Mitigation of environmental effects of frequent flow ramping scenarios in a regulated river

Abstract

In the transition to a society based on renewable energy, flexibility is important in balancing the energy supply as more intermittent sources like wind and solar are included in the energy mix. The storage-based hydropower systems are a renewable energy source that provides the needed flexibility since a hydropower plant can be started and stopped in minutes, and the reservoirs provide stored energy that can be utilized when the demand arises. Thereby, the hydropower plants can balance the variability in other energy sources, e.g., when there is no wind or when solar input is low. This need for increased flexibility has led research toward new hydropower turbines to provide larger ramping rates, more frequent starts and stops, and other system services. A possible drawback of the ramping operation of hydropower plants (often termed “hydropeaking”) are the adverse effects on the environment in receiving water bodies downstream of the power plant outlet, particularly when the hydropower outlets are in rivers. Rapid changes in flow can lead to stranding of fish and other biota during the shutdown of turbines and flushing of biota during the start of turbines. These effects can also be caused by other sudden episodes of water withdrawal, such as during accidental turbine shutdowns. The main objective of this study is to describe a method of designing the necessary volume of water required to mitigate a fast ramping turbine, and present the effect this has on the downstream river reach. We used a 2D hydraulic model to find the areas affected by hydropeaking operation and, furthermore, to define areas with a faster ramping rate than 13 cm/h which is used as a limit in Norwegian guidelines. Based on this, we developed a ramping regime that would prevent fast dewatering of critical areas and provide this as a basis for mitigating the effects of fast dewatering in the downstream river (River Nidelva in Norway was used as a test case). Furthermore, the effect of increasing the frequency of start–stop cycles was studied, and the proposed mitigation was evaluated for the new operational regime.

Effect of flow ramping on stranding potential related to river morphology—Developing hydraulic indices for peaking severity

“…A dampening of the ramping rate is seen in all our study sites as we progress downstream from the outlet, which can be related to the dampening effect of the morphological features of the river. Similar dampening is seen also by Burman et al (2021) who modeled how the duration and frequency of turbine stop propagated in a bypass channel in the Ume River, by Hauer et al (2017) in a study in the Drau River in Austria and by Alfredsen et al (2022) in a study in Nidelva in Norway. Compared to the study by Hauer et al (2017), we also see comparable magnitudes of ramping.…”

“…dampening is seen also byBurman et al (2021) who modeled how the duration and frequency of turbine stop propagated in a bypass channel in the Ume River, byHauer et al (2017) in a study in the Drau River in Austria and byAlfredsen et al (2022) in a study in Nidelva in Norway. Compared to the study byHauer et al (2017), we also see comparable magnitudes of ramping.…”

Exploring sensitivities to hydropeaking in Atlantic salmon parr using individual‐based modelling

“…The hydrodynamic model simulated flows during hydropeaking that were consistent with those measured: simulated and measured water levels were highly correlated ( r 2 = 0.99), and there was only a 3% difference between simulated and measured water‐covered area (see Alfredsen et al, 2022). Water‐covered area and water velocity and depth predicted by the hydrodynamic model greatly differed between maximum (135 m 3 s −1 ; Figure 4a) and minimum (30 m 3 s −1 ; Figure 4b) discharges.…”

“…The hydrodynamic model simulated flows during hydropeaking that were consistent with those measured: simulated and measured water levels were highly correlated (r 2 = 0.99), and there was only a 3% difference between simulated and measured water-covered area (see Alfredsen et al, 2022). Water-covered area and water velocity and depth predicted by the hydrodynamic model greatly differed between maximum (135 m 3 s À1 ; Figure 4a) and minimum (30 m 3 s À1 ; Figure 4b) down-ramping and up-ramping phases, when parr were redistributing themselves towards the changing pattern of optimal habitat, a median of 85% of non-stranded parr were moving towards optimal habitat during each time-step of the simulation.…”

By‐pass valves in hydropower plants: An ecologically important measure to mitigate stranding in rivers due to emergency turbine flow shutdown

“…These dewatering events may originate from planned hydropeaking operations, as well as accidental shutdown of HP turbine flow due to, for example, failure in the electricity system, extreme weather events, lightning events, blocking of HP intakes (e.g., ice run, woody debris) or human errors (Molkersrød, L'Abée‐Lund, & Rørstad, 2019; Ward, 2013). This may result in severe stranding of riverine biota, if there is a lack of adequate structural measures such as for example, retention basins (Alfredsen, Juárez‐Goméz, Refaei Kenawi, Graf, & Saha, 2022; Hayes et al, 2022). Regardless of the cause, a sudden drop of the river flow may be detrimental to the fish populations, as such events do not occur naturally in rivers, especially if they occur irregularly (Halleraker et al, 2003).…”