Determining the effects of dams on subdaily variation in river flows at a whole‐basin scale

Abstract

River regulation can alter the frequency and magnitude of subdaily flow variations causing major impacts on ecological structure and function. We developed an approach to quantify subdaily flow variation for multiple sites across a large watershed to assess the potential impacts of different dam operations (flood control, run-of-river hydropower and peaking hydropower) on natural communities. We used hourly flow data over a 9-year period from 30 stream gages throughout the Connecticut River basin to calculate four metrics of subdaily flow variation and to compare sites downstream of dams with unregulated sites. Our objectives were to (1) determine the temporal scale of data needed to characterize subdaily variability; (2) compare the frequency of days with high subdaily flow variation downstream of dams and unregulated sites; (3) analyse the magnitude of subdaily variation at all sites and (4) identify individual sites that had subdaily variation significantly higher than unregulated locations. We found that estimates of flow variability based on daily mean flow data were not sufficient to characterize subdaily flow patterns. Alteration of subdaily flows was evident in the number of days natural ranges of variability were exceeded, rather than in the magnitude of subdaily variation, suggesting that all rivers may exhibit highly variable subdaily flows, but altered rivers exhibit this variability more frequently. Peaking hydropower facilities had the most highly altered subdaily flows; however, we observed significantly altered ranges of subdaily variability downstream of some flood-control and run-of-river hydropower dams. Our analysis can be used to identify situations where dam operating procedures could be modified to reduce the level of hydrologic alteration.

Modeling the Multi-Seasonal Link between the Hydrodynamics of a Reservoir and Its Hydropower Plant Operation

“…In response, several indexes for measuring the hourly fluctuation have been proposed in the last decade [35][36][37]. The Richard-Baker (R-B) index [35] for flow flashiness is one that has found numerous applications in the last five years [5,6,12,38,39]:…”

How to update design floods after the construction of small reservoirs and check dams: A case study from the Daqinghe river basin, China

“…The simplest one was the comparison between the regulated and unregulated sites. Zimmerman et al (2010) determined the effects of dams on sub-daily variation in river flows for multiple sites across a large watershed by this method. Magilligan and Nislow (2005) assessed hydrological changes associated with dams by a hydrological model, supplemented with orientation statistics for some hydrograph parameters.…”

A New Fluctuation Index: Characteristics and Application to Hydro-Wind Systems

“…This category contains a sort of difference pattern, such as difference between adjacent ordinates, difference between ordinate and its mean. The second category is called the divided category, and it includes the FOD divided by the maximum [17], SD divided by the mean [13,14,18], coefficient of variation [19], normalized SD [20], and Richards-Baker Flashiness (RBF) index [5,19,[21][22][23][24]. The third is the distribution, and contains the distribution of the FOD [4] and the distribution of exceedance [6].…”

“…The RBF, based on Indicators of Hydrological Alteration (IHA) [25] and Richards Pathlength (RP) [26], was proposed by Baker and Richards in 2004 [27] and has subsequently been widely used to describe stream flow fluctuations [5,19,[21][22][23][24]. Due to ignorance of contour variation of process, the FOD, SD and RBF are capable of describing the dispersion of process but inadequate to discern the contour difference.…”