Range Of Variability Approach Method Research Articles

How does the daily regulation hydropower station reduce the hydrological regime impact? A case study in upper Yellow River

ABSTRACT Human activities, particularly the regulation of hydropower stations, have profoundly altered river flow patterns. While studies have extensively assessed the impact of large or multi-year regulated hydropower stations on hydrological regimes using indicators of hydrological alteration (IHA) and range of variability approach (RVA), the impact of daily regulation hydropower stations has received comparatively less attention. This study aims to evaluate the influence of daily regulation hydropower stations on hydrological regime changes, focusing on the upper Yellow River region in China. Using daily runoff data from 1954 to 2020 at the Guide station, the study compares the impacts of multi-year regulated (Longyangxia) and daily regulation (Laxiwa and Nina) hydropower stations. The Mann-Kendall test showed that 27 out of 32 Indicators of Hydrological Alteration (IHAs) had significant trends under Longyangxia operation, which reduced to 18 IHAs with the inclusion of daily regulation stations. The Range of Variability Approach (RVA) revealed that only 46.87% of IHAs exhibited high alteration from the natural regime when daily regulation was considered, down from 75.00% with Longyangxia alone. This suggests that daily regulation can mitigate the negative impacts of multi-year regulation, potentially enhancing the river's eco-hydrological health.

A novel Joint Probability Density Difference Approach for assessing the alteration of hydrologic regime

AbstractThe construction and operation of upstream reservoirs have significantly altered downstream hydrologic regime. Appropriate and quantifiable assessment method for the alteration of hydrologic regime is considerably vital and emergent for ecological protection and restoration. The Range of Variability Approach (RVA) and modified RVA methods have been widely used in practice to assess the hydrological alteration. However, these methods have failed to concurrently describe the distribution of indicator and morphological features in detail, which might inevitably lead to the misjudgment of alteration. This paper proposes a Joint Probability Density Difference Approach (JPDDA) method to address the major drawbacks of these previous methods with the introduction of Gaussian Kernel Density Estimation (KDE) and copula function. The annual average flow is selected as the reference variable to construct a proper joint probability density function between itself and other hydrological alteration indicators. The JPDDA method could describe the marginal distribution in detail through Gaussian KDE and also link the morphological features with copula function. Along with pervious methods, the hydrological alterations at Yichang hydrological station, Yangtze River are estimated based on the measured flow from 1949 to 2022. It is shown that the hydrologic regime has suffered from a moderate or even heavy alteration under the influence of massive upstream cascade reservoirs, and the JPDDA outperforms the other methods in terms of rationality and stability for practical assessments. Thus, the proposed JPDDA method is strongly advised to handle the hydrological alteration and could provide a reasonable reference for ecological operation.

Development of a decision framework for river health and water yield ecosystem service in watershed

Maintaining river health in a changing environment is an important way to improve the service value of the river basin ecosystem. An ecological flow threshold process with multiple ecological constraints was proposed using the Range of Variability Approach method and the Improved Intra-annual Spreading method. When combined with the multi-source dataset and the InVEST model, a 'ecology-function pattern-driven and decision' service framework was proposed. The study found that the important ecological constraints of the ecological flow in the Xiangjiang River basin changed after the hydrological change (1991–2019). High pulse occurrence times were delayed by 3 d, while low pulse occurrence times and durations were advanced by 8 d and delayed by 10 d, respectively. Temperature, precipitation, and evapotranspiration are all important factors influencing the dynamic characteristics of the basin's water yield services. Human activities and climate change have contributed nearly 19% more to the temporal and spatial differentiation characteristics of water yield in the basin than in the natural period. Additionally, it was discovered that excessive rainfall can inhibit the impact of other variables on water yield within the basin. Furthermore, the pivotal levels of significant meteorological factors that affect the water yield value of the basin were elucidated. This research leads to a better knowledge of watershed hydrological health in changing environments and a scientific basis for local water resource management decisions and optimal utilization of ecosystem service values.

Rainfall and Discharge Variability in the Senegal River Basin Based on the IHA/RVA

The hydrological regime of a river is a driving force of its ecosystem. The operation of dams and locks has significant impacts on the hydrological situation of rivers. The objective of this study was to study the change and variability of precipitation and hydrological data in the Senegal River basin and to assess the change in the discharge regime of the Senegal River caused by the operation of the Manantali hydroelectric dam. Based on the IHA (Indicators of Hydrologic Alteration), a range of variability of thirty-three hydrological parameters was calculated and the hydrological alteration associated with the functioning of the dam was quantified. Using the RVA (Range of Variability Approach) method, the hydrological alteration at the Bakel site was evaluated and showed the influence of the dam on the hydrological state. The results showed a strong influence of the dam on the hydrological regime. The fluvial eco-hydrological objectives calculated in this study can constitute certain support for the management of water resources and ecosystems of the Senegal River basin.

Study on water regime assessment and prediction of stream flow based on an improved RVA

Abstract Considering that many hydrological analysis methods compare and analyze the runoff before and after the construction of the reservoir, without restoring the measured data of the hydrological station, in this case, when the length of the measured data series is short, the evaluation results will be affected. In this article, based on the runoff reduction of stations affected by water conservancy projects, an improved range of variability approach (RVA) which can be applied to 1-year hydrological change analysis is proposed by coupling the hydrological variation index with the appropriate upper and lower limit theory of RVA. As Jialing river watershed is selected as the research area, the runoff depth of Beibei station is reduced, and then the improved RVA is employed to analyze the degree of change in river water regime. It is concluded that the change degree of overall hydrological index in Beibei station is high, and the prediction of variation of water regime of Beibei station can be made with the aid of simulating the operation of cascade reservoirs, with the inflow of Beibei station in flood season to reduce, and the inflow in dry season to increase. The example verifies the effectiveness of the improved RVA method, and the analysis results can provide a reference for the adjustment of the operation mode of upstream cascade reservoirs.

Evaluation of hydrological regime alteration and ecological effects in the middle and lower of the Yangtze River, China

Abstract The flow regime is regarded as the key driver of the structure and function of riverine ecosystems. This study uses an ecologically meaningful indicator (range of variability approach method) to assess the dynamic runoff process in the middle and lower reaches of the Yangtze River, whose changes negatively affect the ecosystems in the study area. In addition, the study quantitatively analyzed the contribution rate of human activities and climate change to flow change. The effects of ecological index changes on four famous major carp species (FFMC) resources in the middle and lower reaches of the Yangtze River were studied. The results show that after the Three Gorges Dam (TGD) operation, the hydrological changes of Yichang Station, Hankou Station, and Datong Station were 65, 58, and 46%, respectively. The weight of the impact of human activities on runoff is smaller the farther away from the TGD. The impact weights of human activities at the three hydrological stations in the middle and lower reaches of the Yangtze River are 73.69, 67.98, and 56.84%, respectively. The operation of the Three Gorges Project caused changes in the hydrological regime of the Yangtze River, which adversely affected the structure and quantity of FFMC populations.

Evaluation of ecohydrological regime and its driving forces in the Dongting Lake, China

Study regionThe Dongting Lake (DTL) wetland, China. Study focusAt present, there are few studies on ecohydrological assessments based on the collaborative study of flow and water level. The focus of this study is to use ecologically meaningful indicators (Environmental Flow Components method and Range of Variability Approach method) to evaluate the dynamic process of flow and water level components, whose changes have a negative impact on the DTL wetland ecosystem. In addition, we quantitatively expressed the ecological response process of flow and water level under changing environments, and proposed to use the underlying surface parameters to further clarify the impact of human activities and climate change (evaporation and rainfall) on runoff in different time periods. New hydrological insights for the regionAfter the construction of the Three Gorges Dam, the components of environmental flow in DTL were reduced and the overall change of the flow and water level of the DTL was 37% and 36%, respectively, The results of the wetland ecological response coincided with the trend of habitat fragmentation and miniaturization of fish individuals in DTL. The underlying surface parameters show that the weight of the impact of climate change on runoff is increasing, and the contribution rate of driving forces (human activities, evaporation, and rainfall) to runoff are 49.32%, 20.88%, and 29.80% respectively, and to water levels are 60.00%, 21.3%, and 18.7%, respectively.

Optimum ecological water level of water-carrying lake based on the relationship between water quality and water level

适宜的生态水位能够反映湖区生态系统的多种需求，是湖泊长期稳定健康运转的基本保障. 目前湖泊适宜生态水位的推求大多侧重恢复天然水位情势. 然而过水型湖泊承担着防洪、供水、航运等多种功能，频繁的人类活动导致湖泊水位情势异常复杂. 同时随着社会经济的快速发展，水质恶化对过水型湖泊生态系统造成了较大的负面影响，仅恢复天然水位情势难以反映过水型湖泊的生态需求. 因此，在IHA-RVA法的基础上，本文针对过水型湖泊吞吐性强的特点，利用水质-水位二元响应关系系统地提出了一套逐月修正过水型湖泊适宜生态水位阈值，并确定适宜水位变动率的方法. 以洪泽湖为应用实例，结果表明：1)根据湖泊水文情势和入湖污染物变化情况，湖泊调度周期可以划分为平水期(1—4月)、泄水期(5—6月)、蓄水前期(7—9月)和蓄水后期(10—12月)；2)各时期内，洪泽湖水位和水质呈现较强的相关性，其中平水期、泄水期和蓄水后期水质均随着水位上升而下降，平均Pearson系数达-0.77，仅在蓄水前期水质随水位上升而改善；3)现阶段洪泽湖的自净能力和污染物滞留比例竞争关系激烈，逐月适宜生态水位阈值为：12.92~12.99、12.79~12.99、12.84~12.99、12.86~12.99、12.71~12.89、12.39~12.63、11.97~12.93、12.50~13.07、12.65~13.26、12.90~13.04、12.90~13.04、12.90~13.04 m，除蓄水前期外，基于水位水质关系修正的适宜生态水位范围较IHA-RVA法计算的天然水位范围缩小了73.4 %. 总体而言，基于本文方法设计的湖泊适宜生态水位不仅可以满足生态系统对于水体大小的需求，一定程度上也可以体现湖泊生态系统对于水质的要求，为洪泽湖等过水型湖泊的生态调度、水资源管理提供科学依据.;The optimum ecological water level (OWL) guarantees stable and healthy operation of the lake in the long term by meeting various needs of the lake ecosystem. Previous studies on OWL mainly focused on restoring natural water level regime. However, water-carrying lakes have complicated water lever regimes resulted from flood control, water supply, shipping and other functions. Meanwhile, the water quality was further deteriorated due to rapid economic development. Consequently, the previous methods could not meet all the ecological needs of water-carrying lakes. Basing on IHA (indicators of hydrological alteration)-RVA (range of variability approach) method and relationship between water quality and water level, this paper proposed a method for identifying of the threshold of monthly OWL and determining the OWL variation of water-carrying lake. Taking Lake Hongze as an example, the results indicate that: 1) The lake regulation cycle can be divided into flat period (January-April), discharge period (May-June), early storage period (July-September) and late storage period (October-December) from the angle of hydrological regime and pollution into the lake. 2) There's a strong correlation between water quality and water level in each period as water quality improves with water level rising during the early storage period and deteriorates in other periods (Pearson coefficient was -0.77). 3) Due to the competition between the lake's self-purification capacity and pollutant retention ratio, the monthly OWL threshold from January to December is: 12.92-12.99, 12.79-12.99, 12.84-12.99, 12.86-12.99, 12.71-12.89, 12.39-12.63, 11.97-12.93, 12.50-13.07, 12.65-13.26, 12.90-13.04, 12.90-13.04, 12.90-13.04 m, respectively. The range of OWL modified by the relationship between water level and water quality is reduced by 73.4 % compared with the results of IHA-RVA method except in the early storage period. In general, the OWL designed by methods in this paper can reflect the requirements of lake ecosystem for water quantity and water quality to a certain extent, and provide scientific basis for the ecological regulation and water resource management of Lake Hongze and other water-carrying lakes.

РЕАКЦІЯ БАГАТОРУКАВНИХ РІЧКОВИХ СИСТЕМ НА ФУНКЦІОНУВАННЯ ГІДРОЕЛЕКТРОСТАНЦІЙ

The operation of the hydroelectric power plant is one of the main reasons for the transformation of river runoff. The change in the hydrological regime affects several other processes taking place in the river channel, including the transformation of its geomorphological features. The article presents the impact of the Kaniv and Włocławek dams on the hydrological regime of the middle Dnieper River and the lower Vistula River. The nature and magnitude of changes in the Dnieper and The Vistula rivers flow regime caused by the functioning of the dams were determined using IHA (Indicators of Hydrologic Alteration) and the RVA (The Range of Variability Approach) method. It was demonstrated that the operation of the hydroelectric power plant especially in the hydropeaking system is the cause of a large flow alteration in respect of the frequency and duration of low- and high-flow pulses and the rate and frequency of change in the flow. It was assessed how the change in flow conditions in connection with the deficit of sediments affected the transformation of the Vistula and Dnieper river channels downstream of the dams. Based on our results, the reaction of the fluvial system to changes in the flow regime caused by the operation of the Kaniv and Włocławek hydroelectric power plants consisted in: 1) changing the width and depth of channels; 2) changing the size of the forms separating channels; 3) fixation of the anastomosing fluvial system. More dynamic water flows due to the operation of hydroelectric power plants modify and dynamize the natural process of evolution of a fluvial system into an anastomosing system by causing the incision and narrowing of the main channels, because of which the side channels occupy a higher position above them. On the other hand, the equalization of the water flow in the channels causes a decrease in the water level and the disappearance of the flow in the side channels. As a result, the islands separated by these channels merge and inter-channel areas are formed.

A revised range of variability approach considering the morphological alteration of hydrological indicators

A reasonable assessment of the hydrological regime alteration is a prerequisite for river utilization, restoration, and protection. The hydrological alteration is quantified as changes in different indicators (IHAs) identified by Range of Variability Approach (RVA). However, RVA is unable to reveal the morphological characteristic which demonstrates the overall hydrological regime. This will lead to an incomplete assessment of the hydrological alteration. To supplement the current assessment, this work proposed a revised RVA method in three main steps: (1) to identify the morphological characteristics of each IHA; (2) to quantify the morphological alteration by comparing the Hasse matrices of different time series; (3) to combine the frequency alteration and morphological alteration of IHAs for reflecting overall hydrological alteration. A case study of the upper Yellow River shows that the revised RVA method outperforms RVA in the assessment of the hydrological regime not only because revised RVA captures the hydrological changes of certain IHAs that are not reflected by conventional RVA, but also the alteration identified by revised RVA shows more apparent differences at two stations upstream and downstream the dam than conventional RVA can provide. The revised RVA is more applicable to identify the hydrological alteration due to dam construction which could have negative impacts on river ecosystem since the morphological alteration of time series is considered. As a whole, the new method offers a better understanding of the alteration in hydrological regime, which gives beneficial guidance to river management.

Reappraisal of hydrologic alterations in the Roanoke River basin using extended data and improved RVA method

Hydrologic regime changes of the Roanoke River basin under three different scenarios defined based on different periods of post-impact datasets have been studied. For evaluating the degree of hydrologic alterations, the traditional and improved range of variability approach (RVA) which incorporate periodicity [as an index of periodicity (IP)], trend [as an index of trend (IT)], and symmetry [as an index of symmetry (IS)] of the parameters has been used. Comparative analysis of the results obtained with traditional and improved RVA and that obtained with the histogram matching approach (HMA) has also been performed. The overall degree of hydrologic alteration obtained through traditional RVA for Scenarios-I, II, and III was 0.39, 0.42, and 0.40, respectively. The improved RVA method, when applied to the 32 IHA parameters, indicates that many IHA parameters exhibit a higher IP or IT or IS value compared to the corresponding value of the degree of hydrologic alteration (DR), which underscore the inadequacy of the traditional RVA in assessing the degree of alteration in the flow regime of the Roanoke River. Through principal component analysis, the most ecologically relevant hydrologic indicators for understanding eco-hydrology of Roanoke River have been identified, which include Julian date of maximum flow, monthly flow for July and September, and 90-day maximum flow. Analysis of results further reveals that the combination of improved RVA and HMA can better reveal changes in IHAs and provide a better tool for designing strategies to enhance further the ecosystem services available from a managed river system.

Evaluating effects of dam operation on flow regimes and riverbed adaptation to those changes

The operation of dam and reservoirs is one of the main reasons for the transformation of river runoff. The change in the hydrological regime affects a number of other processes taking place in the river channel, including the transformation of its geomorphological features. The article presents the impact of the Włocławek Reservoir on the hydrological regime of the lower Vistula. The alterations of the river flow downstream of the dam in the conditions of the hydropeaking regime of hydroelectric plant operation and after its change to the run-of-river and interventional operation were characterised. It was assessed how the change in flow conditions in connection with the deficit of sediments affected the transformation of the Vistula river channel downstream of the dam. The nature and magnitude of changes in the Vistula river flow regime caused by the functioning of the “Włocławek” dam were determined using IHA (Indicators of Hydrologic Alteration) and the RVA (The Range of Variability Approach) method. It was demonstrated that the operation of the hydroelectric power plant in the hydropeaking system is the cause of a large flow alteration in respect of the frequency and duration of low- and high-flow pulses and the rate and frequency of change in the flow. The change in the manner of operation of the hydroelectric power plant affected the reduction in the degree of transformation of most features of the flow. The increase in water erosion force downstream of the dam led to the deepening and narrowing of the river channel. The presence of more resistant formations at the bottom of the river channel inhibited riverbed erosion, at the same time intensifying lateral erosion, which increased the width of the river channel. During the operation of the reservoir, the river channel downstream of the dam evolved towards the anabranching type system.

Assessment of environmental flows using hydrological methods for Krishna River, India

Krishna River is significantly affected due to Srisailam dam from past 30 years. The impact of this hydraulic structure drastically reduced the minimum flow regime on the downstream, which made the river nearing to decaying stage. In the present paper, Environmental Flow called minimum flow values released for the dam are estimated with the help of three hydrological methods viz., Range of variability Approach (RVA), Desktop Reserve Model (DRM), and Global Environmental Flow Calculator (GEFC). DRM method suggested considering the intermediate values obtained from among the three methods to preserve the ecosystem on the downstream of the river, which amounts to an average annual allocation of 9378 Million Cubic Meter (MCM) which is equal to 23.11% of mean annual flow (MAF).In this regard GEFC and RVA methods accounted for 22 % and 31.04% of MAF respectively. The results indicate that current reservoir operation policy is causing a severe hydrological alteration in the high flow season especially in the month of July. The study concluded that in the case of non-availability of environmental information, hydrological indicators can be used to provide the basic assessment of environmental flow requirements. It is inferred from the results obtained from the study, that the new reservoir operations can fulfil human water needs without disturbing Environmental Flow Requirements.

Quantitative Assessment of Flow Regime Alteration Using a Revised Range of Variability Methods

The Ecological Limits of Hydrologic Alteration (ELOHA) framework, which can be used to determine and implement environmental flows at regional scales, requires accurate flow regime alteration assessment. The widely used range of variability approach (RVA) evaluates flow regime alteration by comparing the distribution of 32 Indicators of Hydrologic Alteration (IHA). However, the traditional RVA method is not comprehensive, because it neglects both the human-induced inner characteristics of one hydrological year (ICOHY) and the positional information of 32 IHA, which are the main factors behind ecosystem alteration. To address these limitations, we propose a revised RVA method that uses the Tanimoto similarity (TS) coefficient to reflect the ICOHY and a first-order connectivity index to reflect the IHA positional information. The yearly Tanimoto alteration (TA) index is measured using the revised RVA method, and the individual alteration (IA) values of each of 32 IHA are calculated using the traditional RVA method. Then, a new index, the overall degree of flow regime alteration (OA), is derived from the TA and IA values. The effectiveness of the revised RVA method is tested in the upper reaches of the Yangtze River, and the results suggest that the revised RVA ameliorates the limitations of the traditional RVA, and therefore, is preferable for use in the ELOHA framework.

Optimal selection of the most ecologically relevant hydrologic indicators and its application for environmental flow calculation in Lake Dongting

水文改变指标（IHA）能够较为全面地描述水文状况，在评估水文情势改变及其生态系统影响方面具有广泛的应用.尽管该指标体系较为完善，但是数量众多的水文变量仍然存在信息冗余问题.根据洞庭湖城陵矶水文站1955-2014年的径流量数据，采用主成分分析（PCA）筛选了生态最相关水文指标（ERHIs），结合ERHIs改进了用于估算环境流量的变化范围法（RVA），并将其应用在洞庭湖出口的环境流量估算中.基于PCA选取了年最大90日流量、年最小3日流量、年最小流量出现时间、3月流量、6月流量、流量逆转次数和低流量年内平均历时7个变量作为洞庭湖出口的ERHIs.纵向和横向的对比分析都表明选取的ERHIs是合理的.ERHIs不仅有效缓解了IHA的冗余性问题，还有利于抓住最关键的生态水文变量.根据ERHIs改进的RVA方法在设定洞庭湖出口环境流量时，极大地简化原来的众多管理目标，对生态水文研究、水资源管理和生态保护都具有重要的参考价值和借鉴意义.;The method of indicators of hydrologic alteration (IHA) provides a relatively comprehensive way to describe the full range of hydrological regimes and is used globally to assess hydrological alteration and its ecosystem influence. This method is relatively sound, while it still has potential redundancy problems caused by a large number of variables in it. Therefore, the principal component analysis (PCA) was used to select the most ecologically relevant hydrologic indicators (ERHIs), based on the flow data at Chenglingji, a standard observation station of Lake Dongting, from 1955 to 2014. The method of range of variability approach (RVA) was improved by the selected ERHIs and was used to estimate environmental flow in the outlet of Lake Dongting. Based on the results of PCA, seven ERHIs were selected:annual maximum 90-day flow, annual minimum 3-day flow, Julian date of each annual 1-day minimum, March flow, June flow, number of hydrologic reversals and median duration of low pulses. It was proved that the seven selected ERHIs were reasonable with the comparison to previous studies and the redundancy analysis. ERHIs not only reduce the redundancy of IHA but also help to grasp the key component of eco-hydrological variables. Moreover, the improved RVA method greatly simplified the original management targets in estimating environmental flow in the outlet of Lake Dongting. This study is of great value and significance for eco-hydrological research, water resources management and ecological protection.

Impact of Cascaded Reservoirs Group on Flow Regime in the Middle and Lower Reaches of the Yangtze River

A large number of reservoirs have been built in the Yangtze River basin in the last few decades, the operation of which inevitably impacts on natural runoff. It is important to quantify the impacts of a cascade reservoir group operation on the hydrological regime in the downstream Yangtze River. The indicators of hydrologic alteration (IHA), range of variability approach (RVA), and Dundee hydrological regime assessment (DHRA) methods, which are based on five essential characteristics, i.e., magnitude, time, frequency, retardation, and rates of change, have been widely used to quantitatively analyze variation in the hydrological regime before and after the dam construction. The observed flow series at Yichang and Datong hydrological stations, located in the middle and lower reaches of the Yangtze River, respectively, are divided into pre- and post-dam construction periods by the Mann-Kendall (MK) rank correlation method. The results of the MK test reveal that the annual minimum discharge at Yichang Station has significantly changed since 2000. The analysis results of the IHA, RVA, and DHAR methods show that the hydrologic regime changed moderately after 1999 and is close to severe change after 2008 at Yichang station; and changed slightly after 1999 (the post-dam construction period) and moderately after 2008 at Datong station. A new typical year assessment method that can avoid the requirement for a long data series was proposed and compared with the RVA and DHAR methods. The results indicate that the hydrologic regime severely changed at Yichang station and moderately changed at Datong in 2014, which is consistent with the results of the above methods. This study further demonstrates that the changes are mainly reflected in the factors related to low flow such as mean discharge from January to March, minimum discharge, frequency and duration of low pulse, and so on. It is expected that further hydrological alterations will occur as the number of large cascade reservoirs constructed and operated in the Yangtze River basin increases.

Assessing the impact of Danjiangkou reservoir on ecohydrological conditions in Hanjiang river, China

Natural flow variability is the primary driver of riverine ecosystem function and structure. Alterations in hydrologic regimes modify habitat attributes and impair ecosystem connectivity. The indicators of hydrologic alteration and range of variability approach methods are used to investigate the hydrologic alterations due to Danjiangkou reservoir in the middle stream of Hanjiang river, China, over the past five decades. The results show that Danjiangkou reservoir has significantly changed the ecohydrological flow regime downstream of the dam, especially in the spawning time of the famous four major carps. To minimize the negative ecological impacts, it is necessary to optimize the current operation rules of Danjiangkou reservoir for river ecosystem health protection. We hope the results of the current study could support ecosystem management and restoration plans and provide key ecohydrological parameters for the Danjiangkou reservoir ecological operations in the Hanjiang river.

Environmental Flow Requirement and Comparative Study of the Turag River, Bangladesh

Environmental flow is necessary for securing ecological health status of a river. Around the Dhaka city of Bangladesh the Turag, an ecologically critical area, is an important river. Environmental flow assessment of the Turag can help to sustain ecosystem and navigation in it. The aims of the research are to estimate environmental flow of the Turag and to assess current flow condition. Mean daily discharge data recorded by Bangladesh Water Development Board had been collected and analyzed for two periods (1989-2004) and (2005-2009). Mean Annual Flow (MAF), Flow Duration Curve (FDC) and Range of Variability Approach (RVA) methods were used and IHA software had been exercised in calculating environmental flow. According to RVA, FDC and MAF methods estimated environmental flow was found to be 192.72 cms, 206.5 cms and 180.77 cms respectively with the mean of 192.72 cms. It is observed that, in more recent time, the environmental flow is not maintained during the low flow season in the river and overall flow rate is reduced. Mean, maximum and minimum annual flows are reduced about 35%, 42% and 9% respectively from the period (1989-2004) to (2005-2009). Considering environmental flows estimated by RVA and MAF methods, about 40% and 36% of total flow of the period 2005- 2009 flowed below the required environmental flow. In FDC method about 35% flow is flowed below the required environmental flow during the low flow season in the same period. These findings may help the policy makers to manage water resources in the catchment area of the Turag.

Sezonska pojavnost velikih voda na slivu Dunava u Hrvatskoj

The analysis of seasonal occurrence of maximum annual flows, conducted at 95 gauging stations within the Danube river basin, is presented. Burn’s vector method, and RVA Range of Variability Approach method based on elementary statistical analysis of maximum annual flow dates, are used. The analysis shows that the lowest seasonal variability of maximum flows occurs in Gorski Kotar drainage basins, and that this maximum statistically occurs near the end of the year. The seasonal variability of maximum annual flows is much higher for other gauging stations included in the analysis

Hydrologic alteration along the Middle and Upper East River (Dongjiang) basin, South China: a visually enhanced mining on the results of RVA method

This paper presents a visually enhanced evaluation of the spatio-temporal patterns of the dam-induced hydrologic alteration in the middle and upper East River, south China over 1952-2002, using the range of variability approach (RVA) and visualization package XmdvTool. The impacts of climate variability on hydrological processes have been removed for wet and dry periods, respectively, so that we focus on the impacts of human activities (i.e., dam construction). The results indicate that: (1) along the East River, dams have greatly altered the natural flow regime, range condition and spatial variability; (2) six most remarkable indicators of hydrologic alteration induced by dam-construction are rise rate (1.16), 3-day maximum (0.91), low pulse duration (0.88), January (0.80), July (0.80) and February (0.79) mean flow of the East River during 1952-2002; and (3) spatiotemporal hydrologic alterations are different among three stations along Easter River. Under the influence of dam construction in the upstream, the degree of hydrologic changes from Lingxia, Heyuan to Longchuan station increases. This study reveals that visualization techniques for high-dimensional hydrological datasets together with RVA are beneficial for detecting spatio-temporal hydrologic changes.