EXPERIMENT IN STREAM RESTORATION

Aquatic habitats in a deeply incised sand-bed channel were modified by adding 1,380 t of stone and planting dormant willow posts. Restoratio n structures (groin extensions and longitudinal toe protection) were d esigned as complements to existing channel stabilization works. Prior to restoration, base-flow aquatic habitats were characterized by unifo rm conditions, little woody debris or riparian vegetation, shallow dep ths, and sandy bed material. The stage-discharge relationship, channel geometry, and bed material size were unaffected by restoration, but t he average depth of scour holes adjacent to extended groins increased from 32 cm to 72 cm, and pool habitat in the lower half of the study r each increased from 2.9% to 14% of water surface area. Median water de pth at base flow increased from 9 cm to 15 cm. Woody vegetation cover on one side of the channel increased from 38% to 78%. Fish numbers tri pled, median fish size increased by 50%, and the number of species inc reased from 14 to 19. Groin extensions experienced partial failure due to erosion of sand from underneath stones.