The Role of Surface Sealing Caused by Subsequent Rainfall in the Runoff Components at the Kojour Watershed Mazandaran

Abstract

Degradation of aggregates due to rain drop impacts leads to surface sealing formation, roughness reduction, filling of soil pores and consequently increase in the runoff rate and soil loss. Despite the effect on aggregate breakdown and formation of surface sealing, rainfall sequence is among the factors that have been less studied so far. Effect of three subsequent rainfalls and surface sealing formation were investigated on runoff and soil loss components in small experimental plots under simulated rainfalls with the intensities of 50 and 90 mm h-1 and duration of 15 min after time to runoff, in two soil types of sandy-loam and sandy-clay-loam, respectively. The results indicated that soil surface seal was formed by subsequent rainfalls in both of the studied soil textures and rainfall intensities. The rainfall sequence had the significant effect (P<0.01) on the time to runoff initiation, runoff volume and runoff termination. Based on the results of a 3D scanning, soil surface roughness decreased from 1.30 to 1.18 in sandy-loam and from 1.80 to 1.31 mm in the sandy-clay-loam soil as a result of rainfall sequence with the intensity of 50 mm h-1. However, soil surface roughness increased and became 2.37 and 1.99 mm in sandy-loam and sandy-clay-loam soils, respectively, at the rainfall intensity of 90 mm h-1. Regarding the effects of vegetation residues on the structural modification and physical protection of surface soil against raindrop impacts, it is suggested to reduce grazing and also to increase the vegetative cover in the area in order to reduce surface sealing.

Keywords

• aggregate stability
• 3d scanner
• hydrological response
• rainfall simulator
• soil surface roughness