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Wednesday, August 31, 2016

How to design a rain water harvesting system RWH CASE STUDY : TAJ SATS AIR CATERING LTD,IGI AIRPORT COMPLEX, NEW DELHI



manual on rain water harvesting Central ground water board

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web site for rain water harvesting
1.                INTRODUCTION

In spite of astonishing achievment in the field of science and technology, nature remain to be a mystery for human being . Though water is obtained through desalination, artificial rain by cloud seeding etc. the shortage of water even for drinking purpose is a perpetual phenomenon throughout the world,in most of the cities , the water supply sector is facing a number of problems and the income in population in urban area have resulted in exploitation of water resources to the extremes .  Fresh water sources are being heavily exploited to meet the demands of urban population . Failure of monsoon fail to meet the ever increasing demands and ground water reserves are tapped , often to unsustainable levels. Unplanned and uncontrolled extraction of ground water would disturb the hydrological balance . Hence it is necessary to take up measures to conserve and management of the renewable water sources in all possible ways. Ground water recharge by rain water harvesting (RWH) is the simple and cost effective way.

Rooftop Rain Water Harvesting is the technique through which rain water is captured from the roof catchments and stored in underground reservoirs. Harvested rain water can be injected to sub-surface ground water aquifer by adopting artificial recharge techniques to increase the level of ground water. The Main Objective of rooftop rain water harvesting is to stop the depleting water level of ground water and make water available for future use. Capturing and storing rain water in underground tanks for use is particularly important in dry land, hilly, urban and coastal areas. In alluvial areas energy saving for 1m. rise in ground water level is around 0.40 kilo watt per hour.                                                                                       
                  
Need for Rooftop Rain Water Harvesting
1. To meet the ever increasing demand for water
2. To reduce the runoff which chokes storm drains
3. To avoid flooding of roads
4. To augment the ground water storage and control decline of water levels
5. To reduce ground water pollution
6. To improve the quality of ground water
7. To reduce the soil erosion
8. To supplement domestic water requirement during summer, drought etc.up

Advantages of Rain Water Harvesting
1. Provides self-sufficiency to your water supply
2. Reduces the cost for pumping of ground water
3. Provides high quality water, soft and low in minerals
4. Improves the quality of ground water through dilution when recharged to
ground water
5. Reduces soil erosion in urban areas
6. The rooftop rain water harvesting is less expensive
7. Rainwater harvesting systems are simple which can be adopted by
individuals
8. Rooftop rain water harvesting systems are easy to construct, operate and
maintain
9. In hilly terrains, rain water harvesting is preferred
10. In saline or coastal areas, rain water provides good quality water and
when recharged to ground water, it reduces salinity and also helps in
maintaining balance between the fresh-saline water interface
11. In Islands, due to limited extent of fresh water aquifers, rain water
harvesting is the most preferred source of water for domestic use
12. In desert, where rain fall is low, rain water harvesting has been
providing relief to people


A Few Benefits of Water Harvesting
A Foot of Rain Per Year
On average, Pima County receives about 12 inches, or one foot, of rain per
year. As our community has developed, large areas of land have been changed
from native desert vegetation to more impervious surfaces such as houses,
driveways, roads and parking lots. When it rains, these impervious land
areas shed a greater amount of rainfall, which in turn results in more
runoff in area washes and the possibility of local flooding problems.
So Many Benefits for so Little Effort
While many people may not realize it, those few inches of annual rainfall
are a valuable resource. Harvesting rainwater not only helps reduce the
possibility of flooding, but it also decreases the community's dependence on
groundwater for domestic uses. Unlike groundwater, however, rainwater is
remarkably pure with virtually no dissolved salts or minerals. Because of
this, rainwater is perfectly suited for landscape irrigation, use in
evaporative coolers, washing and many other home applications. Using
harvested water to irrigate plants, for instance, flushes salt buildup from
the soil and produces vigorous, healthy plants. When rainwater is used in
evaporative coolers or for washing needs, hardness deposits do no accumulate
and there is no problem with soap scum. Imagine not having to scrap your
evaporative cooler every year! Harvested water may also be used for personal
consumption, but it must be filtered and treated prior to use. By reducing
runoff and using rainwater that falls on your property, you can put a
valuable water resource to work around your house and yard.


Here's Just a Few Benefits from Harvesting Water:
· Conserves valuable groundwater and reduces your monthly water bill.

· Reduces local flooding and drainage problems.

· Flushes salt buildup from soils-- your plants and landscaping will notice
the difference!

· Decreases landscaping and property maintenance needs.

· Provides excellent quality water for many home uses.
 
CHENNAI : An example  worth followed

Chennai, February, 2002: “Chennai is a water-starved city, not a
rain-starved one,” says a leaflet which brings new hope to a population
thirsting for sustenance. Traditionally, this south Indian city has depended
to a large extent on groundwater for its water needs. But large-scale
construction activity has led to large-scale depletion. Over the years,
residents have dug deep to find water with bore wells going down going as
much as 200 feet. In many neighbourhoods, particularly those close to the
sea, saline contamination has resulted in what little water there becoming
brackish.
To make matters worse, the last three years have also seen poor rainfall in
the city with the result that the wells have gone dry and the bores spew
brackish liquid. The situation worsened to the stage where the city has had
to support itself year-round with water-tankers that supply water around
town. Last summer was the worst in recent years, with the government using
railway wagons for transporting water from as far as Neyveli. In addition to
the huge cost of this exercise, only short-term relief is provided by such
measures.
Now experts maintain that the silver lining in the clouds which do not bring
enough rain, lies in a simple, economical and demonstrably successful answer
- Rainwater Harvesting (RWH). Chennai gets an average annual rainfall of
1,290 mm per year, which is more than the national average. The recent
north-easterly monsoons were particularly good and brought 30 per cent more
rainfall than usual. Each year, however, almost 90 per cent of the fresh
water goes into sewers and storm water drains and some of it is lost by
runoff and evaporation. At the same time, the fundamental issue of
conservation by recycling effluent water also needs to be addressed. Sea
water slowly seeping into indiscriminately exploited aquifers could cause
irreversible damage. Controlling and safeguarding precious water reserves
needs greater governance.
A group of concerned activists - of which Shekhar Raghavan, an RWH activist
is a founder-member - has now come together under the aegis of the Akash
Ganga Trust to popularize rainwater-harvesting. The groups runs information
campaigns and helps install RWH systems. Besides distributing signboards
which proclaim, “This house has a RWH system”, the group intends to set up
an independent unit installed with various methods of RWH to act as an
educational exhibit-cum-research facility for water table studies.
This venture has the support of Shantha Sheela Nair, Secretary, Water
Resources in the Chennai Corporation. Said Nair at Akash Ganga’s inaugural
meeting, “The government has made it mandatory to install rainwater
harvesters in all new buildings. I followed this up by insisting that unless
people showed me that something had been done, I would not provide them with
water and sewer connections. My friends from the builders’ lobby wanted to
take me to court. They had a strong case: there was no precedent in case law
which supported my stand.”
But the results of this bold approach are showing. This monsoon, for the
first time in 18 years, newspapers did not carry pictures of the arterial G
N Chetty Road submerged in knee-deep water. It was one of the over 400
locations in which the Corporation had installed percolation pits near
sidewalks for water harvesting. Indian Oil Corporation’s huge office, which
consumed 60,000 litres of water a day by pumping from four bores and buying
two tankers of water daily, now has an RWH system. This company is now
self-sufficient in its water needs, the quality of water has improved
tremendously, the car park no longer floods during the monsoons and the
system has paid itself off already.
There are other examples too. Alacrity Foundations, a reputed blue-chip
building company has made RWH a mandatory part of its project proposals; the
600-acre Anna University campus no longer pays a water bill of Rs 600,000 (1
US$=Rs 48) every month while its neighbour, the prestigious Indian Institute
of Technology (IIT), had to postpone exams last semester and shut down the
campus for want of water. Sriram Rammohan’s industrial unit employs over 400
workers who had no option but to use water from wells that had been
contaminated by over-exploitation and effluents. “Now with RWH, the King
Institute certified our water as potable after just the summer showers - our
staff couldn’t believe it” says Rammohan.
In an attempt to take the movement further, Anna University’s engineering
students do house-to-house canvassing in residential areas for RWH. Over
6,000 households have benefited from superior and surplus water with a
system that pays itself off in less than a year. In the perennially dry
Padmanabha Nagar, a citizen’s movement has seen 80 per cent of the houses
install RWH. Some of them have not had to buy water for over two years.
It is not raining only good results, though. There are 350,000 plots of
residential land and the number covered by RWH is pitiably small. Vast
stretches of public spaces pose another serious concern. Harvesting remains
a privilege outside the economic reach of hutments and slums. And even those
who belong to the more well-off sections of society have not exploited the
benefits of RWH as much as they could have. Via a small network of
percolation pits and interconnected pipes, a complex of six flats (real
estate worth over Rs 10 million) would just need around Rs 20,000 to take
care of its future water needs. And yet, says Raghavan, “It has been an
uphill task convincing people to invest in the system. The challenge is that
of educating the educated.”
Lalitha Sridhar
February 2002
Lalitha Sridhar is a freelance development journalist, based in Chennai.



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 and 6 inches dia.
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  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.

TOTAL COST OF THE PROJECT : Rs. 3,21,600.00
(Rupees Three lac twenty one thousand and six hundred only)

Duration of Project  : Three  Month.

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.
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.