Planning Reclamation of Ravines | Soil Conservation

A simple plan for reclamation of ravine will be as under:- 1. Survey, Planning and Investigation of Land 2. Treatment of Level Land 3. Marginal Land Protection for Intensive Agriculture 4. Main Ravine Land Reclamation 5. Ravine Stabilisation through Biological Measures.

1. Survey, Planning and Investigation of Land:

While formulating any project of crop production, it is essential to have the proper knowledge of land and water resources. Moreover, the inventory of soils constituted the important aspects. In ravine reclamation programmes, which is very tough to handle, as compared to normal soil conservation work, a very comprehensive soil and land use survey is required.

A complete watershed of a single ravine system may be taken up as a plan­ning unit which will be identified on small scale map (1 : 6000). These units would be further classified on the basis of detailed contour maps.

At the Indian Photo Interpretation Institute, a system of ravinous land classification has been developed as detailed below:

(1) Not to slightly eroded, level to undulating table land maximum slope less than 0.3%

(2) Moderately to severely eroded, level to undulating peripheral land maximum slope 0.3 to 0.5%

(3) Moderately to severely eroded rolling peripheral land maximum slope 0.5 to 2.5%

(4) Shallow ravines depth less than 2.5 m

(5) Medium ravines depth between 2.50 to 5.00 m

(6) Deep ravines depth more than 5.00 m

(7) Wide valley bottoms and lower river terraces with maximum width 16 m and slopes less than 5%

(8) Wide valley bottoms with minimum width 16 m and slopes more than 5%

(9) Steeply areas with slope more than 15%

The general plan would consist of classification of the area according to the above ravine classification, land use and proposed ravine reclamation measures, and it would be developed from the relevant aerial photographs (scale 1: 6000) and would consist of the following:

(a) Recognition of flat lands and peripheral lands where ordinary soil conservation measures would be needed to intercept runoff.

(b) Demarcation of areas where intensive soil working would be in­volved in bench terracing and major land levelling.

(c) The selection of ravine waterways. The main distinct waterways would be selected out of the numerous gully heads that are encroach­ing upon the table land. The waterways would be protected by gully head control and gradient control structures for safe disposal of runoff from the relevant watershed.

(d) Selection of sites for tube-wells and tentative alignment of distribu­tion system.

(e) Location of ravine stabilisation structures

The sites for such structures are selected with the help of aerial photographs on the scale of 1: 6000 for collection of data to work out the detailed design of these structures.

The next part of the survey would consist of the field work and be known as a detailed survey. This may be carried out as below:

(a) Planning of terraces and calculation of earth work involved in each terrace, either by measuring the areas and vertical intervals in each grid, or by observing in detail the grid elevation at an interval of 5 m.

(b) From a contour survey at a grid interval of 20 m the contour lines would be drawn on a map on the scale of 160 cm = 1.6 km at an interval of 0.50 m in case of table 1, and 1.0 m in ravine land, submer­gence area etc. for designing of major structures.

(c) Collection of data regarding beneficiaries and preparation of beneficiary-wise cost estimates.

From the above, it may be noted that the work of survey, planning and inves­tigation is quite intensive and most of the field work would consist of surveying and preparation of maps and detailed estimate of the cost. The field unit would be organised mostly on the pattern of survey parties.

In order to assess the nature of ravine problem in the State, sample area in Etawah aod Kanpur district, covering 2.96 lac hectares in watershed of Jamuna and Chambal rivers, was classified according to the land use capability. Aerial photographs of this area were interpreted on the basis of which the following classes of land emerged (Table 7.2).

2. Treatment of Level Land:

The work of table land is a vital element in the treatment of various watersheds. The table land protection aims at systematic handling of the runoff from top of the watershed so that the benefits of soil and water conservation work are even­ly distributed and further spread of ravines is checked.

The objective is to reclaim ravine lands for agricultural purposes. No ravine reclamation can be done safely unless the whole watershed is treated and reclaimed from top to bottom. The work will be in danger of being washed away.

Level lands are cultivated using non-erosive crop sequence. Under rainfed conditions, measures like contour bund farming, contour ridge and furrow help conserving and holding much of rainfall where it occurs. Depending upon the rainfall, soil, topography and cropping system contour bunding should be done.

For light rainfall areas with 0.5% slope contour bunding is suitable. In high rainfall areas with heavy soils of low permeability graded channel terrace should be adapted in preference to contour bunding. The development of sys­tematic waterways will lead to better runoff disposal.

The cost of soil conservation measures adopted in these table lands ranges from Rs. 1,000 to Rs. 1,800/ha depending upon the nature of soil and other physical features of the land.

3. Marginal Land Protection for Intensive Agriculture:

This is most vulnerable strip lying in between the table land and gully head. Unless protected, gully or ravine heads fast extend due to runoff causing water fall erosion. Good table land soon gets engulfed, eventually to be turned into a ravine.

Peripheral bunds are provided along the gully head margin with 0.9 to 1.3 m² cross-section and safe disposal of excess runoff is provided through masonry drops structures for high heads or pipe outlet or sod chutes for low heads.

Ravine reclamation work mostly consists of bench terracing supported by field to field outlets for safe disposal of excess runoff. Benches are laid out between two drainage lines. Since the density of the drainage lines is large in the ravines, most of the terraces will be of short length.

Moreover, the drainage lines are the depressions which are also to be reclaimed by terracing. Thus according to the topography terrace will be of such length as to keep cost of reclamation low. From the past experiences it is observed that 0.20 ha terraces are most economic and size being approximately 50 x 40 m.

Bench terrace operations consist of the following steps:

1. Cutting of earth,

2. Transporting towards the fill and compaction,

3. Construction of risers (bunds),

4. Dressing and consolidation of whole work,

5. Construction of field outlets and runoff control structures,

6. Reconsolidation of work after the rain, and

7. Construction of irrigation structures.

Although in ravine reclamation work, usually cutting of one metre depth of soil is involved, but quite frequently 2 to 3 m height is also required for this purpose. Bulldozers of 180 and 90 HP, provided with angling and titling devices, may be used which would need 6 to 10 ha working for a terrace of 50 x 40 m size.

Dressing of bunds of the prescribed specifications is done by man power. After a rainy season, there are uneven settlement of breaches due to poor com­paction and unattended flow of water. These works would have to be attended immediately after the rains when optimum soil moisture is available. This operation helps in stabilising the newly developed bench terraces.

Field outlets and runoff control structures would also be constructed at this stage. Peripheral bunds need to be planted with grass like Dichanthium annulatum, Andropogon ischaemum or Cenchrus ciliaris for stabilising the bunds.

The average cost of reclamation done at Bah (Agra) with bulldozers in 40 terraces on an area of 8.78 ha comes to Rs. 8,564.00 with 42.20 bulldozer hr/ha. At Etawah, the cost of reclamation in 5.56 ha in 33 terraces is Rs. 9982.00/ha with 49.91 bulldozer hr/ha. At Pukhrayan, where the soils are heavy in 20 ter­races is an area of 4.33 ha and the per hectare cost was Rs. 12,040.00 and bulldozer hours were 60.20/ha.

The reclamation of shallow and medium ravines involves very high cost of Rs. 8,000 to 14,000/ha, unless this reclamation work is supported by ensured irrigation facilities, it will not be possible to get the cost of reclamation recovered from the poor cultivators of the ravinous area. It is, therefore, essential that the State Government should earmark some tube-wells in reclaimed areas.

4. Main Ravine Land Reclamation:

The lower region of the ravinous watershed comprising mostly medium to deep ravines will be stabilized by soil conservation engineering structures installed at the strategic points to ensure ravine stabilisation and to prevent further growth of ravines. The soil conservation engineering structures include drop spillways, dropinlets, chutes, gully plugs and check dams, etc.

Smoothening of hummocks will also be done and the soil available will be trapped behind the erosion con­trol structures. The easened sloped areas can be brought under cultivation. This will add to crop yield from the area.

In areas, where drainage density is very high and each individual watershed has been reduced to 3-5 ha, it may be economical to provide a gully plug at vertical intervals between 2 and 3 m and length between 30 and 40 m. The gully plugs are usually without outlets. This helps in stabilising the gully bed, thus checking the phenomenon of gully extension.

Small check dams with requisite outlets would be constructed at the inter­mediate points of a ravine waterway where adequate area is available for tem­porary submergence.

Such structures would help in reducing the peak intensity of runoff, since it is a primary flood interception structure, the height of the check dam will be determined by flood routing methods. Such structure would have to be designed individually after detailed survey and hydrological analysis.

Suitable sites for farm ponds are not usually met in the ravinous area. There is a great loss due to evaporation and seepage. But wherever suitable sites and conditions are available, farm ponds may be constructed by constructing check dams for collection of runoff water. Stabilisation of ravines may also require some head and grade control structure like chute and drop, etc.

5. Ravine Stabilisation through Biological Measures:

According to land capability class of VI and VII, the most economic use of ravine land is the permanent vegetation. The deep ravines may be stabilised completely by closing the land for grazing and regular afforestation programme supported by engineering measures as check dams, ponds and runoff control structures. The programme of farm forestry, grass land and pasture develop­ment may be undertaken.

The natural vegetation in ravine area mostly consists of the thorny species. Shah (1967) reported that Dalbergia sissoo, Acacia catechu, A. arabica and Dendroclamus strictus do well in the ravines. Plantings of babul, shisham, khair, siris, kanju and neem gave encouraging results along the Yamuna and Chambal rivers in U.P. Srivastava and Qureshi (1966) have recommended that the most suitable species for ravines in low rainfall area are Dalbergia sissoo, Albizzia lebbek, Pongamia glabra, Acacia catechu, A. arabica, Dendrocalamus strictus, Ailanthus excelsa, Prosopis julifera etc.

There is a great demand for grasses because dairying is practised as a sup­plementary profession to agriculture. Grasses such as: Cenchrus ciliaris, Dichanthium annulatum, Cynodon dactylon, Cymbopogon nardus, Heteropogon contortus, Chrysopogon montanous, Saccharum spontaneum, S. munja,

Eragrostis curvula and legumes like Tephrosia Candida, Clitoria ternatea, Des- modium spp. can very well be grown in the ravines.

While reclaiming ravines with vegetative (biological) measures like raising fodder reserves, fuel fodder plantation or industrial plantation or orchards, stabilisation of ravines against erosion is sought through gully plugging. Various types of gully plugs are: brick masonry spillway, brush wood plug, live hedges, boulder cribs, etc. For small gullies, earthen checkdam, brush wood or live hedge gully plugs are recommended.