CREATING A MODEL OF STORM WATER RUNOFF FOR THE CITY OF OXFORD, MISSISSIPPI: WHEN IT RAINS, WHERE DOES IT POUR?

The city of Oxford, Mississippi (home of the University of Mississippi), is experiencing rapid growth and, like many small municipalities, lacks important baseline information critical to planned development. The objective of this project is to create a baseline water budget for the city. Oxford is situated on the highest area of Lafayette County, with no surface water inflows into the city. All surface water input is almost entirely from rainfall, with only minor input from residential and commercial watering systems. The city lies on a surface water divide with all surface drainage flowing to either the Sardis Lake Basin to the north or the Enid Lake Basin to the south. The water budget model being created will comprise rainfall, estimates of irrigation volumes, soil infiltration and natural surface runoff, impervious surface runoff, redistribution of storm water runoff through drains and piping, and estimates of evaporation loss.

Historic rainfall is modeled stochastically using precipitation data from the PRISM Climate Group (available, depending on time period, at 4km to 800m resolution) combined with multi-station daily rainfall measurements made over a 13-month period in the Oxford area. Gridded evapotranspiration data were obtained from the USDA. Storm drain and sewer system data were obtained from the City of Oxford, the University of Mississippi, and by direct measurement with GPS when necessary. Recent LiDar data were available for detailed topography and infrastructure location, supplemented with recent sub-meter resolution satellite imagery. Infiltration rates were measured using the single ring infiltrometer method supplemented with a bucket method for rapid measurement of multiple locations. All data were incorporated into ArcGIS file geodatabases for model development. The final product is a dynamic model, based in GIS and readily modifiable, that will permit calculation of surface water runoff and flooding potential, and be useful as a planning tool in evaluating changes associated with continued urban growth and development in Oxford.