Characterizing Sub‐Daily Flow Regimes: Implications of Hydrologic Resolution on Ecohydrology Studies

Abstract

Natural variability in flow is a primary factor controlling geomorphic and ecological processes in riverine ecosystems. Within the hydropower industry, there is growing pressure from environmental groups and natural resource managers to change reservoir releases from daily peaking to run‐of‐river operations on the basis of the assumption that downstream biological communities will improve under a more natural flow regime. In this paper, we discuss the importance of assessing sub‐daily flows for understanding the physical and ecological dynamics within river systems. We present a variety of metrics for characterizing sub‐daily flow variation and use these metrics to evaluate general trends among streams affected by peaking hydroelectric projects, run‐of‐river projects and streams that are largely unaffected by flow altering activities. Univariate and multivariate techniques were used to assess similarity among different stream types on the basis of these sub‐daily metrics. For comparison, similar analyses were performed using analogous metrics calculated with mean daily flow values. Our results confirm that sub‐daily flow metrics reveal variation among and within streams that are not captured by daily flow statistics. Using sub‐daily flow statistics, we were able to quantify the degree of difference between unaltered and peaking streams and the amount of similarity between unaltered and run‐of‐river streams. The sub‐daily statistics were largely uncorrelated with daily statistics of similar scope. On short temporal scales, sub‐daily statistics reveal the relatively constant nature of unaltered stream reaches and the highly variable nature of hydropower‐affected streams, whereas daily statistics show just the opposite over longer temporal scales. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

An Assessment of Ice Effects on Indices for Hydrological Alteration in Flow Regimes

“…For some sites, finer time resolution than one day could be important information related to environmental effects, e.g., Stickler et al [36] and Alfredsen et al [37] showed sub-daily responses in Atlantic salmon during several ice formation and release events in the river Orkla. The loss of detail in the daily ice data is, in many ways, similar to the loss of accuracy experienced when analyzing hydro-peaking flow data, e.g., Bevelhimer et al [38] found that a sub-daily time step is necessary to capture the dynamics of a peaking flow regime. As discussed, it is a drawback that the assessment of hourly peaking relies on daily ice-corrected data.…”

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

“…However, with the privatization of the power sector and the introduction of renewables, the operational scheme of hydropower plants has intensified its flashiness, especially in the intra-daily time horizon [5,33]. These fluctuations are hardly captured in the original indicators [34]. In response, several indexes for measuring the hourly fluctuation have been proposed in the last decade [35][36][37].…”

Effects of Renewable Energy Production and Infrastructure on Wildlife

“…However, hydroelectric facilities in drier areas and (especially) large hydroelectric dams do store water and disrupt hydrological regimes. Hydroelectric dams may also have specifi c, short-term impacts on river fl ow related to the variability in electricity demand (Bevelhimer et al 2015 ). The daily demand fl uctuations can be translated into large, completely unnatural daily variations in fl ow below hydroelectric dams, with strong negative impacts on the aquatic biota (Cushman 1985 ).…”