Linking environmental flows to sediment dynamics

© 2017 The Authors. This is a policy discussion paper aimed at addressing possible alternative approaches for environmental flows (e- Flows) assessment and identification within the context of best strategies for fluvial restoration. We focus on dammed rivers in Mediterranean regions. Fluvial species and their ecological integrity are the result of their evolutionary adaptation to river habitats. Flowingwater is themain driver for development and maintenance of these habitats,which is why e-Flows are needed where societal demands are depleting water resources. Fluvial habitats are also shaped by the combined interaction ofwater, sediments,woody/organicmaterial, and riparian vegetation.Water abstraction, flowregulation by dams, gravel pits or siltation by fine sediments eroded fromhillslopes are pressures that can disturb interactions among water, sediments, and other constituents that create the habitats needed by fluvial communities. Present e-Flow design criteria are based only on water flow requirements. Here we argue that sediment dynamics need to be considered when specifying instream flows, thereby expanding the environmental objectives and definition of e-Flows to include sediments (extended e-Flows). To this aim, a hydromorphological framework for e-Flows assessment and identification of best strategies for fluvial restoration, including the context of rivers regulated by large dams, is presented

Door de dam heen : Soort- en rivier specifieke effecten van dammen op Europese trekvissen

Dammen vormen wereldwijd de grootste bedreiging voor rivierecosystemen, wat vooral tot uitdrukking komt in de afname van de aantallen trekvissen. De mate waarin vissoorten worden beperkt in hun migratie verschilt echter van rivier tot rivier en van soort tot soort. Recent zijn de effecten van rivierfragmentatie op trekvissen door barrières op Europese schaal onderzocht

Final evaluation of longitudinal-training-walls pilot in the river Waal

Rivers, Ports, Waterways and Dredging Engineerin

Door de dam heen : Soort- en rivier specifieke effecten van dammen op Europese trekvissen

Dammen vormen wereldwijd de grootste bedreiging voor rivierecosystemen, wat vooral tot uitdrukking komt in de afname van de aantallen trekvissen. De mate waarin vissoorten worden beperkt in hun migratie verschilt echter van rivier tot rivier en van soort tot soort. Recent zijn de effecten van rivierfragmentatie op trekvissen door barrières op Europese schaal onderzocht

Modelling restoration of natural flow regimes in dam impaired systems : Biomorphodynamic effects and recovery times

Dams affect the natural flow regime by altering the magnitude, timing and frequency of high and low flows. Many river ecosystems impaired by dams are currently being restored. Restoration success is difficult to quantify and is often assessed by comparing the restored system to an unimpaired static ‘reference’ system. However, restoring a river to past environmental conditions and assessing restoration success by comparing it to a static situation neglects natural system dynamics and non-linear, adaptive system responses. With this modelling study we evaluate long-term changes in river morphology, morphodynamics, riparian vegetation cover and habitat suitability of two fish species and two types of wetland vegetation in a meandering gravel bed river after removal of an upstream dam and complete restoration of the natural flow regime. We assessed the ecological and hydromorphodynamic recovery of systems impaired by two different dam operating regimes and three different time periods the dam was present by comparing these to a dynamic undisturbed situation. Modelling results show that recovery potential depends on how much the system has been changed by the dam and the system state at the start of the restoration, rather than the duration of the pressure. Even if the conditions shortly after restoration are comparable to pre-disturbance conditions, there can still be a time-lag in the system response where the future state of the restored system continues to deviate from the undisturbed situation. When this happens, the system can develop into an alternative dynamic equilibrium where recovery becomes increasingly difficult. These results stress the importance of considering natural variability in restored systems as well as in reference systems, requiring detailed spatio-temporal monitoring to assess restoration effects

Combined effects of climate change and dam construction on riverine ecosystems

River morphology and riparian vegetation continuously adapt to changing discharge conditions, which makes it a challenge to distinguish long-term development driven by natural discharge variation from the impacts of flow alteration due to climate change and due to dams. The aim of this study was to investigate how such flow alterations affect bio-geomorphological processes and habitat suitability of several fluvial plant and animal species. This is done with a numerical model representing dynamic interactions between morphodynamic processes and riparian vegetation coupled to habitat suitability models of fluvial species. We compared a control run with natural flow regime to altered flow for two scenarios with different dam operating regimes, two scenarios with climate change, and for combinations of dams and climate change. Results show that flow stabilization leads to incision, acute reduced seedling recruitment and decline of riparian vegetation. Climate change generates a gradual response, where high flow extremes counteract an otherwise reduced seedling recruitment of pioneer vegetation, while drying reduces riparian vegetation recruitment and causes vegetation shifts towards lower elevations on the floodplain. Modelled habitat availability for facilitated plant and animal species declines most when the synchronicity between critical life history events and habitat requirements is disrupted by altered flow conditions, with opposite effects for different species. Dynamic interactions between bio-geo-morphological processes with somewhat different characteristic timescales create non-linear and adaptive behaviour of morphology, habitat patterns and facilitated species habitat. This implies that only models that include bio-geomorphological feedbacks can forecast impacts of multiple flow alteration pressures, whereas addition of single-pressure regime effects is overly simplistic

Modelling restoration of natural flow regimes in dam impaired systems: Biomorphodynamic effects and recovery times

Dams affect the natural flow regime by altering the magnitude, timing and frequency of high and low flows. Many river ecosystems impaired by dams are currently being restored. Restoration success is difficult to quantify and is often assessed by comparing the restored system to an unimpaired static ‘reference’ system. However, restoring a river to past environmental conditions and assessing restoration success by comparing it to a static situation neglects natural system dynamics and non-linear, adaptive system responses. With this modelling study we evaluate long-term changes in river morphology, morphodynamics, riparian vegetation cover and habitat suitability of two fish species and two types of wetland vegetation in a meandering gravel bed river after removal of an upstream dam and complete restoration of the natural flow regime. We assessed the ecological and hydromorphodynamic recovery of systems impaired by two different dam operating regimes and three different time periods the dam was present by comparing these to a dynamic undisturbed situation. Modelling results show that recovery potential depends on how much the system has been changed by the dam and the system state at the start of the restoration, rather than the duration of the pressure. Even if the conditions shortly after restoration are comparable to pre-disturbance conditions, there can still be a time-lag in the system response where the future state of the restored system continues to deviate from the undisturbed situation. When this happens, the system can develop into an alternative dynamic equilibrium where recovery becomes increasingly difficult. These results stress the importance of considering natural variability in restored systems as well as in reference systems, requiring detailed spatio-temporal monitoring to assess restoration effects

Data underlying the publication: Historical reconstruction of sturgeon (Acipenser spp.) spatiotemporal distribution and causes for their decline in North-Western Europe

This data set has data on historically reported landings and sales of the anadromous sturgeons, Acipenser sturio and A. oxyrinchus, in NW-Europe (especially in the Rhine, Meuse, Scheldt and Ems rivers and the North Sea), in light of evaluating the possibilities for their reintroduction

Effective restoration of aquatic ecosystems: scaling the barriers

The focus of ecosystem restoration has recently shifted from pure rehabilitation objectives to both improving ecological functioning and the delivery of ecosystem services. However, these different targets need to be integrated to create a unified, synergistic, and balanced restoration approach. This should be done by combining state-of-the-art knowledge from natural and social sciences to create manageable units of restoration that consider both the temporal and multiple spatial scales of ecosystems, legislative units, and policy agendas. Only by considering these aspects combined can we accomplish more cost-efficient restoration resulting in resilient ecosystems that provide a wealth of ecosystem services and the possibility for sustainable economic development in the future. We propose a novel conceptual framework that will yield more effective ecosystem restoration: the Operational Restoration Unit. This is based on scale-dependent restoration actions that can adhere easily to the relevant environmental legislation, encompass the spatial and temporal resilience of aquatic ecosystems, and consider the sum of human pressures acting on water bodies. This opens up possibilities for an effective integration of the restoration agenda into the delivery of major policy objectives of economic growth, regional development, and human security