Minimum Ecological Flow Research Articles

Quantifying the impacts of climate change and human activities on ecological flow security based on a new framework

AbstractClimate change and human activities combine to alter river hydrology, thereby threatening the health of river ecosystems. Quantifying the impacts of climate change and human activities on ecological flow assurance is essential for water resource management and river ecological protection. However, fewer studies quantify the impacts of climate change and human activities on ecological flow assurance based on a complete set of frameworks. The present study introduces an integrated assessment framework designed to quantify the impacts of climate change and human activities on ecological flow security. The framework includes the following steps: (1) natural river runoff reconstruction utilizing a semi‐distributed hydrological model (SWAT), (2) calculation of the most suitable ecological stream flow of the watershed ecosystem by using the non‐parametric kernel density estimation method, (3) calculation of the safety and security levels under minimum ecological flow and appropriate ecological flow conditions in the watershed and (4) quantification of the influences of climate change and human activities on the security of ecological flow in the watershed through the application of a quantitative attribution method. The impact of climate change and human activities on the ecological flow assurance level was analysed using three hydrological stations in Xiangtan, Hengyang and Laobutou, which are the main tributaries of the Xiangjiang River Basin, as a case study. The findings indicated a substantial decrease in ecological flow assurance levels across the basin during the period of human impact (1991–2019). The quantitative assessment results suggest that human activities predominantly drive the degradation of ecological flow assurance throughout the period of human impact, accounting for 57.05% of the total impact. Extensive gradient reservoir scheduling and anthropogenic water withdrawals were the main factors contributing to the degradation of ecological flow assurance in the study basin. The methodology and findings presented in this study offer insights into the evolutionary characteristics and driving forces behind ecological flow security in a dynamic environment. Furthermore, they establish a scientific foundation for local water resource management and river ecosystem protection.

Detection and Analysis of the Variation in the Minimum Ecological Instream Flow Requirement in the Chinese Northwestern Inland Arid Region by Using a New Remote Sensing Method

With the development of human society, the balance between the minimum ecological instream flow requirement (MEIFR), which is an essential part of the ecological water demand in arid areas, and anthropogenic water depletion has received increasing attention. However, due to the lack of hydrological station data and river information on arid basins, previous researchers usually considered only the individual ecological water demand of rivers, lakes, or oases. To address this issue, a new method that combines river hydraulic parameters and the wet circumference obtained by an unmanned aerial vehicle (UAV) and remote sensing hydrological station (RSHS) technologies was applied to obtain the MEIFR and, then, systematically and quantitatively explore the balance from the perspective of the entire basin of Aiding Lake from 1990 to 2022, which is the lowest point of Chinese terrestrial territory. The results showed the following: (1) since 1990, the discharge of the seven rivers in the study area increased by 1–6%, and the MEIFR of these rivers increased by 15–100%; both quantities decreased by 3–5% from the upper to the lower reaches of the basin; (2) the surface area and water level of Aiding Lake decreased by 5% and 14%, respectively, but the MEIFR first decreased by 25% from 1990 to 2013 and, then, increased by 66.7% from 2013 to 2022; and (3) from 2011 to 2022, the MEIFR and anthropogenic water depletion exhibited a balance. Against the background of climate change, this research revealed that the MEIFR of the rivers in the Aiding Lake Basin have shown an upward trend over the past 30 years and quantitatively determined the above balance relationship and the period of its occurrence. This study supplied a method that could provide guidance for water resource management by decision-makers at a global level, thus helping achieve the sustainable development goals (SDGs).

Investigation on the influence of spur dikes on the weighted usable area for the two native species in a city-crossing river

Spur dikes, mainly for regulating water flow and protecting river banks in the past, were found recently to have the ability to increase the fish physical habitat and improve aquatic system. However, the effect of spur dikes on aquatic system was generally ignored previously, and the studies on the influence of spur dikes on improving specific native fish physical habitat are still rare. This study reports a numerical investigation for the effects of spur dikes on the physical habitat and the minimum ecological flow in the Jinjiang River. Three spur dikes are placed along the inner bend in the study reach and two fish species of the Pelteobagrus fulvidraco and carps are selected as the target species. Two-dimensional water depth and velocity field are simulated in different discharges and the results are used to predict the corresponding weight use area (WUA). The differences of WUA before and after the building of spur dikes for the two selected fish species show that spur dikes have a significant effect on the physical habitats. And the minimum ecological flows from the instream flow increment approach are different for the two objective fish species and are also considerably impacted by spur dikes.

Determination of ecological flow thresholds for rainfall-recharging rivers based on multiple hydrological methods

Given the threats to the regional river ecological flow, including the sharp increase in per capita water demand, the increase in the number of hydraulic engineering, and the strong seasonal runoff of rainfall recharge channels, we clarified the appropriate ecological flow thresholds for the middle reaches of Bailong River of northwest China. Based on the monthly runoff data in the Wudu Hydrological Station of Bailong River from 1990 to 2020, seven suitable hydrological methods were used to couple the estimation of the ecological flow in the middle reaches of Bailong River, which were tested by runoff satisfaction level analysis, using quadratic fit and 95% confidence interval to determine the monthly ecological flow and threshold of the river in the study area. The results by using the single hydrological methods showed that the calculation results from the monthly minimum ecological runoff calculation method, the improved RVA method, the Tennant method, and the DC method were four better estimation methods, which had a satisfaction level of more than 90% in the whole year. The improved RVA method and the Tennant method were more suitable for the diversion power station whose main task aimed at power generation. Although the economic benefits of hydropower stations were better when the improved RVA method was used to calculate ecological flow, the calculation results from the improved RVA method were tested and analyzed by the Tennant method, which were extremely poor from November to April in the following year, and could not meet the minimum ecological water requirements for the biological community in the river channel. While the other five methods all meet this requirement. We suggest that the minimum ecological flow in the middle reaches of the Bailong River maintained at 27.28 m3⁄s, and the maximum retained at 116.33 m3⁄s. The calculation results were in line with the dynamics of runoff in the study area, which could improve the accuracy of water ecological protection. The calculation results of this study could be used for the middle reaches of the Bailong River and may provide a reference for follow-up ecological restoration research and management in similar ecological zones.

Evaluation of Minimum and Suitable Ecological Flows of an Inland Basin in China Considering Hydrological Variation

Ecological flows in rivers are critical to the health and stability of river ecosystems, especially for inland drylands where ecological conditions are rapidly deteriorating. Climate change and human activities lead to hydrological variation, which in turn alters the hydrological and ecological balance of local ecosystems. Therefore, it is important to study the ecological flow under hydrological variation. In this study, the second-largest inland river basin in China, the Hei River Basin, was selected as the case study. The heuristic segmentation method, monthly minimum average flow method, the Lyon method, the average flow in the driest month method, and the monthly frequency method were employed to calculate the minimum and suitable ecological flow considering hydrological variation. Then, the results of the minimum and suitable ecological flow were evaluated and compared by the Tennant method. Finally, the ecological flows were recommended for the Hei River Basin after comparison and evaluation. Results show that: (1) It is necessary and feasible to calculate ecological flow demand considering hydrological variation in the Hei River Basin. (2) The evaluation results of the minimum ecological flow are mostly at a good level or above, and those of the suitable ecological flows are mostly at the optimum range. (3) Three scenarios with different periods and frequencies were set up to obtain suitable ecological flow; and it shows that the suitable ecological flow of scenario 3 (50% frequency in all months) has the best ecological benefits, and scenario 2 (frequency is taken as 75% in spring and autumn, 50% in summer, and 80% in winter) has the best comprehensive benefits. This study can provide important reference for water resources development and utilization and ecological protection in the Hei River Basin.

Assessment of suitable minimum ecological flow downstream of a dam in the Upper Yellow River based on native fish conservation

Abstract To ensure the ecological operation of the proposed C hydropower stations of the Upper Yellow River, the suitable minimum ecological flow of the study reach after the completion of hydropower station is studied. The native plateau fish was considered as an indicator species of the reach downstream of the dam for ecological conservation. The study is based on a 2D shallow water model with high-precision solution methods and GPU-accelerated performance, combined with Tennant, hydraulics method and habitat suitability models to obtain habitat conditions of river for fish survival during non-spawning periods and effective habitat areas during spawning period under different discharges. The results indicated that the suitable minimum ecological flow downstream of the C hydropower station was 87.5 m³/s to protect fish downstream. This achievement not only provides basic data for the optimal operation of C hydropower station based on the ecological response, but also some reference value for the actual operation management of water conservancy projects. Besides, it is of great ecological significance for the protection of native fish habitat in the Yellow River Basin.

Understanding the influence of check dam and season on habitat use to develop habitat suitability criteria for overwintering tadpoles of Nanorana spp.

AbstractUnderstanding habitat availability and use patterns are essential in developing comprehensive conservation strategies for focal species. Studies on amphibian larval habitat use are limited, especially from modified habitats. We investigated the habitat availability and use patterns of overwintering tadpoles of the Nanorana frog in an anthropogenically modified stream in the western Himalaya. Habitat was assessed in terms of depth, velocity, substrate type, and instream cover. We quantified the microhabitat preference of the tadpoles to develop habitat suitability criteria (HSC) curves, the biological component of habitat simulation tools used in instream flow management. We analyzed the data covering winter and post‐winter seasons using cumulative link mixed models to understand the influence of check dams and seasons on the hydraulic properties of microhabitats used by the tadpoles. We confirm the influence of check dam and season on velocity and the influence of season on depth used by the tadpoles. Based on this, we generated HSCs for tadpoles occurring in natural and modified pools during both seasons. We recommend intermediate water depths (30–60 cm) during the low flow season to sustain the tadpole population in the study stream and other required habitat features. The study underlines the importance of spatial and temporal variation in the habitat suitability for Nanorana tadpoles. These HSCs can be used in hydrological models for estimating the minimum ecological flow for overwintering tadpoles in the study area. A large‐scale study based on the recommendations can lead to a better conservation plan in light of altered streamflow in the western Himalaya region.

Effects of Mountain Rivers Cascade Hydropower Stations on Water Ecosystems

China is rich in hydropower resources, and mountain rivers have abundant water resources and huge development potential, which have a profound impact on the pattern of water resources allocation in China. As the main way of water resources and hydropower development, the construction of cascade hydropower stations, while meeting the requirements of water resources utilization for social development, has also brought adverse effects on river ecosystems. Therefore, the impact of the construction of cascade hydropower stations on mountainous river ecosystems, where the minimum ecological flow of rivers must be ensured and reviewed. In addition, this paper proposed the deficiencies and outlooks for cascade hydropower stations based on previous research results.

Long-term modelling of the Arkun multipurpose reservoir

The Arkun hydropower and dam project is located on the Coruh River in the North-west of Turkey. The project was completed in 2014. The reservoir is mainly used for energy generation. For this purpose, a main powerhouse with 225 MW and an environmental powerhouse with 12 MW were constructed. Additionally, the reservoir and operation scheme shall contribute to mitigate floods. A minimum ecological flow is mandatory in the Coruh River between the river section reaching from the eco powerhouse which is located downstream of the CFSGD dam and the main powerhouse which is connected to the reservoir via a 14 km headrace tunnel. During the feasibility stage the hydropower projects in Turkey frequently applied simplified methods for the estimation of the energy generation potential. This approach led to an overestimation of the energy general in many cases. Therefore, a reservoir operation model was created which considered monthly runoff data from 1963 to 2005. This model considered the operation of the two powerhouses, evaporation, potential irrigation uses, and spilling. In order to provide a reliable annual generation prognosis, the future development status was considered by the adaptation of the run-off time series. The results of this modelling confirm both the estimated power production during feasibility stage and the actual power production during the operation period.

An Environmental Flow Framework for Riverine Macroinvertebrates During Dry and Wet Seasons Through Non-linear Ecological Modeling

A suitable environmental flow is critical for the functional maintenance of riverine ecosystems. Hydropower plants alter the flow regime by decreasing or even drying up the streamflow downstream of the dams, thereby affecting ecosystem sustainability. In this study, we aimed to develop a robust environmental flow framework that can provide scientific evidence for sustainable water resource management. Using ecological niche modeling based on non-linear responses of species to habitat factors, we assessed the environmental flow in the Xiangxi River Basin of Central China during dry and wet seasons from a multi-year perspective. The most abundant macroinvertebrate taxon (i.e.,Baetis) was selected for model testing. The results showed seasonal differences in the minimum ecological water requirements and optimal environmental flow. These two hydrological metrics were higher during the wet season than during the dry season. During the dry season, the minimum ecological water requirement ofBaetiswas 1.3 m3·s−1, and the optimal environmental flow was 1.6 m3·s−1. During the wet season, the minimum ecological water requirement ofBaetiswas 2.5 m3·s−1, and the optimal environmental flow was 2.6 m3·s−1. This study provides a theoretical basis for the robust management of water resources in river basins.

Multi-objective ecological operation of cascade reservoirs based on MGCL-PSO algorithm

The reasonable utilization of river water resources requires the joint operation of cascade reservoirs. Aiming at power generation and ecological environment protection, taking the Qingjiang cascade reservoir group as the research object, a multi-objective optimization model for maximum power generation considering ecological base flow and minimum ecological flow changed is established. The results of the multi group cooperation operation particle swarm optimization (MGCL-PSO) model based on population cooperation show that the multi-objective of power generation and ecology can achieve a better balance by slightly reducing the power generation. Several schemes with good convergence are obtained from the calculation results, which provide a reference for the operation of cascade reservoirs.

Estimation of a Suitable Range of Discharges for the Development of Instream Flow Recommendations

Hydrological variability is of great importance for water resources management. Regardless of how rivers are individually managed, numerous research studies have concluded that aquatic organisms are highly dependent on flow regime variability. Nevertheless, natural streamflow regimes are being altered due to human-induced pressures and climate change/variability, and sufficient biological information in not incorporated in efforts to minimize these effects. Thus, there is an urgent need to develop sustainable environmental flow management guidelines to manage the risk associated with alterations to the flow regime particularly in areas where flow-ecology relationships have not been well studied. This study focuses on a stream with high natural flow regime variability, typical in Mediterranean countries. The major finding of this work is that the estimated Suitable Range of Discharges (SRD) could better address environmental water requirements, rather than simply allocating single value minimum ecological flows. SRD was estimated using advocate statistical analysis of hydrological data series, coupled with habitat suitability models to balance the trade-offs between natural flow variability and human water needs. Combination of the aforementioned approaches was made using the West Balkan trout as a biological component which is a very important species for the quantification of environmental flows. Overall implementation of SRD during dry season is likely to provide large habitat areas for 58 to 67% of the time for the small-size fish and 35 to 55% of the time for the large-size West Balkan trout, according to the Weighted Usable Area0.5 threshold index.

Target species selection and design of fish habitat suitability curves in the Ayuquila-Armería River, western Mexico

ABSTRACT The implementation of hydroecological models requires an understanding of the biological attributes and habitat requirements of the local stream fauna. We describe a procedure for selecting target (fish) species and calculating habitat fitness curves based on depth and velocity and substrate type data in the Ayuquila-Armería river in central-western Mexico. The selected target species were Sicydium multipunctatum, Agonostomus monticola and Allodontichthys zonistius, and selection of these species was based on their endemism, vulnerability and sensitivity. Eighty-four samples from nine sites monitored over 14 years were used to calculate category III univariate curves. The suitability curves proposed for each target species describe their habitat suitability values in terms of depth (m), velocity (m s−1) and substrate type (mm). These curves allow the construction of eco-hydraulic models necessary to define the minimum ecological flow in the Ayuquila-Armería river.

Optimized operation of diversion-type hydropower reservoir to alleviate ecological degradation of the de-watered river reach

Diversion-type hydropower stations usually cause seriously de-watered situation of the natural river reach, which has adverse effects on the downstream river ecosystem. To alleviate the negative impacts on ecosystem of natural river reach, this study quantified the ecological requirements and incorporated them into the reservoir operating schemes to provide the ecological flow, which is beneficial to the balance between ecosystem protection and hydropower generation. The method mainly includes (1) propose an optimal ecological flow calculation method based on runoff probability distribution, (2) combine minimum ecological flow with optimal ecological flow to define the ecological protection degree, and then (3) establish the multi-objective optimization model of reservoir with the goal of maximizing ecological protection degree and power generation (DPM) and solve it with NSGA-II. In the meanwhile, the optimization model with the goal of minimizing ecological water shortage and maximizing power generation (SPM) was established and solved which was regarded as a control batch. A case study performed with the Liujiaping (LJP) reservoir in Hunan Province of South China demonstrates that optimized operation can play a protective role in the ecology of the dewatered section. And DPM has better ecological benefits than SPM under the same power generation benefits, especially when the emphasis is placed on ecological benefits.

A Simplistic Approach for Assessing Hydroclimatic Vulnerability of Lakes and Reservoirs with Regulated Superficial Outflow

This study proposes a simplistic model for assessing the hydroclimatic vulnerability of lakes/reservoirs (LRs) that preserve their steady-state conditions based on regulated superficial discharge (Qd) out of the LR drainage basin. The model is a modification of the Bracht-Flyr et al. method that was initially proposed for natural lakes in closed basins with no superficial discharge outside the basin (Qd = 0) and under water-limited environmental conditions {mean annual ratio of potential/reference evapotranspiration (ETo) versus rainfall (P) greater than 1}. In the proposed modified approach, an additional Qd function is included. The modified model is applied using as a case study the Oreastiada Lake, which is located inside the Kastoria basin in Greece. Six years of observed data of P, ETo, Qd, and lake topography were used to calibrate the modified model based on the current conditions. The calibrated model was also used to assess the future lake conditions based on the future climatic projections (mean conditions of 2061-2080) derived by 19 general circulation models (GCMs) for three cases of climate change (three cases of Representative Concentration Pathways: RCP2.6, RCP4.5 and RCP8.5). The modified method can be used as a diagnostic tool in water-limited environments for analyzing the superficial discharge changes of LRs under different climatic conditions and to support the design of new management strategies for mitigating the impact of climate change on (a) flooding conditions, (b) hydroelectric production, (c) irrigation/industrial/domestic use and (d) minimum ecological flows to downstream rivers.

Application of Probabilistic Method to Evaluate the Rock Mass Foundation Influence over the Probability of Failure by Sliding of Hydraulics Structures: Case Study of Baixo Iguaçu HPP Spillway

In the last decades, accidents involving dams and other hydraulic structures have become more frequent, increasing social pressure on the existing dams safety conditions. This fact demands commitment of professionals and companies with new plant project safety approaches. The failure of a hydroelectric concrete structure can be caused by several factors, however the main causes of failure are related to exceptional floods and foundation-related problems, which are the focus of this paper. In order to understand the influence of the rock mass characteristics, especially the contact plan with the concrete structure, this work considers the variability of geotechnical parameters, drainage efficiency, specific gravities and seismic acceleration to determine the probability of failure of these structures. To achieve this objective, the work makes use of a case study, the spillway of Baixo Iguacu HPP, on Parana/Brazil during its design and construction phase, determining the probability of failure by sliding. The study reproduces the foundation condition throughout a FEM hydrogeological model and determines the acting uplift through seepage analysis. The probability of failure was determined by Monte Carlo method using the probability distribution of each variable, performing 5,000,000 evaluations for each simulation. Simulations were performed for flow range varying from the ecological flow (200 m3/s) to exceptional floods with 10,000 years of recurrence time (56,362 m3/s) and its respective water levels. The most critical condition found was the extended operation at the minimum (ecological) flow, while for a normal operation, at the flow of 2598 m3/s, the order of the probability of failure is one in a million. The paper show how using hydrogeological model can lead to more realistic values of uplift pressures than using simplified methods recommended in the international guidelines, and consequently lead to a more realistic probability of failure.

Modelling past, present and future Ecosystem Services supply in a protected floodplain under land use and climate changes

The understanding of protection initiatives’ effects on the delivery of Ecosystem Services (ESs) is of paramount importance to attain sustainable management in Protected Areas (PAs). Protected floodplains provide important ESs to local populations such as water flow regulation and climate regulation through carbon storage. This study investigates the effects of biodiversity protection initiatives (i.e. declaration of Protected Areas – PAs) and the related spatio-temporal land use/land cover (LULC) changes on ecosystem services (ESs) in the Nature Reserve of Paul do Boquilobo – NRPB (Central Portugal). Special focus was made on climate mitigation (i.e. carbon storage and sequestration) and water-related (flood mitigation, water regulation and supply) ESs. The analysis was performed using InVEST model. Three dates of past LULC conditions were considered in the analysis (1967, 1990 and 2015). Moreover, two future alternative LULC scenarios for 2050 were designed (a “Business”- BUS and a “Naturalization”- NAT scenario). The BUS scenario considers a LULC distribution towards high productive agricultural systems, considering only a restricted central core of natural areas, while the NAT scenario considers full coverage of natural areas. The two future extreme LULC scenarios were analyzed considering both no climate change and climate change effects on water-related services based on the pessimistic rcp8.5 climatic scenario. The results showed that PA declaration of NRPB after 1980 increased carbon storage-sequestration and flood mitigation (higher water storage, lower recharge and runoff). The analysis of future LULC scenarios demonstrated that the complete renaturing in combination with climate change (reduction of precipitation, increase of temperature) may lead to severe reduction of recharge and runoff. These results indicate that conflicts may appear between specific water regulation services by the application of PA initiatives in places where groundwater resources are limited or minimum ecological flows in surface waters are difficult to be preserved.

Economic water management decisions: trade-offs between conflicting objectives in the sub-middle region of the São Francisco watershed

Hydro-economic models can measure the economic effects of different reservoir operating rules, environmental restrictions, maintenance of ecosystems, technical constraints, institutional constraints, land use change, and climate change. To determine the optimal economic water allocation, for its main uses in the sub-middle of the Sao Francisco River Basin, a hydro-economic optimization model was developed and applied. Demand curves were used rather than fixed requirements for water resources. The results show that operation rules of reservoirs and institutional constraints, such as priorities for human consumption, have high impacts on costs and benefits of the principal economic uses in the study area. Especially, costs of environmental demands, like minimum ecological river flow, have high impacts on the water resource management. Scarcity costs of irrigation users associated with maintaining ecosystems and environmental constraints are particularly significant. The results from this study provide a better understanding of the water trade-offs for future policymaking and efficient water management. Policymaking for the water resources should consider the food-water-energy-environment nexus at a regional scale to minimize environmental and economic cost under water scarcity and land use change.

Instream ecological flow and reservoir ecological operation in the upper reaches of Irtysh River

Instream ecological flow (IEF) and flow-related variations were important for healthy river systems. However, water conservancy projects such as reservoirs altered the processes of IEF and thereby posed considerable threat to the health of river systems and aquatic lives. To that end, in this study the effects of reservoir construction on IEF in the upper reaches of the Irtysh River were analyzed using an improved hydrological method. The computed results were in turn used to determine the maximum (MaxIEF), minimum (MinIEF) and optimal (OptIEF) instream ecological flows of the river. Based on the study, reservoir impoundments limited IEF in wet seasons but enhanced it in dry seasons. It also narrowed suitable flow range for reproduction and growth of aquatic life. Reservoirs could be used to regulate Irtysh River discharge. For healthy instream processes in wet years, OptIEF could be set as the lower limit and MaxIEF as the upper limit. For much the same reasons, MinIEF could be set as the lower limit in dry years and OptIEF as a suitable target in normal years.

Investigating the impacts of cascade hydropower development on the natural flow regime in the Yangtze River, China

The Yangtze River is one of the largest and most important rivers in the world. Over the past several decades, the flow regime of the Yangtze River has been altered by human activities, particularly dam construction. Hydrological regimes will be further influenced due to more dams that have been planned and are being built in the upper reach of the Yangtze River (URYR). In this context, to assess the impacts of cascade dam development on the natural flows, four different scenarios of the reservoirs' combination are simulated with a hydrological model (the Soil and Water Assessment Tool) in the URYR. Flow regime changes were investigated using the eco-flow metrics and minimum/optimal ecological flow with the simulated daily river flows. The results indicate that eco-surplus in low flows and eco-deficit in high flows greatly increases due to reservoir operations when more reservoirs are put into service. The minimum ecological flow and the optimal ecological flow cannot be guaranteed from September to November, which is a crucial time for fish spawning. To maintain the natural regime while meeting the requirements for the river ecosystem, we propose that the lower and satisfactory operation limits are 11,680m3/s and 7235m3/s and 16,300m3/s and 9130m3/s, respectively. Optimizing cascade reservoir operational rules is needed to achieve a better balance between ecological and socio-economic demands in the Yangtze River Basin.