Downstream River Channel Research Articles

Analyzing river disruption factors and ecological flow in China's Liu River Basin amid environmental changes.

Water resources variability and availability in a basin affect river flows and sustain river ecosystems. Climate change and human activities disrupt runoff sequences, causing water environmental issues like river channel interruptions. Therefore, determining ecological flow in changing environments is challenging in hydrological research. Based on an analysis of long-term changes in hydrological and meteorological variables and interruption conditions in the semi-arid Liu River Basin (LRB), this study summarizes the controlling factors of river interruption at different temporal and spatial scales and proposes a framework to determine ecological flow under changing environments. Hydrological model and the monthly optimal probability distribution were used to determine the optimal ecological runoff of LRB. The results showed that from 1956 to 2017, precipitation and potential evapotranspiration in the basin showed no significant decreasing trend, but the streamflow significantly decreased, and the downstream interruption worsened, with an average annual interruption duration of 194days at Xinmin Station from 1988 to 2017. The controlling factors of river interruption are as follows: (1) soil and water conservation measures in the upstream significantly reduce the runoff capacity; (2) the operation mode of the controlling reservoir in the middle reaches changes from "all-year discharge" to "winter storage and spring release" to "combined storage and supply," severing the hydraulic connection between upstream and downstream; and (3) siltation in the downstream river channel coupled with over-extraction of groundwater increases the seepage capacity of the river. The monthly ecological flow of Naodehai Reservoir was determined by considering the monthly seepage losses after reconstructing the natural runoff using the SWAT model and determining the optimal probability distribution function for monthly runoff. The findings are important for downstream LRB ecological restoration and for determining the ecological flow of other river basins in changing environments.

A study on the classification of geological background source cadmium migration phases in Zhejiang Province, China

The release of cadmium during the natural weathering process of cadmium-containing strata is a significant source of cadmium pollution in both water and soil. The Hetang formations, wildly located in Jiangxi Province Zhejiang Province and Anhui Province in China, is a typical example of a cadmium-rich black shale stratum and is one of the primary sources of soil cadmium contamination. The bottom coal seam of this formation has been found to contain high levels of cadmium, with concentrations up to 11.26 mg/kg. As a result of water flow eroding the riverbed, parent rocks containing cadmium undergo continuous weathering, releasing cadmium elements. This process contributes to cadmium pollution in downstream soil, originating from the geological background. By utilizing techniques such as FE-SEM, EDS, and optical microscopy, this study investigates the distribution of iron in rock fragments with varying degrees of weathering in the riverbed. The research aims to examine the influence of iron distribution on the migration of cadmium originating from geological background sources. Based on the co-occurrence and co-migration characteristics of iron and cadmium in the study area, this research aims to reveal the migration features of geological background source cadmium by exploring the distribution patterns of iron sediment within rock fragments. By comparing sediment samples from both upstream and downstream river channels, we were able to identify three distinct stages that indicate the presence of cadmium originating from geological sources under weathering conditions: the unweathered stage; the intra-detritus migration stage, and the completely weathered stage; intra-detritus migration stage; and completely weathered stage. Furthermore, after leaving the Hetang formations shale outcrop area, there was a sharp decrease in content for Hetang formations detritus. At this point geological background source cadmium had largely escaped from constraints imposed by rock microstructure and had come into full contact with water. The findings from this research deepen our understanding regarding migration patterns for geological background source cadmium. They also reveal formation processes for geological background source cadmium pollution and provide a theoretical basis for identification and treatment for geological background source cadmium pollution.

Analysis of factors affecting the water regeneration capacity in Tarim River Basin

The formation, evolution and regeneration of water resources follow the general laws of nature. However, in recent years, with the increasing social and economic activities of human beings, the hydrological cycle of nature has undergone significant changes, which has led to a prominent contradiction in the water supply-demand. It has also led to a series of serious environmental and ecological problems, which have caused certain areas, such as the Tarim River Basin (TRB) to face severe conditions of water shortage, downstream river channel cutoff, vegetation degradation and ecological environment deterioration. The lack of water is the main problem to solve these problems, and the water resource reproducible ability, now and in the future, is the key to solving the core problem of water shortage. Through collecting data of precipitation, runoff and temperature of representative hydrographic stations of the Tarim River, as well as the data of geographical location and human activities, this paper studies the factors affecting the water resource reproducible ability in the TRB. The paper draws the following conclusions: (1) The water resource reproducible ability in the source flow area of TRB is increasingwhen the temperature and precipitation is increasing. (2) The water resource reproducible ability in the west of TRB is greater than that in the east. (3) With the elevation of the topography, the water resource reproducible ability in the TRB is stronger. (4) Human activities weaken the water resource reproducible ability.

Influence of Different Particle Sizes of Sediments on the Lower Reaches of the Basin and its Significance in the Liao River Governance

Based on the sand volume and sedimentation volume data for different particle size (PS) groups, the relationship between the annual scouring and silting amount of the Juliu River-Liujianfang section and the yearly sediment volume entering the downstream river channel was established. The critical values of sediment storage and release for the downstream river channel were obtained. It was found to decrease with an increase in the sediment particle size. The correlation coefficient between the annual scouring and silting amount of the Juliu River-Liujianfang section and the annual sediment volume entering the downstream river channel increased with the coarsening of sediment PS. It indicated that the sediment size was proportional to the sediment amount (SA) entering the river channel. As the sediment size increased, the deposition amount increased due to the variation of unit sediment amount. Based on the treatment and achievement of source areas with sediment sizes larger than 0.05 mm, it is significant to concentrate on treatment areas with sediment sizes larger than 0.10 mm.

Multi-temporal analysis of morphological changes in an Alpine proglacial area and their effect on sediment transfer

Proglacial areas in high-mountain environments are among the most dynamic landscape zones in terms of morphological, sedimentological, and hydrological changes. In fact, in such areas both glacial and paraglacial dynamics exert a strong control on water fluxes (and thus on bedload transport capacity) and on sediment supply. Because of the rapid changes undergoing in these environments, the understanding of the dynamics of sediment transfer and the prediction of how this will change in future still remain a challenge. In this study, we used four different high-resolution topographic surveys to quantitatively analyse the spatio-temporal patterns of sediment transport that occurred in the proglacial area of the Sulden glacier (South Tirol, Italy). The topographic surveys covered the period 2013–2019 and – by building DEMs of difference (DoDs) – we calculated the volumes of erosion and deposition occurring at the glacier terminus and along its outflow channels. Our results indicate that, within the analysed time-period and for different areas, erosion and deposition generally show similar values, suggesting that the analysed proglacial areas has been acting both as a sediment trap and as a sediment source for the downstream river reaches. In addition, the results indicate a complex morphological dynamics, which have strongly impacted coarse sediment connectivity in the upper catchment. In particular, high temperatures and the recent and rapid glacier melt, have promoted a direct control on the structural connectivity within the proglacial area. Morphological changes have increased or decreased sediment connectivity depending on pre-existing morphological features. In contrast, extreme precipitation events, both in term of rainfall and snowfall, have locally and temporally increased the functional connectivity, sometimes leading to long-term modifications in the proglacial area. Overall, in the analysed time-period sediment transfer has been extremely dynamic, suggesting that sediment in the downstream river channel may have been supplied with irregular pulses associated with the morphological changes taking place in the proglacial area.

Identifying groundwater resilience zones in an arid inland basin using GIS-based Dempster-Shafer theory

Study regionHotan River Basin, an arid inland river basin, Northwest China. Study focusA method for assessing the spatial distribution of groundwater resilience is constructed by combining the Dempster-Shafer theory model and spatial analysis techniques. The groundwater performance indicator CRS and resilience indicator pi are calculated to present groundwater resilience. Using the Dempster-Shafer theory model to mine the data, nine groundwater conditioning factors are selected as evidential layers of the model, and the mathematical relationships between the resilience indicators and groundwater conditioning factors are established through evidence integration; Ultimately, a groundwater resilience spatial distribution map is generated, and the performance of the map is explored based on the CRS and pi values. New hydrological insights for the regionThe constructed assessment method based on this study reliably and effectively predicts the regional groundwater resilience. Validation of the groundwater resilience prediction map with pi indicates that this indicator outperforms the CRS. The areas with high groundwater resilience are mainly concentrated in the upstream oasis irrigation area and the downstream river channel. The groundwater resilience (pi) zonation map is divided into five categories: very low (Bel of 0–0.072), low (0.072–0.171), moderate (0.171–0.458), moderate high (0.458–0.786), and high (>0.786). The results can provide a scientific basis for groundwater safety and management in the Hotan River Basin.

Evaluation of Lesser Zab River Course Change between Dokan and Dibbs Dams (N-Iraq), Using GIS Techniques

The morphology of the lesser Zab River is influenced, by the presence of two dams (Dokan dam and Dibbs dam) that regulates the natural seasonal flows, this will affect the study area infrastructure and it has varied impacts upon water management strategies. Therefore, this study aims to quantify the morphological changes of the river course in the downstream reaches of the Dokan dam using Remote Sensing and GIS techniques using the Digital Elevation Model (DEM 30x30m) for the period from 1980 to 2020. This study shows that the differences in discharge for a long time will affect the distribution of erosion and deposition along the downstream river channel. The river course has been changed slightly at the upper reach of the study area, and the overall change is towards the middle and the lower reaches of the river, showing a gradual increase in the channel length, increasing meandering index, and the formation of alluvium islands at the river meander. Implications of this study could help identify river changes and their influence on the design and planning of water management projects and infrastructure in the area beside the other risks that might arise in terms of hazards such as floods.

Numerical Investigation of Sediment Flushing and Morphological Changes in Tamsui River Estuary through Monsoons and Typhoons

The removal of reservoir silt and the restoration of existing reservoir capacities through land excavation and hydraulic sediment flushing have become necessary. Hydraulic sediment flushing discharge changes flow and sediment conditions of the downstream river channel. In the Tamsui River estuary in Taiwan, sediment flushing from the Shihmen reservoir upstream has potential impacts on the morphology of the navigation channels and the adjacent coasts. This study employed a validated coastal and estuarine processes model to investigate: (1) the influence of sediment flushing and tidal levels on morphological changes during flood and flushing-discharge operations of the reservoir, and (2) the differences in morphological changes on the estuary between monsoon and typhoon seasons. The prediction of the morphological changes was carried out by simulating hydrodynamic and morphodynamic processes under multi-year synthetic conditions combined by northeast monsoon and three historical typhoon events. The simulation results reveal that during the operation of sediment flushing when the peak discharge of river flood flow reaches the estuary section at ebb tides, more sediment can be transported to the open sea than that at flood tides. Additionally, the nature reserve area on the left bank of the estuary is eroded during monsoon and silted in typhoon seasons.

Impact of the Three Gorges Dam on riverbed scour and siltation of the middle reaches of the Yangtze River

AbstractThis study investigated the influence of the Three Gorges Dam (TGD) on the evolution of nearby channels in the Yangtze River (Changjiang River) system in order to better understand the environmental impact of large‐scale reservoir operations. From 2003 to 2017, the amounts of runoff and sediment transport in the Yangtze River were reduced by 3.3–14.5% and 67.8–92.7%, respectively, relative to 1955–2002 before the TGD was operational. Topographic measurements of the middle reaches (Yichang to Hukou) of the Yangtze River were analyzed from 1975 to 2017, during which time the cumulative erosion of the flood channel was 22.78 × 108 m3, and the dry channel accounted for 90.3% of the erosion. Following commissioning of the TGD, the scouring intensity of the sandy gravel section near the dam initially increased then decreased, whereas the scouring intensity of sandy sections away from the dam continued to increase. Beaches on convex banks of curved sections were scoured, and deep channels on concave banks became silted. In braided sections, the braids tended to shrink, and the diversion ratio of the main branch during dry seasons reduced, resulting in frequent branch alternation. Compared to changes in the downstream river channels of other large reservoirs worldwide, scouring from the TGD is extensive. The findings of this study are significant for river channel regulation and waterway planning in the Yangtze River and worldwide.

Research on Flood Discharge and Energy Dissipation of a Tunnel Group Layout for a Super-High Rockfill Dam in a High-Altitude Region

Under the condition of a large dip angle between the flood discharging structure axis and the downstream cushion pool centerline, the downstream flow connection for the discharging tunnel group is poor, and the lower air pressure in high-altitude areas increases its influence on the trajectory distance of the nappe, further increasing the difficulty of predicting the flood discharge and energy dissipation layout. Based on the RM hydropower project with the world’s highest earth-rockfill dam, this paper studies the problem of a large included angle flip energy dissipation layout of a tunnel group flood discharge using the method of the overall hydraulic physical model test. The test results show that the conventional flip outlet mode has a long nappe falling point, a serious shortage of effective energy dissipation space, a large dynamic hydraulic pressure impact peak value on the bottom slab and side wall of the plunge pool, a poor flow connection between the outlet of the plunge pool and the downstream river channel, and a low energy dissipation rate. Considering the influence of a low-pressure environment, when the “transverse diffusion and downward incidence” outflow is adopted, the nappe falling point shrinks by 11 m, the energy dissipation form of the plunge pool is greatly improved, the effective energy dissipation space is increased by 159%, the RMS of the maximum fluctuating pressure is reduced by 74%, the outflow is smoothly connected with the downstream river, the energy dissipation rate is increased by 0.8%, and the protection range of flood discharge atomization is significantly reduced. This effectively solves the safety problems of large included angle discharge return channels and the energy dissipation and erosion prevention of super-high rockfill dams.

Landslide-lake outburst floods accelerate downstream hillslope slippage

Abstract. The Jinsha River, which has carved a 2–4 km deep gorge, is one of the largest SE Asian rivers. Two successive landslide-lake outburst floods (LLFs) occurred after the 2018 Baige landslides along the river. Using Sentinel-2 images, we examined the LLF impacts on downstream river channels and adjacent hillslopes over a 100 km distance. The floods increased the width of the active river channel by 54 %. Subsequently, major landslides persisted for 15 months in at least nine locations for displacements >2 m. Among them, three moving hillslopes ∼80 km downstream from the Baige landslides slumped more than 10 m 1 year after the floods. Extensive undercuts by floods probably removed hillslope buttresses and triggered a deformation response, suggesting strong and dynamic channel–hillslope coupling. Our findings indicate that infrequent catastrophic outburst flooding plays an important role in landscape evolution. Persistent post-flood hillslope movement should be considered in disaster mitigation in high-relief mountainous regions.

Variability of heavy metal transport during the water–sediment regulation period of the Yellow River in 2018

To understand the impacts of the human-induced flood event on heavy metal (HM) transport, spatiotemporal variations in contents and fluxes of metals (Cr, Ni, Cu, Zn, As, Pb, Cd), Pb stable isotopes and characteristics of water and sediment transport into the sea during Water-Sediment Regulation Scheme (WSRS) in Yellow River (YR) were studied based on field investigation at Xiaolangdi Reservoir (XLD), Lijin Station and Yellow River estuary (YRE). The HM transport was significantly controlled by hydrological process and dominated by particulate form with strong associations with particle size and suspended sediment concentration (SSC). In first stage, dissolved heavy metal (DHM) and particulate heavy metal (PHM) contents both increased significantly as coarser sediment with a mixed source of downstream river channel and XLD, while that maintained higher value for stable source of fine-grained XLD sediment in second stage. The HMs into the sea were mainly originated from upper and middle reaches but also contributed by human emissions from downstream area. As the source of HMs into the sea, the downstream area also acted as an important sink, especially in first stage, playing a role of buffering and filtration. During WSRS, the YR discharged 49%–60% of annual HM flux into the sea, and the second stage is the main transport period, leading to a great alternation in geochemical composition of the YRE sediment.

Effects of sediment content changes on the growth of phytoplankton in Dongting Lake

After the construction of the Three Gorges Dam(TGD) on the Yangtze River, the reservoir’s regulation and storage for upstream flow and downstream river channel erosion (caused by the discharge of clear water) led to a significant reduction in the amount of sediment entering Dongting Lake from the Yangtze River. The decrease in sediment entering the lake led to a decrease in sediment content and an increase in lake transparency. These factors caused the growth of algae in Dongting Lake, and the level of lake eutrophication increased. Based on the AQUATOX aquatic ecology model, this study analyses the responses of phytoplankton and chlorophyll a in each area of Dongting Lake and the changes in the nutritional status of the water body under the scenario of the continuing decline in sediment content while other factors remain unchanged. The results show that as the sediment content decreases, the biomass of phytoplankton and the content of chlorophyll a will show increasing trends in each area of Dongting Lake. In this case, eutrophication will continue to develop in Dongting Lake.

Optimisation of reservoir operation mode to improve sediment transport capacity of silt-laden rivers

The inverse relationship between water and sediment is hindering the regulation of sediment in silt-laden rivers. Under natural conditions and insufficient water flow, sediment deposits along river channels, resulting in the accumulation of suspended river sediments above the ground level on both sides of the river. Then, during flooding, dam collapse and overflow can easily occur, threatening the life of residents in floodplain. The operation of upstream reservoirs to maximise the sediment transport capacity of downstream rivers into the sea is deemed the best strategy for the management of silt-laden rivers. However, as incoming water and sediment form a dynamic system, optimising the operation mode of reservoirs has become the most severe challenge in the field. This study proposes a method to remodel the water–sediment relationship of natural rivers by optimising the reservoir operation. First, data were collected and analysed to investigate sediment transport in the downstream river channel and the response relationship between erosion–deposition. Then, an empirical equation for calculating the desired incoming sediment was derived, and the threshold for sedimentary transport balance in the lower reach of silt-laden rivers was determined through mathematical modelling. Finally, the reservoir operation mode was optimised within the threshold range to study the discharge process of the reservoir with the highest sediment transport efficiency downstream. The Yellow River in China exhibits the highest sediment concentration worldwide and was used as a case study to verify the practicability of the proposed method. The critical threshold for sediment transport balance in the lower Yellow River was determined to be 250 million tons. The results demonstrate that the proposed method improved the sediment transport capacity of the lower reaches of the Yellow River. Moreover, it reduced the siltation of the XiaoLangDi Reservoir and the lower reaches of the Yellow River. The XiaoLangDi Reservoir can be jointly operated with the Guxian Reservoir, which is under construction and is expected to maintain the bankfull discharge of the lower reaches of the Yellow River at 4000 m3 for a long time. The optimisation process described in this study can be used to improve the management of silt-laden rivers.

A PHYSICAL HYDRAULIC MODEL TEST TO SOLVE THE PROBLEM ON SPILLWAY DAM

This research studies about the hydraulic performance and and the problem solving alternativesof spillway design at Fila Tukutaha Dam, Alor District Indonesia. Flow water passing over the spillway of adam typically has a large amount of energy, must be dissipated safely before the floodwaters rejoin to thenatural river system. Therefore, energy dissipation takes place at the downstream end of the chuteway. Thestilling basin at the end of the chute way is commonly used to dissipate energy from the spillway and slow thewater velocity to protect the downstream river channel from erosion and damage. The methodology ofexperiment consists of physical modeling in the Hydraulic and Coastal Engineering Laboratory of CivilDepartement, Sepuluh Nopember Institute of Technology. The discharge design was analyzed by hydrologicalrouting formula over the spillway. The methods include Bernoulli’s formula equation for the steeply slopedchannel, the standard step formula for calculating the energy equation on the transition channel, and the USBRtype 2 for designing the stilling basin. From the experimental result, cross-flow was reduced by adding thehexagonal baffle block on the transition channel, and the effectiveness of stilling basin was occurred by placingthe abrupt rise in the downstream area.

GIS-Based Gully Erosion Susceptibility Mapping: A Comparison of Computational Ensemble Data Mining Models

Gully erosion destroys agricultural and domestic grazing land in many countries, especially those with arid and semi-arid climates and easily eroded rocks and soils. It also generates large amounts of sediment that can adversely impact downstream river channels. The main objective of this research is to accurately detect and predict areas prone to gully erosion. In this paper, we couple hybrid models of a commonly used base classifier (reduced pruning error tree, REPTree) with AdaBoost (AB), bagging (Bag), and random subspace (RS) algorithms to create gully erosion susceptibility maps for a sub-basin of the Shoor River watershed in northwestern Iran. We compare the performance of these models in terms of their ability to predict gully erosion and discuss their potential use in other arid and semi-arid areas. Our database comprises 242 gully erosion locations, which we randomly divided into training and testing sets with a ratio of 70/30. Based on expert knowledge and analysis of aerial photographs and satellite images, we selected 12 conditioning factors for gully erosion. We used multi-collinearity statistical techniques in the modeling process, and checked model performance using statistical indexes including precision, recall, F-measure, Matthew correlation coefficient (MCC), receiver operatic characteristic curve (ROC), precision–recall graph (PRC), Kappa, root mean square error (RMSE), relative absolute error (PRSE), mean absolute error (MAE), and relative absolute error (RAE). Results show that rainfall, elevation, and river density are the most important factors for gully erosion susceptibility mapping in the study area. All three hybrid models that we tested significantly enhanced and improved the predictive power of REPTree (AUC=0.800), but the RS-REPTree (AUC= 0.860) ensemble model outperformed the Bag-REPTree (AUC= 0.841) and the AB-REPTree (AUC= 0.805) models. We suggest that decision makers, planners, and environmental engineers employ the RS-REPTree hybrid model to better manage gully erosion-prone areas in Iran.

Sediment transport of different particle size groups in the downstream channel after operation of the Three Gorges Project

三峡工程蓄水后“清水”下泄，坝下游河段将会长期处于严重不饱和状态，水流含沙量沿程恢复将会引起坝下游长距离冲刷，本文根据三峡工程蓄水前、后的实测资料分析了坝下游河道泥沙输移变化规律，探索不同粒径组沙量沿程恢复对河床冲刷的影响，得到以下结论：在蓄水初期d≤0.031 mm沙量恢复主要受河床补给与江湖入汇共同的影响，随着水库下泄该粒径组沙量递减，使得各站该粒径组年均输沙量均远小于蓄水前的水平，沙量恢复仍主要受河床补给与江湖入汇的影响，这是造成坝下游河道发生长距离冲刷的主要原因之一；在蓄水初期0.031 mm < d≤0.125 mm沙量恢复主要受河床补给的影响，但江湖入汇的影响较大，随着河床补给量逐渐减少，各站该粒径组年均输沙量均小于蓄水前的水平，沙量恢复仍主要受河床补给的影响，江湖入汇的影响逐渐减小，这也是坝下游河道发生长距离冲刷的主要原因之一；d>0.125 mm沙量恢复主要受河床补给的影响，蓄水初期该粒径组沙量在宜昌-监利河段沿程恢复速率较快，且在监利站达到蓄水前的水平，随着时间推移，在宜昌-监利河段沿程恢复且速率仍较快，在监利站达到最大值，其数值逐渐小于蓄水前的水平，这是造成坝下游河道冲刷重点集中在宜昌-监利河段的主要原因.;Sediment concentrations in the downstream would be unsaturated in a serious long-term after the operation of the Three Gorges Project, since sediment concentration recovery causes long distance erosion in middle reach of the Yangtze River. Based on the field data collected after the operation of the Three Gorges Project, the sediment transport patterns in middle reach of the Yangtze River was analyzed, and the influence of sediment recovery along the river bed with different particle size groups on river bed erosion was explored. Result showed that:the recovery of sand content of d ≤ 0.031 mm was mainly affected by the replenishment of riverbeds and the inflow of rivers and lakes in the early stage of water storage. With the decrease of the amount of sand with d ≤ 0.031 mm, the average annual sediment transport amount of that group at each station was much smaller than that before the water storage. Recovery was still mainly affected by riverbed recharge and inflow of rivers and lakes, which was one of the main causes of long-distance erosion in the downstream channel of the dam. In the early stage of water storage, the recovery of sand volume of 0.031 mm<d ≤ 0.125 mm was mainly affected by riverbed recharge, but the impact of rivers and lakes was significant. With the gradual reduction of riverbed recharge, the average annual sediment transport of the particle size 0.031 mm<d ≤ 0.125 mm at each station was lower than that before the water storage, and the sand recovery was still mainly affected by riverbed recharge. The influence of inflow from rivers and lakes is gradually reduced, though this is still one of the main reasons for the long-distance erosion of the river downstream of the dam. d>0.125 mm sand recovery was mainly affected by riverbed recharge, in the initial stage of water storage, the sand content of this particle size group was faster in the Yichang-Jianli section, and it reached the level before the water storage in Jianli Station. In the Yichang-Jianli section, the rate was still relatively fast as time passes, peaking at Jianli Station. The value was smaller than the level before the water storage. This was the main reason that the downstream river channel erosion was concentrated in the Yichang-Jianli River section.

Dynamic 3D Simulation of Flood Risk Based on the Integration of Spatio-Temporal GIS and Hydrodynamic Models

Dynamic visual simulation of flood risk is crucial for scientific and intelligent emergency management of flood disasters, in which data quality, availability, visualization, and interoperability are important. Here, a seamless integration of a spatio-temporal Geographic Information System (GIS) with one-dimensional (1D) and two-dimensional (2D) hydrodynamic models is achieved for data flow, calculation processes, operation flow, and system functions. Oblique photography-based three-dimensional (3D) modeling technology is used to quickly build a 3D model of the study area (including the hydraulic engineering facilities). A multisource spatio-temporal data platform for dynamically simulating flood risk was built based on the digital earth platform. Using the spatio-temporal computation framework, a dynamic visual simulation and decision support system for flood risk management was developed for the Xiashan Reservoir. The integration method proposed here was verified using flood simulation calculations, dynamic visual simulations, and downstream river channel and dam-break flood simulations. The results show that the proposed methods greatly improve the efficiency of flood risk simulation and decision support. The methods and system put forward in this study can be applied to flood risk simulations and practical management.

Analysis of an Ecological Flow Regime during the Ctenopharyngodon Idella Spawning Period Based on Reservoir Operations

The study of fish habitats is important for us to better understand the impact of reservoir construction on river ecosystems. Many habitat models have been developed in the past few decades. In this study, a fuzzy logic-based habitat model, which couples fuzzy inference system, two-dimensional laterally averaged hydrodynamic model, and two-dimensional shallow water hydrodynamic model, is proposed to identify the baseline condition of suitable habitat for fish spawning activities. The proposed model considers the reservoir and the downstream river channel, and explores the comprehensive effects of water temperature, velocity, and water depth on habitat suitability. A real-world case that considers the Ctenopharyngodon idella in the Xuanwei Reservoir of Qingshui River is studied to investigate the effect of in- and outflow of reservoir on fish habitat and the best integrative management measure of the model. There were 64 simulations with different reservoir in- and outflows employed to calculate the weighted usable area and hydraulic habitat suitability. The experimental results show that the ecological flow for Ctenopharyngodon idella spawning can satisfy the basic demand when the reservoir inflow is greater than 60 m3/s and the reservoir outflow is greater than 100 m3/s. The habitat ecological suitability is the best when the reservoir outflow is 120 m3/s. A more reasonable and reliable ecological flow range can be obtained based on the habitat model in this paper, which provides the best scenario for water resources planning and management in the Qingshui River Basin.

Dam Operation for Mitigating Ice Jam Flooding Risks under the Adjustment of River Channel-Forms: Implications from an Evaluation in the Ningxia-Inner Mongolia Reach of the Upper Yellow River, China

Dam operation has been widely deployed to mitigate the risks of ice jam flooding, but it may result in a decrease in the discharging capacities of downstream river channels. The Ningxia-Inner Mongolia reach of the Huanghe River (Yellow River) has historically suffered numerous disasters caused by ice jam flooding, and three large dams have been jointly operated to mitigate such risks since 1968. Whilst the resultant significant increases in both the annual runoff and mean water temperature during the ice jam flooding seasons helped to shorten the freezing-up duration and reduce the thickness of the ice cover, a significant channel shrinkage occurred in the reach when the dam operation took place under the input of a relatively larger amount of sediment from the upstream. In the new flow regime that commenced in 2008, a detailed examination of the river channel-form adjustments and the resultant changes to the discharging capacities identified a slight increase in the discharging capacity of the channel along the entire study reach. This was mainly due to a significantly smaller amount of sediment load being carried by a slightly increased annual runoff. Whilst it was demonstrated that the dam operation was still an effective means for mitigating the risk of ice jam flooding in the Ningxia-Inner Mongolia reach under the new flow regime, care needs to be taken when the favorable flow-sediment condition changes. Furthermore, the effectiveness of the dam operation appeared to vary significantly at the channel sections of different planforms; thus, more detailed studies are required.