Journal of Hydrologic Engineering

Flow through submerged vegetation with inflection in the vertical profile of flow velocity exhibits instability at the interface of vegetation and overflow and causes generation of Kelvin-Helmholtz vortices. In case of flexible vegetation, the vortices cause periodic movement of stems called a monami wave. In this paper, the geometry of a bending stem is derived and the amplitude of the monami wave is calculated as a function of the bending angle. Using continuity and momentum equations, the stem geometry, combined with the temporal density stratification due to the periodic motion of stems, is analyzed to determine the frequency of the monami wave. The wave period, combined with the amplitude, explains the interfacial monami wave. The amplitude and period are derived in terms of easily measurable flow and vegetation parameters.

The time of concentration equation used in Pima County, Arizona, includes a hydrologic parameter representing the impedance to flow for peak discharge estimation on small [typically less than $2.59{\text{km}}^2\left(1{\text{mi}}^2\right)$ ] semiarid watersheds. The impedance-to-flow parameter is similar in function to the hydraulic Manning’s $n$ roughness coefficient in the kinematic wave time of concentration equation; however, the impedance to flow is a hydrologic parameter representing all portions of a watershed rather than a hydraulic parameter representing friction loss during uniform flow. To relate the impedance-to-flow parameter to physical watershed characteristics, impedance-to-flow values were calculated for return period and observed events on five undeveloped rangeland watersheds and correlated with Manning’s $n$ roughness coefficients determined from particle size analysis and simulated flow conditions. Impedance to flow displayed a positive trend with observed peak discharge on each watershed. The results indicate that local impedance-to-flow values can be developed for time of concentration equations using observed rainfall and runoff data, as well as measurable field characteristics. The impedance-to-flow parameter allows for a physical basis in time of concentration estimation without the additional detail of a physically based model.

This paper studied the mass conservation and constancy-preserving conditions of the advection scheme in the Hydrological Simulation Program-Fortran (HSPF) model. Equations were derived to examine the conditions for achieving both mass conservation and constancy-preserving properties. Case studies of simulating conservative materials, water temperature, and dissolved oxygen were conducted to show the impacts of the advection scheme on model applications. The mass conservative condition of HSPF can only be achieved weakly even though the advection equation is written in a mass conserved format for the current advection scheme. The constancy-preserving condition is strongly violated due to the inconsistency with continuity. The advection scheme was modified by the writer to use one single weighting factor for solving both water routing and material advection. Unrealistic results are removed and mass conservation and constancy-preserving conditions are achieved with the modified advection scheme.

Soil moisture is a key state variable from both climate and hydrologic cycle assessment perspectives. Recently, automated measurements of soil moisture with sensors deployed at sites in a real-time monitoring network have provided valuable new data to monitor the soil water resource. However, to assure the quality of the data, quality control (QC) tools are needed. Earlier studies left little literature on the QC of soil water data as measurements were generally not part of a network that routinely collected measurements. This paper presents a systematic QC analysis and methodology to evaluate the performance of candidate QC techniques using a spatially-extensive soil water data set. The six tests included are based on the general behavior of soil moisture, the statistical characteristics of the measurements, the soil properties, and the precipitation measurements. The threshold, step change, and spatial regression test proved most effective in identifying data problems. The results demonstrate that these methods will lead to early identification of potential instrument failures and other disturbances to the soil water measurements.

Low flow spatial scaling relationships have been defined by log-log linearity between 7-, 15-, 30-, and 60-day low flow probability weighted moments (PWMs) and drainage area size in north of Iran. The PWMs are used to avoid the influence of outliers. Across the entire region, the regression relationship is not significant which is believed to be due to climate heterogeneity of the region. Dividing the region into two humid and semiarid regions, the log-log relationship is found to be significant for the humid subdivision while it is not significant in semiarid region. This implies that in a heterogeneous climate regime, scaling alone is a poor method for extending low flow at-site probabilistic behavior to a region. However, for the semiarid subdivision, the relationship between mean annual rainfall and PWMs verges on significant which suggests to the hydrologist that other alternatives to drainage area size should be examined for scaling low flows in such regions.

This paper examines the daily water demand forecasting performance of double seasonal univariate time series models (Holt-Winters, ARIMA, and GARCH) based on multistep ahead forecast mean squared errors. A within-week seasonal cycle and a within-year seasonal cycle are accommodated in the various model specifications to capture both seasonalities. The study investigates whether combining forecasts from different methods could improve forecast accuracy. The results suggest that the combined forecasts perform quite well, especially for short-term forecasting. On the other hand, the individual forecasts from Holt-Winters exponential smoothing and GARCH models can improve forecast accuracy on specific days of the week.

Land subsidence caused by groundwater overpumping in Shanghai is becoming a serious geological hazard. Due to its important economic position, the field data, including compression of individual stratum from extensometer groups and the groundwater levels from observation wells, have been collected over the past 45 years. Considering the fact that different hydrostratigraphic units have different kinds of deformation and that an identical unit may also present different deformation characteristics, such as elasticity, elastoplasticity, and viscoelastoplasticity, at different sites of the cone of depression or in different periods, a nonlinear coupled regional land subsidence model is developed. The coupled model consists of a three-dimensional groundwater flow model and a one-dimensional vertical deformation model, both based on a viscoelastoplastic constitutive laws (called modified Merchant model), and then solved using a multiscale iterative finite-element method. The model is calibrated using 28,184 hydraulic head measurements and 26,732 deformation measurements from 1961 to 2005. The calibrated and evaluated model is then used to assess the future evolution of land subsidence under two groundwater pumping scenarios. Predicted results indicate that restricting groundwater pumping is effective in reducing the annual subsidence rate. Moreover the average cumulative land subsidence from 2006 to 2020 can be controlled less than 40 mm when the groundwater pumping rate is reduced to 25 million cubic meters per year. Although the area affected by land subsidence continues to expand and the cumulative amount of land subsidence still continues to increase because of the deformation delay.

Friction factor plays a fundamental role in hydraulic analysis and design. In coarse-bed rivers friction factor depends on grain size and bed forms. Considering boundary-layer characteristics, this study first determines the total friction factor in gravel-bed rivers with bed forms. Then it determines the grain friction factor by the Keulegan and the Shields parameter methods and compares these methods. Finally it determines the form friction factor by subtracting the grain friction factor from the total friction factor. Field observations are employed to test the methods.

Streamflow trend analyses have so far mainly focused on testing if trends for a specified period are significant. However, the traditional trend tests cannot characterize trend patterns, i.e., if the trend is gradual or abrupt. This study contributes a novel approach to identify the trend pattern of streamflows. This study proposes the use of repeated monotonic trend tests with varying beginning and ending times. The results of the repeated trend tests are plotted along the beginning and ending times. The sensitivity of trends with respect to the period of time is then employed to characterize the trend pattern. Application of the new approach to watersheds within the Susquehanna River Basin demonstrates that the new approach is capable of characterizing trend patterns. A comparison with the results of single monotonic trend tests shows that it is also useful for the exploration of all available data in contrast to a single monotonic trend test that only shows trends for a specified time period.

Using a large set of field and laboratory data, this study investigated the effect of slope and the Shields parameter on the friction factor. It identified the ranges of critical shear stress and bed slope for which Froude number would or would not play an important role in the evaluation of friction. It was found that the prediction of friction factor for slopes less than 0.000 81 was not satisfactory. For the Shields parameter range of $\left(0.01<{\tau }_{\ast c}<0.1\right)$ and the range of slope of 0.000 82–0.01, the prediction of friction factor was satisfactory even without considering the effect of Froude number. On the other hand, the inclusion of Froude number improved the estimation of friction factor for the range of $\left(0.01<{\tau }_{\ast c}<0.05\right)$ and steeper slopes (0.01–0.02). Finally, in gravel/sand rivers in Iran, friction factor can be estimated whether or not the flow velocity is known.