EFFECTS OF URBAN DEVELOPMENT ON BALTIMORE REGION WATER AVAILABILITY

The majority of the world's population now resides in cities, yet we still have an incomplete understanding of how urban development affects water availability. We undertook a study in order to understand the water balance effects of piped and natural inflows and outflows to Baltimore area watersheds. We found that decreases in urban evapotranspiration and increases in groundwater export via sanitary sewer pipes (I&I) had important effects on Baltimore City catchment water balances.

To better isolate the effects of individual urban features, such as less vegetatative cover, greater impervious cover, greater groundwater export through the sewer system, and greater residential well pumping, we have developed a groundwater-surface water model of the Baltimore region. We are using ParFlow.CLM as the integrated hydrologic model. This model is applied to the 13,000 sq. km. Baltimore metropolitan area, which spans the Gunpowder and Patapsco watersheds.

The model domain includes both Piedmont and Coastal Plain physiographic provinces. We have incorporated characteristics of both the natural hydrogeologic system and the superimposed urban environment. Standard hydrogeologic information such as hydraulic conductivity of fractured bedrock, Coastal Plain sediments, and surficial soils, as well as saprolite thickness, porosity, and specific storage properties have been included. We have also quantified a number of aspects representing urban development, such as residential and municipal well pumping, municipal reservoir use, lawn watering, and water supply pipe leakage estimates. We have represented impervious surface coverage using low surface hydraulic conductivity values. The land surface fluxes in CLM (Common Land Model) use surface land cover and therefore represent reduced evapotranspiration in urban areas.

To better understand the feedbacks between urban development and water availability, this model will be coupled with an urban growth model, both of the Baltimore, Maryland, USA region. The urban growth model SLEUTH has been calibrated, validated and run by collaborators at Shippensburg University.