WinDAM, A dam safety engineering tool for breach and non-breach flood events

Authors: Hunt, Sherry; DURGIN, STEVE - Natural Resources Conservation Service (NRCS, USDA); VISSER, KARL - Natural Resources Conservation Service (NRCS, USDA); TEMPLE, DARREL - Retired ARS Employee; Tejral, Ronald; ALI, ABDELFATAH - Orise Fellow

Submitted to: State Dam Safety Officials Association Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 9/11/2018
Publication Date: 9/13/2018
Citation: Hunt, S.L., Durgin, S., Visser, K., Temple, D.M., Tejral, R.D., Ali, A.K. 2018. WinDAM, A dam safety engineering tool for breach and non-breach flood events. In: Dam Safety 2018. Proceedings of the Association of State Dam Safety Officials Annual Conference, 09/09-13/18, Seattle, WA. 3 p.

Interpretive Summary: Flooding is a common news headline. Dams control the release of flood waters downstream. Flooding can still occur even when the dam operates as it was designed. Emergency action plans are detailed plans to assist city planners and emergency mangers during crisis situations. Emergency action plans for dams are equipped with maps outlining the potential impacted areas due to a dam failure, but the plans do not typically include maps for floods that may occur under normal operation or even under non-typical events that do not cause a dam failure but may cause water to spill over the top of the dam or cause water to be released through an opening in the dam as a result of an animal digging or a tree root creating a flow path in the dam. Tools like the software WinDAM (i.e. Windows Dam Analysis Modules) may be coupled with other engineering tools and methods to evaulate the impact of the outflow from spillways, water spilling over the top of the dam, or water being released through a hole in the dam. Using rainfall and soil information, engineers may use WinDAM to evaulate the performance of the dam. WinDAM may be used by engineers to educate city planners, emergency managers, zoning regulators, and lending institutions about potential floods than may occur due to a dam failure, a dam operating under normal conditions (i.e. spillway activation), or a dam experiencing an unintended release of water.

Technical Abstract: Stories of catastrophic floods like those created by Hurricanes Harvey, Irma, and Maria and other major weather events have dominated headline news in recent years. In some cases, dam failures or incidents occurred due to embankment overtopping or internal erosion; however, the majority of dams performed as designed by releasing water through control systems like the principal and auxiliary spillways. To prepare for these types of events, engineers in the private and public sector have developed emergency action plans that typically have a flood inundation map indicating the breach outflow from the dam. Dam failure is extremely rare, yet through proper operation of the dam (i.e. spillway activation), flooding is still possible to downstream areas. Additionally, embankment overtopping or an internal erosion incident may induce flooding without breaching the structure. Typically, emergency action plans are not tailored to include flood maps for these situations, so city planners and emergency managers find themselves unprepared for these lower-magnitude events. Scientists at the USDA-ARS Hydraulic Engineering Research Unit have partnered with the USDA-NRCS and Kansas State University to develop software, WinDAM (i.e. Windows Dam Analysis Modules), for predicting embankment erosion due to overtopping and/or internal erosion. Engineers and other practitioners may use the software to evaluate the potential for breach associated with overtopping or internal erosion as well as to route floods through the reservoir when breach does not occur. Features of the software include: 1) the ability to route the flow through multiple spillways including computing the rating for multiple vegetated auxiliary spillways and some standard principal spillways, 2) the ability to route flow over the top of the dam with the elevation of the dam allowed to vary from point to point and to compute the rating for a vegetated dam crest, and 3) the ability to compute draw down times and discharges with or without inflow to the reservoir. The software provides the outflow hydrograph for practitioners to examine the impact that breach and non-breach events may have in relationship to the dam. The presentation will provide information to the dam safety community on the use of WinDAM and will primarily focus on non-breach flooding events that may occur during normal dam operation or in instances where overtopping or internal erosion may occur without dam failure.