Rainwater harvesting techniques

Submitted by:Megokedono VakhaMSc 4th

semester(Geology)DOS in Earth ScienceUniversity of Mysore

Submitted to: Dr.D.NAGARAJU DOS IN EARTHSCIENCE UNIVERSITY OF MYSORE

Contents

• What is rainwater harvesting?• Principle of water harvesting• Reasons of Shortage of Water• Solution• Rain water harvesting• Objectives and need for rain water harvesting• Roof top rain water harvesting• Rainwater utilization in domestic dwellings• Surface run off harvesting• Advantages and approaches of rainwater harvesting• Conclusions and references

What is rainwater harvesting?Water-elixir of lifeIt means capturing rain where it falls or capturing the run

off. And taking measures to keep that water clean by not allowing polluting activities to take place in the catchment.

In generalwater harvesting is the activity of direct collection of rainwater.

The rainwater collected can be stored for direct use or can be recharged into the groundwater. Water harvesting means to understand the value of rain, and to make optimum use of the rainwater at the place where it falls.

Principle of water harvesting

Reasons of Shortage of Water• Population increase• Industrialization• Decrease in surface area of Lakes, tanks etc.• Deforestation

Solution• Rain water is the ultimate

source of fresh water• Potential of rain to meet

water demand is tremendous• Rain water harvesting helps

to overcome water scarcity• To conserve ground water,

the aquifers must be recharged with rain water

Rain water harvesting is the ultimate answer

Rain water harvesting

Objectives

•The main objectives of rain water harvesting areto conserve the surface run-off during monsoonsto recharge the aquifers and increase availability of

ground waterto improve the quality of ground water where

requiredto overcome the problem of flooding and stagnation

of water during the monsoon seasonto arrest salt-water intrusion

Need for rain water harvesting

•The need for rainwater involves different parameters such asto meet the ever increasing demand of waterto reduce the runoff which chokes storm water drainsto avoid flooding of roadsto augment ground water storageto reduce the soil erosion

to supplement domestic water requirement during crisisto improve the quality of ground water

Two main techniques of rainwater harvesting

Storage of rainwater on surface for future use. Recharge to ground water.

The storage of rain water on surface is a traditional techniques and structures used were underground tanks, ponds, check dams etc.

Recharge to ground water is a new concept of rain water harvesting and the structures generally used are :-•Pits :- Recharge pits are constructed for recharging the shallow aquifer. These are constructed 1 to 2 m, wide and to 3 m. deep which are back filled with boulders, gravels, coarse sand.

Pitstrench

•Trenches:- These are constructed when the permeable stream is available at shallow depth. Trench may be 0.5 to 1 m. wide, 1 to 1.5m. deep and 10 to 20 m. long depending up availability of water. These are back filled with filter. materials.

•Dug wells:- Existing dug wells may be utilised as recharge structure and water should pass through filter media before putting into dug well.•Hand pumps :- The existing hand pumps may be used for recharging the shallow/deep aquifers, if the availability of water is limited. Water should pass through filter media before diverting it into hand pumps.

Hand pumps

Dug wells

Open well

Dug or bored well

Bore well

• Recharge wells :- Recharge wells of 100 to 300 mm. diameter are generally constructed for recharging the deeper aquifers and water is passed through filter media to avoid choking of recharge wells.

• Recharge Shafts :- For recharging the shallow aquifer which are located below clayey surface, recharge shafts of 0.5 to 3 m. diameter and 10 to 15 m. deep are constructed and back filled with boulders, gravels & coarse sand.

• Lateral shafts with bore wells :- For recharging the upper as well as deeper aquifers lateral shafts of 1.5 to 2 m. wide & 10 to 30 m. long depending upon availability of water with one or two bore wells are constructed. The lateral shafts is back filled with boulders, gravels & coarse sand.

Recharge wellsLateral shafts in bore wells

• Spreading techniques :- When permeable strata starts from top then this technique is used. Spread the water in streams/Nalas by making check dams, nalah bunds, cement plugs, gabion structures or a percolation pond may be constructed.

• These techniques can serve the following the following purposes:Provide drinking waterProvide irrigation waterIncrease groundwater rechargeReduce storm water discharges, urban floods and overloading of sewage treatment plantsReduce seawater ingress in coastal areas.

Why Rain water should be harvested

• To conserve & augment the storage of ground water• To reduce water table depletion• To improve the quality of ground water • To arrest sea water intrusion in coastal areas • To avoid flood & water stagnation in urban areas• It is the activity of direct collection of rain water• Rain water can be stored for direct use or can be

recharged into the ground water aquifer• Surface water is inadequate to meet our demand and we

have to depend on ground water.

Roof top rain water harvesting• It comprises of– Roof catchment– Gutters– Down pipe & first flushing pipe– Filter Unit– Storage Tank

The first and foremost thing is that the roof should be kept clean. The rain water should not be transfer to the storage tank for 15 minutes first rain because it might be contaminated with dirt produced by birds, leaves etc.

Surface run off harvesting

• Capturing runoff from local catchments• Capturing seasonal floodwaters from local streams• Conserving water through watershed management

Advantages of rainwater harvesting• Roof catchment are relatively cleaner and free from

contamination compared to ground level catchment• Collection of rainwater from the roof top for domestic need

is popular• Simplest method is keeping a vessel beneath the edge of

roof during rainy season for immediate use• Availability of water during scarcity period for any purposeAwareness among publics, mind-setting. Participation of

publics, financial subsidy, following regulations laid for it and advanced planning can help to approach it easily

ConclusionWater harvesting is the collection of runoff for productive purposes. Instead of

runoff being left to cause erosion, it is harvested and utilizedIt is especially relevant to the semi-arid and arid areas where the problems of

environmental degradation, drought and population pressures are most evident. It is an important component of the package of remedies for these problem zones, and there is no doubt that implementation of WH techniques will expand.

Rain water harvesting is essential because :--Surface water is inadequate to meet our demand and we have to depend on ground water.-Due to rapid urbanization, infiltration of rain water into the sub-soil has decreased drastically and recharging of ground water has diminished.

It is necessary to go for it to conserve water which has become scarce and its availability is minimum due to overexploitaion and continual increase population

thus rainwater harvesting can solve numerous problems of waters

References

• www.google.com• www.wikipedia.org• Brooke(Kenneth), groundwater and watershed

management, 2nd edition, 387-399

Harvesting and conserving water is every individual’s duty. Every drop of rain water is

precious. So save it. It might be the very drop that will quench your thirst one day…

Thank you….