Environmental Flow Regimes Research Articles

Developing hydroecological models to inform environmental flow standards: a case study from England

The concept of defining environmental flow regimes to balance the provision of water resources for both human and environmental needs has gained wide recognition. As the authority responsible for water resource management within England, the Environment Agency (EA) uses the Environmental Flow Indicator (EFI), which represents an allowable percentage deviation from the natural flow to determine where water may be available for new abstractions. In a simplified form, the EFI has been used as the hydrological supporting component of Water Framework Directive classification, to flag where hydrological alteration may be contributing to failure to achieve good ecological status, and to guide further ecological investigation. As the primary information source for the EFI was expert opinion, the EA aims to improve the evidence base linking flow alteration and ecological response, and to use this evidence to develop improved environmental flow criteria and implementation tools. Such tools will be required to make predictions at locations with no or limited ecological monitoring data. Hence empirical statistical models are required that provide a means to describe observed variation in ecological sensitivity to flow change. Models must also strike a balance between generic and local relationships. Multilevel (mixed effects) regression models provide a rich set of capabilities suitable for this purpose. Three brief examples of the application of these techniques in defining empirical relationships between flow alteration and ecological response are provided. Establishment of testable hydrological–ecological relationships provides the framework for improving data collection, analysis, and ultimately water resources management models.This article is categorized under: Water and Life > Conservation, Management, and Awareness

Effect of climate change on environmental flow indicators in the narew basin, poland.

Environmental flows-the quantity of water required to maintain a river ecosystem in its desired state-are of particular importance in areas of high natural value. Water-dependent ecosystems are exposed to the risk of climate change through altered precipitation and evaporation. Rivers in the Narew basin in northeastern Poland are known for their valuable river and wetland ecosystems, many of them in pristine or near-pristine condition. The objective of this study was to assess changes in the environmental flow regime of the Narew river system, caused by climate change, as simulated by hydrological models with different degrees of physical characterization and spatial aggregation. Two models were assessed: the river basin scale model Soil and Water Assessment Tool (SWAT) and the continental model of water availability and use WaterGAP. Future climate change scenarios were provided by two general circulation models coupled with the A2 emission scenario: IPSL-CM4 and MIROC3.2. To assess the impact of climate change on environmental flows, a method based conceptually on the "range of variability" approach was used. The results indicate that the environmental flow regime in the Narew basin is subject to climate change risk, whose magnitude and spatial variability varies with climate model and hydrological modeling scale. Most of the analyzed sites experienced moderate impacts for the Generic Environmental Flow Indicator (GEFI), the Floodplain Inundation Indicator, and the River Habitat Availability Indicator. The consistency between SWAT and WaterGAP for GEFI was medium: in 55 to 66% of analyzed sites, the models suggested the same level of impact. Hence, we suggest that state-of-the-art, high-resolution, global- or continental-scale models, such as WaterGAP, could be useful tools for water management decision-makers and wetland conservation practitioners, whereas models such as SWAT should serve as a complementary tool for more specific, smaller-scale, local assessments.

Progress of the Canterbury Water Management Strategy and some emerging issues

This paper reviews the progress to date of the Canterbury Water Management Strategy and identifies key developments and emerging issues. The paper examines the provision of storage, water use efficiency, environmental flow adjustments, nutrients from land use intensification, biodiversity enhancements and kaitiakitanga. The collaborative process has led to some more sustainable changes. One is the use of off-river storage and tributary storage as alternatives to mainstem storage. A second is improved environmental flow regimes by increasing minimum flows and reducing allocations at low flows; but enabling access to allocations at higher flows and providing time to adjust to new requirements. The parallel achievement of reduced nitrate loads and increased irrigation areas is proving problematic. Water use efficiency is advancing on some fronts – piped distribution replacing canal distribution and ongoing conversions to spray irrigation – but not on others – soil moisture demand irrigation and reallocation of surface and groundwater use to enhance recharge. Biodiversity enhancements and incorporating kaitiakitanga in water management are showing positive progress. Some of the key emerging issues include the allocation of nitrate capacity between existing and new users, and, the need for increased capacity for predictive modelling and field measurement to improve management of the use of scarce water and the cumulative effects of its use.

Taxonomy, metrics or traits? Assessing macroinvertebrate community responses to daily flow peaking in a highly regulated Brazilian river system

ABSTRACTDamming disrupts lotic continuity, creating a lentic water body upstream of the dam and a lotic stretch downstream that is highly vulnerable to temporal fluctuations in flow and physiochemical quality depending on the operational regime of the dam. Thus, an essential part of any dam operation programme must take into account a typologically suitable environmental flow regime, in order to maintain downstream structure and function. We assessed the seasonal impact of daily flow peaking regimes on the taxonomic composition, metrics and traits of the macroinvertebrate community in the lotic section situated downstream of the Itutinga reservoir on the Rio Grande in the state of Minas Gerais in southeast Brazil. The flow manipulation experiments were carried out in both wet (January) and dry periods (July) of 2010. The samplings were carried out in two hydraulic situations (fixed flow and daily flow peaking). Benthic macroinvertebrates and sediment were collected in three habitat types (backwater, fluvial beach and running water). Water variables were measured only in the fluvial beach habitat. Both water column and sediment variables downstream were heavily influenced by the retention capacity of the reservoir rather than the daily flow peak value. The trait approach was more sensitive than abundance and metrics and could detect the effects of daily flow peaking. The benthic macroinvertebrate communities sampled downstream of the Itutinga reservoir were more influenced by the sediment composition at each of the three studied habitats, than by the tested daily flow peaking. However, given the short timescale of this study, it may be difficult to the influence of these two interrelated factors. Copyright © 2013 John Wiley & Sons, Ltd.

Estimating minimum environmental flow requirements for well-mixed estuaries in Spain

Following the principles of the European Water Framework Directive, the current Spanish water management legislation requires the definition of the environmental flow regimes for all water bodies, including estuaries. The scientific community has tried to answer the question of how much freshwater an estuary needs since the mid-1970s, resulting in the development of several methodologies and approaches in different parts of the world. However the ability to reproduce most of these approaches is difficult due to the scarcity of required data and also to the differences between the studied estuaries. In this paper, we present a methodology to calculate environmental flow regimes in well-mixed estuaries based on the numerical modelling of salinity and which takes into account the seasonal climatic and hydrologic pattern of the catchment. The approach follows three sequential steps: 1) Definition of reference conditions based on the unaltered salinity patterns and zoning of the estuary, 2) definition of salinity thresholds and 3) calculation of the minimum flows required to satisfy these thresholds. The application of the methodology to five estuaries on the northern coast of Spain has highlighted the importance of considering the hydrological variability and the division of the estuary into homogeneous zones. Moreover, the studies carried out demonstrate the ineffectiveness of river specific methodologies when used to define environmental flow regimes in several estuaries and periods, and the need to apply specific methodologies. The methodology is based on the principles defined by other already tested approaches, but its greatest advantage lies in the ability to be applied to large scales, when physical and biological data is scarce.

Fish recruitment in rivers with modified discharge depends on the interacting effects of flow and thermal regimes

Summary Alteration of flow and thermal regimes is a key consequence of human use of river and floodplain ecosystems, and these impacts result from a range of interacting ecological mechanisms. Environmental flow regimes are a management strategy to restore or maintain ecologically important aspects of river hydrology. However, inadequate understanding of the processes that determine the effects of flow on population dynamics of biota hinders the maximum benefits of environmental flows. Spawning and recruitment of riverine fish is mediated by temperature, access to nursery habitat and the timing and availability of resources. Differences in population sizes between regulated and unregulated rivers are often attributed to the effect of flow and thermal regime change on population dynamics. Dams and extraction of water have altered the flow and thermal regimes of rivers in the northern Murray–Darling Basin, Australia. Combining three studies, we (i) examined differences in the recruitment of fish and patterns of potential prey availability between a regulated and unregulated river, (ii) studied the relationships between patterns of flow and temperature on spawning of fish in two rivers with contrasting regulated flow regimes and (iii) experimentally tested the effects of environmental flow releases in a regulated river on fish spawning and recruitment by comparing patterns over time against two unregulated rivers. Comparisons between regulated and unregulated rivers indicated that the significantly lower recruitment of Macquaria ambigua in the regulated river was linked with large differences in available prey. Species‐specific differences in the abundance of fish larvae between two regulated rivers indicated that different reproductive strategies determine population‐level responses to flow regulation. Finally, the experimental flow releases in a regulated reach during late spring did not result in a change in spawning and recruitment of fish, although influences of antecedent flow and temperature on larval and juvenile assemblage composition were significant. These findings indicate that the responses of fish spawning and recruitment to flow regime change and restoration are dependent on the conditions that determine the success of these critical life‐history processes. Specifically, key effects of flow regulation are reduced summer water temperatures due to hypolimnetic discharge from dams, and the reduced frequency and duration of low flows. Reduced water temperatures limit opportunities for fish to spawn, and sustained base flows were associated with lower densities of potential prey sources in conjunction with potential flushing of larvae and juveniles, thereby influencing recruitment. The benefits of environmental flow programmes can be enhanced if flow regimes are modified to ensure that abiotic and biotic conditions that support persistence of biota are provided. In conjunction with flow pulses and floods, low flows are a natural and ecologically important component of flow regimes, particularly in dryland rivers. Understanding the interactive and mechanistic effects of flow and thermal regimes on population viability and patterns of biodiversity is critical to maximising the value of environmental flows.

IMPLEMENTING ENVIRONMENTAL FLOWS IN SEMI‐REGULATED AND UNREGULATED RIVERS USING A FLEXIBLE FRAMEWORK: CASE STUDIES FROM TASMANIA, AUSTRALIA

ABSTRACTDespite the many methodologies available for undertaking environmental flow assessments, there are few published examples of environmental flow recommendations that arise from those assessments, and even fewer that evaluate their implementation. This is somewhat surprising considering environmental flow recommendations are effectively testable hypotheses of flow‐ecology responses. We describe a framework to guide the assessment and recommendation of environmental flow regimes in Tasmania, Australia, where environmental values are highly catchment specific and rivers are largely semi‐regulated or unregulated. This means that environmental flows must be focussed on setting water use thresholds to prevent degradation in condition, rather than delivering water to restore condition. The framework retains the philosophy and elements of many other methodologies but differs by having the flexibility to support application across different catchments while catering for catchment‐specific issues. We present two case studies that demonstrate the application of our Framework, its use in the development of scientifically defensible environmental flow recommendations, and their implementation in catchment water management plans. The strengths of the Framework are: (i) using specific ecosystem values to define and communicate the objectives of environmental flows; (ii) using a non‐prescriptive and flexible approach to incorporate catchment‐specific issues; and (iii) framing recommendations in a manner that clearly illustrates flow linkages with ecosystem values so that stakeholders and managers understand the risks associated with water abstraction. Our experience demonstrates the imperative that scientists are not only involved in water planning but also in the implementation, monitoring, and evaluation of plans so that the benefits of adaptive management can be realized. Copyright © 2013 John Wiley & Sons, Ltd.

Linkages between primary seed dispersal, hydrochory and flood timing in a semi‐arid region river

AbstractQuestionsAre seed release and hydrochory of riparian plants coupled with seasonal flood pulses for a river with bimodal flows? What phenological hydrochore guilds are present? How representative of riparian vegetation are hydrochores? What is the role of hydrochory in riparian plant community composition in arid land streams?LocationVerde River, central Arizona, USA.MethodsWe recorded phenology of flowering and primary seed dispersal monthly for >100 riparian plant species, seined hydrochores 12 times during the growing season, sampled the extant plant community, and collected soil seed bank samples. Emergence of seedlings from hydrochore and soil samples was monitored for 1 yr in a greenhouse. Plant species were classified as to wetland indicator status and assessed for traits including life span, growth form and seed mass.ResultsFlowering and primary seed dispersal at the community level was bimodal for dryland species but more constant through time for wetland species. Numbers and richness of wetland hydrochores were high during the three floods that occurred in the atypical study year, while dryland species pulsed during a single flood. Three of 56 hydrochore taxa were vernal flood specialists, characterized by a spring hydrochore pulse during their period of seed release, and one was associated with summer floods. Another six were phenological generalists, with hydrochores constant or semi‐constant through time (including before and after primary dispersal) and persistent soil seed banks. Hydrochorous species spanned a wide range of traits, but overall had smaller seeds and higher wetland affinity than extant riparian vegetation.ConclusionsAs with other regions, hydrochory in dryland rivers is governed by the individual and combined influences of extrinsic factors, such as seasonal flow patterns and hydraulics, and intrinsic factors, such as timing of seed release and seed traits. Floods at different times during the season disperse distinct guilds, emphasizing the importance of flow variability for structuring riparian plant communities. Identifying temporal flood specialists and flood generalists is important, both for informing environmental flow regimes and for understanding patterns of plant distribution. The phenological dispersal plasticity of the generalist hydrochore species allows for adaptability to varying flow conditions and likely contributes to their broad geographic distributions.

Informed Decision Making Process for Managing Environmental Flows in Small River Basins

Numerous examples exist worldwide of partial or complete alteration to the natural flow regime of river systems as a consequence of large scale water abstraction from upstream reaches. The effects may not be conspicuous in the case of very large rivers, but the ecosystems of smaller rivers or streams may be completely destroyed over a period of time. While restoration of the natural flow regime may not be possible, at present there is increased effort to implement restoration by regulating environmental flow. This study investigates the development of an environmental flow management model at an icon site in the small river basin of Bharathapuzha, west India. To determine optimal environmental flow regimes, a historic flow model based on data assimilated since 1978 indicated a satisfactory minimum flow depth for river ecosystem sustenance is 0.907 m (28.8 m3/s), a value also obtained from the hydraulic model; however, as three of the reservoirs were already operational at this time a flow depth of 0.922 m is considered a more viable estimate. Analysis of daily stream flow in 1997–2006, indicated adequate flow regimes during the monsoons in June–November, but that sections of the river dried out in December–May with alarming water quality conditions near the river mouth. Furthermore, the preferred minimum ‘dream’ flow regime expressed by stakeholders of the region is a water depth of 1.548 m, which exceeds 50 % of the flood discharge in July. Water could potentially be conserved for environmental flow purposes by (1) the de-siltation of existing reservoirs or (2) reducing water spillage in the transfer between river basins. Ultimately environmental flow management of the region requires the establishment of a co-ordinated management body and the regular assimilation of water flow information from which science based decisions are made, to ensure both economic and environmental concerns are adequately addressed.

A Bayesian network approach to support environmental flow restoration decisions in the Yarra River, Australia

Many rivers in Australia and elsewhere around the world are flow stressed. There is now considerable activity to restore crucial components of the natural flow regime of such rivers—known as environmental flows, but methods underpinning the decision-making often lack rigour and transparency. The restoration of environmental flow regimes is usually determined using historic flow data, available expertise, sometimes ad-hoc compromise between conflicting and spatio-temporally variable water needs, and then implemented through special environmental allocations or water sharing plans. However, ecological flow requirements are poorly integrated into the decision-making process. This paper reports an eco-hydrological Bayesian network model developed to assist in risk assessment and decision-making on improving the flow conditions for Australian Grayling (Prototroctes maraena) in the Yarra River in south-eastern Australia. The Yarra environmental flow model was adapted from previous work on Australian Grayling in the Latrobe River system, and contained the same ecological model as for the Latrobe River, but with a new hydrological sub-model developed specifically for the Yarra River. The model was used to assess the relative ecological benefits (to Australian Grayling) of restoring specific components of the natural flow regime, in particular autumn freshes and spring freshes.

Integration of hydrological and habitat simulation methods to define minimum environmental flows at the basin scale

AbstractNew environmental policies establish the need to maintain the ecological integrity of freshwater ecosystems. The hydrologic regime is a key element in determining river processes and therefore the definition of environmental flow regimes (EFR) is essential to achieve this goal. The EFR can be broadly defined as the water required to sustain freshwater and estuarine ecosystems, and the human livelihood that depend on these ecosystems. Nevertheless, the role of the EFR and the methods to calculate them has not been clearly stated in many countries. This paper sets out a procedure to calculate EFRs, which includes not only a minimum flow, but also a temporal variability of this flow. The procedure integrates the results of hydrologic and habitat simulation methods in a temporal scale that takes into consideration the natural hydrologic seasonality while providing a certain level of flexibility to regulate water resources still meeting the requirements of the Spanish Water Planning legislation. The results highlighted the advantages of using different methodological approaches to calculate EFRs. Therefore, this study concludes the validity of a relatively simple hydrologic method for defining minimum environmental flows at a period of maximum hydrologic stress, but also the need to consider different approaches to take into account as many ecosystem elements as possible.

Hydrological connectivity structures concordant plant and animal assemblages according to niche rather than dispersal processes

Summary1. Understanding the processes that structure community assembly across landscapes is fundamental to ecology and for predicting and managing the consequences of anthropogenically induced changes to ecosystems.2. We assessed the community similarity of fish, macroinvertebrate and vegetation communities against geographic distances ranging from 4 to 480 km (i.e. distance–decay relationships) to determine the balance between local environmental factors and regional dispersal processes, and thus whether species‐sorting (niche processes) or dispersal limitation (neutral processes) was more important in structuring these assemblages in Australia’s wet‐dry tropics. We investigated whether the balance between niche and dispersal processes depended on the degree of hydrological connectivity, predicting that dispersal processes would be more important at connected sites, and also whether there was spatial concordance among these three assemblage types.3. There was significant but weak spatial concordance among the study communities, suggesting limited potential for surrogacy among them. Distance–decay in community similarity was not observed for any study assemblage at perennial sites, suggesting dispersal was not limiting and assemblages were structured more strongly by local niche processes at these connected sites. At intermittent sites, weak distance–decay relationships for each assemblage type were confounded by significant relationships with environmental dissimilarity, suggesting that dispersal limitation contributed, albeit weakly, to niche processes in structuring our three study assemblages at disconnected sites.4. Two environmental factors, flow regime and channel width, explained significant proportions of variation in all three assemblages, potentially contributing to the observed spatial concordance between them and representing local environmental gradients along which these communities re‐assemble after the wet season, according to niche rather than dispersal processes.

The role of sediment-transport evaluations for development of modeled instream flows: Policy and approach in Texas

Instream-flow scientists embrace streamflow as the master variable driving aquatic and riparian ecosystems, and that natural flow variability is imperative for river conservation and restoration efforts. Sediment transport, which is critical for maintenance of physical habitats in rivers and floodplains, has received less direct attention from instream-flow practitioners. This article serves to highlight the roles of sediment-transport evaluations in modifying or verifying instream-flow prescriptions based on hydrology alone. Two examples of sediment-transport evaluations are discussed in relation to the Texas Senate Bill 3 Environmental Flows allocation process, a mandate to "develop environmental flow analyses and a recommended flow regime" that "maintain(s) the viability of the state's streams, rivers, and bay and estuary systems" using "reasonably available science". The first example provides an evaluation of effective discharge of suspended-sediment load of the lower Brazos River. The magnitude and frequency of effective discharge occurs between typical high-flow pulses and overbank flows, indicating that hydrologic and physical processes are not optimally coupled in some flow-regime models. The second example utilizes the Hydrology-Based Environmental Flow Regime (HEFR) model to prescribe instream flows for the lower Sabine River, and compares modeled bed-material loads for observed and HEFR-prescribed flow regimes. Results indicate that annual water and sediment yields are greatly reduced for the modeled flow regime. It should be noted, however, that different input variables to the HEFR model would have resulted in different computations of water and sediment yields, reinforcing that instream-flow practitioners should exercise great caution when applying rule-of-thumb procedures to generate flow prescriptions.

Morphology and associated environmental flow prescriptions for rivers for water supply

Abstract River morphological change, prescribed environmental flow regimes, and the water supply ability of rivers are correlated. In water-scarce regions, the ability to ensure planned water supply reliability is a major criterion for deciding reasonable environmental flow and the morphology prescription for rivers. In this research, a method is proposed to determine reasonable environmental flow and morphology prescription. Using this method, three major morphology options are considered: 1) allowing the erosion of rivers 2) preserving the existing river morphology, and 3) constructing new, smaller rivers. Different environmental flow regimes are designed that can support the three different morphology scenarios. The effect of river morphological and environmental flow settings on water supply ability is also explored. To demonstrate the applicability of the method, we employ China's Tanghe River as a case study. The results show that the new method is useful for directing water supply and reservoir operations.

Sustainable reservoir operations to balance upstream human needs and downstream lake ecosystem targets

Abstract Reservoirs improve human health by providing a steady water supply, alleviate poverty by producing cheap electricity and strengthen regional economies by providing job opportunities. However, present modes of reservoir operation, without environmental flow targets, have caused ecosystem degradation while satisfying human needs. The degraded aquatic ecosystem conditions caused by tremendous dam construction in China propel a shift from an emphasis on human needs to sustainable modes of reservoir operation. In this paper, an optimizing reservoir operation model was developed to assist the decision making process of balancing human needs and ecological targets. The environmental flow regime paradigm and water shortage ratio of social water supply were respectively used to establish downstream lake ecosystem targets and upstream human needs. An Interactive Dynamic Programming (IDP) was developed to optimize the conflicts of human needs and ecosystem targets. A set of scenarios were designed for reservoir operations in the Baiyangdian basin in a normal year (50% percentage), a wet year (25% percentage) and a dry year (75% percentage), which provided a very useful tool for reservoir operations to balance human needs and ecosystem targets.

IMPLEMENTING ENVIRONMENTAL FLOWS IN COMPLEX WATER RESOURCES SYSTEMS – CASE STUDY: THE DUERO RIVER BASIN, SPAIN

ABSTRACTEuropean river basin authorities are responsible for the implementation of the new river basin management plans in accordance with the European Water Framework Directive. This paper presents a new methodology framework and approach to define and evaluate environmental flow regimes in the realistic complexities that exist with multiple water resource needs at a basin scale. This approach links river basin simulation models and habitat time series analysis to generate ranges of environmental flows (e‐flows), which are evaluated by using habitat, hydropower production and reliability of water supply criteria to produce best possible alternatives.With the use of these tools, the effects of the proposed e‐flows have been assessed to help in the consultation process. The possible effects analysed are impacts on water supply reliability, hydropower production and aquatic habitat. After public agreements, a heuristic optimization process was applied to maximize e‐flows and habitat indicators, while maintaining a legal level of reliability for water resource demands. The final optimal e‐flows were considered for the river basin management plans of the Duero river basin.This paper demonstrates the importance of considering quantitative hydrologic and ecological aspects of e‐flows at the basin scale in addressing complex water resource systems. This approach merges standard methods such as physical habitat simulations and time series analyses for evaluating alternatives, with recent methods to simulate and optimize water management alternatives in river networks. It can be integrated with or used to complement other frameworks for e‐flow assessments such as the In‐stream Flow Incremental Methodology and Ecological Limits of Hydrologic Alteration. Copyright © 2011 John Wiley & Sons, Ltd.

Response by fish assemblages to an environmental flow release in a temperate coastal Australian river: A paired catchment analysis

AbstractDefining appropriate environmental flow regimes and criteria for the use of environmental water allocations requires experimental data on the ecological impacts of flow regime change and responses to environmental water allocation. Fish assemblages in one regulated and one unregulated tributary paired in each of two sub‐catchments of the Hunter River, coastal New South Wales, Australia, were sampled monthly between August 2006 and June 2007. It was predicted that altered flow regime due to flow regulation would reduce species richness and abundance of native fish, and assemblage composition would differ between paired regulated and unregulated tributaries. Despite significant changes in richness, abundance and assemblage composition through time, differences between regulated and unregulated tributaries were not consistent. In February 2007, an environmental flow release (‘artificial flood’) of 1400 ML was experimentally released down the regulated tributary of one of the two catchments over 6 days. The flow release resulted in no significant changes in fish species abundances or assemblage composition when compared to nearby unregulated and regulated tributaries. Flow regulation in this region has reduced flow variability and eliminated natural low‐flow periods, although large floods occurred at similar frequencies between regulated–unregulated tributaries prior to and during 2006–2007, resulting in only moderate changes to regulated flow regimes. Barriers to dispersal within catchments also compound the effects of flow regulation, and findings from this study indicate that the location of migratory barriers potentially confounded detection of the effects of flow regime change. Further experimental comparisons of fish assemblages in regulated rivers will refine river‐specific response thresholds to flow regime change and facilitate the sustainable use of water in coastal rivers. Copyright © 2010 John Wiley & Sons, Ltd.

DEVELOPMENT OF AN INFLOW‐CONTROLLED ENVIRONMENTAL FLOW REGIME FOR A NORWEGIAN RIVER

ABSTRACTHydropower produces 99% of the electricity in Norway, and a large number of rivers are regulated. Currently, static minimum flow regimes are used as a mitigation measure for most of these developments, usually having fixed values for winter and summer flow. Improved knowledge on the importance of variability in flow regimes has led to research on alternative solutions to the static minimum flow regimes. This paper describes the development of an environmental flow regime that is designed to follow the variation in natural inflow. The flow regime is designed using an adaptation of the building block methodology and linked to high, normal and low natural flow conditions. The work is focused on the river Daleelva in western Norway where Atlantic salmon is the key species. The paper also describes how the variable environmental flow regime can be implemented in practice as it pertains to current Norwegian legislation. Copyright © 2011 John Wiley & Sons, Ltd.

Integrated modelling of cost‐effective siting and operation of flow‐control infrastructure for river ecosystem conservation

Wetland and floodplain ecosystems along many regulated rivers are highly stressed, primarily due to a lack of environmental flows of appropriate magnitude, frequency, duration, and timing to support ecological functions. In the absence of increased environmental flows, the ecological health of river ecosystems can be enhanced by the operation of existing and new flow‐control infrastructure (weirs and regulators) to return more natural environmental flow regimes to specific areas. However, determining the optimal investment and operation strategies over time is a complex task due to several factors including the multiple environmental values attached to wetlands, spatial and temporal heterogeneity and dependencies, nonlinearity, and time‐dependent decisions. This makes for a very large number of decision variables over a long planning horizon. The focus of this paper is the development of a nonlinear integer programming model that accommodates these complexities. The mathematical objective aims to return the natural flow regime of key components of river ecosystems in terms of flood timing, flood duration, and interflood period. We applied a 2‐stage recursive heuristic using tabu search to solve the model and tested it on the entire South Australian River Murray floodplain. We conclude that modern meta‐heuristics can be used to solve the very complex nonlinear problems with spatial and temporal dependencies typical of environmental flow allocation in regulated river ecosystems. The model has been used to inform the investment in, and operation of, flow‐control infrastructure in the South Australian River Murray.

Constraints on the recovery of invertebrate assemblages in a regulated snowmelt river during a tributary-sourced environmental flow regime

The impacts of river regulation on aquatic biota have been extensively studied, but long-term assessments of the restoration of biota by environmental flows and the principal mechanisms of recovery have rarely occurred. We assessed whether the provision of an environmental flow regime (EFR) via the decommissioning of an aqueduct on a tributary stream altered downstream macroinvertebrate assemblages in the highly regulated Snowy River, Australia. Macroinvertebrate assemblages of the Snowy River, reference and control sites remained distinct despite the provision of environmental flows. Invertebrate assemblages detrimentally affected by regulation probably remained impaired due to either constraints on colonisation from the tributary stream (dispersal constraints) or unsuitable local environmental conditions in the Snowy River caused by flow regulation (e.g. high levels of fine sediments, elevated temperature regime) suppressing new colonists or recovery of extant populations. Our study showed that restoration may be ineffective if EFRs are too small to ameliorate local environmental factors constraining the recovery of affected biota. Other barriers to recovery, such as dispersal constraints, also need to be overcome. Successful restoration of regulated rivers using environmental flows requires an understanding of the mechanisms and pathways of recovery, together with identification and amelioration of any potential barriers to recovery.