Performance Evaluation of Rock Check Dams through Full-Scale Testing

Marketing Paragraph: Statement of Purpose: This poster presentation will provide an overview of full-scale testing on various rock check dam installations for performance. Key performance indicators for the Iowa Department of Transportation standard installation and modified installations included impoundment depth, length, and flow velocity, which were all compared to the theoretical values that are used in the design of installations, especially spacing of installations. Modified installations that were tested included different rock gradations, the removal of an excavation below the installation, the addition of a geotextile overlay to increase impoundment, and weep holes in the geotextile to allow for dewatering of the installation.

Full Abstract: Complete Proposal for Your Session: Channels on construction projects are prone to erosion before stabilization due to high flow velocities during stormwater runoff events. To protect channels from erosion, ditch check (or check dam) practices are typically installed to reduce flow velocity by facilitating impoundment. Common ditch check practices include wattles, sandbags, straw bales, and rock check dams. Properly spacing ditch checks requires the lowest point on the top of the downstream installation to be at the same elevation as the toe of the installation immediately upstream to protect the entire channel; however, if installations do not fully impound due to high flow-through rates, segments of the channel can be subject to high-velocity erosive flows. Impoundment being unable to reach the top of installations is especially seen in rock check dams, which most Department of Transportation (DOT) standards stipulate as rock placed in a channel with no additional improvements to increase impoundment. Despite large sums of money being spent on installing, maintaining, and removing rock check dams on construction projects, little research has been conducted to improve the impoundment potential of rock check dams. It should be noted that most DOTs have different rock gradient requirements that they specific that can make it difficult to compare performance, therefore research performed for certain DOTs may not translate to others. This research aims to evaluate various configurations of rock check dams for hydraulic performance, including the Iowa DOT standard installation and modifications, to improve the protection provided to unlined channels by rock check dam installations. To determine performance, each installation was subjected to commonly experienced conditions in channels on Iowa highway construction projects. Testing was completed in an Iowa DOT standard channel located at the Auburn University – Stormwater Research Facility under channelized flow rates representative of Iowa conditions. Measurements taken during testing included flow velocity and depth at regular spacing and the length of impoundment to determine the areas in the channel that were protected from high-velocity erosive flows. Initial testing of the Iowa DOT standard rock check dam installation showed that only 1.3 m and 1.8 m (4.2 ft and 5.9 ft) of impoundment was created under the low (0.024 m3/s [0.85 ft3/s]) and high (0.048 m3/s [1.7 ft3/s]) flow rates tested, respectively. These impoundment lengths indicate that only approximately 7% and 10% of the channel is being protected from erosive flows by the standard Iowa DOT rock check dam installation when compared to the theoretical impoundment used in spacing requirements. Modified installations, including the removal of the excavation beneath the installation, using a smaller rock gradation, and the addition of a geotextile overlay, were evaluated to increase performance. Results indicate that the addition of a geotextile overlay is highly effective at increasing the performance of rock check dams; however, all installations did not impound to the maximum theoretical impoundment that spacing guidance is based on.