Forecasting Individual Dam Response to Severe Storms
North Carolina is home to more than 5,700 dams, many of which are aging and unable to contain excess stormwater runoff from increased development and more frequent severe storms.
As part of North Carolina’s recovery and resiliency efforts following recent hurricanes, which includes the governor’s flood control initiative, Draper Aden Associates evaluated more than 50 high-hazard dams in the Neuse and Lumber River Basins. These evaluations will help emergency management officials prioritize responses both before and after extreme storms by providing a clearer picture of the dam’s hydraulic capacity. Specifically, we were tasked with developing hydrologic and hydraulic computer model applications for each dam.
In order to gather the necessary data to develop these models for each dam, we performed field assessments and professional surveying services. We collected spillway dimensions and elevations, dam top elevations and profiles, and information on the material and configuration of the spillway and terminal structures.
We also evaluated the upstream watershed contributing to each reservoir with a suite of geospatial analysis tools. These evaluations allowed us to predict hydrologic responses to a variety of storm scenarios.
Next, we determined the available storage and spillway discharge volumes at incremental stages between the normal pool and the top of the dam for each reservoir.
Ultimately, we input the various data into hydrologic and hydraulic computer model applications to determine the peak reservoir elevation, peak inflow, and peak outflow for storm events with return periods ranging from 25 years to 1,000 years. This analysis allowed for the determination of the critical rainfall amount that would trigger overtopping of each dam.
This critical information will help dam operators and emergency service personnel decide whether they need to lower the amount of water in a reservoir, alert at-risk citizens of flooding potential, or take other decisive action before a storm arrives. Supporting North Carolina’s dam safety initiative with predictive models demonstrates how we continue to make a lasting, positive impact in the communities we serve.
“I speak from everyone on behalf of Dam Safety that we commend you on your thoroughness and overall quality of work that was submitted for the Neuse River Flood Study,” said Erica Langdon of North Carolina State Dam Safety. “It has been a pleasure to work with Draper Aden and we truly hope to continue working together again soon.”