Laboratory Development of a Passive Proportional Sampler for Overland FlowStudies in Agricultural Fields

摘要

Water-quality in manyrivers remains poor and needs to be improved. Diffuse pollutioncontinues to cause difficulties. Some instruments are availablewhich can monitor pollution of rivers from land. They allowmeasurement and sampling of overland flow (OLF), but they donot offer the precision required (proportional sampling andsamples 0.1% of OLF). A laboratory unit was constructed tomimic instrument performance in the field. This was used to testthree sampler designs. A V-notch weir was used in the firstsampler and a Sutro weir in the second and third as this unitpossessed a proportional discharge to head ratio, which the Vnotchweir did not have. Other parameters investigated includedground slope, sampler slope, pipe size and port location. Theremaining issues of nozzle size (0.7, 1.0 and 2.0 mm), thenumber of 1.0 mm nozzles and the effect of aspiration wereinvestigated. The arrangement with the Sutro weir and three 1.0mm nozzles in series gave proportional discharge and the targetlow sampling rate of 0.1%. This will allow the calculation ofsediment and chemical losses for the monitored area and will putthe loss in context with other losses in a catchment.