Twenty mile Creek, was straightened and enlarged about 1910, 1936-37, and in 1966. Extreme channel instability followed the 1966 modifications, and corrective measures (placement of bank protection and construction of three grade control structures (GCS), were taken between 1982 and 1988. This report describes hydraulic and environmental studies which were performed to determine effects of the corrective measures. Environmental studies were structured to investigate recovery mechanisms. Other investigators have noted that other incised Mississippi streams have recovered stability by forming low-flow channels and vegetated longitudinal berms within the enlarged section. Low-flow channels have been suggested as features to ameliorate channel modification impacts on aquatic habitats. Woody vegetation cover on bank lines of selected reaches of Twentymile Creek and two reference streams was mapped from aerial photos taken before (1981) and 3 years after (1985) GCS construction. Aquatic habitat diversity was quantified for selected reaches along Twentymile and Mubby-Chiwapa Creeks by measuring depth, velocity, cover, and bottom type at regularly spaced points during summer low flow and using results to compute a Shannon function index. Fish species diversity and habitat diversity were only weakly correlated.

;Contents: Geomorphology; Channel geometry; Sedimentation; Hydraulics; Fluvial hydraulic models; Investigations of soils conditions; Instrumentation and field surveys; Channel improvement and stabilization measures.