Evaluating an optimum slit check dam design by using a 2D unsteady numerical model

Debris flow could be catastrophic to residents and property located at their downstream. As a result, engineers have designed several structural countermeasures, such as check dams. Regardless of the many investigations on check dams, uncertainty with respect to their design is still persistent. Against this backdrop, the study aims to assess the efficiency and determine an optimal design of slit check dams for mitigating debris flow and sediment-laden flows in steep channels. The study uses an actual slit check dam located at Landao creek, a tributary to the Beng-gai River in the central range of Taiwan. The creek has an average slope of 7 degrees, while its d50 is approximately 100 mm. Steep slopes, extreme precipitation, poor geologic formations, debris flow and landslides characterise the catchment. Concerning the slit check dam design; there were six rectangular concrete piers (width = 1.5 m, length = 4 m, depth = 8 m), linearly spaced at 1 m in a 180° alignment layout, with the middle 2 piers height reduced by 2.5 m. We evaluated the performance of this configuration and further tested two additional configurations by cutting a single pier and three piers at the centre in a 2D model, Nays-2DH. Hydrograph of a selected storm was used for upstream boundary conditions. Surveys using an unmanned aerial vehicle were conducted pre- and post-storm events to validate numerical solutions. Scour and deposition profiles from the different pier configurations formed the basis of our assessment. The numerical computations yielded valuable results and may provide better understanding in the optimal design of slit check dams. Our findings are of paramount importance to engineers and decision makers with regard to debris flow mitigation, especially in a typhoon prone region like Taiwan.