Location: Hydraulic Engineering ResearchTitle: Preliminary results for embankment dam stepped spillway stilling basin research
Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/30/2018
Publication Date: 7/1/2018
Citation: Hunt, S.L., Kadavy, K.C. 2018. Preliminary results for embankment dam stepped spillway stilling basin research. In: Bung, D. and Tullis, B. (eds.) in the 7th IAHR International Symposium on Hydraulic Structures, May 15-18, 2018, Aachen, Germany. 8 p. https://doi.org/10.15142/T3CQ00.
Interpretive Summary: Spillways are structures that control the release of flood waters from dams or levees. A stilling basin is a structure placed at the end of a spillway and is used to reduce the water velocity, so excess water from the dam can be returned safely downstream without damaging the dam. Stilling basin design methods were developed by United States Bureau of Reclamation (USBR) scientists for spillways with a smooth surface. Modernization of concrete mixes allow the spillway surface to be placed as a stepped surface, but dam designers question whether a stilling basin is suitable for flow released from stepped surface spillways. Scientists at the United States Department of Agriculture (USDA) Agricultural Research Service (ARS) Hydraulic Engineering Research Unit (HERU) conducted research to evaluate the stilling basin performance when constructed at the end of stepped spillways. Results of the research were compared to the classical research results reported by USBR scientists. Preliminary results indicate the USBR stilling basin design methods are applicable for stepped spillways.
Technical Abstract: A stilling basin is an energy dissipator for spillways and other hydraulic structures. Designed to generate a hydraulic jump, the structure is meant to contain the jump and return excess flow safely downstream. Traditional design for these structures was developed by United States Bureau of Reclamation (USBR) scientists. Tests were conducted for a range of expected flow conditions (i.e. Froude number, incoming flow depth, tailwater depth, etc.) with a smooth chute providing the incoming flow conditions. A common question among practicing engineers has become: is the stilling basin design criteria applicable if the approach entrance is a stepped chute? Scientists at the United States Department of Agriculture (USDA) Agricultural Research Service (ARS) Hydraulic Engineering Research Unit (HERU) has have developed a research program to evaluate the stilling basin performance associated with stepped chutes. Physical model tests are conducted in a near prototype scale stepped chute facility. Stilling basin Types I, II, III, and IV are being tested. Preliminary results indicate the Froude number at the stepped chute toe ranges from 3.3 = F = 5.5. Hydraulic jumps within this Froude number range were observed to be oscillatory in nature and result in potentially undesirable wave action downstream of the stilling basin for the lower Froude numbers. Preliminary results indicate that the design criteria developed by USBR scientists are applicable for USBR Type IV stilling basins placed at the toe of stepped chutes. This research is expected to extend the knowledge base regarding stilling basins associated with stepped chutes.