Shallow Groundwater and Surface Runoff Instrumentation for Small Watersheds

An acquisition system was constructed to sample and quantify surface runoff and shallow groundwater. The main components of the system for shallow groundwater included hydrologically isolated erosion plots with subsurface drains (installed via horizontal drilling), outlets into sumps, tipping buckets mounted under drain outlets, composite water samplers, and a series of sampling piezometers ranging from 0.3- to 6.1-m (1- to 20-ft) depths positioned in one row of each main plot. The main components of the system for surface runoff from standard-sized erosion plots cropped to corn were appropriately sized collectors, approaches, H-flumes equipped with portable liquid-level recorders, runoff splitters, dataloggers, and composite water samplers. The dataloggers recorded rainfall and runoff every minute and groundwater discharge volume every 15 minutes during storm events. Water samplers were activated by the dataloggers when the cumulative discharge volumes equaled or exceeded a preset condition. Derived variables from surface runoff were incremental discharge rate, cumulative discharge volume, sediment loads, and water quality. Groundwater incremental discharge and total discharge volumes were recorded and the composite of the weighted-discharge samples were analyzed for specific chemicals introduced as fertilizer or pesticides. Depth of free water within each piezometer after major storm events was monitored to determine water movement in the root and vadose zones.