Automated Microstandpipe System for Soil Erosion Research

Abstract

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° 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.

The influence of groundwater on surface flow erosion processes during a rainstorm

“…Thus, TDR was useful for indicating water contents before saturation and standpipes for indicating water table levels after saturation. Correlation of microstandpipe and TDR data gives accurate and precise indication of actual water levels (Rockwell, 1995;Bryan et al, 1999). Infiltrating wetting front depth was also measured with manual scales, every 2-3 min, at the transparent flume wall.…”

“…Design and construction is described fully in Rockwell (1995) and Bryan et al (1999). Standpipes were emplaced 0Ð25 m from the flume wall, as near to the central channel as practical without directly disturbing flow, at distances 0Ð25, 0Ð5, 0Ð75, 1Ð25, 1Ð75, 2Ð5, 3Ð5, 5Ð5, 7Ð5 and 9Ð5 m upflume from the weir.…”

“…Probes were placed horizontally D. L. ROCKWELL Figure 2. Microstandpipe; a full description of circuit design and use is provided in Bryan et al (1999) with the probe base 0Ð15 m from the flume wall, the tip 0Ð25 m. Water content was measured and recorded every 3 min at each probe. With probes at two depths, advance of the wetting front was measured, as well as saturation at each depth.…”

“…Much surface water flow research has addressed this question, especially with regard to erosion increases coincident with rill formation on disturbed agricultural soils, but results have been contradictory. Surface hydraulic parameters thought to be crucial often differ drastically between studies, and there has been little effort or success in coordinating results (Bryan, 1991;Bryan et al, 1999). Despite this lack of agreement, many studies still analyse surface flow hydraulic conditions as the sole factor influencing surface soil erosion, but hydraulic parameters treated independently continue to fail to determine surface flow erosion under varying soil or experimental conditions (Nearing et al, 1991(Nearing et al, , 1999Parsons et al, 1996;Desmet and Govers, 1997;Gabriels, 1999).…”

“…Using a suite of automated subsurface micropiezometers, tensiometers and time domain reflectometry probes (Bryan et al, 1999), as well as along-slope surface hydraulics, sediment, and soil data collection, this study will examine the influence of groundwater on processes of surface flow erosion during a rainstorm, at the rill scale on a disturbed agricultural soil. In order to clarify the likely extent of these effects, and their influence on the geomorphic and environmental consequences of hillslope erosion, effects due to seepage in saturated soils and pore-water pressure change in unsaturated soils will be differentiated.…”