Modification and performance of the Coshocton wheel with the modified drop-box weir

ABSTRACT:

Water-chemistry, sediment, and runoff data from erosion plots and small watersheds are often needed for erosion and water-quality studies where sediment concentrations can be large. Data may also be needed under conditions where approach channels are not appropriate for conventional measuring devices, such as in steep and skewed channels. The performance (sampler fraction) of the modified drop-box weir as the approach to the Coshocton wheel proportional water sampler was evaluated to meet these needs. Three splash-shield configurations on the sampling slot of the Coshocton wheel were investigated to control splashing of water and duplicate water sampling. Of the three shields, a dual-splash shield was required to control water splashing below the sampling slot and to insure proportional sampling of large flows. The Coshocton wheel worked well with the drop-box weir as the sampler approach under steady and unsteady flow conditions. The average proportional sampler fraction for the dual-shield configuration under steady flows was 0.0127 and for unsteady flows was 0.0120. This difference was not statistically significant. Coshocton wheel rotational speed was regular and increased with flow rate to about 35 rpm. After that, rotation became irregular, and the wheel stalled. No difference was found in a maximum-depth-of-flow parameter needed for sizing a drop-box weir based on sampler performance, compared with the parameter determined by performance of the drop-box weir alone (i.e., the wheel sampled proportionally at 100% of the design flow for the weir). This study extends the utility of the combined drop-box weir and Coshocton wheel system to steep and skewed channels.