Emergency Action Planning for Twin Reservoirs in a Highly Urbanized Area
Authors:
- George Eller and Martha Cardona - Hazen and Sawyer
- John Huber - Charlotte-Mecklenburg Utilities
Charlotte-Mecklenburg Utilities will soon complete construction of a 270 million gallon raw water storage reservoir on the site of the Franklin Water Treatment Plant in Charlotte, NC. The new reservoir is located immediately adjacent to another reservoir of similar size at the head waters of Stewart Creek; an urban stream that flows through the heart of the City of Charlotte. Together, the reservoirs hold volumes of 1,400 acre-ft to 1,700 acre-ft, and convey nearly all of the water supply for North Carolina’s largest city. Even though the reservoirs do not receive significant amounts of natural runoff, they lie upstream of a highly urbanized area, which immediately classifies the embankments as High Hazard Dams.
An Emergency Action Plan (EAP) was developed for both reservoirs as part of the certification process finalizing construction of the new reservoir and aids local emergency management in developing evacuation plans and procedures. The EAP contains, among other things, inundation maps of the dam break inundation zone that provides the basis for evacuation route design. The floods simulated at each dam include: overtopping and sunny-day failures for each dam as well as both dams simultaneously. For each significant downstream structure, maximum depth of flooding and peak flood travel time is identified. The identification of affected residences and businesses in this urban area is an important factor to minimize loss of life in the worst case scenario.
The purpose of this paper is to provide an insight into the flood mapping and emergency management processes, from hydrologic and hydraulic (H&H) simulations and models used for these purposes, to mapping tools available. Models such as HMR52, HEC-HMS (Hydrologic Engineering Center – Hydrologic Modeling System), and HEC-RAS (River Analysis System) are examined. Flood maps are developed with tools such as AutoCAD and HEC-GeoRAS.
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