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1.
All river engineering schemes require flood discharge estimates as part of the design and appraisal process. Unfortunately, continuous measurement of flood discharges is limited to those river sites with instrumented gauging stations, which constitute only a small proportion of channel reaches where information is required. Therefore, considerable research effort has been devoted to the development of reliable indirect techniques of flood discharge estimation. Research on the interrelationship of stream channel geometry and river discharge has provided the basis for an indirect method of flood estimation – the channel-geometry method – which employs river channel dimensions alone to estimate discharge characteristics at ungauged river sites. Channel-geometry equations are developed empirically by relating streamflow data from gauging stations and channel dimensions measured from natural river reaches in the vicinity of the gauge, and take the form of power function relations. Once regional channel-geometry equations have been defined, a channel width or channel capacity measurement is the only variable needed to estimate the flood flow characteristics at a specified river site. The method is useful as an alternative to traditional catchment-based approaches or as a rapid reconnaissance technique. In addition to the application for flood discharge prediction, channel-geometry equations could prove helpful in the management of river channels, first, by providing a basis for assessing local deviations in the channel form–discharge relation, deviations which could be employed as indicators of the sensitivity of particular stretches of river channel to change, and secondly, in the computation of natural channel dimensions for use in river channel design and river restoration.  相似文献   

2.
We propose an improvement of the overland‐flow parameterization in a distributed hydrological model, which uses a constant horizontal grid resolution and employs the kinematic wave approximation for both hillslope and river channel flow. The standard parameterization lacks any channel flow characteristics for rivers, which results in reduced river flow velocities for streams narrower than the horizontal grid resolution. Moreover, the surface areas, through which these wider model rivers may exchange water with the subsurface, are larger than the real river channels potentially leading to unrealistic vertical flows. We propose an approximation of the subscale channel flow by scaling Manning's roughness in the kinematic wave formulation via a relationship between river width and grid cell size, following a simplified version of the Barré de Saint‐Venant equations (Manning–Strickler equations). The too large exchange areas between model rivers and the subsurface are compensated by a grid resolution‐dependent scaling of the infiltration/exfiltration rate across river beds. We test both scaling approaches in the integrated hydrological model ParFlow. An empirical relation is used for estimating the true river width from the mean annual discharge. Our simulations show that the scaling of the roughness coefficient and the hydraulic conductivity effectively corrects overland flow velocities calculated on the coarse grid leading to a better representation of flood waves in the river channels.  相似文献   

3.
Continuous monitoring of bed shear stress in large river systems may serve to better estimate alluvial sediment transport to the coastal ocean.Here we explore the possibility of using a horizontally deployed acoustic Doppler current profiler(ADCP) to monitor bed shear stress,applying a prescribed boundary layer model,previously used for discharge estimation.The model parameters include the local roughness length and a dip correction factor to account for sidewall effects.Both these parameters depend on river stage and on the position in the cross-section, and were estimated from shipborne ADCP data.We applied the calibrated boundary layer model to obtain bed shear stress estimates over the measuring range of the HADCP.To validate the results,co-located coupled ADCPs were used to infer bed shear stress,both from Reynolds stress profiles and from mean velocity profiles. From HADCP data collected over a period of 1.5 years,a time series of width profiles of bed shear stress was obtained for a tidal reach of the Mahakam River,East Kalimantan,Indonesia.A smaller dataset covering 25 hours was used for comparison with results from the coupled ADCPs.The bed shear stress estimates derived from Reynolds stress profiles appeared to be strongly affected by local effects causing upflow and downflow,which are not included in the boundary layer model used to derive bed shear stress with the horizontal ADCP.Bed shear stresses from the coupled ADCP are representative of a much more localized flow,while those derived with the horizontal ADCP resemble the net effect of the flow over larger scales.Bed shear stresses obtained from mean velocity profiles from the coupled ADCPs show a good agreement between the two methods,and highlight the robustness of the method to uncertainty in the estimates of the roughness length.  相似文献   

4.
The purpose of this paper is to study denitrification and the conditions for its development in a hyporheic zone. The study site is the riparian zone of a former branch of the Seine River, where the river stage is kept almost constant during the year by hydraulic regulation. Hydrological and geochemical surveys were performed by monitoring four wells, ten shorter piezometers and the river over a 15‐month period. The water fluxes originating from the chalky hillsides and the river converge in a zone parallel to the river that acts as a drainage flow path through the floodplain. The riparian zone between this flow path and the river shows an important depletion of nitrate during the summer and autumn period, which cannot be explained by a simple mixing of waters coming from the river and the chalky hillsides. It can be attributed to denitrification as it occurs when oxygen concentration is below 2 mg l?1, and goes along with a consumption of dissolved organic carbon and a decrease of redox potential. The river completely controls these hydro‐geochemical conditions. It also keeps the wetness of the riparian zone almost constant, which allowed us to isolate the high temperatures in summer and autumn as an important triggering factor for denitrification through its influence on the reaction rate and oxygen deficits. We also found a small isotopic enrichment of nitrate, suggesting that denitrification occurs after diffusion of nitrate through the sediment and riparian zone matrix, which is consistent with the hyporheic functioning of the study site. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

5.
We investigated dam behaviours during high-flow events and their robustness against perturbations in meteorological conditions using the H08 global hydrological model. Differences in these behaviours were examined by comparing simulation runs, with and without dams and using multiple meteorological datasets, at a case-study site, Fort Peck Dam on the Missouri River, USA. The results demonstrated that dam-regulated river flow reduced temporal variability over large time periods and also dampened inter-forcing discrepancies in river discharge (smoothing effects). However, during wet years, differences in peak flow were accentuated downstream of the dam, resulting in divergence in simulated peak flow across the meteorological forcing (pulsing effect). The pulsing effect was detected at other major dams in global simulations. Depending upon the meteorological forcing, the dams act as a selective filter against high-flow events. Synergy between a generic dam scheme and differences in meteorological forcing data might introduce additional uncertainties in global hydrological simulations.  相似文献   

6.
The transition area between rivers and their adjacent riparian aquifers, which may comprise the hyporheic zone, hosts important biochemical reactions, which control water quality. The rates of these reactions and metabolic processes are temperature dependent. Yet the thermal dynamics of riparian aquifers, especially during flooding and dynamic groundwater flow conditions, has seldom been studied. Thus, we investigated heat transport in riparian aquifers during 3 flood events of different magnitudes at 2 sites along the same river. River and riparian aquifer temperature and water‐level data along the Lower Colorado River in Central Texas, USA, were monitored across 2‐dimensional vertical sections perpendicular to the bank. At the downstream site, preflood temperature penetration distance into the bank suggested that advective heat transport from lateral hyporheic exchange of river water into the riparian aquifer was occurring during relatively steady low‐flow river conditions. Although a small (20‐cm stage increase) dam‐controlled flood pulse had no observable influence on groundwater temperature, larger floods (40‐cm and >3‐m stage increases) caused lateral movement of distinct heat plumes away from the river during flood stage, which then retreated back towards the river after flood recession. These plumes result from advective heat transport caused by flood waters being forced into the riparian aquifer. These flood‐induced temperature responses were controlled by the size of the flood, river water temperature during the flood, and local factors at the study sites, such as topography and local ambient water table configuration. For the intermediate and large floods, the thermal disturbance in the riparian aquifer lasted days after flood waters receded. Large floods therefore have impacts on the temperature regime of riparian aquifers lasting long beyond the flood's timescale. These persistent thermal disturbances may have a significant impact on biochemical reaction rates, nutrient cycling, and ecological niches in the river corridor.  相似文献   

7.
In this paper we use multiple field surveys spanning several decades to systematically evaluate the geomorphic consequences of a change in flow hydraulics from uniform flow to backwater flow for the lower Trinity River in east Texas, USA. Spatial changes in lateral migration rate, channel geometry, and point bar size correspond to two distinct geomorphic zones. Within the upstream uniform flow reach, the river channel is defined by fully developed point bars and a high rate of lateral channel migration. This zone transitions where the median channel bottom elevation drops below sea level. At this point flow is affected by the backwater influence of the Trinity Bay water surface elevation, as opposed to being bed slope control dominated. The change in hydraulics within the backwater zone is reflected in the channel morphology, which is characterized by smaller point bars, narrower and more symmetrical cross-sectional channel geometry, lower channel migration rates, and little to no bend deformation or cutoffs. Studying the connection between channel geometry, river bend kinematics, sediment transport, and fluid mechanics in each zone provides a deeper understanding of the relationship between channel shape and river mechanics. © 2019 John Wiley & Sons, Ltd.  相似文献   

8.
A novel methodology for simultaneous discharge and channel roughness estimation is developed and applied to data sets available at three experimental sites. The methodology is based on the synchronous measurement of water level data in two river sections far some kilometers from each other, as well as on the use of a diffusive flow routing solver and does not require any direct velocity measurement. The methodology is first analyzed for the simplest case of a channel with a large slope, where the kinematic assumption holds. A sensitivity and a model error analysis are carried out in this hypothesis in order to show the stability of the results with respect to the error in the input parameters in the case of homogeneous roughness and to analyze the effect of unknown roughness heterogeneity on the estimated discharges. The methodology is then extended to the more general case of channels with mild slope and validated using field data previously collected in three Italian rivers: the Arno (in Tuscany), the Tiber (in Latium) and the Vallo di Diana, a small tributary of the Tanagro river (in Southern Italy). The performance of the proposed algorithm has been investigated according to three performance criteria estimating the quality of the match between the measured and the computed stage and discharge hydrographs. Results of the field tests can be considered good, despite the uncertainties of the field data and of the measured values.  相似文献   

9.
ABSTRACT

Accurate assessment of stage–discharge relationships in open channel flows is important to the design and management of hydraulic structures and engineering. Flow junctions commonly occur at the confluence of natural rivers or streams. The effect of flow junctions on the stage–discharge relationship at mountain river confluences was found by measuring velocity fields and water levels in experimental models. The results show that the backwater and accumulation–separation at flow junctions affect the flow structures and patterns in the channel; also, flow confluences may induce complex flow characteristics of backwater and flow separation at river junctions, indicating potential submerged flooding disasters within the confluence zone. The impacts of flow junctions on the stage–discharge relationship are investigated for two physical confluence models built from river confluence prototype systems in southwest China. The results show that the presence of tributary river inflows tends to increase the water level of the main river. This is important for flood control, flood-risk evaluation and engineering (e.g. hydropower station construction) in mountain rivers. Finally, a comparative quantitative analysis based on flow motion equations is conducted to evaluate the stage–discharge relationship in both uniform and regular confluence systems. The results indicate that more accurate prediction can be made when taking into account the flow non-uniformity induced by flow separation, backwater and distorted bed in the junction region.  相似文献   

10.
A useful tool for identifying the temporal and spatial ambient wellbore flow relationships near a dynamic river boundary is to monitor ambient vertical wellbore flow with an electromagnetic borehole flowmeter. This is important because the presence of the wellbore can result in significant mixing or exchange of groundwater vertically across the aquifer. Mixing or exchanging groundwater within the well-screen section can have significant impacts on the distribution of contaminants within the aquifer and adverse effects on the representativeness of groundwater samples collected from the monitoring well. Ambient monitoring data, collected from long screened wells at Hanford’s 300-Area Integrated Field Research Challenge site, located approximately 260 m from the Columbia River, demonstrate that vertical wellbore flow exhibits both a positive and inverse temporal relationship with periodic river-stage fluctuations that can change over short distances between wells. The spatial distribution of these vertical flows across the well field indicates two general regions of ambient wellbore flow behavior. The western region of the site is characterized by vertical flows that are positively related to river-stage fluctuations. In contrast, the eastern region of the site exhibits vertical flows that are inversely related to river-stage fluctuations. The cause of this opposite relationship is not completely understood; however, the positive relationships appear to be associated with high-energy Hanford formation flood deposits. These flood deposits have a well-defined northwest-southeast trend and are believed to coincide with a local paleochannel. The inverse relationships are attributed to an erosional, subsurface high in the Hanford/Ringold Formation contact between the site and the Columbia River. Under these complex hydrogeologic and hydrodynamic conditions, the behavior of ambient vertical wellbore flow in monitoring wells near a dynamic river boundary can have important implications for collecting groundwater-quality samples, for contributing to contaminant distribution within an aquifer system, and for implementing effective remediation strategies.  相似文献   

11.
Floodplains and terraces in river valleys play important roles in the transport dynamics of water and sediment. While flat areas in river valleys can be identified from LiDAR data, directly characterizing them as either floodplain or terraces is not yet possible. To address this challenge, we hypothesize that, since geomorphic features are strongly coupled to hydrological and hydraulic dynamics and their associated variability, there exists a return frequency, or possibly a narrow band of return frequencies, of flow that is associated with floodplain formation; and this association can provide a distinctive signature for distinguishing them from terraces. Based on this hypothesis we develop a novel approach for distinguishing between floodplains and terraces that involves transforming the transverse cross‐sectional geometry of a river valley into a curve, named a river valley hypsometric (RVH) curve, and linking hydraulic inundation frequency with the features of this curve. Our approach establishes that the demarcation between floodplains and terraces can be established from the structure of steps and risers in the RVH curves which can be obtained from the DEM data. Further, it shows that these transitions may themselves be shaped by floods with 10‐ to 100‐year recurrence. We additionally show that, when floodplain width and height (above channel bottom) are normalized by bankfull width and depth, the ratio lies in a narrow range independent of the scale of the river valley. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

12.
Coefficients describing at‐a‐station power‐law relationships between discharge and width were calculated by applying multilevel models to field data collected during routine hydrological monitoring at 326 gauging stations across New Zealand. These hydraulic geometry coefficients were then estimated for each of these stations using standard stepwise multiple‐linear regression models. Analysis was carried out to quantify how the relationship between width and discharge changed in relation to several available explanatory variables. All coefficients describing the at‐a‐station hydraulic geometry were found to have statistically significant relationships with catchment area. Statistically significant relationships between each of the coefficients were also found with the addition of catchment climate as an explanatory variable. Further statistically significant relationships were found when station elevation and channel slope, as well as hydrological source of flow and landcover of the upstream catchment were added to the explanatory variables. The level of confidence that can be associated with estimates of width at ungauged sites, and sites with limited data availability, was then assessed by comparing model predictions with independent paired data on observed width and discharge from 197 sites. When compared against these independent data, model predictions of width were improved with the addition of predictor variables of the hydraulic geometry coefficients. The greatest improvements were made when climate was added to catchment area as predictor variables. Minor improvements were made when all available information was used to predict width at these independent sites. Although the analysis was purely empirical, results describing relationships between hydraulic geometry coefficients and catchment characteristics corresponded well with knowledge of the processes controlling at‐a‐station hydraulic geometry of river width. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

13.
We examined the influence of river stage on subsurface hydrology and pore water chemistry within the hyporheic zone of a groundwater‐fed river during the summer baseflow period of 2011. We found river stage and geomorphologic environment to control chemical patterns in the hyporheic zone. At a high river stage, the flux of upwelling water in the shallow sediments (>20 cm) decreased at sample sites in the upper section of our study reach and increased substantially at sites in the lower section. This differential response is attributed to the contrasting geomorphology of these subreaches that affects the rate of the rise and fall of a river stage relative to the subsurface head. At sites where streamward vertical flux decreased, concentration profiles of a conservative environmental tracer suggest surface water infiltration into the riverbed below depths recorded at a low river stage. An increase in vertical flux at sites in the lower subreach is attributed to the movement of lateral subsurface waters originating from the adjacent floodplain. This lateral‐moving water preserved or decreased the vertical extent of the hyporheic mixing zone observed at a low river stage. Downwelling surface water appeared to be responsible for elevated dissolved organic carbon (DOC) and manganese (Mn) concentrations in shallow sediments (0–20 cm); however, lateral subsurface flows were probably important for elevated concentrations of these solutes at deeper levels. Results suggest that DOC delivered to hyporheic sediments during a high river stage from surface water and lateral subsurface sources could enhance heterotrophic microbial activities. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

14.
Most of the largest rivers on Earth have multiple active channels connected at bifurcations and confluences. At present a method to describe a channel network pattern and changes in the network beyond the simplistic braiding index is unavailable. Our objectives are to test a network approach to understand the character, stability and evolution of a multi‐channel river pattern under natural discharge conditions. We developed a semi‐automatic method to derive a chain‐like directional network from images that represent the multi‐channel river and to connect individual network elements through time. The Jamuna River was taken as an example with a series of Landsat TM and ETM+ images taken at irregular intervals between 1999 and 2004. We quantified the overall importance of individual channels in the entire network using a centrality property. Centrality showed that three reaches can be distinguished along the Jamuna with a different network character: the middle reach has dominantly one important channel, while upstream and downstream there are about two important channels. Temporally, relatively few channels changed dramatically in both low‐flow and high‐flow periods despite the increase of braiding index during a flood. Based on the centrality we calculated a weighted braiding index that represents the number of important channels in the network, which is about two in the Jamuna River and which is larger immediately after floods. We conclude that the network measure centrality provides a novel characterization of river channel networks, highlighting properties and tendencies that have morphological significance. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

15.
A 1200 m-long river segment of Carmel River (California) was constructed to bypass trapped reservoir sediment when San Clemente Dam was removed from the Carmel River in 2015. Hundreds of large boulders were used to construct 53 steps in an 800 m-long reach of the project. Nearly all the boulders were scattered to new locations in high flows of 2017, and have been relatively stable since that time. We analysed the causes of incipient motion and distance travelled for 226 randomly selected large boulders (0.5–1.8 m) impacted by a flood event in winter of 2019. Channel width, water depth, and isolation from neighbouring boulders were the main variables controlling individual large boulder incipient motion during a 10-year peak flow event in the ‘auto-naturalized’ constructed step-pool river in 2019. There is weak statistical evidence that a combination of shear stress and the presence of boulders located laterally downstream of the subject boulder controlled the distance the boulder moved. Frequentist statistics and Akaike information criterion model comparison determined that boulder size, boulder shape, boulder roundness, and local thalweg slope were not good predictors of large boulder incipient motion or distance transported. Average dimensionless critical shear value for the four largest mobilized boulders (1.5–1.6 m) was 0.014. We describe the geomorphic history of the site and use our results to discuss potential causes of unanticipated large boulder transport at the site that occurred in a <2-year peak flow of winter 2016 soon after step construction. © 2020 John Wiley & Sons, Ltd.  相似文献   

16.
A comprehensive monitoring programme focusing on bedload transport behaviour was conducted at a large gravel‐bed river. Innovative monitoring strategies were developed during five years of preconstruction observations accompanying a restoration project. A bedload basket sampler was used to perform 55 cross‐sectional measurements, which cover the entire water discharge spectrum from a 200‐year flood event in 2013 to a rare low flow event. The monitoring activities provide essential knowledge regarding bedload transport processes in large rivers. We have identified the initiation of motion under low flow conditions and a decrease in the rate of bedload discharge with increasing water discharge around bankfull conditions. Bedload flux strongly increases again during high flood events when the entire inundation area is flooded. No bedload hysteresis was observed. The effective discharge for bedload transport was determined to be near mean flow conditions, which is therefore at a lower flow discharge than expected. A numerical sediment transport model was able to reproduce the measured sediment transport patterns. The unique dataset enables the characterisation of bedload transport patterns in a large and regulated gravel‐bed river, evaluation of modern river engineering measures on the Danube, and, as a pilot project has recently been under construction, is able to address ongoing river bed incision, unsatisfactory ecological conditions for the adjacent national park and insufficient water depths for inland navigation. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

17.
《水文研究》2017,31(6):1283-1292
Flooding in the Mississippi basin has become increasingly uncertain, and a succession of progressively higher, peak annual water levels is observed at many sites. Many record levels set in the central USA by the huge 1993 flood have already been superseded. Methodology developed elsewhere that recognizes trends of river stages is used to estimate present‐day flood risk at 27 sites in the Mississippi basin that have >100 years of continuous stage record. Unlike official estimates that are fundamentally based on discharge, this methodology requires only data on river stage. A novel plot linearizes the official flood levels that are indirectly derived from the complex, discharge‐based calculations and demonstrates that the neglect of trends has resulted in the effective use of undersized means and standard deviations in flood risk analysis. A severe consequence is that official “base flood” levels are underestimated by 0.4 to 2 m at many sites in the central USA.  相似文献   

18.
Intensive field monitoring of a reach of upland gravel‐bed river illustrates the temporal and spatial variability of in‐channel sedimentation. Over the six‐year monitoring period, the mean bed level in the channel has risen by 0·17 m with a maximum bed level rise of 0·5 m noted at one location over a five month winter period. These rapid levels of aggradation have a profound impact on the number and duration of overbank flows with flood frequency increasing on average 2·6 times and overbank flow time increasing by 12·8 hours. This work raises the profile of coarse sediment transfer in the design and operation of river management, specifically engineering schemes. It emphasizes the need for the implementation of strategic monitoring programmes before engineering work occurs to identify zones where aggradation is likely to be problematic. Exploration of the sediment supply and transfer system can explain patterns of channel sedimentation. The complex spatial, seasonal and annual variability in sediment supply and transfer raise uncertainties into the system's response to potential changes in climate and land‐use. Thus, there is a demand for schemes that monitor coarse sediment transfer and channel response. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

19.
This paper presents an approach to incorporate time‐dependent dune evolution in the determination of bed roughness coefficients applied in hydraulic models. Dune roughness is calculated by using the process‐based dune evolution model of Paarlberg et al. ( 2009 ) and the empirical dune roughness predictor of Van Rijn ( 1984 ). The approach is illustrated by applying it to a river of simple geometry in the 1‐D hydraulic model SOBEK for two different flood wave shapes. Calculated dune heights clearly show a dependency on rate of change in discharge with time: dunes grow to larger heights for a flood wave with a smaller rate of change. Bed roughness coefficients computed using the new approach can be up to 10% higher than roughness coefficients based on calibration, with the largest differences at low flows. As a result of this larger bed roughness, computed water depths can be up to 15% larger at low flow. The new approach helps to reduce uncertainties in bed roughness coefficients of flow models, especially for river systems with strong variations in discharge with time. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

20.
Significant growth in mountain rivers research since 1990 has promoted the concept that canyon-confined mountain rivers have complex topographic features nested from base- to flood-stages due to canyon structure and abundant large bed elements. Nesting means literally structures inside of structures. Mathematically, nesting means that multiple individual features and repeating patterns exist at different frequency, amplitude, and phasing, and can be added together to obtain the complete structure. Until now, subreach-scale landform structure, including nesting, has not been quantified sufficiently to understand morphodynamic mechanisms that control and respond to such organization. Geomorphic covariance structure analysis offers a systematic framework for evaluating nested topographic patterns. In this study, a threshold stage in mountain river inundation was hypothesized to exist. Above this stage landform structure is organized to be freely self-maintaining via flow convergence routing morphodynamics. A 13.2 km segment of the canyon-confined Yuba River, California, was studied using 2944 cross-sections. Geomorphic covariance structure analysis was carried out on a meter-resolution topographic model to test the hypothesis. River width and bed elevation had significantly less variability than previously reported for lower slope, partially confined gravel/cobble river reaches. A critical stage threshold governing flow convergence routing morphodynamics was evident in several metrics. Below this threshold, narrow/high “nozzle” and wide/low “oversized” were the dominant landforms (excluding “normal channel”), while above it wide/high “wide bar” and narrow/low “constricted pool” were dominant. Three-stage nesting of base-bankfull-flood landforms was dictated by canyon confinement, with nozzle–nozzle–nozzle nesting as the top permutation, excluding normal channel.  相似文献   

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