Sina Nassiri

Erosion occurs when floodwalls are overtopped due to vertical free fall of water flow. In this study, a laboratory device named cutter erosion test (CET) was developed to identify the erosion rates of fine-grained soils due to floodwall overtopping. This developed test is calibrated with 15 levee-floodwall simulation tests with a 1:20 scale levee-floodwall prototype dimension and soils with various plasticity indices and compaction levels. The plasticity indices had a range from 0 to 40% and degree of compaction ranged from 70 to 90% of the maximum dry density according to standard proctor. The advantages of this device are its small size and its ability to simulate the erosion mechanism and provide estimate of erosion rates in overtopped levee-floodwall systems with soil properties such as plasticity index and compaction.

Best management practices (BMPs) are commonly used to reduce the adverse effects of post-construction runoff. BMP deterioration happens over time when these age and the infiltration rate decreases as a result of sediment accumulation. The objective of this paper was to investigate the effect of sediment accumulation on BMP stormwater runoff volume reduction performances. The BMPs studied included a bioswale and an infiltration trench. To undertake this research, both field tests and numerical simulations were conducted under five different and single rainfall events with a wide range of intensities and duration. The minimal sediment accumulation of 0.22 kg/m²·year was considered in this study. Three different sedimentation accumulation configurations (i.e., new, 2-year-old, and 10-year-old BMPs) were considered. According to the results, the infiltration trench had 100% runoff reduction efficiency in all conditions including high-intensity rain and 10-year-old BMP age. The performance of the bioswale for the first 2 and 10 years deteriorated by about 55% and 70%, respectively.

Prediction of levee erosion rate during floodwall overtopping for materials with various plasticity indices is critical. Levee soil properties, and intensity or duration of flood are the contributing factors in erosion rate and scour depth predictions. In this study, over 15 laboratory scaled levee-floodwalls constructed of soils with plasticity indices of 0%, 6%, 9%, 30%, and 40% were overtopped. The floodwall scale of 1:20 is utilized assuming that a typical full-sized floodwall is 2.1m high. The erosion rates at the levee crest are measured and used to propose an erosion rate prediction model which considers the plasticity index (PI) and compaction level (CL) of soils.