Journal of Hydrologic Engineering

An analytical probabilistic approach was developed in earlier studies to estimate design flood peaks from small urban areas. Developed in this paper are methods of incorporating the curve-number procedure for rainfall loss and Clark’s unit hydrograph for runoff routing calculations into the analytical probabilistic framework. These methods are verified by applying the analytical probabilistic approach to 12 urbanizing watersheds in the Chicago metropolitan area, with calibrated parameters representing two degrees of urbanization. The results are compared with those from single-event design-storm rainfall-runoff modeling. Generally comparable results demonstrate the potential of the analytical probabilistic approach as an efficient alternative for the estimation of design flood peaks from small watersheds.

The Manning’s $n$-value, a fundamental resistance coefficient to balance driving forces of a river stream, is known to depend on the flow condition (depth and velocity) as well as vegetation condition (type and density). In this study, flume experiments were conducted to investigate the variation of $n$-value with flow and vegetation conditions for submerged vegetation in river beds, banks, and flood plains. Artificial plastic plants, for a length of 8 cm, were laid on the floor of a 4-m-long section of a variable slope flume. The Manning’s $n$-values were estimated for different slopes, discharges, flow depths, and vegetation densities. The results reveal that the Manning roughness coefficient ($n$) increases as vegetation density increases, whereas it decreases when the flow depth and velocity increase. The proposed physical model in this study was customized as a subroutine in a numerical model (FASTER) for a large river reach. The estimated water levels and discharges by the model were much closer to the field records than those calculated by FASTER using a constant value for Manning’s $n$. The advantage of the developed model is its capability to estimate the $n$-value in subsections across the main channel and flood plains where cross-section geometry is known. The significant response of the proposed model to flow and vegetation states supports its application in practice.

One of the goals of storm-water infrastructure design is to mitigate effects resulting from extreme hydrologic events. Projected changes in climate are expected to lead to an increase in the frequency and magnitude of extreme rainfall events for many regions. Accordingly, existing storm-water infrastructure may not meet design standards in future decades. The North American Regional Climate Change Assessment Program is currently disseminating high resolution climate data to facilitate climate change impact assessments. A simple framework is presented for assessment of storm-water infrastructure in response to climate change. First, the projected changes in the 6-hour, 100-year design-storm depth for a watershed in Las Vegas Valley, Nevada, are calculated from several climate scenarios by using regional frequency analysis. Climate model projections vary substantially for this region and time scale. Climate model performance is assessed by using gridded reanalysis data. The projected changes in design-storm depths are incorporated into an existing HEC-HMS model. The HEC-HMS simulation results indicate potential exceedences of current design standards for select storm-water infrastructure components under projected climatic change scenarios.

To estimate mean annual water yield on ungauged watersheds, regional regression equations have been developed that are a function of upstream area, precipitation, and temperature, and are commonly used. In this study, the 100-year old Grunsky equation is used as the foundation for a fully implemented generalized Mediterranean water yield model that is based on long-term annual precipitation and temperature. The work here (1) extends and generalizes Grunsky’s equation beyond its original conditions, (2) establishes an underlying hydro-climate generalized model for average annual Mediterranean watershed water yield and loss calculation, and (3) applies the validated model to estimate watershed water yield and predict potential water yield response to watershed temperature and precipitation. The water yield model was applied to watersheds in coastal California, southern France, and Portugal, but might be applied to other Mediterranean sites for which precipitation and temperature data are available. It also can be used to examine the spatial and temporal variability for water yield and predict the effects of long-term climate changes at the regional scale.

This paper reports a case study aimed at optimizing the stream gauge network of the Hantan River Basin in Korea. The dimensionless synthetic unit hydrographs at all potential stream gauge locations were derived and compared by using the distance measure of entropy theory. Based on cluster analysis of the transinformations among stream gauge stations, the entire basin could be divided into four regions with similar subbasin responses. One stream gauge per region would be sufficient to measure the basin response to rainfall input. The optimal set of stream gauges was also derived by applying the concept of maximum total information, where a total of seven stream gauges was found to be needed for the entire Hantan River Basin. However, both applications produced very similar shapes of subbasin clustering over the Hantan River Basin. In particular, most subbasins along the main stream were included in the same group in both cases. Most subbasins in a specific tributary were also found to be included in the same cluster.

Simulation has been an important tool for planners in many fields of knowledge. In the field of water resources, the uncertainties because of unknown data population and the short length of the records work together to make the simulation especially important. The major utilization of water resources at the level needed in modern society makes water storage essential for satisfying the demand. Therefore, the need to reduce the uncertainty in the design of water-storage capacity is an important problem in the field of water-resources utilization. This problem can only be satisfactorily solved with the aid of simulation. The implementation of adequate exploration politics also needs to use simulations to obtain results with low uncertainty. In the simulation of water-resource systems, the use of synthetic time series is a current practice. In this study, the number of generated time series to use in the problems described are analyzed. Annual and monthly synthetic flows were generated, preserving the relevant statistics of the available historical data, and then the number of time series to generate was determined. The results of the case studies indicate that the proposed methodology is a plausible approach to solve the analyzed problem and lead to the conclusion that the number of time series to generate should be 1,200.

The effectiveness of soil conservation practices at reducing watershed sediment yield and effect on reservoir sedimentation is generally difficult to quantify. Here, a sedimentation survey of the Fort Cobb Reservoir in west-central Oklahoma and sediment load measurements on contributing tributaries provide an opportunity to address this question. During the second half of the twentieth century, extensive soil conservation practices were implemented on the Fort Cobb Reservoir watershed. Sediment and flow observations were made on major tributaries in 1943–1950 (preconservation time period) and again in 2004–2008 (postconservation time period). These data were used to compare watershed sediment yield and reservoir sedimentation during pre- and postconservation periods. Suspended sediment-discharge rating curves were developed for each of the two time periods and used to estimate average annual watershed sediment yield. Initial sediment yield estimates for pre- and postconservation conditions were 254,900 Mg/year (3.306 Mg/year/ha) and 247,700 Mg/year (3.213 Mg/year/ha), respectively. The apparent lack of responsiveness of sediment yield to conservation efforts was explained by a shift in the mid-1980s toward wetter climatic conditions. The wetter climate led to increased soil erosion, sediment transport, and sediment yield that offset reductions achieved by conservation efforts. Approximately a 60–65% reduction in sediment yield would have been achieved by conservation efforts if the climate characteristics had been constant over time. The mutually offsetting effects of a wetter climate and conservation efforts on sediment yield resulted in unabated sedimentation of the Fort Cobb Reservoir. The interaction between wetter climate and effectiveness of conservation practices was the basis for projecting future sedimentation rates and reservoir life span, which are shown to vary over a wide range depending on assumptions of prevailing climate over the next decades.

The present research proposed an improved slope-area method for estimating the overbank flow discharge. The prediction of conveyance factor has been improved by including the secondary flows effect using the coherence concept. Field measurements of velocity that reached 540 m were taken in a study of the River Dough, south of Kalale City, Iran, during the February 2004 flood. A nonlinear trend was observed between the depth of the relative flood-marks and the amount of predicted discharge error. The slope-area method significantly overestimated the overbank flow rate, especially in nonhomogeneous cross section, where the interaction effects increase progressively with a relative depth of less than 0.2. The overestimated value of 23% was obtained in prediction of the River Dough overbank flow by the slope-area method. The improved slope-area method predicted the flow rate with an error of 2.58% compared to the flood field measurements. The results show agreement between the proposed method prediction and the measured data.

Flow complexity, which means the degree of uncertainty or the rate of information production of a flow series, is analyzed for the upper reaches of the Yangtze River. Sample entropy (SampEn) is applied to measure flow complexity, and the Mann-Kendall method is applied to analyze the trend of flow-complexity change. Except for the flow complexity of the Jinsha River, which is increasing, the flow complexity of the upper reaches of the Yangtze River is decreasing. The influencing factor of the flow-complexity change is analyzed. On the basis of analysis of the rainfall complexity, which is also measured by SampEn, it is considered that the flow-complexity increase of the Jinsha River may be attributed to the rainfall-complexity increase, while the flow-complexity loss of the upper reaches of the Yangtze River may be attributed to the underlying surface-condition change influenced by human activities, especially reservoir construction. The reservoir operation makes the flow series more regular and self-similar, and leads to the flow-complexity loss.

This paper investigates the applicability of quantile regression technique (QRT) as a viable regional flood frequency analysis (RFFA) method for the state of New South Wales in Australia. The study uses data from 96 small to medium-sized unregulated basins across New South Wales to develop a generalized least squares (GLS)-based QRT. An independent test employing a wide range of statistical diagnostics indicates that the developed regression equations based on the GLS regression can provide quite accurate flood quantile estimates with median relative error values in the range of 13–42%. The developed regression equations are relatively easy to apply and require data for only three predictors—basin area, design rainfall intensity, and stream density.

The influence of moving rainstorms on overland flow is studied by a semianalytical solution and experiments. The effect of the velocity of the moving rainstorms on water depth changes is approximately presented by the kinematic wave method. The effect is also compared with the experimental result and the numerical computation and found to be satisfactory. The semianalytical and experimental results indicate that the changes of peak discharge are dependent on the velocity and direction of the moving rainstorms. The difference of the water depths between the downstream and upstream moving rainstorms with the velocity at the downstream end is proportional to the velocity of the moving rainstorm when the velocity is small. The semianalytical solution indicates that the maximum water depth appears when the velocity of moving rainstorms is equal to that of the flood movement. The effect of the velocity of the moving rainstorm is larger in the watershed of milder bottom slope or larger Manning’s roughness coefficient.

Historical storms with a 24-h rainfall depth exceeding 50.8 mm (2 in.) recorded in southern Arizona were compared with design storms developed both locally and by the USDA Soil Conservation Service (SCS). This study aims to evaluate if those design storms can be representative to southern Arizona. These storm depths represent the return-period storms that pose hazards considered in design. The temporal rainfall distributions, pattern index (PI), and intensity-duration relationships of the observed and design storms were compared. The comparison of the distributions and PIs of 3- or 24-h storms showed that the observed storms were diverse, and it was not clear which design storm fits best with the observed storms. The comparison of the intensity-duration relationships showed that most of the observed storms were less intense than any design storms, especially for short duration. This suggests that the application of any of the 3- or 24-h design storms would result in overestimating rainfall intensities for relatively short duration. The SCS or locally developed design storm poorly represents the temporal distribution and intensities of the observed storms.

Complete elliptic integrals have many applications in water engineering. Examples can be found in different fields such as hydrodynamics, water wave mechanics, groundwater engineering, sediment transport, irrigation and drainage engineering, and shallow water and deep water engineering. In practice, these integrals are evaluated from lookup tables or closed-form solutions (infinite series). Most tables use discrete values of the modulus, which makes accurate interpolation difficult. On the other hand, a series expansion can only be applied to a limited range of the modulus, and is not suitable for manual calculations. Consequently, it is of interest to approximate complete elliptic integrals by simple and accurate algebraic formulas over the entire practical range of the modulus. In current research, the undetermined coefficients method is used for this purpose. Various techniques can be used to determine the unknown coefficients of this method, but most of these do not depend on the integrand. Curve fitting, requiring exact numerical evaluation of the integrals followed by nonlinear optimization, is used as a powerful tool to determine the optimal values of the unknown coefficients as a function of the integrand. The proposed approximations are simple and valid over the full range $0\le k\le 0.99$ with maximum relative errors of 0.31 and 0.12% for the complete elliptic integrals of the first and second kinds, respectively. More complex approximations achieving higher accuracy with percentage errors lower than 0.07% for $0\le k\le 0.99$, are also derived. This approach can also be applied to similar integrals of constant integration limits. As such, it should be of interest to practitioners in the water engineering community.

The linear form of the Muskingum model has been widely applied to river flood routing. However, a nonlinear relationship between weighted-flow and storage volume exists in most rivers, making the use of the linear Muskingum model inappropriate. On the other hand, the application of the nonlinear Muskingum model suffers from hydrologic parameters estimation. The current study aims at presenting the objective approach of the Nelder-Mead simplex (NMS) algorithm for the purpose of estimating the parameters of the nonlinear Muskingum model. The performance of this algorithm is compared with other reported parameter estimation techniques together with a historical example. Results of the implementation of this procedure indicate that the NMS algorithm is efficient for the estimating parameters of the nonlinear Muskingum models. This algorithm is easy to be programmed, and it is quite efficient for finding an optimal solution very quickly. Although this technique requires an initial guess for the parameter estimation, results of the sensitivity analysis of the initial parameter values showed that in 84.8% of the cases, the optimum or near-optimum results are achieved.

We consider the case of pumping a semiconfined aquifer overlain by a phreatic aquifer hydraulically connected to an infinitely long and straight stream. The hydraulics of the system are described by a linearized model in which it is assumed that flow in the aquifers is essentially horizontal, and that drawdown in the phreatic aquifer is small enough to allow the water table to be sufficiently well described by the Theis equation. Fourier-Laplace transforms of drawdown are obtained and numerically inverted. Comparisons are made with another well-known analytic model of Hunt, who considered a single aquifer/aquitard system. It is observed that while both models may have excellent agreement during the initial phase of pumping, the longer-term consequences of sustained pumping are quite distinct.

The sides and bottoms of earthen irrigation channels are erodible. The main design criterion for the earthen channel is to minimize or eliminate channel erosion under design flow conditions. The Manning formula and the tractive force equation were used as governing equations to design erodible and riprap channels. The traditional design approach involves a tedious trial procedure to find the bottom width of trapezoidal channels. Some hydraulic engineering problems require the solution of the bottom width from the Manning formula for nonerodible channels. An approximate equation is available for determining channel bottom width, but it is not applicable for channels with side slopes $z<1$ (1 vertical and $z$ horizontal), which are encountered in practice for nonerodible channels. This technical note presents a direct and accurate equation for determining the channel bottom width (with errors less than 0.1%) using the tractive force concept and a dimensionless form of the Manning formula. The proposed direct solution facilitates the design of erodible and riprap-lined channels. Moreover, the proposed equation can be used to accurately determine the bottom width of rigid (nonerodible) channels for any side slope.