USDA Coshocton-Type Runoff Sampler, N-3

The Coshocton-type runoff sampler is constructed to form a single unit with the small H flume. Three basic models, N-1, N-2 and N-3, have been designed for use with the 0.5, 1.0, and 1.5 foot (15.2, 30.5, and 45.7 cm) H flumes. Models N-1 and N-2 have been used extensively in the field. A typical field installation is shown.

Sampler size and capacity for a given experiment are determined by the capacity of the H flume required to measure peak runoff rates. Slightly oversized flumes and samplers are recommended because the sampling error increases significantly at discharges above 80 percent of flume capacity. For small plot studies the maximum runoff rate is assumed to equal the maximum expected 5-minute rainfall rate. Sample storage capacity is provided for the aliquot sample from the maximum 48 hour runoff event.

Water discharge from the H flume falls on the water wheel, which is inclined slightly from the horizontal, and causes the wheel to rotate. An elevated sampling slot mounted on the wheel extracts an aliquot sample as the slot traverses the flow jet with each revolution of the wheel. The sample is routed through the base of the wheel to a sample storage tank.