Soil erosion and farm water supplies

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Journal of the Department of Agriculture, Journal of the Department of Agriculture, Western Australia, Series 4 Western Australia, Series 4

Volume 5

Number 7 July, 1964 Article 6

1-1-1964

Soil erosion and farm water supplies Soil erosion and farm water supplies

J C. Grasby J. E. Watson

Follow this and additional works at: https://library.dpird.wa.gov.au/journal_agriculture4 Part of the Hydrology Commons, Soil Science Commons, and the Sustainability Commons

Recommended Citation Recommended Citation

Grasby, J C. and Watson, J. E. (1964) "Soil erosion and farm water supplies," Journal of the Department of Agriculture, Western Australia, Series 4: Vol. 5: No. 7, Article 6.

Available at: https://library.dpird.wa.gov.au/journal_agriculture4/vol5/iss7/6

This article is brought to you for free and open access by the Agriculture at Digital Library. It has been accepted for inclusion in Journal of the Department of Agriculture, Western Australia, Series 4 by an authorized administrator of Digital Library. For more information, please contact [email protected].

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F A R M W A T E R S U P P L I E S

W a t e r supplies for stock have an important influence on farm management. In this article Soil Conservation Advisers J. C.

Grasby and J. E. Watson discuss problems of . . .

C E R T A I N types of soil erosion are directly related t o f a r m water supplies a n d the control o f t h i s erosion is a n i m p o r t a n t p a r t o f soil conservation f a r m i n g .

The main problems are concerned with:

A. WATERING POINTS (including dams, soaks and troughs).

• Erosion of stock pads.

• Gateway erosion.

• Overgrazing leading to wind and water erosion.

B. DAM CATCHMENTS AND OVER- FLOWS.

• Erosion of catchments, including scouring of badly designed roaded catchments and drains to dams.

• Erosion caused by overflows from dams.

A . W A T E R I N G POINTS A N D EROSION Erosion of Stock Pads

Many farmers think of soil erosion mainly in terms of the gullying of stock tracks. These tracks or pads, which do seem to be the focal points of erosion in many paddocks, immediately relate erosion to water supply. The most persistent stock tracks on a farm are caused by regular movement to and from watering points.

Water running off sloping land concentrates in natural or artificial channels, including vehicle tracks, firebreaks and stock pads. If a stock pad is mainly across

the slope it will cause little trouble. A stock pad down the slope can carry a water flow sufficient to start a gully which will eat back up the pad.

The problem is most acute where a shortage of watering points, causes long trails from feed to water and back. With the progress of summer, some of these stock pads become well defined as poor supplies gradually fail and the few good supplies are increasingly used.

Often the permanent supplies are creeks or soaks at the bottoms of slopes. The long pads, converging downhill towards such watering points will concentrate run- off water and may start serious gullying.

Gateway Erosion

Gateways become eroded on many farms.

One of the chief causes is the frequent movement of stock through a gateway when going to and from water during the long summer months.

Poor placement of gateways is an important contributing factor. If a gate is in a hollow stock pads leading down to it act as a funnel to concentrate run-off water through the gateway. As far as possible gates should be located on ridges rather than in hollows, and on hard soil rather than soft, easily eroded soil.

The only permanent cure for this is of course to have a watering point in every paddock.

T H E A U T H O R S : J. C. Grasby, B.Sc. ( A g r i c ) , District Soil Conservation Adviser, Geraldton.

J. E. Watson, B.Sc., Soil Conservation Adviser.

426

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These stock tracks lead downhill from the shade of the tree t o - wards a watering point. Run-off water concentrates in the furrows and causes headward erosion of

the gullies

Overgrazing

Good plant cover on the soil is the best insurance against soil erosion. Soil grow- ing improved legume-based pasture is protected from erosion by the cover and the build-up in fertility and the improve- ment in soil structure help prevent and control soil erosion. It follows that overgrazing is one of the main causes of much soil erosion by both wind and water.

Overgrazing is often the result of some fault in the farm water supply position.

If there are too few watering points this leads to overgrazing about those in use,

particularly at the end of a long dry summer. In very hot weather, stock tend to remain near the water rather than go out to feed. Even when they do, they start eating as soon as they strike anything edible. This results in the all-too-familiar pattern of completely bare ground near the water, gradually changing to relatively ungrazed areas farthest away.

The pattern is only slightly modified when there are many small supplies which last part of the summer. Grazing is not usually planned to make the best use of these supplies. If stock have general access

Sheep like to camp and grare near a farm dam

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Overgraz and concentration of stock tracks near water troughs. Watering points in the lowest corner of a paddock cause an erosion hazard. T h e tank and troughs should be moved up the slope

they often drink at the main supplies because they are used to them. The result is the same—overgrazing near the main supplies.

The problem is accentuated if the main supplies are not developed (with mills, troughs and tanks) to serve several paddocks. Stock are grouped together into large mobs so that they may all have access to the watering point. Because of the tendency of sheep to remain in a mob for much of the time the resultant grazing pressure is much greater than if the same number were split into smaller mobs.

The siting of watering points is most important in relation to overgrazing. Sand drift areas, salt-affected ground, low flood- prone areas and similar places are all liable to excessive overgrazing if they have associated watering points. Stock tend to favour grazing these areas at all times, and siting stock water near them really adds to the danger.

Control—Number and Location of Water- ing Points

(1) There must be a permanent water- ing point in every paddock.

This means that the stock should have access to water at all times without hav- ing to go out of the paddock. To achieve this there are many variations. A supply in every paddock from a bore, well, soak,

or dam may be the best way for some farms. Fewer supplies but more development in the form of mills, tanks, piping and troughs may be planned for other farms. Complete reticulation by piping and troughs may even be necessary in some cases.

(2) Individual watering points should be carefully located to reduce stock pad erosion and overgrazing of erosion—prone areas.

As far as possible avoid watering points situated where stock pads will converge downhill. Sometimes moving a watering point just a few chains can alter the stock pad pattern enough to eliminate the worst erosion hazard. To do this of course may mean equipping a dam or soak to pump the water to a trough at a safe site. It may be possible to modify the fencing to alter the stock access to a dam, soak or running creek. When planning a new dam the site can often be selected away from hollows, and the dam filled by contour drains.

B. EROSION I N DAM CATCHMENTS AND OVERFLOWS

Catchments

Some dams in wetter areas are filled by sub-surface seepage, but most dams depend on surface flows. Where water 429

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This dam was built to intercept water flowing down the gully in the foreground. The gully is still active and any erosion will send silt into the dam. Gullies such as this should be controlled by contouring and the dam filled from grassed waterways

and/or contour banks

flows there is always the possibility of soil erosion and the transport of silt in the water.

Silting of a dam can seriously reduce the capacity so that it will not supply the stock needs for which it was planned.

The silt may come from—

• general wash on the slopes of the catchment;

• gullying of waterways;

• scouring of badly designed roaded catchments or collecting drains.

General Wash

General wash (small gullies and rills) on the slopes must be controlled by contouring and clover ley farming. It is dangerous to leave an eroding natural catchment to provide run-off for the dam.

The erosion will become worse, causing serious siltation of the dam and loss of production from the whole catchment.

Soil conservation measures may prevent the dam from filling from its natural catchment; use of contour drains to increase the catchment size, or preparation of a special area of roaded catchment solves this problem.

Gullied Waterways

Gullied waterways may increase the speed of flow to the dam, but they will also cause further erosion and silting.

Large volumes of water should only be allowed to flow in well-grassed stable watercourses. Any silt will be dropped in the grass and none will reach the dam. In small flows there may be some water losses by absorption, but the dam will be protected and remain silt free.

Faults in Roaded Catchments

A badly-designed roaded catchment can easily become an eroded catchment which will shed a lot of silt into the dam. Once eroded, roaded catchments are extremely difficult to repair.

The main faults in roaded catchments which may cause erosion are—

• roads too steep;

• collecting drains with too much grade;

• collecting drains constructed with a "V" drain channel instead of a broad flat channel as recommended for contour banks.

430

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• cutting "V" drains straight downhill in a grassed water way. There gi is no need for this—water will flow tl downhill in grass. Losses from w absorption will be less than the ci possible reduction of capacity from d siltation caused by gullying of a n

"V" drain. b Roaded catchments must be carefully n

planned and constructed to avoid the danger of erosion. Before constructing a roaded catchment advice should be sought fl

from a Soil Conservation Officer. f. Care with Contour Drains

Contour drains to dams should be sur- c

veyed with a grade of 1 in 200, or varied c

as described in Department of Agriculture D

Bulletin No. 2725. It can be very dangerous y to put drains in by eye without checking a the levels. Many large gullies have been

started in this way. e

ii Erosion by Overflow Woter

Overflow water can cause serious gully- e

ing in two ways—in the actual spillway, i and generally down slope before it reaches t a grassed waterway or natural creek. \

• M a H S a B i H H B B H M a a H I I I B M H n H B M B i _ _ I B I M - _ M H H i

t down- Damming of creeks or gullies is not . There generally recommended, but if this is done sill flow the spillway must provide for the overflow

;s from water to return to the creek bed without lan the causing erosion damage. This can be Lty from difficult. The water overflows at a point rig of a many feet higher than the original creek bed so must flow down a steep gradient to return to the creek. In some cases a

a"H th £r a s s e d spillway is satisfactory, but in oid tne o t n e r s stone or concrete structures will be i e g a necessary. Such structures must be care-

! sought f u l l y pja n n e (j a n (j constructed or they will fail. A short diversion channel carrying the water to discharge into another branch of the creek is another possibility. This be sur- channel must, however, be designed to r varied carry the full flow of the creek which has

•iculture been dammed—to allow for a flood flow .ngerous when the dam is full. This of course :hecking applies to all spillways.

ve been The overflow water from an excavated earth tank must also be controlled until it reaches a grassed waterway or main creek. The water should not flow over cultivated slopes where it will cause is gully- erosion. If a grassed waterway cannot be spillway, left below the dam, a contour bank should reaches be used to divert the overflow to a water-

;ek. way or natural creek.

Careful selection of dam sites and control of overflow water in contour berks or grassed waterways is necessary to prevent gullying like this.

433

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Provision for overflow water is even more important where dams are filled by contour drains or roaded catchments.

Four acres of roaded catchment will fill a 2,000 yard dam from 4 inches of run-off.

A wet season may provide more than 10 inches of run-off from an efficient roaded catchment. The surplus water could cause serious erosion problems.

Soil Conservation Farm Planning

The control of erosion related to water supplies is an important aspect of soil conservation. The ideal approach is soil conservation farm planning. This is a method of integrating erosion control measures, fencing, water supplies, farm tracks and firebreaks into one overall plan of development which is put into effect over a number of years. The method is described in Department of Agriculture Bulletin No. 2592.

When preparing such a plan the follow- ing factors are taken into consideration as discussed in this article:—

• Water supply does affect soil erosion.

• The wrong placing of watering points causes erosion along stock pads, through gateways and by over-grazing.

• A deficiency of watering points causes erosion in the same way.

• The correct placing of adequate numbers of watering points helps prevent erosion and aids in its control.

• Proper planning can make efficient use of existing water supplies and show up areas needing further development.

Therefore a farm plan tries to ensure that:—

• Every paddock has at least one individual watering point.

• Watering points are located high up in sloping paddocks.

• Watering points are not located on areas prone to erosion.

• Watering points are central for even grazing.

A WELL-PLANNED DAM

A safe, well-planned hillside dam sited below a steep gravel hill which is left uncultivated. The quick run-off from the gravel hill is supplemented by a contour bank which collects water from a larger catchment. Provision is made for safe

overflow into the prepared waterway, where surplus water can flow down to the creek at the bottom of the slope 434

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