Surface water harvesting and recharging of aquifers

Code No: TMS078 Price: 1300 Category: Water

 

India ranks third in the world for fresh water availability, the front runners being Canada and Brazil.
In spite of receiving 4200 cu.km.(km3) of rain water every year, there is a shortage of water practically in all the states, whether it is Maghalaya, Delhi, Tamilnadu or Andhra Pradesh. This is because rain water is not harvested and utilized in a planned way. A summary of the Techno-Market Survey “Surface Water Harvesting and Recharging of Aquifers” is given below:


1. Scope and Coverage

The scope and objective of the study is to address the following aspects I the context of the topic of the study.

i) Relationship and the importance of the specific topic, to the broad area to which it belongs.

ii) The current status of the technology in the world and in the country. Market (domestic /export) sizes and their potentials.

iii) Assessment of the technology, resource parameters such as energy, raw material, infrastructure and manpower etc. to arrive at preferred technology options available in the country.

iv) Short term and long term economic aspects of preferred options along with their feasibilities.

v) Impact of the preferred options by itself and its spin-offs.

vi) Recommendations:

a) For implementation of preferred technology options-identifying critical inputs such as raw materials, capital goods and human resources required and their availability, investments required to commercialize, and benefits/returns expected.

b) For R&D / Technology development-identifying the requirements of inputs and expected benefits.

vii) Action Plan for implementation of recommendations along with identification of:

a) List of available technologies for Indian industry and,
b) The agencies/groups/individuals for implementation.

viii) Expected impact of recommendations, if implemented.

2. Methodology

The methodology adopted for the study the following steps:

i) In-depth literature survey was undertaken. The references and bibliography are given at the end of the report.

ii) International databases were searched for latest developments and their adoption.

iii) Number of agencies were contacted/surveyed. It covers academic institutes, R&D agencies, government bodies, industry, etc. list of agencies contacted during the study is appended to the report. The information has been gathered through:

- Open ended questionnaires.
- Personal interviews
- Literature requests.
- Brain storming etc.

iv) The information thus gathered was processed, analyzed and complied under various sub-heads.

v) Findings were discussed with the experts and additional/missing information was gathered through another round of survey.

vi) Draft report has been discussed with the experts.                                                                                               Back


3. Highlights of the survey

i) The global distribution of fresh water (less than 3% of total quantity of water) of which annually 20% is available in liquid form.

About 98.4% of this is, in the form of ground water, 1% is in the lakes. The rivers and atmosphere contain 0.1% each while solid body carries 0.2% and the rest negligible amount is considered as biological one.2 For India, the water budget reveals that out of a total water input of 420m. ha m received annually through precipitation ad river flows from outside the country, 70 m. ha m evaporates immediately, 165m. ha infiltrates into the soil and 135 m. ha m remains as surface water in rivers, ponds, lakhs etrc.2 Only 50 m. ha m is available in the form of ground water. An estimated 150 m. ha m of water flows into the sea or to other countries like, Bangladesh and Pakistan.2 Most of the rainfall (over 57%) in the country is received during the south-west monsoon period.

Water resources are required to be handled carefully for their sustainable development. Ground water is an important source of fresh water. Quantum of water that can be extracted economically from ground water aquifers every year has been estimated as 450 km3. Therefore, on an average about 1140 km3 of water may be reckoned as available for exploiation.4

ii) The present (1990) total demand of water for drinking, irrigation, industrial and energy uses is 552 km3 and is expected to increase to 750 km3 by 2000 and to 1050km3 by 2025 (table 1.1.).

iii) There is a large variation in rainfall from region to region, season to season and year to year. Nearly 9% area of the country is arid and 40% is semi-arid (annual rainfall between 500 & 1000 mm)4. Because of the vagaries of the monsoon, semi-arid regions of the country are drought prone.

iv) The National Water Policy enunciates that water is a scarce and precious national resource to be planned, developed and as such conserved, on an integrated and environmentally sound basis. The concept of transferring water from a surplus basin to a deficit basin has been under consideration by water resource planners in the recent past. The policy emphasizes the need for an integrated and multi-disciplinary approach for the planning, formulation, clearance and implementation of projects.

Water resource management for its optimum use is multi-dimensional. This study gives an account of rain water harvesting technologies for domestic and agricultural applications through low investment schemes and artificial recharging of aquifers.

v) Ponds, Nadis, Talabs, Haffirs, impounding ponds etc. are age old practices of rain water harvesting and storage for various purpose such as drinking, washing, irrigation, industrial uses and power generation.

The varied versions of techniques like roof-top harvesting have been primarily used for drinking purposes and the runoff inundation methods like khadins, ahars, submerged tanks, embankments, and farm ponds have been primarily used for agricultural purposes.

It would be wrong to make too sharp a division between domestic and agricultural applications, or between roof and ground surface catchments. All of them have been put to alternate or multiple uses.

vi) Traditional water harvesting systems are not only relevant, but are necessary and in some cases vital today. Some of these systems were in fact neglected when more attractive systems were installed b the government agencies. However, the failures of modern systems have resulted in attempts to regenerate and multiply the traditional ones. These efforts have not been entirely successful due to several reasons including that there is no clear policy regarding traditional water harvesting systems.

vii) Water harvesting techniques have several advantages: they serve local communities, they can be built with local material and skills in a short time. They however, face several problems, the important ones are silting, breaching, seepage, evaporation and submergence of cultivable lands. The technical solutions to these problems have been discussed in the report.                                                                                                                                                            Back   


viii) Run-offs induced by surface treatments have given good results. Classification of surface treatments can be made as follows:

  • Clearing from sloping surfaces the unwanted vegetation and loose material;
  • Improving vegetation management y planting with different species or by cropping;

 

  • Providing most desirable mechanical treatments to the soils, including smoothing and compacting surfaces, on contour steps in micro-catchments as workable units.
  •   Making hard surfaces using traditional soil stabilization techniques (as used on Botswana threshing floor catchments);
  • Reducing soil permeability by te application of chemicals (e.g. sodium salts);
  •   Applying chemical binders such as asphalt to seal the surface.
  •   Covering the catchments with conventional paving materials:
  •   Covering the catchments with other rigid materials;
  •   Covering the catchments with flexible/ plastic materials.

Sheet metal, butyl rubber, asphalt roofing, bentonite paraffin, fiber glass reinforced asphalt, plastic sheeting with gravel cove etc. have been used to cover the contributing areas and thus induce larger volumes of run-off.

As regards chemical treatment of the soil, a lot of research has been carried out on substances which can be mixed with, spread or sprayed over the soil. Experiments have been made with sodium salts (which encourage surface crusting on soil containing clay) with silicones (which are water repellent) and with oil paraffin wax, bitumen or asphalt (which bind soil particles together). The sodium treatment is cheap but may not last for more tan a year leading to increased soil erosion subsequently.

The desirable attributes of a satisfactory ground surface treatment are:

  • The run-off must be non-toxic.
  • The surface should be smooth and impermeable or at least have a low infiltration rate.
  • The surface should have a high resistance to weathering and should prevent internal chemical or physical deterioration.
  • The surface need not have great physical strength, but should be able to withstand hail, intense rain, wind, occasional animals, moderate water flow, plant growth insects, birds, burrowing animals and maintenance vehicles.
  • The treatment should be inexpensive on an annual cost basis. This necessitates low maintenance costs and generally low capital cost.
  • Construction and maintenance should not require special machinery or skills.

However, it is recognized that it is usually necessary to forego one desirable characteristic in order to achieve another, particularly when the overriding objective is lower cost.

ix) Large quantities of water are lost through evaporation from tanks, lakes and talabs. 5 M.ha.m form the total storage of 15 M.ha.m evaporates in the reservoirs, spread all over the country (33% loss).

A number of approaches/techniques have been developed to reduce evaporation from water bodies. Some of these are:

  •  Keeping the area/volume ratio of water body lower.
  • Minimizing exposed surface through reservoirs regulation.
  • Constructing artificial aquifers.
  •   Achieving application of mono-molecular film.
  •   Reducing the energy available for evaporation
  •   Installing wind breaks.

x) The technique of rainwater collection for domestic supply or run-off farming, is essentially small in scale. Where large concentrations of population have to be supported, intensive form of development is inescapable and must sometimes include, large dams and river basin projects.

Traditional systems, in technological terms, are good and have stood the test of time. There is not need for immediate upgradation through research and development, unless the systems are well documented and understood. Modern water managers have shown little interst in traditional ystems due to lack of clear cut policy and encouragement.

The Ghala tank in Kenya is mad eby modifying a traditional granacyh basket or Ghala and plastering it inside and out with a 2:1 sand / cement mixture (see Fig.3.4). Cisterns built in Indonesi and Thailand using bamboo reinforcement instead of metal, have been highly significant in enabling to make low-cost tanks.

Excavated cisterns, suitably lined with cement plaster or other impermeable material, can be cheaper and may collect large volumes of water from ground surfaces. Galvanized corrugated iron tanks also have merits when looked at, in terms of social benefits and livelihoods.

Significant improvements have been made in design and layout of gutters and pipes for hygienic and economical collection of rain water. Technologies for manufacture and laying of system, appropriate to the volumes of water required to be stored, are available. Flexible piping, single tank/multi-tank system, provisions for first flush diversion and /or inlet filter mould are other developments.

Proper maintenance of roofs, tanks, gutters and pipings to ensure hygienic conditions is very essential.

xi) With regard to run-off farming as opposed to the exploitation of flood water, the inundation method used in Sudan, Pakistan and India has been developed to its highest level of sophistication. Techniques differ in details, but the principle is to allow run-off to collect behind a bund and leave he water standing until the planting date for the crop approaches. Then the land is drained and the crop is sown. The area behind the bund is known as a submergence tank, or an ahar (in Bihar), or a khadin (in Rajasthan), and may cover may hectares.

The specific systems are:

a. Khadins
b. Submergence bunds
c. Conservation ditches
d. Embankments
e. Farm ponds, and percolation tanks

xii) Whenever surface or ground water irrigation is developed in isolation form each other, the experience has been constantly bad with regard to resource conservation.

Exclusive reliance on canal irrigations tends to raise the water table, leading ultimately to water logging which in turn produces soil salination in case of arid and semi arid tracts. Exclusive reliance on ground water as a source of irrigation creates the problem in a reverse manner. That is, over exploitation of ground water may occur, leading to a permanent lowering of the ground water table.

xiii) Aquifers can provide a viable solution for storage, if certain topographical, hydrological, geological and socio-economic conditions exist and appropriate recharging technologies are followed. Aquifers have been used as reservoirs for thousands of years and warrant increased attention.

Several method of artificial recharging are in vogue, the choice being dictated by local conditions. The methods may be classified as follows:

a. Spreading method
b. Pit method
c. Induced – recharge method
d. Well method

For artificial recharging, there is a need to identify whether the quality of ground water and that of surface water are compatible. With temperature variations and with reversible flow direction due to ion exchanges, the soluble salts have a tendency to precipitate which results in clogging of pore spaces in spreading basins and clogging of slots in injection wells and reduces artificial recharging rates.                                                                                                                          Back


4. Recommendations and Action Plan

1. A clear-cut policy regarding surface water harvesting, primarily through the application of improved traditional rain water harvesting techniques must be formulated by the government in close association with user segments and NGOs.

2. Exploitation of surface and ground water should be in girth proportions, ensuring balanced water conditions.

3. Special attention is required to be paid to soil conservation measures in the catchments of the existing and future reservoirs to check siltation problems and thereby ensuring the designed lives of the reservoirs.

4. There is a need to standardize the planning and design norms of rain water harvesting for various end-users based upon the most prevailing conditions.

5. The involvement of people is essential for the success of the program as it calls for maintenance of the system consistent with hygienic conditions, (specially for drinking water), and changes in social habits etc.

6. Proper rates and volumes of run-off must be induced by surface treatments. Mechanical treatments must be given in all the cases due weight age for mobilizing local man-power. Wherever budget permits, the catchments areas may be either covered by Flexible/plastics materials or be chemically treated.

7. Environment-friendly chemical treatments having 4-5 years of life needs to be developed.

8. The evaporation losses may be minimized by simultaneous application of:
i) Increase in reservoir depth, to reduce the surface area.
ii) Dense and tall trees around the water reservoir to keep the temperature low and to act as wind breakers.
iii) Mono-molecular film on the water surface.

9. Geo-membranes/super plastics be used in preparation of tanks/reservoirs to minimize the seepage losses.

10. Domestic roof-top rain water harvesting be encouraged for drinking water.

11. Flexible piping systems with a provision for “first flush diversion” be promoted.

12. Storage tanks/ cisterns made of local material for storing water for purposes other than drinking be encouraged.

13. Run-off farming methods be encouraged through various schemes

14. Specific programs be initiated to locate suitable topographical, hydrological and geological sites to be developed as water reservoirs bye converting them into aquifers.

15. Existing aquifers be optimally utilized by storing water during the rainy season and by withdrawals during lean periods.

5. Expected benefits

The implementation of above recommendations will ensure availability of drinking water at every home, throughout the year. It would also increase the agricultural out-put in arid and semi-arid zones. Social and economic life would improve. However, it is very difficult to make a quantifiable assessment of the benefits. Benefits can only be quantified for a specific project for implementation with a specific budget for allocation.


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