Predicted effects of flow diversion by Run‐of‐River hydropower on bypassed stream temperature and bioenergetics of salmonid fishes

Abstract

Many anthropogenic disturbances impact stream ecosystems by changing flow and temperature regimes. The emerging industry of small Run‐of‐River (RoR) hydropower reduces streamflow in bypassed reaches, with largely unknown consequences for water temperatures and fish growth. We used empirical and simulated data from two small RoR regulated streams in British Columbia (Canada) to quantify changes in water temperatures in bypassed reaches and assess the potential impacts to resident rainbow trout (Oncorhynchus mykiss) growth using bioenergetics models under a range of consumption scenarios. We found increases in mean monthly water temperature in bypassed reaches due to flow diversion of 0.5–0.8°C (0.17–0.19°C/km). Bioenergetics models using those temperatures predicted increases in annual O. mykiss growth (compared to natural temperatures) if consumption was unlimited (+200–450%), increases (+15–42%) if consumption was scaled with higher metabolic demand, and small reductions (−5 to 7%) if consumption remained constant. If food availability was reduced by 25%, annual growth was predicted to decline by 45%. Empirical estimates of annual growth of fish sampled indicate modest reductions in annual growth less severe than those modelled by our Scenario 2. Our results highlight that increases in water temperature induced by flow diversion for small RoR hydropower could be large enough to have consequences for O. mykiss growth, but the impacts depend on how and when RoR hydropower affects food supply and consumption.

From a continuous thermal profile to a stepped one: The effect of run of river hydropower plants on the river thermal regime

“…For example, site S4 was around 4°C warmer than S3 (14 vs. 10°C Figure 2) on average with maxima differing more than 8°C (in ~3 km). Such variations were in line with the one estimated by Gibeau and Palen (2020) for the by‐passed stretches of Douglas and Fire creeks (0.46 and 0.33°C/km the annual average up to 0.86–1.24°C/km in summer). By contrast, no marked alterations were observed in the Rhone River (France) where the thermal gradient in the by‐passed stretches and in the unaltered ones was comparable (~0.05°C/km).…”

“…In addition, its sensitivity is close to 0.30, the typical value of reservoir regulated rivers estimated at a regional scale. Similarly, the thermal gradient of the upper Serio is around 0.21°C/km (from S1 to S8) which is a typical value for intermediate responsive rivers (Caissie, 2006) and is slightly below the natural rate of 0.25–0.27°C/km, estimated in the Douglas Creek (British Columbia, Canada; Gibeau & Palen, 2020). The water thermal regime of the upper Serio depends mainly on meteorological conditions (daily mean air temperature and period of the year) but also on the presence of hydropower plants (both high‐altitude reservoir and ROR plants) whose influence, according to our model, is related to the distance from the reservoir and the ROR weir (D and L respectively).…”

“…While several studies investigated the thermal impact induced by low river flow downstream of reservoirs and small dams at different scales (Casado et al, 2013; Chandesris et al, 2019; Maheu et al, 2016; Seyedhashemi et al, 2021; Xu et al, 2021) very few addressed the thermal impacts in by‐passed stretches subjected to power plants. Among them, Wawrzyniak et al (2012) investigated the longitudinal and temporal thermal pattern of the Rhone River (France) in relation to hydroelectric and nuclear power plant diversions and Gibeau and Palen (2020) surveyed the ROR thermal impact in by‐passed reaches of Douglas and Fire creeks (British Columbia, Canada).…”

Modeling Seasonal Effects of River Flow on Water Temperatures in an Agriculturally Dominated California River

“…Given stream temperature's importance and vulnerability to human alterations, water managers need tools to predict stream temperature changes associated with climate change and flow management (Gibeau & Palen, 2020;Null et al, 2017). While process-based (i.e., deterministic) models simulating stream energy budgets can have high predictive accuracy, their use is limited by extensive data input requirements (Brown, 1969;Caissie, 2006;Dugdale et al, 2017).…”

Impact of a small hydropower plant on water quality dynamics in a diversion and natural river channel

“…Instead, the research focus is usually on hydroelectric plants in large reservoirs (e.g., Fantin‐Cruz et al., 2015; Wang et al., 2016; Zhao et al., 2020). Previous research on this topic has found that these plants had the most significant effect on the richness and structure of the ichthyofauna and benthos (Bidoglio et al., 2019; Silverthorn et al., 2018; Álvarez et al., 2020; Česonienė et al., 2021), river continuity (a hydropower plant acts as a transverse obstacle on the path of migration of organisms and causes habitat fragmentation) (Jumani et al., 2019; Gibeau & Palen, 2020; Puzdrowska & Heese, 2019), hydrologic conditions (changes in the amplitudes of fluctuations in the state, daily and annual flows, and the values of these parameters) (Alipour et al., 2020; Ding et al., 2019; Kucukali, 2014), accumulation and erosion of bottom sediments (Anderson et al., 2015; Isaac & Eldho, 2019), and the physicochemical composition of these sediments and water (especially within the context of nutrients and heavy metals, which are highly concentrated within the sediment) (Chen et al., 2018; Fantin‐Cruz et al., 2016; Wu et al., 2018).…”