Changing soil and surface conditions during rainfall - Single rainstorm/subsequent rainstorms

During rainstorms, physical properties of the soil surface change significa ntly. As a result of surface sealing, variations in infiltration rate, wate r content, water suction, bulk density and surface roughness can be observe d and quantified. Dynamic processes taking place on the soil surface were i nvestigated in laboratory and field experiments on a typical loess-derived soil in Germany. This study focused on the effects of continuous and subseq uent rainfall treatments. Furthermore, all laboratory experiments were carr ied out in two different initial moisture regimes. In the laboratory experi ments, a capillary rainfall simulator was used. Water suction was measured with microtensiometers 2 cm below the sealed surface in a 30 s time interva l. The water content was determined with TDR probes in a variable time step , depending on the movement of the infiltration front. Compared to the cont inuous rainfall treatment, the decline of infiltration rate was much steepe r in the subsequent rainfall events. After 2 h of continuous rainfall, a 'd rying effect' could be observed underneath the surface sealing at a depth o f 2 cm. This was not the case in the intermittent treatment. Saturated cond itions 10 cm below the surface sealing were reached in none of the treatmen ts. The variation of bulk density within the first centimeter of the soil w as determined via computed tomography and also with two simple methods usin g micro soil cores [Fohrer, N., 1995. Auswirkungen von Bodenfeuchte, Bodena rt und Oberflachenbeschaffenheit auf Prozesse der Flachenerosion durch Wass er. PhD Thesis, Technical University Berlin, Bodenokologie und Bodengenese, No. 19, 183 pp.] and immersion as described by Roth [Roth, C.H., 1997. Bul k density of surface crusts: depth functions and relationships to texture. Catena 29 (3-4) 223-237.]. Under continuous rainfall conditions, the initia lly dry plots showed a higher compaction than the initially moist treatment s. In the case of subsequent rainstorms, it was shown that the bulk density -depth function is not constant with time. The alteration of surface roughn ess was measured using a laser relief meter. The levelling effect of the in termittent rainfall regime proved to be much stronger in comparison to the continuous event.