Journal of Hydrologic Engineering

This paper introduces an algorithm to calculate outflow in lakes and reservoirs that have multiple outlets. If the inflow into the lake, the surface area, and the morphological characteristics of the outlets are known, this algorithm enables to calculate the outflow at each outlet of the lake at any moment in time. Lake outflow is governed by a mass balance equation and a relationship that relates water level to outflow at each outlet. This algorithm was first validated using a theoretical example and once the method was integrated into the distributed hydrological model HYDROTEL, it was also validated using simulation of Lake Ludger, Quebec, Canada.

The objectives of this study were to link an unsaturated and saturated flow model for the purpose of evaluating mounding and contaminant transport beneath an infiltration basin, to calibrate and test the combined water table flow model using experimental data collected from an infiltration basin, and to evaluate the potential for contaminant transport with a numerical fate and transport model. Mound formation may reduce the thickness of the soil available to retard pollutant movement, reduce the infiltration rate of the basin if the mound intersects the basin bottom, and facilitate contaminant movement away from the basin. A 0.10-ha infiltration basin serving a 9.4-ha residential subdivision in Oconomowoc, Wisconsin, was instrumented. Two storm events were modeled using the three-dimensional saturated numerical model MODFLOW. Recharge used in MODFLOW was taken from the seepage flux of the unsaturated one-dimensional model HYDRUS. A good fit was achieved between modeled and measured timing and magnitude of water table rise for both storms. The three-dimensional saturated fate and transport code MT3D was used to simulate a tracer study. Mounding caused more rapid tracer transport away from the basin compared to the natural gradient.

The three-dimensional Laplace domain solutions of groundwater flow to a well in fractured double porosity confined, unconfined, and leaky wedge-shaped aquifers are developed. Three wedge boundary configurations: (1) two constant head zero drawdown; (2) two impermeable; and (3) one constant head zero drawdown and one impermeable wedge boundary are considered. Dimensionless drawdowns are obtained for different wedge boundary configurations to investigate flow system behavior. Lateral boundary dimensionless flux at a representative line is also calculated for two constant head zero drawdown configuration and its sensitivity to the matrix hydraulic parameters are investigated. Results of our study are presented in the form of dimensionless flux-dimensionless time and dimensionless drawdown-dimensionless time, type curves. The results are useful for evaluating the role of matrix hydraulic parameters on lateral boundary depletion rate and investigation of flow system behavior in double porosity wedge-shaped aquifers with different lateral boundary configurations. The presented analytical solutions can also be used in parameter identification, stream depletion rate estimation and numerical models verification.

Meteorological drought, as an extreme event, takes place when monthly or yearly precipitation goes down below a threshold for a specific duration. Drought events are presented based on different drought characteristics, i.e., duration, magnitude, and severity. Meteorological drought characteristics change territorially and can be analyzed regionally. However, most of the meteorological drought analyses are commonly based on-site frequency analysis of univariate drought characteristics which does not fully describe the drought potential due to the existence of correlation between the drought characteristics and their regional properties. In this research, a regional bivariate analysis is proposed for meteorological drought analysis. Monthly precipitation depths of 41 meteorological stations in Khuzestan province, southwest of Iran, were collected and extended using time series analysis. The interevent volume method is used to pool the meteorological droughts at each meteorological station. Then, the pooled drought events characteristics (e.g., duration and severity) were used to specify the homogenous regions based on the L-moments analysis. The bivariate distribution of drought was estimated using the copulas for each homogeneous region. In this study, Khuzestan province was regionalized based on the bivariate risk of drought events. The proposed methodology is applicable to regional analysis of hydrological and agricultural droughts.

All reservoirs are subjected to sediment inflow and deposition to a certain extent resulting in reduction of their capacity. Trap efficiency $\left(T_e\right)$ , a most important parameter for reservoir sedimentation studies, is being estimated using conventional empirical methods till today. A limited research has been carried out on estimating the variation of $T_e$ with time. In the present study, an attempt has been made to incorporate the age of the reservoir to estimate the $T_e$ . This study investigates the suitability of conventional empirical approaches along with soft computing data-driven techniques to estimate the reservoir $T_e$ . The incorporation of reservoir age, in empirical model, has resulted in a better $T_e$ estimation. Further, to estimate $T_e$ at different time steps, soft computing approaches such as artificial neural networks (ANNs) and genetic programming (GP) have been attempted. Based on correlation analysis, it was found that ANN model (4–4-1) resulted better than conventional empirical methods but inferior to GP. The results show that the GP model is parsimonious and understandable and is well suited to estimate $T_e$ of a large reservoir.

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.

Two-layer system of flow through and above vegetation linked by shear flow exhibits periodic oscillations at the interface called the Kelvin-Helmholtz vortices. A dispersion relation for the vortices is derived as a function of flow and vegetation parameters and extended to aside vortices that exist in horizontally stratified flow. Nonlinearity exists in the oscillations in vertically stratified flow however is suppressed in horizontally stratified flow because of the horizontally bounded flow and depth-wise phase difference in the oscillations. The relation for both the vortex types provides a simple way to calculate vortex frequency using measurable flow and vegetation parameters. Results show that the vortex frequency for rigid plants is a function of flow hydraulics and stem density, whereas for flexible plants it is a function of the geometry of bending stems.

An ensemble extended Kalman filter (EEKF) formulation is applied to a regulated basin. The existing event-based storage function method for the prediction of flow is enhanced to incorporate continuous soil water accounting and to be suitable for application in large watersheds with several tributaries. The formulation is complemented by EEKF, which utilizes flow and reservoir level observations to update catchment soil water and channel states, and reservoir storage estimates predicted by the model. The formulated forecast is suitable for operational application. Ensemble precipitation predictions are generated to serve as input to the forecast system, and the results are intercompared using two different statistical approaches. These predictions together with parametric uncertainty models constitute the basis of the ensemble flow predictions by the model. A case study is presented that demonstrates the implementation and evaluation of the method with respect to the prediction of large flow events in a $4,500{\text{-km}}^2$ regulated basin, a tributary to Nakdong River in Korea, using hourly data for the period January 2006–August 2008. A significant finding is that although the calibrated-model simulations reproduce well the observations, without the updating procedure, it forecasted poorly the high-flow events. The EEKF-based forecast system improves the forecast of the high-flow events with respect to time and magnitude and yields higher scores for the probability of detection and false alarm rate associated with the exceedance of high-flow thresholds.

This study, by incorporating the Philip infiltration solution, constructs from a theoretical perspective an alternative model to replace the Soil Conservation Service curve-number (SCS-CN) method and provides an in-depth analysis of its variants in order to understand their limitations and accuracy. Variants under analyses include the nonlinear $I_a\text{-}R$ relation of Jain et al. and the general and modified Mishra-Singh models which, in spite of favorable consistency with observed data, are obtained by approximation, leaving several odd results unexplained. Along with the crucial assumptions embedded in the SCS-CN method, vital factors dominating model accuracy are examined at constant rainfall intensity. Soil-infinite storage is avoided to reflect the actual situation in most vadose zones, which amends the SCS method and allows the theoretical exploration of the range in which CN usually falls. Using different soils, this study compares the differences and common features of all the models in order to test their proficiency. Finally, the features of a unit hydrograph are integrated into the alternative model to perform a simple evaluation of the impact of catchment urbanization on the river stage.

Understanding watershed systems is a necessary prerequisite for comprehensive management of the overall basin. Applying simple hydrologic techniques, for which fundamental information is available, is a feasible solution for determination of subwatershed contributions to the generation of total runoff. In this study, an attempt was made to develop an analytical procedure through which the outflow hydrographs could be determined for each subwatershed/area. The technique was based on reverse application of the Muskingum hydrologic routing model and the Area-CN role factor. The technique introduced was then tested to determine if it could solve flood routing problems associated with data for which the input hydrographs were known. A high degree of affinity (i.e., relative error below 32%) was observed between the estimated hydrographs and the recorded data, which verified the satisfactory applicability of the developed approach for estimation of the runoff generated by each subwatershed/area.

Parameterization is crucial for the soil and water assessment tool (SWAT) before applying it to simulate hydrology, soil erosion, and nonpoint source pollution. Accordingly, parameter uncertainty should be considered during watershed delineation. In this study, the Upper Daning River Watershed was delineated into different numbers of subwatersheds under various delineation schemes by changing the threshold drainage area (TDA). All schemes were then parameterized and SWAT was run to determine which scheme had the highest modeling efficiency. Results indicate that the simulation under the finest delineation scheme was not the most accurate but moderate level delineation scheme with TDA of 5,000 ha was. Then the parameter uncertainty introduced by model calibration was explained by the coverage of observed data and the width of the 95% prediction band ( $P$ -factor and $R$ -factor). To further investigate the effect of changing the TDA on SWAT modeling, the best fit set of parameter values of the delineation scheme with TDA of 5,000 ha was extended to the other schemes, but the results revealed only slight differences.