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CHAPTER 3
RWH PROGRAM IN CHENNAI CITY
Chennai is one of the four metropolitan cities in India and the
capital city of Tamil Nadu. It is located between 12º 59’10” and 13º 08’50”
North and 80º 12’10” and 80º 18’20” East in the south eastern coast of Indian
Peninsula in the Bay of Bengal. Figure 3.1 shows the location of the study
area, the Chennai city, Tamil Nadu, India.
N
B A Y O F
B E N G A L
IN D IA N O C E A N
S O U T H IN D IA
T h iru v a n a n th a p u r a m
K e r a la
P o n d ic h e r ry(P u d u c h c h e r i)
T a m i ln a d u
C h e n n a i
A n d ra P r a d e s h
B a n g a lo re
K a rn a ta k a
G o a
H y d e r a b a d
M u m b a i
M a h a ra s h tra
Figure 3.1 Location of Study area – the Chennai city
50
Kalakshetra
Inne
r ri
ng r
oad
Trtiplicane
High court
Poonamalle High Road
Chennai
Beach
ROYAPURAM
To Ambattur
New avadi road
Thiruvo
ttiy
ur hig
h R
oad
Perambur
Villivakkam
Ayanavaram
Anna nagar
Kuvam
PurasaivakkamKilpauk
Nunkambakkam
KK Nagar
Kodambakkam
Saidapet
Guindy
Mount R
oad
Mount R
oad
Mylapore
KotturPuram
Anna
University
G.S
.T R
oad
Velacheri
La
ttic
e B
ridge r
oad
Adyar
Buokin
gham
Canal
River Adyar
Chennai
central
George
town
TONDIARPET
VYASARPADI
BAY OF
BENGAL
N Greater Chennai
Figure 3.2 Important landmarks and waterways of Greater Chennai city
51
3.1 DOMESTIC WATER SUPPLY AND GROUNDWATER
SOURCES
Chennai city has an area of about 172 Km2 and is now called the
Greater Chennai; while the Chennai metropolitan area (CMA) has been
expanded to cover 1189 km2 incorporating the north, west and southern
suburban areas. The present study pertains to the greater Chennai city
(Figure 3.2). Chennai has a low lying plain terrain with a very gentle slope
from the western part of the city towards eastern coastline. Two rivers, Adyar
River and Coovum River intersect the city on the west east direction dividing
the city into almost north, central and southern parts. In addition, the
Buckingham canal constructed during pre independence days between
Marakkanam in Puduchery Union territory and Nellore in Andhra Pradesh,
run through the entire city in the north south direction parallel to the coast
intersecting the two rivers. However, flow in these water bodies are seasonal
and at present also carry waste water from city.
The other notable water bodies are the Redhills lake, Porur lake and
Chembarambakkam in the outskirts of the city. The city had as many as 160
tanks, out of which 124 tanks have been used for irrigation and drinking water
purposes while 36 are temple tanks. (Suriyaprakash 1994). Many of these
tanks have disappeared now due to urbanization. These tanks however served
as surface water storages for storm water and promoted groundwater
recharge.
The average annual rainfall for the city area is 1200 mm. The
rainfall occurs mostly during the monsoon season which is from June to
September (South West monsoon) and October to December (North East
monsoon). The rainfall pattern is shown in the Table 3.1.
52
Table 3.1 Average seasonal rainfall (mm) and number of rainfall days in
Chennai
Season DurationRainfall
(mm)Percentage
Rainfall
daysPercentage
Winter Jan – Feb 19.9 1.57 2.2 3.7
Summer Mar –
May
65.5 5.17 3.1 5.3
South
West
Monsoon
Jun – Sep 410.3 32.39 25.8 44.0
North East
Monsoon
Oct –
Dec
771.2 60.87 27.6 47.0
Annual 1266.9 100.00 58.7 100
Chennai has a warm climate and has a bright sunshine for nine
months. During the peak in summer (Apr-May), temperatures may cross 40º
C on many days. Being a coastal city, the land –sea breeze controls the
general climate prevailing over the city.
The geology of the Chennai city area show low lying pre Cambrian
gneisses and charnokites. The charnokites form the major rock types and
residual outcrops can be seen in Guindy area in the southern part of the city.
These formations are overlain by marine, estuarine and fluvial alluvium. The
eastern part of the city is extensively covered by the recent alluvium and runs
parallel to the coastline. The southern part of the city has crystalline rocks
with top soil cover, almost in the region beyond the Adyar river. River
alluvium followed by gondwana, sandstone, clay and crystalline shale
comprise most of the central part of the city between Adyar and Coovum
rivers. The western part of the city has alluvium followed by tertiary
sediments, shales which vary in thickness from 24 m (Kilpauk area) to 130 m
(Koyambedu area). The northern part of the city is covered by recent alluvium
53
underlain by gondwana (clay and shale) and crystalline rocks. (Sivaraman and
Thillaigovindarajan, 2009).
The alluvium covers major part of the city and is made up of sand,
silt and clay and varies in thickness from 10 to 28 m in the city (Ballukraya
and Ravi 1995). Groundwater occurs in all the three types of formations in
Chennai city under the water table conditions. Hard rock aquifers formed by
weathered mantle and fractured zones is mostly seen in the southern part.
Gondwana sandstones, weathered and fractured condition comprise middle
part of the city; parts of Ashok nagar - Kodambakkam area and provide good
yield of water. The alluvial formations around Coovum River and northern
part of the city vary in thickness from 10 to 30 m and form potential aquifers.
The beach sands in the Tiruvanmaiyur area also give high yield and good
quality of groundwater.
3.2 RAIN WATER HARVESTING ACTIVITIES
The Government of Tamil Nadu realizing the importance of the
rain water harvesting brought in a legislation (TN Gazette 2002, Act No 37)
to make it mandatory to implement rain water harvesting structures in public
as well as in private buildings in the city. The act was an amendment to the
Madras Metropolitan Area Groundwater (Regulation) act of 1987 (TN
Gazette 2002). The rules and regulations of the act make it compulsory that
all buildings irrespective of size or area must possess rain water harvesting
structures and that hence forth, (from 2002 onwards), planning permission
shall be accorded by Chennai Metropolitan Development Authority (CMDA
2008) only if the rain water harvesting structures are proposed in site plan.
Further the owners / occupants of the buildings shall properly maintain and
shall not dispense with these structures (Metrowater 2008) in future.
54
In addition to the legal instruments proposed, the government used
the media effectively and addressed the issue of providing rain water
harvesting in existing buildings through several awareness campaigns and
persistent efforts during 2002-2003. As a result, rain water harvesting
structures have been installed in many buildings in different parts of the city.
Table 3.2 shows the details of the different types of the buildings
where rain water harvesting structures have been added to the existing built
up structure in different zones of the city.
Table 3.2 Number of buildings added with rain water harvesting
structures in Chennai City
Zone Residential Commercial Institutional Total
East 41809 13444 206 55459
South 53532 1574 684 55790
Central 52131 4530 241 56902
West 108856 1726 408 110990
North 61140 7051 151 6834
Total 317468 28325 1690 347483
This data was compiled from the Metro water, Chennai which
published this information for the 11 Corporation divisions of the Chennai
city (Metrowater 2008). A total of 347,483 buildings were equipped with rain
water harvesting structures until 2006. It can be observed from Table 3.2, that
of the three groups of the buildings covered, the bulk of them were residential
buildings while institutional buildings were the lowest in number.
3.3 HYDROGEOLOGY
The review of literature suggests that the hydrogeology plays an
important role in the recharge process and has a role in the success of a RWH
55
program. The hydrogeology of the city (Ballukaraya and Ravi 1995; CSE
2008) was therefore considered for evaluation of data collected for the study.
The city has been divided into five zones based on the nature of the lithology
derived from well logs, depth to bed rock and the nature and deposition of the
alluvium. The Table 3.3 and the Figure 3.3 shows the five zones demarcated
in the Chennai city and the general nature of hydrogeology and its
composition.
Table 3.3 Nature of hydrogeology in the five zones of Chennai city
S
NoZone Nature
Approx.
depth (m)Composition
1 North Coastal alluvium
followed by Gondwana
clay
28 – 100 Recent alluvium
Sand / silt
Shale
Sedimentary rocks
2 South Crystalline rocks with
top soil cover
25 Silt / clay
Charnokites
Weathered rocks
3 West Alluvium followed by
Gondwana clay, Shales,
Crystalline rocks
24 – 130 Mixed alluvium
Clay
Shales
Sand stones
4 Central River alluvium followed
by Crystalline rock
30 Alluvium
Silt / Clay
Gondwana shales
5 East Coastal alluvium
followed by Crystalline
rock
5 – 30 Sand / silt
Sand dunes
Marine fluvial clay
Crystalline rocks
The aquifer material is dominated by alluvium and most of it is of
estuarine in origin (Ballukraya and Ravi 1995) and a crystalline ridge along
56
part of the east coast in the north south direction (undergo slow upliftment)
provide probably protection from saline intrusion. The north and eastern part
of the city is mostly covered by alluvium and make good aquifers underlain
by crystalline rocks. The southern part is having silt and clay with rocky
outcrops and weathered rocks. In the western part, the top layer is mostly
alluvium with mixed clay and shales and the depth of the aquifer is more than
100 m in some places.
Figure 3.3 Five zones in Chennai city classified on the basis of
hydrogeology of the area
Hence, Chennai city is divided into five zones for grouping and
analysis of the responses to RWH (Figure 3.3). The zone parallel to the coast
all along the city is the eastern zone; the western and central zone has more of
hard rock terrain, while the southern zone is made up of sedimentary rocks
and alluvium. Since groundwater is influenced by the hydrogeology, these
57
groups were applied in the analysis of water level and water quality data
collected in the city.
3.4 RWH PROGRAM
The details of the RWH activities and its implementation in
different parts of the city were collected from the Metro Water, Chennai. This
data was compiled from the Metro water, Chennai which published this
information for the 11 Corporation divisions of the Chennai city (Metrowater
2008). This data was regrouped into the five zones of the city under study.
The majority of the buildings covered under the RWH scheme were
residential buildings compared to the commercial or institutional buildings in
the city. The details of the number of buildings with rain water harvesting are
given in the Figure 3.4.
East
West
Resid
entia
l
Com
merc
ial
Instit
utio
nal
0
20000
40000
60000
80000
100000
120000
Residential Commercial Institutional
Figure 3.4 Types of buildings covered under Rain water harvesting
program in Chennai city
3.5 RAINFALL
The rainfall data for the period of study (2002 to 2006) was
collected from the rainfall station at Indian Meteorological Observatory,
58
Nungambakkam, Chennai. The seasonal rainfall and the monthly rainfall are
shown in Figures 3.5. and 3.6.
-100
100
300
500
700
900
1100
1300
1500
2002 2003 2004 2005 2006
Post Monsoon Summer SW Monsoon NE Monsoon
Figure 3.5 Seasonal Rainfall during 2002 to 2006 in Chennai city
0
200
400
600
800
1000
1200
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
2002
2004
2006
S7
2002 2003 2004 2005 2006 Series6 Series7
Figure 3.6 Monthly Rainfall received during 2002 to 2007 in Chennai city
2007
59
3.6 GROUNDWATER
The data on physiography, locations and other land cover details
were obtained from the Corporation of Chennai. The information on
groundwater levels is being collected through observation wells located in
different parts of the city by the State Surface and Ground Water Resources
Data Centre, Central Ground Water Board, Metro Water Chennai and the
Corporation of Chennai. The groundwater level data was collected from these
agencies for the duration of the period of study. Based on the location of the
observation wells for which complete data is available, a well is assigned to
one of the five zones (Figure 3.3) identified in the study. The data from each
of these agencies is considered in this grouping of wells. Then, for each zone,
the average water level is computed based on data available and is given in
Table 3.6.
3.7 GROUNDWATER QUALITY
The observations on the groundwater quality responses were
studied through primary collection of groundwater samples and analysing
them for selected chemical parameters in the study. The samples were
collected four times during period of study. The Table 3.4 shows the details of
sample collection schedule.
Table 3.4 Groundwater sample collection schedule followed in Chennai
city
Set Month Year Period
1 February 2002 Before RWH
2 February 2003 Before RWH
3 December 2004 After RWH
4 January 2006 After RWH
60
During each sampling campaign, groundwater samples were
collected in clean polythene containers of 1 litre capacity using a bailer, or
directly from a pumping bore well and transported to laboratory for analysis.
The wells for collection of water samples were chosen based on a grid
sampling design. The entire city area was divided into 2 km2 cells. A
sampling location was selected randomly in each cell and the address of the
location was identified in the map. Forty five locations were selected and one
sample was collected from each location preferably from a shallow source.
The details of the sample collection locations are given in annexure.
One sample from any well having a depth less than 10 m was
chosen to represent the shallow aquifer. The depth of wells could be
ascertained only approximately from the owners and recorded. The land use
characteristics of each well in an approximate radius of 100 m were assessed
during the initial sample collection period and the predominant land use
condition was also recorded.
A total of 45 samples were collected from the wells on each
sampling occasion and transported under cold conditions to the laboratory.
The same well was considered for collection of samples for the entire duration
of study, except when the premises could not be accessed or a sample could
not be collected, a nearby well was considered for collection. However, on
each occasion, there were some missing samples, either unable to collect a
sample or unable to complete the analysis and the same was recorded.
3.8 DATA ANALYSIS
Simple data processing was done in MS Excel and the graphs,
statistical analysis and summary tables were prepared in SYSTAT 12
(SYSTAT 2007). Box-whisker and error bar plots are produced for
comparison. Simple graphical tools of analysis are used to make plots of data
61
for comparison. Simple and two way ANOVA is used to study the
simultaneous effects of the groups of samples and RWH considered in the
analysis.
3.9 RAINFALL ANALYSIS
The actual rainfall received during the period of study in different
seasons from 2002 to 2006 is given in Table 3.5 along with its departure from
short term average in percent scale. The annual rainfall shows that the
monsoon nearly failed during 2003 with a total of 737 mm which is 42 %
deficient on the long term average. However, in 2005, the annual rainfall shot
up to 2566 mm, an increase of 102 % over the long term average. During
other years, the departure from long term average was only about 10%.
Table 3.5 Rain fall (mm) received in Chennai city during different
seasons for the years 2002-2006
Yea
r
Po
st M
on
soo
n
Dep
art
ure
(%)
Su
mm
er
Dep
art
ure
(%)
SW
Mon
soon
Dep
art
ure
(%)
NE
Mon
soon
Dep
art
ure
(%)
An
nu
al
Rain
fall
Dep
art
ure
(%
)
No
rth
Ea
st
Mo
nso
on
Start End
2002 45 125% 17 -74% 355 -14% 985 28% 1402 11% Oct 9th Nov 11
th
2003 0 -100% 6.7 -92% 420 2% 311 -60% 737.7 -42% Oct 20th Dec 25
th
2004 51 155% 214 224% 360 -12% 572 -26% 1197 -6% Oct 18th Nov 12
th
2005 7 -65% 114 73% 337 -18% 2108 173% 2566 102% Oct 12th Dec 19
th
2006 3 -85% 34.4 -48% 393 -4% 892.6 16% 1323 4% Oct 19th Dec 28
th
However, the performance of the south west and north east
monsoon was not similar. The south west monsoon rainfall had a less annual
variation than the north east monsoon which is more erratic (Table 3.5). For
example, in 2003 when annual rainfall is 42 % deficient, the south west
monsoon is 2 % excess than average value, while in 2005, it was -18 % when
62
the annual rainfall is 102 % excess. During the study period, the variation in
the north east monsoon rainfall ranged from -60 % to 173 % excess, dictating
the overall performance of the monsoon season. Though there are similar
wide variations are seen in the summer (-92 % to 224 % excess) and post
monsoon (-100% to 155% excess), the actual quantum of rainfall is smaller
and less likely to have an impact except in 2004 when the summer rainfall
was 214 mm (Table 3.5).
However, the increased quantum of rainfall which is mostly from
the north east monsoon may not be favourable from groundwater recharge
point of view. The rate and quantum of recharge may suffer as more surface
runoff is likely during a shorter period of rainfall in an urban environment.
This can be seen in Table 3.5, which shows the dates of onset and end of
north east monsoon during 2002 to 2006. It is clear that there was a delay in
the onset of monsoon as late as 20th
October in 2003, which has further
restricted the duration of the monsoon.
It is likely that the quantum as well as pattern of rainfall may have
implications in addition to duration of the season for the recharge process of
ground water in Chennai city. This adds significance to the existing artificial
recharge efforts to improve the groundwater storage, and develop strategies
for site specific hydro geological relevance and adaptability.
3.10 GROUNDWATER LEVELS
The Table 3.6 shows the statistical summary of groundwater BGL
in different zones of the city. The groundwater levels in general, showed an
increase after monsoon season, but the responses were not similar in the five
zones.
63
Table 3.6 Groundwater levels (BGL in m) during the pre monsoon (July)
and post monsoon season (Jan/Dec) from 2004 to 2006 in
different zones of Chennai city
Zone Jul 2004 Jan 2005 Jul 2005 Jan 2006 Jul 2006 Dec 2006
East Mean 5.33 3.54 5.90 2.40 3.93 2.89
Std. Deviation 2.76 1.26 3.07 2.03 2.52 2.05
Minimum 2.30 2.21 1.50 0.53 0.85 0.35
Maximum 7.70 4.71 8.20 5.20 6.80 5.35
South Mean 8.32 6.82 8.20 3.38 6.08 3.11
Std. Deviation 1.13 1.05 1.06 0.99 2.31 0.64
Minimum 6.40 5.15 6.70 2.50 3.20 2.30
Maximum 9.00 7.75 9.55 4.90 9.55 4.10
Central Mean 7.34 5.99 6.72 1.79 4.54 3.08
Std. Deviation 2.75 3.36 2.89 1.02 1.29 1.25
Minimum 4.61 2.21 4.14 0.28 3.14 1.80
Maximum 10.85 10.65 10.85 2.53 6.60 4.90
West Mean 7.64 5.55 7.66 2.83 4.80 3.53
Std. Deviation 2.31 2.91 3.25 2.44 2.39 1.69
Minimum 4.59 2.84 4.47 0.69 2.51 1.60
Maximum 11.06 10.46 12.17 6.17 7.95 5.10
North Mean 6.40 4.88 5.13 1.43 4.65 1.63
Std. Deviation 2.97 3.01 3.36 0.04 3.89 0.89
Minimum 4.30 2.75 2.75 1.40 1.90 1.00
Maximum 8.50 7.00 7.50 1.45 7.40 2.26
In the eastern and northern zone, the change in water levels was
similar and the range of variation was wide, varying from 1.43 m to 6.4 m
with oscillating response to pre and post monsoon conditions. A significant
increase can be seen during January and December 2006 in these regions. In
the other three zones, water table was found to be little deeper. The average
levels varied from 2.83 m to 8.32 m. In these three regions, the water table
shows an increase (2 m) compared to 2004-2005 to 2006 levels. In the central
zone, the average water table remarkably increased from 7.34 m (2004) to
1.79 m in January 2006 and 3.08 m in December 2006. A general increase can
64
be noticed in the western zone from 2004 to 2006 in the average levels except
in July 2005.
3.11 GROUNDWATER RESPONSES
The increase in ground water level was computed as the difference
between the pre monsoon (July) and post monsoon (next January) seasons
for each year. The increase in water levels (pre and post monsoon) for the
years 2004 to 2006 show interesting responses in recharge to the rainfall
(Table 3.7).
Table 3.7 Increase in post monsoon groundwater levels (m) noticed from
2004 to 2006 in different parts of Chennai city
Zones of the City 2004 2005 2006
East
Mean 1.79 3.50 1.04
Std. Deviation 2.00 2.25 0.98
Minimum 0.09 0.97 0.00
Maximum 4.00 6.43 2.19
South
Mean 1.50 4.82 2.97
Std. Deviation 0.43 2.03 2.12
Minimum 1.25 1.80 0.90
Maximum 2.25 7.05 6.55
Central
Mean 1.04 3.29 1.46
Std. Deviation 0.98 3.33 1.08
Minimum 0.00 0.00 -0.50
Maximum 2.40 8.32 2.70
West
Mean 2.09 4.83 1.98
Std. Deviation 1.18 1.10 0.82
Minimum 0.60 3.73 1.20
Maximum 3.65 6.00 3.16
North
Mean 1.53 3.70 3.02
Std. Deviation 0.04 3.32 3.00
Minimum 1.50 1.35 0.90
Maximum 1.55 6.05 5.14
65
The average increase in groundwater levels were comparatively
higher during 2005 compared to other years in all the zones as shown in
Figure 3.6. The increase is significant in the western zone and the southern
zone (4.8 m). However, the increase is about 3 m in the other zones also. In
2004, the increases are the lowest varying from 1.04 m in the central zone to
2.09 m in the western zone. In 2006, the increases are better except in the case
of the eastern zone where it is 1.04 m only. But, in the north and south zone,
an increase of about 3.0 m can be noticed while in the central zone the
increase is 1.46 m only.
CentralWestEastSouthNorth
Incre
ase in B
GL (m
)
6
5
4
3
2
1
0
2004
2005
2006
Figure 3.7 Increase in groundwater levels in Chennai city during 2004
to 2006
The increase in groundwater level (Table 3.7) has a direct relation
to the rainfall (Table 3.5) during the period of study as the water levels
measured during 2005 in all the zones were higher than the levels measured
during 2004 and 2006 (Figure 3.7). In addition, the highest increases were
noticed in the western region and southern region of the city. Incidentally, the
western region of the city (Table 3.6) had more RWH structures erected in the
66
area (32%) than the other zones and possibly indicate the impact of the RWH
structures in enhancing the groundwater recharge.
The overall picture that emerges is that different zones of the city
respond differently during the study period and the magnitude of increases
were high in the eastern zone, but fluctuate widely, while it is moderate and
uniform in the western zone and with lesser fluctuations. This may, therefore,
be taken to suggest that the RWH initiatives had a positive impact on the
recharge process and influenced the groundwater level increases in Chennai
city, especially in the western and southern zones.
3.12 RWH and GROUNDWATER QUALITY
The Table 3.8 shows the statistical summary of the quality of
groundwater before and after RWH activities as well as between different
zones of the city which appear variable. Therefore, a two way analysis of
variance (General Linear Model) was applied to test the significance of
changes due to RWH activities and different zones of the city.
Table 3.8 Statistical summary of the quality of groundwater in Chennai
city
Variable RWHEast South Central West North
Statistical
Significance
Mean SD Mean SD Mean SD Mean SD Mean SD RWH Zones
PH Before 7.51 0.5 7.34 0.3 7.42 0.49 7.2 0.37 7.69 0.51 0.03 0.332
After 7.55 0.48 7.57 0.7 7.57 0.52 7.69 0.59 7.01 0.44 * ns
EC Before 3852 2426 4329 4371 2784 2094 2781 2968 2686 2795 0.52 0.000
After 6200 6089 2361 1644 1645 1104 1882 1263 3601 2519 ns ***
CL Before 982 1463 1069 1591 565 717 689 1173 1035 1239 0.529 0.000
After 2186 4019 423 531 369.6 427.3 747.5 585.4 840 909 ns ***
TH Before 670 699 1317 1616 529 302 533.7 205.5 330.8 161.5 0.248 0.005
After 872 703 401.9 333.5 344.6 290.3 359.2 314.7 674 386 ns *
NO3 Before 29.88 16.61 15.25 11.86 18.05 18 19.21 21.28 4.83 0.75 0.941 0.501
After 16.21 13.55 31.22 22.28 28.98 20.78 6.59 2.07 20.35 26 ns ns
*** p < 0.001; ** p < 0.01; * p < 0.05; ns = not significant
67
Z O N E
R W H
N o r t hW e s tC e n t r a lS o u t hE a s t
A f t e rB e f o r eA f t e rB e f o r eA f t e rB e f o r eA f t e rB e f o r eA f t e rB e f o r e
8 . 5
8 . 0
7 . 5
7 . 0
6 . 5
PH
Z O N E
E F
N o r t hW e s tC e n t r a lS o u t hE a s t
2121212121
1 0 0 0 0
7 5 0 0
5 0 0 0
2 5 0 0
0
EC
(u
S/
cm
)
Z O N E
E F
N o r t hW e s tC e n t r a lS o u t hE a s t
2121212121
3 0 0 0
2 5 0 0
2 0 0 0
1 5 0 0
1 0 0 0
5 0 0
0
TH
(p
pm
)
Z O N E
E F
N o r t hW e s tC e n t r a lS o u t hE a s t
2121212121
2 5 0 0
2 0 0 0
1 5 0 0
1 0 0 0
5 0 0
0
CL (
pp
m)
Z O N E
B F / A F
N o r t hW e s tC e n t r a lS o u t hE a s t
2121212121
8 0
7 0
6 0
5 0
4 0
3 0
2 0
1 0
0
NO
3 (
pp
m)
Figure 3.8 Groundwater quality responses to RWH in different zones
of the Chennai city during 2002 to 2006
68
RWH activities produced a statistically significant change in the pH
only whereas the other parameters showed no significant changes. However,
the mean values of Electrical Conductivity (EC), Chlorides and Total
hardness showed more significant changes between different zones. The
mean pH values varied between narrow ranges of 7 to 8 and indicated a small
increase due to RWH activities, except in north zone where it declined from
7.69 to 7.01. The differences between the zones are less as well as due to
RWH activities, but median pH values (Figure 3.8) increased in all the zones,
except north zone.
The mean values of EC however, showed wide variations between
the zones as well due to RWH activities. In fact, the highest average
concentrations were recorded in the eastern zone (6200 µS/cm). The EC
decreased in central (990 µS/cm), western (1705 µS/cm) and southern
(2727 µS/cm) zones after RWH activities, while it increased in the eastern
(2348 µS/cm) and northern (276 µS/cm) zones. The central and western zones
appear to have better groundwater quality (< 2500 µS/cm) than the other three
zones (Figure 3.8).
The mean chloride values decreased in the southern (646 ppm),
central (196 ppm) and northern (195 ppm) zones, while it increased in eastern
(1204 ppm) and western (58 ppm) zones. As in the case of EC, the chloride
concentrations are lower in the central and western zones, while higher in the
other zones. The eastern zone showed highest concentrations with a pre RWH
value of 982 ppm increasing to 2186 ppm during the post monsoon season.
The differences in chloride concentrations between the zones are also highly
statistically significant.
The mean total hardness values are found to be higher in the eastern
and southern zone, while lower in other zones. The total hardness values
increased after RWH activities in the eastern and northern zones, while it
69
declined in other zones. The differences in mean concentration values
between the zones are statistically significant while changes due to RWH are
non significant. The pattern of variations noticed in different zones appears
similar to the chlorides.
The mean nitrate concentrations showed wider variations
(Figure 3.8) and the differences due to RWH as well as the different zones of
the city show less significant changes. In the eastern zone and western zone
(13 ppm), and central (10 ppm) zone nitrate concentrations are low, while
increases are noticed in southern (15 ppm), and northern (16 ppm) zones.
Increased post monsoon nitrate concentrations up to 75.91 ppm in
groundwater adjoining the Adyar River in the study area has been reported by
Venugopal et al (2008). It is of importance to note that the nitrate
concentrations reached the permissible limit for drinking water (45 ppm)
during post monsoon season in parts of the south, central and eastern zones.
Increased nitrate concentrations in groundwater may become a health hazard,
especially for young children.
3.13 IMPACTS OF RECHARGE
The RWH activities have also been shown to be useful in
enhancing the recharge to the groundwater in Chennai city. In the present
study, the analysis of results indicates that the RWH activities make a
difference in the response of the groundwater to the seasonal monsoon
recharge in Chennai city. The increase in groundwater levels is the highest in
the western zone (Figure 3.7) where maximum number of RWH structures
(Table 3.2) has been added to the buildings. Therefore, it may be direct
impact on the recharge process in the western zone of the city that has seen
the additional increase in water levels.
70
The recharge process appears to be influenced by the hydrogeology
as we can see that the increases in post monsoon groundwater levels in
different zones are variable. The highest increases are seen in the eastern zone
and northern zone which are mostly made up of sand and alluvium in the top
layers. The high degree of variability (Table 3.3) seen in different zones may
also be related to the abstraction of water which could not be quantified.
The rainfall received during the period of study in the city also
show high variability and the performance of the monsoon is unpredictable.
The total rainfall during 2003 is only 737 mm (-42%) while during 2005, it
was 2566 mm (+102%) and more than 50% of the rainfall is received during
north east monsoon whose duration (26 rainfall days) is same as that of south
west monsoon where only about 30% of the rainfall is received (Table 3.5).
The results of the RWH activities indicate that the additional harvesting
structures installed appear have an impact on the recharge process taking
place in the city. This is evidenced probably by the enhanced recharge taking
place in the western part of the city where maximum numbers of recharge
structures are installed.
The quality of groundwater in an unconfined aquifer is likely to
change with the lowering and rising of water table due to recharge and or
discharge factors and interaction with aquifer materials (Ballukraya and Ravi,
1999) and land use conditions (Ravichandran and Pundarikanthan, 1991). In
the latter study, the influences of the quality of the water ways of the Chennai
city on the groundwater have been shown through ion contour maps and
regression analysis.
The changes in groundwater quality are found to be significant in
the present study and highly variable across different zones of the city. The
western zone in general showed a decline in the EC as well as other ions
probably due to enhanced RWH activities, an improvement in quality, while
71
in the eastern zone except nitrate, all other parameters increased after RWH,
indicating a decline of quality for beneficial uses. In other zones, the
responses are mixed in nature.
In addition to the control by lithology, the role of saline intrusion
(Ballukraya and Ravi 1999) may also have a role on the quality of
groundwater in Chennai city. The quality of groundwater in the eastern zone
adjoining the coast showed the highest EC as well as chloride levels in this
study, in spite of the significant increases in post monsoon groundwater
levels. The water table contours prepared as early as 1992 (Ballukraya and
Ravi 1995) show the entire eastern part of the city have groundwater table at 1
to -4 m with respect to mean sea level. Therefore, groundwater development
in the past two decades may have led to the ingress of sea water in pockets
along the coast (Venugopal et al 2008). This may also be responsible for the
increased EC of the groundwater recorded in this zone.
In general, this study recorded a positive influence of RWH
activities on the groundwater regime with enhanced recharge, at least in some
parts of the city, with concomitant improvement in quality of the
groundwater.
3.14 HYDROCHEMISTRY
The statistical analysis (ANOVA) of groundwater quality data
indicated that the differences among different zones of the city are significant
than the impact of enhanced recharge due to rainwater harvesting (Table 3.8).
The hydro chemical nature of the groundwater was therefore analysed based
on groups, according to the zones of the city, for further understanding and
classification.
72
The hydro chemical facies can provide more information about the
nature of hydro chemical processes in different zones of the city and this can
be identified by using Piper’s tri linear diagram (AquaChem 2008). The tri
linear chart for each zone was prepared using AquaChem software. Figure 3.9
shows the groundwater samples classified in the Piper diagram showing the
hydro chemical water types. The hydro chemical facies identified in each
zone is given in the Table 3.9.
Table 3.9 Groundwater hydro chemical facies in different zones of
Chennai city
S.No Zone Samples Hydro chemical type % Composition
1 East 31 NaCl 44
NaHCO3Cl 32
Mixed 24
2 North 18 NaCl 34
NaClSO4 17
NaHCO3 33
Mixed 16
3 West 46 NaCl 5
NaClHCO3 68
Mixed 26
4 Central 49 NaClHCO3 53
CaNaHCO3Cl 20
Mixed 25
5 South 22 NaCl 4
NaHCO3Cl 28
CaNaHCO3Cl 28
Mixed 36
The Table 3.9 shows that the hydro chemical process appears
complex in the groundwater in Chennai city as seven major water types can be
73
seen. The mixed water types account more than 25% in all the zones. The major
types are NaCl, NaHCO3Cl, NaHCO3, NaClHCO3, NaClSO4, CaNaHCO3Cl
and CaNaHCO3Cl. The NaCl type dominates the eastern zone (44%) with
NaHCO3Cl closely following it (32%). The sodium dominates the cations while
chlorides and bicarbonates share the dominance in this zone (Figure 3.10A).
80 60 40 2020 40 60 80
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Figure 3.9 Piper tri linear diagram of groundwater samples from
different zones of the Chennai city
A B
CD
E LEGEND
A EAST ZONE
B WEST ZONE
C NORTH ZONE
D SOUTH ZONE
E CENTRAL ZONE
74
In the northern zone, the sodium bicarbonate type (36%) dominates
over NaCl type (9%) with NaClSO4 type accounting 23% (Figure 3.10C). In
the southern zone, the NaHCO3Cl and CaNaHCO3Cl types share equal (28%)
dominance while NaClHCO3 is the dominant water type in western (68%) and
central (53%) zones.
ESO4
ECL
EHCO3ECO3
ECA
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ENA
Figure 3.10 Ionic composition of groundwater samples from different
zones of the Chennai city
LEGEND
A EAST ZONE
B WEST ZONE
C NORTH ZONE
D SOUTH ZONE
E CENTRAL ZONE
Na Red CO3 Light Blue
K Green HCO3 Yellow
Mg Blue Cl Light Grey
Ca Pink SO4 Grey
A B
C D
E
75
The dominance of strong alkalis is seen in all zones except in south
zone where the alkaline and alkaline earth metals share the dominance
(Figure 3.10D). Similarly, non carbonate hardness influence strongly in the
east and northern zone whereas in the central and west zone, the carbonate
hardness is also present. The south zone is the hard rock area in the city and
the source of alkaline earth metals may be due to rock water interaction. The
east and north zones have mostly sand, alluvium and marine clay and might
have been the source of the strong alkaline metals. The source of strong
alkaline metals seen in the west and central zones may be anthropogenic
sources (Ramesh et al 1995) as on land waste water disposal and solid waste
dump leachates can carry considerable amount of soluble substances with
recharging water as sodium chloride is one important constituent of the
leachates (Venugopal et al 2008).
3.15 GROUNDWATER QUALITY
The overall average groundwater quality (standard deviation SD) of
the pH, EC, major ions and nitrate concentration in different zones of city is
given in Table 3.10. The standard values for desirable and maximum
permissible limits for drinking water purposes as per WHO (1993) is also
given in the Table 3.10. The pH fluctuated in a narrow range around 7.0
throughout the study, without having larger variations in each of the zones.
Only in the northern zone, the mean pH was 7.3 with a SD of 0.58. This
suggests that the groundwater is well buffered in nature.
The EC however varied widely. The highest mean concentrations
are seen in the eastern zone, with a high SD of 4824. The lowest mean values
are recorded in the Central (2209) and western (2327) zones of the city. The
SD is also high, suggesting broad variability between sampling wells within
these zones. Besides, the high SD in the case of EC may be the
76
hydrochemistry of the groundwater being not homogeneous (Subramani et al
2010) as these five zones also display different hydro geological patterns. The
north and south zones showed elevated mean values above 3000 µS cm-1
.
These high EC values indicate that the groundwater in general is highly
mineralised and may be classified as medium saline in nature. However, the
median EC values of all the zones are less than the mean values suggesting
the arithmetic mean values are influenced by few wells having EC more than
10,000 µS cm-1
. The percent of wells that exceeded 1500 µS cm-1
was also
calculated for each zone.
The wells that exceeded the maximum limit of 1500 µS cm-1
are
59% of the samples. The eastern and northern zone account for the highest
(76%) followed by western (63 %) central and south zones (58 %). The
recharge effect of monsoon generally increases the EC of the groundwater
(Subba Rao 2005, Prasanna et al 2010), however there have been instances
reported in certain aquifers that there has been a decrease also (Reddy and
Kumar 2010). The increases in the EC may be due to leaching of salts in the
vadose zone (Subba Rao 2008) and solid waste dumps by the recharging
water in the urbanised areas of the city.
In this study, the increases in EC were noticed in the northern and
eastern zone which are adjoining the coastline and are made of sand, alluvium
underlain by marine clay, while the marginal decreases noticed in the central
and western zone has mixed alluvium, shales and clay. The saline intrusion in
parts of the Chennai coast has been reported even during 1990’s (Ballukraya
and Ravi, 1999, Brinda, 2001) due to heavy abstraction of groundwater which
may also have contributed to the increase in salinity of the groundwater.
77
Table 3.10 Average groundwater quality of different zones of the Chennai city during the period of study (all units in
ppm except EC (µS/cm) and pH)
ZONEEast South Central West North WHO (1993)
Mean SD Mean SD Mean SD Mean SD Mean SD Desirable Allowable
pH 7.53 0.48 7.46 0.59 7.50 0.51 7.45 0.55 7.35 0.58 7.5 - 8.5 9.2
EC 5080 4824 3092 3057 2209 1756 2327 2304 3177 2657 500 1500
Na 1349.89 1665.76 693.06 825.44 658.94 672.70 609.42 581.02 715.02 528.98 200
K 84.16 117.70 31.35 27.67 59.24 57.18 42.52 71.60 69.15 59.81
Mg 82.87 76.46 53.77 61.63 35.98 30.57 41.23 35.59 55.25 44.34 50 150
Ca 62.08 55.26 89.31 92.65 46.84 41.98 46.39 39.86 49.94 32.91 75 200
Cl 1593.17 3079.10 673.98 1100.76 465.44 592.40 718.61 918.88 930.45 1065.22 250
SO4 364.95 456.14 237.40 367.50 321.00 1021.68 160.27 305.99 240.97 417.67 500
HCO3 477.62 237.71 557.15 442.21 538.27 411.35 564.78 767.24 572.08 487.98 - -
CO3 44.46 92.80 21.10 24.25 26.18 28.71 13.27 20.68 17.44 24.31 - -
NO3 19.99 15.55 22.62 18.90 21.22 19.35 15.90 19.09 19.06 25.23 45
78
Among the cations, sodium was the dominant ion in all the zones,
with high average values (1349 ppm) in the eastern zone followed by northern
(715 ppm), southern (693 ppm), central (658 ppm) and western zone (609
ppm). Similarly the potassium concentrations are also high in the eastern zone
(84 ppm) and northern zone (69 ppm) while in other zones, the concentration
is nearly half of it (Table 3.10). The alkaline earth metals are the lower in
concentration varying from 62 ppm in the eastern zone to 46 ppm in the
central and western zones. The magnesium concentrations also followed a
similar trend (Figure 3.10).
The dominance of sodium in groundwater is generally attributed to
the process of cation exchange among clay minerals (Subba Rao 2003, 2008;
Reddy and Kumar 2010) in the aquifer matrix and release mechanisms. The
alkaline earth metals have their origin mostly in the dissolution of minerals
like feldspars, pyroxenes, amphiboles (CSE 2008) while the enhanced
magnesium concentration seen in this study in the eastern and northern zone
(Table 3.10) may be due to the ion exchange with soil matrix by the
recharging water (Aghazadeh and Mogaddam 2010).
The anions are dominated by chlorides in all the zones
(Figure 3.10). The abundance is of the order; Cl > HCO3 > SO4 > CO3. The
bicarbonates and carbonates varied from 477 ppm in the eastern zone to 572
ppm in the northern zone with lesser variations among the zones. The average
nitrate concentrations also showed lesser variations from 19 ppm in the north
and eastern zone to 22 ppm in the south zone (Table 3.10).
The source of carbonates and bicarbonates are mostly from the
weathering products and dissolution of calcite and dolomites (Freeze and
Cherry, 1979) and is in equilibrium with carbonic acid in aquifers (Kumar et
al 2010) and dissolution of carbon di oxide.
79
The concentration of chlorides varied widely within the zones as
well as between the zones (Figure 3.10; Table 3.10). The average
concentration varied from 465 ppm in the central zone to 1593 ppm in the
eastern zone. The north zone also indicated an average of 1065 ppm. The high
chloride concentration recorded in the eastern and northern zone also had a
direct correlation with the EC and Sodium concentration.
Since sodium and chloride are found to be the major ions in
groundwater in this study and Chennai being a coastal city, the possibility of
saline water contamination was assessed by computing the Simpson’s ratio
(Todd, 1959). Simpson’s ratio is calculated by dividing the chloride by
bicarbonate concentration of each sample. The interpretation of the ratio is 0.5
for good quality freshwater, 1.3 for slight contamination, 2.8 for medium
contamination, 6.6 for contamination and 15.5 for severe contamination.
Table 3.11 shows the Simpson’s ratio calculated for different zones of the
city.
Table 3.11 Statistical summary of Simpson’s ratio for groundwater
samples from different zones of the Chennai city
Zone Mean Median SD Minimum Maximum
East 3.62 1.41 6.44 0.05 41.25
North 1.7 1.36 1.55 0.12 6.80
South 2.14 0.45 4.74 0.05 23.54
Central 1.02 0.53 1.72 0.04 14.55
West 1.45 0.88 1.75 0.02 11.03
The mean values of Simpson’s ratio is at least twice as the median
values in all except north zone and this may be because of influence by a few
wells having high mineralization. The median values are considered more
80
reasonable. The ratio is less than 1.0 in the case of south, central and western
zones suggesting good quality fresh water and no contamination. The median
values in the case of east and north zones are 1.36 and 1.41 and indicate
contamination probably due to saline water (Mondal et al 2007) as these
zones (Figure 3.2) adjoin the coast line of the city. The average EC values
recorded in these zones in the present study is also higher than other zones,
with sodium and chloride being the dominant ions. The groundwater quality
protection measures against further contamination by saline intrusion needs to
be taken up in these zones.
In general, the suitability of the groundwater in the zones for
drinking purposes by comparison with standards by WHO (1993) shows that
the pH is the only parameter within the desirable range. The groundwater in
all the zones is having values higher than desirable/allowable standards for all
other parameters except nitrate, calcium and sulphates. The high EC values in
all the zones is an indicator of medium to high mineralization of water and
medium to high in hardness of the groundwater. Therefore, most of the wells
in all the zones, especially in the east and north zones require treatment before
it can be used for drinking/ domestic purposes.
3.16 EVALUATION
The foregoing results suggest that in addition to the relevance of
water quality issues, the effectiveness of the RWH program further depends
strongly on the hydrogeology and understanding of the groundwater dynamics
in the Chennai city area. Issues such as recharge to the aquifer, the flow
directions and water balance in the aquifer due to recharge and abstraction for
domestic use in the city appear important to the successful implementation of
the RWH program. Further, in addition to hydrogeology of the local areas, the
location and suitability of the recharge zones can be identified, if the
81
groundwater dynamics are understood better. This requires modelling of the
aquifer which can be a valuable tool to identify groundwater zones and flow
directions to better assess recharge impacts.
A perusal of recent literature also reveals that groundwater
modelling with the help of Visual Modflow has been used to study
groundwater dynamics in response to recharge strategies in some countries.
A visual mudflow model for Mujib aquifer in Jordan (Al-Assad and
Abdullah, 2010) was constructed to study different groundwater management
scenarios such as low, medium, high volume of artificial recharge options and
the response of the aquifer parameters. This is suggested to assist decision
makers’ select suitable management programs in semi arid zones like Jordon.
Similarly in Oman, groundwater simulation in Salalah coastal aquifer
predicted the changes in groundwater flow directions, hydraulic heads and
TDS scenario in 2019, with and without artificial recharge of treated sewage
(Shammas 2008). In another recharge study in Belgium (Camp and
Walraevens 2009), the recovery scenarios in the over exploited Western
Flanders aquifer have been predicted up to 100 years based on a groundwater
flow model.
The groundwater modelling of the Chennai city aquifer may be a
good solution to understand the impact of the RWH program better. However,
as mentioned earlier, and since groundwater modelling of the city aquifer
demands more data and investigations than available, the immediate
calibration of such a model may not be feasible now. However, the utility of
such modelling for managing groundwater can be effectively demonstrated at
a smaller scale. A pilot study was decided therefore, to be conducted in a
smaller area, but in a detailed manner in the campus of St Peter’s Engineering
College campus, Avadi and calibrate a Visual Modflow model of the aquifer.
82
This study can be a model for demonstration and application to other areas for
design and evaluation of RWH systems, including Chennai city.
The next chapter explains the design, investigation, construction
and implementation of the roof top RWH system, monitoring and
development of a groundwater model in the campus of the St Peter’s
Engineering College Campus, Avadi.