Impact of multi-day rainfall events on surface roughness and physical crusting of very fine soils

Abstract

Soil surface roughness (SSR), a description of the micro-relief of soils, affects the surface storage capacity of soils, influences the threshold flow for wind and water erosion and determines interactions and feedback processes between the terrestrial and atmospheric systems at a range of scales. Rainfall is an important determinant of SSR as it can cause the dislocation, reorientation and packing of soil particles and may result in the formation of physical soil crusts which can, in turn, affect the roughness and hydrological properties of soils. This paper describes an experiment to investigate the impact of a multi-day rainfall event on the SSR and physical crusting of very fine soils with low organic matter content, typical of a semi-arid environment. Changes in SSR are quantified using geostatistically-derived indicators calculated from semivariogram analysis of high resolution laser scans of the soil surface captured at a horizontal resolution of 78μm (0.078mm) and a vertical resolution of 12μm (0.012mm). Application of 2mm, 5mm and 2mm of rainfall each separated by a 24h drying period resulted in soils developing a structural two-layered ‘sieving' crust characterised by a sandy micro-layer at the surface overlying a thin seal of finer particles. Analysis of the geostatistics and soil characteristics (e.g. texture, surface resistance, infiltration rate) suggests that at this scale of enquiry, and for low rainfall amounts, both the vertical and horizontal components of SSR are determined by raindrop impact rather than aggregate breakdown. This is likely due to the very fine nature of the soils and the low rainfall amounts applied

Impact of successive rainfall events on the dynamic relationship between vegetation canopies, infiltration, and recharge in engineered urban green infrastructure systems

“…Consistent with previous studies that reported decreased infiltration rates due to the formation of a physical crust (Bullard et al, ; Eze et al, ), the increased duration of surface ponding, especially in BaS Box #2, also suggests crust formation and associated reduced infiltration. Because the vegetation cover protected the underlying soil from raindrop impacts, hindering infiltration, the post‐storm ponding duration observed in VC Box #2 was significantly lower than observed in BaS Box #2.…”

“…The successive rainfall events increased PR in all surface treatment boxes, an observation reported by others (Bullard et al, ; Feng et al, ; Nciizah & Wakindiki, ; Neave & Rayburg, ), suggesting that surface crusts developed and progressed due to the raindrop impact‐induced processes. The rate of crust development was influenced by the area of the surface that was directly exposed to raindrop impact (e.g., that was not protected by canopy); the crust became stronger and continued to develop in the BaS boxes.…”

“…Both hand‐held and pocket penetrometers have been used to measure surface strength (Bullard, Ockelford, Strong, & Aubault, ; Chamizo, Rodríguez‐Caballero, Cantón, Asensio, & Domingo, ; Felde, Chamizo, Felix‐Henningsen, & Drahorad, ; Feng, Sharratt, & Vaddella, ; Moncada et al, ; Nciizah & Wakindiki, ; Rathore, Ghildyal, & Sachan, ). Following the procedure outlined by Bullard et al (), in this study, a Geotester Pocket Penetrometer was used to measure the surface's mechanical resistance to penetration (PR) after each simulation trial. A PR measurement campaign was performed prior to the first rainfall simulation and 24 hr after each subsequent simulation, on two of the three replicates for each surface treatment (BaS Box #1a and #1b, VC Box #1a and #1b; Table ).…”

“…According to Valentin and Bresson (1997) soil crusting can be monitored indirectly through observation of either a decrease in infiltration capacity or an increase in surface strength. Both hand-held and pocket penetrometers have been used to measure surface strength (Bullard, Ockelford, Strong, & Aubault, 2018;Chamizo, Rodríguez-Caballero, Cantón, Asensio, & Domingo, 2015;Felde, Chamizo, Felix-Henningsen, & Drahorad, 2017;Feng, Sharratt, & Vaddella, 2013;Moncada et al, 2014;Nciizah & Wakindiki, 2014;Rathore, Ghildyal, & Sachan, 1983). Following the procedure outlined by Bullard et al (2018), in this study, a Geotester (Yu, 2015).…”

Below‐cloud scavenging of fine and coarse aerosol particles by rain: The role of raindrop size

“…With the beginning of precipitation, a slight increase in the number of particles was recorded first, and then, a slow but steady decline. As stated above, the slight increase in the number of particles may be caused by resuspension (Pruppacher et al, ; Wang et al, ; Josserand and Thoroddsen, ; Bullard et al, ). The peaks in the number of particles occurred when the rain almost completely reduced its intensity.…”