The impact of dams on floodplain geomorphology: are there any, should we care, and what should we do about it?

We undertook a review of the potential for dams to impact floodplain geomorphology, using both a conventional literature review and a systematic review using ‘causal criteria’ analysis. The literature review identified potential impacts on overbank flooding, scour and sedimentation, within-channel bank erosion, meander migration and cutoff frequency, and avulsion characteristics and frequency. The temporal scale of impacts ranged from years and decades, through to millennia. The causal criteria analysis indicated that with the exception of reduced meander migration rates, most impacts had been too poorly documented to be confident of their impact at present. We identify a distinction between ‘passive impacts’ (floodplain disconnection) and ‘active impacts’ (changes in geomorphological processes and functioning). Dams do impact floodplain geomorphology: many of the impacts will be subtle, and over very long timescales (1000s of years), but altered overbank sediment loads have the potential to change patterns of scour and deposition across floodplains. Further research is needed that specifically seeks to identify the impacts of dams on floodplain geomorphology, hydrology-geomorphology-vegetation interactions, and floodplain ecological response. Given the practical constraints on overbank environmental flow releases, there is relatively little that can be done to mitigate dam impacts on floodplain geomorphology. The main options include using within-channel flows to maintain meander migration and partial floodplain connectivity. We suggest that the major action should be that once dams come online, efforts should be made to prevent channel enlargement through scour, channel widening and wood removal, so that geomorphological processes can fully reestablish immediately once the dam ceases to operate

The Potential for Dams to Impact Lowland Meandering River Floodplain Geomorphology

The majority of the world’s floodplains are dammed. Although some implications of dams for riverine ecology and for river channel morphology are well understood, there is less research on the impacts of dams on floodplain geomorphology. We review studies from dammed and undammed rivers and include influences on vertical and lateral accretion, meander migration and cutoff formation, avulsion, and interactions with floodplain vegetation.The results are synthesized into a conceptual model of the effects of dams on the major geomorphic influences on floodplain development.This model is used to assess the likely consequences of eight damand flow regulation scenarios for floodplain geomorphology. Sediment starvation downstream of dams has perhaps the greatest potential to impact on floodplain development. Such effects will persist further downstream where tributary sediment inputs are relatively low and there is minimal buffering by alluvial sediment stores.We can identify several ways in which floodplains might potentially be affected by dams, with varying degrees of confidence, including a distinction between passive impacts (floodplain disconnection) and active impacts (changes in geomorphological processes and functioning). These active processes are likely to have more serious implications for floodplain function and emphasize both the need for future research and the need for an “environmental sediment regime” to operate alongside environmental flows

Water sharing for the environment and agriculture in the Broken catchment

The Commonwealth of Australia Water Act 2007 changed the priority for water use in the Murray-Darling Basin (MDB) to first ensure environmentally sustainable levels of extraction and then to maximise net economic returns to the community from water use. The Murray- Darling Basin Authority (MDBA) is expected to deliver a draft Basin Plan in 2011 providing a framework for future water planning. The Plan will include Sustainable Diversion Limits (SDLs) which define water diversions for consumption while maintaining environmental assets and ecosystem functions. The 2009 MDBA Concept Statement acknowledged that in some areas less information is available to determine the SDLs. The 2010 MDBA Guide to the Basin Plan proposed SDLs reducing the current long-term average surface water diversions to between 25 and 34% for the Goulburn-Broken region. Representative farm-level models of irrigated dairy, horticulture and viticulture, and dryland broadacre, industries were developed to determine the likely impacts on farm income and farm enterprise mix if the price and quantity of irrigation water changes. Water for ecological benefits and ecosystem functioning was determined for a range of river health levels using a bottom-up approach identifying flow requirements for fish, riparian vegetation, invertebrates, and geomorphic and nutrient processes. A novel part of the analysis is the conjunctive use of water for both purposes, e.g. wetland filling and then pumping for irrigation. The linkages between changed land use and surface/ground water outcomes are assessed using a Catchment Analysis Tool. An experimental design of different proportions of water going to the environment and consumptive uses showed potential trade-offs between agricultural, environmental and surface/ground water outcomes. These trade-offs were examined to assess the impact of alternative water management on catchment welfare, and provide information about setting SDLs.Water sharing, environment, agriculture, Murray-Darling Basin, Broken catchment, Resource /Energy Economics and Policy, Q18, Q25, Q28,

Key hydraulic drivers and patterns of fine sediment accumulation in gravel streambeds: A conceptual framework illustrated with a case study from the Kiewa River, Australia

Fine sediment processes in gravel beds may have significant impacts to overall river ecosystem function. In addition to gravitational deposition, horizontal intragravel transport has been recognized to influence fine sediment accumulation. However, the specific hydraulic mechanisms and origin of fine sediment movement are not clearly identified. The purpose of this study was to investigate key hydraulic drivers and patterns of fine sediment accumulation. Using a conceptual framework to set the scene, we implemented an experimental setup in a gravel lateral bar subject to irregular flow fluctuations in the Kiewa River (Australia). We installed nine sets of sediment collector pairs and piezometers into the gravel. Each pair included one horizontally and one horizontally-vertically perforated collector. Mid-range, rather than peak flows, covering the site in water drove fine sediment deposited in the collectors. We estimated horizontal contribution to final deposition as 59%. Such contribution resulted from shear stresses > 3 N m− 2 promoting streamwise near-bed turbulence at the water-sediment interface during flooded conditions. Despite high subsurface hydraulic gradients, intragravel transport in the lower sediment layers via Darcy flow did not show any influence to fine sediment deposition. Our findings contribute to an improved understanding of fine sediment accumulation processes, key for overall river ecosystem functioning, particularly in regulated rivers

Different Conceptualizations of River Basins to Inform Management of Environmental Flows

Environmental flows are a critical tool for addressing ecological degradation of river systems brought about by increasing demand for limited water resources. The importance of basin scale management of environmental flows has long been recognized as necessary if managers are to achieve social, economic, and environmental objectives. The challenges in managing environmental flows are now emerging and include the time taken for changes to become manifest, uncertainty around large-scale responses to environmental flows and that most interventions take place at smaller scales. The purpose of this paper is to describe how conceptual models can be used to inform the development, and subsequent evaluation of ecological objectives for environmental flows at the basin scale. Objective setting is the key initial step in environmental flow planning and subsequently provides a foundation for effective adaptive management. We use the implementation of the Basin Plan in Australia's Murray-Darling Basin (MDB) as an example of the role of conceptual models in the development of environmental flow objectives and subsequent development of intervention monitoring and evaluation, key steps in the adaptive management of environmental flows. The implementation of the Basin Plan was based on the best science available at the time, however, this was focused on ecosystem responses to environmental flows. The monitoring has started to reveal that limitations in our conceptualization of the basin may reduce the likelihood of achieving of basin scale objectives. One of the strengths of the Basin Plan approach was that it included multiple conceptual models informing environmental flow management. The experience in the MDB suggests that the development of multiple conceptual models at the basin scale will help increase the likelihood that basin-scale objectives will be achieved

The politicisation of science in the Murray-Darling Basin, Australia:discussion of ‘Scientific integrity, public policy and water governance’

Many water scientists aim for their work to inform water policy and management, and in pursuit of this objective, they often work alongside government water agencies to ensure their research is relevant, timely and communicated effectively. A paper in this issue, examining 'Science integrity, public policy and water governance in the Murray-Darling Basin, Australia’, suggests that a large group of scientists, who work on water management in the Murray-Darling Basin (MDB) including the Basin Plan, have been subject to possible ‘administrative capture'. Specifically, it is suggested that they have advocated for policies favoured by government agencies with the objective of gaining personal benefit, such as increased research funding. We examine evidence for this claim and conclude that it is not justified. The efforts of scientists working alongside government water agencies appear to have been misinterpreted as possible administrative capture. Although unsubstantiated, this claim does indicate that the science used in basin water planning is increasingly caught up in the politics of water management. We suggest actions to improve science-policy engagement in basin planning, to promote constructive debate over contested views and avoid the over-politicisation of basin science

Massive migration from the steppe is a source for Indo-European languages in Europe

We generated genome-wide data from 69 Europeans who lived between 8,000-3,000 years ago by enriching ancient DNA libraries for a target set of almost four hundred thousand polymorphisms. Enrichment of these positions decreases the sequencing required for genome-wide ancient DNA analysis by a median of around 250-fold, allowing us to study an order of magnitude more individuals than previous studies and to obtain new insights about the past. We show that the populations of western and far eastern Europe followed opposite trajectories between 8,000-5,000 years ago. At the beginning of the Neolithic period in Europe, ~8,000-7,000 years ago, closely related groups of early farmers appeared in Germany, Hungary, and Spain, different from indigenous hunter-gatherers, whereas Russia was inhabited by a distinctive population of hunter-gatherers with high affinity to a ~24,000 year old Siberian6 . By ~6,000-5,000 years ago, a resurgence of hunter-gatherer ancestry had occurred throughout much of Europe, but in Russia, the Yamnaya steppe herders of this time were descended not only from the preceding eastern European hunter-gatherers, but from a population of Near Eastern ancestry. Western and Eastern Europe came into contact ~4,500 years ago, as the Late Neolithic Corded Ware people from Germany traced ~3/4 of their ancestry to the Yamnaya, documenting a massive migration into the heartland of Europe from its eastern periphery. This steppe ancestry persisted in all sampled central Europeans until at least ~3,000 years ago, and is ubiquitous in present-day Europeans. These results provide support for the theory of a steppe origin of at least some of the Indo-European languages of Europe

Genomic insights into the origin of farming in the ancient Near East

We report genome-wide ancient DNA from 44 ancient Near Easterners ranging in time between ~12,000 and 1,400 BC, from Natufian hunter–gatherers to Bronze Age farmers. We show that the earliest populations of the Near East derived around half their ancestry from a ‘Basal Eurasian’ lineage that had little if any Neanderthal admixture and that separated from other non-African lineages before their separation from each other. The first farmers of the southern Levant (Israel and Jordan) and Zagros Mountains (Iran) were strongly genetically differentiated, and each descended from local hunter–gatherers. By the time of the Bronze Age, these two populations and Anatolian-related farmers had mixed with each other and with the hunter–gatherers of Europe to greatly reduce genetic differentiation. The impact of the Near Eastern farmers extended beyond the Near East: farmers related to those of Anatolia spread westward into Europe; farmers related to those of the Levant spread southward into East Africa; farmers related to those of Iran spread northward into the Eurasian steppe; and people related to both the early farmers of Iran and to the pastoralists of the Eurasian steppe spread eastward into South Asia