Environmental-flow assessments for current and future run-off in a large river system regulated for hydropower production

• Main Author: Widén, Åsa
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Umeå universitet, Institutionen för ekologi, miljö och geovetenskap 2021
• Subjects: Environmental flows; eco-hydrology; hydropower; river ecosystem; environmental benefits; climate change; collaboration; resource management; Ekologisk reglering; vattenkraft; produktionsoptimering; hydrologi; hydraulik; akvatiskt ekosystem; miljönytta; klimatförändringar; samverkan; vattenresurs management; Ecology; Ekologi; Northern Sweden
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-187110

In 2019, Sweden implemented legislative changes to renegotiate hydropower permits to both consider environmental rehabilitation and to ensure national supply of hydropower. This means that efforts for environmental rehabilitation of the 2,000 hydropower plants in Sweden need to be considered. Such rehabilitation measures include implementation of environmental flows, enhancing connectivity or morphological restoration. In order to enable prioritization among measures, it is necessary to assess the expected environmental benefits and consequences of implementation. We developed a new method to assess and prioritize among environmental-flow measures that aim to rehabilitate ecosystems in regulated rivers at the catchment level, with the Ume River in northern Sweden as an example. The Ume River is heavily regulated for hydropower production with 19 hydropower stations, with 13 run-of river impoundments in cascade and six storage reservoirs. Our strategy was to identify measures with minimal impact on hydropower production that also provide significant environmental benefits. Based on field studies of remaining natural values and potential for ecological rehabilitation, we quantified the estimated gain in the area of habitat for target organism groups, e.g. lotic fish species and riparian plants, if rehabilitation actions would be implemented along the entire Ume River. Regulated flows imply changes in the seasonal variation in flow, which often means that spring floods are lacking and that flows increase during the winter compared with natural unregulated flows. Hydropeaking, defined as rapid and frequent changes in flow and water levels to optimize hydropower production, is a common procedure that adversely affects habitats in river ecosystems. An important aspect of hydropeaking is zero-flow events, which occurs when hydropower stations are stopped due to low electricity demand or low electricity prices. We quantified the consequences for hydropower production of introducing environmental flows by identifying a ...