EVALUATING RECENT STREAM CHANNEL AND PATTERN CHANGES FOR STREAM RESOURCE PROTECTION AND RESTORATION IN WEST-CENTRAL OHIO

Recent changes in stream channel and pattern morphology, hydrology, and channel and floodplain stratigraphy of nine streams in west-central Ohio are evaluated as part of a data-gathering phase of a stream resource protection plan. The study reaches represent the variation in external and internal drainage basin variables that likely control differences in channel hydrology in the county. Contributing watershed areas range from 5–79 km2, underlain by variable geology, including shallow bedrock, glacial till, and outwash and varying proportions of high-runoff and low-runoff soils. Land use varies from predominantly agricultural to mixed agricultural and high-density urban uses. A longitudinal profile and 6-8 cross sections were surveyed for each reach; particle sizes were measured and bank stratigraphy was described at each cross section. Along most reaches, the overbank deposits can be divided into an upper unit with less organic matter burying a lower, darker unit of greater organic matter. The upper unit is interpreted as floodplain aggradation resulting from deforestation as the land was cleared for agriculture. Currently most streams are entrenched through their basal channel gravels into underlying alluvium, glacial till, or bedrock. The reaches are moderately to slightly entrenched, based on designations from the literature, and the physiographic floodplain is no longer accessible by more frequent flood events (RI < 5 yr) as indicated by landowner observations, soil development on the floodplain, and approximations of bankfull discharge relative to measured or estimated annual flood peaks. Former channel positions were delineated from georeferenced aerial photos from the period 1938 to 2002 and in some cases using an electrical resistivity ground imaging system. General changes observed included decreased active channel width, increased sinuosity, and increased rates of meander migration, in most reaches resulting from less active channel management. Changes in sinuosity, radius of curvature, and meander length between 1938 and 2002 along less-actively managed streams indicate the reaches are moving toward equilibrium relationships between bankfull channel and meander properties. Recommendations for riparian setbacks to enable passive stream restoration will be presented.