Abstract
In the last century, about 50,000 dams have been constructed all around the world, and regulated rivers are now pervasive throughout the Earth's landscapes. Damming has produced global-scale alterations of the hydrologic cycle, inducing severe consequences on the ecological and morphological equilibrium of streams. However, a recognizable link between specific uses of reservoirs and their impact on flow regimes has not been disclosed yet. Here, extensive hydrological data are integrated with a physically-based model to investigate hydrological alterations downstream of 47 isolated dams in the Central Eastern U.S. Our results reveal a strong connection between the anthropogenic use and the hydrological impact of dams. Flood control reduces the temporal variability and spatial heterogeneity of river flows proportionally to the specific capacity allocated to mitigate floods (i.e., capacity scaled to the average inflow). Conversely, water supply increases the relative variability and regional heterogeneity of streamflows proportionally to the relative amount of withdrawn inflow. Accordingly, downstream of our multipurpose reservoirs the impact of regulation on streamflow variability is smoothed due to the compensating effect of flood control and water supply. Nevertheless, reservoirs with high storage capacity and overlapping uses produce regulated hydrographs that increase their unpredictability for larger aggregation periods and, thus, resemble an autocorrelated red noise. These findings suggest that the increase of freshwater demand could redefine the cumulative effects of dams at regional scale, reshaping the trajectories of eco-morphological alteration of dammed rivers.
Highlights
Dams and impoundments have long been designed in response to the ubiquitous imbalance between water needs for anthropogenic uses and the variability of river flows
Extensive hydrological data are integrated with a physically-based model to investigate hydrological alterations downstream of 47 isolated dams in the Central Eastern U.S Our results reveal a strong connection between the anthropogenic use and the hydrological impact of dams
Are there distinctive patterns of river regime alterations associated to specific water uses? May possible shifts in anthropogenic water uses alter observed trends of flow regime modifications in the future? To address these questions, we investigate the relationship between three different water uses, including related reservoir characteristics, and regional alterations of river regimes
Summary
Dams and impoundments have long been designed in response to the ubiquitous imbalance between water needs for anthropogenic uses and the variability of river flows. Existing large-scale investigations have revealed that river impoundments affect the magnitude, frequency and timing of both high and low flows with an intensity that is modulated by the storage capacity of reservoirs and the mean annual runoff [9–11] These alterations are believed to generate a general reduction of daily streamflow variability and, an enhanced homogenization of regional river dynamics [12–14]. The analysis is conducted by investigating the impact of river regulation on a number of flow statistics, including the mean discharge, the coefficient of variation of daily flows, the integral scale and the frequency stability These hydrological indexes retain important information about the extent of ecological and morphological alterations of regulated rivers (sensu Richter et al [16]). The approach is applied to 47 isolated dams, spanning the range of hydro-climatic settings typical of the Central-Eastern United States and three different water uses, namely flood control, urban water supply and hydropower production
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