Introduction
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Documentation
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Introduction
The Spatial Water Budget Model (SWBM) was developed at the Crop Modeling Systems Laboratory of the University of Florida, Gainesville, Florida, in close cooperation with, and funded by, the International Center for Tropical Agriculture (CIAT), Cali, Colombia.
SWBM is a continuous, distributed parameter, watershed scale model that simulates water supply and demand over space and time on a daily basis using Geographical Information System (GIS) data structures. SWBM delineates streams and computes availability of stream water as it flows down slope or is (partially) extracted for domestic, industrial and agricultural uses. The model can simulate the effects on hydrology and water yields of changes in land use, water use for domestic, industrial and agricultural purposes, different locations of water extraction, and impedance by dams on a daily basis. Processes that are simulated by SWBM are: (i) land unit water balance, (ii) water flow to streams, (iii) stream water flow balance, (iv) water storage in dams and small reservoirs, and (v) water extraction from reservoirs and streams for domestic, agricultural and industrial uses. The model does not simulate peak flow, sediment loading, soil erosion and vegetation growth.
SWBM is a tool for assessing water availability and use under different development pathways at a watershed scale to determine whether water security is a potential problem, and if so, when and where it occurs. The model has been developed in particular for application in agricultural hillside watersheds in Latin America and the Caribbean of up to approximately 50,000 ha in size and for which few biophysical data are available, but it can be applied to watersheds in other areas as well. SWBM fills the gap between current needs of rural communities in developing countries and data demands of established, more complex models designed for application in developed countries. Simulation results obtained with SWBM can be used for supporting local decision-making processes to guide development to the benefit of local communities, as well as for teaching local stakeholders about basic functions of multiple community watershed components such as relationships between land and water resources, effects of water use, and upstream-downstream relationships. The model was not designed for engineering specific hydrologic projects or for describing the movement of water based on detailed physical processes.
SWBM has been programmed in Avenue, the scripting language of ArcView GIS software. It runs on Windows and Unix based systems on which ArcView GIS 3.1 or higher along with the Spatial Analyst v1.1 extension have been installed. Routing an accumulation of water as it flows down slope is computed using the GIS-intrinsic Flow Direction and Flow Accumulation functions. Data requirements are relatively low compared to those of existing hydrological models. Data are inputted as ARC/INFO grids and through user-friendly menus. Simulation results, which are saved in ARC/INFO grids and in dBase-IV files, can be processed using Avenue scripts and spreadsheet software.
