ALAWAT - A SPATIALLY ALLOCATED WATERSHED MODEL FOR APPROXIMATING STREAM, SEDIMENT, AND POLLUTANT FLOWS IN HAWAII, USA

The Ala Wai Canal Watershed Model (ALAWAT) is a planning-level watersh ed model for approximating direct runoff, streamflow, sediment loads, and loads for up to five pollutants. ALAWAT uses raster GIS data layer s including land use, SCS soil hydrologic groups, annual rainfall, and subwatershed delineations as direct model parameter inputs and can us e daily total rainfall from up to ten rain gauges and streamflow from up to ten stream gauges. ALAWAT uses a daily time step and can simulat e flows for up to ten-year periods and for up to 50 subwatersheds. Pol lutant loads are approximated using a user-defined combination of rati ng curve relationships, mean event concentrations, and loading/washoff parameters for specific subwatersheds, land uses, and times of year. Using ALAWAT, annual average streamflow and baseflow relationships and urban suspended sediment loads were approximated for the Ala Wai Cana l watershed (about 10,400 acres) on the island of Oahu, Hawaii. Annual average urban suspended sediments were approximated using two methods : mean event concentrations and pollutant loading and washoff. Paramet ers for the pollutant loading and washoff method were then modified to simulate the effect of various street sweeping intervals on sediment loads.