Environmental Flow Allocations Research Articles

A multiple criteria decision-making approach for water allocation of environmental flows considering the value trade-offs - A case study of Fen River in China

In the water-scarce basin, the allocation of environmental flows needs to achieve the equilibrium between ecological protection and economic development. One of the challenges is the lack of quantitative analysis of the value of water in the economy and ecosystem, which could not effectively support the decision-making. This paper proposed a new multi-criteria decision-making approach that considers the value trade-offs between the environmental flows and the economic water use of rivers. The value of environmental flows was assessed using the modified equivalent factor method combined with the hydraulic method, which considers the influences of the hydraulic characteristics of rivers on value assessment. The value of the economic water use was estimated using the modified Cobb-Douglas production function. The ideal point method was applied to obtain the optimal solution of the multi-criteria decision with the objective of maximum values of the economic water use and maximum values of environmental flows (or the value of multiple recommended environmental flows). This new method was applied to determine the optimal environmental flows in the Fen River, the second-largest tributary of the Yellow River of China. The results indicated that the reasonable environmental flows were 51.1 % or 40.4 % (considering the water shortage for development) of the natural runoff of the Fen River. This work could provide a valuable reference for determining the water allocation of environmental flows in the water shortage area of China.

Environmental flow assessment for intermittent rivers supporting the most poleward mangroves

The most vulnerable and dynamic ecosystems in terms of response to climate change and fluctuations in hydrological conditions are mangroves, particularly those located on the edge of their latitudinal range limits. The four primary Iranian mangrove forest sites: Nayband, Qeshm, Gabrik, and Govatr, located in the northern part of the Persian Gulf and the Gulf of Oman already exist near the limit of their tolerance to extreme temperature, precipitation, and salinity. Due to extreme climate conditions at these locations, the mangrove trees are usually smaller and less dense as compared with mangroves closer to the equator complicating their monitoring and mapping efforts. Despite the growing attention to the ecological benefits of mangrove forests and their importance in climate change mitigation, there are still a few studies on these marginal mangroves. Therefore, we investigated whether the variation in mangrove ecosystem health is related to the changes in physical parameters and differs between estuarine and sea-side locations. We developed a comprehensive database on NDVI values, associated rainfall, temperature, and river flow based on in-situ and remote sensing measurements. By understanding the normal hydrologic patterns that control the distribution and growth of mangroves in arid and semi-arid regions, we are questioning the need for environmental flow allocation to restore mangrove ecosystem health. This brings us to the second gap in the literature and the need for further studies on Environmental Flow assessment for intermittent and ephemeral rivers. Alike other mangroves studied, forests showed greenness seasonality, positively correlated with rainfall, and negatively correlated with temperature. As there was no clear difference between estuarine and marine sites, freshwater influence in the form of river flow, unlike temperature, cannot be considered a major limiting factor. Nevertheless, during prolonged droughts mangroves could benefit from the recommended allocation of Environmental Flow during the cold period (November–March).

A Comparative Study for Provision of Environmental Flows in the Tapi River

Environmental flows are defined as the flow required into a stream to maintain the river’s ecosystem. The notion of Environmental Flow Allocation (EFA) ensures that a sufficient amount of water is delivered to the stream to maintain ecological integrity. The objective of this study is to examine environmental flows and determine the best acceptable strategy for providing flows into the river in the Lower Tapi Basin. To achieve this objective, daily discharge data from three sites, Ukai (period 1975–2020), Motinaroli (period 1990–2021), and Ghala (period 1995–2005) were collected and analyzed using the Tennant, Tessman, variable monthly flow (VMF), and Smakhtin methodologies. A comparative analysis was carried out on all three sites using the four methodologies. The Tessman and VMF approaches have a strong connection with the computed environmental flow requirements (EFR), according to the results. The calculated EFR was found to be in the range of 30–35% of mean annual flows (MAF). The maximum EFR found at station Ghala is about 54.5% of MAF according to the Tessman method. Such research will help to prevent future degradation of the river by supplying flow in accordance with the EFR, and it will also be used by stakeholders and policymakers to allocate water to preserve the ecosystem.

Enhancing the functionality of environmental flows through an understanding of biophysical processes in the riverine landscape

While water resource managers and river scientists recognize the inherent interconnections among hydrology, river structure, biophysical processes and ecological patterns, management of environmental flows still pays insufficient attention to the ecological and geomorphological functionality of particular aspects of the flow regime. Implementation of more natural flow regimes has improved habitat conditions for native species in many moderately impaired rivers but mimicking a natural flow regime in heavily modified riverine landscapes cannot be expected to yield successful ecological outcomes unless such flows trigger functional processes. For example, the restoration of peak flows may not regenerate habitats if the river is starved of sediment or if the river channel is highly confined. High biodiversity is supported when variable flow regimes interact with spatially variable (heterogeneous) river channel and floodplain forms. In contrast, as rivers become homogeneous, biodiversity decreases when these dynamic spatiotemporal interactions are limited by flow alterations, blocked by channel levees, or perturbed by sediment deficit or surplus. Thus, the design of a more natural environmental flow regime without consideration of the implications for sediment transport and implicit recognition of channel–floodplain geomorphology is likely to have limited success in river management and restoration. To enhance the functionality of environmental flows, considerations of physical, biogeochemical, and ecological processes and the inherent heterogeneity of the riverine landscape must be included. A Functional Flows approach enhances the benefits from limited environmental flow allocations by focusing on the ecological and geomorphological functionality of particular aspects of the flow regime, considering geomorphic context, and emphasizing spatiotemporal diversity at key locations in the riverscape, such as adjacent floodplains or tributary junctions. In this paper, we outline and illustrate the concept of Functional Flows using a flow-chain model and provide two case study examples from Australia and the United States, where improvements in channel habitat and reconnection with the floodplain help to achieve the desired functionality of environmental flows.

Assessment of Environmental Water Requirement Allocation in Anthropogenic Rivers with a Hydropower Dam Using Hydrologically Based Methods—Case Study

Anthropogenic activities such as damming have caused an alteration in the natural flow regime in many rivers around the world. In this study, the role of constructing a hydroelectric dam on the natural flow regime of the Kor River, Iran, is investigated. Nine different methods, which fall into the category of hydrological methods, were used to determine the environmental water requirement (EWR) of the Kor River. In addition, two indices are introduced to evaluate the environmental flow allocation in anthropogenic rivers. The results show that although the supply of environmental flow in some months is in relatively acceptable conditions on average, there is a deficiency in the allocation of EWR in the range of 1.92–30.2% in the spawning period of the dominant fish species. The proposed indicators can provide a general picture of the status of environmental flow allocation in rivers where little ecological data is available and the hydrological regime has changed due to human activities, particularly in rivers with hydropower plants. Moreover, after the construction of the dam, no major floods have occurred in the river, which has led to the loss of the morpho-ecological balance in the river and disruption of the natural state of habitats. Therefore, the negative impact of dam construction on the environmental conditions of the river should be considered in the active management of the dam outlets.

An ecological interval two-stage fuzzy shadow price model for environmental flow allocation in the Shaying River Basin

Abstract In recent years, social water is pressurizing ecological water, causing the environmental flow to not be guaranteed and destroying the ecological environment. This research aims to coordinate social and natural water use to bring about optimal economic benefits, while ensuring environmental flow requirements. In this study, an interval two-stage fuzzy shadow price model (ITS-SPM) has been developed, which combines two-stage programming (TSP) and system of water value to optimize environmental flow. The ITS-SPM is mainly characterized as system benefits constituted by expected water resource benefits and water shortage penalty. This model has removed the uncertainties of economic data and environmental water demand (expressed fuzzy and interval). It has been found that adjusting the social water structure can effectively solve the problem of insufficient ecological flow. The ITS-SPM can make the adjustment of social water use more reasonable, which will produce benefits, unlike the current agricultural water reduction policy. Under the premise of guaranteeing optimal economic benefits, the added value of environmental water use in different scenarios is (social water structure adjustment) as follows: in 2020, it was expected that Shaying River water would increase by at least 13.49%; in 2025, it is expected to increase by at least 33.35%; in 2030, the increase will be by at least 57.54%; and in 2035, it will be by at least 77.50%.

Connectivity but not recruitment: Response of the fish community to a large‐scale flood on a heavily regulated floodplain

AbstractRecent environmental flow management in the Murray–Darling basin, south‐eastern Australia, has centred on restoring natural flooding regimes to meet ecological requirements, including the promotion of native fish recruitment, despite uncertainty about the effectiveness of managed environmental flooding. This study investigated recruitment responses of small‐bodied native and non‐native fish species to a large natural flood, supported by managed environmental flows in the Macquarie Marshes of the Murray–Darling basin. We surveyed the fish community within the heavily regulated, dryland floodplain system of the marshes, the year after breaking of the Millennium drought (2002–2009). During the spring–summer of 2010, the Macquarie Marshes experienced a one‐in‐10‐year flood, sustained by two environmental flow allocations, flooding 174,000 ha of floodplain. Five native species were collected across the nine study sites. Two non‐native species were particularly abundant during the flood, outnumbering the five native species in a ratio of 32:1, with Gambusia holbrooki the most abundant species, comprising 87% of all native and non‐native individuals captured. There was no marked effect of flood stage on the total abundance of small‐bodied native or non‐native fishes, but the composition of the fish community varied between surveys of the rising and falling phases of the flood. We did not capture any larval or post‐larval fish despite using a variety of suitable sampling methods. The lack of larvae in the Macquarie Marshes, following extensive flooding, most likely reflected the overall poor condition of native fish communities and low standing stocks of mature fish, resulting from deleterious long‐term effects of flow regulation exacerbated by drought. A gradual rebuilding of ecosystem health, fish health, and resilient fish populations by active management of environmental flows to impose more natural boom and bust dynamics may be needed to restore fish reproduction and recruitment in this regulated river.

Planning for Environmental Water Allocations: Hydrology - Based Assessment in the Awash River Basin, Ethiopia

The research is financed by the Egyptian Government through the Nile Sector bilateral cooperation project Abstract With expanding water demand due to rapid socio-economic growth and shrinking supplies due to pollution and climate change impact, there is an increasing strain on the water resources of the Awash river basin. Furthermore, flow alterations due to the existing and the ongoing water resources infrastructure projects may adversely impact the natural life cycle of aquatic ecosystems in the river basin. In order to manage these consequences, compensation releases or allocation of environmental flows may be mandatory and calls for the establishment of environmental flows framework in Ethiopia. In this study, the environmental flows at selected five existing and proposed dam sites in the Awash river basin were investigated using six worldwide used hydrology-based methods, viz.: Desktop Reserve Model (DRM), Global Environmental Flow Calculator (GEFC), Tennant, Tessman, 7Q 10 and Q 95 . The environmental flow volumes from the six methods were compared on mean annual, monthly average and monthly basis and it is found that the predictions from the DRM and GEFC are more reliable than the others. Comparative results indicate that minimum annual average flow rates of 4.4 m 3 /s (15 % of Mean Annual Flow (MAF)), 10.5 m 3 /s (19 % of MAF), 16.4 m 3 /s (22 % of MAF), 2.5 m 3 /s (17 % of MAF) and 24.2 m 3 /s (26 % of MAF) are required at the immediate downstream reaches of Melka kuntre, Koka, Awash Compensation, Kesem and Tendaho dams respectively. Accordingly, the annual average environmental flow throughout the basin varies from 15-26 % of the natural MAF. Although preliminary, being the first attempt in the Awash river basin, this study is expected to stimulate dialogue among experts and decision makers in Ethiopia. Keywords: EFR, EFA, Tennant, Tessman, Q 95 , 7Q 10 , DRM, GEFC Software, Awash DOI : 10.7176/JEES/9-11-08 Publication date: November 30 th 2019

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

AbstractEarly 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.

Tradeoffs between Water Uses and Environmental Flows: A Hydroeconomic Analysis in the Ebro Basin

Environmental water uses and their social values have been mostly overlooked in traditional water management over the last few decades, and recently, the maintenance of environmental flows has been considered a key issue in water policies. Addressing the more sustainable management of water resources involves introducing new water allocation policies. However, these policies are often associated with tradeoffs across sectors, stakeholders, and spatial locations. This study aims to evaluate the tradeoffs and political economy aspects of allocating water among economic water uses and environmental flows in water-scarce river basins. An empirical analysis has been conducted in the Ebro River basin (Spain) as a case study, where an intense debate on the environmental flow allocation of the Ebro mouth is taking place. The study uses a hydroeconomic model that includes the major water uses in the Ebro to analyze the effects of different water allocation policies under combinations of water availability and environmental flow scenarios. The results of this study highlight the importance of assessing the opportunity costs and political implications of reallocating water from economic activities to the environment under impending climate change impacts. Moreover, the results indicate that well-functioning water allocation policies should be not only economically efficient but also socially acceptable to reduce the likelihood of failure of water reallocation to the environment.

Assessing and planning future estuarine resource use: A scenario-based regional-scale freshwater allocation approach

Rapid urbanisation and industrial growth in South Africa increases the need for proactive allocation of freshwater resources on a regional scale. A nine-step method is described that sets long-term targets for water resource condition and future use with a focus on estuary water quantity and quality requirements. The approach specifically focuses on the environmental flow allocation to estuaries, nested within a broader, regional (multi-catchment and multi-estuary) water resource landscape. The method differs to most other approaches in that the responses of multiple estuaries to escalating future development in a region are coherently quantified (versus only considering a single estuary in a single catchment). A case study that assessed the health, biodiversity importance and resilience to current and future pressures of 64 estuaries is used to illustrate the method. Projected growth in the study area was integrated into a range of future dam development and wastewater discharge scenarios. The results showed that estuaries around the urban centres were in poor condition, but those in the more rural areas in a more natural state. As a result of their small size, most of the estuaries in the region had little resilience to changes in freshwater quantity and nutrient loading. In contrast, the larger systems, targeted for dam development, only showed sensitivity to water abstraction during low-flow periods when base-flow reduction caused mouth closure and changes in nutrient processes. Broadly, the approach aimed to find a balance between ecological requirements and socio-economic development, which meant that maintaining larger systems in relatively good condition would be at the expense of smaller systems that are already in a poor condition. The approach developed was successful in quantifying the responses of multiple estuaries to escalating future pressures on a regional scale, and could be replicated to assist in managing water resources elsewhere in data-limited environments.

Simulating the effect of environmental flow duration on seedling emergence from riparian seed banks of the Upper Hunter River, New South Wales

AbstractPassive riparian revegetation techniques are important tools in river rehabilitation. However, the utility of the sediment seed bank as a passive riparian regeneration option is poorly understood. After modelling a range of flows for field‐surveyed cross sections, a glasshouse seedling emergence experiment was undertaken to compare the effects of simulated flow duration on seedling emergence of desirable riparian species that occur on benches of the gravel‐bedded Hunter River near Muswellbrook, New South Wales. The duration of inundation did have an effect (although not always significant) on seed germination for most species. The most successful simulated flood conditions differed among species, with the control treatment (no inundation) resulting in the most germination for only two of the 10 species examined. These findings suggest that although environmental flows for the sole purpose of stimulating the riparian seed bank in order to facilitate regeneration of desirable riparian species would be largely ineffective and complicated by differing inundation responses among species, seed bank stimulation using environmental flows could be a value‐added benefit from flows allocated for other purposes. As such, consideration of flow duration is worthy of inclusion in environmental flow allocation planning.

Centralized versus distributed reservoirs: an investigation of their implications on environmental flows and sustainable water resources management

Abstract. Storage of surface water is widely regarded as a form of insurance against rainfall variability. However, creation of surface storage often endanger the functions of natural ecosystems, and, in turn, ecosystem services that benefit humans. The issues of optimal size, placement and the number of reservoirs in a river basin – which maximizes sustainable benefits from storage – remain subjects for debate. This study examines the above issues through the analysis of a range of reservoir configurations in the Malwatu Oya river basin in the dry zone of Sri Lanka. The study produced multiple surface storage development pathways for the basin under different scenarios of environmental flow (EF) releases and reservoir network configurations. The EF scenarios ranged from “zero” to “very healthy” releases. It is shown that if the “middle ground” between the two extreme EF scenarios is considered, the theoretical maximum “safe” yield from surface storage is about 65–70 % of the mean annual runoff (MAR) of the basin. It is also identified that although distribution of reservoirs in the river network reduces the cumulative yield from the basin, this cumulative yield is maximized if the ratio among the storage capacities placed in each sub drainage basin is equivalent to the ratio among their MAR. The study suggests a framework to identify drainage regions having higher surface storage potential, to plan for the right distribution of storage capacity within a river basin, as well as to plan for EF allocations.

Analysis of Effective Environmental Flow Release Strategies for Lake Urmia Restoration

Saline lakes have diminished considerably due to large-scale irrigation projects throughout the world. Environmental flow (EF) release from upstream reservoirs could help conserve and restore these lakes. However, experiences from regions lacking environmental legislation or with insufficient water resources management show that, despite EF allocation, farmers tend to use all available water for agriculture. In this study, we employed a new method for designing environmental flow release strategies to restore desiccated terminal lakes in arid and semi-arid regions with intensive cultivation within the catchment. The novelty of the method is that it takes into account farmers’ water use behavior and the natural flow regime in upstream systems to design an optimum monthly EF release strategy for reservoirs. We applied the method to the water resource system of Lake Urmia, once the largest saline lake in the Middle East and now one of the most endangered saline lakes in the world. The analysis showed that the EF released is exploited by lowland farmers before reaching Lake Urmia and that inflow to the lake from some rivers has decreased by up to 80%. We propose a new EF release strategy that requires a considerable change in practice whereby water is released in the shortest possible time (according to reservoir outlet capacity) during the period of lowest irrigation demand in winter. Restoring the lake to minimum ecological level would require 2.4–3.4 km3 EF allocation by different methods of release based on the recent condition (2002–2011) of the lake.

Short‐ and long‐term evapotranspiration rates at ecological restoration sites along a large river receiving rare flow events

AbstractMany large rivers around the world no longer flow to their deltas, due to ever greater water withdrawals and diversions for human needs. However, the importance of riparian ecosystems is drawing increasing recognition, leading to the allocation of environmental flows to restore river processes. Accurate estimates of riparian plant evapotranspiration (ET) are needed to understand how the riverine system responds to these rare events and achieve the goals of environmental flows. In 2014, historic environmental flows were released into the Lower Colorado River at Morelos Dam (Mexico); this once perennial but now dry reach is the final stretch to the mighty Colorado River Delta. One of the primary goals was to supply native vegetation restoration sites along the reach with water to help seedlings establish and boost groundwater levels to foster the planted saplings. Patterns in ET before, during, and after the flows are useful for evaluating whether this goal was met and understanding the role that ET plays in this now ephemeral river system. Here, diurnal fluctuations in groundwater levels and Moderate Resolution Imaging Spectroradiometer (MODIS) data were used to compare estimates of ET specifically at 3 native vegetation restoration sites during 2014 planned flow events, and MODIS data were used to evaluate long‐term (2002–2016) ET responses to restoration efforts at these sites. Overall, ET was generally 0–10 mm d−1 across sites, and although daily ET values from groundwater data were highly variable, weekly averaged estimates were highly correlated with MODIS‐derived estimates at most sites. The influence of the 2014 flow events was not immediately apparent in the results, although the process of clearing vegetation and planting native vegetation at the restoration sites was clearly visible in the results.

River flow availability for environmental flow allocation downstream of hydropower facilities in the Kafue Basin of Zambia

The Government of the Republic Zambia (GRZ) will install a new hydropower station Kafue Gorge Lower downstream of the existing Kafue Gorge Station (KGS) and plans to start operating the Itezhi-Tezhi (ITT) hydropower facility in the Kafue Basin. The Basin has significant biodiversity hot spots such as the Luangwa National park and Kafue Flats. It is described as a Man-Biosphere reserve and the National Park is a designated World Heritage Site hosting a variety of wildlife species. All these natural reserves demand special protection, and environmental flow requirements (e-flows) have been identified as a necessary need to preserve these ecosystems. Implementation of e-flows is therefore a priority as Zambia considers to install more hydropower facilities. However before allocation of e-flows, it is necessary to first assess the river flow available for allocation at existing hydropower stations in the Kafue Basin. The river flow availability in the basin was checked by assessing the variability in low and high flows since the timing, frequency and duration of extreme droughts and floods (caused by low and high flows) are all important hydrological characteristics of a flow regime that affects e-flows. The river flows for a 41 year monthly time series data (1973–2014) were used to extract independent low and high flows using the Water Engineering Time Series Processing Tool (WETSPRO). The low and high flows were used to construct cumulative frequency distribution curves that were compared and analysed to show their variation over a long period. A water balance of each hydropower station was used to check the river flow allocation aspect by comparing the calculated water balance outflow (river flow) with the observed river flow, the hydropower and consumptive water rights downstream of each hydropower station. In drought periods about 50–100 m3/s of riverflow is available or discharged at both ITT and KGS stations while as in extreme flood events about 1300–1500 m3/s of riverflow is available. There is river flow available in the wet and dry seasons for e-flow allocation at ITT. On average per month 25 m3/s is allocated for e-flows at ITT for downstream purposes. On the other hand, it may be impossible to implement e-flows at KGS with the limited available outflow (river flow). The available river flow from ITT plays a very vital role in satisfying the current hydropower generating capacity at KGS. Therefore, the operations of KGS heavily depends on the available outflow (river flow) from ITT.

Simulation Modeling to Secure Environmental Flows in a Diversion Modified Flow Regime

AbstractThis paper describes the development and application of a spreadsheet model to evaluate effects of water management on diversion modified flow regimes, enabling the exploration of novel ways to meet proposed environmental flow standards. Mill Creek, a northern California river with an altered flow regime that impacts aquatic species, was used as a case study. Test cases examined how water management alternatives, such as groundwater pumping, water rights transfers, and water exchange agreements, can improve environmental flow allocations given irrigation water demands. Four test cases include passage flows for Chinook salmon and steelhead trout, a minimum instream flow, 80% of natural flow, and a spring recession flow with functional flow components. The model identified late October as consistently water-scarce, even in wet years. These analyses suggest that fall shortages for fish migration could be eliminated through a water exchange agreement combined with use of wells. All cases except the mi...

Muddied Waters: The Case for Mitigating Sediment and Nutrient Flux to Optimize Restoration Response in the Murray-Darling Basin, Australia

The waters of the Murray Darling Basin, Australia, have endured multiple stressors for more than a century. Detectable salinisation impacts are evident from 1880 CE and elevated fluxes of sediments and nutrients are now widespread. Most wetlands examined paleolimnologically have shown increased sedimentation rates or have lost aquatic plant communities due to the shading effect of increased turbidity, prompting the observation that the waterways of the Murray Darling Basin are among ten Australian ecosystems most at risk from tipping points. This post-European heightened sediment flux threatens the potential ecological recovery from the application of scarce and expensive environmental water. Nutrients and fine sediments are implicated as drivers of regime shifts that advantage phytoplankton and inhibit the growth of productive macrophyte beds. However, with the river channels identified as likely sources of sediments and sediment-bound phosphorous, it remains possible that the documented ecological changes represent an ongoing response from continued doses from the River. Syntheses of multiple paleolimnological records provide evidence for the management focus to be on sediment supply to maximise the ecological benefit from environmental flow allocations. Here we use paleolimnology to examine in detail the nature and magnitude of the response in a subset of 17 wetlands, to propose means of optimising the ecological bounce from the release of river waters, encumbered with high doses of sediments and nutrients, to wetlands and floodplains.

A simulation tool for managing environmental flows in regulated rivers

Environmental flows provide river flow regimes to restore and conserve aquatic ecosystems, creating considerably different demands compared to conventional water extraction. With increasing incorporation of environmental flows in water planning worldwide, governments require decision support tools to manage these flows in regulated rivers. We developed the Environmental Water Allocation Simulator with Hydrology (eWASH), a fast, flexible and user-friendly scenario-based hydrological modelling tool, supporting environmental flow management decisions for single- or multi-reservoir systems. Environmental flow demands and management rules are easily specified via the graphical user interface, and batch processing functions aid in uncertainty assessment. eWASH modelled main processes of complex regulated rivers and the tool is widely applicable. We calibrated eWASH for the Gwydir and Macquarie Rivers of Australia's Murray–Darling Basin. Modelled monthly environmental flow allocations exhibited Nash–Sutcliffe efficiencies of 0.55 for the Gwydir and 0.72 for the Macquarie catchments respectively when validated.

Development of monthly optimal flow regimes for allocated environmental flow considering natural flow regimes and several surface water protection targets

A key question in environmental flow (EF) allocation from reservoirs is the annual distribution of flow. Flow release from reservoirs can be partly supplemented or compensated for by natural runoff from the downstream (residual) part of the catchment. Here we present a new hydrological approach to estimate the optimal intra-annual flow regime for EF which also considers water inflow from the downstream residual sub-catchment. First, the standard intra-annual regimes at downstream target points are defined for reference. This annual hydrograph is then divided into two main parts: a variable hydrograph (related to upstream of the reservoir and the point of EF release) and a residual hydrograph (associated with downstream catchment runoff). Based on the magnitude of the residual hydrograph, the allocated EF is estimated by optimization. This method provides a first estimate of the intra-annual EF regime based on hydrological data, but biological, geomorphological, and other effective components can also be included in the optimization procedure. To test the method, the intra-annual EF regime was estimated for four different points of the Kor river in southern Iran. The results showed that the best fit between the EF regime and the natural river regime at the reference point depended on the magnitude of allocated flow and the allocation site in the catchment.