manual on rain water harvesting Central ground water board
+++++++++++++++++++++++++++++++++++
web site for rain water harvesting
http://www.ccsindia.org/ccsindia/policy/enviro/studies/wp0076.pdf
Rain water Harvesting System
Broadly rainwater can be harvested for two purposes
Storing rainwater for ready use in containers above or below ground
Charged into the soil for withdrawal later (groundwater recharging)
Source: A Water Harvesting Manual For Urban Areas
From where to harvest rain
Rainwater harvesting can be harvested from the following surfaces
Rooftops: If buildings with impervious roofs are already in place, the catchment area is effectively available free of charge and they provide a supply at the point of consumption.
Paved and unpaved areas i.e., landscapes, open fields, parks, stormwater drains, roads and pavements and other open areas can be effectively used to harvest the runoff. The main advantage in using ground as collecting surface is that water can be collected from a larger area. This is particularly advantageous in areas of low rainfall.
Waterbodies: The potential of lakes, tanks and ponds to store rainwater is immense. The harvested rainwater can not only be used to meet water requirements of the city, it also recharges groundwater aquifers.
Stormwater drains: Most of the residential colonies have proper network of stormwater drains. If maintained neatly, these offer a simple and cost effective means for harvesting rainwater.
Whether to store rainwater or use it for recharge:
The decision whether to store or recharge water depends on the rainfall pattern and the potential to do so, in a particular region. The sub-surface geology also plays an important role in making this decision.
DATA FOR DESIGN::
The following data is required to design a system and evaluate cost of construction
1.Rooftop area in square meter from where rain is to be harvested
2.Rain water drain pipe from the roof to the ground level
3. Drain at ground level to carry the rain water to the injection well
4.Water level at your area to find ot the depth of boring required at your site
Source of the article: http://www.indiawaterportal.org/questions/frequently-asked-questions-faqs-rainwater-harvesting-rwh
http://bangalore.citizenmatters.in/articles/587-rwh-guide
Rain water Harvesting System
Broadly rainwater can be harvested for two purposes
Storing rainwater for ready use in containers above or below ground
Charged into the soil for withdrawal later (groundwater recharging)
Source: A Water Harvesting Manual For Urban Areas
From where to harvest rain
Rainwater harvesting can be harvested from the following surfaces
Rooftops: If buildings with impervious roofs are already in place, the catchment area is effectively available free of charge and they provide a supply at the point of consumption.
Paved and unpaved areas i.e., landscapes, open fields, parks, stormwater drains, roads and pavements and other open areas can be effectively used to harvest the runoff. The main advantage in using ground as collecting surface is that water can be collected from a larger area. This is particularly advantageous in areas of low rainfall.
Waterbodies: The potential of lakes, tanks and ponds to store rainwater is immense. The harvested rainwater can not only be used to meet water requirements of the city, it also recharges groundwater aquifers.
Stormwater drains: Most of the residential colonies have proper network of stormwater drains. If maintained neatly, these offer a simple and cost effective means for harvesting rainwater.
Whether to store rainwater or use it for recharge:
The decision whether to store or recharge water depends on the rainfall pattern and the potential to do so, in a particular region. The sub-surface geology also plays an important role in making this decision.
For example, Delhi, Rajasthan and Gujarat where the total annual rainfall occurs during 3 or 4 months, are examples of places where groundwater recharge is usually practiced.
In places like Assam, Kerala, Mizoram, Tamil Nadu and Bangalore where rain falls throughout the year barring a few dry periods, one can depend on a small sized tank for storing rainwater, since the period between two spells of rain is short. Wherever sub-strata is impermeable recharging will not be feasible. Hence, it would be ideal to opt for storage.
Salient features of this approach:
Delhi Jal Board
Rainwater Harvesting Assistance Cell Varunalaya-I, karol Bagh, New Delhi-110005.
Ph. 3678380-82 extn. 246,240.
or
Officer Incharge, Central Ground Water Board, State Unit Office, Gallery no. 18/11, Jamnagar House,
Mansingh Road, New Delhi-110011
e-mail: niccgwb@sansad.nic.in; cgwa@nic.in; cgwa@vsnl.com
website: www.cgwaindia.com
Ph. 3384355. Fax. 3386743.
http://www.delhijalboard.nic.in/djbdocs/consumer/conservation.htm
Design of storage tanks
The volume of the storage tank can be determined by the following factors:
The volume of the storage tank can be determined by the following factors:
- Number of persons in the household: The greater the number of persons, the greater the storage capacity required to achieve the same efficiency of fewer people under the same roof area.
- Per capita water requirement: This varies from household to household based on habits and also from season to season. Consumption rate has an impact on the storage systems design as well as the duration to which stored rainwater can last.
- Average annual rainfall
- Period of water scarcity: Apart from the total rainfall, the pattern of rainfall -whether evenly distributed through the year or concentrated in certain periods will determine the storage requirement. The more distributed the pattern, the lesser the size.
- Type and size of the catchment:Type of roofing material determines the selection of the runoff coefficient for designs. Size could be assessed by measuring the area covered by the catchment i.e., the length and horizontal width. Larger the catchment, larger the size of the required cistern (tank).
Dry season demand versus supply approach
In this approach there are three options for determining the volume of storage:
In this approach there are three options for determining the volume of storage:
- Matching the capacity of the tank to the area of the roof
- Matching the capacity of the tank to the quantity of water required by its users
- Choosing a tank size that is appropriate in terms of costs, resources and construction methods.
IllustrationSuppose the system has to be designed for meeting drinking water requirement of a five-member family living in a building with a rooftop area of 100 sq. m. The average annual rainfall in the region is 600 mm (average annual rainfall in Delhi is 611 mm). Daily drinking water requirement per person (drinking and cooking) is 10 litres.
| Design procedure: Following details are available: Area of the catchment (A) = 100 sq. m. Average annual rainfall (R) = 611 mm (0.61 m) Runoff coefficient (C) = 0.85 1. Calculate the maximum amount of rainfall that can be harvested from the rooftop: Annual water harvesting potential = 100 x 0.6 x 0.85 = 51 cu. m. (51,000 litres) 2. Determine the tank capacity: This is based on the dry period, i.e., the period between the two consecutive rainy seasons. For example, with a monsoon extending over four months, the dry season is of 245 days. 3. Calculate drinking water requirement for the family for the dry season = 245 x 5 x 10 = 12,250 litres As a safety factor, the tank should be built 20 per cent larger than required, i.e., 14,700 litres. This tank can meet the basic drinking water requirement of a 5-member family for the dry period. A typical size of a rectangular tank constructed in the basement will be about 4.0 m x 4.0 m x 1.0 m |
Salient features of this approach:
- Simplest approach to system design but is relevant only in areas where distinct dry seasons exist
- Provides a rough estimate of storage volume requirements
- This method does not take into account variations between different years, such as the occurrence of drought years. It also entirely ignores rainfall input and the capacity of the catchment to deliver the runoff necessary to fill the storage tank.
- This technique can be used in the absence of any rainfall data and is easily understandable to the layperson.These points are especially relevant when designing systems in the remote areas of developing countries where obtaining reliable rainfall data can be difficult.
Delhi Jal Board
Rainwater Harvesting Assistance Cell Varunalaya-I, karol Bagh, New Delhi-110005.
Ph. 3678380-82 extn. 246,240.
or
Officer Incharge, Central Ground Water Board, State Unit Office, Gallery no. 18/11, Jamnagar House,
Mansingh Road, New Delhi-110011
e-mail: niccgwb@sansad.nic.in; cgwa@nic.in; cgwa@vsnl.com
website: www.cgwaindia.com
Ph. 3384355. Fax. 3386743.
http://www.delhijalboard.nic.in/djbdocs/consumer/conservation.htm
DATA FOR DESIGN::
The following data is required to design a system and evaluate cost of construction
1.Rooftop area in square meter from where rain is to be harvested
2.Rain water drain pipe from the roof to the ground level
3. Drain at ground level to carry the rain water to the injection well
4.Water level at your area to find ot the depth of boring required at your site
Source of the article: http://www.indiawaterportal.org/questions/frequently-asked-questions-faqs-rainwater-harvesting-rwh
http://bangalore.citizenmatters.in/articles/587-rwh-guide
What quantity of rainwater can be collected?
The rainwater harvested depends upon the catchment area, the rainfall pattern in the area and the drianage/ collection system used.
To understand the potential for rainwater harvesting, lets take the example of a house in Delhi with a terrace area of 100 sqm. Taking the average annual rainfall in Delhi as 600 mm, and assuming 70% harvesting efficiency (as some rainwater will be lost due to evaporation, collection etc.), we can calculate the amount of water harvested thus:
Volume of water harvested = 100 x 0.6 x 0.7
= 42,000 litres
This volume is more than twice the annual drinking water requirement of a 5-member family, whose average daily drinking water requirement is 10 lpcd.
What should be the depth of a recharge well/pit?
For effective recharge in Bangalore like conditions, a 15-20 feet depth is needed. (Provided you do not hit rock before that depth). If you hit water while digging the pit, you need to ask the workers to be careful while they continue digging. The diameter of the pit you choose depends on two things: space available and the quantity of water you will send in. A 3 feet dia X 20 feet pit will ‘hold’ around 4000 litres (for recharging the ground). A 5 feet x 30 feet structure can hold 16000 litres.
ENVO CASE STUDY : TAJ SATS AIR CATERING LTD,IGI
AIRPORT COMPLEX, NEW DELHI
Roof Top harvesting potential
In
order to study the rooftop harvesting potential, the total roof-top area was
calculated and is depicted in table (1). In this method, the roof-top areas of
various buildings in Taj Sats Air Catering Ltd, New Delhi was calculated and 25
mm of rainfall was observed in 15 min time. So, we got the roof-top potential
of each building (depicted in table (1)).
Total
quantity of water
to be collected (cu.m.) = |
Roof Top
Area (Sq.m.)
x Average Monsoon Rainfall (m) x 0.8 |
ANNUAL
TEMPERATURE & RAINFALL CHART FOR
NATIONAL CAPITAL REGION OF DELHI
|
||||
MONTHS
|
MAX
|
MIN
|
RAINFALL
|
|
JANUARY
|
21
|
07
|
25
|
|
FEBRUARY
|
24
|
10
|
22
|
|
MARCH
|
30
|
15
|
17
|
|
APRIL
|
36
|
21
|
07
|
|
MAY
|
41
|
27
|
08
|
|
JUNE
|
40
|
29
|
65
|
|
JULY
|
35
|
27
|
211
|
|
AUGUST
|
34
|
26
|
173
|
|
SEPTEMBER
|
34
|
25
|
150
|
|
OCTOBER
|
35
|
19
|
31
|
|
NOVEMBER
|
29
|
12
|
01
|
|
DECEMBER
|
23
|
08
|
05
|
|
Availability of Rain Water through Rooftop Rain Water Harvesting |
||||
Rooftop
Area (sq.m.)
|
Rainfall (in mm)
|
|||||||||||||
100
|
200
|
300
|
400
|
500
|
600
|
800
|
1000
|
1200
|
1400
|
1600
|
1800
|
2000
|
||
Volume of Water (in cum)
|
||||||||||||||
20
|
1.6
|
3.2
|
4.8
|
6.4
|
8
|
9.6
|
12.8
|
16
|
19.2
|
22.4
|
25.6
|
28.8
|
32
|
|
30
|
2.4
|
4.8
|
7.2
|
9.6
|
12
|
14.4
|
19.2
|
24
|
28.8
|
33.6
|
38.4
|
43.2
|
48
|
|
40
|
3.2
|
6.4
|
9.6
|
12.8
|
16
|
19.2
|
25.6
|
32
|
38.4
|
44.8
|
51.2
|
57.6
|
64
|
|
50
|
4
|
8
|
12
|
16
|
20
|
24
|
32
|
40
|
48
|
56
|
64
|
72
|
80
|
|
60
|
4.8
|
9.6
|
14.4
|
19.2
|
24
|
28.8
|
38.4
|
48
|
57.6
|
67.2
|
76.8
|
86.4
|
96
|
|
70
|
5.6
|
11.2
|
16.8
|
22.4
|
28
|
33.6
|
44.8
|
56
|
67.2
|
78.4
|
89.6
|
100.8
|
112
|
|
80
|
6.4
|
12.8
|
19.2
|
25.6
|
32
|
38.4
|
51.2
|
64
|
76.8
|
89.6
|
102.4
|
115.2
|
128
|
|
90
|
7.2
|
14.4
|
21.6
|
28.8
|
36
|
43.2
|
57.6
|
72
|
86.4
|
100.8
|
115.2
|
129.6
|
144
|
|
100
|
8
|
16
|
24
|
32
|
40
|
48
|
64
|
80
|
96
|
112
|
128
|
144
|
160
|
|
150
|
12
|
24
|
36
|
48
|
60
|
72
|
96
|
120
|
144
|
168
|
192
|
216
|
240
|
|
200
|
16
|
32
|
48
|
64
|
80
|
96
|
128
|
160
|
192
|
224
|
256
|
288
|
320
|
|
250
|
20
|
40
|
60
|
80
|
100
|
120
|
160
|
200
|
240
|
280
|
320
|
360
|
400
|
|
300
|
24
|
48
|
72
|
96
|
120
|
144
|
192
|
240
|
288
|
336
|
384
|
432
|
480
|
|
400
|
32
|
64
|
96
|
128
|
160
|
192
|
256
|
320
|
384
|
448
|
512
|
576
|
640
|
|
500
|
40
|
80
|
120
|
160
|
200
|
240
|
320
|
400
|
480
|
560
|
640
|
720
|
800
|
|
1000
|
80
|
160
|
240
|
320
|
400
|
480
|
640
|
800
|
960
|
1120
|
1280
|
1440
|
1600
|
|
2000
|
160
|
320
|
480
|
640
|
800
|
960
|
1280
|
1600
|
1920
|
2240
|
2560
|
2880
|
3200
|
|
3000
|
240
|
480
|
720
|
960
|
1200
|
1440
|
1920
|
2400
|
2880
|
3360
|
3840
|
4320
|
4800
|
|
Design Of Rain Water Harvesting System By Injection Well Method
The
rainwater harvesting system suggested for Taj Sats Air Catering Ltd, New Delhi
is as follows :-
6.4.1 Design For Roof Top Area
Rooftop
potential (really a good source of unpolluted water) as depicted in table (1)
is of nearby buildings taken together. The volume of water is collected from
rooftops and conveyed to the injection well through main pipes in such a way
that it is economical and optimal use of the ingredients used in easy flow of
the water. The injection well should be so located so that it comes into crest
of the land and does not fall on the trough. For this purpose such a portion of
the area be used which is not required for any further construction in future.
This
requires a thorough study on the basis of work-study principles-flow diagrams,
ground contours, ground water contours, foundation details (injection well
should be min 10 m away from any foundation). Layout Plan of Taj Sats Air Catering Ltd, IGI , Airport
Authority Complex, New Delhi, sewage pipes, sewage pumps, Electrical fittings
and other important under ground installations would also be taken into
consideration.
On
the basis of the volume of water flowing through the main pipes in the
injection well, the injection well’s parameters were fixed and depicted in
table (3).
6.4.2
Interconnecting pipes:
a)
Drain Pipe : The rain
water collected in the roof is allowed to come down to ground level via drain
pipes.Drain pipes are made of MS .
b)
Inflow Pipe network :
The water coming down from roof via drain pipes is led to the inflow pipe
network placed on ground level. The pipes of the network are joined together at
all intersecting points by junction boxes provided. The pipe network is made of
MS and having dia 6 inches. The pipes are laid with proper slope to the
recharge pit. The pipe ends are joined together by means of flanzes.
6.4.3 Recharge pit
1. Two Recharge
pits as per required volume as indicated in the above chart are constructed to recharge the
shallow aquifer.
2. After excavation, the pit is refilled
with boulders and pebbles at the bottom followed by gravel. 3. The collected
water from the rooftop is diverted to the pit through a drain pipe and inflow
pipe network . 4. Recharge
water is filtered through the pit. 5. The upper
layer of material in the pit should be
removed and replaced every year after rainy season.
Recommendation
Since
the rainwater harvesting system is used for the groundwater recharging in the
trough zone of the aquifer system by virtue of which the aquifer system of the
study area will be saturated and as a result the failure of the tubewell will
be stopped and tubewell life will be enhanced . The groundwater quality will
certainly be improved due to more percolation of rainwater other than the
natural course of action of percolation, through the two Injection wells
installed. It is recommended
that, monitoring system for the impact of rainwater harvesting for groundwater
recharging should be installed for the
periodic assessment to be carried out in the study area in order to monitor the
improvement of the groundwater quality and potential of the study area. The
installation of the two injection wells as per location given in map are executed for the roof top harvesting
.The details of the Injection Wells are mentioned in table no.3 and the
strata encountered are given in the
figures.
SUMMERY OF THE PROJECT::
SUMMERY OF THE PROJECT::
1.
Two Injection Wells in the study
area are installed for Rainwater Harvesting for Groundwater
Recharging,
2.
Calax / Reverse Rotary rig is used for drilling .
3.
MS pipes are used for
interconnecting the roof with injection wells.
4.
Junction boxes are
provided between drain pipe coming from roof to interconnecting pipes going to
injection wells.
PROPOSAL FOR RECHARGE PIT :
Total Area Contributing to Run Off : 10,000 sq feet= 1000 Sq Mtr
For design consideration, rainfall intensity of 25 mm has to be taken into account
Considering four recharge pits,
Recharge Pit Size : 2 x 2 x 2.25 Mtr ; Filter material Depth = 0.9 mtr
Depth to water level in summer (Pre Monsoon)= 25 mtr bgl , Hence bore well depth should be atleast 25 mtr bgl
COST ESTIMATE OF WELL : Four Lacs Only per pit
PIT SIZE : 2 x 2 x 2.25 mtr, 4 nos , Filter material Depth =0.9 mtr
COMPLETION CERTIFICATE OF THE PROJECT