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To evaluate sediment removal in dry detention basins, one of the most frequently used Best Management Practices (BMPs), a particle pathline model using plug flow assumption was proposed in a previous study. The model requires numerical integration, thus it may not be convenient for quick evaluation and design of detention basins. To overcome the difficulty a simpler continuous stirring tank reactor (CSTR) model is proposed and used to compare outflow Suspended Sediment Concentrations (SSCs) from different size storms using a nondimensionalized time scale. The CSTR model satisfactorily predicts sediment removal and outflow SSC measured using a physical model. The paper presents the time nondimensionalization and CSTR model application processes and discusses the critical characteristics of the proposed models.

Permeable friction course (PFC) is a porous asphalt pavement placed on top of a regular impermeable roadway. Under small rainfall intensities, drainage is contained within the PFC layer; but under higher rainfall intensities, drainage occurs both within and on top of the porous pavement. A computer model—the permeable friction course drainage code (Perfcode)—is developed to study this two-dimensional unsteady drainage process. Given a hyetograph, geometric information regarding the roadway layout, and hydraulic properties of the PFC media, the model predicts the variation of water depth within and on top of the PFC layer through time. The porous layer is treated as an unconfined aquifer using Darcy’s law and the Dupuit-Forchheimer assumptions. Surface flow is modeled using the diffusion wave approximation to the Saint-Venant equations. A mass balance approach is used to couple surface and subsurface phases. Straight and curved roadway geometries are accommodated via a curvilinear grid. The model is valida...

This paper describes a method for incorporating the hydraulics of various bridge rail geometries on a bridge structure to determine the impacts on the surrounding floodplain during extreme flood events. Typical floodplain analysis either does not include the geometry of the bridge rails or simply increases the thickness of the bridge roadway deck to account for the bridge rails. These methods either underpredict or overpredict, respectively, the impact of the bridge rails and do not account for open space in the rails. The use of a previously developed rail rating curve and submergence model can be incorporated in floodplain mapping software such as HEC-RAS. The rail rating curve model can be used to determine the upstream specific energy as a function of the flow rate passing over the rail. Floodplain analysis software typically models flow over bridge structures using the weir equation. Therefore, the weir coefficient is altered such that the weir equation and rail rating curve model result in the same upstream specific energy. This method results in an iterative approach for incorporating the hydraulics of various bridge railing systems into floodplain analysis software. The method is outlined and a simple single bridge example is provided.

On a curved section of highway, the cross slope of the road is often designed to be superelevated to balance the centrifugal force and gravity applied on vehicles. The accumulation of storm-water runoff (sheet flow) near superelevation transitions may significantly increase due to the extended flow path and converging flow lines. A two-dimensional finite-volume-based diffusion wave model is developed to simulate the sheet flow on these geometrically complex surfaces. Both Dirichlet- and Neumann-type boundary conditions are developed for open boundaries based on kinematic wave theory. Results show that the distribution of sheet flow is closely related to the cross slope, longitudinal slope, rainfall intensity, and the width of the road. The analysis of sheet flow characteristics on superelevation transition areas suggests that the optimal longitudinal slope in the range of 0.3–0.4% minimizes the depth of storm-water runoff on the road surface.

Treatment of storm-water runoff may be necessary before discharge to surface waters. In urban areas, space constraints limit selection of conventional treatment systems, and alternative systems are needed. This research program involves design and laboratory testing of a small footprint nonproprietary detention basin which consists of pipes and box culvert sections with a specialized inlet and outlet system. This system can be placed below grade near the roadway section as part of the conventional drainage system and does not require additional right-of-way. A mathematical model, based entirely on hydraulic principles, is developed to estimate particle removal efficiency of the rectangular detention basin for the treatment of storm-water runoff by extending ideal horizontal tank theory under the condition in which water level is varied. A physical model was built in 1/5 scale to measure particle removal performance and validates the conceptual model. Experiments were performed for steady inflow conditions with different inflow rates, durations, and suspended sediment concentrations. Measured time series outflow suspended sediment concentrations and particle removal efficiency compare well with calculated results from the conceptual model. The outflow particle-size distribution can also be estimated using the conceptual model.

This paper presents results from an extensive experimental study of sheet flow on rough impervious surfaces that are used to represent highway pavement. Experiments were performed on three surfaces under no-rainfall and simulated rainfall conditions, and with slopes of 1, 2, and 3%. Measurements include flow depth and unit discharge. Turbulent boundary layer theory for a rough surface is used to describe the depth-discharge relationship, resulting in a model with a single parameter directly related to the surface roughness. Comparisons are made with Manning’s equation, and the variability of the Manning coefficient is assessed. Hydraulic effects of rainfall are generally found to be small compared to other factors.

This paper describes a three-parameter model used for determining the hydraulic performance of bridge rails during extreme flood events as well as two submergence models. Typically the geometry of the bridge rails is not considered when conducting floodplain analysis. The use of certain bridge rails with large height or minimal open space may adversely impact the surrounding floodplain. Therefore, a mathematical model used to characterize the hydraulic performance of bridge rails has been developed in order to understand how different bridge rail systems may impact a floodplain. Physical modeling experiments are conducted in order to determine rating curves for various rail geometries that describe the upstream specific energy as a function of the flow rate passing over the rail. In addition, the effects of the submergence of bridge rails by an increase in downstream water surface elevation are also evaluated, as well as the submergence effects of two bridge rails in series. Two different mathematical models are used to approximate and characterize the effects of rail submergence.

This paper presents a versatile two-parameter model describing the hydraulic performance of highway culverts operating under inlet control for both unsubmerged and submerged conditions. Applications show that the model can accurately represent the Federal Highway Administration (FHwA) performance curves (which use four parameters) for a range of culvert types and materials. Laboratory data from an investigation of the hydraulic performance of single- and multiple-barrel low-headwater box culverts are also used, and the resulting model predicts a smaller culvert size as compared with the FHwA equations for a given design discharge. Design recommendations are presented for low-headwater box culverts.

Vegetative storm water controls include grassed swales and vegetated filter strips. The effectiveness of these controls for removing pollutants found in runoff from highways and other urban areas has not been demonstrated to the satisfaction of regulatory agencies; therefore, these technologies have been limited to applications as pretreatment devices for other structural runoff controls. Many highways in Texas and other areas discharge storm water to grassy medians and shoulder areas, which act as both filter strips and grassed swales. The runoff flows overland down the sides of the median as in a filter strip and then parallel to the highway as in a grassed swale. This study investigated the capability of vegetated highway medians for treating storm water runoff in the Austin, Tex. area. Two medians on major highways were monitored to document pollutant removal efficiencies. The medians were designed solely for storm water conveyance and differed in slope and vegetation type. In addition, the highways a...

Storm-water data collected from an expressway in the Austin, Tex. area were used to develop regression models for predicting loads for a number of constituents commonly found in highway runoff. The goal of the model development was to identify the processes that affect the quality of highway runoff. Linear regression was selected as the most appropriate technique for analyzing the data because of its ability to identify constituent specific causal variables. The regression equations indicate that the majority of variations observed in highway storm-water loading can be explained by causal variables measured during the rainstorm event, the antecedent dry period, and the previous rainstorm event. Loads for each of the constituents were dependent upon a unique subset of the identified variables, indicating that processes responsible for the generation, accumulation, and washoff of storm-water pollutants are constituent specific. Loads of some constituents, such as total suspended solids, were dependent on th...

Water quality of highway runoff in the Austin, Texas, area was determined by monitoring runoff at three locations on the MoPac Expressway. Daily traffic volumes, surrounding land uses, and highway drainage system types were different at each site. The concentrations of constituents in runoff at all sites were similar to median values compiled in a nationwide study of highway runoff quality. A grassy swale at one site was effective in reducing the concentrations of most constituents in runoff. The lower runoff coefficient at this site is attributable to infiltration of runoff into the grassy swale. The pollutant loads discharged from the pipe draining the swale were lower than those observed at the sites where runoff drained directly from the pavement. A first flush effect (i.e., higher pollutant concentrations at the beginning of an event) was evident during selected events, but was generally limited to a small volume. The overall effect was negligible when all monitored events were considered.

An analytic approach is developed for quantifying the distribution of fluid passage times in a heterogeneous porous medium. The basic methodology employed utilizes a diffusion theory description for the displacement of a purely advected fluid subject to a random field of hydraulic conductivity. Within this framework, a governing model is formed using the backward form of the statistical Kolmogorov equation, which yields the inverse Gaussian distribution as a solution to the fluid passage time problem. In proposing the methodology, a rationale is presented for quantifying the associated model parameters using a simple appli- cation of the mean and variance to Darcy's law, with subsequent comparisons being made to previous results obtained for perturbation solutions of the associated stochastic partial differential equations. In addition, the validity of the model is discussed within the bounds of a Markovian description for ground-water flow under a continuum-based modeling framework. Here, it is argued that acceptably accurate results may be achieved for a statistical Peclet number in excess of 70.

Groundwater quality monitoring network design is defined as the selection of sampling sites and temporal sampling frequency to determine physical, chemical, and biological properties of ground wate...

A comparison is conducted between Monte Carlo simulation and first‐order uncertainty analysis within the framework of an exposure assessment procedure. The modeled scenario consists of contaminated soil located directly above an aquifer and upgradient of a water supply well. For the exposure assessment procedure, the exposure point concentration is predicted by performing Monte Carlo simulation using a one‐dimensional vertical, soil‐water solute‐transport model coupled with a two‐dimensional, horizontal ground‐water fate and transport model. The result is expressed as a probability distribution of the contaminant concentration at the point of human exposure (water supply well). To complete the exposure assessment procedure, the concentration corresponding to a prespecified risk level (usually 5%) is evaluated against the appropriate and/or relevant health‐based standards for the site. First‐order uncertainty analysis is another probabilistic method that under certain circumstances may be applied in place ...

The need for skimming of fresh groundwater above a saline water body without producing an unacceptable contamination in the pumped water calls for the investigations carried out in this research work. Two axisymmetric models, namely the steady state and the transient upconing models, are developed with the assumption of an abrupt interface. Finite element method with an iterative scheme is employed in solving the steady state model whereas a method of finite element in space and finite differences in time is used with iterative schemes for the transient model. The models are calibrated with the analytical solutions for the case of radial flow to a fully penetrating well in an unconfined aquifer. A method of superimposing the effects of hydrodynamic dispersion on the upconing is discussed. The simulation results of both models, together with the technique of dimensional analysis, provide information for establishing design criteria for optimal pumping or choice of well depth or both.