Large-scale stepped spillway testing

Authors: Hunt, Sherry; Kadavy, Kem

Submitted to: State Dam Safety Officials Association Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 7/29/2010
Publication Date: 9/21/2010
Citation: Hunt, S., Kadavy, K.C. 2010. Large-scale stepped spillway testing. In: Dam Safety 2010. Proceedings of the Association of State Dam Safety Officials Annual Conference, September 19-23, 2010, Seattle, WA. (CDROM).

Interpretive Summary: Dams constructed with the financial and technical assistance of the USDA-Natural Resources Conservation Service provide flood protection, wildlife habitat, municipal and rural water supplies, wetlands, and recreation. Originally designed to protect agricultural land, these dams today often provide flood protection for growing communities throughout the nation. These residential developments surrounding these dams required more stringent state and federal guidelines to be met. Therefore, changes to the dam are often required to insure they continue to function in a safe manner. In many cases, these dams are required to release more water than they were originally designed to release, so engineers make changes to the dam to accommodate the safe release of floodwaters downstream. One way to safely release water downstream is through a stepped spillway; however, practical design guidance for these structures are limited. Researchers at the USDA-Agricultural Research Service Hydraulic Engineering Research Unit conduct scientific studies to determine design parameters related to the stepped spillways. The objective of this paper is to discuss a new stepped spillway testing facility, the testing plan of the facility, and preliminary test results. This paper will assist engineers with the design of these structures.

Technical Abstract: Hazard classifications for many earthen embankment dams have changed due to shifting demographics surrounding the structures. Originally designed to protect agricultural land, these embankments are now surrounded by residential communities and other infrastructure. To meet federal and state dam safety regulations as set by the new hazard classification, dam rehabilitation is often required. The USDA-ARS Hydraulic Engineering Research Unit (HERU) in Stillwater, OK, is conducting generalized research on roller compacted concrete (RCC) stepped spillways to address rehabilitation needs. Stepped spillways are typically placed as a retrofit over the existing embankment and used to increase spillway capacity. Practical design guidance on stepped spillways is limited, so researchers at HERU have developed a large-scale testing facility to determine useful design parameters like the inception point location, flow depth, velocities, and energy dissipation in stepped spillways with slopes flatter than 22 degrees. The scope of this paper is to discuss the new large-scale 3(H):1(V) stepped spillway testing facility, the objectives of the large-scale generalized stepped spillway research, and preliminary results of inception point obtained from this large-scale model. Preliminary results show that the inception point data location may be directly manipulated by changing the step height; thereby changing the energy dissipation within the stepped spillway and the design parameters of the stilling basin.