08-TYPES-OF-SOIL-EROSION-SEDIMENTATION.pdf

SOIL EROSION AND SEDIMENTATION TYPES OF SOIL EROSION For. Jeshaiah Chen Mopheth B. Aguilar What is Erosion? Erosion is the physical wearing away of the earth’s surface by the agents of wind, ice, water, or movement in response to gravity. Surface soil material is removed in the p...

SOIL EROSION AND SEDIMENTATION TYPES OF SOIL EROSION For. Jeshaiah Chen Mopheth B. Aguilar What is Erosion? Erosion is the physical wearing away of the earth’s surface by the agents of wind, ice, water, or movement in response to gravity. Surface soil material is removed in the process. The severity of erosion depends on a combination of many factors, including the amount and intensity of precipitation, the texture of the soil, the steepness of the slope, and the amount of ground cover. Erosion is often quantified in terms of tons of soil loss per acre per year. A ton of soil may be visualized as the thickness of a sheet of paper spread over an acre. What is Sedimentation? Once soil material is broken free, it may be carried away and deposited elsewhere. Sediment is solid material that is or has been transported from its site of origin by air, water, gravity, or ice. The process of depositing eroded material is known as sedimentation. Some indications of sedimentation are mud in the street around storm drains and decreased water-holding capacity of a stream, reservoir, or pond. Soil erosion and sedimentation are naturally occurring processes. In fact, a certain amount of erosion is healthy for ecosystems, but too much erosion can cause problems. Why Should We Be Concerned About Erosion? 1. Erosion removes topsoil and reduces soil - A loss of topsoil, which often has important minerals, nutrient-rich soil organic matter, and high amounts of biological activity, creates a less favorable environment for plant growth. 2. Soil removed by erosion often ends up in waterways- Excess sediment in streams, rivers, ditches, and reservoirs, reduces their capacity to store water resulting in more frequent and severe flooding and increased property damage. 3. Excess sediment degrades water quality and aquatic habitat- Habitat areas and food sources are destroyed when fine silts cover the sand and gravel streambed.  Types of Soil Erosion Splash Erosion- occurs on the surface of the soil, when particles are displaced by the force of falling raindrops.  Types of Soil Erosion Sheet Erosion- occurs when rain is falling faster than the soil can absorb it, causing water to collect and flow over the ground. Splash and sheet erosion is nearly imperceptible to the untrained eye. Left untreated, it slowly and insidiously wears away topsoil, also known as the “A” horizon. Solution- The best way to alleviate excessive sheet erosion is a good vegetative cover.  Types of Soil Erosion Rill Erosion- results when surface runoff concentrates and forms small, yet well-defined channels, called rills. Types of Soil Erosion Gully Erosion- are formed when rills become deeper channels. Soil is rapidly removed by water gushing over the “headcut,” or uphill end of the gully. Large, wide channels carved by running water. As a rule of thumb, a gully is large enough that it cannot be smoothed out with conventional tillage equipment. Rill and gully erosion occurs when sheet flows build velocity over unprotected soil and begin to establish paths. This type of erosion is more visually noticeable than sheet erosion. Solution- These are best prevented by minimizing sheet flows with good vegetative cover. - Restoration of native plant communities will frequently help prevent recurring problems in critical or badly-damaged areas.  Mass Wasting Gravity is a constant force, always pulling towards the center of the Earth. This tireless force moves material downhill in a process known as mass wasting. Any downslope movement of rock and sediment is often referred to in general terms as a landslide. This occurs when certain factors cause a change in normal conditions.  Mass Wasting A natural slope will try to reach a balanced equilibrium. If the conditions change, then this balance may be upset, and a sudden mass movement may take place. The factors that most influence stability are: Gravity The shape and steepness of the slope. Water, which weakens the cohesive strength of certain saturated soils. Sensitive soils, or materials which are particularly susceptible to sliding. Triggering events or natural events like earthquakes and storms.  Types of Mass Wasting Fall- a sudden, nearly vertical movement of rock or soil. For example from an overhanging cliff.  Types of Mass Wasting Slump- the most common type of mass wasting in Napa County, involves the rotational movement of soil or other material along a curved surface.  Types of Mass Wasting Slide- is similar to a slump except the material does not rotate. Block slides are coherent blocks moving down the hillside, while a debris slide is a jumble of material.  Types of Mass Wasting Flow- is the movement of well-mixed, water saturated soil and rock.  Streambank Erosion This is a natural phenomenon. Creeks and rivers in equilibrium are dynamic systems: moving and depositing predictable amounts of sediment and shifting, eroding, and meandering within definable, usually well-vegetated riparian belts. -fin-