Contour and peripheral bunding.   After the closure of the ravine lands, the immediate problem to be tackled is to stop the devastating rate of soil erosion and the growth of gullies and the conversion of the cultivated tablelands into wastelands for this purpose, it is essential to retain as much precipitation a possible on the land in the semi-arid and sub-humid areas and safely dispose of the excess run-off in humid areas. In the semi-arid and the sub-humid area of India, contour and peripheral bunds of various cross-sections have been found ideal for this purpose. In Gujarat, it is now recommended that for alluvial soils the contour and peripheral bunds should be 0.9 sq m to 1.2 sq m in cross section and should be spaced at 90 cm to 120 cm vertical intervals. The contour and peripheral bunds are stabilized by sodding with Dicanthium annulatum, Cenchrus ciliaris and Panicum antidotale. It has been observed at Vasad in Gujarat that land directly under bunds can give a net annual income of Rs 385 per ha from the sale of these grasses. The excess run-off is safely disposed of through grassed ramps or pipe outlets. In the Chambal ravines, where the soil are relatively fine and the rainfall is heavier, graded bunds in association with grassed waterways and drop structures for the safe disposal of water have been found to be better than the contour lands.

Gully plugging.   the eroding and deepening of gully beds can be prevented with gully plugs. Gully plugs protect the gully beds by reducing the speed of run-off water, redistributing it, increasing its percolation, encouraging silting and improving thesoil-moisture regime for establishing a plant cover.

Gully plugs of various materials, e.g. brushwood live hedges, earth, sand bags, brick masonry and boulders have been tried in India. The size and material of the gully plugs depends on the width, length, and the bed slope of a gully and the anticipated run-off. All types of gully plugs are effective either in retaining or retarding the run-off. Earth is the cheapest and most readily available material and it is, therefore, easire and economical to construct the earthen gully plugs, wherever possible. Boulder gully plugs are equally effective if the material is available.

Brushwood is often available, but there is likely to be a shortage of wooden posts. Moreover, brushwood gully plugs cannot survive the severe attack of white ants, in spite of the fact that the wooden posts are coated in tar, they disintegrate in a couple of years. In the long run, they prove to be costly. For the same considerations of short life and high costs, the sand-bag gully plugs are not recommended. Gully plugs of brick masonry are constructed at the confluence of all gully branches of a compound gully. For gullies where no run-off is expected from the top, earthen gully plugs of 1.1 sq m cross-section (with a grassed ramp, 22.5 cm below the level) and spaced at 45-60 m horizontal intervals are suitable; for gullies in which run-off from the top is expected, an earthen gully plug of 2.2 m cross-section with a pipe outlet is to be provided. The diameter of the pipe shall be determined by the catchment area (15 cm diameter A.C.C. spun pipe up to a discharge of 2 to 3 cusecs from an effective catchment of 1.6 ha is suitable). A composite check dam of earth and brick masonry (spillway portion) is necessary for larger catchments (more than 1.6 ha). This is located at the confluence of a big compound gully with the main drainage system or in the bed of the main drainage system at 1.2 m vertical intervals or 120 m horizontal intervals.

The belief that all the gullied land can be reclaimed for cultivation by making level benches in gully beds is not feasible. This may be possible if no limit is fixed on expenditure. It has been observed that small and medium gullies can be conveniently, safely and economically reclaimed for cultivation, whereas deep and narrow gullies should be retired to a permanent vegetative cover of grasses and trees.

Reclamation of small gullies.   Small gullies are reclaimed by clearing, minor levelling with bulldozers and constructing diversion-cum-check bunds of 1.5 sq m cross-section spaced at horizontal intervals of 30-45 m. Grassed ramps are provided for the disposal of excess run-off at the ends of bunds near the gully sides. Consecutive grassed ramps are diagonally opposite to one another so that the path of run-off is lengthened and its flow velocity is reduced so as not to cause any scouring. At the end of the small gully, a composite check dam of earth and brick masonry spillway portions constructed.

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 levelling the bed and constructing a series of composite earth and brick masonry check dams at vertical intervals of 1.2 m (which gives a horizontal interval of 120 m on 1% slope of the gully bed) and terracing the side slopes.

Design of composite check dams.   The design discharge (maximum run-off) through the drainage channel is computed from the empirical formula :
Q = 0.0028 C.I.A.
Where
Q = Run-off in cubic metres per second (m³/sec)
I = Rainfall intensity in mm/hr
A = Watershed area in ha

The length of the spillway is determined from the formula :
Q = 1.70 LH³/2
Where
Q = Run-off in cubic metres per second (m³/sec)
L = Length of the weir notch in metres H = Height in metres of water flow above the spillway level

TERRACING OF SIDE SLOPES.   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 intervals. The terraces are given a back slope of 1 in 50 and a longitudinal grade of 1 in 200 towards the grassed outlet. A ridge bund of 0.3 sq 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 the gully sides are having a uniform slope for a length of at least 120 m to justify the cost of terracing. The terrace faces, grassed outlets and earthen checked dams are stabilized by sodding or growing them with suitable grasses. Dicanthium annulatum and Cenchrus ciliaris have been found suitable for this purpose, specially in Gujarat and in the ravine son the banks of the Jamuna river. Bench terraces and the check dams require careful maintenance for the first two years in view of the unsettled conditions of the soil.

Reclamation of deep and narrow gullies.   As mentioned earlier, the best land use of ravine lands is to retire them to permanent vegetation comprising grasses and trees. This type of land use is a must for the deep and narrow gullies.

The natural tree species of the ravine lands of Gujarat comprise Acacia nilotica, A. senegal, A. leucophloea, Azadirachta indica, Albizia lebbeck, Feronia elephantum, Prosopis spicigera, etc. With closure to grazing and other biotic interferences, these species make very good growth which is further helped by silvicultural operations, such as climber-cutting and thinning. Afforestation with a number of species has been tried. Acacia nilotica, Ailanthus excelsa, Albizia lebbeck, Azadirachta indica, Dalbergia sissoo, Dendrocalamus strictus, Eucalyptus camaldulensis, E. citridora, E. hybrid, Pongamia glabra, Phyllanthus embilica, Salmalia malabarica and Tectona grandis are quite promising species for ravines in Gujarat.

For the afforestation of ravines along the banks of the Yamuna river at Agra, Dalbergia sissoo, Acacia nilotica, Azadirachta indica, Albizia lebbeck, Pongamia pinnata, Holoptelia integrifolia, Dendrocalamus strictus and Eucalyptus hybrid have been found to be the most suitable species.

In Kota, Rajasthan, Dendrocalamus strictus, Salix tetrasperma in gully beds and Acacia nilotica on the top and marginal lands have been found to be very suitable.

Landslide control.   Landslides pose an immense threat to highways, villages, agricultural lands, lines of communication, etc. The problem of landslides is more serious in the Himalayan region than anywhere else in India. One landslide about 4 ha in area in Nalotakhala watershed at Dehra Dun has been controlled.

The Nalota Nala landslide was controlled by protecting the landslide against the scouring action of the torrent (by training the lower reaches of the torrent, stabilizing the debris cone, stabilizing the middle reaches of the torrent), by stabilizing the landslips and landslides (by wattling to provide temporary support to bare erodible slopes with grass and brush, by planting deep-rooted shrubs and grasses, such as Pennisetum purpureum, Ipomoea carnea, Vitex negundo and Pueraria hirsute).

Based on the observations on the landslide control, it is recommended that the control methods may be adopted, depending on the kinds of materials available in the area, the cause of the problem, the type and the rate of the movement of the slide. These factors vary so greatly from slide to slide that details of remedial measures are required to be tailored to deal with each slide.

Torrent-training and stream-bank erosion.   The torrent problem is of immense magnitude, extending all along the foothills and the plains abutting the Himalayas and the Siwaliks in Northern India. A study was, therefore, undertaken at the Soil Conservation Research Centre, Dehra Dun, in the lower reaches of a torrent (Bainkhala Torrent) to develop a co-ordinated technique based on suitable vegetative and engineering measures for torrent-training and stream-bank protection. The Bainkhala Torrent-treatment measures were observed for 10 years. Their performance and utility were evaluated as under :

(i) Out of the various species tried, for planting live hedges and rainforcing spurs, Vitex negundo was found to be most suitable followed by Arundo donax and Ipomoea carnea. Ipomoea carnea in the case of its planting along spurs was found to be damaged by the abrasive action of debris and boulders moving with flood waters.

(ii) The species found suitable for planting on sloped banks were Aristida cynantha, Chrysopogon fulvus, Arundo donax, Pennisetum purpureum (Napier) and Cynodon plectostachyus (giant star grass).

(iii) Boulder rip-raps on sloped banks invariably gave way owing to scouring at the toe, in spite of the 1 m deep foundation. Even the planting of a live hedge at its base was not much help, unless the main current was deflected from the bank by erecting spurs, etc.

(iv) Jetted posts and jacks provided good protection against bank erosion by inducing siltation, but these structures were usually damaged by the villagers and graziers who often took away the wooden posts for use as fuel. Jacks were found particularly suitable for a straight reaches of the banks.

(v) The repelling type of spurs were found to be most suitable for quick reclamation of concave banks, since these spurs induced heavy siltation both on the upstream and downstream sides. However, they needed special protection of their nose which was subjected to excessive scouring.

(vi) The wooden posts in the log spurs and cross barriers started rotting after 2 to 3 years.

(vii) Out of the various species tried for wooden posts, Salmalia malabarica, Cordia myxa and Broussonetia papyrifera gave better performances. It was seen that shoot development took place in most of the species tried, but it was not followed by root development. The shoot died within a few months. On the whole, posts from younger branches were better in sprouting and surviving than those from the older branches.

(viii) Out of the various types of spurs tried, the boulder spurs reinforced with vegetation and gabion spurs (both with 'nose' protection) gave better performance.

(ix) The best months for erecting vegetable structures and making planting was found to be in January and February, when some winter showers are received and the vegetation can get sufficient time to get established before the floods during the monsoon.

(x) Pennisetum purpureum (Napier) was found to be the best species for stabilizing fresh deposits of silt near the spur and other structures. For a site having coarse deposits (shingle and boulders), Aristida cynantha and Saccharum spontaneum proved to be useful. The data on the forage yield of Napier from the torrent bed have shown that an average yield of about 4,000 kg/ha can be obtained.

(xi) For the utilization and stabilization of the reclaimed areas behind the banks, fuel-cum-fodder plantations of Dalbergia sissoo (sisham) and Chrysopogon fulvus (gorda grass) were found to be quite suitable.