A GIS Assessment of the Total Loads and
Water Quality in the Corpus Christi Bay System
By Ann Marie Quenzer, M.S.E. and David R. Maidment
ABSTRACT
A method is presented for determining raster maps of mean annual water
flow and pollutant loading from the land surface, and for determining
the resulting concentrations in receiving water bodies. The method is
illustrated by application to the Corpus Christi Bay system in South
Texas. A mesh of 100m digital elevation model cells is laid over the
drainage area and cell to cell connectivity established to link each
land surface cell with a corresponding water body segment. Non-point
source constituent loads are determined for each cell as the product
of runoff and expected mean concentration, and accumulated down to the
bay system. Point source and atmospheric loads are added, water quality
computed in each bay system, and compared to observed data. A strong
South to North runoff gradient is observed in the study area. The majority
of the constituent loading comes from non-point sources, except for
oil and grease, which arise mainly from point sources. Nitrogen and
phosphorus concentrations in the bay 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. The computed metals
concentrations are low and suggest a significant source in sediment
or elsewhere that is presently not accounted for.
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