Impact Of Flow Regulation Research Articles

Impact of flow regulation on stream morphology and habitat quality distribution

The importance of interactions among stream hydrology, morphology, and biology is well recognized in studies of stream ecosystems. However, when quantifying the impacts of altered flow on aquatic habitat, results are often based either on combined changes in topography and flow, or with altered flow over static topography. Here, we study the potential beneficial effects of restoring unregulated flows on salmonid habitat and separate the relative influences of changes in flow vs. topography. We hypothesize that flow restoration will increase topographic complexity and that the coevolution of topography with altered streamflow will produce stronger changes in habitat than predicted for static topography. We address this hypothesis by quantifying spawning and juvenile rearing habitat distributions for Chinook salmon (Oncorhynchus tshawytscha) from a set of quasi-three-dimensional hydromorphodynamic models for two morphologically distinct reaches along the Lemhi River, Idaho (USA): an engineered, straightened, plane-bed reach, and a less-altered, meandering, pool-riffle reach. Sediment transport was modeled with hydrographs predicted for actual interannual variability of flow and for a synthetic annual flow representing the ensemble actual hydrographs for 60 years of regulated and unregulated flows. The actual and synthetic hydrographs predicted from the model produced similar morphologic results, which implies that interannual flow variation and hydrograph order did not have a strong effect on the modeled topography. Unregulated hydrographs enhanced the geometry and frequency of pools in the meandering reach compared to regulated flows. These morphological changes did not increase habitat quality predicted from suitability indices, but the large growth of pools likely improved winter refugia for juvenile salmon. In the straight reach, both regulated and unregulated scenarios resulted in a plane-bed morphology, suggesting that flow restoration in highly altered reaches is not sufficient to improve ecological function.

Impacts of flow regulation on geomorphic adjustment and riparian vegetation succession along an anabranching reach of the Upper Yellow River

Closure of Longyangxia Dam in 1986, the uppermost large dam along the trunk stream of the Upper Yellow River in western China, permanently altered the flow regime in Guide reach, an anabranching section of river located 41 km downstream of the dam. Two smaller hydropower structures, Nina and Laxiwa Dams, were constructed between Longyangxia Dam and Guide in 2003 and 2009 respectively, but they had a minor influence on the flow regime. This study uses the Indicators of Hydrologic Alteration model, satellite imagery and field analyses to assess how the magnitude and duration of changes to the flow regime impacted upon geomorphic adjustments and riparian vegetation succession from 1987 to 2015. Flow impoundment resulted in near instantaneous reduction in the width of the active channel zone. Human activities have manipulated the additional floodplain areas created by these changes. Aggregation of mid-channel bars into larger compound features decreased channel multiplicity. Negligible bed incision likely reflects local supply of sediment from tributary sources downstream of the dam. Significant correlations are shown between changes to the balance between channel depositional and erosional processes induced by flow regulation and the functional composition of vegetation succession patterns. Maintenance of a higher water table for longer periods of time is inferred to have altered mutual interactions between hydrogeomorphic processes and riparian vegetation in this semi-arid setting.

The impact of flow regulation by hydropower dams on the periphyton community in the Soča River, Slovenia

The effects of hydropower dams and, in particular, the impacts of reduced river flows on the periphyton community were assessed in the Soča River, Slovenia. Sampling sites were selected upstream and downstream of the Podsela and Ajba dams. Sampling was carried out in 1998 during a period of low flows. Reaches downstream from the dams experienced prolonged periods of reduced flows, and a corresponding decrease in flow velocity and water depth. The chain of hydropower dams has stopped sediment inflow from the upstream reach. Below the dams, the oscillations of water temperature, dissolved oxygen and oxygen saturation are much larger than at unregulated sites upstream. The impact of prolonged periods of reduced flows, a lack of sediment supply from upstream and changes in physicochemical variables has caused high periphyton biomass, proliferation of green algae and increases in the number of periphytic algae species below the dams. This has significant implications for the design of environmental flow strategies that provide a sediment supply to maintain a healthy periphyton community.Editor Z.W. Kundzewicz; Associate editor M. AcremanCitation Smolar-Žvanut, N. and Mikoš, M., 2014. The impact of flow regulation by hydropower dams on the periphyton community in the Soča River, Slovenia. Hydrological Sciences Journal, 59 (5), 1032–1045.

Impacts of flow regulation on slackwaters in river channels

Key Points Slackwaters are ecologically important low velocity and shallow environments Slackwater total area, patch area and number are explicitly related to discharge Flow regulation halves slackwater area and reduces patch size by five times

Impact of flow regulation on near-channel floodplain sedimentation

Rates and the spatial extent of near-channel floodplain sedimentation on regulated and unregulated reaches in two upland rivers in central Vermont, U.S.A. are measured using the short-lived fallout radionuclide 210Pb. We find consistent profiles of 210Pb inventories across all sites; inventories are low immediately next to the channel, increase to a peak value as the inundation frequency decreases and then asymptotically diminish with distance from the channel to the equilibrium inventory associated with atmospheric deposition alone. We infer from our data that flow regulation has impacted sediment deposition to floodplains below the dam; total sediment deposition is less and it is constrained to a narrower band immediately along the active channel. Flow regulation does not appear, however, to impact the general form of the 210Pb inventory profile, suggesting a uniformity of process across regulated and unregulated floodplains.

Intra-tidal variation of stratification in a semi-arid estuary under the impact of flow regulation

The Jaguaribe River is the largest semi-arid Brazilian river and represents an important water source for the state of Ceará. The Castanhão Weir, built to regulate the flow of the Jaguaribe, began operating successfully in the 1990s. As a result, the hydrodynamic regime of the estuary has undergone alteration and is no longer subject to the former annual climatological variability of the dry and rainy seasons. This paper introduces an assessment of the changes in the hydrological conditions resulting from the construction of the weir and investigates the structure of the density stratification in the estuary. A field experiment was conducted at the end of the dry season in November 2009, during which salinity and temperature were monitored at different levels for three tidal cycles. The temporal variations in salinity and temperature during the tidal cycles were 16 psu and 1.5°C, respectively. The salinity exhibited a vertical variation of four units, while the temperature variation was much lower. Several stratification indicators were calculated from the observed density: the stratification coefficient, the Brunt-Väisälä frequency and the potential energy anomaly. The results showed that the parameters behave similarly, differences being observed only in their relative magnitudes. The vertical structure of the estuary exhibited marked stratification during the ebb tide but vertical homogeneity during both flood and high tide. With the regularized flow existing under present conditions, the estuary exhibits hyposaline and a partially mixed structure for the period studied, despite the typical expectation of a hypersaline and well-mixed vertical structure.

Impacts of flow regulation on freshwater pearl mussel (Margaritifera margaritifera) habitat in a Scottish montane river

The River Moriston in NW Scotland is a cobble–gravel bedded river that has been dammed and regulated for hydroelectric power (HEP) since 1956. The river supports a functional population of the critically endangered freshwater pearl mussel (Margaritifera margaritifera) in the lower part. In contrast the population in the upper reach is sparse and shows no signs of juvenile recruitment, leading to speculation that hydrological and geomorphic changes associated with HEP have degraded the habitat they depend on. A combination of historical analysis, field mapping and geomorphic survey of channel and active bar sites was used to assess habitat changes and current quality. During the post-dam period, the naturally stability of much of the channel has increased, active bars have been stabilised through vegetation colonisation, riparian tree cover has increased and the active channel width has significantly reduced locally (>50%); adjustments that are indicative of a reduction in the incidence of competent flows caused by flow regulation. However area and stability of habitat for freshwater pearl mussels have not been reduced greatly. The channel sites examined are characterised by mixed cobble–gravel substrates (D50 range=46–188mm), predicted to be highly stable, that provide suitable habitat for adult freshwater pearl mussels. However a degree of bed compaction at one site was observed that could be limiting the recruitment of juvenile mussels. It is hypothesised that the sparse, non-functional status of the freshwater pearl mussel population reflects significant historical pearl fishing and the limitation of recovery due to HEP related pressures of fish migration obstruction and bed compaction. The implications of these factors for conservation of the species are discussed.

A demonstration of the flow events method: environmental flow requirements of the Broken River

The Flow Events Method is a procedure for (i) assessing the ecological impact of flow regulation, (ii) developing environmental flow rules and (iii) optimising the operation of a water resource scheme to maximise environmental performance. The method is a systematic, transparent and defensible tool for use in environmental flows studies that makes use of available knowledge and facilitates the inclusion of expert opinion where necessary. It is not presented as a new technique, rather it is a logical and transparent procedure for integrating the concepts and data commonly used in environmental flow studies in Australia. The primary component of the method is the assessment of flow regulation based on changes in flow events that are considered to be important for specific ecological processes. This paper describes the application of the Flow Events Method to assess the impact of flow regulation in the Broken River catchment, including data and modelling requirements for this study. Six aspects of the flow regime are considered: (i) rapid increases in flows, (ii) rapid reduction in flows, (iii) the availability of slow water habitats, (iv) drying of the streambed, (v) the availability of shallow water habitats and (vi) inundation of channel benches.

Potential impact of groundwater augmentation of river flows on fisheries: a case study from the River Ouse, Yorkshire, UK

Many lowland rivers in the UK are under increasing pressure from abstraction of water for potable supply or irrigation. Many schemes, both existing and proposed, attempt to mitigate the loss of flow by augmentation from upstream reservoirs or pumping of groundwater into adjacent rivers. The impact of flow regulation by reservoirs is well documented, but little attention has focused on the effect of groundwater augmentation on the biota, particularly fisheries, in the receiving river. The present paper examines the potential effects of pumping groundwater into minor tributaries of the Yorkshire Ouse in England on the cyprinid fisheries downstream of the discharge points and in the main river channel. Concerns were raised with respect to poor water quality and reduced water temperature. In particular, it was predicted that small reductions in river water temperature brought about by discharge of cold (≤ 10 °C) groundwater could have serious detrimental effects on cyprinid fish recruitment and juvenile growth in the receiving river, leading to a decline in stocks.