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

Abstract

As water demand drastically increased due to growing population and urbanization over the last century, a vast installation of reservoirs proliferated worldwide, fundamentally changing the water cycle (Ripl, 2003). Large-scale water regulation and conveyance systems currently determine present and future water availability to society (Sivapalan et al., 2003, Vogel et al., 2015Vörösmarty & Sahagian, 2000). 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 (

Dynamic Flow Alteration Index for Complex River Networks With Cascading Reservoir Systems

“…This observation matches with the restoration of the annual frequency signal as demonstrated recently by Hwang et al. (2021) using wavelet coherency analysis on natural and modified flows in the CRB. This reappearance of annual signal is also the reason why the mean LDOR differs from the high regulation value of 2.84 years reported by Lehner et al.…”

“…The flow from these relatively less regulated tributaries and the operations of Hoover Dam reduce the CDOR (1.82 years at Hoover Dam) by bringing the peak monthly outflow in sync with the natural peak flow season. This observation matches with the restoration of the annual frequency signal as demonstrated recently by Hwang et al (2021) using wavelet coherency analysis on natural and modified flows in the CRB. This reappearance of annual signal is also the reason why the mean LDOR differs from the high regulation value of 2.84 years reported by Lehner et al (2011) who used the ratio of storage capacity to simulate average annual runoff.…”

“…We have discussed how the impact of these ecological measures is captured by the proposed regulation measures in Section 4.4. For instance, in our study, after the Hoover Dam, DOR reduces as the annual signal is recovered (Figure 6; see also Hwang et al., 2021) due to reservoir re‐operation, which could reduce the flow alteration (H. Wang et al., 2015).…”

“…Currently, four collaborative management programs are operational in the CRB with a goal to conserve or restore species listed under the Endangered Species Act, while continuing to meet water and hydropower demands: Upper Colorado River Endangered Fish Recovery Program, Glen Canyon Dam Adaptive Management Program, and Lower Colorado River Multi-Species Conservation Program (Campbell et al, 2008).We have discussed how the impact of these ecological measures is captured by the proposed regulation measures in Section 4.4. For instance, in our study, after the Hoover Dam, DOR reduces as the annual signal is recovered (Figure 6; see also Hwang et al, 2021) due to reservoir re-operation, which could reduce the flow alteration (H. Wang et al, 2015).…”

“…Although, the selection excludes many dams, it retains the biggest dams such as the Hoover, Glen Canyon, Davis, and Flaming Gorge dams whose storage capacities are much greater than the rest (84.5 km 3 or 70% of the basin’s total storage capacity of 120.63 km 3 ) (Graf, 1999). More than 99% of the reservoir storage in the basin was commissioned before 1987, and thus no new regulation was introduced due to post‐1987 dam construction (Hwang et al., 2021). Given this, it is safe to assume that any changes in the regulation after the year 1987 would be due to dam operations only and not due to addition of new capacity.…”