The concern voiced by the second world water forum at its recent meeting in The Hague in Netherlands on the likelihood of water scarcity worsening in the years to come is timely. This makes it imperative for administrators, policy makers, planners, management experts and scientists to evolve ways and means to tackle the water crisis on a war footing.

A few years ago the director of the United Nations Environment Programme predicted that there would be “ Water wars”. The over exploitation of this natural resource is already creating problems all over the world. In India, hundreds of villages still do not have a single source of potable water.

This is the time to use water judiciously with proper management. The hunger for water can be satisfied to a great extent by harnessing the water that goes as a waste over small watersheds.

Water harvesting is no longer a subject for academic discussion. It is a living subject. The only way to solve   India's water crisis is to capture this bounty through traditional community-based and urban water harvesting.

In India, hundreds of villages still do not have a single source of potable water. But the rich continue to overexploit groundwater, sinking tube wells deeper into the earth to draw out this precious resource.

The cycle of drought, poor irrigation facilities and bad management of water resources has become a nightmare. In cities too, water scarcity is alarming. But if people begin conserving water particularly rainwater, this periodic water crisis can be averted. It is learnt that some 210 billion cubic meters of rainwater that is lost as runoff can be stored underground and 160 billion cubic meters of this water utilised.

What is rainwater harvesting? It allows water to seep into the ground rather than just letting it flow on the ground. Due to impermeable nature of structures like roads, etc water instead of draining into the earth and recharging aquifers, flow into storm water drains and is wasted.

In roof top rainwater harvesting, water is collected from the roof and directed into the ground through a pipe where it is stored in a reservoir. Roof top rainwater harvesting is the solution for water problems where there is inadequate groundwater supply or surface resources are absent or insignificant.

Rainwater harvesting can also cleanse water. Storage of treated wastewater and storm runoff in underground aquifers purges it of disease-causing organisms. This allows the water to be recycled for irrigating parks, gardens, and farms.

Important considerations for successful rainwater harvesting are :

•  location of recharge points;

•  hydrogeological properties responsible for recharging the aquifers; and

•  social responsibilities of the people.

Owing to the importance   of conserving water, a proposal was made    to implement   a pilot project to harvest the rain water   in SIT   campus, Tumkur (Karnataka).

The SIT campus spreads over an area of 25 hectares and is situated in Tumkur city along Bangalore – Honnavar Road at 65 km from Bangalore city. The campus is ideally located in a serene quiet country amidst well developed lawns and avenues of tree plantations providing a congenial atmosphere for the students. The campus has a total occupancy of 1500 inmates in hostels. The day scholars, staff and residential quarters total to about 3,500, at present lawns and gardens are formed in an area of about 5 hectares. The buildings with flat and sloped roof tops covers an area of 25,000 sq.m   i.e. 2.50 hectares. The daily requirement of water for domestic use and for landscape irrigation of the campus is obtained by withdrawal of ground water from 6 borewells in the campus. The overall yield from all these borewells is around 2.2 lakh liters. There is a water demand of 1.5 lakh liters for domestic use and for irrigation of lawns and gardens there is a demand for 2,00,000 liters daily. Therefore in total there is a requirement of 3.5 lakh liters of water per day. The terrain of the campus is having a gentle slope such that surface runoff drains from north-east towards south-west. The proposal made in this regard would improve the yield of existing borewells and   recharge the campus aquifer as well as   use the roof top water for direct pumping to the lawns and gardens   of the campus.

The average annual rainfall in the area is 822 mm, which says that total amount of rainwater received in the campus is 2,05,500 cu.m per year or 563 cu.m daily. If efforts are taken to capture 40% of the rainfall, irrigation demand can easily be met with.

The soil samples at 6 representative points are tested for physical   and chemical characteristics . The following are the results:

Soil - Physical Properties:-

1. Moisture content     -           -           3.48% to 15.66%

2. Specific Gravity      -           -           -1.88 to 2.65

3. Permeability m/day-           -           -0.216 to 0.794

4. Wet density g/cm 3-           -           -1.67 to 2.08

5. Dry density g/cm 3 -           -           -0.95 to 1.64

Soil Chemical Properties:-

1. pH           -           -           5.43 to 7.82

2. Sodium, mg/l    -           -35 to 69

3. Potassium, mg/l    -        7 to 16

4. Calcium, mg/l-   -          -7.08 to 26.30

The rain water samples were also collected   from roof surfaces of different buildings of the campus and the following is the result of analysis for important chemical constituents found.

Rainwater Characteristics:-

    Parameter                                                  Concentration

1. Acidity, mg/l as CaCO 3 -           -range 2 to 68

2. Alkalinity mg/l as CaCO 3 -        -12 – 14      

3. Sodium, mg/l as Na           -       -0 – 3

4. Potassium, mg/l as K           -    -13 – 25

5. TDS mg/l           -           -           1300 – 1400

6. Sulphates mg/l    -                     -3.8 – 5.0

7. Conductivity ms      -           -      0.10 – 0.10

8. Total hardness mg/l as CaCO 3 - 1.45 to 1.64

9. pH -           -           -           -           7.8 to 8.50

The soil, water and other conditions are favourable for gardening. Ground water recharge is possible as the soil possess better drainage characteristics.

The water harvesting proposals made here include provision of percolation ponds, borewells point recharges, roof top water collection and storage in sumps, soak pits etc.

* Dept. of Civil Engineering, Siddaganga Institute of Technology, Tumkur, Karnataka, India.

** UGC-ASA Centre in Fluid Mechanics, Central College Campus, Bangalore. Karnataka, India.

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