Environmental Flow Assessment Based on Different Metrics of Hydrological Alteration

The concepts of hydrological alteration and the related natural flow paradigm conceive variable environmental flows that preserve as much as possible the natural variability of flows, with a particular focus on a suite of specific characteristics, the so-called indicators of hydrological alteration (IHA). In the paper we propose a simple simulation approach for a preliminary desk-top assessment environmental flows, whose principle is to maximize the possible utilization of water while complying with the alteration targets according to a global alteration metric. We investigate the use of three different alteration metrics, with the aim of measuring the sensitivity of environmental flow assessments respect to the index and the corresponding low and moderate alteration target thresholds.An application of the methodology to a case study area in Sicily, comprising several rivers sections, is carried out. Results show that a significant sensitivity of the optimal environmental flows to the alteration metric, both in the pattern and in the amount. While some metrics privilege environmental flow patterns that follow the natural variability of IHA parameters, other yield to optimal environmental flows that follow the long-term means of the IHA parameters. Results also show that in general the attainment of the low alteration target is quite demanding, since at least the 30 % of natural flows should be addressed to environmental flows, while for a moderate alteration hydrological status this percentage reduces to 15 %.     

Determining the effects of dams on subdaily variation in river flows at a whole‐basin scale

River regulation can alter the frequency and magnitude of subdaily flow variations causing major impacts on ecological structure and function. We developed an approach to quantify subdaily flow variation for multiple sites across a large watershed to assess the potential impacts of different dam operations (flood control, run‐of‐river hydropower and peaking hydropower) on natural communities. We used hourly flow data over a 9‐year period from 30 stream gages throughout the Connecticut River basin to calculate four metrics of subdaily flow variation and to compare sites downstream of dams with unregulated sites. Our objectives were to (1) determine the temporal scale of data needed to characterize subdaily variability; (2) compare the frequency of days with high subdaily flow variation downstream of dams and unregulated sites; (3) analyse the magnitude of subdaily variation at all sites and (4) identify individual sites that had subdaily variation significantly higher than unregulated locations. We found that estimates of flow variability based on daily mean flow data were not sufficient to characterize subdaily flow patterns. Alteration of subdaily flows was evident in the number of days natural ranges of variability were exceeded, rather than in the magnitude of subdaily variation, suggesting that all rivers may exhibit highly variable subdaily flows, but altered rivers exhibit this variability more frequently. Peaking hydropower facilities had the most highly altered subdaily flows; however, we observed significantly altered ranges of subdaily variability downstream of some flood‐control and run‐of‐river hydropower dams. Our analysis can be used to identify situations where dam operating procedures could be modified to reduce the level of hydrologic alteration. Copyright © 2009 John Wiley & Sons, Ltd.     

Assessment of hydrologic alterations caused by Chi‐Chi diversion weir in Chou‐Shui Creek,Taiwan: opportunities for restoring natural flow conditions

The Range of Variability Approach (RVA) is used to investigate the hydrologic impacts of a diversion weir on Chou‐Shui Creek, Taiwan. Thirty‐two hydrologic parameters, called Indicators of Hydrologic Alteration (IHA), are used to evaluate the flow conditions before and after weir construction. One standard deviation from the mean for each of the pre‐construction hydrologic parameters is set as the management target range. Under the prevailing diversion rules, large hydrologic alterations are observed, especially for low flows. The means of 19 hydrologic parameters presently fall outside of the targets and the average non‐attainment rate for the 32 indicators is 73.2%. Increasing the instream flow release or reducing diversions could mitigate the hydrologic impacts of weir construction. Increasing the instream flow to 40 m³/s and reducing monthly water demands by variable percentages significantly improves the altered flow conditions. Under the proposed water release and diversion scheme, 29 hydrologic parameters will fall within the management targets and the average non‐attainment rate will be reduced to 35.6%, much closer to the pre‐construction value of 25.3%. Restoring the natural flow variability is expected to promote the natural stream biota. Copyright © 2004 John Wiley & Sons, Ltd.     

Impact of Human Intervention and Climate Change on Natural Flow Regime

According to the ‘natural flow paradigm’, any departure from the natural flow condition will alter the river ecosystem. River flow regimes have been modified by anthropogenic interventions and climate change is further expected to affect the biotic interactions and the distribution of stream biota by altering streamflow. This study aims to evaluate the hydrologic alteration caused by dam construction and climatic changes in a mesoscale river basin, which is prone to both droughts and monsoonal floods. To analyse the natural flow regime, 15 years of observed streamflow (1950–1965) prior to dam construction is used. Future flow regime is simulated by a calibrated hydrological model Soil and Water Assessment Tool (SWAT), using ensemble of four high resolution (~25 km) Regional Climate Model (RCM) simulations for the near future (2021–2050) based on the SRES A1B scenario. Finally, to quantify the hydrological alterations of different flow characteristics, the Indicators of Hydrological Alteration (IHA) program based on the Range of Variability Approach (RVA) is used. This approach enables the assessment of ecologically sensitive streamflow parameters for the pre- and post-impact periods in the regions where availability of long-term ecological data is a limiting factor. Results indicate that flow variability has been significantly reduced due to dam construction with high flows being absorbed and pre-monsoon low flows being enhanced by the reservoir. Climate change alone may reduce high peak flows while a combination of dam and climate change may significantly reduce variability by affecting both high and low flows, thereby further disrupting the functioning of riverine ecosystems. We find that, in the Kangsabati River basin, influence of dam is greater than that of the climate change, thereby emphasizing the significance of direct human intervention.     

A dynamic corridor‐searching algorithm to seek time‐varying instream flow releases for optimal weir operation: comparing three indices of overall hydrologic alteration

A full range of natural flow regime has been widely recognized as a primary driving force for sustaining the integrity of a riverine ecosystem. Existing instream flow methods strive to assure a constant minimum flow but not the natural flow variability. We present in this paper a dynamic corridor‐searching algorithm to seek the optimal time‐varying scheme for instream flow releases. A compromise programming (CP) is employed to search the optimal solution of an objective function aggregating the ecosystem and human needs objectives. The ecosystem need objective is represented by an overall index of hydrologic alteration, which integrates 32 indicators of hydrologic alteration (IHA) derived from the range of variability approach (RVA). The human need objectives are expressed by shortage ratios for the agricultural and municipal water supplies. The proposed method is applied to a weir operation in Taiwan. Three approaches to evaluating the overall degree of hydrologic alteration (i.e., the three‐class, fuzzy‐based, and overall‐mean approaches) are compared here. The results show that the time‐varying schemes improve the human need objective, but only slightly deteriorate the ecosystem need objective. Such advantages increase with the time‐varying frequency. For the wet periods, smaller flow releases may be prescribed; for the dry periods, however, greater releases must be specified to secure a lower degree of overall hydrologic alteration. It is also revealed that use of the three‐class approach to evaluate the overall hydrologic alteration facilitates to eliminate highly altered IHA and maintain those low‐flow characteristics subtle to flow diversions. However, such outcomes are achieved at the cost of greater deficits for human water demands. Copyright © 2007 John Wiley & Sons, Ltd.     

A functional flows approach to selecting ecologically relevant flow metrics for environmental flow applications

The science and practice of environmental flows have advanced significantly over the last several decades. Most environmental flow approaches require quantifying the relationships between hydrologic change and biologic response, but this can be challenging to determine and implement due to high data requirements, limited transferability, and the abundance of hydrologic metrics available for evaluation. We suggest that a functional flows approach, focusing on elements of the natural flow regime known to sustain important ecosystem processes, offers a pathway for linking understanding of ecosystem processes with discrete, quantifiable measures of the flow regime for a broad range of native taxa and assemblages. Functional flow components can be identified as distinct aspects of the annual hydrograph that support key biophysical processes, such as wet season flood flows or spring recession flows, and then quantified by flow metrics, such as 5% exceedance flow or daily percent decrease in flow, respectively. By selecting a discrete set of flow metrics that measure key functional flow components, the spatial and temporal complexity of flow regimes can be managed in a holistic manner supportive of multiple ecological processes and native aquatic species requirements. We provide an overview of the functional flows approach to selecting a defined set of flow metrics and illustrate its application in two seasonally variable stream systems. We further discuss how a functional flows approach can be utilized as a conceptual model both within and outside of existing environmental flow frameworks to guide consideration of ecological processes when designing prescribed flow regimes.     

Regionalization of natural flow regime: application to environmental flow optimization at ungauged sites

In this work we use the regionalization approach (RA) to derive the natural flow regime at an ungauged site. The derived natural flow regime, expressed by the regional cdf models of 32 indicators of hydrologic alteration (IHA) is used in the histogram matching approach (HMA) to seek the optimal environmental flows for a proposed multiobjective diversion weir in Taiwan. The results reveal that the outcomes associated with the planning constant scheme are significantly improved by the optimal time‐varying scheme. The histogram dissimilarities of 32 IHA associated with the planning scheme are consistently greater than those associated with the optimal scheme, especially for low‐flow IHA. Despite the inherent discrepancy between different approaches to generating flow data at the ungauged site, the optimal outcomes resulting from the RA‐based natural flow regime appear to be plausible and consistent with those reported in the previous work, thus validating the RA used in this work. We also explore the effect of weighting factors on the optimal outcomes. The results reveal that the weighting factor of the ecosystem needs objective dominates all optimal outcomes, while those of the agricultural demands and interbasin transfers objectives have minor effects on the optimal outcomes. The global optimal solution is obtained with a full or null weighting assigned to the ecosystem needs objective, while the least optimal solution is obtained as the interbasin transfers objective is given a null weighting and the agricultural demands objective is weighted more than the ecosystem needs objective. River managers and decision makers may select more balanced weir operation strategies based on the results presented in this work. Copyright © 2008 John Wiley & Sons, Ltd.     

一种新的水文情势改变度综合估算法

基于 33 个水文改变指标,分别采用变化范围法、直方图匹配法、直方图比较法和修正变化范围法 4 种方法, 计算汉江中下游黄家港水文站的水文变异性,并对比分析各方法的优缺点。变化范围法忽略了水文指标在极值 和目标范围的具体变化;直方图匹配法和比较法考虑了水文指标在各范围的分布;修正变化范围法涵盖了形态变 化的概念。通过主客观组合赋权,融合直方图比较法和修正变化范围法的结果,提出一种新的综合估算法,既保 留水文情势的分布、频率和时空变化信息,又避免数据冗余。综合估算法结果表明：各月月均流量和极端流量大 小的改变度均为中度改变,分别为 41.28% 和 64.83%;流量增减变化率的改变度为高度改变（80.53%）;汉江中下游 水文情势的整体改变度为中度改变（55.70%）。该法可降低计算结果的不确定性,避免水文变异性结果出现异常, 从而更加合理可靠。     

滦河流域大中型闸坝水文生态效应

为揭示滦河流域水库对下游河流水文影响,辨析其生态效应,建立了流域闸坝水生态效应评估体系,运用河流影响因子(RI)法评估了闪电河、庙宫、潘家口和桃林口水库的水生态效应,进一步运用水文变化范围(RVA)法评估了潘家口水库的水生态效应。结果表明:1各水库对水文的影响程度为:潘家口桃林口闪电河庙宫,水库的水文效应同时受其级别(库容)和河流原始径流量影响,小型河流水库的水文生态效应不容忽视。2潘家口水库IHA指标(RVA法)总改变度为0.88,第1~2组指标发生了高度改变(0.91),第3~5组指标发生中度改变(0.45),强烈改变了鱼类洄游、底栖生物和植物群落等生态过程。生态水文同步监测与生态模型构建将有助于提升河流生态系统预警能力,为河流生态恢复提供科学依据和技术工具。     

CLASSIFICATION OF FLOW REGIMES FOR ENVIRONMENTAL FLOW ASSESSMENT IN REGULATED RIVERS: THE HUAI RIVER BASIN,CHINA

Flow regime characteristics (magnitude, frequency, duration, seasonal timing and rates of change) play a primary role in regulating the biodiversity and ecological processes in rivers. River classification provides the foundation for comparing the hydrologic regimes of rivers and development of hydro‐ecological relationships to inform environmental flow management and river restoration. This paper presents a classification of natural flow regimes and hydrologic changes due to dams and floodgates in the Huai River Basin, China, in preparation for an environmental flow assessment. The monthly natural flow regime of 45 stations in the upper and middle Huai River Basin were simulated for the period 1963–2000, based on the hydrological model SWAT (Soil and Water Assessment Tool). Six classes of flow patterns (low or high discharge, stable or variable, perennial or intermittent, predictable or unpredictable) were identified based on 80 hydrologic metrics, analysed by hierarchical clustering algorithms. The ecologically relevant climatic and geographic characteristics of these flow classes were tested for concordance with, and to strengthen, the hydro‐ecological classification. The regulation of natural flow patterns by dams and floodgates changed flows at some locations within each flow class and caused some gauges to shift into another class. The research reported here is expected to provide a foundation for development of hydro‐ecological relationships and environmental flow methods for wider use in China, as well as setting a new scientific direction for integrated river basin management in the Huai River Basin. Copyright © 2011 John Wiley & Sons, Ltd.     

EVALUATING TRADEOFFS BETWEEN ENVIRONMENTAL FLOW PROTECTIONS AND AGRICULTURAL WATER SECURITY

River basin managers responsible for water allocation decisions are increasingly required to evaluate tradeoffs between environmental flow protections and human water security. However, the basin‐scale effects of environmental flow regulations on water users are not well understood, in part because analyses are complicated by the spatial and temporal variation in water availability, human demands, and ecosystem needs. Here, we examine alternative regional environmental flow policies and their effects on a distributed network of water users in a small (182 km²) river basin in coastal California. We use a hydrologic model to simulate water diversion operations under three policy scenarios and quantify potential impacts to bypass flows for adult migrating salmon and agricultural water storage. The results indicate that there are inherent tradeoffs between environmental flows and agricultural water security, with the most restrictive environmental policy associated with the greatest impacts to water users. Surprisingly, the moderate environmental flow policy had larger impacts to bypass flows than the unregulated management scenario, suggesting that ecological benefits of the moderate policy are small relative to the adverse effects on agricultural water users. Conflicts between environmental and human water needs were greatest in upper catchments (<2.5 km²), where flow protections caused the greatest reduction in water storage. Although natural supplies were adequate for meeting water needs in most years regardless of policy restrictions, potential for conflict between environmental flow protections and water security was evident in dry years. Therefore, strategies are particularly needed for drought‐year water management to ensure adequate environmental flows while reducing human water allocations in an equitable manner. Copyright © 2013 John Wiley & Sons, Ltd.     

Predicting the natural flow regime: models for assessing hydrological alteration in streams

Understanding the extent to which natural streamflow characteristics have been altered is an important consideration for ecological assessments of streams. Assessing hydrologic condition requires that we quantify the attributes of the flow regime that would be expected in the absence of anthropogenic modifications. The objective of this study was to evaluate whether selected streamflow characteristics could be predicted at regional and national scales using geospatial data. Long‐term, gaged river basins distributed throughout the contiguous US that had streamflow characteristics representing least disturbed or near pristine conditions were identified. Thirteen metrics of the magnitude, frequency, duration, timing and rate of change of streamflow were calculated using a 20–50 year period of record for each site. We used random forests (RF), a robust statistical modelling approach, to develop models that predicted the value for each streamflow metric using natural watershed characteristics. We compared the performance (i.e. bias and precision) of national‐ and regional‐scale predictive models to that of models based on landscape classifications, including major river basins, ecoregions and hydrologic landscape regions (HLR). For all hydrologic metrics, landscape stratification models produced estimates that were less biased and more precise than a null model that accounted for no natural variability. Predictive models at the national and regional scale performed equally well, and substantially improved predictions of all hydrologic metrics relative to landscape stratification models. Prediction error rates ranged from 15 to 40%, but were ≤25% for most metrics. We selected three gaged, non‐reference sites to illustrate how predictive models could be used to assess hydrologic condition. These examples show how the models accurately estimate pre‐disturbance conditions and are sensitive to changes in streamflow variability associated with long‐term land‐use change. We also demonstrate how the models can be applied to predict expected natural flow characteristics at ungaged sites. Copyright © 2009 John Wiley & Sons, Ltd.     

A spatial assessment of hydrologic alteration within a river network

Maintaining natural hydrologic variability is essential in conserving native riverine biota and river ecosystem integrity. Hydrologic variation plays a major role in structuring the biotic diversity within river ecosystems as it controls key habitat conditions within the river channel, the floodplain, and hyporheic (stream-influenced ground water) zones. Alterations in streamflow regimes may modify many of these habitat attributes and impair ecosystem connectivity. We demonstrate use of the ‘Range of Variability Approach’ for assessing hydrologic alteration at available streamgauge sites throughout a river basin. We then illustrate a technique for spatially mapping the degree of hydrologic alteration for river reaches at and between streamgauge sites. Such maps can be used to assess the loss of natural hydrologic variation at a river basin scale, thereby facilitating river restoration planning. © 1998 John Wiley & Sons, Ltd.     

Do Environmental Stream Classifications Support Flow Assessments in Mediterranean Basins?

Natural flow regimes are of primary interest in designing environmental flows and therefore essential for water management and planning. The present study discriminated natural hydrologic variation using two different environmental classifications (REC-Segura and WFD-ecotypes) and tested their agreement with an a posteriori (hydrologic) classification in a Spanish Mediterranean basin (the Segura River, SE Spain). The REC-Segura was developed as a two-level hierarchical classification based on environmental variables that influence hydrology (climate and source-of-flow). The WFD-ecotypes were developed by the Spanish Ministry for the Environment to implement the Water Framework Directive (WFD) using hierarchical hydrologic, morphologic and physicochemical variables. The climate level in the REC-Segura broadly described the hydrologic pattern observed along the NW-SE aridity gradient of the basin. However, source-of-flow (defined by karstic geology) was only able to discriminate variation in flow regimes within one climatic category. The WFD-ecotypes, despite incorporating hydrologic variables, did not fully discriminate hydrologic variation in the basin. Ecotypes in tributary streams located in dry or semiarid climates embrace different flow regimes (both perennial and intermittent). There was little agreement between environmental and hydrologic classifications. Therefore, the authors advise against the use of environmental classifications for the assessment of environmental flows without first testing their ability to discriminate hydrologic patterns.     

Building Hydrologic Foundations for Applications of ELOHA: How Long A Record Should You Have?

The Ecological Limits of Hydrologic Alteration framework for making regional assessments of environmental flows requires a ‘hydrologic foundation’ of flow data for current and undeveloped conditions. This raises the question how long a record is needed for an adequate hydrologic foundation? The answer depends on the variance in the flow record and on how much uncertainty is tolerable in metrics developed from the flow data. Copyright © 2017 John Wiley & Sons, Ltd.     

黄河水量统一调度与调水调沙对河口的生态水文影响

从具有生态学意义的流量、频率、出现时间、持续时间和变化率等5种水文要素出发，采用水文变化指标体系定量评估了黄河水量统一调度与调水调沙对河口段生态水文情势的影响，讨论了河口环境水流需求以及调水调沙后水文情势对环境水流的满足程度。研究结果表明，与水量统一调度前相比，水量统一调度与调水调沙后利津断面水文情势有所改善，年极小值流量明显增加，但是水文过程变化率降低，洪水漫滩过程消失，水文过程趋于平缓。目前河口段水文情势能够满足枯水期适宜生态流量需求，汛前4—5月关键期无法满足适宜生态流量与流量脉冲过程，汛期除缺乏洪水脉冲过程外，基本能够满足高流量输沙需求。     

Sensitivity of the Red River Basin Flood Protection System to Climate Variability and Change

An original modeling framework for assessment of climate variation and change impacts on the performance of complex flood protection system has been implemented in the evaluation of the impact of climate variability and change on the reliability, vulnerability and resiliency of the Red River Basin flood protection system (Manitoba, Canada). The modeling framework allows for an evaluation of different climate change scenarios generated by the global climate models. Temperature and precipitation are used as the main factors affecting flood flow generation. System dynamics modeling approach proved to be of great value in the development of system performance assessment model. The most important impact of climate variability and change on hydrologic processes is reflected in the change of flood patterns: flood starting time, peak value and timing. The results show increase in the annual precipitation and the annual streamflow volume in the Red River basin under the future climate change scenarios. Most of the floods generated using three different climate models had an earlier starting time and peak time. The assessment of the performance of Red River flood protection system is based on the flood flows, the capacity of flood control structures and failure flow levels at different locations in the basin. In the Assiniboine River Basin, higher reliabilities at downstream locations are obtained indicating that Shellmouth reservoir plays an important role in reducing downstream flooding. However, a different trend was identified in the Red River Basin. The study results show that flood protection capacity of the Red River infrastructure is sufficient under low reliability criteria but may not be sufficient under high reliability criteria.     

Assessment of Environmental Flow Requirements by Entropy-Based Multi-Criteria Decision

Environmental flow methodologies based on hydrological indices have increasingly evolved, because they play an important role in a riverine ecosystem management. Moreover, human activities, such as dams, in many basins have altered their natural hydrologic processes and they also change habitat for aquatic and riparian species. Decision making by echo-managers considering these multi-variables has been subjective. Therefore, to provide eco-managers with guidelines, an eco-index with entropy related to the probability density function (pdf) and Ordered Weighted Averaging (OWA) operator is been suggested in this study. The index was applied to Geum River in South Korea with 33 Indicators of Hydrologic Alteration (IHA) by Richter et al. (1998) through IHA software (TNC 2009). The objective of this paper is to outline an entropy-based hydrologic alteration assessment of biologically relevant flow regimes using gauged flow data. On the Geum River, dams have affected river flow measured at four stations and the eco-index suggests that more attention needs to be paid to the tributaries between Gongju and Gyuam stations. Echo-Index with maximum entropy and OWA operator reflects the effect of every parameter and helps with determination considering multi variables. In future more temporal and spatial information needs to be examined for ecosystem alteration.     

The influence of environmental conditions and hydrologic connectivity on cyanobacteria assemblages in two drowned river mouth lakes

We evaluated the temporal and spatial variability of cyanotoxins, water chemistry, and cyanobacteria communities in two lakes of different trophic status. Bear Lake is a hypereutrophic system that flows into mesotrophic Muskegon Lake. Total microcystins (MC) in Bear Lake (mean, 1.66 μg/L) were composed of multiple structural analogs: 43% MC-LR, 50% MC-RR, and 7% MC-YR. Total microcystins in Muskegon Lake (mean, 0.52 μg/L) consisted of MC-LR (76%), MC-RR (14%), MC-YR (6%), and MC-LA (3%). The lakes were dominated by the cyanobacteria Microcystis spp., which accounted for 75% of phytoplankton biovolume in Bear Lake and > 90% in Muskegon Lake. Total microcystin concentration was positively correlated with cyanobacteria biovolume and turbidity (Muskegon Lake) and total phosphorus (Bear Lake), while negatively correlated with ammonia (Bear Lake) and nitrate (both lakes). The relationships between microcystins and environmental factors differed between lakes, despite hydrologic connectivity, suggesting that local conditions have a greater influence on toxin production than regional effects. Cylindrospermopsis raciborskii was found in both systems; however, the assemblage does not appear to be capable of producing cylindrospermopsin due to the absence of the PKS gene. Although the Bear Lake discharge appears to be the source of C. raciborskii, the physical/chemical properties of Muskegon Lake (lower turbidity and temperature, higher nitrate) may constrain the growth of this invasive species. Thus, local conditions in each lake are important in determining which species are capable of maintaining a viable population.     

Desirable Low Flow Releases below Dams: Fish Habitats and Reservoir Costs

ABSTRACT

Streamflowpattern and catcbment characteristics are examined in Guyana, a tropical country located on the northeastern part of South America. Only streamflow data of ten major rivers are considered, because long-term records are not available for all the rivers. The catchments are grouped into three hydrologic environments based on rainfall and vegetation. A number of characteristics such as annual variability of flows, seasonal variability of flows, flow duration curves, flood flows and low flows were compared. The study showed that these were variations in hydrologic characteristics between the three environments. It also indicated that apart from rainfall several other factors, particularly geology play key roles in influencing the hydrologic characteristics. In order to study this phenomenon and other hydrologic characteristic particularly floodflow a rigorous data analysis is required. The need for additional hydrologic data for a detailed analysis of streamflow characteristics in a tropical country such as Guyana is emphasised throughout the study.