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One step at a time: Developing design criteria for stepped spillways

Hunt, Sherry L, Kadavy, Kem C
Dam Safety 2011. Proceedings of the Association of State Dam Safety Officials Annual Conference 2011 pp. 12
Agricultural Research Service, agricultural land, air, concrete, conservation practices, conservation programs, drought, energy, engineers, hydraulic structures, infrastructure, streams, watersheds, Oklahoma
The story of the USDA Small Watershed Program began seventy-five years ago when the U.S. was experiencing years of drought followed by years of flooding. The Flood Control Acts of 1936 and 1944 and the Watershed Protection and Flood Prevention Act of 1954 set the stage for one of the most successful conservation programs in U.S. history. The Program established the principle of combining conservation practices in a watershed with flood control dams on tributary streams. With the dams originally designed to protect agricultural land, we fast forward to today to find residential communities and other infrastructure in the immediate vicinity of the dams, resulting in hazard classifications changes for these dams. To meet the new hazard classification requirements and subsequent federal and state dam safety regulations, dam rehabilitation is 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. In rehabilitation, stepped spillways are typically placed as a retrofit over the existing embankment and used to increase spillway capacity. Research on stepped spillways has primarily been focused on gravity-style spillways with slopes steeper than 22 degrees, and insufficient to address the concerns related to stepped spillways applied to embankment dams where slopes are typically flatter than 22 degrees. The research program initiated by engineers at HERU involves the large-scale testing of a stepped spillway over a broad range of discharges and step heights. Inception point location, flow depth, velocity, air entrainment, and energy dissipation are important aspects for the design of these structures. The objective of this paper is to discuss the design parameters being developed in this research program, more specifically energy dissipation, with the plans to provide useful and practical design guidance to engineers faced with the design of these structures even if it means providing the guidance one step at a time.