On June 8 1993, a beaver dam on Rocky Creek, a small stream in central Alberta, failed and released about 7500 m(3) of water. The estimated peak of the resulting flood wave was 15 m(3) s(-1), which is 3.5 times the maximum discharge recorded for the creek over 23 years. The flood wave destroyed five hydrometric stations, scoured some channel reaches, and deposited sediment in others. Large trees and debris from old beaver dams were carried downstream and deposited in piles across the channel and adjacent banks. The flood wave peak was dampened to 6% of the estimated upstream flood peak as it passed through a 90-ha wetland characterized by both organic and mineral soils, sedge meadow and willow, and containing a small lake and several beaver ponds. Although the peak flow resulting from the dam outburst was extreme, the volume, most of which was probably detained in the wetland, was not. The volume amounted to only 7% of the combined basin runoff from precipitation and the beaver dam outburst. This extreme event showed that beaver activity can greatly affect the hydrology of small streams and demonstrated the importance of taking wetland storage into account when conducting hydrologic studies on watersheds that contain sizeable areas of wetlands.
