Downstream River Research Articles

Understanding the vulnerability of surface–groundwater interactions to climate change: insights from a Bavarian Forest headwater catchment

Headwaters play a crucial role in maintaining forest biodiversity by providing unique habitats and are important for the regulation of water temperature and oxygen levels for downstream river networks. Approximately 90% of the total length of streams globally originate from headwaters and these systems are discussed to be especially vulnerable to impacts of climate change. This study uses an integrated hydrological model (HydroGeoSphere) in combination with 23 downscaled ensemble members from representative concentration pathways (RCPs) 2.6, 4.5 and 8.5 to examine how climate change affects water availability in a headwater catchment under baseflow conditions. The simulations consistently predict increasing water deficits in summer and autumn for both the near (2021–2050) and far future (2071–2099). Annual mean water deficits were estimated to be 4 to 7 times higher than historical levels. This is mainly due to a projected reduction in precipitation inputs of up to – 22%, while AET rates remain similar to those observed during the historical reference period (1992–2018). The declining groundwater storage reserves within the catchment are expected to result in a significant decline in surface water availability during summer and autumn, with a reduction in mean annual stream discharge by up to 34% compared to the reference period. Due to declining groundwater levels, upstream reaches are predicted to become intermittent in summer leading to a reduction of the total stream flow length by up to 200 m. Findings from this study will enhance our understanding of future water availability in headwater systems and may aid in the development of effective management strategies for mitigating local impacts of climate change and preserving these vulnerable ecosystems.

Impacts of the Koka hydropower dam on macroinvertebrate assemblages in the Awash River Basin in Ethiopia

The Koka hydropower dam is one of the oldest large dams in Ethiopia. Damming is one of the anthropogenic activities impacting the distribution of aquatic life forms. However, to date, little attention has been focused on the dam’s impacts on the river macroinvertebrate assemblages in Ethiopia. The objective of this study was, therefore, to assess the impacts of the Koka hydropower dam on macroinvertebrate assemblages in the Awash River basin in Ethiopia. In the three river reaches on the Awash River (upstream near the source of the river, midstream above the dam, and downstream below the dam), a total of 15 sites were selected for sampling. The statistical analysis tested the null hypothesis that there are no differences in macroinvertebrate assemblage patterns or a range of univariate metrics between the three river reaches. Additional analyses involved the identification of taxa responsible for significant differences in macroinvertebrate structure (e.g., percentage similarity) and an exploration of the variables that structure macroinvertebrates (e.g., canonical correspondence analysis). In the upstream, midstream, and downstream reaches of the Awash River, we recorded a total of 73 taxa belonging to 43 families and 12 orders. Trichoptera was the dominant order in the upstream river reach, whereas Diptera dominated the midstream and downstream river reaches. The diversity of macroinvertebrates decreased from upstream to midstream and downstream. The three river reaches differed significantly in Shannon and Simpson diversity indices, % EPT, EPT taxa abundance, total taxa richness, evenness index, % collectors, and % scrapers. In this study, we observed that macroinvertebrate assemblage differences and spatial patterns were significantly associated with values of river flow changes (velocity), phosphate concentration, and substrate index. The findings of this study have broad implications for the assessment of the impacts of dam construction on the rivers of the studied region in the future.

Ecological Impact of Hydraulic Dredging from an Alpine Reservoir on the Downstream River

The evacuation of impounded sediments is one of the most critical aspects associated with reservoirs, with possible drawbacks on the water quality, biodiversity, and ecosystem integrity of downstream river reaches. In this study, the impacts of hydraulic dredging at the Ambiesta Reservoir (Eastern Italian Alps) on the physical habitat and the biological communities (i.e., benthic macroinvertebrates and fish) of the downstream river were assessed by comparing the pre-dredging conditions with data collected on three post-dredging occasions. The dredging operation lasted 68 days and removed an overall sediment volume of 30,600 m3. During this operation, suspended sediment concentration (SSC) was monitored by turbidimeters and, on average, it was considerably lower than the SSC limit of 1.5 g/L, which exceeded approximately 15% of the overall operation time. Additionally, the dredging operation resulted in negligible deposition of fine sediment on/into the riverbed (0.24–0.7 kg/m2). Results for fish and benthic macroinvertebrate communities indicated weak differences in the density (~20% reduction) and diversity of these organisms between pre- and post-dredging sampling occasions. Moreover, the results on the biomonitoring indices based on macroinvertebrates showed a recovery during the last two sampling occasions. Compliance with the SSC limit and avoidance of high SSC peaks, along with limited fine sediment deposition, allowed to successfully mitigate the ecological impacts of this relatively long operation of sediment removal.

Assessment of Stoplog Gates’ Operational Effectiveness for Improving Discharged-Water Temperatures during the Thermal Stratification Period in a Reservoir

The discharge of low-temperature water from the middle and lower layers of thermally stratified dam reservoirs leads to thermal pollution and adversely affects fish production and reproduction in downstream rivers. Selective water withdrawal using stoplog gates is an effective approach to address this issue. However, comprehensively and effectively evaluating the effects of stratified withdrawal and optimizing the scheduling of stoplog gates to provide better ecological services to downstream habitats pose significant challenges for reservoir managers. In this study, an equivalent elevation method (EEM) was developed based on in situ observation data of water temperature. The EEM calculates the equivalent withdrawal elevation (EWE) in the far dam area corresponding to the discharge-water temperature (DWT), facilitating the evaluation of stoplog-gate effects. EEM was applied to a thermally stratified dam reservoir in southwestern China (Guangzhao reservoir, GZ). The results showed a significant positive correlation (r > 0.7, p < 0.05) between DWT and the vertical-water-temperature structure in the far dam area. The average EWEs for the 5-layer, 4-layer, and 3-layer stoplog gates in GZ were 697.2 m, 690.8 m, and 689.9 m, respectively. Utilizing the EEM findings, a scheduling operation scheme was proposed to improve DWT while reducing the number of stoplog-gate operations, thereby increasing their efficiency and saving the cost of invested labor and time. This method provides a reference for reservoir managers in optimizing stoplog-gate-scheduling strategies to mitigate potential risks to aquatic ecosystems caused by abnormal water temperature.

Advances in using mathematical optimization to manage floods with assessment of possible benefits using a case study

Abstract This paper presents the benefits of using mathematical optimization for reservoir operation based on the assumed availability of short-term runoff forecasts. The novelty is the inclusion of the SSARR hydrological routing as optimization constraints in multiple time step optimization, where the routing coefficients are adjusted dynamically as functions of the channel flows. The paper shows significant reduction of downstream peak flows in flood-prone areas even with a forecast horizon of only 2 days, and it also includes the results of testing the effects of different lengths of forecasting horizons on model results. The case study is conducted on the Damodar River Basin in the Indian State of West Bengal, where basin development started in the 1950s, with flood protection of the downstream river valley as the highest management priority, in addition to water supply and hydro power. The solution methodology and the model results presented in this paper pave the way for eventual introduction to automated management of reservoir outflows that could shape water resources industry in much the same way that auto-pilot and driverless cars are revolutionizing the transportation industry, assuming that runoff forecasting capabilities continue to improve.

Connectivity and short‐term flood interactively affect fish community composition in drainage ditches of paddy fields in an agricultural landscape

AbstractCommunity assembly can change over time following variations in connectivity among habitats. Previous studies have demonstrated the influence of seasonal pulse floods on community structures by facilitating species dispersal, but the effects of short‐term flash floods have been poorly investigated. We investigated fish community structures before and after a short‐term flood in drainage ditches of paddy fields in the Kita River basin, Japan. The study sites were classified into three connectivity types, “Transient” (connected only during the flood, with a temporally disappearing vertical gap between drainage ditches and downstream rivers), “Connected” (always connected, without the vertical gap), and “Disconnected” (always not connected, with the vertical gap). The abundance of Misgurnus anguillicaudatus, the only species that dispersed from paddy fields to drainage ditches, increased after the flood irrespective of the connectivity types, although the total abundance of the other species significantly increased after the flood only in the “Transient” sites. The dissimilarity of species composition between the (n − 1)‐th and n‐th surveys at each site was consistently low in the “Connected” and “Disconnected” sites, whereas it rose just after the flood and gradually declined in the “Transient” sites. Species composition was significantly different among the connectivity types, indicating that some fish species need stable connectivity even during the non‐flood period. The results showed that the short‐term flood facilitated fish dispersal from paddy fields by the increased water discharge and that from downstream rivers by the temporary removal of vertical gap, emphasizing the importance of hydrological connectivity for biodiversity conservation in an agricultural landscape.

Characteristics and Attribution of Spatiotemporal Changes in Qilian Mountains' Runoff Over the Past Six Decades

AbstractTibet's Qilian Mountains (QM) include critical water conservation areas and important ecological barriers, which help maintain downstream inland river oasis stability. For decades, contemporaneous climatic and cryospheric variation has severely impacted QM's hydrological processes, challenging local water resource management and sustainable development. However, due to prevalent data and methodological limitations, QM research has primarily focused on runoff change at a basin scale. Spatial distributions and temporal changes in runoff subsequently remain unclear. Based on multi‐source data and the literature, we estimated that QM's mountain outlets generate approximately 15.671 km3 in total annual runoff, exhibiting a spatially decreasing pattern from northeast to southwest. Moreover, runoff distribution and trend variation at seasonal and annual scales depend upon the river replenishment source type. Beginning in the 1950s and 1960s, eastern rain‐fed rivers experienced a downward trend while those dominated by meltwater or simultaneously fed by multiple sources in its central and western regions experienced an upward trend. As an integrated product of mixed multi‐factor effects, runoff is regulated by temperature, precipitation, and cryospheric meltwater. Moreover, the main controlling runoff factors varied seasonally under different water source concentrations. Annually, precipitation was the main driver for runoff change in the eastern region while, correspondingly, temperature was in the western region where glaciers and the snow line boundary predominant. Besides, this study highlighted that the existing literature has significant limitations in understanding interactions among different cryospheric components and hydrologic process mechanisms when exploring the reasons for runoff variations, which needs further exploration in the future.

Optimization of selective withdrawal strategy in a warm monomictic reservoir based on thermal stratification

Selective withdrawal from reservoirs is an effective strategy for balancing economic goals and environmental demands. Multilevel intake operation (MIO) is one of the main options for improving the thermal regime of deep reservoirs. In this study, a combination of measured data and a two-dimensional hydrodynamic model (CE-QUAL-W2) was utilized to analyze the impact of MIO processes on the thermal stability of a reservoir and the improvement effect of the withdrawal water temperature (WWT). The purpose of this study was to identify an optimal selective withdrawal strategy to meet the water temperature needs of fish downstream during their spawning and breeding activities. The results showed that the MIOs raised the withdrawal water intake position (8.3–11.2 m) for the WWT. Meanwhile, MIOs resulted in statistically significant changes in the water temperature structure of the reservoir (p < 0.01). The stratification stability of the water column weakened (6.8 %-34.5 %), and there were interannual differences. The WWT increased by 0.0 °C∼1.9 °C every ten days, and the time to reach the optimum temperature (18 °C) for fish spawning was 7 to 17 days earlier. There was a statistically significant positive correlation between the WWT improvement and the stability index (SI) (R = 0.7817, p < 0.01). The threshold values of the SI (above the water intake) for average WWT improvements of 0.5 and 1.0 °C were 90.3 and 221.9 kg/m2, respectively, and the recommended operating period was from early-April to May. Under MIOs, the weakening stratification and the increasing WWT during the warming period reduced risks to the water quality and ecological health in the reservoir and downstream rivers. This study provides a helpful reference for the implementation of selective withdrawal operations and the optimization of water quality management strategies in similar large, deep reservoirs.

Development of a two-dimensional model to assess carbon dynamics and anthropogenic effects on CO2 emissions in the Tan river, southern China

Tidal rivers are key biochemical reaction channels along the land-ocean aquatic continuum, receiving carbon from wastewater and agricultural drains, which can considerably affect CO2 emissions. We developed a two-dimensional hydrodynamic and ecological model coupled with an inorganic carbon module along the Tan River in southern China. The simulations of and observations regarding discharge, temperature, total organic carbon (TOC), total inorganic carbon (TIC), and other common water quality variables were generally in good agreement. Based on the validated model, we employed statistical and scenario analyses to evaluate the carbon distribution, TOC and TIC budgets, and the imbalances induced by climatic and anthropogenic changes, providing insights into their potential greenhouse effect. The Tan River was consistently supersaturated with CO2 with an annual mean air-water CO2 emission flux (FCO2) of 226.1 ± 84.9 mmol m−2 d−1, and significant temporal and spatial variations of FCO2, TOC, and TIC were observed. Urban small streams tended to emit additional CO2 during wet seasons, and rural tributaries usually had an increase in TOC concentrations during the dry season. FCO2 was significantly positively correlated with air temperature and negatively correlated with total nitrogen, total phosphorus, and TOC. The annual riverine input of carbon to the urban river network was 17.37 Gg C yr−1, with 59.82% of TOC, and carbon output was 15.31 Gg C yr−1, with 66.87% of TOC. The retention rates for TOC and total carbon were 50.7% and 11.8% in the urban branch, respectively. Furthermore, warming and wastewater treatment could prevent urban river networks and downstream rivers from becoming carbon sources. Therefore, our findings suggest that riverine management strategies change the global CO2 release from tidal rivers and estuarine systems under climate change.

Effects of water level management on lake littorals and downstream river areas

The Interreg “Parks Verbano Ticino” (PVT) project was conceived within the technical committee dedicated to the “Experimentation of the regulation of the Lake Maggiore levels” following the requests of the water manager to raise the spring-summer maximum levels of the lake compared to the levels normally held in the same period to respond to the industrial, agricultural, touristic, and environmental needs...

Tributary mitigates river discontinuity by dam depending on the distance from dam to the tributary confluence

AbstractRiver ecosystems host a continuum of various discontinuities, such as dams and tributary inflows, which shape the habitats of aquatic organisms; this makes it important to evaluate the interactions among discontinuities and effects of a single discontinuity point. Herein, we focused on tributaries in dammed rivers to elucidate a manner to mediate discontinuities and hypothesized that the effects of the tributary inflow on the downstream river were mediated by the (1) distance between the dam and tributary inflow, (2) size ratio between the dam and tributary, and (3) ability of the tributary to transport fine sediments, such as sand and gravel. We conducted field investigations to measure 24 environmental factors, including the water column, riverbed, and river topography, along eight dammed rivers to test the three hypotheses. Only five factors differed significantly between the upstream and downstream sites of the tributary confluence, whereas 12 factors differed significantly between the tributary and mainstem. We also classified the variation pattern using principal component analysis (PCA). The correlation between each PCA axis and environmental factors suggests that the modifications of the water quality factors by tributary inflow were significantly correlated with the distance between the dam and the tributary inflow, and that the flux of various riverbed factors, that is, was significantly correlated with the ability to resupply of fine riverbed sediments by the tributary. Overall, tributary‐inflow downstream of a dam has the potential to be applicable in environmental restoration, especially in terms of resupplying fine sediment.

Shifted sediment-transport regimes by climate change and amplified hydrological variability in cryosphere-fed rivers.

Climate change affects cryosphere-fed rivers and alters seasonal sediment dynamics, affecting cyclical fluvial material supply and year-round water-food-energy provisions to downstream communities. Here, we demonstrate seasonal sediment-transport regime shifts from the 1960s to 2000s in four cryosphere-fed rivers characterized by glacial, nival, pluvial, and mixed regimes, respectively. Spring sees a shift toward pluvial-dominated sediment transport due to less snowmelt and more erosive rainfall. Summer is characterized by intensified glacier meltwater pulses and pluvial events that exceptionally increase sediment fluxes. Our study highlights that the increases in hydroclimatic extremes and cryosphere degradation lead to amplified variability in fluvial fluxes and higher summer sediment peaks, which can threaten downstream river infrastructure safety and ecosystems and worsen glacial/pluvial floods. We further offer a monthly-scale sediment-availability-transport model that can reproduce such regime shifts and thus help facilitate sustainable reservoir operation and river management in wider cryospheric regions under future climate and hydrological change.

Using Data-Driven Prediction of Downstream 1D River Flow to Overcome the Challenges of Hydrologic River Modeling

Methods for downstream river flow prediction can be categorized into physics-based and empirical approaches. Although based on well-studied physical relationships, physics-based models rely on numerous hydrologic variables characteristic of the specific river system that can be costly to acquire. Moreover, simulation is often computationally intensive. Conversely, empirical models require less information about the system being modeled and can capture a system’s interactions based on a smaller set of observed data. This article introduces two empirical methods to predict downstream hydraulic variables based on observed stream data: a linear programming (LP) model, and a convolutional neural network (CNN). We apply both empirical models within the Colorado River system to a site located on the Green River, downstream of the Yampa River confluence and Flaming Gorge Dam, and compare it to the physics-based model Streamflow Synthesis and Reservoir Regulation (SSARR) currently used by federal agencies. Results show that both proposed models significantly outperform the SSARR model. Moreover, the CNN model outperforms the LP model for hourly predictions whereas both perform similarly for daily predictions. Although less accurate than the CNN model at finer temporal resolution, the LP model is ideal for linear water scheduling tools.

Research on the adsorption rule of porous media on supersaturated total dissolved gas

AbstractDischarge of high dams may result in supersaturated total dissolved gas (TDG) in water, which could cause fish that live downstream river to suffer from gas bubble disease. If supersaturated TDG water was taken as a water source for breeding and proliferation stations, farmed fish was confined and may face more severe problems than fish living in the river. Therefore, it is critical to develop strategies to reduce the negative effects of supersaturated TDG. In this research, the adsorption effect of porous media on supersaturated TDG was explored, including biofilter adsorption experiments and previously existing activated carbon adsorption experiments. The experimental results showed that adding porous media to the water effectively accelerated the dissipation of supersaturated TDG, and the adsorption effect was associated with the specific surface area, mass density, and initial TDG saturation. To quantitively evaluate the adsorption effects of the porous media, the porous adsorption coefficient was proposed to express the adsorption rate of porous media on supersaturated TDG. The porous adsorption coefficient was related to the initial TDG saturation and the specific surface area of the porous media. The porous adsorption coefficient increased with increasing the specific surface area and decreasing initial TDG saturation. Based on this, an equation related to the specific surface area, initial TDG saturation, and the porous adsorption coefficient was developed. This equation may be used to evaluate the adsorption effect of porous media on supersaturated TDG. This study could serve as a crucial resource in reducing the adverse impacts of supersaturated TDG.

Optimal tracer identification for dissolved organic matter (DOM) source tracking in watersheds using point source effluent load data

In this study, we characterized the optical and molecular weight (MW) properties of dissolved organic matter (DOM) with various sources in an agriculture-forestry watershed. We proposed a guideline to identify optimum DOM source tracers for downstream rivers during both rain and non-rain events, utilizing the load of dissolved organic carbon (DOC) from point sources. Six descriptors were pre-selected based on established criteria in the literature, and fifteen pairs of these descriptors were evaluated for their applicability in end-member mixing analysis (EMMA). The results from EMMA provided inconsistent estimates of relative contributions from DOM sources across the fifteen pairs, with optical descriptors outperforming MW-based descriptors and their combinations. The optimal source tracers were determined by comparing relative contributions of DOM from upstream effluent wastewater using DOC load ratios calculated from on-site monitoring data and predictions based on EMMA. The pair of optical descriptors, HIX (humification index) and BIX (biological index), closely matched the measured load ratios with minimal discrepancies (0.4 ± 0.4 %). According to the EMMA results using pairs of HIX and BIX, non-rain events were primarily influenced by oil-cake fertilizer and treated effluent wastewater, while rain event samples were dominated by manure and soils. These findings offer insights into managing non-point organic pollution sources in agricultural-forestry watersheds, contributing to our understanding of carbon and nutrient cycling in aquatic systems. Notably, this study proposes a validation guideline that employs load ratios of point sources, such as effluent wastewater, to enhance source tracking accuracy.

Long-term analysis of sediment load changes in the Red River system (Vietnam) due to dam-reservoirs

The sediment regime of the Red River system, the second largest in Vietnam, has undergone changes since the implementation of dams and reservoirs, with implications for downstream river processes. We analyzed long-term datasets of daily discharge and suspended sediment concentrations collected at key gauging stations downstream of the three main tributaries: HB on the Da River, YB on the Red River (main channel), VQ on the Lo River, and ST, the outlet of the Red River system. The results indicated a sharp reduction in the annual sediment load transported by the Red River system, as observed at the four stations. For example, at the ST station, there was a dramatic decline of 91% in sediment load, dropping from 117.9 × 106 ton/yr in the period 2009–2021 to 10.5 × 106 ton/yr in the period 1958–1987. The Red River system experienced two notable declines in sediment load. The first decline occurred from 1988 to 2008, which can be attributed to the commencement of Hoa Binh dam's operation in 1988. The second decline has taken place since 2009, coinciding with the utilization of new dam-reservoirs. Meanwhile, an abrupt change in water discharge was observed clearly since the end of 2008 at all four stations. However, the reductions in water discharges were found to be less pronounced when compared to the sediment budget. Based on our analysis, we concluded that the impacts of dam-reservoirs have had a more substantial influence on the system compared to variations in climate, such as air temperature and precipitation.

Mechanisms of 137Cs leaching based on long-term observations in forested headwater catchments in Yamakiya, Fukushima Prefecture, Japan

Dissolved radiocesium (mainly 134Cs and 137Cs) is thought to be leached mainly from suspended sediment in downstream rivers, while organic matter, such as leaf litter, contributes to catchments in forested headwater streams. It is also known that dissolved 137Cs in headwater streams exhibit seasonal variation with water temperature. Some mechanisms have been proposed as the causes: ionic competition of potassium ion (K+) and ammonium ion (NH4+), leaching associated with the decomposition of organic matter, and thermodynamic adsorption-desorption processes. We investigated the relationship between K+ and the dissolved organic carbon (DOC) concentrations and seasonal changes in dissolved 137Cs concentration using a large number of samples from a headwater's small catchments. We examined temporal trends in 137Cs concentrations in coarse organic matter, suspended sediments, and dissolved forms at four sites (one decontaminated site and three undecontaminated sites) in the Yamakiya area since 2011. The distribution coefficients (Kdcss and Kdorg) of dissolved 137Cs concentrations relative to suspended sediment and coarse organic matter 137Cs concentrations were calculated, and differences in temporal changes due to decontamination were investigated. In addition, we examined the relationship between water temperature and DOC, K+, NH4+ and 137Cs concentrations in the headwater catchments. The suspended sediment 137Cs concentrations at the decontaminated headwater site (IBO) decreased significantly after decontamination and remained low thereafter. In contrast, dissolved 137Cs concentrations decreased temporarily during the decontamination period, but returned to pre-decontamination levels. Almost no NH4+ has been detected in headwater streams in our catchments. In the SET and ISH watersheds, where the distance from the groundwater spring is short, a correlation was found between DOC concentration and dissolved 137Cs concentration. In contrast, in the IBO watershed, where the distance from the groundwater spring is long, temperature dependence and a good correlation between K+ and 137Cs were observed. Therefore, microbial decomposition of organic matter may have a significant effect on the seasonal variation of dissolved 137Cs in forested headwater streams at short distances from the spring, but the influence of competing ions is expected to increase gradually as the water flows downstream.

Dynamic variations in thermal regime and surface deformation along the drainage channel for an expanding lake on the Tibetan Plateau

ABSTRACT The outburst of Zonag Lake in 2011 triggered a series of floods in the continuous permafrost region of the hinterland of the Qinghai-Tibet Plateau. This re-distributed the surface water in the basin and caused rapid expansion of the tail lake (Salt Lake). To avoid potential overflow of the expanding Salt Lake, a channel was excavated to drain the lake water into a downstream river. In this study, to investigate the permafrost thermal regime and the surface deformation around the expanding Salt Lake and the channel, in-situ monitoring sections were settled from Salt Lake to the downstream of the channel to obtain the permafrost temperature. Additionally, using small baseline subset interferometric synthetic aperture radar (SBAS-InSAR), the surface deformation around Salt Lake and the channel was measured. The data showed that the ground temperature at the channel was 0.6°C higher than the natural field and the mean subsidence rate around the channel was 1.5 mm/yr higher than that at Salt Lake. These results show that the permafrost temperature in the study area changed considerably with variations in the distance from the lake/channel, and the deformation in the study area was dominated by subsidence.

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.

Fish entrainment model for decision support in ecosystem management: A case study from China's Maling Reservoir

Fish entrainment from reservoirs to downstream rivers by various water release structures may result in serious consequences for reservoir ecosystems. This study proposed an integrated modeling approach for determining fish entrainment risk zones and suitable reservoir regulations. The modeling approach combines hydrodynamic and fish risk assessment modeling with using fuzzy rules set defined by expert knowledge in fish ecology. We applied this modeling approach in the Maling Reservoir in China, where fish entrainment in the reservoir has been observed in the turbine, spillway, and irrigation system. Percocypris pingi (Tchang, 1930) and Onychostoma simum (Sauvage & Dabry de Thiersant, 1874), representing the main and protected fish species, were selected as target fish species. Five reservoir operation schemes were investigated under normal and designed water levels. The modeling results suggest that the fish entrainment risk for protected fish species (Onychostoma simum) is higher than that for the main fish species (Percocypris pingi). The results indicate a ranking of the fish entrainment risk from high to low in the following scenarios: with all spillways in operations, with one spillway in operation, with intakes in operation, with an irrigation system in operation, and with intakes and the irrigation system in combined operations. In addition, under normal and designed water levels, dead fish entrainment zone areas and percentages were extremely low compared to the entire forebay of the reservoir. These results indicate that the operation of the Maling Reservoir does not affect the ecological status of fish. These findings are generally applicable to any fish species in reservoirs that balance reservoir operations and ecological protection of fish, and could assist reservoir managers in making informed decisions on how to mitigate and compensate for fish entrainment.