Experimental floods in the River Spöl, Swiss National Park: Framework, objectives and design

Between 2000 to 2002, 11 experimental floods were released from 2 reservoirs separating different regulated segments of the Spöl River in the Swiss National Park. The riverbed of the Spöl had been altered substantially by regulated flows since energy production started in 1970. This 3-year experiment aimed to test whether an annual flood regime could restore riverine dynamics to this regulated river and, if so, how the floods must be managed in respect to a minimal but regular flow disturbance required to maintain riverine dynamics in a near natural state. This article outlines the framework, objectives and design of the experimental flood program on the River Spöl. The study involved a number of institutions controlling operational, economical, legal and ecological matters related to the floods, and was planned under the constraint that the floods would result in no increase in total water release during each year and no loss in total energy production. Concomitant cross-disciplinary environmental studies monitored the diverse impacts of each flood on the respective regulated segments. The various results, as shown in the accompanying reports, suggest that one or two annual high flows may be sufficient to enhance and sustain the ecological integrity of the Spöl over the long term.