Instream Large Wood Enhances the Benefits of e-Floods in Regulated Mountain Rivers

Abstract

Environmental high flows, or e-floods, released from dams are a key management strategy to mitigate the impacts of dam regulation and restore aquatic and riparian habitats. While there is extensive literature on the design and implementation of e-floods, the role of instream large wood—downed trees, trunks, branches, and root wads—in enhancing e-flood outcomes in regulated rivers has not been adequately explored. This paper presents insights from the Spöl River in the Swiss Alps, where years of observations highlight the significant impact of large wood on the success of e-floods. Large wood contributes to geomorphological dynamics, increases habitat complexity, and enhances ecosystem resilience, yet it has been largely overlooked in e-flood planning. The study argues that the inclusion of instream wood can define the difference between success and failure in e-floods by supporting the continuity of the wood regime, which, along with flow and sediment regimes, is crucial for ecological integrity, and emphasizes the importance of integrating wood management into e-flood design. The Spöl River serves as a case study, demonstrating how wood management during e-floods can restore or sustain essential functions, ultimately improving the ecological health of river systems. The insights gained can be applied to the management of other regulated mountain rivers.