Frans J.P.M. Kwaad,
Soil conservation in Europe
Ephemeral Gully Erosion
Economic costs of soil erosion
In this site, 12 slideshows of features of soil erosion are presented. See further down.
A soil erosion event near Beni Boufrah, Rif Mountains, Morocco
Soil erosion research started in the 1920's in the USA (Gilley and Flanagan, 2007). Despite 90 years of research, soil erosion still continues to be a serious problem, worldwide. According to Napier (ESSC Newsletter, 2012/1, pp. 3-10) the explanation of this lies in the fact that soil erosion control is not mainly, or not anymore, a scientific problem or a technical problem or a matter of education or information of the farmers, at least in the USA. Farmers know what to do to combat erosion on their fields. The problem is how to induce farmers to implement or to maintain conservation measures on their farm, in a time of economic crisis with reduced public conservation funding, the upcoming of grain-based energy, increased grain prices and an expected mass exodus from land set-aside programs. No longer can be relied on voluntary participation in conservation programs, the cornerstone of US conservation policy for decades, because most conservation production systems are seldom profitable in the short-term and, often, not even in the long term. Some form of coercion will be required to achieve participation, according to Napier (2012) in his analysis of the conservation situation in the USA. For Europe, see the final report of the SoCo-project: Addressing soil degradation in EU agriculture and Soil conservation in Europe. For a world view of erosion see Glasod.
The article by Napier (2012) can be read online in Newsletter 1/2012 of the ESSC on the website of the ESSC (European Society for Soil Conservation).
There is discussion regarding the magnitude of the erosion problem. Pimentel (2006 and older
publications) claims the yearly damage of erosion to be 400 billion US
(1995) disagrees with this. See also Boardman
erosion science: Reflections on the limitations of
current approaches. This paper is a must-read for everyone engaged
in soil erosion research!
The issues of the extent and scale and persistence of the erosion
problem are not discussed any further in this site. It is the purpose
of this site to provide examples of the various aspects of soil
erosion, mainly for educational use.
What is soil erosion?
Do erosion and topsoil formation than take place simultaneously? Yes. Erosion is the removal of soil material at the soil surface by the process of rain wash. Soil formation is the downward growth and extension of the soil profile, and its various horizons, by percolating rain water and through biologic activity. Under natural conditions (e.g. forest) on sloping land, there is a balance between the process of soil formation on the one hand and surface removal of soil material on the other hand. When and where this is the case, we speak of geologic or normal erosion. The soil profile is the long term expression of this balance. This balance can and will be disturbed, when sloping land is used for agricultural purposes. The rate of soil loss by erosion increases ten to hundred-fold under agriculture, without a concomitant and comparable, compensating increase of the rate of soil formation. This is called accelerated erosion above the geologic norm, or soil erosion s.s. It leads to the rapid loss of the soil's superficial horizons, called truncation of the soil profile. Ultimately, the soil can be washed away altogether, down to the underlying bed-rock. In this way, soil that was formed over a period of hundreds or thousands of years, can be lost within years. Besides, linear erosion features (rills and gullies) can develop in the soil and its underlying substrate, if this is composed of unconsolidated material. The productivity of land and soil decreases, when this happens. This is an irreversible process, that cannot be made good with fertilizers. Once the soil is gone, it is gone for many generations to come.
The counterpart of soil erosion in certain parts of the landscape, is increased deposition or sedimentation in other parts of the landscape. Even river regimes can be altered, due to upsetting of the water balance by soil erosion, giving rise to problems of flooding and siltation. These so called off-site effects of soil erosion can be just as deleterious as the on-site effects.
Soil conservation is the protection of the soil against soil erosion. It comprises the whole range of measures that can be taken to prevent or reduce soil loss by soil erosion. The goal of soil conservation is to maintain sustained productivity of the soil and to combat the off-site effects of soil loss.
Soil erosion by rainwater occurs, when more rain falls than can be absorbed by the soil. When this is the case, part or all of the rainwater flows downslope across the soil surface. This is termed overland flow. The overland flow carries soil particles that are detached by the flow and/or by the impact of falling raindrops (splash erosion). Concentration of overland flow can give rise to rill erosion and ultimately to gully erosion.
Two different sets of conditions can give rise to overland flow:
(a) During high intensity rainfall, more rain may fall per time unit than can enter the soil through the soil surface. Only part of the rain infiltrates into the soil. The excess rainfall moves downslope as overland flow. The soil may be dry, when this happens. In technical terms: the infiltration capacity (i.e. maximum rate of infiltration) of the soil is exceeded by the rainfall rate or intensity, both expressed in mm/hour. The rate of infiltration is controlled by the state of the soil surface. The soil surface is susceptible to changes. Breakdown of the soil structure can occur due to raindrop impact if the soil is bare. This can lead to slaking and crusting at the soil surface and a reduced rate of infiltration of rain water.
(b) The infiltration of rainwater in the soil is completely checked, when a (perched) groundwater table is present at, or rises to, the soil surface during rainfall. The storage capacity of the soil for water above an impeding layer is the controlling variable in this situation, expressed in mm of rain.
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2. Degradation of
soil structure, surface sealing and crusting (24
Breakdown of soil structure sets the stage for soil erosion by running water. Through welding, slaking and dispersion of structural elements of the soil (clods, crumbs), sealing and crusting of the soil surface can take place. The maximum rate of infiltration of rainwater is lowered by this, leading to overland flow and erosion. Photo's are taken in the Netherlands (Zuid-Limburg, Meinweg), Luxembourg and Morocco. On the first two slides an overview of 8 slaking classes (Dutch: verslempingsklassen) is given, as compiled by Boekel. This photosheet can be used in the field as a reference when describing the actual state of slaking, by comparison with the 8 photo's. The term slaking refers to the loss of soil structure that can be observed in the field with the naked eye. More technically, slaking is defined as the disintegration of structural elements of the soil into micro-aggregates and skeleton grains (sand grains). This leads to clogging of soil pores and to a lowering of the infiltration capacity of the soil for rainwater. There is discussion on the exact causes and mechanism of slaking and other forms of structural breakdown. See Imeson-Kwaad, 1990 and Kwaad-Mucher, 1994 for more information.
erosion, interrill erosion (11 images)
The concept of sheet erosion is not as clear as it may seem at first sight. Originally, sheet erosion or sheet wash was described by Bennett (1939, p. 96) as: "Sheet washing is the more or less even removal of soil in thin layers over an entire segment of sloping land." He adds: "Sheet erosion grades so imperceptibly into rill erosion that the two cannot everywhere be sharply differentiated." Concerning rill erosion he writes: "Instead of flowing evenly over a sloping field, runoff water generally tends to concentrate in streamlets of sufficient volume and velocity to generate increased cutting power." This implies that sheet erosion was seen as being caused by a film or sheet of water flowing over the land. Later, it appeared that such 'sheet flow' is rare (Schwab et al., 1966, p. 164). More often than this, the water is not deep enough to flood the higher parts of the uneven soil surface (the so-called soil microtopography or surface roughness). The water only fills and follows the depressions of soil microtopography. This is termed 'rill flow' (or maybe better 'pre-rill flow'), with 'interrill flow' occurring on the areas between the rill flowpaths. Not all rill flowpaths become real erosion rills. It cannot be said beforehand which ones will. We don't even know for sure if erosion rills (always) develop from the rill flowpaths governed by soil microtopography (Favis-Mortlock, 1998; Darboux et al., 2001). On the interrill areas, interrill erosion takes place. This is mainly splash erosion. In the Glossary of Soil Science Terms (1978) it is said that sheet erosion often is interpreted to include rill and interrill erosion. So, today, sheet erosion is seen as the combined effect of rill and interrill erosion. No 'more or less even removal of a thin layer of soil' takes place during rainfall. It is by tillage after rainfall that the soil loss, that is due to rill and interrill erosion, is more or less evenly smeared out over the eroded field, resulting in an almost imperceptible (but very real) lowering of the soil surface. Bennett (1939) speaks of sheet erosion as "the least conspicuous and the most insidious type of erosion". By some authors sheet erosion is equated with interrill erosion. Photo's were taken in Morocco (Rif Mountains) and The Netherlands (Zuid-Limburg).
5. Rill erosion
Rill erosion is the formation of rills that can be removed by normal tillage. They are short-lived features. Mostly, they are formed during a single rain storm. Two types of rills are shown in the slides: (1) series of closely spaced parallel rills on slopes, and (2) single rills in wide and shallow topographic depressions. Maybe the latter ought to be termed ephemeral gullies or proto-gullies. Photo's were taken in Luxembourg (Gutland), The Netherlands (Zuid-Limburg) and Morocco.
erosion (26 images)
Guly erosion is the formation of gullies that are too deep to be removed by normal tillage. Gullies are formed in unconsolidated soil material, with the deeper parts sometimes penetrating in underlying soft rock types such as (partly weathered) chalk or marl (e.g. slides nrs. 10 and 13). Several types of gullies can be distinguished, a.o. valley side gullies, valley bottom gullies, V-shaped gullies, U-shaped gullies, continuous gullies, discontinuous gullies, arroyo's, badlands. Photo's were taken in Morocco, Rif Mountains, 40 km west of Al Hoceima.
gully erosion (26 images)
Ephemeral gullies are shallow gullies that are very much wider than deep. They can be removed by normal tillage. They tend not to go deeper than the plough layer. Photo's were taken in The Netherlands (Zuid-Limburg), aerial photographs taken by D. Koeman. The slides nrs. 07 to 14 are of an event of 55 mm of rain in 2 hours incl. 30 mm in 30 minutes. For a more detailed discussion of ephemeral gullies see: Jeroen Nachtergaele.
Piping is the formation of pipes or tunnels by subsoil erosion. Piping occurs under specific conditions, such as a salt containing soil (the white material on some of the images). Photo's were taken in Morocco, Rif Mountains, 40 km west of Al Hoceima.
of colluvium (24 images)
Eroded soil is deposited as colluvium on lower parts of the slope or at the foot of slope, and also as sediment in rivers, lakes and reservoirs. This is a so-called off-site effect of erosion. Photo's were taken in Luxembourg and The Netherlands (Zuid-Limburg).
11. Damage to
crops, roads and built-up areas (29 images)
By soil erosion, damage to crops (uprooting, or burial with colluvium) can occur, or damage to roads (removal of pavement, deposition of mud) and to residential areas (flooding, mud deposition, undermining of houses). Photo's were taken in The Netherlands (Zuid-Limburg) and Morocco, Rif Mountains near Bni Boufrah. These are forms of short-term damage by soil erosion. The long-term damage lies in the irreversible loss of fertile topsoil, as caused by the various forms of erosion mentioned under nrs. 3 tot 8.
Click to view this slideshow on tablet: Damage by erosion
Besides erosion by running water, there are other processes that can cause downslope movement of soil material on sloping land. An important group of processes is so-called mass wasting (soil creep, frost creep, solifluction, mudflow, slumping, landslide, rockfall). Another process is the net downslope displacement of soil material on sloping arable land as a direct effect of soil tillage. This is called 'tillage erosion'. In fact, it shows more resemblance to soil creep than to soil erosion. It has been studied in great detail by Govers (2006). Tillage erosion can contribute to the formation of 'lynchets'.
12. Lynchets (10 images)
Lynchets are terrace-like steps on slopes, aligned parallel to the contours. They were not constructed intentionlly but gradually have taken form on agricultural land at field boundaries that are grown or planted with hedgerows. Loss of soil material at the downslope side and accumulation at the upslope side is involved in the formation and development of lynchets. This can be due to erosion and/or tillage. Some are very old, semi-permanent features of cultural landscapes in Europe, (partly) inherited from the past, representing former land use practices and patterns. Many have been bulldozered away, e.g. in Dutch South-Limbourg. They are named 'graften' in Dutch, 'rideaux' in French, 'Stufenraine' in German. Photo's were taken in The Netherlands (Zuid-Limburg) and Morocco.
Soil erosion songs
Soil, floods and erosion have inspired people to write songs with titles such as "A love song for soil" and "Don't treat it like dirt". Listen, sing along and enjoy!
- Bennett, H.H., 1939. Soil Conservation. McGraw-Hill Book Company, New York, 993 pp.
- Boardman, John, 2006. Soil erosion science: Reflections on the limitations of current approaches. Catena 68, pp. 73-86. Text online.
- Crosson, Pierre, 1995. Soil erosion estimates and costs, with Response by Pimentel et al. Science, Vol. 269, 28 July 1995, pp. 461-465. Text online.
- Darboux, F., Davy, Ph., Gascuel-Odoux, C. and Huang, C., 2001. Evolution of soil surface rougness and flowpath connectivity in overland flow experiments. Catena 46, pp. 125-139. Text online
- Favis-Mortlock, D., Boardman, J., Parsons, T. and Lacelles, B., 1998. Emergence and erosion: a model for rill initiation and development. From Abrahart, R.J. (ed.) (1998). Proceedings of the Third International Conference on GeoComputation (CD), University of Bristol, 17-19 September 1998. Text online
- Gilley, J.E. and Flanagan, D.C. 2007. Early investment in soil conservation research continues to provide dividends. Transactions American Soc. Agric. Biol. Engineers, Vol. 50 (5), pp. 1595-1601. Text online
- Imeson, A.C. and Kwaad, F.J.P.M., 1990. The response of tilled soils to wetting by rainfall and the dynamic character of soil erodibility. In: Boardman, J., Foster, I.D.L. and Dearing, J.A. (editors), Soil erosion on agricultural land. Wiley, Chichester, pp. 3-14. Text online
- Kwaad, F.J.P.M. and Mücher, H.J., 1994. Degradation of soil structure by welding - a micromorphological study. Catena, 23, pp. 253-268. Text online
- Kwaad, F.J.P.M., Van der Zijp, M. and Van Dijk, P.M., 1998. Soil conservation and maize cropping systems on sloping loess soils in The Netherlands. Soil and Tillage Research, Vol. 46, pp. 13-21. Text online
- Lindstrom, Michael J., 2002. Tillage erosion, description and process of. USDA. Text online.
- Napier, Ted L., 2012. US conservation achievements threatened by future prosperity of the agricultural sector. Guest Editorial, ESSC Newsletter, 1/2012, pp. 3-10. Text online.
- Pimentel, David, 2006. Soil erosion: a food and environmental threat. Environment, Development and Sustainability, 8, pp. 119-137. Text online
- Schwab, G.O., Frevert, R.K., Edminster, T.W. and Barnes, K.K., 1966. Soil and Water Conservation Engineering. Second Edition. John Wiley and Sons, New York, 683 pp.
- Soil Net for education on soils
- Soil Science Society of America, 1978. Glossary of Soil Science Terms, 36 pp.
- Van Oost, K., Govers, G., De Alba, S. and Quine, T.A., 2006. Tillage erosion: a review of controlling factors and implications for soil quality. Progress in Physical Geography, 30, pp. 443-466.
Viewing the slide-shows on tablet or
For the slide-shows on this website, Adobe Flash Player is used. Flash is not supported by iOS and Android. Therefore, it is not possible to view the slide-shows on tablet or smartphone. However, there are apps to overcome this obstacle. See for instance these lines taken from a review of Flash vs. HTML5 :
2. Mobile devices do support HTML5, but also Flash - through the appstore.
Android devices support Flash in the mobile browser up to Android v 4.0, but iPads and iPhones do not. The future of Flash on mobile devices and tablets is not in the web-browser though but in the appstore. These are Flash apps specifically designed for touch-screen interfaces. iPads and iPhones do support Flash-based apps through the appstore, and Android devices through the Google Play Store. Many of the most popular iPad and Android apps are Flash-based (you just don't know it, because it is not advertised anywhere).
Hopefully, visitors of the site can find their own way in this new
development of mobile access to images and sounds. The author has tried
to put up three of the slide shows (nrs. 1, 10 and 11) in a non-Flash
coding, by way of experiment. The coding used is not ideal, however,
because of problems with portrait vs. landscape pictures. Please, let
me know, if you know of a better solution.