Tennant Method Research Articles

Linking curve number with environmental flows: a novel approach.

Change in flow regime is one of the major reasons which influence the services offered by rivers and integrity of their aquatic ecosystems requiring certain amount of flow in the river known as environmental flow. In this study, the environmental flows described by Tennant's method are correlated with a very versatile index defined in terms of Curve Number (CN) that incorporates hydrometeorological and geomorphological characteristics of catchment. Parameter CN is commonly known to be closely related with catchment characteristics (viz., land use, soil type, etc.). The rainfall-runoff data of 17 catchments from five major Indian river basins (i.e., Brahmani-Baitarani, Godavari, Mahanadi, Mahi, and Narmada) of low flow season (October-June) are used to derive the relationship between percentage of average annual flow (%AAF) and CN. The %AAF is seen to increase linearly with increasing CN, and vice versa, for all catchments and the correlation (R) is found to be greater than 0.7 for 16 (out of 17) catchments. The correlation between %AAF and CN is maximum for Dhariawad (R2 = 0.899) and Baronda (R2 = 0.814) catchments, indicating excellent relationship between %AAF and CN, which can be useful for the environmental flow prediction based on catchment characteristics. The existence of such a relationship is further strengthened by the relation established between the standard normal deviate of CN and the Standard Flow Index (SQI), a variation of %AAF, using the same field data.

An improved hydraulic method for calculating ecological flow considering the changes of rainfall and temperature within a year

Ecological flow (Hereinafter referred to as EF) is vital for sustaining the health of aquatic ecosystems, whereas fluctuations in rainfall and temperature markedly influence the water needs of riverine aquatic organisms. However, traditional hydrological methods for calculating EF provide a single, fixed EF value throughout the year or for specific periods (such as the flood season or non-flood season), neglecting the dynamic effects of these environmental variables on flow requirements. Building on regression analyses of rainfall and temperature, this study proposes an improved hydraulic method (Hereinafter referred to as IHM) that integrates both rainfall and temperature effects. Utilizing the three cascade hydropower plants on the mainstream of the Liuxi River in Guangdong Province, China, as case studies, the proposed method expands upon traditional hydraulic methods by establishing a relationship between river hydraulic parameters and flow, and employing the ecological suitability thresholds of indicator species as constraints to calculate the EF solution sets for the three hydropower plants. By fitting functions to the basin’s rainfall and temperature data, linear interpolation was applied to distribute the EF solution sets across 12 months within a year. The IHM is subsequently compared and validated with the evaluation standards of the traditional method. The results demonstrate that the monthly EFs by the IHM for the three cascaded hydropower plants address the constraints of fixed EFs by traditional hydraulic methods, offering more accurate and context-specific EFs for each month. The monthly EFs by the IHM also typically conform to the Tennant method’s 10 % standard (fair status) and, during certain months, reach the 40 % standard (good status), thereby effectively preserving the stability of the river’s aquatic environment. The IHM provides a robust technical foundation and theoretical framework for the accurate determination of EFs in riverine hydropower plants.

Minimum environmental flow assessment: a fuzzy TOPSIS decision-making system for selecting the best approach

The literature has explored various methods for assessing minimum environmental flow. Implementing holistic approaches proves to be prohibitively expensive and impractical for many small and medium projects. Hence, desktop and cost-effective methods are commonly employed without an integrated decision-making system to justify the assessed values. This study introduces a systematic decision-making framework aimed at selecting the most suitable method for assessing the actual needs of river habitats. Employing a fuzzy technique known as the Order Preference Similarity to the Ideal Solution (FTOPSIS), the study considers factors such as physical, thermal, and dissolved oxygen habitat suitability, maximum habitat area, and water demand loss function to determine the most appropriate method among established ones, including the Tennant method, flow duration curve analysis method, wetted perimeter method, and physical habitat simulation method. The results prioritize physical habitat simulation, wetted perimeter by slope method, and flow indices of 70%, 75%, and 80% by flow duration curve analysis method as the optimal approaches for assessing minimum environmental flow. This proposed decision-making system offers a viable platform to explore the applicability of existing cost-effective methods for assessing minimum environmental flow. It also serves as an effective mechanism for reducing negotiations among stakeholders by comprehensively considering all relevant aspects in the environmental management of river ecosystem requirements.

Determination of River Ecological Flow Thresholds and Development of Early Warning Programs Based on Coupled Multiple Hydrological Methods

In order to safeguard the health of river ecosystems and maintain ecological balance, it is essential to rationally allocate water resources. This study utilized continuous runoff data from 1967 to 2020 at the Zhouqu Hydrological Station on the Bailong River. Five hydrological methods, tailored to the hydrological characteristics of the Zhouqu hydrological cross-section, were employed. These methods included the improved dynamic calculation method, the NGPRP method, the improved monthly frequency computation method, the improved RVA method, and the Tennant method. Ecological flow calculations were conducted to determine the ecological flow, with analysis carried out through the degree of satisfaction, economic benefits, and the nonlinear fitting of the GCAS model. We established an ecological flow threshold and early warning program for this specific hydrological cross-section. Ecological flow values calculated using different methods for each month of the year were compared. The improved RVA method and Tennant method resulted in small values ranging from 4.05 to 36.40 m3/s and 7.65 to 22.94 m3/s, respectively, with high satisfaction levels and economic benefits, but not conducive to ecologically sound development. In contrast, the dynamic calculation method, NGPRP method, and improved monthly frequency calculation method yielded larger ecological flow values in the ranges of 21.79–97.02 m3/s, 23.90–137.00 m3/s, and 28.50–126.00 m3/s, respectively, with poor fulfillment and economic benefits. Ecological flow thresholds were determined using the GCAS model, with values ranging from 16.72 to 114.58 m3/s during the abundant water period and from 5.03 to 63.63 m3/s during the dry water period. A three-level ecological warning system was proposed based on these thresholds, with the orange warning level indicating optimal sustainable development capacity for the Zhouqu Hydrological Station. This study provides valuable insights into the scientific management of water resources in the Bailong River Basin to ensure ecological security and promote sustainable development.

Multi-objective integrated decision method of cascade hydropower stations based on optimization algorithm and evaluation model

The establishment and functioning of cascade hydropower stations have significantly altered the natural state of rivers, leading to increasingly severe ecological impacts downstream. To mitigate the adverse effects of cascade reservoir impoundment on river ecosystems and achieve the multi-objective goals of hydropower development and environment protection, this study presents an integrated decision model for optimizing the operation of cascade hydropower stations, utilizing the lower Jinsha River as a case illustration. The proposed model comprises three main components: ecological flow calculation, establishment of a multi-objective optimization model, and scheme evaluation. The ecological flow threshold for the river was determined using the Tennant method. The multi-objective optimization model was formulated with objectives including power generation, ecological flow shortage, and navigation disruption days. The NSGA-II algorithm was employed to resolve the optimization framework. The improved TOPSIS method was adopted for evaluating the operation schemes. The case study conducted in the downstream region of the Jinsha River revealed significant conflicts between the objectives of power generation and ecological conservation. Moreover, different typical years exerted a considerable influence on determining the optimal operation scheme. The proposed integrated decision model provides a scientific framework for guiding the water resource dispatching of cascade hydropower stations and achieving the harmonization of economic and ecological benefits. Overall, this research contributes to the academic field by addressing the complex difficulties related to optimizing the operation of cascade hydropower stations while considering ecological concerns. The findings underscore the importance of adopting a comprehensive decision-making approach that integrates multiple objectives and utilizes advanced algorithms for sustainable river management.

Use of hydrological models to calculate the ecological flow of the Jequetepeque river, upstream of the Gallito Ciego dam, Peru

The research allowed to use of hydrological models for the calculation of the ecological flow of the “Jequetepeque” river, upstream of the “Gallito Ciego” dam, Peru. Information on average monthly flows was used, which was divided into two periods (1943-1987) and (1988-2019). To calculate ecological flow, seven hydrological methods were used. For the period 1943-1987, the ecological flow was calculated with the percentage establishment method (0.47 m3s-1), followed by the Tennant method (0.57 m3s-1).The period of 1988-2019, the ecological flow was calculated with the percentage establishment method (0.36 m3s-1), followed of the Tennant method (0.59 m3s-1).The analysis of variance of one factor, significant differences were compared and verified between the ecological flow calculated of the indicated methods and the minimum low-water flow taken as a baseline for comparison. With the Tukey test, it was verified that the ecological flow estimated of the hydrological method of establishing percentages for the period (1943-1987) and (1988-2019), it did not present significant differences with respect to the minimum low-water flow. It concluded that the ecological flow of the “Jequeteque” river upstream of the “Gallito Ciego” dam is 0.36 m3s-1, it obtained through the percentage establishment method.

Analysing and evaluating environmental flows through hydrological methods in the regulated Indus River Basin

AbstractEnvironmental flows (EFs), essential for upholding the ecological integrity of rivers and aquatic habitats, have been disrupted significantly by diverting water for agricultural, industrial and domestic uses. This underscores the imperative of implementing sustainable water resource management to harmonize agricultural and environmental needs. The study was conducted in the Indus River Basin (IRB), a region extensively transformed by human interventions. EFs were determined through various techniques, including the flow duration curve shifting method, flow duration curve analysis, low‐flow indices, the Tennant method, the Smakhtin approach, the Tessmann method and the Pastor method. Analysing the estimated EFs alongside downstream flows unveiled specific timeframes (days, months and seasons) of unmet EF requirements. To safeguard the downstream ecosystems, the following EFs were estimated for the respective locations: 880 m3/s (38% of the mean annual flow [MAF]) for the Indus River at Tarbela Dam, 412 m3/s (48% of the MAF) for the Jhelum at Mangla Dam, 425 m3/s (44% of the MAF) for the Chenab at Marala headworks, 389 m3/s (56% of MAF) for the Ravi at Balloki headworks, 184 m3/s (50% of MAF) for the Sutlej at Sulemanki headworks and 231 m3/s (38% of MAF) below Kotri Barrage. The study revealed that violations of EFs occurred 41%, 43%, 44% and 52% of the time during the study period for the Chenab at Marala headworks, the Ravi at Balloki headworks, the Sutlej at Sulemanki headworks and the Indus River at the Kotri Barrage, respectively. The results highlighted that the Chenab, Ravi and Sutlej rivers are particularly susceptible to vulnerability, as the estimated EFs were not consistently upheld in these rivers. These findings underscore the urgent need to take appropriate measures to ensure EFs are not violated, thus safeguarding the downstream ecosystems.

Comparações entre Metodologias para Estimativa de Vazões Mínimas de Referência utilizadas em Concessão da Outorga

The State Water Resources Policy aims to ensure control, for current and future users, of water use and its use in satisfactory quantity, quality and regime. Current legislation provides, as one of the instruments for managing water resources, the granting of the right to use water to its holder for a pre-established period and in a personal and non-transferable manner. As only part of the minimum reference flows can be granted, there is a limitation on the use of water. In periods of lower water availability, it is necessary to analyze the influence of the seasonality of flows in the criteria for granting water use, creating alternatives for the management of water resources. In this context, the present work was carried out with the objective of evaluating and comparing the minimum reference flows and verifying the possibility of an increase in water availability for different users. Data from five fluviometric stations of the Alto Iguaçu and Ribeira watersheds, both located in the state of Paraná, were used, comparing values required by current legislation with those obtained by methodologies used mainly in the United States and Europe Method, Q_7,10Tennant Method, Wet Perimeter Method. The results obtained allowed us to state that the minimum reference flows can be adjusted since the methodologies applied to the same fluviometric stations result in different values for the minimum reference flows.

Impacts of ecological water supplement projects on fish habitat suitability in a high-leakage river in China

Ecological water supplement projects (EWSP) aimed at restoring damaged river ecosystems can change river hydrological processes, and loss of water through river leakage can potentially affect the spatiotemporal differences of river hydraulic factors, thus further affecting the habitat suitability of aquatic organisms. Therefore, assessing the impact of EWSP on habitats, considering leakage, is critical for high-leakage rivers recharging underlying and adjacent groundwater. In this study, a river habitat suitability simulation framework was established based on the surface water and groundwater coupling model and a fuzzy logic model. This framework was implemented to simulate the habitat suitability of a high-leakage reach of the Yongding River in China under different scenarios. The results showed that neglecting leakage would lead to overestimation of fish habitat suitability. The impacts of EWSP on the habitat were positive in spring; however, it was the opposite in autumn, which was affected by factors that led to spatiotemporal differences in leakage, such as topography and geology, water supplement season, and magnitude and duration of discharge. The optimal water supplement discharge of the Yongding River was 15–25 m3/s, which is consistent with the optimal discharge range recommended by the Tennant method. In the future, with the gradual decrease in leakage, habitat suitability will continue to improve, and the water quantity of EWSP required to maintain the same degree of weighted usable area will continue to decrease.

Impact of interbasin transfer hydroelectric project on downstream aquatic habitat

AbstractThe recent surge of anthropogenic activities like damming is causing a severe threat to the aquatic ecosystem. A scope of minimizing the degradation of biota exists by modifying the dam operation policy. This can be achieved by releasing a minimum environmental flow (EF), which further requires more scientific investigations. The present study investigated the impact of an interbasin transfer hydropower dam on the downstream habitat of an endangered fish species, Tor putitora, using an adaptive modelling framework. The framework consists of coupling a reservoir operation and a hydrodynamic model. This study analyses the scope of releasing different EFs from a hydropower dam to meet the environmental flow requirement (EFR) at downstream with satisfactory power production efficiency. The EFR was estimated using flow duration curve and Tennant's method. A lean period inflow hydrograph was incorporated into the model with a series of alternate EFs. Two scenarios were explored, with 4 and 6 h of peaking hours, along with the three cases of different initial reservoir storage. The total usable area over the river reach of the mentioned fish species was evaluated from the flow parameters simulated by the hydrodynamic component of the model. The power production efficiencies and area utilization rates were assessed in all these cases to prepare an easy‐to‐use decision support tool in a tabular form depicting the possible states of EF. The generalized methodology adopted in this analysis will help the decision‐makers quantify EF to be released from the dam within an acceptable power generation efficiency.

Environmental flow assessment for benthic macroinvertebrate communities using pseudo‐2D hydraulic habitat modelling at a green small hydropower plant

AbstractThe determination of minimum flow requirements for green small hydropower plants (GSHP) in China primarily relies on hydrological methods such as the Tennant method with no seasonal variation. However, the direct application of hydrological methods without local ecological data for calibration lacks ecological validity, potentially resulting in unsuitable minimum flow recommendations for local aquatic biota. Hydraulic‐habitat modelling (HHM) is assumed to provide more ecologically relevant and reliable environmental flow recommendations (EFRs), but benthic macroinvertebrates (BMs), crucial in the aquatic food web, have rarely been the focus in HHM studies. Moreover, the strong subjectivity in HHM processes hinders the comparison of EFRs across different biota and geographical regions. This study aims to investigate the ecological validity of using the Tennant method to set minimum flow requirements for local BM communities and the impacts of various methods used in HHM on derived EFRs. To achieve this, a pseudo‐2D HHM approach is employed, integrating the 1D hydraulic models HEC‐RAS and CASiMiR with the habitat model HABFUZZ. The EFRs downstream of Jiufeng reservoir, one of China's first GSHPs, are derived for wet (April–June) and dry seasons (July–September). Our findings highlight that setting minimum flow alone is inadequate for preserving BM community integrity downstream of GSHPs. It is crucial to incorporate more diverse environmental flow criteria, including minimum flows and peak flows, into GSHP assessment standards, with recommended flow levels varying across different seasons. Additionally, the development of a standardized HHM methodology is essential to mitigate the inherent subjectivity in HHM and facilitate the comparison of EFRs generated from different studies. This study's innovative modelling framework and findings will enhance the optimization of minimum flow assessment criteria for GSHP in China, deepen understanding of seasonal e‐flow requirements of BM communities, and refine the methodology used in BM HHM for e‐flow recommendation.

Ecological Base Flow Characteristics of Typical Rivers on the North Slope of Kunlun Mountains under Climate Change

Under climate change, river ecological base flow becomes particularly critical for the health and stability of inland river ecosystems in arid regions. Taking three typical seasonal inland rivers, including the Kriya River, the Niya River, and the Qarqan River, all on the northern slope of the Kunlun Mountains, as research objects, meteorological data from 1958 to 2019 and hydrological data from 1978 to 2014 were selected to analyze the characteristics of ecological base flow under climate change. The results show that in the past 60 years, the temperature in the Kriya River, Niya River, and Qarqan River basins has warmed at rates of 0.235 °C•(10a)−1, 0.223 °C•(10a)−1, and 0.177 °C•(10a)−1, respectively, while the precipitation has increased at the rates of 0.88 mm•(10a)−1, 3.90 mm•(10a)−1, and 7.92 mm•(10a)−1. The Tennant method was determined as the best algorithm for ecological base flow of inland rivers in arid regions. The interannual maximum values of ecological base flow all occurred in 2010, with three rivers increasing by 5.098 m3·s−1, 2.416 m3·s−1, and 11.343 m3·s−1 respectively, and the regional average increasing by 6.286 m3·s−1. The maximum ecological base flow within the year is in July, and the minimum value is in January, with a high proportion of the flood season. The monthly ecological base flow of rivers has a strong correlation with the monthly temperature and precipitation, with the strongest correlation in the Qarqan River basin and the correlation coefficients of 0.876 and 0.917. We propose ecological base flow guarantee objectives for the three rivers during the dry season, and clarify that the flood season is the key point of ecological base flow guarantee. The guarantee objectives are 0.974 m3·s−1, 0.154 m3·s−1, and 2.167 m3·s−1, for the three rivers, respectively. Our research results can provide scientific reference for the management and regulation of water resources and ecological protection of the northern slope of the Kunlun Mountains.

Minimum Instream Environmental Flow in Shatt Al-Hillah River

To maintain river flows necessary to meet social and ecological objectives, instream environmental flows are frequently used as a strategy. The capability of three alternative historical flow approaches to protect against low flows is shown in this study using gage stations in the Shatt Al-Hillah River in Iraq. The extension of the Shatt al-Hillah River is the focus of this research discussion on environmental flow assessment. The available data on discharge in this research were adopted for ten years from 2012-2021. Different flow methods were adopted to establish a minimum environmental flow in the Shatt Al-Hillah River. Three hydrological-based approaches: Tennant, modified Tennant, and low-flow metrics like 7Q10, were used to compare the results of the methods with the provision of a minimal environmental flow. The Tennant method relies on 30 % of the annual discharge rate as the minimum environmental instream flow. The modified Tennant method is based on 30% of the monthly average discharge rate as a minimum environmental instream flow. The 7Q10 method is based on the lowest daily discharge rate in 7 consecutive days for ten years. The results showed that the minimum instream environmental flow given by the Tennant method is 42.26 m3/s while the lowest value of the minimum instream environmental flow obtained from modified Tennant was 37.2 m3/s in January, and the largest value was 47.22 m3/s in August. The one obtained by the 7Q10 method was 50 m3/s in this research.

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.

Sensitivity of river ecological baseflow to climate change in arid areas

River ecological baseflow is key to river ecosystem health and stability and has become particularly important with global climate change aggravation. By considering the Niya River Basin in Xinjiang, based on meteorological data from 1958 to 2021 and hydrological data from 1978 to 2018, the Tennant method was determined to be the best basin ecological baseflow calculation method, the M–K test was used to analyze the abrupt ecological baseflow and climate change characteristics, and the ecological baseflow regression response and sensitivity coefficient models concerning climate change were established. The results showed that 75% of the ecological baseflow in the Niya River Basin ranged from 15 to 31 m3•s−1 in 1978–2018, the average annual temperature increased by 1.6°C at a 0.22°C•(10a)−1 rate, and the annual precipitation increased by 6.3 mm at a 0.98 mm•(10a)−1 rate. The prediction accuracy of the regression model was good, R2 exceeded 0.7, the ecological baseflow response to climate change lagged, and precipitation greatly impacted ecological baseflow. The basin sensitivity coefficient showed a decreasing trend from upstream to downstream, with the annual maximum value in 2010, the minimum value in 1984, the monthly maximum value in April and the monthly minimum value in November. Based on the climate change trend and the social water use of the basin, the ecological baseflow protection targets and measures were proposed according to the season and the hydrological period for actual water resource management and scheduling of the river in this and similar regions.

THE ENVIRONMENTAL FLOW METHOD FOR SUPPLEMENTING THE WATER NEEDED FOR THE MANAGEMENT OF SELANGOR RIVER, MALAYSIA

The shortage of water resources is one of the main problems in the world today, and water pollution and under-utilization of water resources are two factors contributing to this shortage. Appropriate supplement environmental flow can have a positive impact on dilution of pollutants, and consequently on fish habitats and the characteristics of the river channels. The purpose of this study is to determine the environmental water demand of the lower Selangor River, known as Sungai Selangor, through the Tennant Method, and then compare the data with the findings in available documents in order to ascertain the most economical and favorable supplement environmental flow method. The results of this study show that the months of November and December between the years 2009 and 2018 were the peak periods of discharge, with it being important for the discharge of these two months to meet 200% of the average annual flow needed to maintain fish habitats and channels in downstream Sungai Selangor. To meet the requirements of supplement environmental flow and improvement of water quality, it is recommended that the spillway working gate of the Sungai Kerling hydropower plant be modified so that the flow can be discharged downstream to supplement the environmental flow. Providing environmental flows for downstream would generate economic benefits and allow upstream and downstream regions to share resources.

A comprehensive ecological flow calculation for a small hydropower development river: A case study

AbstractSmall hydropower projects play a significant role in supplying clean energy and promoting economic development all around the world. The calculation of a river's ecological flow, that is, not only the quantity but also the quality of flowing water, in the watershed where small hydropower projects are located play an important role in scientifically guiding the discharge of small hydropower stations in the upper reaches of the river. By combining Gini coefficient with hydrological variation diagnosis, this study provided a novel approach to test the randomness of hydrological series and assess the evenness of runoff distribution. Furthermore, this study is the first attempt to calculate ecological flow for two separate periods (flood and low‐water periods), and thus is able to better reflect annual runoff variations. In the meantime, the Tennant method was improved by introducing of monthly runoff coefficient and median substitution, and integrating four other hydrological methods (empirical method, Qp method, annual distribution method and minimum monthly average measured runoff method) into the comprehensive calculation and analysis. The above methods were applied to the ecological base flow calculation for a small hydropower project in Dongjiang River basin of China. Through comprehensive and comparative analysis, better applicability was demonstrated by the improved Tennant method and the annual distribution method. The recommended values of ecological base flow for each month were derived at the range of 407–431 m3/s during the flood period and 179–239 m3/s during the low‐water period. This study demonstrated that the method could meet the ecological flow calculation requirements for river ecosystem and provide scientific basis for the delineation of ecological flow thresholds, and thereby ensure the healthy and sustainable development of small hydropower and the healthy river aquatic ecosystem.

A Practical Approach for Environmental Flow Calculation to Support Ecosystem Management in Wujiang River, China.

To promote ecosystem protection in the Wujiang River, this paper proposes a practical approach for calculating the environmental flow. The proposed approach combines the idea of the “guarantee rate” of the flow duration curve (FDC) method and the grading idea of the Tennant method. A daily flow series of the Wujiang River was compiled from 1956 to 2019 and used to compare the effect of the proposed approach versus the traditional approaches in four selected sections along the river. The results show that the environmental flow of the Wujiang River can be divided into five levels by the T-FDC method, with a level-by-level disparity, and all levels can capture the temporal and spatial variability of river flow. Additionally, the calculated basic environmental flow process ranges between the historical minimum and second minimum monthly average flow, and the threshold width of the optimal flow is more reasonable than the Tennant method. The T-FDC method can provide technical support for Wujiang River ecosystem management and sustainable development.

Comparative study on the calculation methods of ecological base flow in a mountainous river

As the social economy is further developed, there have been increasingly severe ecological and environmental issues. For instance, rivers located in mountainous areas are often encountered with the issue of zero flow. The ecological base flow was put forward to ensure the continuous flow of rivers, to realize the minimum ecological function, and to meet the most fundamental requirements of sustaining the river ecosystem. Wulong River Basin in Yantai City of China was taken as example here. Based on the runoff data collected in the Tuanwang Hydrological Station from 1960 to 2016, the measured runoff data was restored to natural runoff sequence by adopting the item-by-item investigation method. The different ecological base flows of Wulong River were calculated by adopting the Tennant Method, the Qp90 Method, the Texas Method, the Base Flow Ratio Method, the Tessman Method, and Wetted Perimeter Method. The research findings have shown that the Base Flow Ratio Method proves to be the optimal approach for calculating the ecological base flow of Wulong River. Based on the analysis of the assurance degree of ecological base flow, the period from April to June is the period with the lowest assurance degree of ecological base flow.