Hazard Classification and Hydraulic Remediation Options for Flat-Topped and Ogee-Crested Low-Head Dams

The dangerous hydraulic conditions that can form downstream of a low-head dam were investigated. These dangerous hydraulic conditions have been the cause of hundreds of drowning incidents since the construction of the first low-head dams. Two primary objectives were identified for this study, each of which were primarily performed using the Computational Fluid Dynamics software, Flow-3D®, with physical models used to verify the numerical results. The first objective was the identification of a risk factor made up of easily measured parameters that could accurately predict when the dangerous hydraulic conditions are present at a low-head dam. The risk factor that was found to achieve this objective was calculated as (hu – hd)/P, where hu and hd are the upstream and downstream water depths, respectively, and P is the dam height. For the flat-topped dams tested, the dangerous condition was present within the range of risk factors from 0.343 to 0.708. For the ogee-crested dams tested, the dangerous conditions were present between risk factors of 0.093 and 0.798. The second objective was to identify possible solutions to the danger created by low-head dams, therefore reducing risk to the public. It was also desired to keep the options easily and inexpensively implemented. Two different solutions were found to this end, and consisted of either upstream facing ramps spaced along the width of the channel below a low-head dam, or spaced platforms protruding from the downsteam face of the dam slightly below its crest. Three different designs of each of these configurations were tested. The options were evaluated based on how long it took for human dummies introduced into the flow to pass through the high risk region of the simulations, with the maximum allowed time being 50 seconds. Any test in which a dummy remained in the danger region for longer than 50 seconds was deemed ineffective. The option found to perform the best was the P2 design, which had an overall performance time of about 17.4 seconds