This presentation gives an overview on how to design effective rainwater harvesting systems based on the underlying rock structure and hydrogeology of an area.

1. Effective RWH
Systems – Significance of Geology
and Hydrogeology
J.Saravanan
Consulting Hydrogeologist
Thrust Geoconsultants P Ltd, Chennai
1

2. Presentation
Structure
•What
is effective RWH System?
•What
is the Geology & Hydrogeology of
Chennai city?
•How
do I know the hydrogeology of my
locality?
•Why
effective RWH?
•Towards
effective water management in
Chennai city

3. Effectiveness wrt RWH
Coverage…

4. Effective wrt RWH
design a RWH system
Designing
(particularly in the case of )
groundwater recharge based on
the hydrogeology of an area.
•
•
•
•
Better functioning of the system
Maximum realisation of benefits
Cost benefit
Case of Besant Nagar, Anna
Nagar, Tambaram

5. Besant
Nagar
Coastal Alluvium
•
•Sandy
strata (aquifer)
•Good Porosity and Permeability
•Water table : Shallow
Coastal Alluvium
(Sandy)

6. Anna Nagar
•Gondwana
- Clay /Shale mainly with
intermittent silt / fine sand
•Highly Porous but poor in permeability
•Water Table Shallow to moderate
Clay
Fine Sand / Silt
Clay
Shale

7. Tambaram
•Hard
rock area
•Weathered / fractured rock ( aquifer)
•Moderate to Poor in Porosity and
Permeability
•Water Table : Shallow? To Deep
Top Soil / Weathered
rock
Partly Weathered /
Fractured rock
Fr. Rock
Hard rock w

10. Geology of Chennai
Era
Formation
Hydro
Recent and
Sub-Recent
Alluvium,laterite,
Conglomerate &
Black clay.
Good
Coastal,
(exl. Clay) central chennai
Tertiary(2.6 M
yrs)
Sand and
sandstone mainly
Good to
North Chennai,
very good Ambattur..
Sriperumbudur Clay, Shales,
beds (150 M
Felspathic
yrs)
Sandstone.
Poor
Lower
Gondwanas
Green Shales and
boulders.
Poor
Archaean
(4500 M yrs)
Dolerite,
Charnockite and
Gneiss.
Moderate
- Poor
Type area
East Chennai,
Porur,
Annanagar
South
Chennai

13. Chennai’s Aquifer capacity
The total storage capacity of chennai city aquifer works out to 392 mcm.
(1 mcm is 1000 MLt; 2.74 MLD)
The storage capacity reduces drastically with falling water table.
The capacity at 10m water level is 259 mcm ie., 66% of the total
storage capacity
The storage capacity at 20m water table is 126 mcm which is about
32% of the total storage capacity.
This may be due to the fact that the major yielding zones are restricted
to the top 30m bgl which is mainly alluvium.
Beyond 30m depth the porosity and specific yield of the formations such
as shale and hard rock is very poor and hence cannot store nor yield
sufficient quantity of groundwater.
This also corroborates with the reduction of yield in borewells during
summer when the water table depletes drastically.
13

14. Hydrogeology of my locality
Geotechnical Report for foundation
designing

15. Hydrogeology of my locality…
Hydrogeological Report for
groundwater surveys
Observing BW drilling in
neighbourhoods (hand auger, rotary,
DTH)
Government Departments –
CGWB, CMWSSB, TWAD, PWD
Groundwater.
http://cgwb.gov.in/District_Profile.html
http://www.mdws.gov.in/node/2623

16. Hydrogeology of my locality…
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17. Public Supply Vs Water Policy Vs RF
Alternate Days Supply
GW Reg. Act
Telugu Ganga Opted
RWH Mandatory for new buildings
Alternate Days Supply
Telugu Ganga Realised
100MLD Desal Unit
Piped water supply stopped
RWH Mandatory for all buildings
Veeranam tapped
17

18. Source Dependance by Chennai ite’s
Source
% of dependance to meet the daily
water requirement
Metro Water
35 %
Groundwater
62 %
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19. Status of Public Supply

Present Public System is highly subsidised and
hence lacks economic sustenance

Cost varies from Rs. 10 to Rs. 45 per KL

At present tanker supply costs Rs. 100 per KL

Sources :
AK Basin

Surface Water
T G
Veeranam
Neyveli Aquifer
Kollidam??
RO
Lowest Per capita supply in the country
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20. Towards Effective Water
Management System

Water Requirement Estimation

Percapita requirement (70.…135….150lpcd)????
Development should be based on
resource availability or FSI or
Guideline Value?



Case of OMR and other High value projects
Aquifer carrying / bearing capacity….
Development
based on public water
supply system???
Environment Consideration….

Importance to sea facing or sustained fresh water
availability?

21. 21

22. Effective management…
Need
for a comprehensive study on
Chennai’s groundwater resources
Mapping
of Aquifers – Aquifer Potential – Recharge sources –
Safe Yield estimation – Conservation and Management
Conducting
Groundwater Studies
prior to construction


Geology, Hydrogeology, Geophysical Surveys
Part of EIA – (Safe, Critical, Semi Critical, Over Exploited)
Identifying
potential groundwater
sources within the site
Selection of suitable drilling
technique
Borehole diameter

23. Effective management ….
Record
on Wells, drilling, well
designing and construction – to record
lithology and decide slot position
Well
the
development and yield
measurement through V notch plate
Water level measurement after well
drilling / development
Selection of suitable pump based on
the total working head, yield of the
borewell and water level
Well completion report containing all
the above details

24. Effective management ….
Provision
of space, atleast to drill a
borewell in future in the rest of identified
potential pockets.
Dug wells still a viable option at localities
– case of Selvaraj Nagar, Urapakkam; Ramapuram
Tapping shallow zone during post
monsoon by provision of slots in borewell
casing
Shallow water table zones with clayey
Soil
Safe disposal of waste water during
construction

25. Do’s and Do’nts….
Constant
depletion of water table is
an indication of
Over
exploitation of GW sources
Reduced recharge
Sustaining
the water table
fluctuation through RWH and
GWR&R to avoid dwindling of water
table
Periodic water quality analysis