Evaluating Curb Inlet Efficiency for Urban Drainage and Road Bioretention Facilities

Abstract

An updated two-dimensional flow simulation program, FullSWOF-ZG, which fully (Full) solves shallow water (SW) equations for overland flow (OF) and includes submodules modeling infiltration by zones (Z) and flow interception by grate-inlet (G), was tested with 20 locally depressed curb inlets to validate the inlet efficiency (Eci), and with 80 undepressed curb inlets to validate the inlet lengths (LT) for 100% interception. Previous curb inlet equations were based on certain theoretical approximations and limited experimental data. In this study, 1000 road-curb inlet modeling cases from the combinations of 10 longitudinal slopes (S0, 0.1–1%), 10 cross slopes (Sx, 1.5–6%), and 10 upstream inflows (Qin, 6–24 L/s) were established and modeled to determine LT. The second 1000 modeling cases with the same 10 S0 and 10 Sx and 10 curb inlet lengths (Lci, 0.15–1.5 m) were established to determine Eci. The LT and Eci regression equations were developed as a function of input parameters (S0, Sx, and Qin) and Lci/LT with the multiple linear regression method, respectively. Newly developed regression equations were applied to 10,000 inlet design cases (10 S0, 10 Sx, 10 Qin, and 10 Lci combinations) and comprehensively compared with three equations in previous studies. The 100% intercepted gutter flow (Qg100) equations were derived, and over-prediction of Qg100 from previous methods was strongly correlated to smaller S0. Newly developed equations gave more accurate estimations of LT and Eci over a wide range of input parameters. These equations can be applied to designing urban drainage and road bioretention facilities, since they were developed using a large number of simulation runs with diverse input parameters, but previous methods often overpredict the gutter flow of total interception when the longitudinal slope S0 is small.

Evaluating Efficiency Improvement of Deep-Cut Curb Inlets for Road-Bioretention Stripes

“…The differences, ∆E ranged from −3.2% to 13.2%, with an average ± standard deviation of 3.5 ± 3.5% for local depressed curb inlet cases. The percent differences, PDE of the simulated and observed intercepted efficiencies ranged from −6.0% to 28.7%, with an average ± standard deviation of 6.6 ± 7.3% [12]. In a previous study by Fang et al [8], the differences ∆E ranged from −7.0% to 17.6%, with an average ± standard deviation of 1.0 ± 4.87% in their 3D FLOW-3D simulations for local depressed curb inlet.…”

“…The cell size of DEMs for all 200 cases was 0.025 m determined by a sensitivity analysis. The simulated water depth along the curb increases along the x-direction first and then starts to decrease after it reaches the curb inlet (x > 10 m) [12]. The depth limit equal to 0.2 mm was used to determine LT and already tested and verified in the previous study [12].…”

“…The 2D-1D grate-inlet drainage submodule enables the program to simulate the 2D overland runoff flowing into a grate inlet then to a 1D underground drainage pipe using the weir equation [11]. The model was tested and validated in the previous studies [12][13][14] by comparing it with the collected experimental data.…”

“…They demonstrated that an advanced CFD model could be used as a virtual laboratory to evaluate the performance of curb inlets with different geometry and inflow conditions. In this study, full-scale numerical models were built up and simulated with two-dimensional (2D) FullSWOF-ZG (Li et al 2019), which fully (Full) solves shallow water (SW) equations for overland flow (OF) and includes submodules modeling infiltration by zones (Z) and flow interception by grate-inlet (G), to study the hydraulic performance of curb inlets.…”

Performance Analysis for Road-Bioretention with Three Types of Curb Inlet Using Numerical Model

“…The differences of simulated and observed curb inlet interception efficiencies (∆E) ranged from −3.7% to 4.4% with an average ± standard deviation of 0.8 ± 2.6% for undepressed curb inlet cases [33]. The ∆E ranged from −3.2% to 13.2%, with an average ± standard deviation of 3.5 ± 3.5% for local depressed curb inlet cases [34]. In a previous study by Fang et al [8], the ∆E ranged from −7.0% to 17.6%, with an average ± standard deviation of 1.0 ± 4.87% in their FLOW-3D simulations for local depressed curb inlet.…”