The basic flow method for incorporating flow variability in environmental flows

The Basic Flow is a methodology used to calculate environmental flow needs for river regulation. It has gained increased recognition in Spain for hydrological planning. It is based on the study of irregularities in hydrological series of daily mean flows using the simple moving average model as a tool to extract the relevant information. The Basic Flow Methodology (BFM), beyond providing a unique minimum flow value, constitutes a complex management proposal for regulated rivers which includes other management aspects affecting the biological functioning of a river (such as the necessity of flow variability, bankfull flows or varying flow rates) through the establishment of monthly instream flow requirements. This paper presents a practical application of the BFM in the Silvan stream, a natural mountain stream impacted by a hydroelectric regulation project. Results are discussed in terms of physical habitat created and compared to those obtained from the application of another method based on the Instream Flow Incremental Methodology, using a set of computer programs (RHYHABSIM) for physical habitat simulation. Copyright © 2010 John Wiley & Sons, Ltd.     

Reservoir system management and environmental flows

Considerable attention has been paid to the downstream effects of reservoirs on the ecology of rivers, streams and wetlands. However, most reservoirs were constructed well before ecological concerns became prominent. Little attention has been given to the question of what extent existing structures and management systems can accommodate changes. The paper discusses this matter and a range of associated issues. It is concluded that many problems can be rectified by structural means but that such rectification will be very expensive. While based primarily on Australian systems, the conclusions and examination are considered to be globally applicable.     

A hydrogeomorphic dynamics approach to assess in‐stream ecological functionality using the functional flows model,part 1—model characteristics

The functional flows model integrates hydrogeomorphic processes and ecological functions for stream physical habitat evaluations. Functional flows are discharge values that serve ecological uses. Assessments of functional flows are based on evaluation of shear stress dynamics. The analysis is based on the occurrence of sediment transport regimes defined by threshold values of Shields stress estimated from discharge (Q), a parameter (f) governing depth response to incremental discharge changes, water surface slope (S) and media grain size (D₅₀). As an example, the model was tuned for fall‐run Chinook salmon spawning. Ecological functions studied were bed occupation (spawning, incubation and emergence) and bed preparation (river bed reworking periods)—both reliant on shear stress dynamics. A numerical experiment and sensitivity analysis using a wide range of realistic values of input variables indicated the effect of each variable on flow functionality. Combinations of S = 0.001, 0.005 and 0.01, D₅₀ = 0.02, 0.05, 0.1 m, f = 0.2, 0.3, 0.4, 0.5 and four sediment transport stages produced 144 scenarios. Ranges of functional flows were greater for scenarios for low f (0.2) with low slope (0.001,0.05), for high f (0.5) with small grain size (0.02 m) and for intermediate low f (0.3) with coarse grain size (0.1 m). The functional flows model incorporates in‐stream habitat processes by including metrics of hydrologic, hydraulic, geomorphic and ecologic dynamics. Model uncertainties related to input data, calculation algorithms, and model structure are analysed. Functional flows analysis can be useful in studying water management alternatives to improve habitat conditions for target species and lifestages. Copyright © 2009 John Wiley & Sons, Ltd.     

A multiple criteria decision‐making approach to estimate minimum environmental flows based on wetted perimeter

Minimum environmental flows in rivers provide a certain level of protection for the aquatic environment. The relationship between wetted perimeter and discharge can be used to define the minimum environmental flows by the slope method (SM), or curvature method (CM), especially for cases with poor understanding of the aquatic ecosystem. SM and CM derived inconsistent values of minimum environmental flows. It was not clear which method better defined minimum environmental flow. Moreover, the computation and optimization procedures are both time consuming and error‐prone, especially for complicated wetted perimeter–discharge relationships. In this study, flow regulation for rivers was regarded as a multiple criteria decision‐making problem, with the objectives of minimum river discharge and maximum wetted perimeter. Ideal point methods (IPMs) with the scaling coefficient r = 1 (IPM1) and r = 2 (IPM2) were used to solve this model to determine optimal environmental flows. IPM was simple in computation, especially when the wetted perimeter–discharge relationship was given as scattered data pairs. Meanwhile, it was applicable to a wider range of wetted perimeter–discharge relationship than SM and CM. Environmental flows estimated by IMP1 are the same as that by SM. The analytical results for environmental flows using SM, CM, IPM1 and IPM2 were compared for wetted perimeter–discharge relationship expressed as power or logarithmic function. It showed that CM is not a good method to define environmental flows. SM with unity slope and IMP1 were recommended. CM, SM and IPM were examined for the determination of environmental flows in a river in North Xinjiang, China. Environmental flows for different transects of the studying river reach were estimated to be 21% of the mean annual flow by SM or IPM1, which provided the satisfactory wetted perimeter, water depth and average velocity for aquatic organisms. Copyright © 2007 John Wiley & Sons, Ltd.     

Current practices for establishing environmental flows in Brazil

This paper addresses current practices adopted by Brazilian states for establishing environmental flows. At the national level, the newly created National Water Agency has not yet recommended a standard practice. Confronted with the requirement to grant or deny water rights to users, states have set minimum instream flows using low flow frequency analysis. However, efforts are currently being made to include ecological variables in the decision‐making process. One difficulty with the process is the dearth of information regarding instream flow needs for Brazilian species and recreation. International experience on setting environmental flows is valuable, but care must be taken in its application to the Brazilian reality. Finally the authors express their views on the directions that Brazilian regulatory agencies are likely to adopt in the near future for setting environmental flows. Copyright © 2004 John Wiley & Sons, Ltd.     

A collaborative and adaptive process for developing environmental flow recommendations

Many river restoration projects are focusing on restoring environmental flow regimes to improve ecosystem health in rivers that have been developed for water supply, hydropower generation, flood control, navigation, and other purposes. In efforts to prevent future ecological damage, water supply planners in some parts of the world are beginning to address the water needs of river ecosystems proactively by reserving some portion of river flows for ecosystem support. These restorative and protective actions require development of scientifically credible estimates of environmental flow needs. This paper describes an adaptive, inter‐disciplinary, science‐based process for developing environmental flow recommendations. It has been designed for use in a variety of water management activities, including flow restoration projects, and can be tailored according to available time and resources for determining environmental flow needs. The five‐step process includes: (1) an orientation meeting; (2) a literature review and summary of existing knowledge about flow‐dependent biota and ecological processes of concern; (3) a workshop to develop ecological objectives and initial flow recommendations, and identify key information gaps; (4) implementation of the flow recommendations on a trial basis to test hypotheses and reduce uncertainties; and (5) monitoring system response and conducting further research as warranted. A range of recommended flows are developed for the low flows in each month, high flow pulses throughout the year, and floods with targeted inter‐annual frequencies. We describe an application of this process to the Savannah River, in which the resultant flow recommendations were incorporated into a comprehensive river basin planning process conducted by the Corps of Engineers, and used to initiate the adaptive management of Thurmond Dam. Copyright © 2006 John Wiley & Sons, Ltd.     

确定河流生态流量的几种湿周法比较

为比较不同湿周法在计算河流生态流量中的适用性,采用幂函数描述无量纲化的湿周～流量关系,利用曲率法、斜率法及多目标评价法中的线性加权和法、理想点法(尺度系数r分别取1,2,∞)、乘除法等7种方法计算河流生态流量。结果表明:曲率法的结果偏小;斜率法、理想点法(r=1)、线性加权和法的结果相同,且位于各方法的中间;另外3种多目标评价方法得到的河流生态流量大于斜率法等的结果,但湿周的增加比例明显小于流量增加比例。在湿周～流量关系符合幂函数关系时,利用斜率法或理想点法(r=1)、线性加权和法确定河流生态流量的方法是适宜的。     

Operationalizing the allocation of environmental flows: A U.K. perspective on Baxter's Schedule

Early attempts to gauge streams were used by George Baxter in 1961 to propose a pioneering scheme for deriving and allocating water for what today may be recognized as environmental flows in the United Kingdom, but the approach was not accepted into practice. A fundamental concern was the quality of river flow data. Stream gauging was advanced by the 1963 Water Resources Act, and prior to this, the allocation of water resources to compensation flows below dams was based on the basic principle of one third of the reliable yield, estimated using rainfall data. Despite the increased availability of river flow data since the 1970s, it is suggested that low‐flow data quality has severely constrained the management and allocation of water resources and remains so today. Today, pressures and demands on water resources are increasing, but the accuracy of low‐flow measurement is still hindering the operational determination and implementation of environmentally robust, seasonally variable environmental flows. Successful river regulation and restoration relate to a complex suite of public policy questions and given uncertainty over the quality of low‐flow data, transparent, pragmatic decisions about societal allocations of water need to be made.     

Including cultural water requirements in environmental flow assessment: an example from the upper Ganga River,India

The rituals of riparian communities are frequently linked to the flow regimes of their river. These dependencies need to be identified, quantified and communicated to policy makers who manage river flows. This paper describes the first attempt to explicitly evaluate the flows required to maintain the cultural and spiritual activities in the upper Ganga River basin. Riparian dwellers and visitors were interviewed and the responses analyzed to obtain an overview of the needs and motivations for cultural flows. The approach enhances the overall concept of environmental flow assessment, especially in river basins where spiritual values ascribed to rivers are high.     

River regulation and riparian woodlands: Cottonwood conservation with an environmental flow regime along the Waterton River,Alberta

Following water withdrawal, riparian cottonwoods have declined downstream from some dams in western North America. Analyses of aerial photographs and field observations in the 1980s suggested that the black and narrowleaf cottonwoods (Populus trichocarpa and Populus angustifolia) along the Waterton River, Alberta, were declining due to drought stress following the 1964 damming and diversion. This raised concern for the riverine ecosystems and in 1991, “functional flows” commenced with 2 changes: (a) the minimum flow was increased from 0.9 to 2.3 m³/s (mean discharge 21.9 m³/s) and (b) flow ramping provided gradual stage recession after the spring peak. This provided an environmental flow regime that was delivered for 2 decades and this study investigated the consequent river flow patterns and riparian woodlands upstream and downstream from the Waterton Dam. Analyses of aerial photographs from 1951 to 2009 assessed 4 flow management intervals: (a) the free‐flowing predam condition, (b) the initial dammed interval to the mid‐1970s, (c) a drought interval in the 1980s, and (d) with the environmental flow regime after 1991. Analyses revealed woodland reduction from 1961 to 1985 due to losses through bank erosion with major floods and apparent decline due to low flows following a regional drought and water withdrawal for irrigation. With the subsequent environmental flow regime, there was apparent woodland recovery, despite drought in 2000 and 2001. This study demonstrated that the correspondence between river flow patterns and the extent of riparian woodlands and the benefit from the environmental flow regime that probably reduced drought stress and mortality.     

Spatial scales in instream flow modeling: Why and how to use ecologically appropriate resolutions

This paper discusses why and how to use ecologically appropriate spatial resolutions (e.g., cell size or range of cell sizes) when modeling instream flow effects on aquatic animals. Resolution is important because relations between habitat and animal habitat use vary with spatial resolution, and different habitat variables may best predict habitat use at different resolutions. Using appropriate resolutions consistently would bring clarity and coherence to how we quantify and model habitat characteristics and habitat use by fish, facilitate the use of standard and more credible measures of habitat preference, incorporate more fisheries knowledge to improve models for different kinds of fish, and avoid well-known (and perhaps unknown) biases. Doing so involves describing habitat, and habitat use by fish, with spatially explicit measures with clear resolutions; using the same resolution for physical habitat and fish habitat use; selecting that resolution for ecological reasons; and using habitat variables and fish observation methods appropriate for the resolution. The choice of resolution considers factors such as how much space fish use for specific activities and the size of important habitat patches. For drift-feeders, cell sizes and fish habitat use observations should use a resolution no smaller than feeding territories. Piscivores typically hunt over large areas so should be modeled with larger habitat units. Models of small and less-mobile organisms (e.g., benthic invertivores) may need fine resolutions to capture the small areas of unusual habitat they depend on. Because of such differences, instream flow studies (like any spatial ecology exercise) should clearly state what resolution(s) they use and why.     

Multiple lines of evidence for the beneficial effects of environmental flows in two lowland rivers in Victoria,Australia

The aim of this study was to identify whether environmental flows released into two lowland rivers (the Glenelg and Wimmera Rivers, western Victoria, Australia) during the spring to autumn period had successfully ameliorated the negative effects of multiple human impacts. Macroinvertebrates and a range of physico‐chemical variables were sampled from three reaches in each river. Both rivers were sampled during three environmental release seasons with average‐sized releases (1997–1998, 1998–1999 and 2001–2002) and two drought seasons with limited releases (1999–2000 and 2000–2001). The effects of releasing average‐sized environmental flows on macroinvertebrates and physico‐chemical variables were assessed by comparison with data from the two drought seasons. For the Glenelg River, data from a reference season prior to the release of environmental flows (1995–1996) was also compared to data from the five environmental flow seasons. Multivariate analyses revealed four pieces of evidence indicating that the release of environmental flows effectively slowed the process of environmental degradation in the Glenelg River but not in the Wimmera River: (1) the magnitude of the river discharge was dependent on the size of environmental flow releases; (2) in the Wimmera River, water quality deteriorated markedly during the two drought seasons and correlated strongly with macroinvertebrate assemblage structure, but this was not observed in the Glenelg River; (3) the taxonomic composition of the macroinvertebrate assemblages among contrasting flow release seasons reflected the severe deterioration in water quality of the Wimmera River; (4) despite two drought seasons with minimal environmental flow releases, the macroinvertebrate assemblage in the Glenelg River did not differ from the average‐release seasons, nor did it return to a pre‐environmental flows condition. Therefore, it appears that environmental flow releases did sustain the macroinvertebrate assemblage and maintain reasonable water quality in the Glenelg River. However, in the Wimmera River, release volumes were too small to maintain low salinities and were associated with marked changes in the macroinvertebrate assemblage. Therefore, there are multiple lines of evidence that environmental flow releases of sufficient magnitude may slow the process of degradation in a regulated lowland river. Copyright © 2007 John Wiley & Sons, Ltd.     

基于湿周法的河道最小生态需水量多目标评价模型

以湿周与流量关系为基础,建立了基于多目标评价方法的河道最小生态需水量估算模型,以湿周最大和河道流量最小作为栖息地保护和水资源开发利用的目标,采用理想点法求解,以增江下游麒麟咀站为例计算河道最小生态需水量,并将该模型的计算结果与斜率法和曲率法的计算结果进行了比较分析。结果表明:增江下游河道最小生态需水量阈值范围为20.8～26.3 m3/s,相应的平均流速范围为0.42～0.44 m/s;模型计算结果比传统的湿周法适用性更强,且能较好体现生态用水和经济用水的均衡发展。     

清潩河流域河流环境流量计算与应用

针对北方地区河流环境流量短缺和污染并存的现状,在综合考虑水质保护与水量维持的情况下界定了河流环境流量的概念和内涵,并探讨不同功能目标下河流环境流量的组成。通过分析河流水系特征及河段的空间结构特征,建立了改善河流水质所需环境流量计算模型,同时建立了Tennant和湿周模型计算河流生态系统所需环境流量。利用临颍高村桥的水文水质数据,对清潩河为改善河流水质和生态系统所需环境流量进行了初步评价,为河流应急补水提供了调控建议,并提出了河道应常年保持的流量水平。     

水电工程下泄生态基流常用计算方法及软件开发

为了分析及确立生态基流,为水电工程环境影响评价提供依据,针对水电工程生态基流估算及决策过程繁复等问题,以2001—2015年水电工程环境影响评价及相关法律法规为基础,分析我国生态基流管理实践中使用最广泛的4种计算方法,即Tennant法、月基本流量法、最小流量法及7Q10法,并编制生态基流决策支持软件,并应用软件在汉江流域进行实例验证。结果表明,该软件能够提供多种计算方法及对比分析功能,可为水电工程下泄生态基流计算及决策提供计算平台。4种计算方法在汉江流域计算结果差异较大。总体而言,干流适合最小流量法及Tennant法,支流适合Tennant法。研究成果具有较大的实际应用和推广价值。     

Fish passage modelling for environmental flows: Hawkesbury‐Nepean River,NSW, Australia

Robust, objective, and repeatable approaches that define flow thresholds for fish passage across critical natural barriers such as riffles, rapids, and waterfalls are required for determining environmental flow strategies. These approaches also provide an opportunity to garner community sector backing for environmental flow releases from dams in support of tangible environmental beneficiaries—native fish. This paper outlines the results of a two‐dimensional hydraulic modelling approach to fish passage assessment for Australian bass (Percalates novemaculeata) that was used to inform the development of an environmental flow regime downstream of Warrragamba Dam, NSW, Australia. Flow rates of ≥500 MLd^?1 were found to facilitate depth‐limited upstream passage through a 20‐km river reach that contained 19 natural passage barriers to adult Australian bass up to 400–450 mm in length. Ideal passage conditions were determined at flow rates of ≥1,000 MLd^?1. Juvenile bass passage was found to be inhibited by high velocities at flow rates >250 MLd^?1, with flows of 100–250 MLd^?1 providing ideal conditions for juvenile passage. Fish length, body depth, and caudal fin depth data, as used in this study for Australian bass, provided more precise fish passage depth thresholds. Precision in fish passage assessments is important as each centimetre of additional flow depth influences cost–benefit analyses of environmental flow releases versus consumptive water uses. Although hydraulic modelling and field‐based approaches to fish passage assessment are well established, there is currently a lack of published data on native Australian freshwater fish length, body depth, and caudal fin depth data for use in fish passage assessments and for inclusion in “fish‐friendly” government policy initiatives.     

Differences in river ecological functions due to rapid channel alteration processes in two California rivers using the functional flows model,part 2—model applications

This study applies the functional flows model (FFM) that integrates hydrogeomorphic processes and ecological functions to assess physical habitat. Functional flows are discharge values that serve ecological uses. The model was adjusted to evaluate gravel‐bed riffle functionality for fall‐run Chinook salmon with respect to river rehabilitation on the Mokelumne River and flood‐induced channel change on the Yuba River. The goal was to test if differences in ecological performance were traceable to differences in hydrogeomorphic conditions. Ecological functions studied were bed occupation (spawning, incubation and emergence) and bed preparation (river bed reworking periods)‐ both reliant on shear stress dynamics. Model outputs included number of days that have functional flows, ranges of functional flows that provide favourable sediment transport stages and the efficiency of a site to produce functional flows. Statistical significance of results was tested using non‐parametric tests. Functional flows analyses before and after geomorphic alteration indicate that river rehabilitation on the lower Mokelume River increased the number of days with functional flows, while the Yuba River May 2005 flood increased the functional ranges of flows for the test sites. Reach‐scale analyses indicated similar ecological performance at reference sites in both rivers. A comparison between both rivers showed that despite a greater geomorphic potential of the Mokelumne River sites to have functional flows, Yuba River sites actually experienced better ecological performance for fall‐run Chinook salmon freshwater life stages due to greater flow availability. The FFM provided an objective tool to assess changes in ecological functionality at hydrogeomorphically dynamic sites. Copyright © 2010 John Wiley & Sons, Ltd.     

Bayesian network models for environmental flow decision‐making: 1. Latrobe River Australia

Current methods underpinning environmental flow (eFlow) decisions often lack transparency, do not adequately consider uncertainties and rarely include adaptive management principles. We report the development and application of an eFlow Bayesian Network (BN) model that links four flow components with an ecological model to predict the spawning and recruitment of two important native fish species, the Australian Grayling and River Blackfish, in the highly regulated and flow‐stressed lower Latrobe River in Victoria, Australia. Autumn high flows, in conjunction with low stream temperature, are critical for Grayling spawning. The BN model was used to predict the probability of spawning and recruitment of these two native fish species for four flow scenarios. Quantitative data, flow simulation models and expert judgement were used to parameterize the BN model. The model results showed clearly that currently, and into the future, there is a very low likelihood of spawning and recruitment of Australian Grayling in the lower Latrobe. River Blackfish are minimally affected by the predicted reductions in flow and increased stream temperatures. Management scenarios aimed at modifying flows and stream temperatures to increase the likelihood of successful spawning and recruitment of Australian Grayling were assessed. Self‐sustaining populations of Australian Grayling could conceivably be achieved in the upper reaches of this river if fish passage was provided through an on‐stream reservoir. A major benefit in building and applying an eFlow BN model is that it can facilitate meaningful analysis and discussion of the ecological effects of particular eFlow regimes. Copyright © 2010 John Wiley & Sons, Ltd.     

Examining the ecological consequences of restoring flow intermittency to artificially perennial lowland streams: Patterns and predictions from the Broken—Boosey creek system in northern Victoria,Australia

The reinstatement of natural flow regimes is a rapidly emerging issue in river restoration worldwide. In northern Victoria, Australia, efforts are presently underway to restore a natural, intermittent flow regime to several streams which have received perennial diversions for both irrigation and stock and domestic water‐supplies for over 100 years. A pipeline to deliver water to landholders will significantly reduce transmission losses throughout the system allowing irrigation canals and diversion weirs to be decommissioned. The motivation for flow alteration in this system lies primarily in reducing inefficiencies in water delivery which, in turn, will be used to meet escalating demands on water resources. The ecological impact of the flow regime shift on these streams is likely to be substantial. This study utilized an existing artificial hydrological gradient (from perennial to intermittent) in two creek systems, to explore relationships between flow regime and a range of ecological variables. These data provide a benchmark against which to assess ecological changes once flow has been altered and form the basis for predicting changes that can assist future management decisions. Data collected from 10 sites across a strong hydrological gradient detected clear differences in geomorphology, water quality and biotic assemblages (macrophytes, macroinvertebrates and fish). By examining the relationship between flow regime and the distribution of biota we identify both the positive and negative outcomes of restoring naturally intermittent flow regimes within artificially perennial lowland streams. The reinstatement of intermittent flow regimes in artificially perennial streams will continue in many parts of the world as water delivery via these systems becomes increasingly uneconomical. While flow restoration may in principle be regarded as a positive step, these findings emphasize the need to consider fully the ecological consequences of restoring historical hydrological regimes to streams within the context of other human induced catchment disturbances. Copyright © 2009 John Wiley & Sons, Ltd.