How Does Flow Alteration Propagate Across a Large, Highly Regulated Basin? Dam Attributes, Network Context, and Implications for Biodiversity

Abstract

Dams are a major contributor to flow regime alteration: they increase water residence time, mute peak flows, shift the timing of ecologically important high and low flows, and alter flow periodicity (Poff et al., 2007;Ruhi et al., 2018;Vorosmarty, 1997). These alterations adversely affect riverine and riparian biodiversity because the life-history, morphological, and behavioral adaptations of organisms are often at odds with the novel environmental regime (Bunn & Arthington, 2002;Lytle & Poff, 2004;Mims & Olden, 2013). Such flow regime alteration is also often detrimental to society, as it may disrupt floodplain fishing, flood-recession agriculture, and a wide range of recreational and cultural values (Anderson et al., 2019). Despite intense scrutiny, flow alteration by dams has largely been estimated via methods that do not take into account the spatial context in which these changes

National‐Scale Detection of Reservoir Impacts Through Hydrological Signatures

“…As found in previous studies (Ferrazzi & Botter, 2019; Ruhi et al., 2019; Singer, 2007), our results highlight the importance of using a suite of signatures. None of the reservoir catchments are above/below the benchmark thresholds for all five signatures, one is picked up by four of the five signatures (the Brenig at the Llyn Brenig outflow; 67003; picked up by all but the WB signature) and 10 catchments exceed the benchmark thresholds for three of the five metrics.…”

“…Catchments with the highest degree of alteration, or those flagged by multiple signatures, usually also have high contributing area (>70%) and normalized upstream capacity (>0.2). In line with other studies, this finding highlights the importance of a reservoirs size and location for determining the magnitude of flow alteration at a given downstream gauge location (Arheimer et al., 2017; Cipollini et al., 2022; Jumani et al., 2022; Ruhi et al., 2019; Singer, 2007). These catchment descriptors could therefore be useful for environmental flow planning and forecasting significant flow alteration (Grantham et al., 2014).…”

Quantifying Dam‐Induced Fluctuations in Streamflow Frequencies Across the Colorado River Basin

“…In the United States (U.S.) alone, more than 90,000 dams change the quantity and variability of natural flow regimes, altering an estimated >85% of inland waterways (National Research Council, 1992). The impacts of such alteration propagate through river networks and affect the fluvial ecosystem in multiple ways: by preventing sediment transport (Willis & Griggs, 2003), by stabilizing channel morphology (Brandt, 2000; Graf, 2006; Topping et al., 2000), by fundamentally changing thermal and flow regimes (Olden & Naiman, 2010; Poff et al., 2007; Ruhi et al., 2019), and by altering the composition and dynamics of aquatic biota (Bunn & Arthington, 2002; Poff et al., 2007).…”

Spectral Signatures of Flow Regime Alteration by Dams Across the United States

“…More generally, our work provides a broad perspective on the alteration of flow frequencies as a function of dam purpose, residence time, and regional hydroclimate. Detailed watershed‐level research is needed to reduce the hydrologic impacts of dams (Chen & Olden, 2017; Wang et al., 2015), as well as to predict the spatial propagation of flow alteration impacts (Ruhi et al., 2022).…”

“…Considerable research has demonstrated widespread consequences of dam operations for riverine hydrology. Dams have been shown to homogenize flows across large spatial scales (Poff et al., 2007), and within a given watershed, flow alteration may accumulate spatially, with downstream sites “inheriting” alteration signatures of upstream dams and tributaries (McManamay, 2014; Ruhi et al., 2022). The assessment of changes within flow classes, or streams sharing similar hydrology (and/or hydrological controls) can help identify patterns of hydrologic alteration due to dam regulation (McManamay et al., 2012).…”