Evaluating Recent Stream Channel and Pattern Changes for Stream Resource Protection and Restoration: An Example from 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, including watershed area, underlying geology, and land use. 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. Former channel positions were delineated from georeferenced aerial photographs from the period 1938 to 2002. Currently most streams are moderately to slightly entrenched into their basal channel gravels and the underlying till, outwash, or bedrock. Entrenchment is likely the result of channel straightening, mostly after 1938, but may also be due to reduced sediment yield resulting from improved soil conservation practices or urbanization. The physiographic floodplain is no longer accessible by more frequent flood events (RI < 5 yr), but active point bars and unit bars confined within the entrenched channels are redefining bankfull conditions and incipient meander migration is developing a new floodplain. Changes in sinuosity, radius of curvature, and meander wavelength between 1938 and 2002 along less-actively managed streams indicate the reaches are moving toward equilibrium relationships between bankfull channel and meander properties. A first approximation of the space in which the equilibrium pattern will develop is provided by the equilibrium relation between bankfull channel width and channel belt width.