ARTIFICIAL RECHARGE AND CONJUNCTIVE USE

Water conservation is becoming an important past of world’s water management program. In India, with vast population having layer requirement of water and food, the scarcity of this precious resources has become on daunting issue. The ground water resources are two types viz. static and dynamic. The Static ground water reserves (i.e., aquifer below the level of ground water level fluctuation) of the country have estimated as 10,812 B.C.M. The present policy discourages utilization of the static reserves to prevent groundwater mining. There is, however scope for development of this resource in periods of consecutive drought.

In our country, the area irrigated by ground water source has increased five fold during the past four decades. Groundwater over draft occurs the amount of water extracted from an aquifer exceeds the amount of water recharged into the aquifer over a period of years. Due to this, some packets face severe problems of water scarcity due to the impact of ground water development. Artificial recharge of sub-surface reservoir/ aquifer in the viable alternative to control the depletion of ground water levels.

Artificial Recharge in the past

Our ancestors were practicing various techniques of augmenting this natural resource for their day today needs. During rainy season run-off from a large area is collected in a village tank through several collection Channels. In hilly area, people used to divert water from streams to their agricultural fields through simply designed artificial channels

Artificial Recharge In Indian Context

Artificial recharge efforts are basically augmentation of the natural movement of surface water into ground water reservoir suitable civil construction technique or other similar methods. The basic requirement is the availability of sub-surface storage space in different Hydrogeological situations of the country.

Artificial Recharge

It is defined as a process of replenishment of the ground water reservoir by human activities. The main objectives are
To enhance the sustainable yield in areas where over-development has de-saturated the aquifer
Conservation and storage of excess surface water for future requirement
To improvement the quality of existing groundwater through dilution
To remove bacteriological and other impurities from sewage and waste water so that water is suitable for re-use Prevention of land subsidence
To speed up extraction of oil

Principle

In Artificial recharge, two hydraulic effects are generating the hydraulic head (gradient), which is applied in the recharge area and the mass of water, which is introduced into the aquifer through the recharge one.

Controlling Factors

The storage of ground water artificial recharge is dependent on the following factors
Physical characteristic of geological formation like (i) porosity, (ii) hydraulic conductivity
Physio- graphical, characteristic of geological units as ground water reservoirs
Hydraulic factors- such as, Water table, zone of saturation, hydraulic conductivity, specific yield, specific coefficient etc.,
Chemical Factors – quality of water
Structure of ground water reservoirs.
Planning Of Artificial Recharge Studies
Artificial recharges are site specific. The various step in planning of the project are given below
Identification of the area
Hydrometeorology of the area
Hydrological studies
Soil infiltration studies
Hydrogeological studies
Geophysical studies
Chemical quality of source water

Artificial Recharge Technique

Direct Surface Technique

Flooding
Basin or perculation tanks
Stream augmentation
Ditch and furrow system
Over irrigation

Direct Sub-Surface Technique

Injection wells or recharges wells
Recharge pits and shafts
Dug well recharge
Bore hole flooding
Cavity filling, natural opening
Sub surface dykes
Combination Surface-Sub-Surface Technique
Basin or perculation tank with pit shaft
Indirect Technique
Induced recharge from surface water resources

Aquifer modification

Monitoring and Impact Assessment
The monitoring of water levels and water quality is of prime importance in any scheme of artificial recharge of ground water. The periodic monitoring of water levels can demarcate the zone of benefit. The impact assessment of artificial recharge schemes can generally be enumerated with following point
Conservation and harvesting of surplus monsoon
Rise in water level
Ground water structures in the benefited zone of Artificial recharge gain sustainability and the wells provides in lean moths
Change in cropping pattern
Change in vegetation cover
Quality of ground water
Besides the direct measurable impacts, the artificial recharge schemes will generate indirect benefit in terms of decrease in soil erosion, improvement in fauna and flora influx of migratory birds etc.,
CONJUNCTIVE USE OF SURFACE AND GROUND WATER
Conjunctive use is a planned and co-ordinates harnessing of ground water and surface water resources so as to active optimal utilization of total water resources. The ground water may be used to supplement surface-water supplies to reduce peak demands for irrigation and other uses or to meet deficits in years of low rainfall. On the other hand, surplus surface water may be used in over-draft area increase the ground water storage by artificial recharge. Better understanding of irrigation method, irrigation intervals, crop requirement salinzation etc., is of much importance to successful implementation of conjunctive use project.
Irrigation
In the rural area, with availability of surface water almost throughout the year farmers found it nearly necessary to use the groundwater with the result that ground water utilization because almost nil. This resulting rise in groundwater levels giving rise to water logging conditions. In addition water logging also results in salinity of the soil by way of direct evaporations of water from the soil and the accumulation of salt in the topsoil ground surface rendering it infertile. In conjunctive use, the highly salinity will bring down to within unusable limit by mixing them in suitable pro-portion with freshwater.
Advantage
Use of groundwater helps reduce peak demands for irrigation
Rising multiple crops, even if rainfall is delayed
Increased water resources in tail end area and areas of higher elevation.
Reduces the dense of water logging of consequent wastage of water for leading of soils
Surface and sub-surface out flow are minimized
During period of Peak water demand, irrigation requirements can be met by surface water sources so the power saved and it can be diverted to other sectors.
Disadvantage
Deterioration in groundwater quality due to the over pumping
Increased power consumption to sustain pumpage from well
Operation, supervision and control of conjunctive use and artificial recharge project are more complex.

Watershed Characteristics

Watershed is a geo-hydrogeological unit draining at a common point by a system of streams. The depth of a watershed may extend from the top of the vegetation to the confining geological strata beneath (Fig 15.1). In areal extend, it may vary up to few thousand hectares. Watershed management must consider the social, economic and institutional factors operating within and outside the watershed. It is an integrated and inter-disciplinary approach aiming at increased agriculture production, generation of rural employment and balance growth of the national economic.
Watershed Characteristics
Physiography
Size The size of watershed is an important parameter in determining the peak rate of runoff. The rate and volume of runoff increases with increases in size of watershed
Shape
Long and narrow watershed will have longer rainwater infiltration and low runoff rate.
Land Slope
Slope is an important factor to find out the speed and extend of runoff and also to know the land use pattern
Drainage and Density
Drainage density and pattern is main Characteristic of a watershed. High drainage density is a Characteristic of shale, clay and schistose formation. The coarser drainage texture, the higher the conductivity.
Soil and Geology
Soil and geology of the watershed determines the infiltration and percolation rates of water, runoff and soil erosion, drainage pattern, drainage density etc.,
Land Use
The land in a watershed has to be used for numerous purposes like cultivation, housing, water harvesting etc, the land use affects rate of runoff, infiltration rates.
Vegetation Cover
Vegetation cover in watershed influences rainfall, runoff, erosion, rate of evaporation and rate of infiltration. A good cover of vegetation, treat the watershed from land and water scarcity and hazards.
Rainfall
Rainfall in a watershed is an important key to determine its behavior, that why the amount, frequency and intensity of rainfall are important in a water shed.
Socio-Economic factor
In every watershed, three socio-economic factors namely demographic profile, sociological factors and economic factors are important. These there are interrelated to each other.
Causes of Watershed Deterioration
Land, water, flora and fauna and community constitute the four components of a watershed, which are complementary to each other. Any distortion in any one has been carried over to all the components thereby creating a vicious circle, which is capable of deteriorating the watershed.
Watershed Management
Watershed management defined as the process of formulating and carrying out a course of action involving in the manipulation of natural, agricultural and human resources of a watershed to provide resources that are desired by and suitable to the watershed community, but are not adversely affected.
Selection of Watershed Villages
The selection of watershed villages are based on the following category
At least 5% of the cost of investment shall be contribution by the community
At least 10% of the investment on individual work on private property must come from the beneficiary/ user
A resolution from Gram panchayat expressing its willingness to take over and maintain.
A resolution from Gram Panchayat and watershed community willing to share the benefit from those created assets.

Selection of Watershed
The selection of water shed based on following criteria
Watershed which has acute shortage of drinking water
Watershed having large SC/ST population
Watershed which has preponderance of common and waste land
Watershed having special problems like drought, soil erosion ground water stress and quality problems
Land and Water Management
The basic idea of land and water management is to use the resources to its utmost capability and its treatment according to its needs. Thus the knowledge of land capacity classification is a pre-requisite in integrated water shed development programme. The land capability classification is defined as a systematic arrangement of different. Kinds of land according to these properties that determine the ability of the land to reproduce on a virtually permanent basis. Land is arrangement in various capacity classes after considering factor like soil texture, soil depth, permeability, soil chemistry, slope, and frequency of overflow, climate and rainfall.
Ground Water Management
The groundwater management objectives are based on geological, hydrological, economic, ecological and legal consideration. Proper ground water basin management involves the development and maximum utilization of sub-surface water at a least cost for economic or community purposes. Hence, the optimal use of groundwater can made by conjunctive use of both surface and groundwater.

LANDSLIDES, AN INDIAN CONTEXT

Landslides are the rapid movement of earth materials under the influence of gravity and belong to that family of short lived and suddenly occurring natural phenomenon that can cause extraordinary landscape changes and destruction of life and property. In the strict sense, landslides are relatively rapid down slope movement of soil and rock, which takes place characteristically on one or more discrete bounding slip surfaces which define the moving mass (Hutchinson, 1988). The causes of landslides are defined as external, which increases shear stress while shear strength remains constant, or as internal, which decreases the shear strength and leave the shear stress unchanged (Terzhaghi, 1950). Examples of external causes are steepening or heightening of slopes by erosion at the base, tectonic uplift or excavation, deposition of material on the upper part of the slope, and ground acceleration during earthquakes. Examples of internal causes are increase in soil water pressure, decrease in cohesion due to weathering or solution, and decrease in binding strength of roots caused by alteration or removal of vegetation. Such conditions or events seldom act alone to cause landslides (Terzhaghi, 1950; and Baker and Marshall, 1958). Factors such as slope steepening, progressive decrease in cohesion etc. operate so slowly that they are termed underlying causes. Other events or conditions may occur suddenly, such as rise of pore water pressure during a rainstorm or an earthquake. These are termed triggering causes. Landslides occur when a slope, already weakened by one or more underlying causes, is subjected to triggering event (Terzhaghi, 1950).

In India, it is estimated that the annual loss due to this phenomenon is about rupees 200 crores, emphasising the need for a concerted effort to mitigate its many fold miseries (Thampi et al., 1997). If one accepts the susceptible nature of the hilly regions in India by the very nature of the terrain with its steep slopes undergoing the natural diastrophism under tropical monsoon climate, the following regions need detailed assessment in terms of landslide hazards.
1. Western Himalayas
2. Eastern and North eastern Himalayas
3. Naga - Arakkan Mountain belt.
4. Western Ghats including Nilgiris
5. Plateau margins in the Peninsular India and Meghalaya in the North east India.

While the Himalayan region is known for its active tectonics which trigger the landslides, the Western Ghats and Nilgiris are geologically stable but has uplifted plateau margins influenced by neotectonic activity.

Being a heavy rainfall region, the hilly terrain of Kerala, falling in the Western Ghats belt, in general is prone to landslides. While the torrential, incessant rains or cloud bursts experienced in localised areas, are the immediate cause of most of the landslides in Kerala, the geological setting and the structural geological make up of the region can be attributed as the main cause of the landslides. The most prevalent, recurring and disastrous type of mass movements noted in Kerala are the “debris flows”. In local vernacular the event is called “Urul Pottal”. The characteristic pattern of this phenomenon is the swift and sudden downslope movement of highly saturated overburden containing varied assemblage of debris material ranging in size from soil particles to huge boulders destroying and carrying with it every thing that is lying in its path.

Davison (1889) was the first to use the term ‘creep’ after inventorying the landslides in polar areas. Varnes (1958) has classified landslides based on two main variables namely the type of materials and the type of movements and accordingly classified them as falls, slides (rotational and transitional), flows and complex slides. Hutchinson (1977) has indicated that the drainage is the principal measure used in the repair of landslides.

Choudhary (1980) categorised landslides into three types as (i) landslides due to exceptional causes (ii) ordinary landslides and (iii) landslides due to no apparent causes. Steepness of slope was demonstrated to be an important factor in both rainfall - triggered and earthquake - triggered landslides (Wieczorek et al., 1985).

Landslide events of some parts of Alps were attributed to the reactivation of Subric lineament caused due to post collision tectonics according to Schmidt et al., (1989). Bartarya and Valdiya (1989) observed that intense storms, even of short duration, generated widespread landslides along roads in many parts of Himalayas. Jagannathan (1991) in his geoenvironmental studies of landslide prone areas of Wayanad and Calicut districts of Kerala related the soil characteristics and weathering and lateritization to the occurrence of landslides.

Anbalagan (1993) related the landslide hazards of the Nainital area with the unplanned urbanization. Pradeep and Sinha (1995) have observed that structural discontinuity of lithological features and geotechnical parameters like shearing strength of soil, caused slope instability in Kaliaswar landslide of Garhwal Himalayas. Iverson (2000) studied the effects of rainfall infiltration on triggering landslides.

References

Anbalagan, R. and Tyagi, S.K., 1996. Landslide hazard mapping of a part of Kumaon Himalaya, U.P. India, Proc. Int. Conf. Disasters and Mitigation, Madras, 1, A 4.1 - A 4.11
Backer, R.F. and Marshal, H.C., 1958. Control and Correction, In : Landslides and Engineering Practice, Eckel, E.B., Editor, HRB Special Report 29, PP. 150 - 188.
Bartarya, S.K. and Valdiya, K.S., 1989. Landslides and erosion in the catchment of the Gaula river, Kumaun Lesser Himalaya, India, Mountain Research and Development, Vol. 9, No.4, PP. 405 - 419.
Chowdhary, R.N., 1980. Recent progress in evaluation and control of Landslides, Proceedings, International Symposium on Landslides (ISL 1980),April 7 - 11, New Delhi, Vol.1, PP. 313 - 318.
Davison, S., 1889. On the creeping of soil cap through the action of frost, Geology Magazine, New Ser ., Vol.3 No.6, PP. 255 - 261
Hutchinson, J.N. , 1977. Assessment of effectiveness of corrective measures in relation to geologic condition and types of slope movements, Bulletin of the International Association of Engineering Geology, No. 16, PP. 131 - 155.
iverson, R.M., 2000. Landslide triggering by rain infiltration, Water Resources Research, Vol.36, PP.1897 - 1910.
Jagannathan, V., 1991. Geoenvironmental studies of landslide prone areas in parts of Wayanad and Calicut districts, Kerala, Records of Geological Survey of India, Vol. 124, Part - 5, pp. 208 - 210.
Pradeep, K. and Sinha, U.N., 1995., Influence of structural discontinuity, petrographic features and geotechnical parameters on stability of Kalrasaur landslides, Garhwal Himalayas, Symposium on recent advances in Geological studies of NorthWest Himalyas and the fore deep, Abstracts, Lucknow, India, Feb. 21 - 23, PP. 318 - 319.
Schmidt, S.M., Aebli, H.R ., Heuer, R. and Zingg, A., 1989. The role of Pariadriatic line in the tectonic evolution of the Alps, In : M.P. , coward ,D. Dietrich, and R.G. Park, Editors, Alpine Tectonics, Geological Society, Special publication, Vol. 45, pp. 153 - 178.
Terzhaghi, K., 1950. Mechanism of landslides, In : Paige, S, Editor, Application of Geology to Engineering practice (Berkley volume), Geological Society of America, PP. 83 - 123.
Thampi, P.K., John Mathai., Sankar, G. and Sidharthan, S., 1997., Evaluation study in terms of mitigation in parts of Western Ghats of Kerala, Project report CESS.
Varnes, D.J., 1958. Landslides types and processes, In : E.B. Eckel, Landslides and engineering practice : Washington Highway research board, Special report 29, NAS - NRC Publication - 544, PP. 20 -47.
Wieczorek, G.F., Wilson, R.C. and Harp, E.L., 1985. Siesmic slope stability map of San Manteo County, California, U.S. Geological Suryey Miscellaneous Geologic Investigation map I - 12570, Scale 1: 62,500.