Automated microstandpipe system for soil erosion research

The influence of soil water on erosion is well known, but the full effect of variations in water conditions on erosional processes has only recently been recognized. Micro time domain reflectometer (TDR) probes and microtensiometers have provided some precise temporal and spatial data necessary for soil erosion models, but data on local water table dynamics are also needed to explain rill incision and network development processes. An automated multiprobe microstandpipe system we developed provides continuous water table data at spatial and temporal scales comparable to those from microtensiometers and TDR microprobes (temporal precision: 1-3 min). The new system uses small probes etched with open-ended conductors to provide incremental information on water table height with +/- 0.25 cm resolution. It has been used in a range of soil erosion experiments, one of which is used to demonstrate the system by examining drainage of interrill slopes in response to rill incision. This experiment was carried out in a 10 m by 0.8 m by 0.3 m laboratory flume under simulated rainfall at 43.4 mm h(-1) on a 5 degree slope, using a composite mixture of Arenic Hapludalf sandy mixed mesic and Aquic Hapludalf clayey mixed mesic soils at 4:1 ratio. The microstandpipe system showed sensitive response to a saturated wedge that progressively extended upflume after initiation at the terminal weir. Despite separation between instruments, agreement between the microstandpipe system, microtensiometers and micro TDR probes was good. Rigorous statistical analysis was not possible, but data suggest that temporal agreement of +/- 5% is realistic. Despite instrumental precision, the expected interrill drainage response to rill incision was not apparent.