The Ohio State University 1983-06 Photographic History of Forest Encroachment in Several Relict Prairies of the Edge of Appalachia Preserve System , Adams County ,
Forest encroachment into several relict prairies located within the Edge of Appalachia Preserve System, Adams County, Ohio, was studied using a series of U.S.D.A. aerial photographs taken in 1938, 1950, 1965, and 1971. The corresponding photointerpretations reveal increased herbaceous cover after abandonment of cultivated field sites and illustrate the conversion of prairie and prairie glades to forest. All sites studied exhibited decreased percentage of prairie from 1938—1971. OHIOJ. SCI. 83 (3): 109-114, 1983
Ohio's Natural Heritage
This publication was produced jointly by The Ohio Academy of Science and the Ohio Department of Natural Resources.
Velocity moments in alongshore bottom stress parameterizations
The time-averaged alongshore bottom stress is an important component of nearshore circulation models. In a widely accepted formulation the bottom stress is proportional to , the time average of the product of the instantaneous velocity magnitude |u→| and the instantaneous alongshore velocity component υ. Both mean and fluctuating (owing to random, directionally spread waves) velocities contribute to . Direct estimation of requires a more detailed specification of the velocity field than is usually available, so the term is parameterized. Here direct estimates of based on time series of near-bottom currents observed between the shoreline and 8-m water depth are used to test the accuracy of parameterizations. Common parameterizations that are linear in the mean alongshore current significantly underestimate for moderately strong alongshore currents, resulting in overestimation of a drag coefficient determined by fitting modeled (with a linearized bottom stress) to observed alongshore currents. A parameterization based on a joint-Gaussian velocity field with the observed velocity statistics gives excellent overall agreement with the directly estimated and allows analytic investigation of the statistical properties of the velocity field that govern . Except for the weakest flows, depends strongly on the mean alongshore current and the total velocity variance but depends only weakly on the mean wave angle, wave directional spread, and mean cross-shore current. Several other nonlinear parameterizations of are shown to be more accurate than the linear parameterizations and are adequate for many modeling purposes.