal drainage in a DEM. Fill Sinks - fills the sinks in a DEM, creating a new DEM. Flow Accumulation - calculates the accumulated flow, or number of up-slope cells, based on a flow direction grid. Watershed - creates watersheds based upon a user specified flow accumulation threshold. Area - calculates the area of each watershed in a watershed grid. Perimeter - calculates the perimeter of each watershed in a watershed grid. Length - calculates the straight-line distance from the pour point to the furthest perimeter point for each watershed in a watershed grid. Flow Length - calculates the length of flow path for each cell to the pour point for each watershed if you choose Yes, or the length of flow path for each cell to the furthest perimeter point of each watershed if you choose No. Flow Length by Watershed - calculates the maximum distance along the flow path within each watershed. Franco, R. HWDO 19
Shape Factor by Watershed - calculates a shape factor for each watershed. Shape factor is calculated as watershed length squared, divided by watershed area. Stream Network As Line Shape - creates a vector stream network from a flow accumulation grid based on a user specified threshold. Centroid as Point Shape - creates a point shape file of watershed centroids. Pour Points as Point Shape - creates a point shape file of watershed pour points. Mean Elevation - calculates the mean elevation within each watershed. Mean Slope - calculates the mean slope within each watershed. Mean Precipitation - calculates the mean precipitation in each watershed. Mean Curve Number - calculates the mean curve number for each watershed. Some works have been using water balance with GIS but for precise objectives, as identification of desertification prone areas, and as such not fully functional for other cases (Pimenta, 2000). The others developments are mainly relative to interfaces between GIS and existing hydrologic or hydraulic models (Djokic and Maidment, 2000). Theorical research applied in the conception of ArcGIS from ESRI (Maidment, 2002) presents appropriate diagrams to structure an hydrogeomatic database. But in water management perspective, there is a need to implement other specific procedures, as : calculation of watershed physiographic characteristics: it concerns geometric and topologic parameters about the watershed polygon, the principal river line and the stream network; models of water quantity : water balance, relation precipitation-flow; models of water quality. A complete integrated management of the water resources should also take into account methodologies that allow the consideration at the same time of superficial and ground water, quantitatively and qualitatively, as well as spatial transfers and time evolution. Furthermore, it would be useful to establish a standard for hydro-geomatics modules, with userfriendly interface explaining the purpose of each functions and helping in the validation of the input required. 0(7+2'6 The objective of the research is the development of a well organized extension for watershed management purpose, in generic terms independent of the GIS software and hardware to permit implementation in whichever platform. For the development of an hydrogeomatic module for watershed analysis, there is mainly three parts to consider : the geo-database structure, the algorithms of the functions to implement the organization of the interface. First and essential to be able to process the information, the geo-database structure has to follow some rules of integrity depending on the type of representation. point entities, as measure stations line entities, as stream network polygon entities, as watershed surface attribute, as elevation Franco, R. HWDO 20
Topological relations specific to hydrology must be present. This implies the implementation of functions that help the user to import and convert its original data to the adequate structure. For the hydrologic functions, the purpose is to collect and adapt to the same environment the more efficient algorithms already developed, with the required validation. In the organization of the interface, the idea is to group functionalities sometimes used for other purposes (as area calculation) with the ones that apply only for hydrologic studies, to facilitate its use by a non GIS specialist. 5(68/76$1'',6&866,21 In a first step, the implementation of the watershed analysis module was applied to the watershed physiographic characteristics for the GIS software ArcView from ESRI, using the internal object oriented programming language Avenue. The principal problem to address for this part is the validation of the input data and above all in case of errors in the data, the specification of instructions to the user in the aim of helping him to correct the structure of the information available. Figure 1 illustrates the functioning of the first submenu calculating geometric parameter of the watershed, while Figure 2 shows the different windows that can be generated by the function determining the Strahler orders. Figure 1. Results generated by the submenu for the evaluation of geometric watershed parameters Franco, R. HWDO 21
Figure 2. Results generated by the submenu for the determination of Strahler orders &21&/86,216 The originality of the research in course resides in the following points : taking advantage of the GIS structures, optimizing existing hydrologic algorithms in a GIS environment with adequate validation, design of a user-friendly interface. As this research is in progress, the design allows the aggregation of more functionalities since a further step to contemplate will be the development of new functionalities almost only possible in a GIS environment given that the spatial and multi-thematic dimensions must be considered as it is the case for water contamination and risk assessment. 5()(5(1&(6 Burrough P.A. and McDonnell R. (1998). Principles of Geographical Information Systems. 6SDWLDO,QIRUPDWLRQ6\VWHPVDQG*HRVWDWLVWLFV 6HULHV. Oxford University Press, UK. 333 p. Djokic D. and Maidment D.R. (2000). Hydrologic and Hydraulic Modeling Support with Geographic Information Systems. ESRI Press, 232 p. Eastman J.R. (2003). IDRISI Kilimanjaro. Guide to GIS and Image Processing. Manual Version 14.00. Clark Labs, Clark University. 328 p. Maidment D. (2002). Arc Hydro: GIS for :DWHU5HVRXUFHV. ESRI Press. 218 p. Pimenta M.T. (2000). Water Balances Using GIS. 3K\V&KHP(DUWK,, (7-8), 695-698. Franco, R. HWDO 22