Transactions on Information and Communications Technologies vol 18, 1998 WIT Press, ISSN

Transcription

1 STREAM, spatial tools for river basins, environment and analysis of management options Menno Schepel Resource Analysis, Zuiderstraat 110, 2611 SJDelft, the Netherlands; Abstract The STREAM instrument was designed by Resource Analysis on the basis of the RHINEFLOW model build by Resource Analysis in cooperation with the University of Utrecht, The concept of this model has been extended in order to assess various exogenous impact factors on the fresh water hydrology within river basins The result is a generic River Basin Management instrument that can be adjusted easily to meet requirements in non-standard cases. The setup makes it possible to introduce local (cell size) variations of exogenous factors in the model. 1 Introduction 1.1 The GBM Model In the first effort was made by Resource Analysis and the University of Utrecht to build a new type of river basin management tool based on a GIS environment that could be used for the interpretation of water balances, climate changes and land-use development. This tool was designed in MS-DOS to assess the vulnerability of the River Rhine basin for Climate Change. This concept has been extended and applied

2 44 GIS Technologies and their Environmental Applications on the Ganges/Brahmaputra/Meghna (GBM) to assess impacts of climate change on the water availability of the GBM basin. The STREAM instrument covers the Rhine and GBM concept aiming at environmental and development impacts of large basins using spatial data. The model enables the analysis of impacts induced by human developments or climate change on the fresh water hydrology of the basins. The STREAM model simulates the hydrological process in a spatial distributed environment and is capable showing which areas are drought prone or have still available water potential. At the same time it is a very strong tool for analyzing the impacts of scenario variables like climate change or tendencies, e.g. increasing water demands, increasing irrigation demands. STREAM is the Windows version of the GBM model. It carries the same functionality as the GBM model: 1. The use of spatial data 2. Interactive spatial modeling possibilities using a script language. But moreover, STREAM is designed around an user friendly interface in order to facilitate both the technical as well as the less technical user. Beside the standard program a thematic module (STREAMS/,) has been developed to analyze the impact of sea level rise for low land areas. 2 Model Description 2.1 Model Concept In this model the hydrological cycle has been represented as a combination of the rational method and the routing method, frequently applied in catchment runoff modeling, as developed by Van Deursen and Kwadijk (1994). This methodology represents the hydrological process as a three level lumped reservoir model containing reservoirs for 1) a snow cover storage, 2) the soil component (including storage, interception, evaporation and transpiration) and 3) a ground water component. A flow diagram of the linkage between the processes is presented in figure 1. This well known hydrological approach has been combined with the characteristics of raster based Digital Elevation Model (DEM) giving a discrete model of the river basin. As a result a calculation matrix is obtained that can be used to simulate the hydrological process. The matrix represents the grid cells, each containing an independent hydrological model calculating the water balance for that grid cell.

3 GIS Technologies and their Environmental Applications 45 Precipitation Runoff Figure 1: Flow diagram of the hydrological processes Because of its set-up, it is possible to feed each cell with local data and combine the basic data with a number of maps to specify the local conditions of the hydrology (e.g. for urban areas, forest, irrigation, bedrock). In models consisting of 10,000 to 500,000 or more grid cells this will result in simulations giving not only a high accuracy but also the spatial representation of the hydrological situation within the river basin. 2.2 Required Input The model is based upon a DEM and requires due to the methodology only limited amounts of data. These data can be obtained from databases, maps or Remote Sensing images, making the model applicable in the most remote areas. The model requires the following input (in maps): Topography (DEM map) Soil type Land-use Precipitation Temperature These maps give the user of the model not only the possibility to analyze the present situation but also impacts of changes that can be induced through these maps (scenarios or cases). The soil type map can be used to include e.g. erosion, degradation of soils, while the land-use map can

4 46 GIS Technologies and their Environmental Applications be used to study the impact of the increasing population and the related growth of urbanization, agricultural and industrial activities. 2.3 Obtained Output The results of the calculation can be divided in time series and maps. The time series can be obtained for every point in the river, to be defined by selection. The following types of time series can be obtained: Discharges Evapotranspiration Groundwater Snow cover Soil moisture The maps can be saved for selected features and at pre-defined time steps. Maps can be obtained representing the following features: Aridity soil moisture Snow cover Groundwater The results of the simulations for the 'present situation' and 'scenarios' give the policy maker and decision maker the possibility to analyze the impact of the simulated scenario. Especially the impact over longer periods is of major importance in relation to sustainable use of natural resources, environmental or climate change issues. 3 Program Design 3.1 Boundary Conditions Because of the wide acceptance of the Windows operating system, the program was rewritten to make it Windows compatible. The software design was aimed at developing a program that was user-friendly for the different end users. Three groups of end users can be expected: Decision makers Model makers Other technicians (hydrologists, agronomists, etc.) To fulfill the needs of these different groups a multi level approach has been implemented.

5 GIS Technologies and their Environmental Applications 47 In the original instrument the different models could be very easily implemented using a MS-DOS batch file. One of the objectives when designing the STREAM instrument was to maintain this flexibility. A scripting language was developed that enables model makers to edit or renew models easily. As a result of the format of part of the input data (the continuous DEM) and the cell based approach of the hydrological model, the instrument had to be raster based. The GIS functionality within STREAM has been build in standard programming languages. This makes it possible to distribute the STREAM instrument for a price that is affordable for the end users, even if they are located in less developed countries. In order to be generic it had to be possible to introduce new maps to apply the instrument for different regions and scenarios. Therefore conversion tools to and from widely used GIS formats (ESRI and IDRISI) are incorporated into the instrument To make it possible that various parameters influencing the river basin outflow can be changed, a map editing tool was build-in. 3.2 Multi Level Approach Within the program there are different lines that can be followed, the user can choose to run the default model using default values for the different parameters. For the user that has no in-depth knowledge about the calculation model or the different parameters it is nevertheless possible to change parameters like the number and the time interval of the iterations. Furthermore the user can change the in- and output datasets enabling a choice between different scenario's and/or different regions. For users that have knowledge about the calculation model a simple model editor is provided to add their own model or change the default model. This model editor is text driven and therefore the models are easy to understand and build. The user that is interested in changing the actual parameters that are used for the calculations can use the map editor which enables him to edit pixel values on the input maps (e.g. land use, climate). 3.3 Scripting Language In order to maintain the flexibility in designing and changing models that was available in the original model, the STREAM instrument

6 48 GIS Technologies and their Environmental Applications contains the specially designed BLAISE scripting language. This scripting language converts enables the model maker to write batch files in the integrated text editor (or any other ASCII- editor) and use these as models. 3.4 GIS Functionality To enable visualization and comparison of the output maps, user interaction has been added to the program. Standard GIS functionality related to visualization of spatial data like zooming, panning and displaying coordinates is available. As a result of the changing condition in the river basin the output maps can differ significantly over the time span considered. To ease up the orientation the user can project base maps in vector format over the output maps (e.g. Administrative Boundaries, Urban Areas). The user has the choice whether he wants to see on or more vector layers. Because the user must be able to change input parameters of the model and all the input parameters are in the form of maps a map editor has been integrated into the instrument. A separate screen is available where users can edit pixel values in a map using on-screen digitizing. The user defines the area of interest by digitizing a polygon andfillsin the appropriate (changed) value for the parameter. 3.4 Three Dimensional Visualization As an aid for the visualization of different input maps a 3D-Viewer has been added. The input for this viewer is in VRML-format. A conversion tool for the input maps into VRML-format has been developed. This 3Dviewer uses a public domain program that has been integrated in the STREAM instrument. With this viewer the user can fly over the different input maps. Besides this major landmarks can be labeled to improve the orientation. When the user needs more detailed data (e.g. valleys, surroundings of major cities) these can be provided as extra maps and they can be visualized by clicking on the appropriate location on the map. 4 Program Description The Graphical User Interface (GUI) has been built using the Delphi programming environment. The result is a set of windows that are ordered by functionality. From the main screen the user can enter three

7 GIS Technologies and their Environmental Applications 49 sub-screens containing: 1. Background information and manual 2. River Basin Management Case selection Input/Output selection Map editing Script selection and editing Model execution Output viewer 3. 3D viewer This functional setup increases the accessibility for new users. This is of special importance because many of the decision makers who will be using this program are infrequent computer users. 4.1 River Basin Management The River Basin Management screen can be considered as the core of the program. In this screen most of the functionality and user options are concentrated Case Selection The case selection screen offers the user the choice of a case or scenario that has been provided or defined earlier. When choosing a case the input/output options will be changed automatically in the input/output selection screen Input/Output Selection In this screen the user can change the source directories for the input files and the target directory for the output files. The user can enter the simulation time for the calculations. For more experienced users there are options to change the locations for which time series are computed and perform pixel editing on input maps Script Selection and Editing This screen provides the user with an script-editor which enables him to select the script that he wants to use or add new scripts. Another option is to change the default script or earlier developed scripts. This option in combination with the possibility to change the location of the input and

8 50 GIS Technologies and their Environmental Applications output files gives the opportunity to compare the calculations with different scripts and input files to see their influence on the outflow of the river basin. The BLAISE scripting language makes it possible that even not very experienced users can make small script changes Model Execution The run button opens a screen where the progress of the calculations is visualized by showing comment lines from the script. Error messages are shown containing information about the type of error and the place of the error within the script Output Viewer When the calculation has finished or when an already existing case has been selected the output maps can be viewed in the output viewer. In this viewer a map window is shown. A list containing the output maps and charts (showing the time series) and a list showing the available vector files is displayed next to this. All the output maps are numbered according to the iteration in which they were produced (every iteration in the calculation produces one or more output maps) and therefore trends in the model can be seen. Within the maps as well as the charts zooming and panning is possible. As an extra the charts can be viewed using a 3D effect. The map viewing window was build using ESRI MapObjects software, the output maps that can be seen in this window are in bitmap format with a linked worldfile that takes care of the georeferencing. These worldfiles are automatically created during the calculations using the documentation files of the input (IDRISI) maps. Within the script palettes can be set for each output map. The legend for the output map is scaled automatically and can be visualized on request. The cartographic symbols used in the vector files (shapefile format) are generated automatically from their ArcView Legendfiles (AVL). These AVL files are converted into INIfilesthat are used by STREAM to draw the vector files with the right symbols (colors and markers). The vector files are presented in a tree-view that is expanding automatically when the vector file is drawn on the screen showing the legend. The map window can be printed or saved to file. 4.2 Strong Points STREAM The single basic model: The composition of the DEM, the soil type map and the possibility to integrate the spatial distribution into the analysis

9 GIS Technologies and their Environmental Applications 51 give this tool an unique capacity compared with the traditional lumped models used for river basin management. The process components (e.g. water withdrawal in agriculture, interception in forests or snowmelt) are all represented at the appropriate level of detail and for each of the gridcels. Therefore, the basic model does not have to be changed when different options have to be analysed. If the land use function changes only the landuse in this gridcell has to be changed, the corresponding hydrological parameters are already integrated. This change automatically results in a changes in the runoff from this gridcell. This facilitates development and policy studies of the water basin without continuous calibration or manual changes. Detail at gridcell level. The more regional specific hydrological parameters can be taken into account. The seepage of evaporation values are given for the specific grid cells. These values will change depending on the soils, slopes, soil depth etc. If required the model can be built with the local values for the different parameters. It is not necessary to enter these values manually but the GIS capabilities can be used for this purpose. Flexible resolution in time and space: The hydrological process is not defined per valley of catchment but based on gridcells, which are usually a magnitude smaller. The hydrological parameters are related to the gridcells and defined by the input (e.g. landuse, slope, soil). The size of the gridcell is therefore the only parameter determining the resolution of the model as long as it does not exceed the accuracy of the input data. In this case the accuracy of the model is depending on the size of the gridcells. The timestep used in the model is related to the size of the gridcells. A smaller time step supports a smaller gridcell size. With gridcells in the order of 1x1 km timesteps of 2 days-to 1 week can be used. Flexible output: Timeseries: For every location (gridcell) a time serie can be saved of any of the results parameters, e.g. soil storage, runoff, snow storage, etc. The user has a free choice to select the locations according requirements. Maps: For every time step and for every parameter a map can be produced. This means that a good insight in the spatial distribution of every parameter can be obtained (e.g. wet and dry areas). Maps with topographic features (e.g. cities, roads), or maps with different socio-economic features (e.g. population density, economic value) can be superimposed. By combining these data it will be possible to develop and analyse policy strategies and mitigating programs. Flexibility: The two most important aspects determining the

10 52 GIS Technologies and their Environmental Applications flexibility are 1) the input in the model is compatible with maps produced in Idrisi and ArcView, the most commonly used GIS packages worldwide and 2) the data requirements of the model are relatively low compared to more deterministically based models. These two aspects guarantee the applicability of the model in the case where many other models are not applicable anymore due to lack of data. 4.3 Weak Points STREAM Minimum catchment area: The model is, Inherent to the approach used, only applicable in areas bigger then 1000 km2. The simplification of the hydrological process will influence the simulations if smaller area are covered and make the results invalid. Missing routing component: The model is a steady state model with a value for each time step. The routing through the river channel is neglected and is covered for by the calibration. This means that hydrodynamic river studies can not be executed with this tool. This is a simplification inherent to the used of the lumped reservoir model. 5. Company Information Resource Analysis is a research and consulting company with a very strong track record in water resources and coastal zone planning and management, capacity building and institutional development, in the Netherlands as well as internationally. Resource Analysis has its main core of expertise and experience in the development and implementation of government policy related to management of coastal zone planning, water resources, environment, natural resources and impacts assessments of water and air quality. Much of the success of RA has been due to its founders' early adoption of a policy analysis and structured systems approach to the management of natural resources. More recently, as RA has developed, this approach has been incorporated into computerized software tools that has allowed government departments a greater understanding of the analysis procedure. RA staff are continuously active in building bridges between science and government, thus building the capacity for integrated planning and management, while effectively making scientific data available and understandable to the decision making process.