Numerical Study on the Hydraulics of Stormwater Catch Basin Grate Inlets  under Clean and Clogging Conditions
Creators: Li, Xiangdong
Publisher: name: University of Alberta Library
Year: 2023

<p>Accurate assessment of urban drainage system is vital for municipalities. Stormwater catch basin (CB) inlets are critical linkages between the two dimensional (2-D) urban street flow and the 1-D underground sewer network flow. So far, extensive studies have been conducted to quantify the performance of various types of CB inlets, focusing mainly on CB inlet capacity and efficiency under clean conditions. However, in reality, CB inlets can be easily clogged by debris, garbage, leaves and others, largely reducing their capacity and efficiency. There has been no numerical study that investigates the clogging effect, despite there are a few limited experimental studies. <br>
This thesis was written as paper-based, including two pieces of work. The first piece of work (Chapter 2) is a comprehensive literature review on each of the three major types of CB inlets: grate inlets, curb-opening inlets and combination inlets. The second piece of work is a 3-D numerical modeling study using a commercial computational fluid dynamic (CFD) package, FLUENT, to assess hydraulics of CB grate inlets under different conditions: clean and clogging conditions, large water depth on street, vertical depression of grate inlets compared to street surface, and outflow through grate inlets due to surcharging of underground sewers. <br>
The CFD model was first calibrated with the physical experiments of CB grate inlets under both clean and clogging conditions, and the results showed that the model built with the RANS and RNG k- ϵ equations and the VOF approach can simulate grate inlet hydraulics satisfactorily. Based on the calibrated model, the clogging factor for the grate inlets was calculated to be 0 - 0.7, depending on the clogging area, approaching flow and road slopes. Generalized clogging patterns tend to overestimate grate inlet intercepted flow rate, compared to the real clogging patterns. During urban flooding, large water depth on streets generate near-constant clogging factor, independent of approaching flow rate; and a discharge coefficient of 0.6 can be used with the orifice flow equation to predict the inlet intercepted flow rate. If the grate inlet has a vertical depression of 2 cm (i.e., 2 cm lower than road surface), it will increase the inlet intercepted flow rate and efficiency and decrease the clogging factor, compared to the non-depressed case. When underground sewers are surcharging via CBs to road surface, it was found that road slopes (longitudinal and transverse slopes) have no impact on the discharge coefficient, but the approaching flow on road will decrease the discharge coefficient. The suggested value of the discharge coefficient, 0.6, would overestimate the outflow via the grate inlet. Moreover, based on the simulation results, new formulas were proposed in this study for CB grate inlet efficiency, clogging factor, and orifice discharge coefficient. The predicted results of the formulas agreed well with the simulated results.<br>
General conclusions and future research directions were provided at the end of the thesis.</p>