![]() ![]() Rill erosion also has a tremendous potential to move soil material. These small channels can transform into larger gullies. Rill erosion occurs when channelized runoff flows in an uncontrolled manner. Runoff on uneven surfaces or areas where soils are dispersive can result in rill erosion. Sheet erosion is common in areas which have poor soil structure, or are not managed properly. During a storm event, several tons of soil can be lost due to sheet erosion. With sheet flow, rain dislodges organic matter and topsoil which flows downstream resulting in significant soil loss. Both sheet and concentrated flow present a significant risk of erosion and scour to unprotected surfaces. Concentrated flow occurs when runoff flows through defined pathways (rills, catch drains, drainage channels, waterways etc.). Sheet flow occurs when runoff flows overland in a uniform sheet pattern. The two basic flow patterns for runoff are sheet flow and concentrated flow. Excessive runoff volume can also cause drainage problems by flooding of the low-lying areas. The surface runoff causes the secondary damage to unprotected soil by dislodging and washing away nutrient rich topsoil. A synthetic erosion control blanket or an impermeable liner can also mitigate evaporation. Vegetation is the most ideal way to mitigate the damaging impact of raindrops because a high percentage of total rainfall onto exposed soil evaporates. The resulting impact of a raindrop is potentially huge as it exerts significant erosive and compaction forces on bare soil. Eventually, the large raindrop assumes a bubble shape and bursts into numerous micro-droplets.Īs mentioned above, the terminal velocity of large raindrops can approach 36 km/hr. For rain drops with a diameter greater than 6 mm, the excessive aerodynamic forces result in their undersurface becoming concave. The interaction between the particles within the rain drop and the surrounding environment (surface tension) keeps the rain drops spherical however, rain drops greater than 2 mm diameter have greater forces acting on them which result in a flatter shape. For large drops and around 2 meters per second (7 km/hr) for the smallest drop of rain. It is interesting to note that terminal velocities of raindrops are approximately 10 meters per second (36 km/hr). Large drops of rain (greater than 6 mm diameter) loose stability and disintegrate while travelling through the atmosphere. Storms of high intensity can carry the large rain drops (5 mm or larger). Liquid precipitation less than 0.5 mm diameter is classified as drizzle.ĭuring a given storm event, rainfall comprises an array of drop sizes. The universal definition of rain is a form of liquid precipitation that drops greater than 0.5 mm in diameter. Precipitation can be either liquid (drizzle, rain) or solid (snow, hail). Our blue planet’s hydrologic cycle has three main components (evaporation, condensation, and precipitation).
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