Large-Scale Performance Evaluation of Various Rock Check Dam Installations | IECA 2025 Technical Paper of the Year

Despite the widespread use of rock check dams, little research has been conducted on improving the impoundment potential of installations to adequately protect channels on construction sites from erosion. Large-scale performance evaluations at the Auburn University - Stormwater Research facility on Iowa DOT rock check dam installations have indicated that the impoundment produced to protect the channel from erosion by the standard installation, which is similar to installations commonly used in other US jurisdictions and around the world, can be improved through modifications. This presentation will delve into past rock check dam research, rock check dam standards around the US and world, testing methodology, results, and conclusions formed from large-scale testing.

Full Abstract: 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 practices are typically installed to reduce flow velocity by facilitating impoundment. Common ditch check practices include wattles, sandbags, straw bales, and rock check dams. Ditch check spacing requirements typically require 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. 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 two different flow rates, 0.024 m3/s and 0.048 m3/s (0.85 ft3/s and 1.7 ft3/s), representing commonly seen conditions in channels on Iowa highway construction projects, in an Iowa DOT standard channel located at the Auburn University – Stormwater Research Facility. Flow velocity and depth measurements were taken at regular spacing to develop a flow profile. Additionally, the location of the hydraulic jump, representing the transition between erosive supercritical flows and slow-moving subcritical flows that do not lead to erosion in non-stabilized channels, was recorded and compared to the theoretical impoundment used in spacing guidelines. 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 and high flow rates tested, respectively; these impoundment lengths indicate that only approximately 6% and 9% 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. A modified installation using a smaller gradation of rock used on Iowa DOT construction projects has also been evaluated; results indicate that using a smaller gradation of rock while keeping all other installation aspects the same can increase impoundment potential to 32% and 49% of the theoretical impoundment while not risking washout of rock. Additional modified installations have been developed and are currently in the process of being evaluated, including removing the excavation below the check dam, adding a geotextile overlay over the upstream face of the installation, and adding a choker stone on the upstream face of the installation; all modifications aim to increase the impoundment potential of the installation and have the goal of facilitating impoundment that reaches the top of each installation. Overall, testing of rock check dams at the Auburn University – Stormwater Research Facility has indicated that the impoundment potential and protection of channels from high-velocity erosive flows of the Iowa DOT standard rock check dam installation can be improved without excessive cost increase.