Soil Erosion.pdf

7/28/2019 Soil Erosion.pdf

http://slidepdf.com/reader/full/soil-erosionpdf 1/25

1

But it could be that we………will forever be unable toUnderstand, that is, to think and speak about, the thingswhich we are able to do.

-Hannah Arendt: “The Human Condition”



2

Table of Contents

Soil Erosion .................................................................................................................... 4Types of Erosion: ....................................................................................................... 5

Sheet Erosion ......................................................................................................... 5Rill Erosion ............................................................................................................ 7Gully Erosion ......................................................................................................... 8Wind Erosion ....................................................................................................... 10Tunnel Erosion ..................................................................................................... 12Coastal dune Erosion ........................................................................................... 13Stream bank Erosion ............................................................................................ 14

Causes of Erosion .................................................................................................... 16Terrestrial Forces ................................................................................................. 16

Slumping .......................................................................................................... 16Sliding .............................................................................................................. 16Soil Creep......................................................................................................... 16

Frost action....................................................................................................... 16Aquatic Forces ..................................................................................................... 17Wave action ..................................................................................................... 17

Natural Shoreline Processes ............................................................................. 17Longshore drift ................................................................................................. 17Ice push ............................................................................................................ 17Storms .............................................................................................................. 18

Human Activities ................................................................................................. 18Urbanization ..................................................................................................... 18Construction of Shoreline Projects .................................................................. 18Clearing of natural vegetation .......................................................................... 18Agriculture ....................................................................................................... 18

Human Influences .................................................................................................... 19Land uses ............................................................................................................. 19Administrative Use .............................................................................................. 23Visitor Use ........................................................................................................... 23

Humans Cause More Soil Erosion Than Rivers, Glaciers ....................................... 24Minimizing Soil Erosion .......................................................................................... 24



3

List of Figures

Figure 1: A figure displaying soil erosion. .................................................................... 4Figure 2: An idealized figure representing Sheet, Rills, and Gullies . ........................... 5Figure 3: A figure representing Sheet Erosion. ............................................................. 7Figure 4: A figure representing Rill Erosion.People working can be taken as scale. .... 8Figure 5: A figure representing two instances of Gully Erosion. ................................ 10Figure 6: A figure showing Wind Erosion. .................................................................. 11Figure 7: A figure showing Tunnel Erosion. .............................................................. 13Figure 8: A figure representing Stream bank Erosion. ................................................ 15Figure 9: A figure showing the loss of agricultural land by Erosion. .......................... 20Figure 10: A figure reperesenting villege on terrace which is dangrous for living. .... 20Figure 11: A figure showing mining process which is also a cause of Soil Erosion. .. 22Figure 12: The soil erosion process during construction. ............................................ 22



4

Soil Erosion

Erosion

1. The process of eroding or the condition of being eroded.2. The group of natural processes, including weathering, dissolution, abrasion,

corrosion, and transportation, by which material is worn away from the earth'ssurface.

Erosion in all its forms involves the dislodgement of soil particles, their removal and eventual deposition away from the original position. This natural process isfundamental in landscape and soil development. Susceptibility to erosion and the rateat which it occurs depend on land use, geology, geomorphology, climate, soil texture,soil structure and the nature and density of vegetation in the area.The growth of intensive agricultural activities last century resulted in the removal of native vegetation across large areas. This has inadvertently increased the exposure of soils and their vulnerability to natural erosion processes.

With water erosion, raindrops are the predominant initiating factor. An average-size

raindrop (5 mm diameter) falling through still air contacts the soil at around 32km/hour. Wind gusts and larger drops result in higher velocities. Drops behave aslittle bombs when falling on exposed or bare soil, displacing soil particles and destroying soil structure. With continued rainfall, displaced particles reorientate onthe surface, filling in larger soil pores and so restricting water infiltration into the soil

profile. Further rainfall causes ponding and the water will eventually begin to movedownhill as run-off. Initially this run-off will be 'muddy' or 'turbid' from the soil

particles displaced by rainfall and as it continues to move it will further erode the soilsurface.

Soils generally increase in erodibility as particle size decreases and are particularlysusceptible to erosion under heavy summer rainfall, when vegetative cover is low.

These erodible fine particles of organic material, silt and clay are the life essence of the soil, containing most of the nitrogen, potash and phosphoric acid.Humans and all forms of land life draw life from the sun, clouds, air and earth througha tenuous film of topsoil, indispensable, and if rudely handled, impermanent.

Figure 1: A figure displaying soil erosion.



5

Types of Erosion:

Soil erosion has different types among which the important types are as follow:

Sheet erosion

Rill erosion Gully erosion

Wind erosion

Tunnel erosion Coastaldune erosion

Streambank erosion.

Figure 2: An idealized figure representing Sheet, Rills, and Gullies which are the possible sites of

Erosion.

Sheet Erosion

Description

Sheet erosion involves the removal of a uniform thin layer of soil by raindrop splashor water run-off. This thin layer of topsoil often disappears gradually, making itdifficult to monitor because the damage is not immediately perceptible. This insidious

process is often overlooked until the subsoil is exposed.



6

Process

Raindrop action on bare soil disrupts aggregates, dislodges soil particles and compactsthe erodible soil surface. If rainfall exceeds infiltration, a surface film of water forms,

building up into flows 2-3 mm deep. Continuing rainfall causes turbulence within theflow that may increase the water's erosive effect up to 200 times.

ImpactsLoss of the finest soil particles, to which the bulk of plant-available nutrients and organic matter adhere, affects the productivity of the land. Erosion may also result inremoval of seeds or seedlings and reduce the soil's ability to store water for plants todraw upon between rainfall events. Soil deposited off-site through this type of erosioncauses crop and pasture damage, water-quality deterioration and stream, dam, lakeand reservoir sedimentation.

Potential Problem Areas

Generally, repeatedly cultivated soils, fallow soils or soils that are bare throughovergrazing by stock or pest animals are particularly vulnerable. The problem iscommon across north central and western Victoria. Within these areas susceptible

soils include red-brown (duplex) cropping soils on slopes of 0-5 %.

Early Signs

As organic matter is removed and vegetation cover decreases, aggregates break downand many soils begin to form a crust which air and water can no longer penetrate.Between grass tufts, small but increasing crusted areas will appear and in slopingareas this often begins at mid slope. Other clues include sorting of soil particles bywater leaving small heaps of washed sand, and light clay-particle coating in smalldepressions.

Watch for water puddling rapidly following the commencement of rain, and for coloured or 'muddy' water run-off indicating soil in suspension. Look for areaswhere removal of topsoil has revealed subsoils or stony soils, clumps of grass wherethe root system can be seen and areas of uniformly exposed tree roots. Similarly,where darker topsoil is eroded a change in soil colour may occur and lighter or

bleached subsoils may become visible at a break in slope. Soil deposits on the highside of obstructions such as bits of wood or fences may also indicate active sheeterosion.

Action

Aim at retaining vegetative cover to avoid leaving soil bare, especially when there is arisk of high-intensity rainfall. Keep vegetation levels high during summer (perennialsare best - they grow under summer rainfall). Modify fallow, cultivation and rotationof cropping land. Control grazing pressures. Improve vegetation and soil management

to maximise rainfall infiltration and use by vegetation.



7

Figure 3: A figure representing Sheet Erosion.

Rill Erosion

Description

Rill erosion often occurs with sheet erosion and is commonly seen in paddocks of recently cultivated soils following high-intensity rainfall. It is easily identified as aseries of little channels or rills up to 30 cm deep.Process

If rainfall exceeds infiltration, a surface film of water forms. Rill erosion results froma concentration of this surface water into deeper, faster-flowing channels whichfollow depressions or low points through paddocks. The shearing power of the water can detach, pick up and remove soil particles making these channels the preferred routes for sediment transport. Rill erosion is often described as the intermediate stage

between sheet and gully erosion. Impacts

The loss of topsoil and nutrients reduces productivity greatly, as the remainingsubsoils are often much less fertile. Also related soil deposition off-site causessedimentation of streams, dams and reservoirs, resulting in water-quality deteriorationand damage to aquatic habitats.Potential Problem Areas

Rill erosion is common on agricultural land devoid of vegetation and so is often seenin cropping areas after tillage. Following intense rainfall cultivated topsoils overlyingdenser cohesive subsoils often exhibit rill erosion. Texture-contrast (duplex) soils aresusceptible, as are poorly managed pasture areas where overgrazing occurs.Early Signs

Watch for the development of surface water flows generated from moderate rainfallevents. Beware in cropping areas of leaving soil bare during periods of high-intensityrainfall. Red-brown earths on slopes are particularly predisposed to erosion. Rills up



8

to 30 cm deep will be easily visible in recently cultivated soils or areas cleared of vegetation. In tilled soils, rills will often extend to the depth of the tilled layer.

Muddy run-off may indicate high sediment loads; look for evidence of off-site soil deposition. In some cropping situations, jolting of harvest machinery mayindicate rills.Action

Revise land use on potential problem areas, avoid extensive summer fallow. Modifycultivation and rotation of cropping land. Control grazing pressures, improvevegetation cover and soil management to increase organic matter and promote water infiltration and evapotranspiration by plants.

Figure 4: A figure representing Rill Erosion.People working can be taken as scale.

Gully Erosion

Description

Once rills are large enough to restrict vehicular access they are referred to as gulliesor gully erosion. Major concentrations of high-velocity run-off water in these larger rills remove vast amounts of soil. This results in deeply incised gullies occurringalong depressions and drainage lines.Process.

Removal of topsoil and subsoil by fast-flowing surface water creates abrupt deep and wide gullies, of two different kinds: scour gullies and headward erosion. In scour gullies, run-off water concentrated in rills or depressions removes soil particlesthrough sluicing - the washing effect of running water on loose grains.Material commonly moved is the size of fine to medium sand or may be derived fromslaking, when large aggregates disintegrate upon wetting. Scour gullies are oftenassociated with gently undulating landscapes. In headward erosion the gully extendsupstream as a result of waterfall undercutting and gravitational slumping of the gullyhead. It is often associated with (although not confined to) steeper landscapes. In bothcases gullies may widen through lateral erosion, where water undercutting causes



9

subsequent slumping of the sides. Gully sides may also be subject to splash, sheet or rill erosion.Impacts

Gully erosion means the loss of large volumes of soil. Deep wide gullies, sometimesreaching 30m deep, severely limit the use of the land, while off-site deposition of soilcauses water-quality decline in streams or rivers and sedimentation of dams and

reservoirs. Large gullies disrupt normal farm operations, creating access problems for vehicles and stock.Potential Problem Areas

Gully erosion often occurs on lower slopes, but can form quite high in the landscapein particularly susceptible areas. Areas commonly affected have dispersible subsoilswhen exposed.Early Signs

Watch for the formation of 'nick points' (these may be rabbit burrows, old root holes,stock or vehicle tracks) on slopes or drainage lines, which may initiate gully erosion.Alternatively, high rates of run-off may lead to a concentration of water in existingrills, especially in sloping paddocks or on hills. Remember that rill erosion is a

preliminary step to gully erosion and under the right climatic and topographic

conditions can extend into gully erosion, exposing subsoil and sometimes bedrock. If the gully is discontinuous (it does not link with a channel further downslope), eroded soil will be deposited in a fan causing damage and instability lower in the landscape.

Drainage water moving over the sides of erosion gullies, as well as enteringvia the gully head, can result in lateral gullies forming - this is often called 'branching'. Deposition of eroded material at the foot of slopes or along fencelines issymptomatic of water erosion and will be reflected by the increasing size of the gully.In terms of severity discontinuous gullies are minor, continuous gullies are moderateand branching accompanies severe gully erosion.Action

Review the suitability of current land use and management techniques to determinecause of the problems. Attempt to reduce the amount of water reaching the gully byincreasing plant water use where the rain falls, so reducing run-off. Control dependson the size and scope of the problem, but may include diversion banks, gully

battering, drop structures, groynes and detention dams. In association withearthworks, replace vegetation to stabilise banks and exclude stock. Gully head erosion is a key form of gully growth and may require independent work such as gullyhead structures. But we must always contact local consultants, or government agencystaff before undertaking earthworks.



10

Figure 5: A figure representing two instances of Gully Erosion.

Wind Erosion

Description

Wind erosion is the movement and deposition of soil particles by wind.Process

Wind erosion occurs when soils bared of vegetation are exposed to high-velocitywind. When its velocity overcomes the gravitational and cohesive forces of the soil

particles, wind will move soil and carry it away in suspension. Wind moves soil particles 0.1-0.5 mm in size in hopping or bouncing fashion (known as saltation) and those greater than 0.5 mm by rolling (known as soil creep). The finest particles (lessthan 0.1 mm) detach into suspension. Wind erosion is most visible during thesuspension stage, as dust storms, or subsequently as deposition along fencelines and across roads.Impacts

The process sorts soil particles, removing the finer material containing the organicmatter, clay and silt through suspension and leaving the coarser, less fertile material

behind. In the short term this reduces the productive capacity of soil, as most of thenutrients plants need are attached to the smaller colloidal soil fraction. Over a longer

period the physical nature of the soil changes as the subsoil is exposed. Wind erosion

also causes damage to public utilities, for example soil deposition across roads, and reduces crops through sandblasting. It has been estimated that 700 000 ha in Victoriaare affected, with another 2 800 000 ha susceptible when poor management and unfavourable weather conditions combine. The associated loss in production costs $3million annually.Potential Problem Areas

Wind erosion mainly affects inland farming (especially cropping) areas with annualrainfall below 375 mm per year and having predominantly sandy soils with low levels



11

of organic matter. Generally the Mallee and northern Wimmera are seen as the biggest problem areas in Victoria, but wind erosion is by no means confined to these areas.Early Signs

Watch for fine soil particles carried as dust during windy conditions (often described as 'smoking paddocks'). Following wind erosion, soil may look lighter as organicmatter, clays and iron oxides have been removed and the soil surface may be smooth

with little sign of previous cultivation. In areas with sandy soils, particles may besorted leaving the surface covered with a coarse sandy layer. The biggest problemsseem to occur when strong winds combine with drought periods to create dust stormsthat carry fine soil fractions hundreds of kilometres, for instance the 1983 dust stormthat engulfed Melbourne.

Soil deposition along fence lines or against trees indicates either severe wind erosion events or erosion happening over a long period of time. Also look for damageto young crops from sandblasting.Action

Avoid letting ground cover reduce below 30% on sandy soils. Effectively manipulatewind access to the soil - usually through stubble or mulch retention at the soil surfaceor by maintaining soil roughness - and control wind speed over a property through

shelterbelt planting. Slopes with a north-west aspect may need special attention, asthey are often the driest and exposed to harsh northerly winds. Modify fallowing

practices and machinery use by employing minimum tillage and direct-drillingtechniques. Reduce grazing or stocking rates and try to pre-empt likely wind erosionseasons. In some areas dry autumns or winters may lead to increased wind erosion thefollowing summer.

Figure 6: A figure showing Wind Erosion.



12

Tunnel Erosion

Description

Water scouring or seeping through susceptible subsoils can form underground channels. Tunnelling often accompanies poor vegetative cover, sheet erosion and

increased surface run-off.

Process

Tunnel erosion is initiated by water moving into and through dispersive subsoils. Itoften results from water accumulating and moving along cracks or channels or intorabbit burrows and old tree root cavities. Dispersive clays are the first to be removed;steadily the route enlarges as more water moves through. Tunnels require an adequategradient to initiate the runoff speed necessary to drive free water through the soil. Asthe tunnel increases in size, parts of the tunnel roof collapse resulting in potholes and gullies.

Impacts

Such erosion leads to loss of productive capability, deposition of infertile subsoils inlower more fertile landscapes and high sediment loads in streams or rivers. In theworst cases tunnels provide a hazard by collapsing, restricting safe access and forming gullies.

Potential Problem Areas

Generally cleared hilly terrain with an average rainfall of 300-650 mm, particularly onerodible soil.

Early Signs

Any factor that promotes variation in soil permeability encourages tunnel erosion; for

example, areas suffering sheet erosion may promote a concentration of water into thesubsoil or irregular absorption of water through low spots such as rabbit burrows or old stump holes, initiating tunnelling. A good indication is the occurrence of a finesediment fan downhill of a developing tunnel outlet point or hole, or water seepage atthe foot of a slope.

Large tunnels and those that have already begun to collapse and form gulliesare very easily identified. Less conspicuous are the smaller potholes and outlet holesassociated with newly formed or forming tunnel erosion.

Action

Break down existing tunnels; revegetate areas to increase soil organic matter,infiltration and water use by plants. Serious tunnelling problems may require

extensive earthworks, including ripping and repacking of existing eroded area.Revegetation plays a dual role: it protects the soil surface from direct raindrop action,and reduces run-off by using rain water where it falls.



13

Figure 7: A figure showing Tunnel Erosion.

Coastal dune Erosion

The coast is the focus of economic, social and recreational activity. The pressure of human activity, combined with continuing natural processes of wind and water, hasaccentuated coastal dune erosion.Description

Removal of, or damage to, dune vegetation exposes sand dunes to high coastal windsand wave action which eventually cause dune blowouts and sand drifts.Process

A vegetated and stable frontal dune acts as a buffer, providing an erodible reservoir of sand that circulates between the front dune, the beach, the surf zone and seabed according to sea and wind conditions. Loss of protective vegetation through pressurefrom grazing, foot and vehicular traffic, fires and building exposes sand to high-velocity coastal winds and wave action, often resulting in erosion.Dune erosion has two types: wind and wave. Wind erosion moves sand grains in aseries of hopping movements (saltation) or by rolling them along the surface of thedune (soil creep). The larger grain size prevents the long-term suspension that occurswith finer soil particles. In this way sand from dunes is mobilised and forms

transgressive dunes that creep inland, covering roads, vegetation and buildings.Within the dune itself blowouts may occur. These usually follow disruption tovegetation on the frontal or primary dune. They are aligned with the prevailing wind and form a U-shape in a lower section of the dune, which funnels wind, raising itsvelocity and increasing the loss of sand.Wave energy plays a key role in beach formation, periodically depositing and removing beach materials. The wash of the waves carries material onto the beachwhile the backwash carries material away. During calm periods the material forms a

beach, while during storms beaches may be eroded by the destructive backwash of the



14

waves. Construction of buildings and roads on front dunes interupts the buffering rolethe dune plays in the wider beach zone. Vegetation removal associated withconstruction and traffic reduces the dune's ability to trap wind-blown sand that would replenish sand removed by waves in storms.Impacts

Transgressive (mobilised) dunes cause major problems for land-owners inland from

the original dune system as sand covers roads, property or farming land. Similarlythey can limit access and recreation. The creation of reflective rock walls, groynesand breakwaters to protect property on frontal dunes interrupts natural beach

processes, sometimes increasing erosion risk and beach scour, which oftennecessitates artificial replacement of sand. In severe situations dwellings close to the

beach or cliff may be undermined by wave activity, causing property damage.Potential Problem Areas

Dune systems under pressure from residential development, recreational access,grazing and engineering works, are prone to erosion throughout the Victoriancoastline.Early Signs

Look for disruption to vegetation on frontal or primary dunes. Removal of vegetation

through grazing, fire or building works will ultimately cause erosion problems.Similarly, tracks caused by recreational vehicles such as motor bikes, cars or evenhorses and people often trigger sand drift and dune blowouts.

Eroding beaches are characterised by coarse sand and steeply sloping narrow berms that drop sharply into deep water. If you count more than 15 wave crestsreaching the shore per minute the beach is likely to be eroding. Check dunes wherevegetation has died or been covered with sand, areas where sand has blown acrossroads or beach paths and dune blowouts.Action

Re-establish protective vegetation, control or restrict foot traffic, vehicles and firesand construct sand traps or wind barriers. The most sensible scenario is not to disturbthe dune and coast system; locate building development and infrastructure behind thedune system.

Stream bank Erosion

Description

Streambank erosion is the direct removal of banks and beds by flowing water.Typically, it occurs during periods of high stream flow. It is sometimes confused withgully erosion as this has similarities with seasonal or ephemeral streams.Process

Erosion of stream or river banks through lateral (side) erosion and collapse often

causes high sediment loads in creeks and rivers. The problem is often initiated byheavy falls of rain in catchments with poor vegetation cover, causing excess run-off.The resultant high volume and velocity runoff will concentrate in the lower drainagelines or streams within catchments. When the stress applied by these stream flowsexceeds the resistance of the local soil material, streambank erosion occurs. As thesediment load increases, fast-flowing streams grind and excavate their banks lower inthe landscape. Later, the stream becomes overloaded or velocity is reduced, and deposition of sediment takes place further downstream or finally in dams and



15

reservoirs. Streambank erosion is exacerbated by the lack of riparian zone vegetationand by direct stock access to streams.Impacts

In addition to loss of productive land due to bank erosion, dramatic changes in thecourse of a river or creek often restrict access on properties. Subsequent deposition of soil causes problems on productive land downstream and sedimentation in reservoirs.

Other problems include reduction in water quality due to high sediment loads, loss of native aquatic habitats, damage to public utilities (roads, bridges and dams) and maintenance costs associated with trying to prevent or control erosion sites.Potential Problem Areas

Catchments with little vegetation cover and steep gradients will often have high ratesof water run-off that result in high-velocity stream flows. Stream straightening,dredging or realignment to accommodate roads or rail lines leads to increased stream

power and velocity, which in turn will increase the energy applied to stream banks.The erosive impact of these high-velocity stream flows will depend on the stability of the bank material. For instance, sand will erode more easily than gravel and silt willerode more easily than sand.Early Signs

In grazing areas the summer dieback of annual pasture species exposes the soil torainfall and thunderstorms. Consequent high run-off will result in high-velocitystream flows. Along poorly vegetated stream banks, obstructions such as dead treescan divert water flows initiating erosion downstream, while rocks, roots and treestumps create turbulence that may initiate erosion at 'nick points' in the bank. Look for subsequent high sediment loads in streams, and lateral streambank erosion collapseand retreat.

Creeks or streams may change direction or cut new channels very rapidly instorms, while over longer periods they may change course. Sediments deposited inlower-flow periods may obstruct the natural flow of streams or ultimately fillreservoirs.Action

Reduce run-off by replacing vegetation and keeping cover levels high. Store water inthe catchment for as long as possible by maintaining high vegetation cover and employing engineering measures such as retarding dams. Limit stock access to streamfrontages and encourage revegetation of banks and creek lines.

Figure 8: A figure representing Stream bank Erosion.



16

Causes of Erosion

Causes of erosion can be grouped into the following categories:

• Terrestrial Forces• Aquatic Forces• Human Activities

Terrestrial and aquatic forces generally work together, and each can cause specifictypes of shoreline erosion.Since our main area of concern is Human Activities as acause of erosion so we will discuss it in detail later on.

Terrestrial Forces

Terrestrial forces erode shorelines and carry material to beaches. They includeslumping, sliding, soil creep, frost action, and wind action. Erosion caused by these

forces is a natural process although human activities can be a contributing cause.Generally these types of erosion occur on banks and unconsolidated shorelines withno vegetation.

Slumping

This downward movement of a mass of unconsolidated material moving as a unit iscommonly caused by groundwater that exerts outward pressure on soil particles,causes the formation of a drainage area, and creates a landslide.

Sliding

This movement of soil or rock is similar to slumping and is caused mainly bygroundwater, but occurs less frequently.

Soil Creep

This gradual downhill movement of soil and loose rock material on a slope onlyinvolves soil erosion, not landslides. Gravity, combined with an aquatic force, is ausual cause.

Frost action

Frost action generally occurs in poorly drained soils such as clay, and often results inthe development of heaves or depressions. Wind erosion Banks and shorelines that arecomposed of fine, dry soil are prone to wind erosion; banks and shorelines made of saturated, wet soil are less prone. The amount of rainfall an area receives has a direct

effect on wind erosion. Wind breaks such as trees, shrubs, sedges, and grasses willslow down the rate at which wind erosion occurs.



17

Aquatic Forces

Aquatic forces include raindrop splash, sheet erosion, rilling, gullying, wave action,longshore drift, and ice push. Aquatic forces remove material from the beach as wellas the bank during high lake levels and often remove material from one area and

deposit it elsewhere. Raindrop splash Soil erosion occurs when raindrops hit directlyon exposed soil. In heavy storms a significant amount of soil can be splashed up in theair. This occurs on both level and steep banks but has more severe results on steeper slopes.

Wave action

This is the impact of waves hitting directly on exposed soil. Lake Champlain wavesvary with wind speeds and duration, water depth, and the continuous length of water over which winds blow in one direction. Wave heights can be calculated when these

properties are known. Choosing and designing a shoreline stabilization method requires knowing the maximum height of waves affecting the property. Eachshoreline along the lake is different. Waves on Lake Champlain can also be created byheavy boat traffic near shorelines.The extent of soil erosion from wave action depends greatly on the bank slope,vegetation, and bank composition. Natural beaches serve as Paved roadways builtalong the shores of a lake increase the velocity of stormwater runoff that accelerates

bank erosion.

Natural Shoreline Processes

The Lake Champlain shoreline is not static. Wave and wind action, changing water levels, currents, and sediments carried in by rivers all work together to exert constant

pressure on the lakeshore. These forces both erode and build the shoreline. It isimportant to consider the natural forces along a particular stretch of shoreline in order

to avoid interfering with a beneficial natural process.One such process is longshoredrift.When waves come at the shore at even a slight angle, sediment is moved alongthe shore. This sediment results in the creation and maintenance of beaches on theshore. Stabilizing such a critical bank would likely result in erosion of that beach or other stretches of shoreline if its sediment supply is cut off.

Longshore drift

This occurs when waves strike the shoreline at an angle. Longshore drift movesshoreline material from one location to another and is an essential natural process in

beach formation and resupply. The effects of longshore drift are often made worse bydeflectors or structures which redirect wave energy, causing erosion elsewhere.Structures perpendicular to the shore, such as groins, cut off sediment movement and

cause erosion elsewhere.

Ice push

The lake is usually partially frozen from December to March. When the ice begins tomelt in the spring, it may push, destroy, or lift objects, particularly if it is aided bywind and rising water levels. Often the ice is pushed ashore in blocks or sheets that

pile up and erode the shoreline. Ice also moves in response to water level changesduring the winter months. Ice push on larger lakes, such as Lake Champlain, is caused



18

by wind and not necessarily ice expansion. In small bays, ice expansion can createerosion.

Storms

Storms accelerate the loss of soil due to aquatic and terrestrial forces such as wind,wave action, and ice damage. A great amount of natural vegetation along the Lake

Champlain shoreline was lost in the 1998 ice storm. Shoreline vegetation is lost eachyear due to heavy storms that occur in the Lake Champlain region.

Human Activities

Activities such as clear-cutting of forests and shorelines, increasing and concentratingstormwater runoff, agriculture, urbanization, and construction cause or increase soilerosion. Erosion is a natural process, however, human influences can contributesignificantly to increases in sedimentation and runoff.

Urbanization

Beaches that are modified for personal use or land that is cleared for housing or roadways increase the opportunity for soil erosion.Urbanization has lead to a hugeloss of natural vegetation along the Lake Champlain shoreline increasing the rate of erosion. Development of housing uphill of a bank can result in increased stormwater runoff over the bank.

Construction of Shoreline Projects

Shorelines and beaches erode naturally and stopping the natural process is not alwaysthe best choice. Human influence is often overlooked as a cause of erosion. Shorelinestabilization projects such as sea walls commonly affect property elsewhere due to theredirection of waves away from the area in which the wall was constructed onto

adjacent properties, with possible adverse impacts on the natural longshore drift of sediment. Structures developed along a lakeshore (including houses) may createerosion problems or simply transfer them elsewhere.buffers for the bank and absorbsome of the wave action before it hits the bank. Erosion due to wave action is greatlyreduced when there is a gently sloped beach or a beach composed of pebble or

boulders that break up the waves before they hit. Soil erosion caused by wave actioncommonly occurs during high water, when beaches are completely submerged inwater and the bank is exposed.

Clearing of natural vegetation

This procedure, done by many landowners to expand their view or increaserecreational area, removes live natural vegetation and wildlife habitat and destroys the

roots of the plants that provide significant stabi-lization to a bank or shoreline.Stormwater runoff Impervious structures such as pavement on driveways, buildings,roofs, drainage ditches, berms, and common stormwater collection methods increasethe velocity and energy of stormwater, which, if directed down a slope or bank, cancause rilling or gullying.

Agriculture

Agricultural practices like plowing, irrigation, drainage ditches, and grazing all canmodify the rate of erosion. Water runoff from agricultural land is the greatest in the



19

spring months when snow is melting and the soil is saturated. Construction of anerosion stabilization project may result in a stretch of shoreline becoming covered with unsightly stone riprap and causing erosion elsewhere.

Human Influences

The term “human influence” is our central theme. The term has purposefully beenselected in order to explore the full breath of possibilities. The largest problem that

pertains to soil is the erosion of soil, which encompasses water running over thesurface, raindrops breaking up the soil, and wind erosion. Many of the factorsmentioned earlier, such as Stalinization, lateralization, and soil compaction, make soilmore prone to erosion. There are many consequences of soil erosion: increased likelihood of flooding, landslides, and increased sediment loads leading to silting upof reservoirs. All of these "consequences" of soil erosion usually are referred to asnatural events, but, as one can see, humans do play a large part in the cause of natural

disasters.

Adjacent land use, consumptive activities, administrative practices as well as publicvisitation can all influence earth surface processes like erosion and also other natural

processes. An effective way to illustrate human influences on the processes is to gothrough some examples.

Land uses

Agriculture- Soil erosion is a gradual process that occurs when the impact of water or

wind detaches and removes soil particles, causing the soil to deteriorate. Soildeterioration and low water quality due to erosion and surface runoff have becomesevere problems worldwide. The problem may become so severe that the land can nolonger be cultivated and must be abandoned. Many agricultural civilizations havedeclined due to land and natural resource mismanagement, and the history of suchcivilizations is a good reminder to protect our natural resources. transformation of nutrients and water, mineralisation of organic matter or wastes dumped on land,fixation of nutrients by microorganisms, conversion of pollutants to less harmfulsubstances and elimination of toxics. There are on-site as well as off-site impacts of soil erosion apart from the loss of topsoil. The on-site impacts are mostly reduced yield.



20

Figure 9: A figure showing the loss of agricultural land by Erosion.

Terrace –Dangrous living sites -People make houses and roads cutting the streamchannels which is extremely dangrous for living and can cause erosion when thewater is absorbed by the land and it overcomes the force of friction which holds it.Soil erods.

Figure 10: A figure reperesenting villege on terrace which is dangrous for living.

Grazing – overgrazing can cause loss of vegetation which ultimately lead to soilerosion and create conditions conducive to fires. Winter precipitation, whether it'srain, sleet, or snow, can lead to pasture erosion. Grazing livestock on frozen soilusually causes minimal pasture damage, but grazing pasture when soil is wet or muddy can lead to soil compaction, erosion, and long-term to pasture sod. Producerswho manage livestock on pasture should consider the potential of soil erosion fromwinter grazing, particularly on sloped areas.



21

Deforestation – intensive logging or clear cutting creates conditions for increased erosion; sediment carried away can cause increased sediment loading in streamswhich could effect fluvial habitat. For every ton of maize, wheat, sugar or other agricultural crop produced, for example, South Africa loses an average of 20 tons of soil through erosion.. The loss of protective vegetation through ploughing,overgrazing and fire makes soil vulnerable to being swept away by wind and water. In

addition, over-cultivation and compaction cause the soil to lose its structure and cohesion and it becomes more easily eroded. Erosion will remove the topsoil first, and once the nutrient-rich layer is gone, few plants will grow in the soil again. Withoutsoil and plants the land becomes desert-like and unable to support life. Over-cultivation, over-irrigation can lead to soil erosion. If the irrigated area is subject toheavy soil-water losses through evapotranspiration, the salts in the water remain in thesoil, causing salinisation. If the infiltration of large volumes of water causes a rising inthe water table, the zone of saturation may be brought closer to the surface, causingthe soil to be waterlogged. In dry regions, farmers often apply heavy amounts of irrigation to keep salts from accumulating in the soil.Deforestation is caused by demands of fuelwood requirements and commercial fellingand, has two-fold impacts: on the livelihood of the people who depend on the forests,

and ecological impacts including soil erosion, siltation, and flooding. The land of thecountry mainly suffers from two major ailments – denudation and erosion, whichresult in loss of the productive base. largely associated with negative impacts on thelimited land resource of the country. Since forest degradation is on the increase, itsimpact on the way of life and the national economy is also being felt. Given the steepterrain with fragile geology and heavy monsoon rains one can perceive that theimpacts of loss of vegetation cover could be dramatic.

Mining done by humen for the exploration of potential resources like metallic and nonmetallic minerals etc. causes the great threat to our soil and is a big danger as itactivates soil erosion. The mining activities wastes 40-45 million tons of soil everyyear which is the most as compared to any natural hazard. Soil is stockpiled atstrategic locations around the mine for subsequent recovery and for spreading over reformed spoil piles. Scrapers are usually worked on the contour to avoid creatingtracks which may become sites for gully erosion after a heavy rain.During miningfailure of pipes may contaminate soil and wet soil is more readily active for erosionater systems and failure of pond liner may contaminate soil and water.



22

Figure 11: A figure showing mining process which is also a cause of Soil Erosion.

Urbanization – This can cause a host of influences, but a few stand outs are; changein drainage patterns, increased erosion, affects on surface and groundwater, qualityand quantity, release of toxins into the air, increased humidity in arid regions.

Construction can activate the soil erosion. When we construct a road or sky-scrapper the soil is disloudged and placed onto an other place which is then under the influenceof transporting agents wind, water etc. This causes soil erosion.

Figure 12: The big machines are stimulating the soil erosion process during construction.

Surface disturbances such as overgrazing, plowing or removing vegetation caninfluence the material available for transport.



23

Dredging, beach mining, river modification, installation of protective structuresremoval of back-shore vegetation alterations of the near-shore can potentially alter shoreline processes, position and morphology by changing the sediment supply.

Adminis trative Use

Roads, dams & bridges – Often these have been constructed with little or no

consideration for natural processes. Roads can disrupt drainage, cause erosion and create hillslope instability. The abutments for bridges can change the flow and morphology of streams and rivers.

Parking lots – Their construction and location can cause harm. Large paved areas(acres) deprive the surface of an opportunity to absorb precipitation. Water flowingfrom the parking lots can cause erosion and gullying if not directed properly. Runoff

pollution affects surface and groundwaters.

Facilities placed over caves – Contaminants from restrooms and other water usage, plus runoff can reach the cave and karst system below causing damage to the fragilesubterranean ecosystem.

Water consumption – Parks located in arid environments need special considerationfor all aspects of water usage (restrooms, watering lawns, domestic use for staff maintenance shops, etc.)

Trails – If they are poorly located with respect to soil, rock and vegetationconsiderations, they have the potential to exacerbate erosion, rock falls and slopeinstability.

Armoring streams, rivers and coast – Sometimes, in our zeal to keep nature in it’s

place by rock armoring, we change the fluvial and shoreline processes therebyaffecting the ecosystem.

Visitor Use

Trampling, Compaction of Soil – Over use by too many people in a small area cancompact the soil and diminish its capability to function and maintain itself as a viable

part of the ecosystem.

Social trails – Depending on the fragile nature of the environment, wandering off-

trail can serious damage fragile resources (such as in caves, wetlands, cryptobioticcrust, cinder cones, tundra, etc.)

Touching fragile features – A number of geologic features have taken years to formthrough geologic processes, and although seemingly rock-hard, they can be rather fragile. Examples include stalactites and stalagmites in caves. Also included areerosional features, such as, arches, bridges, hoodoos, and badlands. Crystals areanother example. Visitors touching or climbing on all these features can causeirreparable damage.



24

Power boating – Over a period of time, wakes from small and large boats alike cancontribute to shoreline erosion. Fuel contamination can affect water quality.

Humans Cause More Soil Erosion Than Rivers, Glaciers

Humans are stripping soil from the surface of the Earth far faster than nature canreplace it. Human activity causes 10 times more erosion of continental surfaces thanall natural processes combined.People have been the main cause of worldwide erosion since early in the firstmillennium, and many researchers have tried to assess the impact of human activityon soil loss but most have only guessed.Scientists used existing data on sedimentary rock distributions and abundances tocalculate rates of natural erosion from glaciers and rivers compared with that caused

by human activity - mainly agriculture and construction."If you ask how fast erosion takes place over geologic time - say over the last 500million years - on average, you get about 60 feet every million years,"But in those parts of the United States where soil is being eroded by human

agricultural activity, the rate averages around 1,500 feet per million years, and rates are even higher in other parts of the world.

Natural processes operate over areas larger than those affected by agriculture and construction, but even taking that into account,"the bottom line is, we move about 10times as much sediment as all natural processes put together.""This situation is particularly critical because the Earth's human population is growingrapidly and because almost all potentially arable land is now under the plow."

Minimizing Soil Erosion

Preventing soil erosion requires political, economical and technical changes. Politicaland economic changes should address the distribution of land, and the possibility of

incentives to encourage farmers to manage their land sustainably. Aspects of technicalchange include:

• the use of contour ploughing and wind breaks;• leaving unploughed grass strips between ploughed land;• making sure that there are always plants growing on the soil, and that the soil

is rich in humus. This organic matter is the glue that binds the soil particlestogether and plays an important role in preventing erosion;

• avoiding overgrazing and the over-use of croplands;• allowing indigenous plants to grow along the river banks instead of ploughing

and planting crops right up to the water’s edge;• encouraging biological diversity by planting several different types of plants

together; and • conservation of wetlands

Erosion occurs when beating rain and moving water dislodge and carry soil particles,organic matter and plant nutrients into waterways. Erosion affects us directly and indirectly. Valuable soil can be lost from your property when it is washed or blownaway. Bare, eroded areas not only detract from a home's appearance, but can causemore serious consequences. Erosion along a home's foundation can eventuallyundermine it. Gullies may form and mud from eroded areas can build up ondriveways, sidewalks, and other places. Eroded soil can cause serious problems by



25

filling roadside ditches, plugging culverts and clogging stream channels, impairingtheir use for flood control and wildlife habitat.our property's vulnerability to erosion depends on several factors including the soiltype, vegetative cover, length and steepness of slopes, and the degree to which the soilhas been disturbed. Some evidence of erosion is easily seen, but other signs are moresubtle and may be visible only following a rain. Small problems require prompt

attention so that they don't become larger problems.The following can reduce soil erosion:

1. Revegetation-Planting trees can reduce the wind speed by acting as awindbreak around the fence lines of farms. In order to minimize the soilerosion we must recultivate more and more plants as well as we must stopagencies like fire etc. which disturb our plants and trees.

2. Stopping overgrazing, can result in a cover of plants that can hold the soiltogether and reduce wind speeds. Overgrazing will be reduced as farmersimprove their management strategies and by the control of rabbits.

3. In cropping areas, leaving a cover of mulch at the end of a growing season asa protective blanket over the soil. This mulch reduces the impact of raindrops

hitting the soil surface and dramatically reduces the wind speed over the soilsurface. In effect, this mulch helps form a buffer zone between the soilelements, and absorbs a lot of the energy from wind and rain that would otherwise soften the upper surface of the soil and make it prone to erosion.

4. Crop management is also important when we talk to minimize erosion. Wemust have the knowlede to mentain the vegetation cover on the critical time of year i.e; rainy season.

5. Keeping steep slopes non-ploughed, reduces the risk of water erosion.Perennial crops such as grapes, fruit trees and flowers, are better alternativesof land use compared to annual crops for sloping land.

6. Using more perennial plants as a food source reduces the need for annual ploughing of the soil which reduces the risk of wind and water erosion. Thereis currently a great deal of interest by both farmers and researchers indeveloping new, perennial crops that could replace annual crops.

7. Sacrifice a certain area for grazing.8. Preventation of erosion by point sources (roads, feedlots etc.)is also very

effective when we are planning for minimizing soil erosion.Channeling of drainage water to non susceptable areas, intelligent geomorphic resources, and covering the banks, cuttings etc with vegetation can help in our cause of minimizing soil erosion.

9. Not ploughing when the soil is dry and dusty reduces the risk of wind erosion.This is very important, because soil is lost during the ploughing process, but isalso lost if the following days are windy, and there is no rain to settle the fine

soil particles.10. Plant residue management is another way of controlling soil erosion byintercepting raindrops, thereby reducing surface runoff and protecting soilsurface particle detachment by raindrop impact.

11. Pre Mine Surveys should be done to characterise the existing topography and ecology of the entire mine path. Topographic, vegetation, soil, fauna, cultural,and hydrological surveys provide baseline data necessary for planning and monitoring, environmental management, and rehabilitation requirements and development.

Soil Erosion.pdf

Documents

Transcript of Soil Erosion.pdf