FLOOD07038

• County: Statewide
• Community: All
• Stream Name: All
• Basin: South Platte
• Title: ASFPM Abstracts, etc. 1994
• Date: 1/1/1994
• Prepared For: ASFPM
• Prepared By: ASFPM
• Floodplain - Doc Type: Educational/Technical/Reference Information

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COMPREHENSIVE WATERSHED STUDIES THROUGH
GEOGRAPmC INFORMATION SYSTEMS

by
Michael J. Colgan
and
Mow-Soung Cheng

Prince George's County has an ,area covering over 480 square miles with 41 watersheds. After having
completed flood management studies for approximately 80% of the County over a IS-year period, only
rural or relatively minor watersh.eds need to be evaluated, as well as updating the existing studies. The
effort required to complete (or update) the studies in both time and resources was determined to be
significant. Additionally, the County has embarked upon a major effort to complete comprehensive water
quality studies for the entire COlmty. The effort required to adequately address the multi-faceted water
quality studies which include chemical, biological and habitat assessments; stream restoration; stream
classification and enhancement; wetland assessment and analysis; and public education, to name a few, is
tremendous. Also, the questions as to whether these studies should be undertaken on a regional, watershed
or sub-basin scale must be answered. The lag time for completion of these studies is also of concern.

Prince George's County has decided the best methods to manage comprehensive watershed studies which
includes flood management and water quality components is through a Geographic Infomtation System
(GIS) using ARCIINFO. For 1ne flood management studies, a user friendly TR-55 model has been
completed which determines drainage areas, run-off curve numbers, time of concentration and discharges
for any storm event. The TR-20 model is currently under development to be followed by the HEC-2 model.
Once completed, these models will allow hydrologic and hydraulic modeling to be done quickly and
accurately on a productivity bas,ed software tool which enables complicated GIS tasks to be completed
without extensive knowledge in GIS theory.

For the water quality studies, a GIS-based Watershed Simulated Model (GWSM) was developed in
conjunction with continuous simulation output data from the Storm Water Management Model (SWMM)
to help prioritize storm water problems and develop cost effective management techniques. The current
model utilizes the strengths of a GIS and SWMM to calculate pollutant loadings on a watershed scale and
to determine the water quality improvements resulting from proposed best management practices (BMPs),
either structural or nonstructuraL The results will then be graphically displayed in both tabular and
graphical fomtats. Currently, a water quality model to develop a comprehensive County-wide strategic
watershed management plan is utlder production. This water quality model involves the major tasks of
georeferencing on ARCIINFO of industrial and commercial activities, developing a database of potential
pollutants generated by various industrial and commercial activities and analyzing the pollutant loadings
from roadways or parking lots.

Michael 1. Colgan, Water Resource Engineer, Natural Resources Division, Maryland national Capital
Park and Planuing Commission, 14741 Governor Oden Bowie Drive, C.A.B., Upper Marlboro, Maryland
20772, Tel. [phone].

2

Dr. Mow-Soung Cheng, Section Head, Prince George's County Department of Environmental Resources,
9400 Peppercorn Place, Suite 600, Landover, Maryland 20785, Tel. [phone]