Journal of Hydrologic Engineering

Many storm-water modeling problems consider watersheds comprised of complex flow networks including surfaces, streets, pipes, and channels. Ideally, hydrologic methods would be used to model the accumulation of runoff on surfaces while hydraulic methods would be used to explicitly model the flow in each street, pipe, and channel. In many practical circumstances, only the largest pipes and channels are explicitly modeled with hydraulic methods. Thus, most subcatchments include numerous streets and small pipes that can affect the accumulation and movement of flow. Digital elevation models (DEMs) are widely used to determine geometric characteristics of these subcatchments, but street gutters and pipes are not resolved in such data. To overcome this problem, known streets and pipes are often “burned” into the surface by reducing the local elevations by a specified amount before calculating flow paths and the associated subcatchment characteristics. In this paper, existing and proposed methods for including these conduits into DEM surfaces are evaluated. The results suggest that the derived characteristics are sensitive to the selected method. We also find that a new method, which makes use of known pipe elevations, is most successful at reproducing realistic flow paths. Finally, we find that errors in the implied watershed characteristics are difficult to overcome by calibration of other model parameters.

Low-impact development (LID) allows for greater development potential with less environmental impacts using on-site distributed storm-water controls that achieve a good balance among conservation, growth, ecosystem protection, and public safety. The qualitative statement of the ultimate goal for LID can serve as guidance for engineering designs, but it is inadequate for comparison and selection among the innovative alternatives. This paper presents an innovative method by which the long-term runoff statistics are employed as the basis to quantify the impact of the development on the watershed hydrologic regime. In this study, the standard LID detention volume is defined by the storm-water storage volume required to preserve the predevelopment mean and standard deviation for runoff volume population. Consequently, a detention basin is considered oversized if the after-detention runoff volume population has a lower mean flow while the undersized counterpart produces a mean runoff volume higher than that under the predevelopment condition. This simple but quantifiable method is very useful for detention alternative comparisons, and can serve as a guide to retrofit an existing detention basin, according to the proposed LID initiative.

This paper presents a popular fuzzy rule-based model for river flow forecasting for an Indian basin. To set up the fuzzy rules, a cluster estimation method is adopted to determine the number of rules and the membership functions of variables involved in the premises of the rules. The most appropriate set of input variables was determined by trial and error procedure to test the coherence of the different input variables in forecasting flood. It is observed that the last time steps of measured runoff are dominating the forecast. The developed model is used to forecast up to 12 h in advance. The values of three performance evaluation criteria namely, the coefficient of efficiency, the root-mean-square error and the coefficient of correlation, were found to be very good and consistent for flows forecasted 1 h in advance by the model. The performance is decreasing as the forecast horizon is increasing and a reasonable forecast is obtained up to 9 h ahead. A set of fuzzy rules is extracted and used for understanding of the behavior of the developed model. It is observed that the developed model follows the trend of the input membership grade in antecedent part of the fuzzy model.

Hydrometeorological analyses of rainfall and flood response are presented for urbanizing drainage basins in the Philadelphia metropolitan region. Research focuses on major flood events resulting from Tropical Storm Allison (June 16 and 17, 2001), Hurricane Floyd (September 16 and 17, 1999), an extratropical cyclone on October 19 and 20, 1996, and a squall-line snowmelt event on January 19 and 20, 1996. We also examine the rainfall distribution from an organized thunderstorm system (June 12 and 13, 1996), which produced extreme flooding in ungauged watersheds of the region. The largest flood peaks for many of the USGS stream gauging stations in the Philadelphia metropolitan region were produced by Hurricane Floyd. The most extreme flooding in the Philadelphia metropolitan region in small drainage basins was due to Tropical Storm Allison, which produced localized storm total rainfall accumulations greater than 300 mm. Hydrometeorological and hydrologic studies illustrate the important role of landfalling tropical cyclones for flood hazards for major urban regions of the northeastern United States. Analyses of high-resolution radar rainfall fields are presented, with special emphasis on radar rainfall error structure and the spatial and temporal variations of flood-producing rainfall. Diagnostic and hydrologic model studies in Pennypack Creek, Wissahickon Creek, and the Little Neshaminy Creek are carried out to examine the controls of land surface processes and space-time rainfall distribution on extreme flood response in urban watersheds. Land surface processes and the contrasting distribution of rainfall in space and time from the storm systems that affect the northeastern United States combine to shape the scale-dependent distribution of extreme floods in urban watersheds.

This paper presents a set of pollutant removal efficiency charts that can be used as an aid for quick evaluation of existing, retrofitted or trial-designed dry detention basins. They can also be employed for preliminary sizing of new extended dry detention basins as well as their water quality outlets. These charts are developed using the predetermined numerical solutions to the flow routing and the suspended solids routing equations. The flow routing is based on the hydrologic storage equation, and the pollutant routing procedure is based on the complete-mixing concept and settling of suspended solids under turbulent conditions. A finite difference scheme is used to solve these equations. The basic mathematical model is verified by using a set of published experimental data. The equations are then written and solved numerically in terms of a set of dimensionless variables. The solutions thus obtained are generalized using the principle of hydraulic similarity and presented in chart form. Dry detention basins having orifice-type water quality outlets are considered. Different shapes of inflow hydrographs and nonuniform runoff pollutant concentrations are allowed in the model.

River discharge is typically derived from a single valued stage-discharge relationship. However, the relationship is affected by different sources of uncertainty, especially, in the measurement of discharge and stage values. The measurement uncertainty propagates into stage-discharge relationship curve and affects the discharge values derived from the relation. A fuzzy set theory based methodology is investigated in this paper for the analysis of uncertainty in the stage-discharge relationship. Individual components of stage and discharge measurement are considered as a fuzzy numbers and the overall stage and discharge uncertainty is obtained through the aggregation of all uncertainties using fuzzy arithmetic. Building on the previous work—fuzzy discharge and stage measurements, we use fuzzy nonlinear regression—in this case study for the analysis of uncertainty in the stage-discharge relationship. The methodology is based on fuzzy extension principle and considers input and output variables as well as the coefficients of the stage-discharge relationship as fuzzy numbers. Two different criteria are used for the evaluation of output fuzziness: (1) minimum spread and (2) least absolute deviation criteria. The results of the fuzzy regression analysis lead to a definition of lower and upper uncertainty bounds of the stage-discharge relationship and representation of discharge value as a fuzzy number. The methodology developed in this work is illustrated with a case study of Thompson River near Spences Bridge in British Columbia, Canada.

The area of a looped rating curve for a channel cross section is indicative of the dynamic effects of a flood wave. These effects may be used as a criterion to decide the suitability of a simplifying approximation, such as dynamic, kinematic or diffusive wave modeling, for the analysis of dam-break flow. Two approximate models to calculate the area of the nondimensional loop for dam-break flow are developed herein based on the computed results for several hypothetical dam failure cases. A comparison of the results obtained from the approximate models and those by simulations shows that approximate models can be used to predict the nondimensional loop area for short distances from the dam. As expected, the area of the nondimensional loop decreases as the flood wave moves downstream, it increases as the breach width increases and it decreases for increased breach time and/or flood-plain width.

The objectives of this study were to examine records from long-term rain gauges in Mākaha Valley for data homogeneity and to compare methods of estimating missing data. Double mass analysis was used to investigate data homogeneity. Results show that tree growth near one gauge has reduced rainfall catch by 21–25% since 1974. Four methods for estimating missing daily rainfall data were then tested using index gauges selected from a network of 21 active rain gauges. The number of index gauges and their order of selection were varied according to proximity and correlation. Selection by correlation significantly improved the performance of the station average and inverse distance methods for most cases, as well as the normal ratio method for the case when only one gauge is used. The normal ratio method produces the lowest error when two to five index gauges are used; the inverse distance method yields the lowest error when six or seven index gauges are used. Direct substitution produces better accuracy than the normal ratio method when using only one index gauge. Problems related to multicollinearity, heteroscedasticity, and assumptions of data normality preclude the use of multiple linear regression.

Pervious concrete is a novel paving material with macropores that aid in maintaining natural hydrologic infiltration rates on developed properties. There is a concern that the pores in the pervious concrete might clog due to long-term deposition of fine materials in runoff, or due to a catastrophic event(s) such as the failure of upstream erosion control measures or flooding. This research focuses on these extreme events and presents a laboratory procedure mimicking a series of catastrophic clogging cycles with clay laden runoff. It is predicted that the clay materials would tend to remain near the surface of pervious concrete systems since most placements have a vertical porosity distribution with the smaller pores near the top. The cores used were from actual field placements and the results indicate that extreme events with substantial deposition of clay on a pervious concrete pavement will substantially reduce its service capability, even temporarily fully “clogging” the pavement. However, most of the clay remains on or near the surface and the infiltration capacity of the pervious concrete was restored to acceptable, although lower, levels with simple maintenance such as surface sweeping, and subsequent rinsing similar to subsequent rainfall events.

Analyzing the dynamic hydrologic conditions of the Sandhills is critical for water and range management and sustainability of the sandhills ecosystem as well as for dune stability. There are complex models available to quantify both surface and subsurface hydrological processes. However, we present in this study an application of a relatively simple model to arrive at best estimates of the water balance components. Using the Thornthwaite-Mather model, water balance components were estimated for four automated weather data network weather monitoring stations. Estimated averages of the water balance components suggested that mean annual precipitation of these four sites was only about 420 mm but water loss through plant evapotranspiration (ET) was 861 mm, with potential ET of about 1,214 mm. Our investigation shows that there was surplus of water between December and March and a deficit occurs at the start of the growing season in May and extends through senescence in September–October. This study also suggests that the High Plains aquifer possibly met the plant water requirement during this deficit period as well as during the soil water extraction period, from May through September.