IJETAE_0613_66

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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 6, June 2013)

384

Assessment of Efficacy of a Rainwater Harvesting SystemNaved Ahsan1

1Associate Professor, Department of Civil Engineering, Jamia Millia Islamia, New Delhi, India

Abstract In most of the part of the world, rainwaterharvesting has been adopted to reduce the gap between

demand and availability of water. In many cases it has

become mandatory to provide rainwater harvesting systems in

newly constructed buildings or other such infrastructures.

Huge amount of financial resources are allocated to provide

these systems. Unfortunately, either due to poor design or due

to poor maintenance of adequately designed rainwater

harvesting system often end up with low outcome. This paper

presents an assessment of performance of an existing

rainwater harvesting system provided in a residential colony.Several crucial aspects that have come across during the

assessment study are presented in this paper.

Keywords design and maintenance of RWH systems,groundwater recharge, rainwater harvesting, urban

residential areas

I. INTRODUCTIONFor any society, water is one of the most important and

essential elements in its socio economic development.

Many civilizations have been developed in the close

vicinity of great rivers. When there is no perennial river in

the area the man has constructed a large number of small

storage structures such as tanks to store the runoff. Tamil

Nadu state in India is a good example for this situation. In

Tamil Nadu, tanks are the prominent water harvesting

structures. A tank may be defined as a small storage

reservoir to impound the runoff from the monsoon rains

(which occurs from July to December in Tamil Nadu) and

regulating the supply of water through a network of main

and field channels for irrigation. There are about 39,200

tanks in the Tamil Nadu state irrigating an area of about

0.91 M.ha in total. Tamil Nadu accounts for 17% of all

tanks in the country. Apart from surface irrigation, the tank

serves as a recharging structure for the underlying aquifer.

The quantity of water recharged mostly goes as aquifer

outflow due to non-pumping (Jothiprakash et al, 2002).The rising population, social & economic growth,

scientific & industrial advancement and development of

urban settlements have exerted excessive pressure over the

existing land and water resources. Continuously increasing

demand for water on one hand and deteriorating quantity

and quality of water due to over exploitation of ground

water have resulted in alarming situations.

Secondly unprecedented drought conditions have

concentrated attention on art and science of harvesting

water in many parts of world (Trivedi and Patel, 2002).

Rain water harvesting, though attaining extensive

acceptance in the past few decays, has it traces its history to

biblical times. Extensive rain water harvesting systems

have been found to exist, through their traces, 4000 years

ago in the Palestine and Greece. In ancient Rome,

residences were built with individual cisterns and paved

courtyards to capture rain water to augment water fromcitys aqueducts. As early as the third millennium BC,

farming communities in Baluchistan and Kutch Impounded

rain water and used it for irrigation dams. In most of the

part of the world, rainwater harvesting has been adopted to

reduce the gap between demand and availability of water.

In many cases it has become mandatory to provide

rainwater harvesting systems in newly constructed

buildings or other such infrastructures. Huge amount of

financial resources are allocated to provide these systems.

Unfortunately, either due to poor design or due to poor

maintenance of adequately designed rainwater harvesting

system often end up with low outcome.

This paper presents an assessment of performance of anexisting rainwater harvesting system provided in a

residential colony. Several crucial aspects that have come

across during the assessment study are presented in this

paper.

II. STUDY AREAFor the present study a residential colony at Andrew

Ganj, New Delhi has been identified. It is a general pool

residential colony of Central Govt. Employees, located in

southern part of the city of Delhi in between. There are a

total number of 1192 residential quarters of different types

(Type-I-760 Nos., Type-III-356 Nos., & D-II-76 Nos.)

The total campus area being maintained by CPWD isapproximate 1, 85,000 sqm and is distributed over nine

number of pockets.

The rainwater harvesting system provided in the study

area includes 17 number of recharge structures of

consisting of four different types (Fig. 1 to 4), at different

locations, with recharge tube well up to a depth of 40m.

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Strom water drains have also been constructed wherever

required to divert the runoff into the recharge structures.Salient features of the rainwater harvesting system are as

given below:

TABLEI

DETAILSOFEXISTINGRAINWATERHARVESTING

STRUCTURES

PPoocckkeettss RRaaiinnwwaatteerr HHaarrvveessttiinngg SSttrruuccttuurreess

TTyyppee NNooss..

PPoocckkeett -- 11 AA 33

PPoocckkeett -- 22 AA 11

PPoocckkeett 33 BB 44


PPoocckkeett

55 AA 22

PPoocckkeett 66 -- --


PPoocckkeett 88 -- --

PPoocckkeett -- 99 BB 33

Fig. 1(a) Type-A Rainwater Harvesting Structures

Fig. 2 Type-B Rainwater Harvesting Structures

Fig. 3 Type-C Rainwater Harvesting Structures

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Fig. 4 Type-D Rainwater Harvesting Structures

III. ASSESSMENT OF EXISTING RAINWATERHARVESTINGSYSTEM

In order to assess the efficacy of the rainwater harvesting

system, the runoff from the study area has been computed

on the basis of various datas collected from Indian

Meteorological Department (IMD), New Delhi and

imperial formulae recommended by the Central

Groundwater Board (CGWB), New Delhi. Average

intensity of rainfall has been taken as 0.712 m and

maximum hourly intensity as 0.02 m. Coefficient for runoff

for rooftop surfaces, paved areas, and for parks/lawns have

been taken as 0.80, 0.50, and 0.20 respectively. Runoff thus

computed for different pockets in the study area is shownin Table II.

The sub-surface storage capacity has a crucial role in the

artificial recharge. The quantity of water that can be

recharged depends upon the sub-surface storage capacity. It

largely depends upon the specific yield of the soil present

in the study area. The specific yield of the study area has

been calculated on the basis of sub-surface strata of the

study area collected from CPWD.

Data collected from the CPWD shows depth to water

table equal to about 25 m and average specific yield ofvarious soil strata has been taken as 10.5 %. Sub surface

storage capacity computed for different pockets of the

study area is presented in Table III.

The Sub Surface storage capacity of whole study area is

4,81,655 cum. It may be observed from Table III that the

sub surface storage capacities of different pockets are not

uniform. The sub surface storage capacity of pocket-3 is

the maximum and that of pocket-7 is the least. It may be

inferred that maximum runoff can be harvested in pocket-3

and in the pocket-7 least runoff can be harvested.

TABLEII

DETAILSOFEXISTINGRAINWATERHARVESTING

STRUCTURES

Pocket

No.

Area (m2) Average

Annual

Runoff

(m3)

Max

Hourly

Runoff

(m3)

Roof

top

Road/

Pavement

Park/

Lawns

1 5655 1680 17273 6279 176

2 3430 982 15886 4565 129

3 7920 1387 26796 8821 248

4 9549 2656 16835 8782 247

5 2691 1197 13522 3885 109

6 - - 20906 2977 84

7 1237 1115 2178 1413 40

8 1436 - 13088 2682 75

9 4821 1290 9958 4624 130

TABLEIII

SUBSURFACESTORAGECAPACITYINVARIOUSPOCKETSOFSTUDYAREA

Pocket Volume of

unsaturated

zone (m3)

Total sub-surface

storage potential as

Vol. of water (m3)

Pocket-1 615200 64596

Pocket-2 507450 53282

Pocket-3 902575 94770

Pocket-4 726000 76230

Pocket-5 435250 45701

Pocket-6 522650 54878

Pocket-7 113250 11891

Pocket-8 363100 38126Pocket-9 401725 42181

As mentioned above there are different types of

rainwater harvesting structures provided in different

pockets of the study area. The recharge capacity of Type-A,

Type-B, Type-C, and Type-D structures has been computed

to be 53.28, 26.3, 46.65, and 24.52 m3/h respectively. The

number of each type of rainwater harvesting structures and

their capacity to recharge the groundwater differs widely.

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Table IV shows the runoff in excess to the recharge

capacity available in each pocket.

TABLEIV

RUNOFFINEXCESSTORECHARGECAPACITYINEACH

POCKET

Pocket Available

Runoff

(m3/h)

Capacity of

RWH

Structures

(m3/h)

Excess Runoff

(m3)

Pocket-1 176 160 + 16

Pocket-2 129 53 + 76

Pocket-3 248 105 + 143

Pocket-4 247 79 + 168

Pocket-5 109 107 + 2

Pocket-6 84 0 + 84

Pocket-7 40 26 + 14

Pocket-8 75 0 + 75

Pocket-9 130 79 + 51

Total 1238 609 629

TABLEV

ADDITIONALREQUIREMENTOFRECHARGESTRUCTURES

Pockets Excess

Available

Runoff

RWH Structures Proposed to harvest

excess runoff

Type Nos Capacity Runoff

Harvested

1 16 D 1 24.52 24.52

2 76 A

D

1

1

53.28

24.52

77.80

3 143 D 6 24.52 147.12

4 168 C 4 46.65 186.60

5 2 - - - -

6 84 C 2 46.65 93.30

7 14 D 1 24.52 24.52

8 75 B 3 26.30 78.90

9 51 B 2 26.30 52.60

It may be inferred from the above Table that about 629

m3/h of runoff can also be recharged which is in excess tothe available recharge capacity of rainwater harvesting

system currently provided. Thus, there is a need to increase

the recharge capacity of the rainwater harvesting system.

Therefore, additional structures are required as shown in

Table V.

IV. CONCLUSIONThe study for performance assessment of rainwater

harvesting system in a residential area has been presented

in this paper. The results of the study show that the

maximum runoff (intake) by existing rainwater harvesting

system is 629 m3, however available runoff (per hour) is

1238 m3. Thus, it may be concluded that existing rainwaterharvesting structures are inadequate in number and size.

Therefore, some additional rainwater harvesting structures

need to be provided to harvest excess available runoff of

about 672 m3.

REFERENCES

[1] Annamalai P.L et al (2000) Rain water harvesting techniques,Proceedings of the Conference on ground water resource

development, Tirupati 235 to 239

[2] Jothiprakash. V, Kuppusamy. K.A, Sasireka. K, Shanmuganathan. P(2002), Ground Water Harvesting through Community Wells for

Sustainable Irrigation in Tank Commands in Water andWastewater: Perspectives of Developing Countries (eds. Devi R. and

Ahsan N), International Water Association IWA), UK.

[3] Panigrahi, B., Panda, S. N., and Mull, R. (2001) Simulation of waterharvesting potential in rainfed ricelands using water balance model.

Agric. Systems, 69(3), 165-182.

[4] Trivedi Sejal H. and Patel H. M., (2002), Artificial RechargePractices in Industrial AreaA Case Study of Apollo Tyres Industry

at Waghodia, Vadodara in Water and Wastewater: Perspectives ofDeveloping Countries (eds. Devi R. and Ahsan N), International

Water Association IWA), UK.

[5] Verma H.N et al (2000) Water harvesting technologies formanagement of rainwater in 21st century. Proc of conf on ground

water resource development, Tirupati pp 227234.

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