chapter 3 study area - inflibnetshodhganga.inflibnet.ac.in/bitstream/10603/26423/8/08...28 the...
TRANSCRIPT
25
CHAPTER 3
STUDY AREA
3.1 GENERAL
The South-Eastern peninsular Rivers are affected by monsoon rains
and physiographic characteristics. Chennai Basin is one such area which
comprises of ephemeral to intermittent streams along with a good
groundwater resource. The distance between hills to coast is on an average
160 km along the River course. The groundwater resources spanning a
distance of 72 km across the Rivers provide the needed water resources for
the Chennai Metropolitan and its neighborhoods. The details of the selected
study area are presented in the following sub headings.
3.2 STUDY AREA – CHENNAI BASIN
The Chennai Basin comprises of the four Rivers namely: Araniar,
Kosasthalaiyar, Coovum, and Adyar River. The index map of Chennai Basin
is presented in Figure 3.1 below. The Rivers originate from North to South on
the Western side from the hills of altitude ranging from 100 m to 200 m and
flows to the Bay of Bengal on the East to North-East. Chennai city is usually
considered as a plain land surface with a gentle slope towards Bay of Bengal.
The land elevation is within 10 m and the maximum elevated lands are
located on the South-Western part of the City.
26
On an average the topography is even and the land throughout the
districts renders subdivisions into natural regions rather difficult. Surprisingly
the Rivers though originating at different locations have a tendency to merge
on the surface or below the surface. This is justified by the fact that though
the Rivers remain dry at the surface yet they are able to provide the
groundwater supply for a period of 2 years even after the worst monsoon
season.
27
Figure 3.1 Index map of study area
28
The Chennai metropolitan is located in the North-Eastern corner of Tamil
Nadu State. The drainage basin taken up for study is located between latitudes
12º 40' N to 13º 40’ N and longitudes 79o 15’ E to 80o 50’ covering an area
of 5542 sq km. It is bound by Bay of Bengal in the East, Thiruvallur district in
the North and West and Kancheepuram district in the South.
The River basin authority has designated this River basin 4C. The sub-
basins of this River basin are given in Table 3.1. The first three components
refer to River Araniar which drains into the Pulicat lagoon. The next three
refers to the watersheds between River Kosasthalaiyar and Coovum. While
the last watershed represents River Adyar and the previous last two the upland
areas of River Kosasthalaiyar. The three components of each River except
that of River Adyar respectively represent the head, middle and tail reaches.
The head reach of River Adyar is included as it represents a transition from
storage to dynamic flows. This concept is utilized in this research for
providing the augmented head using the attenuated flood.
Table 3.1 Watershed code
S.No Watershed code Watershed name
1 4C2D1 PULICAT
2 4C2C7 ARANIAR
3 4C2B6 ARANIAR
4 4C2C4 KOSASTHALAIYAR
5 4C2A7 POINI
6 4C2C3 COOVUM
7 4C2B2 KAIGAL,MALATTAR
8 4C2C5 NANDI
9 4C2C2 ADYAR
29
The administrative classification of the Chennai basin is shown in table
3.2. The Vellore district with four Taluks and blocks forms the source area of
River Kosasthalaiyar and Coovum. The Thiruvallur district with eight Taluks
and 13 blocks provides the base for the integrated water resources
management. Therefore, a detailed description of this is given under the
section conceptualization of the study area. The Kancheepuram district with
three taluks and two blocks feeds the River Adyar. The Chennai district with
5 taluks forms the tail end areas of Rivers Coovum and Adyar.
30
Table 3.2 Tamil Nadu state list of districts, taluks and blocks
S.No District Name Nos. Taluk Name Nos. Block
1
Chennai - coastal 1 Kottai – Tondiarpet -
Tanks 2 Purasawalkam – Perambur -
Coovum 3 Egmore – Nungambakkam -
Coastal 4 Mylapore – Tiruvallikeni -
Adyar 5 Mambalam - Guindy -
2 Kancheepuram – Adyar
6 Kancheepuram
1 Kancheepuram 7 2 Walajabad 8 Tambaram 4 Thomas malai
13 Sriperumpudur 12 Sriperumbudur 13 Kundrathur
3
Thiruvallur – Kosasthalaiyar 14 Thiruvallur
14 Thiruvallur
Coovum 15 Kadambathur Nandhi
15 Tiruthani 16 Tiruthani
Kosasthalaiyar 17 Tiruvelangadu Nagari
16 Pallipattu 18 Pallipattu
Nandhi 19 R.k.pet Coovum
17 Ambattur 20 Villivakkam
Coovum 21 Puzhal Kosasthalaiyar
18 Uthukottai 22 Poondi
Araniar 23 Ellapuram
Kosasthalaiyar 19 Ponneri 24 Minjur 25 Sholavaram
Adyar 20 Poonamallee 26 Poonamallee Araniar 21 Gummidipoondi 27 Gummidipoondi
4
Vellore 22 Walajapet
28 Walajapet 29 Sholinghur
Kosasthalaiyar and Coovum 23 Arakonam
30 Arakonam 31 Nemili 32 Kaveripakkam
Source: Groundwater atlas of Tamil Nadu, State Ground and Surface Water Resources Data Centre, Taramani, Chennai-113
31
3.3 HYDROLOGICAL SCENARIO
The total basin area is 7282 km2, with 1740 km2 in Andhra Pradesh
and the remainder in Tamil Nadu. Chennai receives rain from South-West
monsoon and North-East monsoons. The former is usually not sufficient to
increase the surface storage; however, it does contribute in improving the
groundwater table during the crucial period after summer. The North-East
monsoon manages to fill many of the surface storage tanks and helps to
recharge the groundwater. The basin receives 943 mm rainfall each year with
75% dependability. The average annual rainfall in Chennai basin is presented
in Table 3.3 below.
Table 3.3 Average annual rainfall in Chennai region
No. Region Raingauge Station
Average annual rainfall (mm)
1 Hills
Sholingur 952 Tirutanni 1047 Pallipet 895 2
Plains
Thiruvallur 1088 Sholavaram 1289 Minnal 959 Poondi 1292 Arakkonam 1070 3
Coast
Tambaram 1424 Meenambakkam 1324 Saidapet 1286 Nungambakkam 1215 Chepauk 1112
Generally, the average annual rainfall is high in coastal areas and low
in hills. However, within the coastal areas, the hills in Tambaram and
Meenambakkam have higher rainfall compared to the plains. This may be
32
considered as the main cause of floods in Chennai. If this rain water is not
harvested, it will drain off as flood discharge to the Bay of Bengal. Therefore,
the need for integrated management of flood with groundwater basin
resources becomes necessary for efficient flood management. The dependable
rainfall values of the River basins, which indicates the assured amount of
rainfall for 50% to 75% of the considered time period (years), are presented in
Table 3.4.
Table 3.4 Dependability analysis of rainfall of Chennai region
RIVER BASIN
Rainfall
50%
Dependable
75%
Dependable
ADYAR 1385 mm 1211 mm
ARANIAR 1274 mm 1099 mm
COOVUM 1246 mm 1030 mm
KOSASTHALAIYAR 1072 mm 818 mm
River basins can also be considered as a single basin of Thiruvallur
district as indicated in Figure 3.2 and Tables 3.5 and 3.6. The Thiruvallur
district is bounded by the Chembarampakkam as a storage zone that recharges
the River Coovum below the Korattur diversion. Between the diversions of
Kesavaram and Koratur of the River Coovum can be considered as a drainage
zone towards Chembarampakkam. Below Korattur diversion across the River
Coovum, heavy pumping for catering to the city requirements is taking place.
The sustainable groundwater in the zone makes one realize the concept that
the hard rock areas between Sriperampudur and Chembarampakkam are
33
contributing to the ground in the zone. Therefore, the alluvial belt with a
thickness of 25 m can be considered as spanning the diversions of Korattur
and Thamaripakkam and extending to Periyapalayam. Surprisingly the
surplus level of Chembarampakkam, the Korattur diversions, Thamaripakkam
diversion and Periyapalayam are almost at the same altitude above mean sea
level. This has led to the concept of considering the area between the Pallipat
to Ramakrishnarajpet (RK pet) as a high alluvial plain that allows sub-surface
flow to the Korattur diversion on the western side. From the Korattur
diversion, the alluvial soil extends from southwest to northeast spanning
Thamaraipakkam and Periyapalayam. This area is heavily exploited for its
groundwater use. The three districts of Kancheepuram, Thiruvallur, and
Chennai form a single groundwater basin though the origin of the Rivers may
be considered as independent units.
34
Table 3.5 River basin and sub basin of Chennai
Name of the River basin Name of the sub basin
ARANIAR
KOSASTHALAIYAR
BASIN
1.Pulicat
2. Araniar III
3. Araniar II
4. Araniar I
5. Sholavaram Tank
6. Redhills lake
7. Mettupalayam
8. Poondi
9. Allikuzhi canal
10. Nagari River
11. Arungulam
12. Murukkampattu
13. Pallipattu
14.Nandhi River
15. Srikalipuram
16. Kosasthalaiyar-1
17. Coovum -1
18. Mappedu
19. Chembarampakkam
20. Nemam
21. Coovum –II (Source: State Ground and Surface water resources Data centre, Chennai)
35
3.4 GEOLOGY
In the Chennai region there are extensive outcrops of the granitic
basement and of the Gondwanas represented by shales, sandstone and
conglomerates. In places all of these are overlain unconformably by much
younger strata, namely some tertiary but mainly quarternary alluvial and
marine littoral deposits, generally related to the present surface drainage
regime and coastline. In the area under discussion, the upper catchments of
the Rivers (west of the Poondi Reservoir and the Kesavaram Diversion) are
predominantly uncovered basement, whereas the lower catchments lie mainly
on sedimentary outcrops, in the case of the Kosasthalaiyar, Coovum and
Adyar mostly on alluvium.
Despite the range of rock outcrops, the lower catchments are in the
form of a flat, featureless plain; even the upper catchments are of subdued
topography and might be described as sloping plains. The most dramatic
topographic features are those caused by igneous intrusions and recent
geomorphic processes: some post Archean intrusions form rocky hillrocks,
which although mainly less than 33m in height stand out in the otherwise
featureless topography. Two ridges running parallel with the coast are
probably the result of normal geomorphic processes (such as are responsible
for the accumulation of sand dunes in many coastal areas) in the presence of
an advancing shoreline, either because of sea level changes related to the
Pleistocene ice age, or due to tectonic movements of the margin of the sub-
continent. The crystalline basement rocks have no primary porosity and
permeability when fresh and unaltered, but groundwater occurs in small
quantities in the weathered zone, normally 10 to 20m thick and occasional
deeper fissure zones.
Large diameter wells in such strata may yield as much as 5 l/s, though
normally the discharges are less. The Gondwana sediments, particularly the
36
sandstones, probably possess some primary porosity, but permeabilities are
likely to be dominated by secondary features such as weathering, fissures and
joints; in fact their water bearing properties are not vastly different from those
of the Basement. The Quarternary and Tertiary strata are extremely variable
in geometry and lithology, but the alluvium forms highly productive aquifers,
in some places suitable for high yielding drilled wells. The coastal sands also
form a good aquifer, but the capacity of this for groundwater development is
limited by the pressure of sea water in the immediate vicinity and the threat of
saline intrusion into wells with high discharges.
37
Figure 3.2 Geological formations encountered in Chennai basin
38
Table 3.6 Hydro-stratigraphy of Chennai basin
Age of rock Rock type Description of different
units Groundwater bearing capacity
Recent Alluvium Sandy, sandy silts and beach formations High to Very high potential
Tertiary Sedimentary deposits
Sand, sandstones, clay and shales
Very high capacity in sand and sandstones (good to moderate potential)
Gondwana Sandstone, Siltstone, Grit, Claystone
Clay stone compact rock, grit with fine compact fine sand clayey rocks with yellow ochre
Poor to very poor groundwater availability is seen in sandstone, grit, clay stone, siltstone region.
Archaen Crystalline complex, hard basement
Granites, Charnockites, different metaforms of gneiss's and transformed granites and gneiss.
Very poor to poor yielding capacity
39
3.5 HYDROGEOLOGY
The total surface area of the Araniar-Kosasthalaiyar Basin is about
1000 km2 of which some 275 km2 is underlain by a buried channel system;
probably that of the Palar; its geometry and hydraulic properties have been
studied by drilling and pumping tests. the listed transmissivity range from 80
to 6535 m2/day and the storativity values are from 6.5 x 10-5 to 0.105.
The main aquifer in the area is the Quarternary alluvium, reflecting a
buried channel system. Here the alluvium is up to 50m thick, and much of it is
sandy, though clays are sufficiently persistent in places to make its lower part
behave like a confined aquifer.
The Coovum – Adyar Basin covers an area of about 350 km2 and is
underlain by some 20m of alluvial strata, some of them sandy. However,
drilling at few some sites penetrated predominantly clayey deposits. Two
pumping tests were carried out by the UN project to evaluate the properties of
the aquifers. Yields from both wells were estimated to be about 25l/s.
In addition to these inland basins, significant exploitable groundwater
occurs in the Quarternary deposits near the city and along the coastal sand
ridge to the south of the city. These aquifers are probably partly alluvial and
partly of marine littoral origin. In both cases the saturated thicknesses are
probably small and their proximity to the sea limits, the productive potential.
In Chennai there are thousands of dug wells and bore wells most of which are
still used, because supply from the public water supply system is inadequate.
Recharge conditions in the whole area are generally favorable. The
land is mainly flat with poorly developed surface drainage; soils are often
light with a high potential infiltration intake and the Rivers and the reservoirs
40
can be expected to have high losses, though the Rivers carry flow only for
limited periods at best. Relatively high recharge confirmed by large seasonal
water table fluctuations, often in the range of 2 to 5m. From experience
elsewhere, natural recharge to the alluvial aquifers would be expected to be
about 25 to 30% of average rainfall. This compares well with the UN project
computation of annual recharge to the Araniar-Kosasthalaiyar basin of 170
Mm3 during a wet year.
The present status of these rivers at various locations is shown in
Figures 3.4 to 3.14.
Figure 3.3 Upstream sand deposits at River Nagari
Figure 3.4 Upstream reach of River Kosasthalaiyar
41
Figure 3.5 Sandy areas of Kosasthalaiyar
Figure 3.6 Diversion weir across River Coovum at Korattur
Figure 3.7 Head regulator of New Bangaru channel at Korattur
42
Figure 3.8 Hydraulic particulars of diversion and regulator
Figure 3.9 New Bangaru channel at Thirumazhisai
Figure 3.10 New Bangaru channel near Chembarambakkam
43
Figure 3.11 Chembarambakkam reservoir
Figure 3.12 River Adyar at Chembarambakkam
Figure 3.13 Upstream reach of River Adyar
44
Groundwater quality is variable. In the inland basins it is mainly good,
with overall mineralization of less than 1000 mg/l (in the deeper, high
permeability layers often less than 500 mg/l). Nevertheless there are potential
quality problems in several areas:
Sea water intrusion of the coastal aquifers and part of the Arani
Korattalayar Basin
Increasing salinity of some aquifers through groundwater
recirculation by irrigation
Severe pollution of the aquifers underlying urban and industrial
areas, particularly Chennai City itself
Long term pollution of potable supply well fields by agricultural
chemicals; with relatively thin phreatic aquifers and extensive use
of chemical fertilizers and insecticides, some index compounds,
such as nitrate and indane, should be monitored in wells used to
provide drinking water.
3.6 DEMAND AND SUPPLY SCENARIO OF CHENNAI
METROPOLITAN AREA
The demand and supply scenario of Chennai Metropolitan area
comprising of water supply agencies requirement and the demand-supply
requirements of Chennai City is shown in Tables 3.7 to 3.9 and Fig. 3.15
45
Table 3.7 Water consumption in Chennai city
S. No. Agencies Summer (%)
Winter (%)
1 Metrowater pipe supply 32.80 40.40
2 Metrowater supply by tanker lorries 5.70 3.20
3 Private tanker lorry supply 0.09 0.06
4 Private Open wells 26.07 26.40
5 Private Bore wells 34.09 28.47
6 Other sources 1.25 0.97
Total 100 100
Suppy pattern by various agencies - Summer
32.8
5.7
0.0926.07
34.091.25
Metrowater pipe supply
Metrowater supply by tankerlorries
Private tanker lorry supply
Private Open wells
Private Bore wells
Other sources
Supply pattern by various agencies - Winter
40.4
3.2
0.0626.4
28.470.97
Metrowater pipe supply
Metrowater supply by tanker lorries
Private tanker lorry supply
Private Open wells
Private Bore wells
Other sources
Figure 3.14 Seasonal water supply patterns by various agencies
46
Table 3.8 Estimates of total water demand for Chennai (1991-2021) (Mm3)
S. No
Agency 1991 1995-96 2001 2011 2021
1 Murugappa Chettiar Research Centre
…… 312 347 440 560
2 Chennai Metropolitan Development Authority (CMDA)
344 …… 438 549 ……
3 Chennai Metropolitan Water Supply and Sewerage Board (CMWSSB)
332 …… 418 526 ……
4 S.N. Ayyadurai
(Chennai city) …….. …… 354 485 565
5 Institute for Water Studies (for Chennai Basin)
…… 315 (1994) 536 …… ……
Table 3.9 Estimates of total water supply for Chennai (1991-2021) (Mm3)
S.
No. Agency 1991 1994 2001 2011 2021
1 Chennai Metropolitan Development Authority
158 ……. ……. 514 …….
2 Central Groundwater Board 169 ……. ……. 374 …….
3 S.N.Ayyadurai (Chennai City) 127 ……. 294 294 498
Source: Nigam et al (1998)