A geographic information system (GIS)-hydrologic model link was used t
o aid in forming input files for the hydrologic model, SWAT (Soil and
Water Assessment Tool). The link and SWAT prediction of streamflow vol
ume were then tested for the Lower Colorado River basin of Texas. With
no calibration, simulated monthly streamflow volume along the river w
ar underestimated for the extreme events, but the relationship was sig
nificant (R(2) = 0.75). Model results also suggest that urbanization f
urther upstream can significantly affect streamflow downstream. The sy
stem is general enough to be applicable to other river systems.