Govt. Polytechnic Navsari

"Rain water Harvesting"

Created by;Sharma Raj .s En.no =149750306052

1.Rain water Harvesting : Rain water harvesting is the accumulating and

storing of rain water for it reachen the aquifer. It has been used to provide drinking water, water for

livestock, water for irrigation, as well as other typical uses.

It can supplement the subsoil water level and increase urban greenery.

Water collected from the ground, sometimes from areas that are especially prepared for this purpose, is called stormwater harvesting.

Benefits of Rain Water Harvesting;

1. Availability of water for drinking, water for live stock,water for irrigation etc.

2. Recharge of ground water table.3. Increase in greenery in urban areas4. system can be simple to construct from inexpensive

local materials. 5. It is environment friendly. 6. Prevents soil erosion and flooding in urban areas.7. Inculcates a culture of water conservation in the

people. 8. Community water resources act as social temples.

Roof top rain water harvesting System : Roof top rain water harvesting or domestic rainwater

harvesting is the technique through which rain water is captured from roof components and stored in tanks/reservoirs/ground water aquifers.

It consists of conservation of roof top rain water in urban areas and utilizing it to augment ground water storage by artificial recharge.

This technique is particularly useful in dryland, hilly, urban and coastal areas. If the system is properly installed and maintained, clean water fit for drinking can be collected and stored

Components of roof top rain water harvesting system

The various components of roof top rain water harvesting system are

1. Roof/ catchment area 2. Gutters and downpipes 3. Filter unit or leaf screen 4. Storage tank 5. Delivery system 6. Water treatment unit

1. Roof/catchment area: The terrace of a building act as a

catchment area for collecting water in this system.

A flat roof is usually made of RCC. If tiles are fixed on the top of the

roof,good quality of water can be obtained.

2.Gutters and Downpipes Water from roof/ catchment area is

collected into gutters. Commonly two types of gutters are

used 1. Eaves gutter 2. Box gutter

3.Filter unit or Leaf screen The rain water collected from the roof

should be allowed to reach the storage tank only through a filter unit.

Rubble, sand and charcoal, as used the traditional three-pot filtration, can be adopted here

4.Storage Tank Water from filter unit is stored in the storage

tank. Mainly three types of storage tanks are constructed for roof water harvesting.

They are as ;1. under ground, 2. on the ground 3. above ground tanks. The under ground tanks are usually made of masonry or Rcc. The overhead tanks are made of PVC or masonry

5.Delivery system : The water from the storage tank is

delivered to the treatment unit through delivery pipe system.

6. Water treatment unit : The water stored in the storage tank should be

treated if it is to be used for drinking. Normally, filtration, sedimentation, disinfection,

etc. processes are followed for the treatment of water.

design of storage : The design of storage tank depends

upon (i) Average annual rainfall (ii) Size of catchment (iii) Drinking water requirements

Example: Design a storage tank for drinking water for the following data :

Number of members in the family = 5 Roof top area = 100 m Average annual rainfall = 600 mm Runoff = 0.85 coeficient coefficient for evaporation, Spillage and first flush, etc. = 0.80 Daily drinking& cooking requirement = 10 litre/person

Solution: = (area of roof top )x (annual rainfall(in m)) x

(Run off coefficient) x (Coefficient for evaporation first flush etc.)

= 100 x 0.60 x 0.85 x 0.80= 40.8 m3= 40,800 litres The tank capacity has to be designed for dry

period i.e. the period two consecutive rainy seasons. With monsoon extending over 4 months, the dry season is of 245 days is considered.

Drinking water requirement for family for dry season: = 245 x 5 x 10 = 12,250 litres As a safety factor, the tank should be

built 20% larger than required. quantity of water to be stored in the tank= 1.2 x 12,250 = 14,700 litres= 14.70 m3

Size of rectangular tank: Size of rectangular tank == 3.5 m x 2.5 m x 1.7 m= 14.875 m3

Recharge Structures : The water conected from roof tops of large buildings

can be used for artificial recharge of ground water. The various type of recharge structures are

1. Recharge through abandoned Dug well 2. Recharge through hand pump3. Recharge pit4. Recharge Through Trench 5. Gravity Head Recharge Tube well 6. Recharge Shaft

• References ;1. U.R.patel,V.A. patel,M. Balya and H.M.

Rajgor.Roof top rain water harvesting (RRWH) at SPSV campus Visnagar : gujarat – A Case study, international journal of research In engineering and technology ,3(4),2014,821-825

2. S.D. Khandagale & V.A. Joshi Rain water harvesting: grab hold of water where falls.