Measurement Tool for Dynamics of Soil Cracks

Abstract

Shrinkage cracks in soil function as a dominant control on the partitioning and distribution of moisture fluxes in the vadose zone. Their dynamics influence the moisture balance and control water availability for runoff, deep infiltration, and near‐surface storage. We present a new low‐cost field instrument to monitor the temporal change in crack volume as affected by shrinkage and swelling cycles. The proposed crack‐o‐meter is composed of a sealed impermeable bag connected by a hose to a standpipe. An automated level logger records changes in the water level in the standpipe, which correspond to volumetric changes of the crack. The results from two laboratory experiments showed that the volume change observed by the crack‐o‐meter instrument scales linearly with the actual volume change, with an average error of 3%. The instrument was then used in a field experiment in Chile, where it measured the closing of cracks due to soil swelling.

Hillslope run-off thresholds with shrink-swell clay soils

“…Representative surface-connected cracks were chosen within the plots for monitoring. Monitoring consisted of two approaches: (1) large cracks within three plots were instrumented with the crackometer instrument (Stewart et al, 2012), which consisted of a 1-L intravenous therapy bag placed within the crack that was then filled with water from a connected standpipe, enabling measurement of relative volume change over the sampled area and (2) medium-to-large sized cracks from within five plots were marked by 0.5 × 0.5-m frames and then imaged throughout the experiment from a height of 0.6 m using a Pentax K-x digital SLR and a 28-mm lens. The surface area of the cracks was quantified by converting the image to black and white, representing the crack and soil, respectively, and then counting the number of black pixels.…”

“…If cracks do initially seal at the soil surface, the utility of surface‐based crack measurements (Zein el Abedine and Robinson, ; Ringrose‐Voase and Sanidad, ; Návar et al ., ; Wells et al ., ; Arnold et al ., ; Abou Najm et al ., ) may be limited. Instead, techniques that monitor subsurface crack dynamics, such as electrical resistivity tomography (ERT) (Samouëlian et al ., ; Samouëlian et al ., ; Amidu and Dunbar, ; Sentenac and Zielinski, ; Greve et al ., ; Greve et al ., ), or physically installing subsurface monitoring instruments into representative cracks (Stewart et al ., ) may prove more informative about the rate and degree to which cracks close.…”

Field measurements of soil cracks

“…In an attempt to directly measure relative changes in crack volumes, Stewart, Abou Najm, Rupp, and Selker (2012) developed a displacement-based instrument that is installed directly into a representative crack (see below). In its most basic configuration, the instrument consists of a bladder (inserted into the crack) that is filled with water or a similar fluid.…”

Advancing ecohydrology in the 21st century: A convergence of opportunities

“…Many of these sensors are well suited for use in environmental applications. For example, the pressure sensors from diving watches are accurate to within 1 mm of pressure‐head up to depths of 10 m, cost under US$10 each, and require only minimal energy (micro Amps; e.g., Stewart, Abou‐Najm, Rupp, & Selker, 2012). Accelerometers, regularly used in smartphones and game controllers, are inexpensive and ubiquitous.…”