How much surface water can gilgai microtopography capture?

- Water capturing capacity of gilgai microtopography in Vertisols was calculated.
- An average circular gilgai depression can hold 0.78 m3 of water.
- Findings indicate a 0.024 m3 m−2 surface water capturing capacity in a typical gilgai landscape.

SummaryGilgai microtopography is associated with landscapes of strongly shrinking-swelling soils (Vertisols) and affects spatial and temporal variability of runoff, and thus the generation of stream flow and plant-available water. However, no report is available on the amount of surface water that a landscape with gilgai depressions can retain. Our objective was to assess water capturing capacity of a typical Vertisol landscape with gilgai depressions in the Blackland Prairie Major Land Resource Area of Texas. The 45 by 40 m study site was located on a Vertisol with circular gilgai covered by improved pasture on a summit with slope of less than 3%. A digital elevation model (DEM) with 0.25 m2 cell size was created from elevation data acquired by using GPS. Water capturing capacity of gilgai depressions was estimated at 10 randomly selected local gilgai basins by analyzing spatial distribution of Topographic Wetness Index (TWI). Our findings indicate that the average circular gilgai depression can hold 0.78 m3 of water leading to an estimate of 0.024 m3 m−2 water capturing capacity in a circular gilgai landscape, assuming no infiltration. The gilgai could capture a maximum of 43.74 m3 of rain and runoff water at the 1800 m2 study site. Consequently, if the soil were saturated and not infiltrating any water, no runoff would be expected following a 24.3 mm m−2, 1 h precipitation, affecting estimates of streamflow (runoff) and plant available water (redistribution and infiltration) at the m to km scale.