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2019 Annual Report
Objectives
Objective 1: Improve the WinDAM model to predict the erosion of complex embankment geometries and composite materials, and the allowable overtopping flows for alternative materials, including articulated concrete blocks or riprap integrated with vegetation.
Subobjective 1A: Quantify the impact of complex vegetated embankment geometries on erosion process during overtopping including: convergence zones at the intersection of the earthen embankment and valley walls and embankment berms and toes.
Subobjective 1B: Quantify the impact of changes in soil materials (specifically zoned vs. homogenous) on erosion processes and rates of earthen embankment erosion and breach.
Objective 2: Develop engineering guidance to determine hydraulic performance of alternative stepped chute designs.
Subobjective 2A: Develop guidelines for alternative step and/or chute geometry for stepped chutes constructed over existing earth dams.
Subobjective 2B: Improve engineering design guidance for stilling basin design for stepped chutes.
Approach
Large-scale physical model testing on intergraded surface protection (i.e. vegetation or vegetation integrated with riprap and/or ACBs) of steep embankment channels coupled with data from vegetated channel databases will be used to develop knowledge on erosion of complex embankment geometries (i.e. berms and convergence zones) and the materials (i.e. vegetation, riprap, and/or ACBs) intergraded within the embankment as surface protection. Large and small-scale models will be used to evaluate and to develop knowledge of fundamental processes and rates of erosion of zoned embankment materials. These tests will provide knowledge to develop key algorithms related to earthen embankment erosion. Large and small-scale physical models will be used to develop knowledge on the affect step and/or chute geometry has on the design of stepped chutes and stilling basins. Data from these physical models will be used to develop new relationships and/or tools or expand the use of existing technology for embankment erosion prediction and spillway and stilling basin design. USDA-ARS HERU scientists will collaborate with other ARS, government, university, international scientists, and consultants to carry-out these objectives. Research results will be integrated into new or existing evaluation tools, software, design criteria, and management practices; thereby, allowing for the continued service and increased benefit of our nation's multi-purpose agricultural infrastructure.
Progress Report
An ARS scientist in Stillwater, Oklahoma, made progress on Objective 2: develop engineering guidance to determine hydraulic performance of alternative stepped chute designs. Under Objective 2A, a three-dimensional model of a converging stepped chute was modified from a 2(H):1(V) stepped chute slope to a 4(H):1(V) stepped chute slope. Flow depth data along converging training walls, ranging from 0 degrees to 90 degrees convergence, were collected. Installation of the stilling basin for a 4(H):1(V) converging stepped chute was completed and testing commenced. Preliminary data analysis indicates previously developed theoretical relationships for predicting the flow depth along converging training walls are applicable to other embankment chute slopes (e.g. 4(H):1(V) and 2(H):1(V)). Under Objective 2B, progress was made toward comparing the performance of varying designs of United States Bureau of Reclamation (USBR) stilling basin types associated with stepped chutes to those associated with traditional non-converging smooth chutes. A USBR Type II stilling basin with a dentated end sill appears to dampen wave oscillations, lessening the impact of propagating waves in the downstream channel.
Accomplishments
1. Stepped spillway design criteria adopted by federal agencies and architectural and engineering (A&E) consulting firms. Roller compacted concrete (RCC) stepped spillways provide embankment overtopping protection and increased spillway capacity for aging embankment dams. An ARS researcher in Stillwater, Oklahoma, developed a systematic step by step RCC spillway design guideline for rehabilitation of aging embankment dams. The USDA-Natural Resources Conservation Service (NRCS) is incorporating the criteria into their National Engineering Handbook and expects it to be implemented on approximately 1,200 aging USDA-assisted dams. NRCS believes the criteria will provide construction cost-savings ranging from $600 million to $1.2 billion when compared to other embankment overtopping protection systems. The U.S. Army Corps of Engineers are integrating the criteria in their revised spillway design technical manual (EM 1110-2-1603). In addition, this research has become an industry standard among architectural and engineering (e.g. A&E) consulting firms (e.g. Kentucky's Fox Creek Watershed Site 4, $2 million project and West Virginia's New Creek Watershed Site 14, a $12 million project) across the U.S. for upgrading aging dams. This technology is assisting dam safety engineers in preserving the $2.3 billion in annual benefits (e.g. flood control, rural and municipal water supplies, irrigation for agricultural production, recreation, wildlife habitat, among others) provided by USDA-assisted dams.
