AWWA CO50849

A method is presented for determining raster maps of mean annual water flow andpollutant loading from the land surface, and for determining the resultingconcentrations in receiving water bodies. The method is illustrated byapplication to the Corpus Christi Bay system in South Texas. A mesh of 100mdigital elevation model cells is laid over the drainage area and cell to cellconnectivity established to link each land surface cell with a correspondingwater body segment. Non-point source constituent loads are determined for eachcell as the product of runoff and expected mean concentration, and accumulateddown to the bay system. Point source and atmospheric loads are added, waterquality computed in each bay system, and compared to observed data. A strongSouth to North runoff gradient is observed in the study area. The majority of thepollutant loading comes from non-point sources, except for oil and grease, whicharise mainly from point sources. Nitrogen and phosphorus concentrations in thebay system are reproduced reasonably well provided a decay rate of 0.01-0.02 day-1 is used. Oil and grease are reproduced well as conservative constituents. Thecomputed metals concentrations are low and suggest a significant source insediment or elsewhere that is presently not accounted for. Includes 4 references, figures.