A TALE OF TWO STREAMS: RESTORATION STRATEGIES COMPARED

Abstract: Many stream ecosystems are severely limited by damaged physical habitat. Channelization and associated accelerated erosion is a primary cause of damages in agricultural watersheds. Cost-effective strategies are needed to address erosion problems and restore stream corridor habitats. Detailed studies of restoration outcomes are rare. Herein we present a case study of two small streams (watershed size = 12 and 14 km2) damaged by channel straightening and incision. One stream was stabilized using a low drop grade control structure and dormant willow post planting, while the other was treated with a stone weir, stone toe bank protection, and willow sprout planting. Effects of restoration were monitored by collecting physical and biological data for one to two years before restoration and two to three years afterward. Following construction, channel planforms were stable, but up to 1 m of deposition and erosion occurred along the thalweg profile. Willow planting was not successful, so canopy, bank vegetation and woody debris density were unchanged. Pool habitat area increased from less than 5% to more than 30%. Fish species richness was unchanged, but species composition shifted away from cyprinids that occur in shallow, sandy runs toward pool-dwelling types (catostomids and centrarchids). Response to restoration was more modest than for two nearby restoration projects. Potential causes include less ambitious restoration design, greater initial degradation, and isolation from less-degraded sites which could serve as sources of colonists