Agroforestry: Conservation Trees and Erosion Prevention☆

I. McIvor , ... Z. Pu , in Reference Module in Food Science, 2017

Gully Erosion

Gully erosion ( Fig. 6) occurs where concentrated surface water scour out the regolith and underlying rock with the debris being either deposited downslope or transported into river systems creating major downstream problems. The gully form and severity is very dependent on the rock type. The very severe to extreme gully erosion is restricted to argillites (crushed), mudstone, and fine siltstones with each rock type having its characteristic gully shape.

Figure 6. This gully formed overnight in 1900-year-old uncemented ignimbrite west of Taupo, New Zealand. In this environment, as an erosion prevention measure all drainage lines in pastured hill country are pair planted with tree willows at 15–20   m spacing and measures taken to insure the grassed surface is not broken, so allowing a gully head to form. Terrace edges need to be protected and either grassed waterways developed or flumes constructed.

Prevention is much more effective than repair as once the erosion is into the bedrock it is very difficult to get trees (or any other plant material) established. The large gullies cannot be repaired. The whole catchment needs to be retired from grazing and planted in closed canopy trees with the eroding surfaces repeatedly planted with willow wands to create a vegetated surface. These sites take many generations before they are repaired.

The construction of debris dams (Lancaster and Grant, 2006) at intervals up the gully coupled with pair planting of willows has successfully controlled erosion from small gullies. The willow root mats grow across the gully bed and over the surface of the dam covering and protecting the eroding surface (Fig. 7B). Tree pairs are spaced from 8 to 15   m up the gully depending on severity. Discontinuous gullies (Fig. 7A) are very common in hill country. Large erosion events fill the valley bottoms and smaller events begin to scour them. Prevention is by pair or single planting of willows up the valley bottom at 15–20   m spacing and at weak points developing a planted block with 2–3 rows of willows planted at 1.5   m spacing across the valley bottom and in an area fenced out from grazing.

Figure 7. (A) A discontinuous gully and (B) gully control achieved by stabilizing the base level through construction of debris dams supported by willows. Note the willow root mat grown over the dam structure.

 Photos G. Eyles.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780081005965223822

Gully Erosion Monitoring

James S. Aber , ... Johannes B. Ries , in Small-Format Aerial Photography, 2010

Publisher Summary

This chapter discusses gully erosion monitoring. Gullies are permanent erosional forms that develop in many parts of the world, particularly in arid and semi-arid environments. Gullies function as sediment sources, stores, and conveyors that link hillslopes to downstream channels. Human land use, and especially changes in land use, may accelerate gully expansion by head cutting, sidewall collapse, piping, floor erosion, and other processes, which lead to widespread land degradation and potential damage to human structures and activities. The results achieved with small-format aerial photography for monitoring gully erosion continue to demonstrate that SFAP can be considered an advantageous alternative to field methods or conventional aerial photography. Change quantification based on the detailed maps and DEMs provides additional information on the differences in headcut retreat behavior which cannot be described by simple linear measures, and the spatially continuous survey of the entire form offers the possibility of distinguishing different zones and processes of activity both at the gully rim and within the gully interior.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780444532602100134

Challenges of Addressing Natural Disasters in Nigeria Through Public Policy Implementation: An Examination of Isuikwuato Erosion and the Ecological Fund

Emeh Ikechukwu Eke , Kalu T.U. Ogba , in Economic Effects of Natural Disasters, 2021

25.1 Introduction

Handicapped by the disastrous gully erosion threats confronting them, the Isuikwuato Local Government Council resorted to caution the users of Uturu-Isuikwuato road of the danger of the road split. This caution became necessary given the danger to lives and properties the ditch portends as many unsuspecting commuters have fallen into the ditch leading to life-threatening injuries, destruction of vehicles, and loss of valuables and lives. Indeed, the people of Isuikwuato in particular and Abia North Senatorial District in general have been subjected to untold ecological, economic, and psychological ordeals to erosions, which have swept off farmlands and business outfits and threatened their ancestral homes. Of the adverse effects of this gully erosion (natural disaster), the ripping off and shutting down of the only commutable access to their ancestral homes (villages) is gruesome and the only option of diverting into the bush to meander around the terrible spots has gone bizarre; hence, people are now exposed to armed robbery attacks, kidnaping, raping, and herdsmen attacks. These security challenges are reminiscent of Igwe and Fukuoka's (2010) assertion that erosion has affected nearly every part of the country but more aggressive in the southeastern part where it has killed people; torn roads in shreds; destroyed homes, schools, and farmlands; and displaced people from their homes.

Unfortunately, extant literature from the West has not seem to accord due recognition to erosion as a natural disaster with life-threatening capacity. But, in Nigeria, an avalanche of literature has shown that erosion is a natural disaster with unmatched capacity to wreak havoc on both the environment and the economy of the people; hence, almost every state in Nigeria is currently threatened by soil erosion (see Figs. 25.1–25.4), especially the southeastern states, with Abia, Imo, and Anambra topping the list. In these states, evidence abounds that erosions have caused severe damages to structures and systems as buildings have collapsed and properties swept away. The effect is felt more during raining seasons when flooding increases and crops and farmland are swept away. During this period also, fragile buildings yield to the pressures of increased flooding and are uprooted, same goes to roads. Unfortunately, the movement of debris (e.g., remains of buildings and roads uprooted) also causes extensive damage to farmlands.

Figure 25.1. The straight view of the road ruptured by erosion gully at Mgbelu-Umunnekwu, Isuikwuato.

Figure 25.2. The right hand side view of erosion gully at Mgbelu-Umunnekwu from Uturu and the right hand side view of erosion gully at Mgbelu-Umunnekwu from Ovim-Isuikwuato.

Figure 25.3. Electric pole pushed down and destroyed by erosion gully at Mgbelu-Umunnekwu.

Figure 25.4. Road breakage as a result of erosion gully menace at Mgbelu-Umunnekwu, Isuikwuato.

While Igwe (2012) had asserted the gradual but constant dissection of the landscape by soil erosion, which threatens settlements and scarce arable land as the greatest threat to the environmental settings of southeastern Nigeria, Ofomata (1975) remarked that more than 1.6% of the entire land area of eastern Nigeria is occupied by gullies. This figure is very significant for an area that has the highest population density 500 persons per km2 in Nigeria then, because it portends high vulnerability and susceptibility to extinction. This is because before the 1980s the classical gully sites in the region were the Agulu, Nanka, Ozu-item, Oko in Aguata area, Isuikwuato, and Orlu. Unfortunately, since the 1980s till now, the situation has not abated, instead exacerbated such that the southeast has about 2800 active erosion gullies currently (Igwe & Fukuoka, 2010; Nwankwo, 2018).

It is this kind of circumstance that necessitated the establishment of Ecological Fund in 1981 as an intervention fund for the amelioration of ecological problems such as soil erosion, flood, drought, desertification, oil spillage, pollution, and general environmental pollution. Unfortunately, this establishment that currently receives 3% of the federation earnings monthly has been characterized by gross mismanagement (Tables 25.1 and 25.2). This gross mismanagement of the Ecological Funds spurred Senator Mohammed Hassan to lead a debate on the proper usage of the Ecological Funds. The essence of the debate, as it seems, was to instill discipline, transparency, and accountability in the administration of the Ecological Fund because according to the senator, while erosion has ravaged the southeast (where Isuikwuato is), the north is threatened by dessert encroachment, yet, instead of putting the funds where they are statutorily meant to go into, they are diverted into other things not captured by the mandates and objective of the Ecological Fund.

Table 25.1. Revenue Sharing Formula for the Three Tiers of Government.

S/No Tier of Government Derivation Ecology Total
1 Federal 0.49 0.97 1.46
2 State 0.24 0.48 0.72
3 Local 0.20 0.40 0.60
Total 2.78

https://www.osgf.gov.ng/storage/app/media/uploaded-files/background%20on%20ecological%20fund.pdf.

Table 25.2. Adjusted Special Funds Under the Federal Government.

Special Funds Before 2004 (%) 2004 to Date (%)
FGN Share of Derivation and Ecology 1.46 1.00
Development of Natural Resources 3.00 1.68
Stabilization Fund 0.725 0.5

https://www.osgf.gov.ng/storage/app/media/uploaded-files/background%20on%20ecological%20fund.pdf.

These points raised by that bill and total exclusion of Isuikwuato in the publication from the Ecological Fund Office (EFO) on the projects approved between May 2015 and September 2019 are the main concerns of this chapter. Thus, given the dreaded situation of Isuikwuato erosion, a total exclusion from the Ecological Fund distribution within the 5 years published only calls for a reexamination of public policies implementation toward the vulnerability of the people of the country whose lives and properties are threatened by natural disasters. This chapter, therefore, examined the challenges of addressing the erosion menace in Isuikwuato in Abia North senatorial zone, Abia State, Nigeria, through the Ecological Fund administration.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B978012817465400025X

TERRACES AND TERRACING

G.R. Foster , in Encyclopedia of Soils in the Environment, 2005

Benefits and Limitations

Terrace systems are highly effective at preventing excessive rill erosion, eliminating ephemeral gully erosion, reducing sediment yield, conserving soil moisture, protecting landscape quality, and increasing land value.

Terraces are topographic modifications that require soil displacement to construct them. They work best on deep soils, such as loess soils. Terraces require a significant investment to build and maintain. Farming with terraces may be inconvenient, and they may limit the choice of farming practices. Terrace systems that do not fit local conditions can be worse than no terraces at all.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B0123485304002496

Coal Storage and Transportation☆

J.M. Ekmann , P.H. Le , in Reference Module in Earth Systems and Environmental Sciences, 2014

Coal pile flowslides

Instability in coal piles results from two types of slope failure: shallow slipping and deep-seated sliding, which is the type that causes flowslides.

In the first case, wetting of the surface layer can lead to erosion gullies and to shallow slipping with small flows depositing saturated coal at the toe of the slope. In the second case, deep-seated sliding causes a major flowslide within a short time. The stockpile shows a flat final slope and a temporary steep scarp that subsequently slumps back to the angle of repose. This slope failure results in economic loss associated with cleanup costs, loss of production, damage to equipment, and danger to personnel. Significant conditions that could lead to flowslides include the following:

1.

Saturation of the stockpile base due to the infiltration of heavy rainfall, leading to the potential of a deep-seated slip;

2.

Redistribution of moisture within the coal at placement (there is a threshold moisture content below which no saturated zone develops);

3.

Loosely stacked coal (prone to structural instability);

4.

Particle size distribution (migration of fine coal particles under the influence of water flow causes local water saturation and reduction in shear strength).

Failures can happen with relatively fresh coal (placed within the previous 2 weeks), and a significant coal pile height increases the risk of collapse.

Ideally, strategies to prevent and control flowslides would mean modifying the stacking method and the overall stockpile installation, but in reality operational and other factors may preclude major modifications to the existing operations. Consequently, a more practical approach is to adopt safety precautions and adjust the height of the stockpiles as prevention measures:

1.

Excluding pedestrians and mobile equipment from stockpiles thought to be prone to flowslides or from coal piles with modified characteristics, particularly in the week after heavy rain or placement of wet coal.

2.

Minimizing stockpile height during the rainy season; in case of busy shipping schedules and heavy rain, access roads should be closed to personnel; if a coal slide occurs, it should be cleaned up and restacked.

3.

Reclaiming the coal from the toe of the pile by front-end loaders should be avoided because of the hazard; as coal dries out and adhesion between particles becomes weaker, the unstable sides of the pile may collapse.

To control flowslides, experience has shown that:

1.

Controlling the moisture content of the pile can decrease the risk of flowsliding.

2.

Compacting the entire coal pile, or selected areas of it, can reduce the tendency for the saturated coal to suddenly lose strength and to flow.

3.

Building drainage slopes can facilitate surface runoff.

4.

Constructing the pile with an appropriate profile and top facilitates runoff (with convex longitudinal profile and no flat-topped center, or slightly concave cross-sectional profile, or slightly crowned top for compacted piles).

5.

Sealing the coal pile is useful in heavy rain areas but is not practical for working piles.

6.

Enclosing the pile keeps the coal dry but is an expensive option and not applicable at coal blending terminals.

7.

Draining the stockpile toe is beneficial for preventing minor instabilities that could lead to an overall failure.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780124095489090102

Desertification

James F. Reynolds , in Encyclopedia of Biodiversity (Second Edition), 2013

A Stakeholders Perspective

To a large extent, the degree to which land is considered degraded in a particular area depends on the priorities of local users. Clearing native woodland in order to grow crops may increase soil erosion and negatively impact the economic business of firewood collection, but increase food production. With respect to land degradation, changes in the characteristics of soils, water, and vegetation do not have a linear relationship to the productivity potential of the land. Reynolds and Stafford Smith (2002) provide an example to illustrate how different stakeholders may view land degradation through the lens of their particular needs and priorities.

Imagine a cattle ranch in central Mexico, where a herd of cattle is grazing in a pasture that has a large number of erosion gullies (e.g., Figure 1(b)). Whereas one might deduce that these gullies are the result of overgrazing, which removes plants and exposes the soil to water and wind erosion (which is usually true), alternative stake-holder views of these gullies are possible (Figure 4):

Figure 4. Vastly different perceptions by state-holders arising from concerns over erosion gullies, illustrating how land degradation is a concept that resides in the "eye of the beholder."
1.

the erosion gullies are the result of natural phenomena (wind and water);

2.

in some landscapes gullies, whether natural or induced by overgrazing (and depending on the severity and length of time since forming), may have no effect on what matters in terms of human values (such as meat production);

3.

although the erosion gullies may not connote a loss in meat production on this ranch per se, they may be creating salinity problems downstream from the ranch or threaten the survival of endemic plant species; and

4.

even if the gullies are the direct result of overgrazing, there is room for debate as to whether the root cause is overstocking by the rancher, a product of the land tenure system of this area, climate-driven, or an indication of broader institutional problems (or possibly any combination of these).

An ecologist will view erosion gullies as representing a loss of ecosystem structure and function, for example, the ability of the soil to retain water, nutrient cycling, long-term soil stability, and reduced forage production. Although true, this may resonate with a local rancher only if it has a demonstrable impact on his beef production. Of course, broader concerns for appearances or genuine environmentalism may also arise, but the rancher would unlikely invest in gully control on these grounds alone unless, for example, it was linked to an environmental accreditation scheme for the ranch. Gullies could also matter to a local tourist operator who finds that ecotourists are put off by the appearance of environmental damage. Simply put, different stakeholders may see this problem differently.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780123847195002896

Land Degradation

M.A. Stocking , in International Encyclopedia of the Social & Behavioral Sciences, 2001

3 Land Degradation: Biophysical Processes

Land degradation is usually described by the natural resource that is being depleted (e.g., soil/vegetation/environmental degradation) or the biophysical process by which it operates (e.g., soil erosion by wind or water, sodication, salinization, deforestation). In all these processes of environmental change, the soil is normally seen as the focal resource that diminishes in quality with land degradation. As vegetation degrades in quantity and species composition, for example, the soil changes chemically, physically, and biologically. A vicious cycle is evident in most degradation processes: as the soil degrades, so is its ability to support plant growth or other life-support functions. In soil degradation six processes usually are recognized:

(a)

Water erosion . This includes the splashing of soil particles by raindrop impact; sheet erosion whereby a layer of topsoil is removed by flowing water; and gully erosion where a channel is formed. Gullies are often perceived as the most serious form of water erosion because they are obvious features in the landscape. However, sheet erosion by water removes far greater quantities of soil. Worldwide it is by far the most common land degradation process in both amount of soil lost and impacts on production.

(b)

Wind erosion. This is the removal and deposition of soil by wind. It is commonest in, but by no means restricted to, arid and semi-arid areas. A principal cause is the removal of vegetation by, for example, overgrazing or preparation for cultivation.

(c)

Excess of salts. Salts may accumulate in the water held in the soil (salinization) or sodium cations may increase in proportion to nutrient cations such as calcium attached electrochemically to solid soil particles (sodication or alkalinization). The first is typical of semi-arid areas and of poorly managed irrigation schemes, while the second is largely a natural process accelerated by water runoff and associated concentrations of sodium induced by human land use.

(d)

Chemical degradation. This includes a variety of processes. Some are related to the loss of plant nutrients by percolating water (e.g., calcium) or by chemical fixing into a form unavailable to plants (e.g., phosphorus); another is the build-up of toxic levels of chemicals. The pH-related change of aluminum into a free form that can be accessed by plants causes the severest impact on production in certain vulnerable tropical soils.

(e)

Physical degradation. Adverse changes in properties such as porosity, permeability, bulk density and structural stability may arise through farming practices. The commonest physical degradation is the formation of a surface crust by raindrop impact, causing decreased water infiltration and greater runoff.

(f)

Biological degradation. Organic matter is a transient component of soils. Where it is lost through natural processes such as mineralization at a rate significantly faster than it is resupplied by vegetation, the soil deteriorates in its overall biological functions. This happens on most intensively farmed agricultural soils.

These processes of degradation in soils all threaten the sustainability of agriculture. Usually, several processes occur simultaneously. Water erosion, for example, results in loss of soil structure, surface crusting, waterlogging, reduction in organic matter, and breakdown of stable aggregates. In the face of such an onslaught, soil resources very quickly deteriorate. Farming becomes more difficult and more costly.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B008043076704184X

HYDROLOGY | Soil Erosion Control

J. Croke , in Encyclopedia of Forest Sciences, 2004

Minimizing Connection of Sediment Sources with Streams

The term connectivity is now commonly applied to describe the level of interaction between disturbed areas such as roads and tracks and the stream. There are a variety of degrees of connectivity that express whether a sediment source is fully or partially connected to the stream. For example, a road network is fully connected to a stream at a stream crossing or when there is a continuous gully that extends the full length from the source to the streams (Figure 10).

Figure 10. There is a range of degrees of 'connection' between sediment sources such as roads and receiving waters. Sources may be fully connected to a stream, as occurs at stream crossings or where a gully has formed at a road drainage outlet. Partial or nonconnected pathways also exist. Direct connection between a sediment source and stream should be avoided by appropriate planning of road location and drainage.

Opportunities to reduce overland flow through vegetated hillslope areas and streamside buffer strips are plentiful in forested catchments, as long as gully erosion does not occur. Runoff from roads and tracks can disperse in vegetated areas where flow is not concentrated and shear stresses remain low. The risk of gully development is increased as a result of poor road and track drainage and this should be avoided where possible. Once initiated, gully erosion is difficult to halt and these features then effectively bypass the potential filtering effect of vegetation in reducing runoff and sediment fluxes.

Connection between sediment sources and the stream can also be minimized by appropriate road and track planning. Minimizing the number of stream crossings by the location of roads along ridge-tops is preferable to the distribution of roads along valley bottoms where the distance to streams is short. The procedure of uphill yarding or snigging is also a key measure in minimizing connection between compacted surfaces, sediment sources, and the stream. This encourages the location of roads and tracks away from the streams and results in a downslope divergence of the associated skidder track pattern.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B0121451607002702

Tropical Stream Conservation

Alonso Ramírez , ... Karl M. Wantzen , in Tropical Stream Ecology, 2008

A. Erosion-Prone Soils in the Brazilian Cerrado

The Brazilian Cerrado is a large biome supporting a highly-diverse flora and fauna that is adapted to marked changes between dry and wet seasons, intrusion by cold air masses, and recurring fire events (Gottsberger and Silberbauer-Gottsberger, 2006). Cerrado vegetation once covered about 2 million km2 or 20% of the Brazilian territory. After aggressive government-led development programs in the 1970s and 1980s, more than half of the Cerrado was destroyed and converted into agriculture (Mittermeier et al., 1999 ), mainly for soy bean, corn, sugar cane, and cotton. Streams and their riparian zones are now protected by law, but enforcement is lacking. Human impacts are evident and include selective logging, poaching, invasion of cattle and goats, construction of aquaculture ponds, dams and irrigation, and pesticide spills. An overriding problem is stream siltation due to gully erosion from dirt roads and sediments from gold and diamond mining ( Wantzen, 2006; see also Section III-A). Erosion gullies drain riparian wetlands, change the vegetation structure and release large amounts of carbon from drying soils (K.M. Wantzen, unpublished observations). All rivers and streams flowing toward the Pantanal, which is the largest wetland in the world, carry excess sediment loads that impact riparian vegetation, destroy spawning habitats for fishes, and block secondary channels that connect main channels to floodplain lakes.

Attempts are being made to mitigate siltation impacts on streams. State governments in Brazil are now requiring farmers to prove that they are applying all possible techniques to reduce erosion. Some suggested technical solutions are expensive and unlikely to be used widely in impoverished areas, but farmers are developing innovative solutions. Construction of small dams along gullies is one option, creating impoundments that can serve as fish ponds. At the same time, the reservoir increases soil fertility around the gully and allows the reestablishment of native vegetation reducing erosion. The economic return from the fishpond often compensates for the investment in dam construction (Wantzen et al., 2006).

Erosion from areas of intense agriculture can be a serious problem for stream conservation (see Section III-B), but a viable response seems to be reforestation of riparian zones to buffer the impact of agriculture on streams. In addition to stream protection, riparian reforestation can allow reconnection of isolated 'islands' of Cerrado vegetation into integrated corridors. The chances of success of this approach will be enhanced by combining reforestation with the selective use of non-wood products by human populations, providing added economic incentives for stakeholders (Wantzen et al., 2006).

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780120884490500121

DEGRADATION

C.J. Ritsema , ... S.M. de Jong , in Encyclopedia of Soils in the Environment, 2005

Types of Soil Degradation

The type of soil degradation refers to the nature of the degradation process. Soil particles may be displaced by the action of water or wind (erosion and sedimentation), which may cause damage to crops, infrastructure, buildings, and the environment in general. Erosion can be linear, i.e., concentrated along certain channels (rill or gully erosion and mass wasting such as landslides), sometimes creating very deep scars in the landscape ( Figure 1). Less conspicuous, but often even more detrimental to crops is the gradual removal of the topsoil layer (sheet erosion). Off-site effects of erosion may consist of siltation of reservoirs and river beds and/or flooding, or dune formation and 'overblowing' in the case of wind erosion. Degradation in situ, i.e., without movement of soil particles, can be chemical (soil pollution by chemical wastes or excessive fertilization; fertility decline due to nutrients being removed by harvesting, erosion and leaching; salinization due to irrigation with saline groundwater and/or without proper drainage in semiarid and arid areas, acidification due to pH-lowering additions to the soil from fertilizers or from the atmosphere), or physical (compaction due to the use of heavy machinery; deteriorating soil structure such as crusting of the soil surface; waterlogging due to increased water table or its opposite, aridification).

Figure 1. Severely degraded soils on the Loess Plateau of China.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B0123485304000916