Rainfall erosion

Weakening of Foundations, Diminishing Slope Stability, Erosion Landslides from Increased Rainfall. 

Steppes and steppic regions (pampas, prairies) receive between 250 and 500 mm of precipitation annually, i.e. more than twice the quantity that falls in true desert areas where rainfall is insufficient to support a vegetation that could protect the land from erosion. 

The semi-arid areas receiving somewhat higher rainfall are covered by a steppe-like fairly continuous vegetative cover of Xerophilous shrubs and grasses. In the Central Asian Plains, east of the Caspian Sea, wind erosion and transport are the dominant features. Sand dunes dominate the landscape for hundreds of kilometers. 

Because of the irregular rainfall distribution, mean precipitation values have little meaning in the (semi)-arid zone, if not also the range of variation is indicated. This variability refers to both temporal and spatial variability. Temporal variability affects not only the onset and duration of the rains in the year, but plays also a role in year-by-year differences. The variability is highest in the hyper-arid zone, where the mean precipitation value is composed of a few intensive rainstorms. When these fall on a heated barren surface - as is often the case in the arid zone - a part of it is immediately evaporated and lost for soil processes. High rainfall intensity results on the other hand in a rapid saturation of the surface layers and creates lateral runoff and erosion, in particular on sloping land. Many arid and semi-arid soils show therefore features of gully and sheet erosion. 

Wet-weather processes have, in general, been excluded in the text, because they are based on a different concept and perform differently. Microbial and physicochemical processes are contrary to the physical processes dominating in sewers during dry-weather transport of the wastewater. When dealing with combined sewer networks in terms of pollutant loads during overflow events, dry-weather solids deposition and erosion and solids transport during high-flow events are, in addition to the rainfall/runoff hydraulic and sewer solids characteristics, the central physical in-sewer processes. Quite different process approaches are, therefore, required to describe dry-weather and wet-weather sewer performance. 

Rizzo N, Sardo V, Vella P, Zimbone SM (1994) Investigations on hillslope erosion by means of simulated rainfall. Proceedings of the international symposium on forest hydrology. Tokyo, Japan, Oct 1994... 

The extent of transport of dissolved contaminants in overland runoff is controlled by the topography and morphology of the land (also affected by anthropogeiuc activity), the depth of chemical incorporation into soil, and the time between rainfall initiation and surface runoff commencement. In addition to these factors, transport of adsorbed contaminants on suspended particles is affected by rainfall intensity, which favors soil erosion. 

A reactive contaminant may be adsorbed on the soil surface prior to rainfall then, following rainfall that canses erosion, the soil is transported by rnnoff water in the form of suspended particles redistribnted on the land snrface. In general, the settling velocity distribntion dnring runoff indicates that the finer particles are resettled initially (Proffit et al. 1991), although the details of the settling process are affected by different environmental factors, such as soil type and rainfall rate. 

The water supply in both watersheds is primarily from rainfall, surface runoff, and springs that are entirely recharged by rainfall. This means that between late May and early September the watersheds receive too much water resulting in terrain instabilities, erosion, and flooding. After September there is continuous drying until late May with only the occasional occurrences of rainstorms. The historic rainfall records are of limited duration and apart from the extreme seasonal variability, it was not possible to show any evidence of changes in the rainfall pattern over the past 10 years [14]. 

Prolonged or heavy rainfall may produce erosion, moving the surface soil to other locations. It will almost certainly produce runoff that carries dissolved... 

Mudllows/dehris-llows that prograde downhill at high velocities, destroying obstacles in their path and depositing thick mantles of spoil on the surface Rill-erosion of spoil surface by surface runoff, especially where spoil is low permeability/rainfall is intense... 

The weight of soil carried in the surface runoff has been estimated by relating the sediment load to the rate of energy dissipation at the land surface by the rainfall and flowing water. The resistance of the soil to eroding forces has also been considered (4), and a method has been developed to estimate the net effect of erosion on radioaerosol transport. The volume of the liquid phase is estimated on a continuous basis by the Stanford watershed model, through consideration of a water budget. This feature has been retained in the HTM-1. 

Kutiel, R, Lavee, H., Segev, M., and Benyamini, Y. (1995). The effect of fire-induced surface heterogeneity on rainfall-runoff-erosion relationships in an eastern Mediterranean ecosystem, Israel. Catena 25, 77-87. 

Soil sediment from erosion was found in the Big Raccoon Creek in Indiana in the early 1980s. Some dry spells in the 1980s improved the situation, due to lower sediment loads. Rainfall was much heavier in the 1990s. However, sediment erosion has decreased due to the adoption of conservation tillage. In 1989, about 10% of corn and soybean acreage was no-till. By 1997, 84% of soybean was no-till, and 41% of com was no-till or strip-till (Brunoehler,... 

Grass and riparian hlter effectiveness in the North Carolina Piedmont varied based on storm intensity and watershed erosiveness, but decreased total sediment from 60% to 90% across a wide variation of natural rainfall (Daniels and Gilliam, 1996). 

The climatic conditions in India facilitate its role as a global contamination source for persistent toxic substances. Many geographers characterize the climatic changes in India as violent. There are often abrupt changes on the onset of monsoon rains, sudden flooding, rapid erosion, extremes of temperatures, tropical storms and unpredictable fluctuations in rainfall (www.indianchild.com/climate india.htm). By all these, India represents wide range of climates. 

Index Entries Corn stover wheat straw rainfall erosion wind erosion tolerable soil loss. 

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