Let it flow: Modeling ecological benefits and hydropower production impacts of banning zero-flow events in a large regulated river system

Åsa Widén; Birgitta Malm Renöfält; Erik Degerman; Dag Wisaeus; Roland Jansson

doi:10.1016/j.scitotenv.2021.147010

Let it flow: Modeling ecological benefits and hydropower production impacts of banning zero-flow events in a large regulated river system

Sci Total Environ. 2021 Aug 20:783:147010. doi: 10.1016/j.scitotenv.2021.147010. Epub 2021 Apr 10.

Authors

Åsa Widén¹, Birgitta Malm Renöfält², Erik Degerman³, Dag Wisaeus⁴, Roland Jansson⁵

Affiliations

¹ Department of Ecology and Environmental Science, Umeå University, 901 87 Umeå, Sweden. Electronic address: asa.widen@umu.se.
² Department of Ecology and Environmental Science, Umeå University, 901 87 Umeå, Sweden. Electronic address: birgitta.malm-renofalt@umu.se.
³ Institute of Freshwater Research, Department of Aquatic Resources, Swedish University of Agricultural Sciences, 178 93 Drottningholm, Sweden. Electronic address: erik.degerman@slu.se.
⁴ AFRY, Frösundaleden 2, 169 70 Stockholm, Sweden. Electronic address: dag.wisaeus@afconsult.se.
⁵ Department of Ecology and Environmental Science, Umeå University, 901 87 Umeå, Sweden. Electronic address: roland.jansson@umu.se.

PMID: 34088117
DOI: 10.1016/j.scitotenv.2021.147010

Abstract

Hydropeaking, defined as rapid and frequent changes in flow to optimize hydropower production, is an increasingly common procedure negatively affecting lotic habitats in riverine ecosystems. An important aspect of hydropeaking is zero-flow events, occurring when hydropower stations are stopped due to low energy demand or low electricity prices. We quantified the ecological benefits and consequences for hydropower production of restricting zero-flow events. The 19 major hydropower stations in the Ume River system in northern Sweden stand still with no discharge 9% to 55% of the time a hydrologically normal year, transforming lotic habitat to stagnant water. The duration of zero-flow events is exacerbated in dry years, with no discharge for 28% of the time in a typical station, to be compared with 7% in a wet year. Zero-flow events affect the behavior of fish, altering the fish community, and potentially result in low oxygen levels and low food supply to filter-feeding macroinvertebrates. We modelled the consequences of restricting zero-flow events by introducing minimum flows equaling mean annual low flow or higher for the entire Ume River catchment. The measure would result in an additional 240 ha of shallow lotic habitat with gravel to boulder streambeds having flow velocity exceeding 0.1 m/s, i.e. suitable for lotic species such as grayling Thymallus thymallus. In addition, the measure would enable creating another 107 ha of similar habitat after structural rehabilitation of river reaches. All measures would result in a mean loss of hydropower production of 0.5% per year for the entire river system, 98% of which would occur between May and October when the demand for electricity is lower. Hydropower production would also be partly moved from daytime to nighttime. As zero-flow events are common in several other river systems, restrictions on their frequency and duration could be implemented in many areas.

Keywords: Ecological restoration; Environmental flows; Hydropeaking; Hydropower production; Regulated rivers; Water flow velocity.