Rainfall Characteristics

The force exerted by a raindrop is one measure of ero-sivity. Empirical studies have shown a direct relationship between rainfall intensity and soil loss. Raindrop size is positively correlated with rainfall intensity. Higher-intensity storms will have a larger drop size, a greater kinetic energy, and more capacity to detach particles when striking the soil. In empirical studies, researchers found the product of maximum 30min rainfall intensity and storm total kinetic energy, the rainfall parameter, most closely related to storm erosion from standard 22.1-m-long runoff plots. Many process-based models use intensity squared to calculate raindrop detachment during a short period within a storm.

The recurrence interval of a storm of a given size in a given period of time, for example 100 mm in 24 h, is important in designing conveyance structures, storage ponds, road culverts, cross-slope bunds or terraces, ridging systems, basin pitting, and other supporting practices. The selected recurrence interval is based on the damage that may occur if the structure or practice fails. For supporting practices on cropland, a recurrence interval of 10 years is frequently used in design. This means that maintenance on terraces and other constructed practices will be expected about every 10 years. If the terraces are worn down by tillage, the recurrence interval will decrease. Erosion damage from failure of contour or cross-slope earthen structures on hillslopes can be severe.

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