Q & Ans - Related to Rain Water Harvesting (Civil Engineering - Works)

 Questions -

a.  Explain rain water harvesting, why it is required?

 b. Explain advantages of rain water harvesting. 

c. Explain methods of rain water harvesting & maintenance tips for rainwater harvesting. 

d. Short Note0n Rain water Harvesting. 

e.  Introduction, Necessity, Basic Types & Advantages of Rain Water Harvesting.

ANS. a.  i. Rain water harvesting For our water requirement we entirely depend upon rivers, lakes and ground water. However rain is the ultimate source that feeds all these sources. Rain water harvesting means to make optimum use of rain water at the place where it falls i.e. conserve it ad not allow to drain away and cause floods elsewhere. The rain water harvesting may be defined as the technique of collection and storage of rain water at surface or in sub-surface aquifer before it is lost as surface run off. The augmented resources can be harvested whenever needed.

 ii. Need for rain water harvesting

Water is one of the most essential requirements for existence of living beings. Surface water and ground water are two major sources of water. Due to over population and higher usage levels of water in urban areas, water supply agencies are unable to cope up demand from surface sources like dams, reservoirs, rivers etc. this has led to digging of individual tube wells by house owners. Even water supply agencies have resorted to ground water sources by digging tube-wells in order to augment the water supply. Replenishment of ground water is drastically reduced due to paving of open areas. Indiscriminate exploitation of ground water results in lowering of water table rendering many bore-wells dry. To overcome this situation bore wells are drilled to greater depths. This further lowers the water table and in some areas this leads to higher concentration of hazardous chemicals such as fluorides, nitrates and arsenic. In coastal areas like Chennai, over exploitation of ground w2ater resulted in seawater intrusion thereby rendering ground water bodies saline. In rural areas also, government policies on subsidized power supply for agricultural pumps and piped water supply through bore wells are resulting into decline in ground water table. The solution to all these problems is to replenish ground water bodies with rain water by manmade means.

Q b) Advantages of rain water harvesting

ANS - a) Promotes adequacy of underground water 

 b) Mitigates the effect of drought 

c) Reduces soil erosion as surface run-off is reduced 

d) Decreases load on storm water disposal system 

e) Reduces flood hazards 

f) Improves ground water quality/decreases salinity 

g) Prevents ingress of sea water in subsurface aquifers in coastal areas. 

h) Improves ground water table, thus saving energy (to lift water) 

i) The cost of recharging subsurface aquifer is lower than surface reservoirs 

 j) The subsurface aquifer also serves as storage and distribution system 

k) No land is wasted for storage purposes and no population displacement is involved 

l) Storing water underground is environment friendly.

Q c) Methods for harvesting rain water

Ans . 

There are three methods of harvesting rain water are given below:- 

i. Storing rain water for direct use 

ii. Recharging round water aquifers, from roof top run off. 

iii. Recharging ground water aquifers with runoff from ground area.

i. Storing rain water for direct use In place where the rains occur throughout the year, rain water can be stored in tanks. However, at places where rains are for 2 to 3 months, huge volume of storage tanks would have to be provided. In such places, it will be more appropriate to use rain water to recharge ground water aquifers rather than to go for storage. If the strata is impermeable, then storing rain water in storage tanks for direct use is a better method. Similarly, if the ground water is saline/unfit for human consumption or ground water table is very deep. This method of rain water harvesting is preferable.

ii. Recharging round water aquifers, from roof top run off Rain water that is collected on the roof top of the building may be diverted by drain pipes to a filtration tank (for bore well, through settlement tank) from which it flows into the recharge well. The recharge well should preferably be shallower than the water table. This method of rain water harvesting is preferable in the areas where the rainfall occurs only for a short period in a year and water table is at a shallow depth. The various methods of recharging ground water aquifers from roof top runoff.

iii. Recharging ground water aquifers with runoff from ground areas The rain water that is collected from the open areas may be diverted by drain pipes to a recharge dug well/bore well through filter tanks. The abandoned bore well/dug well can be used cost effectively for this purpose. The various methods of recharging ground water aquifers with runoff from ground areas.

Q. d. Short Note on Rain water Harvesting. 

Ans:- Rain water harvesting :- it is technique of collection and storage of rain water at surface or in sub surface aquifer. Before it is lost as surface run off. The augmented resource can be harvested when need. Thus it comes wide range of means of collecting and storing water but popularly this items is becoming synonymous to artificial recharging of ground water aquifer. Following are the three basis type follow for rain water harvesting. a. Roof top rain water harvesting and storage in tanks. 

e.  Introduction, Necessity, Basic Types & Advantages of Rain Water Harvesting:-

Ans - 

i) Introduction: - Rain water harvesting is the accumulation and deposition of rain water for reuse rather than allowing it to run off. In other word it is the technique of collection and storage of rain water at surface or in ground. 

ii) Necessity:-Water is most essential requirement for existing living beings. Surface water and ground water are two major source of water, due to heavy demand ground water table goes down day by day. By harvesting water table get charged. 

iii) Basic Types:- 

a) Roof top rain harvesting and storage in tank. 

b) Roof top rain water harvesting and recharge sub surface aquifer. 

c) Surface run of harvesting and recharging sub surface aquifer. 

iv) Advantages:- 

a) Provide adequacy of underground water. 

b) Mitigate effect of draught. 

c) Reduce soil erosions as surface run off is reduced. 

d) Decrees load on storm water disposal system. 

e) The cost of recharging sub-surface aquifer is lower than surface reservoirs. 

f) Storage water under ground is environment friendly.