Physical Model Study of a RCC Stepped Spillway for Renwick Dam, North Dakota

Abstract

The North Dakota NRCS requested a specific model study of a RCC stepped spillway proposed for the rehabilitation of Tongue River Dam M-4, also known as Renwick Dam. The USDA- ARS Hydraulic Engineering Research Unit (HERU) constructed a two-dimensional, 1:8 scale physical model to evaluate the energy dissipation of a section of the structure. The proposed spillway entrance consists of a broad crested weir, with flow continuing down a 4(H):1(V) stepped chute. Prototype step heights ranging from 0.3 m (1 ft) to 0.61 m (2 ft) will be tested to compare the influence on energy dissipation. Stepped spillways provide a significant amount of energy dissipation compared to relatively smooth spillways. Additionally, stepped spillways require shorter stilling basins than smooth spillways, and the rough surface created by the step height influences the stilling basin design. The stepped spillway modeled with the larger step heights is expected to create more energy dissipation; thereby, creating the need for a shorter stilling basin and allowing for some cost savings. This research is expected to impact the development of design guidelines for stepped spillways planned on relatively flat slopes (θ ≤ 22°).