How To Control a Gully

C. J. Francis.

A system for disposing of water is essential on all farms on which runoff occurs. It will control the runoff and erosion so that gullies will not form. The natural processes of erosion have created natural drainage patterns. The runoff from fields and within fields is collected in these drainageways and carried to the mainstream channels.

Natural waterways are selected to carry runoff from individual fields and farms. The waterways are shaped where necessary to provide a channel having sufficient capacity to carry the expected runoff at nonerosive velocities.

The channels are maintained in grass. During the plowing and cultivation of fields, equipment is raised when crossing the waterways so as not to damage them or reduce their capacity. Grass seed and forage may be harvested from the waterways. Often they can be grazed to good advantage.

A good conservation plan put into effect before an extensive system of gullies has formed insures protection against gullies. It also will transform many gullies into good vegetated waterways and increase farm values.

Gullies that have developed can be stabilized or improved to serve as adequate water disposal systems. The cost of repairing a gully generally is proportional to its size. Some gullies have been allowed to advance to the point where it does not pay to repair them. A small gully is considered to be less than 8 feet deep, a medium gully less than 8 to 15 feet deep, and a large gully more than 15 feet deep. The drainage area that is, the area draining into a gully at any given point also affects the type of control that may be used. Gullies whose drainage areas cover less than 50 acres are considered to have a small drainage area. Drainage areas of 50 to 150 acres are considered medium sized. Drainage areas greater than 150 acres are large.

Small gullies with small to medium drainage areas are the ones that can best be improved and controlled by the farmer.

The measures used to control, improve, or obliterate gullies depend on the size of the gully and its drainage area.

ONE OF THE SIMPLEST and cheapest ways to arrest the advance of small-to medium-sized gullies having small drainage areas is to fence them and exclude livestock a common procedure in areas that are gullied badly and cannot feasibly be restored to cropland.

The fence should completely enclose the area to be controlled. It should be placed far enough from the banks of the gully to allow a good growth of vegetation to form. A good rule is to set the fence back from the edges of the banks a distance approximately equal to twice the gully depth.

Once the area is fenced, natural re-vegetation often will give adequate protection, but natural revegetation usually is a slow process. Grass, shrubs, or trees used separately or in combination give good results. If natural growth does not give adequate control or if the farmer wants a particular type of vegetation, the gully should be planted.

When trees are used, the process of control can be speeded up by planting adapted species.

It is hard to give a complete list of adapted species to cover all sections and conditions, but the following list is suggestive:

Northeast: Eastern redcedar, Scotch pine, red pine, pitch pine.

Middle Atlantic States: Eastern red-cedar, red pine, Scotch pine, Virginia pine, shortleaf pine, pitch pine.

Southeast: Shortleaf pine, Virginia pine, eastern redcedar, loblolly pine.

Northern Great Plains: Red pine, eastern redcedar, willow, elm, poplar.

Southern Great Plains: Eastern red-cedar, incense-cedar, poplar, willow.

Northwest: Ponderosa pine, Scotch pine, Douglas-fir, poplar.

Southwest: Ponderosa pine, incense-cedar, poplar, pinyon.

Mountain States: Ponderosa pine, Douglas-fir, Scotch pine.

When a gully is planted, it may be necessary to do some bank sloping to permit successful planting or seeding of steep areas. Usually a satisfactory growth can be established without extensive sloping.

When a gully is to be retired to wood-lot or grass and if stabilization is the primary factor, only little bank sloping should be done.

DIVERSION OF RUNOFF from a gully is an effective control measure.

The use of diversions is limited to small drainages because of the difficulties in handling large volumes of water. A diversion can be used only at sites where a satisfactory outlet exists. If the outlet is subject to erosion, the water should not be diverted. No advantage comes from diverting water from one gully if there is danger of forming another.

Diversions are best used in connection with small gullies in pastures in which satisfactory outlets are commoner.

The areas above a diversion should be in grass or woods to reduce siltation in the channel. Diversions below cultivated fields may silt rapidly and create maintenance problems. The diversion should be set upstream from the head of the gully a distance not less than 3 to 4 times the depth of the gully.

The diversion is like a terrace, except that it normally has a larger cross section. Its capacity should be sufficient to carry the runoff from the heaviest storm that is likely to occur about once in 10 years. A velocity of 4 to 6 feet a second normally will protect the channel from erosion when a good stand of grass is established. A grade of 6 to 12 inches per 100 feet usually is safe. By diverting water from a gully, natural revegetation may provide adequate control. Diversions also are used to provide protection to vegetated waterways during the period that vegetation is being established. The diversion is removed when vegetation is established.

IN PLACES WHERE LEVEL TERRACES or contour furrows are used, runoff into gullies may be reduced to the extent they will become stable through natural revegetation.

Level terraces and contour furrows should be applied to the major part of the area draining into the gully. The spacing of level terraces to control erosion and conserve water will reduce runoff enough to provide for gully control. The spacing and water-holding capacity of contour furrows depend on their purpose.

Contour furrows built solely to improve range or pastureland may not store enough runoff to be wholly effective in controlling gullies.

DEVELOPMENT OF STOCKWATER in range sections or pastures may help to solve gully problems. A dam built near the head of a gully or in a gully may store a large part of the runoff. The storage of water behind a dam reduces runoff downstream, and the reduction in runoff may permit natural revegetation to control erosion for a reasonable distance below the dam.

The development of a water disposal system for a farm requires the use of most of the natural drainageways. The drainageways that are gullied or have an improper cross section can be improved to carry the runoff safely.

A practical way to transform a gully into a satisfactory waterway is to shape it and seed it to adapted species of grasses. This method is best adapted to small and medium gullies that have small to medium drainage areas. A properly shaped earth channel with good vegetative cover will carry the runoff from the average farm or field without causing erosion.

If a vegetative waterway is to function effectively, the velocity of flow should be about 3 to 6 feet a second, depending on soil type and grasses used. The channel cross section should be broad and flat to keep the water spread uniformly over a wide area.

Usually the depth of flow in a vegetated channel should be about 6 to 18 inches, depending on the slope in order to keep velocities within reasonable limits. The slope of the channel that is, the drop per unit of length normally should not exceed to feet per 100 feet. Steeper slopes usually cause the water to flow too fast to maintain a good vegetative cover.

One cannot give a simple rule for determining the velocity of flow for a specific cross section and given slope. However, one point to remember is: As the slope of the channel increases, the depth of flow must decrease to maintain velocities in reasonable limits.

Because vegetated channels cannot be constructed to precise dimensions, it is hard to maintain flow at shallow depths uniformly over wide areas. Therefore the maximum width of waterways rarely should exceed 50 feet. It is advantageous to divide the waterway into two parallel channels when greater widths are required. That can be done easily by constructing a small ridge of earth down the center of the proposed channel. Each waterway is then planned and built as one unit.

Vegetated waterways carry runoff without erosion when the runoff lasts a relatively short time and flows at reasonable velocities.

A waterway should not remain wet over long periods. Continued wetting may kill desirable vegetation. It softens the soil to the extent that the vegetation is not effective in protecting the soil when stronger flow occurs.

As the size of the drainage area increases, the duration and volume of flow increases. Therefore vegetated waterways having drainage areas larger than 150 to 200 acres usually are not successful. Melting snow and resultant runoff in northern sections may cause flow for long periods and should be considered in planning a waterway.

Because natural waterways occur at elevations below the level of the adjoining field, seepage may cause the area to be wet and boggy. A tile drainage system may then be required. A proper system of drainage will remove ground water to the extent required to dry up the waterway and make it work.

A GULLY that is to be changed into a waterway should first be shaped to the cross section needed to carry the runoff. A direct relationship exists between the size of the drainage area and the amount of runoff that occurs when rain falls.