Scour in Stormwater Catchbasin Devices – Experimental Results from a Full-Scale Physical Model
Hydrodynamic devices have long been proposed as sediment traps in storm drainage systems. The earliest, and simplest, hydrodynamic device is an inlet with a catchbasin sump (Lager et al. 1977). Early use of these devices has been to act as a trap to capture large debris, minimizing their deposition in the storm drainage system. Moreover, a number of research studies have investigated the performance of catchbasins as stormwater quality control devices by evaluating their sediment and pollutant removal capacities (Lager, et al. 1977, Pitt 1979, 1985, 1994, 1998, and 1999, Aronson, et al. 1983, and Butler, et al. 1995). Currently, sediment scour is a major subject of concern when evaluating the performance of catchbasins and related hydrodynamic separators in stormwater systems, and when developing protocols for scour evaluation, such as are being examined by the Wisconsin Department of Natural Resources (WDNR) (Brzozowski 2006).
A series of experiments have been conducted at the University of Alabama over the past few years to evaluate sediment scour potential in stormwater catchbasins. Two types of experiments were performed with a full-scale physical model as part of these tests: (i) a hydrodynamic testwhere velocities were measured at different locations in the control volume of the catchbasin and for different flow rates and inlet geometries, and (ii) a scour test where turbidity, particle size distribution, and total suspended solids at the outlet were measured for different conditions of sediment depth and flow rates. The experimental results presented in this chapter show the effect of two different inlet geometries (rectangular and circular) on the velocity field in the control volume, the benefit of the overlying water in protecting the sediment from being scoured, the scour behavior under the effect of sediment armoring, and the mass losses of scoured sediment under varied flow conditions, among other findings.
These results will be used to calibrate and validate a three-dimensional Computational Fluid Dynamics (3D-CFD) model that can simulate a variety of scenarios and geometries to determine the scour mass and pattern under different conditions. This chapter is complementary to the previous publication (in Monograph 16) in which the factors affecting scour of pre-captured sediment from catchbasin sumps were evaluated (Avila, et al. 2008). This chapter extends that initial discussion by presenting the results of the field tests of scour from catchbasin sumps.
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