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• A SSC model in ice-covered channels is proposed based on gravitational theory. • A new formula is presented to evaluate Reynolds shear stress. • The proposed model performs well in predicting the SSC profile. Rivers in cold high latitude northern regions usually freeze during winter, thereby forming an ice cover on the water surface. The additional ice cover significantly changes the flow characteristics of the rivers and hence affects the process of water and sediment transport. Understanding the vertical profile of suspended sediment concentration (SSC) in ice-covered channel flows is helpful for investigating the sediment deposition and the bed morphology of rivers located in cold regions. To predict the SSC distribution in ice-covered channels, this study is based on the gravitational theory and puts forward a new SSC model by dividing the flow underneath the ice cover into the upper ice layer and the lower bed layer with the maximum streamwise velocity and the zero Reynolds shear stress as the interface. The calculated results of the new SSC model agree well with the collected experimental data, and the accuracy of the prediction results is evaluated by error analysis. Besides, the differences in the governing equations and the prediction accuracy between the gravitational theory and the diffusion theory are discussed, and thus the pros and cons of the proposed SSC model are illustrated. Although the gravitational theory has the controversial point, the validation results and discussions demonstrate that adopting the gravitational theory to estimate the SSC distribution in ice-covered channels is effective. The theoretical approach used herein can provide some guidance for studying the sediment-laden flow of freezing rivers in high-latitude northern regions. [ABSTRACT FROM AUTHOR]

A methodology based on general hydraulic relations for rivers has been developed to estimate the discharge (flow rate) of rivers using satellite remote sensing observations. The estimates of discharge, flow depth, and flow velocity are derived from remotely observed water surface area, water surface slope, and water surface height, and demonstrated for two reaches of the Yukon River in Alaska, at Eagle (reach length 34.7 km) and near Stevens Village (reach length 38.3 km). The method is based on fundamental equations of hydraulic flow resistance in rivers, including the Manning equation and the Prandtl-von Karman universal velocity distribution equation. The method employs some new hydraulic relations to help define flow resistance and height of the zero flow boundary in the channel. Estimates are made both with and without calibration. The water surface area of the river reach is measured by using a provisional version of the U.S. Geological Survey (USGS) Landsat based product named Dynamic Surface Water Extent (DSWE). The water surface height and slope measurements require a self-consistent datum, and are derived from observations from the Jason-2 satellite altimeter mission. At both reach locations, the Jason-2 radar altimeter non-winter heights consistently tracked the stage recorded at USGS streamgages with a standard deviation of differences (error) during the non-winter periods of less than 7%. Part of the error may be due to differences in the gage and altimeter crossing locations with respect to the range of stage change and the response to changes in discharge at the upstream and downstream locations. For the non-winter periods, the radar derived slope estimates (mean = 0.0003) were constant over the mission lifetime, and in agreement with previously measured USGS water surface slopes and slopes determined from USGS topographic maps. The accuracy of the mean of the uncalibrated daily estimates of discharge varied between reaches, ranging from 13% near Stevens Village (N = 90) to −21% at Eagle (N = 246) based on the absolute error, and 5% to −6% based on the error of the log of the estimates. Calibrating to the mean of USGS daily discharge estimates from the streamflow rating for the same period of record at each streamgage resulted in mean absolute errors ranging from 1% to 2%, and log errors ranging from 1% or less. The error pattern of the estimates shows that without calibration, even though the mean is well simulated, the high and low end values over the range of estimates may have significant bias. [ABSTRACT FROM AUTHOR]

Headwater catchments provide substantial streamflow to rivers even during long periods of drought. Documenting the mean transit times (MTT) of stream water in headwater catchments and therefore the retention capacities of these catchments is crucial for water management. This study uses time series of 3 H activities in combination with major ion concentrations, stable isotope ratios and radon activities ( 222 Rn) in the Lyrebird Creek catchment in Victoria, Australia to provide a unique insight into the mean transit time distributions and flow systems of this small temperate headwater catchment. At all streamflows, the stream has 3 H activities (<2.4 TU) that are significantly below those of rainfall (∼3.2 TU), implying that most of the water in the stream is derived from stores with long transit times. If the water in the catchment can be represented by a single store with a continuum of ages, mean transit times of the stream water range from ∼6 up to 40 years, which indicates the large retention potential for this catchment. Alternatively, variations of 3 H activities, stable isotopes and major ions can be explained by mixing between of young recent recharge and older water stored in the catchment. While surface runoff is negligible, the variation in stable isotope ratios, major ion concentrations and radon activities during most of the year is minimal (±12%) and only occurs during major storm events. This suggests that different subsurface water stores are activated during the storm events and that these cease to provide water to the stream within a few days or weeks after storm events. The stores comprise micro and macropore flow in the soils and saprolite as well as the boundary between the saprolite and the fractured bed rock. Hydrograph separations from three major storm events using Tritium, electrical conductivity and selected major ions as well a δ 18 O suggest a minimum of 50% baseflow at most flow conditions. We demonstrate that headwater catchments can have a significant storage capacity and that the relationship between long-water stores and fast storm event subsurface flow is complex. The study also illustrates that using 3 H to determine mean transit times is probably only valid for baseflow conditions where the catchment can be represented as a single store. The results of this study reinforce the need to protect headwater catchments from contamination and extreme land use changes. [ABSTRACT FROM AUTHOR]

The velocity distribution in natural channels is of considerable interest for streamflow measurements to obtain information on discharge and flow resistance. This study focuses on the comparison of theoretical velocity distributions based on 1) entropy theory, and 2) the two-parameter power law. The analysis identifies the correlation between the parameters of the distributions and defines their dependence on the geometric and hydraulic characteristics of the channel. Specifically, we investigate how the parameters are related to the flow resistance in terms of Manning roughness, shear velocity and water surface slope, and several formulae showing their relationships are proposed. Velocity measurements carried out in the past 20 years at Ponte Nuovo gauged section along the Tiber River, central Italy, are the basis for the analysis. [ABSTRACT FROM AUTHOR]

• Velocity distribution and averaged velocity in gravel-bed streams derivate from seepage flow and mixing length models. • Experiments demonstrate the flow velocity in the gravel layer and surface layer are affected by gravel array spatial density. • The bed context effects are found to be slightly more sensitive parameters for flow velocity than hydraulic effects. The standard exponential and logarithmic laws for flow velocity evaluation cannot be applied for gravel-bed streams due to the effect of large-scale roughness. An analytical model based on a two-layer subdivision approach was developed to predict flow velocity over a gravel array with different densities. The velocity distribution in the gravel layer was derived by solving the Darcy-Forchheimer-Brinkman (DFB) differential equation based on the concept of porous medium flows. The velocity in the surface layer was modeled by the mixing length theory with the length scale modified by taking into account the porous effect of the gravel (ball) arrays. To assess the model, flow velocities over gravel beds simulated by Ping-Pong ball arrays with different densities (or porosities) were measured in a laboratory flume. The results show that the predicted velocities by this subdivision model agree well with experimental data, reflecting that the porosity of the gravel array essentially impacts the flows both in the gravel layer and surface layer. In comparison with the existing models not considering the porous effect of the gravel bed, this model can effectively predict vertical velocity distributions and thereby flow resistances in gravel streams. The permeable interface velocity atop the gravel layer, as the boundary condition for the two-layer model, is sensitive to the bed context effect rather than the hydraulic effect, suggesting that the inflection point of the full velocity profile might be vital in determining the accuracy of the model. Moreover, with other data sources over dense gravel-bed, our model is suitable for data pre-dealt with the spatially averaging, where the spatial non-uniformity effect is great. [ABSTRACT FROM AUTHOR]

Summary: Torrential floods characterized by extremely high discharges and sediment transport rates are common in Mediterranean areas. Few field data is available for such floods due to sudden increase in water discharges and short flood duration. This paper presents the field data collected during a major flood event in a 90° confluence of two torrential rivers of the Mediterranean area. A two-dimensional model was used to describe the flow characteristics at the confluence. The influence on water levels of the torrential character of both rivers and some morphological processes as the tributary mouth gravel bar has been assessed. Although channel roughness coefficients and sediment deposits influence final water surface elevations they have lesser effect than the discharge ratio between main and tributary rivers. [Copyright &y& Elsevier]

Summary: A model is presented for solute transport in rivers including transient storage in hyporheic zones. The model consists of an advection–dispersion equation for transport in the main channel with a sink term describing diffusive solute transfer to the hyporheic zone. This system of equations is solved analytically for instantaneous injection of a conservative tracer in an infinite uniform river reach with steady flow. The solution enables to estimate the temporal and spatial evolution of tracer concentrations downstream of the injection point with fewer parameters than any other model before. The solution is linked to a non-linear least squares optimisation algorithm to analyse breakthrough curves and estimate solute transport parameters. The model is applied to tracer experiments conducted in the Chillán River, Chile, which were previously analysed with a model including mass exchange between the river and a stagnant storage zone. The fit between observations and model results is good, except for some experiments where the tailing of the fitted curves is more pronounced than observed. Estimates of the water flow velocity are practically identical with previous findings, but the estimates of the cross-sectional area and the dispersion coefficient are markedly different. Estimated values for the diffusion coefficient in the hyporheic zone agree with values cited in literature and with the magnitude of chemical diffusion coefficients in porous media. [Copyright &y& Elsevier]

Abstract: The use of quantitative rainfall forecasts as input to a rainfall-runoff model, thereby extending the lead-time of flow forecasts, is relatively new. This paper presents results from a study in which real-time river flow forecasts were calculated for the River Uruguay basin lying within southern Brazil, using a method based on observed rainfall, quantitative forecasts of rainfall given by a regional numerical weather-prediction model, and rainfall-runoff simulation by a distributed hydrological model. The performance of discharge forecasts was evaluated over a continuous 167-day period and from one selected flood event, using rainfall forecasts at three spatial resolutions. The performance of these forecasts was also compared with that of forecasts obtained (a) by assuming that no further rain would fall, and (b) by assuming that rainfall forecasts were equal to the rainfall actually recorded, this representing a surrogate for ’perfect’ rainfall forecasts. The results show that for the basin considered, there is plenty of scope for improving usefulness of rainfall forecasts. [Copyright &y& Elsevier]

The aim of a flood frequency analysis is to make inferences about the frequency with which extreme river flows occur at a location of interest, hereafter referred to as the target site. It is a common practice to use information from several locations for this purpose, especially when flood data are limited or non-existent at the target site. A crucial issue is then how information from different locations is combined. Should data from the target site be predominant or should the estimated flood characteristics be some sort of average of those at the locations used? How should information on the variability in flood characteristics between different locations be used? How best can information on important hydrological variables be incorporated? This article examines these issues. Two likelihood-based approaches, a regression model and an empirical Bayes analysis, are described and related to the widely used region-of-influence approach. In the discussion a regression model incorporating random site effects is proposed. [Copyright &y& Elsevier]

The efficient method presented herein is based on the regularity of water flow in an open channel, which is maintained by nature at a constant ratio of mean to maximum velocities at a channel section. This ratio is a function of a parameter of a probability distribution that is equivalent to velocity distribution in the physical space. The maximum velocity can be determined quickly by measuring only a few velocities from a single vertical axis. As well as the ratio, the location of the sampling vertical axis on which the maximum velocity occurs tends to remain invariant with time. The mean velocity in a section can be rapidly determined by estimating the product of the maximum velocity multiplied by the ratio. The cross-sectional area of an open channel can be determined by the relation between gage height and area. Thus, the discharge in an open channel may be estimated as the product of mean velocity multiplied by the cross-sectional area. This efficient method can be used with any current meter to reduce the time and cost of discharge measurement in open channel flows under tidal effect. The available data of the Tanshui River downstream reach of which is in an estuarine area is used to illustrate the accuracy and reliability of the method. The results show that the simple but reliable method is capable of estimating discharge in tidal streams. [Copyright &y& Elsevier]

• We evaluate HLM performance comparing simulated and observed streamflow at 150 locations in Iowa. • We explore the effect of including an interflow component in model structure. • We test a routing model adapted to the flow velocity of each stream order. • We study the effect of bias correction in radar rainfall products. This study evaluates the performance of Iowa Flood Center's real-time distributed hydrologic model, Hillslope-Link Model (HLM). The HLM provides information about current and future streamflow conditions for over 1000 locations in Iowa, including small communities and stream gauge locations. The HLM uses a calibration-free approach in which a system of ordinary nonlinear differential equations represents the processes of rainfall to runoff translation as well as the transport of water in the river network. The authors developed a comprehensive evaluation framework to improve the model performance through modification of its structure, and not by parameter calibration. The authors explored modifications to the runoff generation modeling, and to the approach for routing water in channels. Model performance was assessed using different metrics: Nash Sutcliffe efficiency (NSE); Kling Gupta efficiency (KGE); mean absolute error of river stages (MAE); percent bias (PB); annual peak difference; ratio of hits, misses and false alarms, and timing difference. The inclusion of an interflow component alleviated problems of volume underestimation. Timing of model simulations was found to be more accurate when the routing component considered the channel stream order. In the study, effect of rainfall input on the model performance was verified with Stage IV, which includes bias adjustment using gauge information, and a radar rainfall product created in real-time by IFC without bias correction. Open-loop simulations obtained with Stage IV and IFC rainfall show similar performance. Out of all the simulations obtained with Stage IV, 88% have NSE > 0; 95% have KGE > 0; 65% have MAE < 1 foot; 83% have |PB| < 40; 35% have hit rate >40%; average peak estimation errors are below 5% at large basins and below 20% at small basins; and the average timing difference is smaller than three hours. The characteristics of landforms and the impact of agricultural practices in the region are related to the spatial distribution of model performance. The study provides the basis for future improvements of the model. [ABSTRACT FROM AUTHOR]