Environmental Water Allocations Research Articles

Reliability and resilience of environmental flows under uncertainty: reconsidering water year types and inconsistent flow requirements in California

Abstract Environmental water allocation in California is a complex legal process involving various government agencies and stakeholders. E-flow requirements can be based on annual runoff typologies called water year types (WYTs), which dictate water volume, timing, and duration. In this study, we examined hydropower licensing documents of the major water and power projects in the Central Sierra Nevada to catalog e-flow requirements by WYT. In this study case, we identify how WYT classification systems and categories vary across and within different basins. Additionally, we assessed the impacts of climate change on hydrology, the frequency of WYTs identified, and the reliability and resilience of e-flows using future projections (2031–2060) of 10 Global Circulation Models (GCMs). We then propose a potential adaptation strategy using a 30 year moving percentiles approach to recalculate WYTs. We identified eight WYT classifications systems were identified, and their WYT distributions statistically significantly changes across all GCMs, even though most GCMs indicate no statistically significant change in hydrology. Disparities in future impacts are observed among and within hydropower projects, with some river reaches showing negative impacts on reliability and resilience. The adaptation strategy can generally boost resilience and improve reliability, but simply updating existing WYT thresholds without flexible regulatory frameworks reconsidering WYTs and e-flows thresholds, may not yield substantial improvements. Challenges in managing e-flows in California within regulatory and hydroclimatic contexts are intricate due to the lack of standardized approaches, leading to inconsistencies and potential conflicts among stakeholders, that will likely be exacerbated by climate change. Thus, we emphasize that targeted, site-specific, and adaptive management strategies are crucial, besides the need for a harmonized and consistent approach to defining and applying WYT categories and methods and/or e-flow assessments.

Assessment of environmental water strategies for improving fringing vegetation health by modelling vegetation condition in a connected floodplain lakes system

AbstractAcross the globe, environmental water has been allocated with the purpose of preserving the health and vitality of floodplain vegetation. However, the influences of environmental water volume and environmental water delivery strategies have not been studied widely because of shortage of on‐ground monitoring data. Remotely sensed data can bridge this gap by providing long‐term and continuous information; Landsat imagery from 1988 to 2020 was used in this research. We used the normalized difference vegetation index (NDVI) as an indicator of physiological condition of lake‐fringing trees on the Hattah Lakes floodplain, south‐east Australia. We employed the random forest (RF) regression method to model the relationship between NDVI and various climate and hydrological factors, such as the volume of water delivered to the connected lakes system as environmental water allocations or natural floods. The RF models performed well overall, with a mean R2 value of 0.73. The analysis identified the monthly total of environmental water delivered 3 months prior to the Landsat image date as a more crucial factor than natural floods over the same period for driving vegetation condition. Environmental water from 3 months previously exerts a positive influence on NDVI until the volume reaches a specific threshold. We have observed significant improvements in floodplain vegetation through the current environmental water strategy, particularly since the construction of pumping infrastructure in 2013. We suggest that managers aim to inundate the lake fringing area every 3 years, specifically from August to September, by delivering environmental water up to the modelled threshold volume. Finally, the use of infrastructure has proven to be an effective and efficient method for irrigating floodplain lakes, leading to improvements in vegetation condition while conserving water resources.

Vegetation and inundation characteristics of waterbird breeding sites in the Murray–Darling Basin, Australia

Context The Murray–Darling Basin serves as a crucial habitat for aggregating waterbirds; however, decades of large-scale regulation of rivers and water resources have adversely affected waterbird breeding in the Basin. Aims To understand the characteristics of wetlands that attract and support aggregating waterbirds, focusing on identifying environmental conditions conducive to waterbird breeding. Methods In total, 52 wetland sites across the Murray–Darling Basin, with high waterbird abundances, were identified, of which 26 supported waterbird breeding. Classification models were developed using temporally static and dynamic environmental datasets to discern wetland characteristics associated with waterbird breeding. Key results Analyses showed that wetlands supporting waterbird breeding contained a maximum inundated area of ‘other shrublands’ exceeding 3.635 km2 and variation in normalised difference vegetation index, possibly reflective of a ‘boom and bust’ ecological response. Conclusions Understanding the habitat requirements of wetlands to prompt waterbird breeding is critical for effective environmental water management and conservation strategies. Implications Targeted wetland management and environmental water allocation to support waterbird breeding populations in the Murray–Darling Basin is essential for continued waterbird breeding. There is a need for continued research to refine management strategies and ensure the long-term sustainability of waterbird populations in the face of ongoing environmental challenges.

Change in centre of timing of streamflow and its implications for environmental water allocation and river ecosystem management

Timing of delivery of environmental water is essential for restoring and conserving riverine ecosystems. However, change in the timing of occurrence of streamflow and its implications on environmental water allocation and river ecosystems are often ignored in current environmental water research and management. We adopted the centre of timing approach to analyse the change in the occurrence of streamflow due to climate change (through a change in rainfall) and river operations (flow regulation and diversion) in the Goulburn-Broken catchment, Victoria, Australia. It was found that annual streamflow in the catchment declined by an average of 47%, while centre of timing increased by an average of 36%. These changes were 52% attributable to rainfall decline and 48% to river regulation. A decline in annual streamflow (35%) and an increase in centre of timing (21%) across the Goulburn River would be observed by 2050 as an impact of climate change. Current management efforts should be directed at reversing the change in centre of timing to support the sustainable management of riverine systems. The Goulburn-Broken catchment is typical of managed catchments in many areas of the world with forecast rainfall reduction, and the findings are likely to be widely applicable.

Community perceptions of environmental water: a review

SummaryAllocation of water specifically to the environment (often dubbed ‘environmental water’ or ‘environmental flows’) can be contentious within government, among irrigators and between community members. The reduction in supply of fresh water has led to questions surrounding the efficiencies and ecological value of securing these adequate flows for waterways. This literature review examines the evidence on these perceptions of environmental water allocations, focusing foremost on general public, irrigator, Indigenous and decision-maker perspectives. Existing studies are predominantly in Global North areas such as Australia, Canada and the USA. Two themes featured strongly in the papers: the importance of personal values in the acceptance of environmental water and the perception of fairness in environmental water allocation processes. Although the research area has been expanding, there is still limited representation in types of study, disciplinary backgrounds and study locations, and as such many research opportunities remain.

Hydrology method for environmental flows assessment of Johor River Basin under regulated and non-regulated conditions

This paper evaluates the capability of hydrology method for environmental flow (Eflow) assessment of Johor river basin under non-regulated and regulated conditions due to dam construction. Daily river flow data from 1971 to 2017 was used for the assessment. Generalized extreme value distribution was applied in order to estimate exceedance probabilities associated with historical observation data at different return periods. Environmental water allocations of the river at different ecological conditions were estimated using the intra-annual and inter-annual flows. This study has estimated the hydrological yearly conditions (very dry, dry, average and wet) for the river basin. Moreover, the method has also successfully proposed the environmental water allocations to achieve the desired ecological conditions, which are very good ecological (Eflow class A), good ecological (Eflow class B), medium ecological (Eflow class C), and deficient ecological conditions (Eflow class D). In general, the proposed method has been capable and acceptable for the assessment of Eflow of Johor river basin in line with sustainable water management goal.

Evidence-based Risk Assessment of Ecological Damage due to Groundwater Abstraction; the Case of Doñana Natural Space, Spain

Many regions of the world are facing mounting water stress as competition increases for this vital resource that may become scarcer under future climates. More water is being allocated to our needs for food, public supply, hydro-electric power and industrial goods to support growing populations and mounting life-style expectations. To achieve this, less water is often being retained for water-dependent ecosystems. Environmental protection agencies and conservation organisations have highlighted the resulting threat to freshwater biodiversity and associated ecosystem services that support human livelihoods and well-being. Careful assessments are therefore required to advise on the optimum allocation of water and to determine the risk of developments that require redistribution of water resources.Along the northern fringes of the Guadalquivir River delta and estuary in southern Spain about 40% of all jobs derive from agriculture. The production of olives, fruit trees, rice and berries is a major component of the local economy producing large exports, but it requires significant water from local rivers and the underlying aquifers. The economy is also reliant on tourism that brings many thousands of people to the area in the summer for which groundwater abstraction is augmented. The delta is the location of the Doñana wetland complex of lagoons, marshlands, fixed and mobile dunes that was designated as a Biosphere Reserve by UNESCO in 1980, as wetland of international importance (Ramsar Site) under the Convention on Wetlands in 1982 and as a World Heritage Site by UNESCO in 1994. Fears have been expressed that increasing human water use is putting the wetlands at risk of drying out, despite efforts by the river basin authority to limit abstraction to sustainable levels.This paper reports on a methodology that analyses best available eco-hydrological scientific knowledge together with information on the likely success of abstraction control measures to determine the risk to the wetland ecosystem of current and future planned water allocation. The method was applied to Doñana by the joint UNESCO/IUCN/Ramsar Reactive Monitoring mission to in 2020. The results are also provided in the paper, which raised many important scientific and related political, legal and social issues concerning the impacts of water withdrawals on the ecology of the wetlands. The methodology has wide application to environmental water allocation assessments.

Securing the Environmental Water Requirements of Seasonally Ponding Wetlands: Partnering Science and Management through Benefit Sharing

Although environmental flow regime assessments are becoming increasingly holistic, they rarely provoke water managers to enact the adaptive water reallocation mechanisms required to secure environmental water for wetlands. The conditions that cause science-based environmental flow assessments to succeed or fail in informing the management of environmental water requirements remain unclear. To begin to resolve these conditions, we used process tracing to deconstruct the sequence of activities required to manage environmental water in four case studies of seasonally ponding wetlands in Mediterranean and Mesoamerican watersheds. We hypothesized that, when the flexibility and equitability of the socioeconomic system do not match the complexity of the biophysical system, this leads to a failure of managers to integrate scientific guidance in their allocation of environmental water. Diagnostic evidence gathered indicates that science-management partnerships are essential to align institutional flexibility and socioeconomic equitability with the system’s ecohydrological complexity, and thus move from determination to reallocation of environmental water. These results confirm that institutions e.g., river basin organizations need to be supplemented by motivated actors with experience and skill to negotiate allocation and adaptive management of environmental water. These institutional-actor synergies are likely to be especially important in water scarce regions when the need to accommodate extreme hydrological conditions is not met by national governance capacity. We conclude by focusing on benefit sharing as a means to better describe the conditions for successful science-based environmental flow assessments that realize productive efficiency in environmental water allocation i.e., recognition of multiple values for both people and ecosystems.

Assessing alterations of water level due to environmental water allocation at multiple temporal scales and its impact on water quality in Baiyangdian Lake, China

Lakes in arid/semiarid regions face problems of insufficient inflow and degradation of water quality, which threaten the health of the lake ecosystem. Baiyangdian Lake (BYDL), the largest lake in the North China Plain, is confronted with such challenges. The objective of this study was to improve understanding of how changes in water level influence water quality in the BYDL at different temporal scales, especially related to implementations of intermittent environmental water allocation activities in the past two decades, by using data on monthly lake water level, climate factors of precipitation and temperature, and lake water quality. The Mann-Kendall method and continuous wavelet analysis revealed that the lake water level shows a significant decreasing trend after 1967, and the period of 16-year was identified as the principal period for 1950–2018. Based on cross-wavelet transform and wavelet coherence analysis, the periodic agreement and coherence between water level and climatic factors decreased after 1997, when environmental water allocations started, indicating that the influences of climatic factors, i.e., precipitation and temperature, became weak. By utilizing the cross-wavelet transform and wavelet coherence analysis methods, the relationships between lake water level and water quality parameters of chemical oxygen demand, ammonia nitrogen, total nitrogen, and total phosphorus were investigated. We found that the change in source and amount of environmental water allocation is one possible reason for the temporal evolution in joint variability between lake water level and water quality. Meanwhile, a dilution effect of freshwater allocated to BYDL was detected in the time-frequency domain. However, the result also indicates that the driving mechanism of water quality is complex due to the combined impacts of water allocation, nonpoint source pollution in the rainy season, and nutrient release from lake sediment. Our findings improve the general understanding of changes in water level in lakes located in arid and semiarid regions under climate change and intensive human activities, and also provide valuable knowledge for decision making in aquatic ecosystem restoration of BYDL and other similar lakes.

The terminal lakes of the Murray River, Australia, were predominantly fresh before large-scale upstream water abstraction: Evidence from sedimentary diatoms and hydrodynamical modelling

The Murray River is Australia's longest river, draining the continent's largest exoreic catchment. The river is Australia's most economically valuable, but is highly degraded by water extraction. The Murray River's terminal lakes, Lakes Alexandrina and Albert, formed following the mid-Holocene marine transgression. These lakes are part of one of the most ecologically important wetland ecosystems on the Australian continent and are recognised as internationally significant by the Ramsar Convention. As a result of upstream water extraction, the Lower Lakes are threatened by rising salinity. To combat this threat, water is allocated to maintain the Lower Lakes as freshwater ecosystems. This practice is part of the Murray-Darling Basin Plan, one of the largest environmental water allocation plans in the world. The water allocations and the natural history of the Lower Lakes are the subject of academic and public debate, since the water would otherwise be used for consumptive purposes, particularly irrigated agriculture, upstream. Recent modelling postulated that the lakes were saline for much of the period between 8500 and 5000 years ago. However, using new sedimentary diatom and hydrodynamic modelling evidence, we demonstrate that the Lower Lakes were fresh for most of this time, particularly after 7200 years ago. Elevated Murray River discharge between 7200 and 6600 years ago prevented sea water ingress, despite sea levels +1 m higher than present. After 6600 years ago, the lakes remained predominately fresh. Current management is, therefore, consistent with the lakes' history before European colonisation.

Evaluating the influence of different environmental water allocation schemes on the water level of a typical shallow lake in semiarid regions: From the perspective of an integrated modeling approach

Many lakes in semiarid regions around the world rely on environmental water allocation to maintain the health of the lake ecosystem. However, under changing environments, the competition for water resources between human society and natural ecosystems has intensified. How to manage environmental water allocation more reasonably and precisely has become an important issue. The largest lake on the North China Plain, Baiyangdian Lake (BYDL), is a typical lake facing such challenges. To provide feasible strategies for sustainable water allocation to BYDL, with the proper parameterization of hydrological processes, this study developed a 10-day temporal scale lake water level prediction model to quantify how environmental water allocation regulates the BYDL water level under different hydroclimatic conditions. Evaluation of model performance revealed that environmental water allocation rather than natural climatic periodicity dominates the variation in the BYDL water level. The model structure could be further improved with consideration of more detailed observations of both the surface runoff entering BYDL and the water area beneath the canopy of the reeds in BYDL. Analysis of 72 model simulation scenarios indicated that water allocations from multiple sources are indispensable and that the water resources that guarantee maintaining the BYDL water level within the ecologically suitable range vary substantially under different hydroclimatic conditions. More elaborate allocation plans are required both to improve the water quality and health of the aquatic ecosystem of BYDL and to reduce the risk of flooding. The findings from this study are valuable for guiding the implementation of environmental water allocations to lakes in semiarid regions worldwide.

Pareto Optimality and Compromise for Environmental Water Management

AbstractWater management usually considers economic and ecological objectives, and involves tradeoffs, conflicts, compromise, and cooperation among objectives. Pareto optimality often is championed in water management, but its relationships with the mathematical representation of objectives, and implications of tradeoffs for Pareto optimal decisions, are rarely examined. We evaluate the mathematical properties of optimized tradeoffs to identify promising regions for compromise, suggest strategies for reducing conflicts, and better understand whether decision‐makers are more or less likely to cooperate on environmental water allocations. Cooperation and compromise among objectives can be easier when tradeoff curves are concave and more adversarial when tradeoff curves are convex. “Knees,” or areas with maximum curvature, bulges, or breakpoints in concave Pareto frontiers, suggest more promising areas for compromise. Evaluating the shape of Pareto curves based on each objective's performance function can screen for the existence of knees amenable to compromise. We explore water management and restorations actions that improve and shift the location and prominence of knees in concave Pareto frontiers. Connecting river habitats and other non‐flow management actions may add knees on locally concave regions of Pareto frontiers. Managing multiple streams regionally, rather than individually, can sometimes turn convex local tradeoffs into concave regional tradeoffs more amenable to compromise. Overall, this analysis provides a deep investigation of how the shape of tradeoffs influences the range and promise of decisions to improve performance, and illustrates that management actions may encourage cooperation and reduce conflict.

Assessing environmental water requirement for groundwater-dependent vegetation in arid inland basins by combining the copula joint distribution function and the dual objective optimization: An application to the Turpan Basin, China

Preserving groundwater-dependent terrestrial ecosystems through environmental water allocation is critical for sustainable development in arid inland basins. Assessing the environmental water requirement is challenging due to the complex relationship between vegetation growth and groundwater depth. This study proposed a new assessment method by combining the copula joint distribution function and the dual objective optimization. The copula joint distribution function was used to describe the relationship between vegetation and groundwater depth instead of the traditional regression analysis. Given an ecological protection target, the conditional probability of achieving the target was estimated using the copula joint distribution. The groundwater depth interval with relatively high probability was suitable for vegetation growth and correspondingly conducive for ecological protection. In addition to ecological protection, the socio-economic water requirement was incorporated into the environmental water assessment, resulting in a dual optimization problem that could be resolved by the ideal point method. The optimization analysis revealed a groundwater depth with a high probability of successful ecological protection and low groundwater evapotranspiration to balance vegetation and human demands for groundwater. The proposed method of environmental water assessment by combing copula joint distribution function and dual objective optimization was applied in the Turpan Basin, an arid inland basin in Northwest China. The environmental groundwater depth ranged between 6 and 20 m, and the optimized interval was 7–8 m. The optimal environmental groundwater depth resulted in a probability of 0.46 to achieve the ecological protection target and annual evapotranspiration of 983 mm. The proposed method was practical and reliable and could be an effective tool for assessing the environmental water requirement of groundwater-dependent vegetation in arid inland basins.

Determining water requirements for Black Box (Eucalyptus largiflorens) floodplain woodlands of high conservation value using drip‐irrigation

AbstractBlack Box (Eucalyptus largiflorens F. Muell.), is a keystone tree species of lowland semi‐arid floodplain ecosystems in south‐eastern Australia. E. largiflorens woodlands are of high conservation value and threatened by climate change‐induced drought and irrigation water diversions due to their location on upper floodplain areas where flood frequency has declined. Water requirements of E. largiflorens have not been well quantified using empirical data. Accordingly, knowledge gaps exist in relation to volumes of environmental water required to maintain and improve ecological condition for disconnected floodplain woodlands. To further assist conservation and water resource management, we tested the use of drip irrigation to provide a variety of water regimes to experimental plots in order to monitor tree responses. Water was provided via irrigation delivery across four regimes representing known volumes of water, referred to as an environmental water provision, applied over a 22‐week period for two Austral summers. Benefits to trees were identified by measuring transpiration and plant water status using sap flow sensors and a Scholander pressure chamber, respectively. Results indicate that volumes of 0.3, 0.4, 0.7 and 0.8 ML increased transpiration and improved plant water status in comparison to a control, with delivery recommended to commence early autumn. Greater volumes (1.4 ML), substantially increased transpiration and improved water status, especially when delivered at a rate of ~25 mm week−1 compared to a monthly 'burst' which broadly represented natural, sporadic summer rainfall in the region. For an environmental watering provision of 25 mm week−1, ~178 ha of E. largiflorens woodland can be watered with a 1 GL environmental water allocation. The study methods presented are relevant worldwide and our results further the collective understanding of the benefits environmental water provides to E. largiflorens.

Planktonic Metabolism and Microbial Carbon Substrate Utilization in Response to Inundation in Semi‐Arid Floodplain Wetlands

AbstractIn semi‐arid floodplain wetlands, planktonic metabolism, a balance of gross primary productivity of phytoplankton (GPP) and planktonic respiration (PR), may be affected by hydrology, geomorphology, carbon, and microbial communities. Understanding relationships between these factors helps develop effective water and land management plans for these wetlands. In this study, variations in planktonic metabolism and microbial carbon substrate utilization were investigated in the semi‐arid floodplain wetlands of the Macquarie Marshes, south‐eastern Australia, by comparing three geomorphologically distinct zones with different historical inundation frequencies (zones 1: moderate, 2: low, and 3: very low). Floodplain soil samples collected from each zone were inundated artificially in controlled laboratory conditions. GPP and PR were determined using biological oxygen demand methods. Biolog EcoPlates™ were used to assess microbial utilization of carbon substrate. Among the zones examined, zone 1 had the highest GPP and lowest PR, while zone 3 had the lowest GPP and highest PR. GPP/PR showed zones 1 and 2 autotrophic, and zone 3 heterotrophic. EcoPlates showed the highest and lowest microbial activity in zone 3 and zone 1 respectively, indicating a strong link between microbial carbon substrate utilization and PR for heterotrophy in the rarely inundated zone. Inundation of drier wetland zones may lead to a large pulse in PR, at least for a short period of time, potentially leading to anoxic water events. When making decisions for environmental water allocations, the antecedent hydro‐geomorphological and microbial condition of the targeted wetlands should be considered to help predict expected aquatic ecosystem responses.

Morphodynamic modelling of dryland non-perennial riverscapes, with implications for environmental water allocation

Reach-scale river restoration or environmental water allocation (EWA) exercises typically address the magnitude and temporal dynamics (frequency, duration, timing, rate of change) of flows required to sustain desirable ecological conditions along a river. The role of geomorphology in this process is to broaden the gaze beyond flows to consider larger and longer-term interactions between valley lithological structure, and the feed and fate of flow-sediment mixtures. This paper proposes the integration of numerical morphodynamic modelling in evaluations of environmental water requirements for non-perennial riverscapes (channel–riparian–floodplain environments). The paper presents a methodological framework, and proof of concept case study from the Touws River, South Africa, for the application of morphodynamic modelling in EWA. The paper illustrates operational approaches to modelling the complexity of dryland mixed bedrock-alluvial (and mixed-load) riverscapes with highly variable non-perennial flow regimes, including an approach to generating initial bed conditions for numerical experiments by ‘morphodynamic spin-up’, and approaches to synthesising and presenting numerical experiment output in the form of a dynamic range of potential variability in metrics of physical habitat suitability and diversity, and disturbance/renewal regimes. Such efforts can assist in enhancing field observations and testing field-based hypotheses of flow-sediment regime–physical habitat associations, extending the timescales of analysis beyond field observation, and constraining uncertainty about the dynamic range of variability in responses to predicted future flow-sediment regime modifications. Further research is needed to develop growth models appropriate for key non-perennial river vegetation types, to support biomorphodynamic modelling of geomorphology–vegetation interactions, and to determine or predict appropriate inlet sediment concentrations for historical and future modification scenarios.

Assessing Effects of Flow Regulation and an Experimental Flow Pulse on Population Size Structure of Riverine Fish with Contrasting Biological Characteristics.

Despite effects of dams and water extraction on river hydrology and consequences of aquatic ecosystems being broadly appreciated, empirical evidence is lacking for many regions (e.g. subtropics). Evidence is necessary to determine (i) the circumstances where environmental flows are necessary to protect or improve ecological processes and (ii) what hydrological events are required to achieve those ecological characteristics. Here, temporal variation in the size structure of two small-bodied fish species with contrasting ecological characteristics (Australian smelt, Cox's gudgeon) was compared between two pairs of unregulated and regulated rivers in subtropical Australia. Frequency of in-channel flow pulses in each regulated river was lower compared to paired unregulated rivers. An experimental flow pulse was delivered to one regulated river to assess the ecological outcomes of in-channel flow pulses and inform future decisions about the use of environmental water allocations. Temporal changes in the population size structure of both species were similar between unregulated and regulated rivers and showed no response to the experimental pulse. While the experimental flow briefly suppressed in-stream temperature, changes in temperature were not beyond the thresholds at which spawning occurs or the thermal tolerances for either species. Similar population structure between unregulated and regulated rivers can be attributed to the magnitude of flow regulation being insufficient to alter the physico-chemical conditions, habitat and trophic mechanisms supporting population dynamics during the study period. This suggests current regulated hydrology is protective of local populations of Australian smelt and Cox's gudgeon in these study rivers.

Evaluating the Ecological Benefits of Management Actions to Complement Environmental Flows in River Systems.

Globally, many river systems are under stress due to overconsumption of water. Governments have responded with programmes to deliver environmental water to improve environmental outcomes. Although such programmes are essential, they may not be sufficient to achieve all desired environmental outcomes. The benefits of environmental water allocation may be improved using 'complementary measures', which are non-flow-based actions, such as infrastructure works, vegetation management and pest control. The value of complementary measures is recognised globally, but their ecological benefits are rarely well understood, either because there is limited experience with their application, or the importance of context- and location-specific factors make it difficult to generalise benefits. In this study, we developed an approach to evaluate complementary measures at different levels of detail as a mechanism to aid decision-making. For systems that require a rapid, high-level evaluation, we propose a score-based multi-criteria benefit assessment module. If more ecological detail is necessary, we outline a method based on conceptual models, expert elicitation and probability assessment. These results are used to populate a cumulative benefit assessment tool. The tool evaluates the benefits of proposed measures in the wider context by including variables such as flow, dependence on ongoing maintenance and additional ecological values. We illustrate our approach through application to the Murray-Darling Basin, Australia. As many water recovery programmes mature into their evaluation phases, there is an increasing need to evaluate the ecological benefits of including complementary measures in the toolkit available to policy makers.

Frequency of occurrence of flow regime components: a hydrology-based approach for environmental flow assessments and water allocation for the environment

ABSTRACT Hydrological methodologies are the most efficient approaches for environmental flow (eflow) assessments. This paper presents a hydrological methodology for determining eflows in rivers with scarce development to promote proactive environmental water allocations that limit flow alteration and unsustainable water use. The analysis includes the natural intra-annual and inter-annual ranges of flow variability. Eflows are determined based on four hydrological low-flow conditions and a flood regime. The main contribution is that the flow regime components are adjusted to a four-tiered environmental objective class system based on a novel “frequency-of-occurrence” approach. The method is applied in three rivers in western Mexico with highly variable flow regimes. The eflows are largely (96%) within the central range of previous implementations, and the outcomes reveal an overall good and acceptable level of the method’s performance (for 83% of the cases R 2 ≥ 0.84, slope = 1 ± ≤ 0.2), consistent with supporting indices of flow variability.

River management and environmental water allocation in regulated ecosystems of arid and semi-arid regions – A review

Rivers make a significant contribution in providing goods and services for human well-being. Today, many rivers and streams have been heavily regulated to ensure adequate provision of water resources for anthropogenic uses. Riverine ecosystems, especially those in arid and semi-arid regions, are experiencing severe stress due to the increasing demands on the ecosystem services they provide, coupled with anthropogenic catchment-scale impacts and factors associated with natural and human-induced climate variability and change. In this paper, the various flow components in regulated riverine ecosystems and the methods to determine environmental flows are reviewed. The review also focuses on the concurrent developments of eco-hydrological models and on the new opportunities for improving environmental flows of rivers by sustainably adjusting consumptive flows to fine-tune environmental flows and maximize the ecological benefit. In fact, the present paper highlights the role of consumptive flows, towards improving environmental flows, which has largely been neglected by river scientists and water managers. Indeed, consumptive flows can provide an opportunity to improve and support environmental flows in regulated riverine ecosystems. Addressing these challenges may aid water management efforts in finding sustainable solutions in riverine ecosystems by balancing environmental/ecological and human water requirements.