Erosion • outline a cause of soil erosion in  NSW due to: – an agricultural process – urbanisation and identify a management strategy that prevents or reduces both of these causes of soil erosion (2.2.1) • gather information from first- hand or secondary sources to evaluate a program or strategy used in NSW to treat soil erosion

Weathering vs erosion vs deposition Weathering is the breaking down of rocks, soils and sediments into smaller particles. Weathering may be either chemical (e.g. dissolution of minerals in water) or physical (e.g. action of wind and water). Erosion is the transportation of rocks, soils and sediments to a new location. Two main erosive forces are wind and water, but may include glaciation, gravity, actions of animals. Deposition is the placement of transported material in a new location, e.g. some soil may be eroded from the side of the hill and deposited on the creek bank.

Causes of erosion The severity of erosion can be affected by factors such as: Geomorphology (shape of landforms) intensity of wind/rainfall patterns of water runoff (e.g. streaming, fanning) slope vegetation cover soil texture and particle size human activities e.g. ploughing

Wind erosion The wind is usually only responsible for moving surface layers of the soil. Wind erosion can be particularly damaging in agricultural situations when the topsoil has been exposed through ploughing. Can result in the movement of soil over large distances

Preventing wind erosion Due to the large scale loss of fertile top-soil over long time periods, the agricultural sector is trying to implement methods to reduce wind erosion. Planting windbreaks reduces wind speed. Reducing paddock size in combination with above will reduce wind intensity. Maintaining cover by using trees in grazing areas and stubble or ground covers in cropping areas. Surface roughening uses ridges and furrows to break up wind flow at the land surface and encourage deposition of air-born soil particles. Minimum tillage reduces soil disturbance and maintains structure

Minimum tillage Minimum tillage is an agricultural practice of tilling the land (through ploughing, ripping, etc.) as little as possible. Minimum tillage uses mulching to suppress weeds, improve soil structure and introduce organic matter. This replaces conventional practices such as rotating the soil by ploughing fallow (weeds) into the ground. Minimum tillage increases surface roughness by maintaining surface cover throughout the year. The soil is only tilled when absolutely necessary and should leave at least 30% of the soil undisturbed.

Costs/benefits of minimum tillage Greater reliance on manual labour rather than on machines Can be more expensive Benefits: Less erosion of soil through the action of wind and water More effective weed control Suppression of water loss through evaporation Land can be used all year around through crop rotation Soils need less fertilisers and herbides Greater soil health over the long term

Cut and fill On sloped lands in urban environments it is a common practice to use cut and fill to level out the land. Soil is cut from the upslope side of the land and used to fill the downslope side of the land. If the soil which has been cut and filled properly this can lead to soil erosion. The school oval is a good example of soil that has been cut and filled.

Retaining cut and filled land Both the upslope (cut) and downslope (filled) surfaces will need to be retained. Common methods of retaining include: retaining wall, which may be of rock, brick or hardwood geotextile sheets, e.g. silt barriers planting of fibrous rooted species such as grasses or Lomandras Gabions Often a combination of methods will be used to best retain the soil.

Gabions Gabions are wire structures filled with rocks of varying size. Generally, the steeper the slope to be retained, the larger the rocks. Gabions are often used in large projects involving cut and fill such as construction of roads.

Gabions

Gabions

Advantages of gabions Advantages: Protects against wind erosion and surface runoff Long lasting Can be pre-made or made on site Allow for good drainage Flexible so allow for some movement

Disadvantages of gabions Can be unsightly Little to no habitat value Can be expensive Difficult to replace breakages Often requires heavy machinery to install

Textbook questions Questions 1 & 4, p. 122 Questions 1,4 & 5 p. 127