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1.
The ‘range of variability approach’ (RVA) and mapping technique are used to investigate the spatial variability of hydrologic alterations (HA) due to dam construction along the middle and lower Yellow River, China, over the past five decades. The impacts of climate variability on hydrological process have been removed during wet and dry periods and the focus is on the impacts of human activities, such as dam construction, on hydrological processes. Results indicate the following: (1) The impacts of the Sanmenxia reservoir on the hydrologic alteration are relatively slight with a mean HA value of 0·48, ranking in the last place among the four large reservoirs. (2) Xiaolangdi reservoir has significantly changed the natural flow regime downstream with mean HA value of 0·56, ranking it in first place among the large reservoirs. (3) The results of ranked median degrees of 33 hydrologic alteration indicators for 10 stations in the Yellow River show that the hydrologic alteration of Huayuankou ranks the highest among 10 stream gauges. (4) Impacts of reservoirs on hydrological processes downstream of the dams are closely associated with the regulating activities of the reservoirs. At the same time, alterations of streamflow regimes resulting from climatic changes (e.g. precipitation variability) make the situation more complicated and more hydrological observations will be necessary for further analysis. The results of the current study will be greatly beneficial to the regional water resources management and restoration of eco‐environmental systems in the middle and lower Yellow River characterized by intensified dam construction under a changing environment. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

2.
This paper describes the hydrological changes caused by inter‐basin water transfer and the reservoir development on the hydrological regimes of two rivers. The Sabljaki Reservoir in the Zagorska Mre?nica River and the Bukovik Reservoir in the upper Dobra River began operation in 1959. Both are part of the hydroelectric power plant (HEPP) Gojak, whose installed capacity is 50 m3/s. Their water volumes at the spillway altitudes of 320·10 and 320·15 m a. s. l. are 3·3 × 106 and 0·24 × 106 m3 respectively. Both the Dobra and Mre?nica Rivers are losing, sinking and underground karst rivers. A 9376‐m‐long tunnel provides water from the Sabljaki Reservoir to the HEPP Gojak, which was constructed in the Lower Dobra River. The Sabljaki Reservoir is located in the Pla?ki karst polje, while the Bukovik Reservoir is located in the neighbouring Ogulin karst polje. The consequences of the inter‐basin water transfer are strong and have caused abrupt changes in the hydrological regimes of the downstream sections of both rivers. At the same time, the construction and development of both the reservoirs have also caused hydrological changes to the upstream section of the Upper Dobra River. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

3.
Water fluxes in highly impounded regions are heavily dependent on reservoir properties. However, for large and remote areas, this information is often unavailable. In this study, the geometry and volume of small surface reservoirs in the semi-arid region of Brazil were estimated using terrain and shape attributes extracted by remote sensing. Regression models and data classification were used to predict the volumes, at different water stages, of 312 reservoirs for which topographic information is available. The power function used to describe the reservoir shapes tends to overestimate the volumes; therefore, a modified shape equation was proposed. Among the methods tested, four were recommended based on performance and simplicity, for which the mean absolute percentage errors varied from 24 to 39%, in contrast to the 94% error achieved with the traditional method. Despite the challenge of precisely deriving the flooded areas of reservoirs, water management in highly reservoir-dense environments should benefit from volume prediction based on remote sensing.  相似文献   

4.
This study presents a method to estimate streamflow in rivers regulated by lakes or reservoirs using synthetic satellite remote sensing data. To illustrate the approach, the new reservoir routing method is integrated into the Hillslope River Routing model, and a case study is presented for the highly regulated river in the Cumberland River basin (46,400 km2). The study period is April–May 2000, which contains a significant flood event that occurred in 1–2 May 2000. The model is shown to capture storage/release characterises in eight reservoirs with a mean normalized root mean square error (NRMSE) of 20% for entire simulation period and 27% for the May flood event. These errors are 69 and 75%, respectively, less than the NRMSE if reservoirs are not included in the model. Given the limitations of satellite missions, the impacts of the revisit cycles and operational periods are quantified. We used 26 observation sets of satellite altimetry over Cumberland River basin that are generated by considering both repeat cycles and satellite operation periods. For the revisit cycles, increasing the interval of repeat cycle leads to a corresponding increase of mean NRMSE from 27 to 59% as a result of sampling fewer flood events and smoothing of the change in storage signal as a result of longer intervals between visits. For the operation periods, the impact of data periods is limited because of the strong seasonal pattern of reservoir operations. Overall, the results suggest that the generalized routing model derived from reservoir stage observations can be used to simulate reservoir operating conditions, which can be used in forecasting hydrologic impacts of land cover or climate change. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

5.
朱珍香  杨军 《湖泊科学》2018,30(2):567-580
水库是福建重要的水资源.通过2013-2015年遥感影像结合Google Earth和天地图提取福建水库3353座,分布在81个县区,总面积647.51 km2,约占全省土地面积的0.5%;其中面积≤1 km2水库3248座,总面积197.16 km2,面积1 km2水库105座,总面积450.35 km2.基于经验公式估算总蓄水量188.18亿m3,其中小型水库3078座(91.80%),蓄水总量37.06亿m3(19.69%),大中型水库275座(8.20%),蓄水总量151.12亿m3(80.31%).从空间分布格局来看,福建水库水资源空间分布不均,沿海六市水库密度大于三个内陆市,大中型水库主要分布于福建西北部,蓄水量呈现西北多、东南少的特点.单位陆地面积水库数量沿海城市县区均多于内陆,而单位人口水库数量则相反;单位面积水库蓄水量沿海与内陆差异不大,而人均蓄水量则沿海大部分县区远小于内陆.仅以水库作为供水水源,不能满足沿海地区用水,但内陆地区供水充足.水库蓄水对河流水体的平均滞留时间为0.053~0.341 a,除晋江流域受水库蓄水强烈影响外,其他流域受水库中等程度影响.  相似文献   

6.
The US Geological Survey has maintained a network of stations to collect samples for the measurement of tritium concentrations in precipitation and streamflow since the early 1960s. Tritium data from outflow waters of river basins draining 4500–75000 km2 are used to determine average residence times of water within the basins. The basins studied are the Colorado River above Cisco, Utah; the Kissimmee River above Lake Okeechobee, Florida; the Mississippi River above Anoka, Minnesota; the Neuse River above Streets Ferry Bridge near Vanceboro, North Carolina; the Potomac River above Point of Rocks, Maryland; the Sacramento River above Sacramento, California; the Susquehanna River above Harrisburg, Pennsylvania. The basins are modeled with the assumption that the outflow in the river comes from two sources—prompt (within-year) runoff from precipitation, and flow from the long-term reservoirs of the basin. Tritium concentration in the outflow water of the basin is dependent on three factors: (1) tritium concentration in runoff from the long-term reservoir, which depends on the residence time for the reservoir and historical tritium concentrations in precipitation; (2) tritium concentrations in precipitation (the within-year runoff component); (3) relative contributions of flow from the long-term and within-year components. Predicted tritium concentrations for the outflow water in the river basins were calculated for different residence times and for different relative contributions from the two reservoirs. A box model was used to calculate tritium concentrations in the long-term reservoir. Calculated values of outflow tritium concentrations for the basin were regressed against the measured data to obtain a slope as close as possible to 1. These regressions assumed an intercept of zero and were carried out for different values of residence time and reservoir contribution to maximize the fit of modeled versus actual data for all the above rivers. The final slopes of the fitted regression lines ranged from 0.95 to 1.01 (correlation coefficient > 0.96) for the basins studied. Values for the residence time of waters within the basins and average relative contributions of the within-year and long-term reservoirs to outflow were obtained. Values for river basin residence times ranged from 2 years for the Kissimmee River basin to 20 years for the Potomac River basin. The residence times indicate the time scale in which the basin responds to anthropogenic inputs. The modeled tritium concentrations for the basins also furnish input data for urban and agricultural settings where these river waters are used.  相似文献   

7.
As a result of climate change/variation and its aggravation by human activities over the past several decades, the hydrological conditions in the middle Yellow River in China have dramatically changed, which has led to a sharp decrease of streamflow and the drying up of certain tributaries. This paper simulated and analysed the impact of sediment‐trapping dams (STDs, a type of large‐sized check dam used to prevent sediment from entering the Yellow River main stem) on hydrological processes, and the study area was located in the 3246 km2 Huangfuchuan River basin. Changes in the hydrological processes were analysed, and periods of natural and disturbed states were defined. Subsequently, the number and distribution of the STDs were determined based on data collected from statistical reports and identified from remote sensing images, and the topological relationships between the STDs and high‐resolution river reaches were established. A hydrological model, the digital Yellow River integrated model, was used to simulate the STD impact on the hydrological processes, and the maximum STD impact was evaluated through a comparison between the simulation results with and without the STDs, which revealed that the interception effect of the STDs contributed to the decrease of the streamflow by approximately 39%. This paper also analysed the relationship between the spatial distribution of the STDs and rainfall in the Huangfuchuan River basin and revealed that future soil and water conservation measures should focus on areas with a higher average annual rainfall and higher number of rainstorm hours. © 2015 The Authors Hydrological Processes Published by John Wiley & Sons Ltd.  相似文献   

8.
Recent emphasis on sediment connectivity in the literature highlights the need for quantitative baseline studies on the patterns and distribution of sediment stores to facilitate understanding of how sediment moves through the landscape at various temporal and spatial scales. This study evaluates the distribution and make‐up of sediment stores within the dramatically incised landscapes of the upper Yellow River, where basin fill deposits up to 1200 m in depth have been extensively reworked following incision by the Yellow River. Field and GIS analyses highlight the discontinuous distribution of sediment stores in Garang catchment, a 236 km2 tributary of the upper Yellow River. Volumetric estimates of sediment storage were obtained through a combination of field mapping, GPR transects, and GIS analyses. Sediment stores cover 20% of the Garang catchment, with an estimated volume of 474.0 × 106 m3, and inferred residence times from OSL and 14C dating of 103–104 years. Fans and terraces reworked from basin fill deposits, and associated cut and fill terrace features, are the dominant forms of sediment storage (~90% of total). A space‐for‐time argument is used to assess stages of basin infilling and subsequent landscape responses to incision, outlining a dramatic example of changes to sediment dynamics and connectivity relationships within the upper Yellow River. Sediments within the upper catchment lie above the regional basin fill level, offering a glimpse of pre‐incisional conditions. This contrasts markedly with the enduring influence of basin incisional history seen within the middle catchment, and the contemporary landscapes of the lower catchment where nearly all available sediment has been excavated from the basin and the landscape effectively operates under post‐incisional conditions. The need to contextualise catchment‐scale studies in terms of landscape history is emphasised. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

9.
Considering the highly stochastic nature of the hydrological process, wavelet transform was used to analyse the characteristics, trends and causes of variations in annual run‐off (1917–2006) into Tianjin in the Haihe River Basin. Run‐off was steadily declining due to climate change and human activity and a significant decrease in run‐off along the time series was discovered around the 1960s; however, the change in precipitation was insignificant. The time series of run‐off was heavily influenced by a nonlinear feature and mainly influenced by the natural climate before the 1960s, but after the 1970s the change remained steady, with an annual run‐off that fluctuated between 0·2 and 48·4 mm and was maintained at a low level (9·3 mm). The main cause of the run‐off decline in the 1960s was that more than 1900 reservoirs with a total holding capacity of up to 83 mm were constructed in the upper and middle reaches, which controlled 85% of the total run‐off. These projects have played an active role in the reservoir action and water conservation since they were implemented. At the beginning of the 1980s, the demand for water resources increased with the rapid growth of the population and the large‐scale development of industry and agriculture in the Haihe River Basin, which caused a reduction in run‐off into Tianjin. Overall, the hydrological effects of water storage projects regulating river run‐off were beneficial to flood control, but might cause a serious reduction in river run‐off into Tianjin and the lower reaches of the basin. In addition, a decrease in annual precipitation and changes in temperature in Northern China have also had an adverse effect on natural run‐off, which caused a greater decline in water resources, but this did not have a powerful influence on the overall decline in the run‐off. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

10.
Guoqiang Wang  Zongxue Xu 《水文研究》2011,25(16):2506-2517
A grid‐based distributed hydrological model, PDTank model, is used to simulate hydrological processes in the upper Tone River catchment. The Tone River catchment often suffers from heavy rainfall events during the typhoon seasons. The reservoirs located in the catchment play an important role in flood regulation. Through the coupling of the PDTank model and a reservoir module that combines the storage function and operation function, the PDTank model is used for flood forecasting in this study. By comparing the hydrographs simulated using gauging and radar rainfall data, it is found that the spatial variability of rainfall is an important factor for flood simulation and the accuracy of the hydrographs simulated using radar rainfall data is slightly improved. The simulation of the typhoon flood event numbered No. 9 shows that the reservoirs in the catchment attenuate the peak flood discharge by 423·3 m3/s and validates the potential applicability of the distributed hydrological model on the assessment of function of reservoirs for flood control during typhoon seasons. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

11.
V. Hrissanthou 《水文研究》2006,20(18):3939-3952
The Yermasoyia Reservoir is located northeast of the town of Limassol, Cyprus. The storage capacity of the reservoir is 13·6 × 106 m3. The basin area of the Yermasoyia River, which feeds the reservoir, totals 122·5 km2. This study aims to estimate the mean annual deposition amount in the reservoir, which originates from the corresponding basin. For the estimate of the mean annual sediment inflow into the reservoir, two mathematical models are used alternatively. Each model consists of three submodels: a rainfall‐runoff submodel, a soil erosion submodel and a sediment transport submodel for streams. In the first model, the potential evapotranspiration is estimated for the rainfall‐runoff submodel, and the soil erosion submodel of Schmidt and the sediment transport submodel of Yang are used. In the second model, the actual evapotranspiration is estimated for the rainfall‐runoff submodel, and the soil erosion submodel of Poesen and the sediment transport submodel of Van Rijn are used. The deposition amount in the reservoir is estimated by means of the diagram of Brune, which delivers the trap efficiency of the reservoir. Daily rainfall data from three rainfall stations, and daily values of air temperature, relative air humidity and sunlight hours from a meteorological station for four years (1986–89) were available. The computed annual runoff volumes and mean annual soil erosion rate are compared with the respective measurement data. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

12.
An analysis of the hydrological effects of vegetation changes in the Columbia River basin over the last century was performed using two land cover scenarios. The first was a reconstruction of historical land cover vegetation, c. 1900, as estimated by the federal Interior Columbia Basin Ecosystem Management Project (ICBEMP). The second was current land cover as estimated from remote sensing data for 1990. Simulations were performed using the variable infiltration capacity (VIC) hydrological model, applied at one‐quarter degree spatial resolution (approximately 500 km2 grid cell area) using hydrometeorological data for a 10 year period starting in 1979, and the 1900 and current vegetation scenarios. The model represents surface hydrological fluxes and state variables, including snow accumulation and ablation, evapotranspiration, soil moisture and runoff production. Simulated daily hydrographs of naturalized streamflow (reservoir effects removed) were aggregated to monthly totals and compared for nine selected sub‐basins. The results show that, hydrologically, the most important vegetation‐related change has been a general tendency towards decreased vegetation maturity in the forested areas of the basin. This general trend represents a balance between the effects of logging and fire suppression. In those areas where forest maturity has been reduced as a result of logging, wintertime maximum snow accumulations, and hence snow available for runoff during the spring melt season, have tended to increase, and evapotranspiration has decreased. The reverse has occurred in areas where fire suppression has tended to increase vegetation maturity, although the logging effect appears to dominate for most of the sub‐basins evaluated. Predicted streamflow changes were largest in the Mica and Corralin sub‐basins in the northern and eastern headwaters region; in the Priest Rapids sub‐basin, which drains the east slopes of the Cascade Mountains; and in the Ice Harbor sub‐basin, which receives flows primarily from the Salmon and Clearwater Rivers of Idaho and western Montana. For these sub‐basins, annual average increases in runoff ranged from 4·2 to 10·7% and decreases in evapotranspiration ranged from 3·1 to 12·1%. In comparison with previous studies of individual, smaller sized watersheds, the modelling approach used in this study provides predictions of hydrological fluxes that are spatially continuous throughout the interior Columbia River basin. It thus provides a broad‐scale framework for assessing the vulnerability of watersheds to altered streamflow regimes attributable to changes in land cover that occur over large geographical areas and long time‐frames. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

13.
Casey Lee  Guy Foster 《水文研究》2013,27(10):1426-1439
In‐stream sensors are increasingly deployed as part of ambient water quality‐monitoring networks. Temporally dense data from these networks can be used to better understand the transport of constituents through streams, lakes or reservoirs. Data from existing, continuously recording in‐stream flow and water quality monitoring stations were coupled with the two‐dimensional hydrodynamic CE‐QUAL‐W2 model to assess the potential of altered reservoir outflow management to reduce sediment trapping in John Redmond Reservoir, located in east‐central Kansas. Monitoring stations upstream and downstream from the reservoir were used to estimate 5.6 million metric tons of sediment transported to John Redmond Reservoir from 2007 through 2010, 88% of which was trapped within the reservoir. The two‐dimensional model was used to estimate the residence time of 55 equal‐volume releases from the reservoir; sediment trapping for these releases varied from 48% to 97%. Smaller trapping efficiencies were observed when the reservoir was maintained near the normal operating capacity (relative to higher flood pool levels) and when average residence times were relatively short. An idealized, alternative outflow management scenario was constructed, which minimized reservoir elevations and the length of time water was in the reservoir, while continuing to meet downstream flood control end points identified in the reservoir water control manual. The alternative scenario is projected to reduce sediment trapping in the reservoir by approximately 3%, preventing approximately 45 000 metric tons of sediment from being deposited within the reservoir annually. This article presents an approach to quantify the potential of reservoir management using existing in‐stream data; actual management decisions need to consider the effects on other reservoir benefits, such as downstream flood control and aquatic life. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

14.
In the Brazilian semi-arid region, thousands of small dams have been built over time to enhance water availability, accumulating water and hydraulic energy at high altitudes. Simulations were performed in this study to assess how the arrangement of reservoirs impacts on the power demand for water distribution in the Banabuiú River Basin (19?800 km2), Brazil. The power required to pump water from 1405 reservoirs to all districts with diffuse demands is 6.5 GWh/year, whereas in the scenario with only the 12 larger strategic reservoirs, the power demand reached 45.3 GWh/year. Alone, the largest reservoir in the basin can supply water to all districts. Nonetheless, in that scenario, the power demand would reach 195 GWh/year, which is 30 times the power required in the real reservoir arrangement. Thus, decentralization by small reservoirs not only promotes more democratic access to water, but also increases energy efficiency by storing it at higher altitudes and closer to the diffuse demands.  相似文献   

15.
Methane emissions from hydroelectric reservoirs can comprise a considerable portion of anthropogenic methane. However, lack of data on CH4 emissions in different geographical regions and high spatial‐temporal variability in the emission rates of reservoirs has led to uncertainties regarding regional emission estimates of CH4. In the subtropical plateau climate region, we used the Ertan hydroelectric reservoir as a study area. The CH4 flux at the air‐water interface was assessed by floating chambers and factors influencing emissions, including the distance from the dam, water depth, seasonal variation in wet and dry season, air‐water temperature gradient and wind speed, and was also studied through a year‐long systematic sampling and monitoring experiment. The results showed that the surface of the reservoir was a source of CH4 during the sampling period and the annual average CH4 flux was 2·80 ± 1·52 mg m?2 d?1. CH4 flux (and its variation) was higher in the shallow water areas than in the deep‐water areas. CH4 flux near the dam was significantly higher than that of other locations farther from the dam in the dry season. The seasonal variations of CH4 emission in wet and dry seasons were minor and significant diurnal variations were observed in wet and dry seasons. Exponential relationships between the CH4 flux and air‐water temperature gradient were found. Air‐water temperature gradient was an important factor influencing diurnal variations of CH4 flux in the Ertan hydroelectric reservoir. These results indicate that systematic sampling is needed to better estimate CH4 flux through coverage of the spatial variation of different water depths, measuring‐point distance from the dam, seasonal variation in wet and dry seasons and changes in climate factors (such as air‐water temperature gradient). Our results also provide a fundamental parameter for CH4 emission estimation of global reservoirs. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

16.
A key aspect of large river basins partially neglected in large‐scale hydrological models is river hydrodynamics. Large‐scale hydrologic models normally simulate river hydrodynamics using simplified models that do not represent aspects such as backwater effects and flood inundation, key factors for some of the largest rivers of the world, such as the Amazon. In a previous paper, we have described a large‐scale hydrodynamic approach resultant from an improvement of the MGB‐IPH hydrological model. It uses full Saint Venant equations, a simple storage model for flood inundation and GIS‐based algorithms to extract model parameters from digital elevation models. In the present paper, we evaluate this model in the Solimões River basin. Discharge results were validated using 18 stream gauges showing that the model is accurate. It represents the large delay and attenuation of flood waves in the Solimões basin, while simplified models, represented here by Muskingum Cunge, provide hydrographs are wrongly noisy and in advance. Validation against 35 stream gauges shows that the model is able to simulate observed water levels with accuracy, representing their amplitude of variation and timing. The model performs better in large rivers, and errors concentrate in small rivers possibly due to uncertainty in river geometry. The validation of flood extent results using remote sensing estimates also shows that the model accuracy is comparable to other flood inundation modelling studies. Results show that (i) river‐floodplain water exchange and storage, and (ii) backwater effects play an important role for the Amazon River basin hydrodynamics. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

17.
Spatially distributed hydrologic models can be effectively utilized for flood event simulation over basins where a complex system of reservoirs affecting the natural flow regime is present. Flood peak attenuation through mountain reservoirs can, in fact, mitigate the impact of major floods in flood‐prone areas of the lower river valley. Assessment of this effect for a complex reservoir system is performed with a spatially distributed hydrologic model where the surface runoff formation and the hydraulic routing through each reservoir and the river system are performed at a fine spatial and time resolution. The Toce River basin is presented as a case study, because of the presence of 14 active hydroelectric dams that affect the natural flow regime. A recent extreme flood event is simulated using a multi‐realization kriging method for modelling the spatial distribution of rainfall. A sensitivity analysis of the key elements of the distributed hydrologic model is also performed. The flood hydrograph attenuation is assessed. Several possible reservoir storage conditions are used to characterize the initial condition of each reservoir. The results demonstrate how a distributed hydrologic model can contribute to defining strategies for reservoir management in flood mitigation. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

18.
Dam construction greatly alters the channel boundary of rivers, making the dammed river system a human‐controlled system. Based on hydrometric data in the upper Changjiang River basin, the change in behaviour of sediment transport of some dammed rivers was studied. As a result, some phenomena of threshold and complex response were found. When the coefficient (Cr,a) of actual runoff regulation by reservoirs, defined as the ratio of total capacity of reservoirs to annual runoff input, is smaller than 10%, suspended sediment load at Yichang station, the control station of the Changjiang River, shows a mild decreasing trend. When this coefficient becomes larger than 10%, suspended sediment load decreases sharply. The coefficient of 10% can be regarded as a threshold. The Cr,a of 10% is also a threshold, when the variation of suspended sediment concentration (SSC) with Cr,a at Yichang station is considered. The impacts of reservoir construction can be divided into several stages, including road construction, dam building and closure, water storage and sediment trapping. During these stages, some complex response was identified. At the station below the dam, SSC increases and reaches a maximum, and then declines sharply. This phenomenon was found on the main‐stem and several major tributaries of the upper Changjiang River. In the Minjiang River, where a series of dams were built successively, the response of SSC is more complicated. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

19.
Retrogressive erosion, a widespread phenomenon of sediment transport in reservoirs, often impacts on both the reservoir capacity and the sedimentation in the downstream river channel. Based on field data from the Sanmenxia Reservoir and the Lower Yellow River over the past decades, three courses of ret-rogressive erosion with distinctive features were analyzed. The results indicate that retrogressive erosion, especially caused by rapid reduction in the water level till the reservoir is empty, often results in the serious siltation of the lower Yellow River and threatens the safety of the flood control in the Lower Yellow River. Unreasonable operation of the reservoir and incoming hyperconcentrated floods accom-panied by retrogressive erosion also aggravate the siltation of the main channel of the river. However, a reasonable operation mode of the reservoir so named"storing the clear (low sediment concentration) water in the non–flood season, and sluicing the muddy(high sediment concentration) water in the flood season" was found, which might mitigate the deposition in both the reservoir and the Lower Yellow River. This operation mode provides important experience for the design and operation of large reser-voirs in other large rivers carrying huge amounts of sediment.  相似文献   

20.
Soil loss, fluvial erosion, and sedimentation are major problems in semi‐arid environments due to the high associated costs of decreasing services such as provisioning and regulating water resources. The objective of this research is to analyse sediment yield in a mountainous semi‐arid basin, paying special attention to the sources of sediment, the associated uncertainties, and the transport processes involved. The segregation hypothesis along a reservoir of the sediment coming from hillslopes or fluvial systems is also evaluated. For this purpose, bottom‐set and deltaic deposits of a reservoir (110 hm3 ) in southern Spain have been measured and compared with basin erosion and fluvial transport monitoring over a 12‐year period. The volume of sediment stored at the bottomset of the reservoir shows a relative match with parametric predictions based on the Revised Universal Soil Loss Equation/Modified Universal Soil Loss Equation hillslope models and rating curves, estimated as being between 7 and 13 t·ha?1·year?1. Similarly, the measured volume of deltaic deposit fits the average value of stochastic simulations from different bedload transport equations. These contributions represent 50–65% of the total volume measured regarding suspended sediment inputs, way above that described in previous works. This highlights the importance of considering bedload when estimating the useful life of reservoirs in semi‐arid environments. The major differences in sediment grain size between hillslopes and river systems, and the size fractions measured along the reservoir, support the assertion of segregation hypothesis. Nonetheless, based on the processes observed and the uncertainty related to modelling, that assertion has to be taken with caution. At basin scale, a specific sediment yield of between 19 and 24 t·ha?1·year?1 has been estimated, which includes hillslopes and fluvial contributions. This rate is in the range of sediment yield reported for Mediterranean mountain areas of a torrential character. The pulse‐like nature of the system and the spatial heterogeneity of fluvial and hillslope erosion rates points out the importance of considering mid to long‐term and process‐based approaches and emphasizes the limitations of annual estimations for management purposes.  相似文献   

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