Culvert Composite Sampler: A Cost-Effective Storm-Water Monitoring Device

Abstract

A low-cost urban storm-water sampling device (culvert composite sampler) has been designed, developed, and field tested. The device provides an economical alternative to current procedures used for collecting flow-weighted composite samples required for NPDES monitoring, assessing urban storm-water inputs, and evaluating the effectiveness of best management practices. The composite sample volume collected during a runoff event is used to estimate the total runoff volume transported by a culvert during the storm. The sample is easily transferred to a laboratory bottle for chemical analysis that, with the total culvert flow estimate, is used to determine the pollution loading contributed by a drainage area to a receiving water body. The device costs less than $100, has no moving parts, and uses gravity flow. Initial studies of the proof of concept compared the performance of the culvert composite sampler against that of a flowsplitter composite sampler and manual sampling during three storm events at an established monitoring site. Tests were also performed in the controlled conditions in a laboratory hydraulic flume. The chemical results indicated that the culvert composite sampler closely approximated the flow-weighted composite collected with the flowsplitter (a true flow-weighted sampler). The culvert composite sampler estimated total culvert flow within 12% of the flow calculation based on manual sampling field measurements. Additional tests are in progress to observe the performance of the culvert composite sampler in a greater number and variety of storms events.