Control of Gullies: 5 Steps | Soil Conservation

This article throws light upon the five main steps to be followed for controlling gullies. The steps are:- 1. Closing Gullies to Biotic Interference 2. Checking the Growth of Gullies 3. Stabilisation of Active Gully Head 4. Reclamation of Gullies for Cultivation 5. Control of Deep and Narrow Gullies.

Step # 1. Closing Gullies to Biotic Interference:

The problem of gully erosion is further accentuated by grazing and interference by other animals. Tejwani (1961) reported that closing the area or making it un-accessable to animals had beneficial effect on gullies.

Closer to grazing not only increased desirable species of grasses like Eremopogon faveolatus, Heteropogon contortus, Dichanthium annulatum and Cenchrus spp. but also los­ses of water and soil were progressively reduced.

Kaul (1962) also reported the quantitative and qualitative increase in useful species like Dichanthium an­nulatum, Cenchrus ciliaris mutica. Thus, closing the land for graz­ing provides a usable crop and hence supplementary income from such an area which otherwise would generally be waste land.

This also resulted not only qualitative but also quantitative increase in yield of grasses. Mirchandani et al. (1958) indicated that soil loss was reduced to 0.1 tonne/ha as against 3.3 ton­nes/ha under overgrazed conditions. Similarly, the length and weight of roots may increase to 44 and 184% as a result of closer of gully for grazing.

Step # 2. Checking the Growth of Gullies:

(a) Contour and Peripheral Bunding:

After closer of the gullies, the immediate problem to solve is to stop the growth of gullies. This would necessitate to retain as much precipitation as possible on the land in semi-arid and sub-humid regions and safely dispose off the excess run-off water in humid areas.

Contour and peripheral bunds of various cross sections have been found ideal for this purpose at Vasad. Peripheral bunds should be 0.9 to 1.2 m² cross section and should be spaced at 90 to 120 cm vertical interval. Generally, bunding is recommended for lands up to 6% slope. Slopes steeper than 6% should be bench terraced.

The results at Vasad, indicated that on such type of soils, with 6-12% slope, bunds (1.3 m² in cross-section) at vertical interval of 1.8 to 3.6 m could be advantageously constructed. At Kota, where soils are clay loam to clay, graded bunding has been found suitable up to 4% slope. The graded bunds have 0.7 to 1.0 m² cross-sectional area and 0.1 to 0.6% grade.

(b) Gully Plugging:

Plugging of gullies can be done by either or in combination of brush wood, live hedges, earth, sand bags, brick masonry and boulders. Gully planting should always be made of both trees and shrubs with several different species.

All gully control planting should be fenced from livestock unless they are in an area where it is definitely known that livestock will not damage. Trampling and grazing by domestic animals in the critically eroding areas will prevent vegeta­tion from forming a good cover which is highly essential in preventing erosion.

Earth is the cheapest and most readily available material and, therefore, easier and economical to construct the earthen gully plugs wherever possible. Boulder plugs are equally effective if material is available. Brush wood can also be used for gully plug, however, it is likely to be damaged by white ants in-spite of its coating with tar, thus becoming more costlier. It is because of the con­sideration of durability and cost sand bags being not recommended.

Brick masonry gully plugs are constructed at the confluence of all gully branches of a compound gully. For gullies, where no runoff is expected from top, earthen gully plugs of 1.1 m² cross-section, (with a grassed ramp, 22.5 cm below top level) and spaced at 45-60 cm horizontal interval are suitable.

For gullies, in which excess runoff from the top is expected, an earthen gully plug of 2.25 m^: cross-section with a pipe outlet has to be provided. The diameter of the pipe will be determined by the catchment area. A pipe of 15 cm dia of A.C.C. spun pipe up lo 2 to 3 cusec discharge from an effective catchment of 1.6 ha is suitable.

A composite check dam of earth and brick masonry (spillway portion) would be required for catchment more than 1.6 ha. This is located at the con­fluence of a big compound gully, with main drainage system, or in the bed of the main drainage system at 1.2 m vertical interval on 1% slope of the gully bed and terracing the side slopes.

An apron will generally be necessary to protect the structure from action of the runoff as it is discharged from the spillway. It has been observed that several low check dams are desirable than one large dam of equivalent height.

Low dams are less likely to fail and after they silt up and rot away, the vegetation can protect low overall at these sites much easier than high one. Generally, the maximum height of a temporary dam should not exceed two feet. Dam of lesser height functions more satisfactorily.

It is not only enough to have bund but is equally important to stabilise the bunds with suitable grasses. Studies at Vasad by Srinivasan et al. (1962) revealed that for stabilising the earthen bunds in ravines of Gujarat, Dichanthium annulatum, Amphilophis glabra and Andropogon ischaemum are supe­rior soil binder because they have extensive root system, excellent ground cover and also produce good fodder field.

Cenchrus ciliaris is also good for stabilis­ing the bunds. In Chambal ravines, where the soils are relatively fine and rain- fail is heavy, graded bunds in association with grassed waterway and drop structure for safe disposal of water have been found better than contour bunds.

Step # 3. Stabilisation of Active Gully Head:

Very deep and vertical gully heads in association with the phenomena of under­cutting need immediate attention. The chief problem is that in order to cover up the vertical and active gully heads by providing the natural angle of repose, valuable table land have to be encroached to a great extent, thus making it un­economical and wasteful.

The only measure is to fill in the caved face of gully head up to 2/3 height from the bottom, then ease the gully for the remaining top 1/3 portion of the vertical face.

The newly formed slope is stabilized by sowing or transplanting of grasses such as Dichanthium annulatum, Cenchrus ciliaris or Apluda mutica. This treatment is feasible and economically justified when ac­tive, caved and vertical gully heads are threatening to undermine bridge abut­ments, rail and road embankments and buildings.

Trees like Prosopis juliflora, Acacia nilotica, A. tortilis, A. Catechu and Dendrocalamus strictus are also suitable for planting.

Step # 4. Reclamation of Gullies for Cultivation:

Due to acute shortage of land for cultivation in India, farmers have developed some techniques of reclaiming lands for cultivation. In the process of reclama­tion, adopted by farmers, the sides of the gullies are cut every year to broaden its bed to render it suitable for cropping. The broadening of gully bed may be done either manually or by encouraging severe erosion.

Various types of crops are grown depending upon the soil and climatic conditions. However, these efforts are fruitful only when some cash crops or orchard are planted. For instance on reclaimed gullies in Gujarat, bidi tobacco is grown which is more paying.

(a) Reclamation of Small Gullies:

Small gullies are reclaimed by clearing, minor leveling with bulldozers and constructing diversion-cum-check bunds of 1.5 m^: cross-section spaced at horizontal interval of 30-45 cm. Grassed ramps are provided for the disposal of excess runoff at the ends of the bunds near the gully sides.

Consecutive grassed ramps are diagonally opposite to one another so that the path of runoff is lengthened and its flow velocity is reduced so as not to cause any scouring. At the end of small gully, a composite check dam of earth and brick masonry spillway portions constructed.

(b) Reclamation of Medium Gullies:

A small gully gets transformed into a medium gully along the length of the main drainage system. A medium gully is reclaimed by clearing and leveling the bed and constructing a series of composite earth and brick masonry check dams at vertical interval of 1 to 2 m which gives a horizontal interval of 120 on 1% slope of the gully bed and terracing the side slopes.

After clearing and leveling the bed of medium gully is ready for cultivation.

(c) Terracing of Side Slope of Medium Gully:

The uneven side slopes of the medium gullies having 8 to 15% slope are bench terraced into level terraces at 0.9 to 1.2 m vertical interval. The terraces are given a back slope of one in 50 and a longitudinal grade of 1 in 200 towards the grassed outlet.

A ridge bund of 0.3 m” cross-section is provided at the edge of each terrace. Terrace faces are given a slope of 1.5 : 1. Bench terraces are constructed when gully sides are having a uniform slope for a length of at-least 120 m to justify the cost of terracing.

During the process of terracing, the top soil on the surface is covered with the poor sub-soil. This requires a planned programme to raise the fertility level of soil involving good crop rotations and heavy manuring. The terraces require careful maintenance for the first two years, in view of the unsettled conditions of the soil.

The ridge bund, terrace faces, graded outlets and earthen check dams were stabilized by sodding or growing with suitable grasses like Dichanthium annulatum and Cenchrus ciliaris. Medium gullies may thus be reclaimed economically for cultivation, if it is possible to grow cash crop of orchards under rainfed conditions, or irrigation facilities are available.

Step # 5. Control of Deep and Narrow Gullies:

Deep and narrow gullies may be controlled by reduction of the surface inflow or by shaping and intensive natural or artificial vegetation.

(a) Control of Inflow:

In the regions, where deep and large gullies are of common concurrence, there would be a watershed area either of considerable size or the one having high runoff potential. Diversion terraces, constructed above the gully head will prevent channel erosion and can be used to intercept runoff from the watershed area above the gully and then convey it to a safely stabilized outlet area.

(b) Sloping Gully Bank:

Bank sloping should be done only to the extent required for establishment of vegetation or for facilitating tillage operations. Where trees and shrubs are to be established, rough sloping of the banks to about 1: 1 should be sufficient.

Where gullies are to be reclaimed as grassed waterways, sloping of banks to 4 :1 or flatter usually is desired. Sloping banks of small gullies may be accomplished with ploughs, discs and other farm tools. Large gullies must be shaped with heavy earth moving equipment’s.

(c) Natural Revegetation:

If runoff is diverted, gullies are closed by fencing for livestock natural vegeta­tion will grow naturally. A gradual succession of plant species eventually will protect the gullied area with grasses, vines, shrubs or trees.

The growth of vegetation may be stimulated by fertilising and by spreading a mulch to con­serve moisture and protect young plants. Vertical gully banks may be roughly sloped to prevent caving and provide improved conditions for natural seeding.

(d) Artificial Revegetation of Deep and Narrow gullies:

These gullies should be retired to permanent vegetation of grasses and trees. This has been the observation throughout India. The natural tree species of the ravine lands of Gujarat comprise of Acacia arabica, A. Senegal, A. leucophloea, Azadirachta indica, Albizzia lebbak, Feronia elephantum, Prosopis spicigera.

The afforestation with a number of species like Acacia arabica, Ailanthus excelsa, Albizzia lebbek, Azadirachta indica, Dalbergia sissoo, Dendrocalamus strictus, Eucalyptus camaldulensis, E. citriodora, E. hybrid, Pongamia glabra, Phyllanthus emblica, Slmalia malbarrica and Tectona grandis are quite satisfactory species for Gujarat ravines.

For afforestation of ravines along the bank of Yamuna river at Agra Dalber­gia sissoo, Acacia arabica, Azadirachta indica, Albizzia lebbek. Pongamia pin- nata, Holoptelea integrifolia, Dendrocalamus strictus and Eucalyptus hybrid have been found most suitable species.

At Kola (Rajasthan) Dendrocalamus strictus, Selix tetraspenna in gully beds and Acacia arabica on the top and marginal lands have been found most suitable.