Incised stream physical habitat restoration with stone weirs

Abstract

AbstractThe initial results are described of the restoration of 1 km long reach of Goodwin Creek, a channelized sand and gravel bed warm‐water stream draining a 21 km2 lowland catchment in north‐west Mississippi. Although a series of grade control weirs and bank protection works had been constructed before restoration, sediment production from channel erosion remained high (> 1200 t km−2 y−1) and aquatic habitats were of poor value. At base flow, only 5–20% of the water area was classified as pool habitat (depth >30 cm and velocity <10 cm s−1). Restoration works were designed to be compatible with existing channel stabilization works and economic critera. Stone was added to extend the existing groynes across the base flow channel to create 18 small weirs. The effects of restoration were quantified by collecting fish and physical habitat data semi‐annually for two years before and during the first year after restoration from the restored reach and from two reference streams. Restoration increased pool habitat availability, overall physical heterogeneity, riparian vegetation, shade and woody debris density. After restoration, mean width, depth and velocity exhibited changes of +56, +150 and ‐56%, respectively, despite discharge levels that averaged 43% lower during data collection periods. The pool area increased to 72% of the water area. Bed types became more heterogeneous, with larger fractions of clay, debris and riprap, and less sand and gravel. The fish response to restoration measures was modest, but distinct. Before restoration cyprinids and centrarchids comprised 74 and 11%, respectively, of the numerical catch, but 32 and 55% after restoration. Fish species composition and relative abundance after restoration were slightly more similar to that of the non‐incised reference site than before restoration. The median lengths of five selected fish species were greater after restoration, but were unchanged at reference sites.