A Review of Literature of Erosion of Soils

Introduction

Numerous work and research have been undertaken on erosion of soils for many decades. The following literature review is focusing on the relevant topics in terms of soil erosion process as well as the parameters and factors of soil erosion .Moreover, the literature reviews is primarily focusing on the management and control the soil erosion.

1 Soil Erosion by Water

To perform this study, it was necessary to understand how soil erosion occurs. Usually it occurs at a low level but can become a problem when the ecological balance disturbed by human’s activities or severe weather .The risk of erosion by water when soils with a high sand or silt content that exposed to heavy rainfall. (Defray 2005). It is crucial that considering rainfall and runoff factors when assessing a water erosion problem (BC.S.Baldwin 2003) .Although the soil erosion caused by long-lasting or less-intense rainfall is not as spectacular .But soil movement by rainfall is most noticeable during the short-time, high-intensity thunderstorms and the amount of soil loss can be considerably, especially when compounded over time. While the excess water on a slope that cannot be absorbed into the soil or trapped on the surface, the runoff will occur. The amount of runoff can be increased if infiltration is reduced due to soil compaction. (BC.S.Baldwin 2003)

Two stages process involved in the soil erosion, which depend on water detaching and transporting soil. Rainsplash is a key determinant of detachment of soil particles in the first stage of erosion. However, if a growing crop covers the soil surface, the erosive power of rain will dramatically reduced. Once it detached, surface water run off plays a key role in the process of soil particles being transported. Surface run-off can be easily happening during the heavy storms or prolonged rainfall. (BC.S.Baldwin 2003)

Tess Wynn investigated the streambank retreat. Normally it is called streambank erosion, the occurrences involved the combination of three processes, subaerial process, fluvial entrainment and mass wasting. Specifically. The term “subaerial process” is used to describe the climate- related phenomena that reduce the strength of soil .It mainly controlled by climatic conditions, and overly independent of flow. Subaerial processed are often called “preparatory processes” due to they increase the susceptibility of soil to erosion at high flows (Wolman, 1959;Lawler, 1993)

Apparently. Fluvial entrainment means the direct removal of soil particles or aggregates from the streambed or banks by flowing water. (Tess Wynn 2006), but the fluvial erosion of cohesive soils is extremely complex and related to soil properties and test conditions (Grissinger, 1982). The susceptibility of a cohesive soil to erosion influenced by numerous of the parameters of soil, including grain size distribution, soil density, pore water content and chemistry (Grissinger, 1982)

Mass wasting also known as bank failure, it occurs when the weight of the bank exceeds the shear strength of soil. The mass wasting can be attributed to increasing the bank height or bank angel due to fluvial erosion or the presence of tension cracks (ASCE, 1998).Research has proved that bank geometry, properties of bank materials and the density and the type of bank vegetation play the key role the occurrence of mass wasting.

Hu Liu, Theodore G. Cleveland, and Keh Han Wang conducted the laboratory tests of dependence on properties of soils and. In their study, rainfall was generated by the rainfall simulator; along with flume .The rainfall simulator consist of a wooden frame and a group of PVC pipes with small holes. The soil sample was placed at one end of the flume .In the experiment, the simulator activated by the adjustment of the slope. In addition, six type of soil with different texture and classifications used in this laboratory experiments. The results show more soil erosion produced by the higher rainfall intensity. Besides, the unit soil volume loss affected by shear strength, compressive strength and rainfall intensities but less influenced by the bed slope. (Hu Liu, Theodore G. Cleveland, and Keh Han Wang, 1999) Jill Fernqvist and Ida Florberger conducted their research in South Africa .Their study indicated the fires are one the important factor that changes the soil properties .their study has been taken in the Western Cape,. The fieldwork focused on water repellency has detrimental influence upon the post-fire erosion Jill Fernqvist and Ida Florberger(2003)

2 Soil Erodibility

Soil erodibility is an estimate of the ability of soils to resist erosion in term of the physical characteristics of soil. Generally, the faster infiltration rates of soil, the higher levels of organic matter and improved soil structure have a greater resistance to erosion silt, very fine sand, and certain clay textured soils tend to be more erodible than Sand, sandy loam and loam textured soils cropping practices which lower soil organic matter levels, cause poor soil structure, and result of compacted contribute to increases in soil erodibility. Compacted subsurface soil layers result in decreased infiltration and increased runoff. A formation of a soil crust, can create the decreased of infiltration, however, normally the growth of runoff water is attended by the greater soil erosion problems. (BC.S.Baldwin 2003)

There is a definite link between Past erosion and soils. The original soils tend to be less erodible than the exposed subsurface soils on eroded sites were, owing to their lower organic matter or poorer structure .The lower nutrient levels usually related with subsoils contribute to lower crop yields and generally poorer crop cover, which in turn provides less crop protection for the soil. (BC.S.Baldwin 2003)

Gregory J. Hanson provided the complex problem about how to predict the erodibilty of soil material by flowing water. Base on the knowledge of hydraulic characteristics and the characteristics of cohesive soils .Laboratory Jet tests were carried out on soil samples compacted at different moisture content dynamic. Jet detection apparatus and method description of the excess stress parameters determined kd and tc. An example of this is used to test the soil in the laboratory to determine the appropriate placement in the field. The flume tests and field trials were carried out to verify the plane corrosion. (Gregory J.2002)

3 Slope Gradients and Length

Basically. The steeper slope areas, the greater amount of soil erosion by water.Soil erosion of water also increased with slope length due to the greater accumulation of runoff. The consolidation of small fields into larger results is often no longer the slope length of the potential for erosion, because water with an increase rate that allows a greater degree of scouring (carrying capacity of the sediment) (BC.S.Baldwin 2003)

4 Soil Deposition

Soil particles of all sizes may be moved during run-off. When flow stopped, these start to settle. According to the US Environmental Protection Agency (USEPA), sediment is a root cause of water quality impairment (USEPA, 2002).excess Suspended sediments to reduce diversity and rich of aquatic organisms, reduce reservoir capacity, improve drinking water treatment costs, and serve as a carrier of pollutants.(Tess Wynn,2006)

The erosion process of cohesive sediment was studied in Masato Sekine and Nobuaki Iizuka study .To full understand the process, they also conduct an experiment .Clay mixed with different compositions were used to test samples of the form of erosion of water pipes in a closed experimental apparatus. Specifically .Experiments carried out a square circle closed pipeline system cross-section 400 centimeters in length and 10 centimeters wide, 10 centimeters deep.

5 Vegetation

The potential of soil erosion is increased, if the soil with little or no vegetation, plants and crop residues. Residue cover to protect plants and soil from rain splash, tends to slow down surface runoff flows, and ensures excess surface water infiltration.

Erosion soils reducing the efficiency of the plant or residue cover depends on the category, degree and quantity of cover. Combination of vegetation and residue completely covered the soil, and to intercept all falling raindrops, and near the surface and the most effective control of soil (such as forests, permanent grassland). Part into the residue and the root is also very important because they provide the channel that allows surface water into the soil.

The effectiveness of any crop, management system or protective cover also depends on how much protection can be at different times during the year, the relative amount of erosive rainfall during these periods belong to. In this aspect , the crops with food, protective cover a major part of the year (for example, alfalfa or winter cover crops) can reduce soil erosion can be far more than crops leave the soil bare for a longer period of time (such as row crops) , especially during the high erosive rainfall (spring and summer).( C.S.Baldwin 2003)

I.J. Shelton also investigated tillage operations influence upon the soil erosion, which depending on the depth, direction and timing of the plowing, the types of farming equipment and a number of passes. Generally speaking, the less interference or residual vegetation cover at or near the surface, the more efficient farming practices, and reduce soil erosion (I.J. Shelton 2003)

Soil erosion potential is affected by tillage operations, depending on the depth, direction and timing of plowing, the type of tillage equipment and the number of passes. Generally, the less the disturbance of vegetation or residue cover at or near the surface, the more effective the tillage practice in reducing erosion.

Regarding the effects of vegetation on streambank stability , Tess Wynn examined the vegetation influences the chemical and properties of steambanks and the local micro climate .The multiple effects on subaerial process produced by riparian vegetation including the dense cover of vegetation absorbs the energy of rainfall ,reducing soil detachment by raindrop . But it should be noted that the effects of vegetation on stream hydraulic varies with the stream stage, width and season. Additionally. Distribution of energy and sediment in a stream influenced by the vegetation. (Tess Wynn 2006)

Tess Wynn 2006 addressed the vegetation cover problem. Extensive erosion by wind may result from the lack of permanent vegetation cover in certain locations. Loose, dry, bare soil is the most susceptible; however, crops that produce low levels of residue also may not provide enough resistance. Besides, crops that produce a lot of residue which not protect the soil in severe conditions. Therefore, an adequate network of living windbreaks along with good tillage, residue management, and crop selection are considered to be the most effective vegetative cover for protection. (Tess Wynn 2006)

South Africa is a country which lack of the water, but the Jill Fernqvist and Ida Florberger have described the theory of fire -induced water repellency and the following soil erosion in their study. Generally, In South Africa, alien species require more water than the indigenous one. Therefore, alien vegetation provides a poor ground cover compared to the indigenous vegetation, which could result in surface run off and soil erosion (.Jill Fernqvist and Ida Florberger 1996).

Jill Fernqvist and Ida Florberger observed the Alien vegetation apparently has been considered as a key issue in the ecosystem of Western Cape. Water yield was decreased in the long term due to the alien vegetation consume a large amount of water, as a result, the biodiversity is threatened. In addition, fire in the alien vegetation for the results of erosion-prone slopes. (Jill Fernqvist and Ida Florberger, 2003)

Defra (2005) summarized the Management Practices using Vegetables and Salad Crops in soil erosion Control. And offered some solutions to prevent the soil erosion when undertaking the cultivations, irrigation and harvest. (Defra 2005)

6 Soil Erosion by Wind

Soil is also erosion by wind, although the effect is not noticeable like the erosion by water. C.S.Baldwin studied the rate and magnitude of soil erosion by wind is decided by many factors: Erodibility of Soil The wind suspends very fine particles and then transported great distances. Fine and medium size particles can be lifted and deposited by wind. While coarse particles can be blown along the surface (commonly known as the saltation effect). Soil Surface Roughness Soil surfaces only provide little resistance to the wind. However, ridges can be filled in and the roughness broken down by abrasion to produce a smoother surface susceptible to the wind in a long time. Excess tillage is a threat to soil, because it breakdown the soil structure and increased erosion. Climate There is a define link between the speed and duration of the wind and extent of soil erosion. The levels of Soil moisture can be very slightly low at the surface of excessively drained soils or during periods of drought, and releasing the particles for transport by wind. It occurs in freeze drying of the surface in winter.

Adverse operating conditions maybe created by wind erosion in the field. Crops can be completely ruined so that costly delay and reseeding is necessary (C.S.Baldwin 2003)

7 Effects of Soil Erosion

The negative changes from bank erosion including farmland productivity losses, damage to building structures such as bridges, roads etc. I.J. Shelton defined the on-site effects and off-site effects. On-site effects mean extension of the elimination of the impact of soil erosion of valuable topsoil. Crop emergence, growth and yield a direct impact on the loss of, natural and applied fertilizer and soil nutrients. Seeds and plants may interfere with or completely abolish the erosion site. Organic matter in soil, residues and any applicable fertilizer, a relatively light weight, can be transported off-site, especially in the spring thaw conditions. While the off-site effect is not always obvious as on-site effects, but Eroded soil, deposited down slope can inhibit or delay the emergence of the seed, bury small seedling, need to replant in the affected areas. Soil quality, structure, stability and texture can be affected by the loss of soil. The breakdown of aggregates and the removal of smaller particles or entire layers of soil or organic matter can weaken the structure and even change the texture. Textural changes can in turn affect the water-holding capacity of the soil, making it more susceptible to extreme condition such a drought. (I.J. Shelton 2003) According to the C.S.Baldwin (2003), Sediment can contribute to road damage, accelerate bank erosion, and reduce downstream water quality. What is worse, Pesticides, and fertilizers, which contained in the soils. They frequently transported with eroded soil pollution or contamination of water downstream and entertainment district.

8 Conservation Measures

While, based upon research, various conservation measures can be taken to reduce soil erosion by both water and wind. Tillage, cropping practices, and land management practices, have a direct impact on the overall soil erosion problem and solutions to a farm. When crop rotations or changing tillage practices are not enough areas where erosion control method or a combination of more extreme measures may be necessary. For example, contour plowing, strip cropping, or terracing may be considered. (C.S.Baldwin 2003)

The defra (2005) advised measures about how to control the soil erosion. In their study, four categories of solution were presented. It is crucial to understand that erosion control on susceptible soil types can be successfully achieved to reduce the impact of rainfall erosion and maintain soil infiltration rate, so that the surface flow are avoided. It can be achieved by 1 To protect the soil from rainfall impact, whether it is permanent vegetation cover or land rotation, timely crop establishment and retention of surface crop residues. 2 Avoiding smooth, flat finishes to exposed field surfaces, so that good water seepage rates remain unchanged. 3 Avoiding tramlines, wheeling or cultivation features that can channel surface flow. 4 Seeking to increase the organic matter content in the means of improving the stability of the soil in the longer term.

Steep slope and erosion because of increased risk, the efficiency of these measures is becoming increasingly important. When deciding on the combination of measures to apply in any particular situation, consideration should always be the serious erosion that may occur, if the case happened. In some cases, a measure aimed at controlling erosion may increase. For example, work along the contour is sometimes used to reduce runoff, but if the profile is not strictly followed, the accumulation of water at low points which might break over the cultivation features. (Defra 2005)

Meanwhile, good management practices play a pivotal role in the control of soil erosion. Some examples and considerations were presented in defra (2005) study. In order to minimize the soil erosion when soil in the most vulnerable condition, the different type and timing of cultivations should be planned. Obviously, the overall aim should be the soil maintain in a less vulnerable condition as long as possible .Therefore, defra (2005) provided the good management of the farm to reduce erosion risks in terms of seedbed preparation, directions of cultivations and irrigation.

9 Conclusion

Soil erosion is a natural and slow process. It has the detrimental effect on the environmental. Normally the agents of soil erosion are water and wind, the soil erosion is affected by many factors .But soil erosion could be effectively controlled and minimized by taken appropriate measures.

References

Abernethy, B. and I. D. Rutherfurd. 1998. Where along a river’s length will vegetation most effectively stabilize stream banks? Geomorphology. 23(1):55-75

ASCE. 1998. River width adjustment. I: Processes and mechanisms. Journal of Hydraulic Engineering. 124(9):881-902.

Coppin, N. J. and I. G. Richards. 1990. Use of Vegetation in Civil Engineering. Butterworths.London

Department for environment food and rural affairs .2005 .Controlling soil erosion, Defra Publications, London.

G.J.de Boer .2002.on the consolidation and erosion of cohesive sediments.Deflt University of Technology .Civil Engineering and Geosciences

G. Wall, C.S. Baldwin and I.J. Shelton. 2003. Soil Erosion – Causes and Effects .Face Sheet.Queen`s print for Ontario

Jill Fernqvist, Ida Florberger 2003. Fire and post-fire soil erosion in the Western Cape, South Africa: Field observations and management practices. Committee of Tropical Ecology, Uppsala University, Sweden.

Tess Wynn.2006. Streambank Retreat: A Primer. Vol. 4, No.1 January – March 2006. Watershed Update

Thorne, C. R. and N. K. Tovey. 1981. Stability of composite river banks. Earth Surface Processes and Landforms. 6(5):469-484