Potential on the use of GIS watershed modeling for river basin planning : case study of Attanagalu Oya Basin, Sri Lanka

Abstract

Careful management for identifying and allocating available water resources is important, to preserve water for present as well as future users. Modeling at basin scale can provide necessary information on river basin planning and support policy makers in their decisions on allocating water resources in the basin. This study focused on identifying the potential of GIS for spatially distributed modeling of watersheds for river basin planning. The spatially distributed GIS model represents the simulation of runoff in selected river basins. Selected river basins are characterized by nodal network approach and sub-catchment areas calculated using GIS tools. Runoff is assumed to be triggered by rainfall and mainly dependent upon land use, soil type and slope conditions. Spatially varied land use, soil and slope data for the selected catchments were digitized using GIS (vector format) and land parcels created by overlay operations in GIS showing different catchment characteristics were used in the model. All calculations were performed with standard GIS tools of ArcGIS software. A simple conceptual model was used to compute runoff from each land parcel. The model is capable of calculating runoff from catchment characteristics based on predetermined runoff coefficients at the presence of precipitation data. A nodal representation of case study basin was prepared using MIKE BASIN to estimate streamflow at each node. The runoff coefficient for Attanagalu Oya basin with the spatial variation of parameters was estimated as 0.51 using this approach. Model provides streamflow at any node provided in the model. The average streamflow identified to fluctuate between 10m3/s to 60m3/s without taking water extractions into consideration. Land use, soil, slope patterns can be changed in the GIS model to calculate new coefficients with new spatial variation and can be incorporated to the nodal modal to visualize the changes in streamflow patterns. Model results indicate the potential of the use of spatially distributed model for decision making when carrying out river basin planning.