Results of Field Testing of Infiltration in Assassuni and Batiaghata

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Workshop on
ACTION RESEARCH ON GROUNDWATER BUFFERING IN BANGLADESH
24 February, 2011
Prospects of Artificial Recharge for
Augmentation of the Upper Dupi Tila Aquifer
in Dhaka City, Bangladesh
Sarmin Sultana
Department of Geology, University of Dhaka
Presentation Outline
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What is AR & what are the techniques
Why AR in Dhaka city
What is the source of water for AR
Objectives of this study
Results and discussion
Conclusions
On going research
The Megacity
Needs
introduction
WaterDhaka
Demand
and no
Supply
Ground Water
14%
86%
Surface Water
Why AR in Dhaka city
Uniqueness of Dhaka in terms of GW problem
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GW Dependant City
No imported water
Big Gap between supply and Demand
Heavy GW abstraction and well deepening
Rate of water table decline 3.5 m/y
Aquifer dewatering
No GW management !
Cone of depression
1970
1980
1995
2007
GW hydrograph of Upper Dupi Tila
Water Table Elevation Contour demonstrates a steady down ward slope.
for dry season as on 2008
Is going Deep a sustainable Solution?
Rainfall in Dhaka
300
4
Mirpur (GT-2648010)
7-Day rainfall
GWL
3
1
0
GWL (m,PWD)
7-Day rainfall (mm)
2
200
100
-1
-2
0
-3
Jan-77 Jan-77 Feb-77 M ar-77 Apr-77 M ay-77 M ay-77 Jun-77 Jul-77 Jul-77 Aug-77 Sep-77 Sep-77 Oct-77 Nov-77 Nov-77 Dec-77
300
Dhaka station (R009}
GWL
-6
200
-9
150
100
-12
50
0
-15
Jan-93 Jan-93 Feb-93 M ar-93 M ar-93 Apr-93 M ay-93 M ay-93 Jun-93 Jul-93 Aug-93 Aug-93 Sep-93 Oct-93 Oct-93 Nov-93 Dec-93 Dec-93
GW hydrographs and
corresponding 7-day rainfall are
plotted for 1977 and 1993.
GWL (m,PWD)
7-Day rainfall (mm)
250
7-Day rainfall
Objectives
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To estimate the current open space
available for natural recharge to take
place;
To delineate potential zones for
implementing site-specific artificialrecharge techniques using GIS analysis;
and
To assess suitability and applicability of
Artificial Recharge in Dhaka.
Natural Recharge Area Map
in
Area
Area in
sq.km
sq.km
Area in
in %
%
Area
Water Body
Body (inside
(inside the
the city)
city)
Water
4.44
4.44
4.04
4.04
Open
Open Area
Area (vegetation
(vegetation reflection)
reflection)
24.39
24.39
22.2
22.2
Open Area(sand reflection)
1.46
1.33
Natural water body (periphery)
43.93
39.99
Low-lying area (depression)
35.62
32.43
Total
109.84
100
Class Name
Name
Class
Bar Diagram of Recharge Area Classes
40
30
20
10
Low-lying
area
(depression)
Natural
water body
(periphery)
Open
Area(sand
reflection)
Open Area
(vegetation
reflection)
0
Water Body
(inside the
city)
Area in %
50
Infiltration Test at the pond of Institute of Fine Arts
Status of the pond immediate
after rain
Status of the pond after 3 days
from raining
Potential Zones
Rules for selecting prospective
zones of artificial recharge
Zone
Clay
thickness
(m)
Zone 1
0 - 10
& open area
available
Zone 2
10 - 15
near water
bodies
Zone 3
15 - 25
Zone 4
25 - 50
Volume of Rainwater Available in Dhaka city (Sources: BBS)
City area
(sq. km)
Avg. annual
rainfall
(m)
Total volume
rainfall
(M L)
No of total concrete
house available for
rain water collection
Each roof
area (sq, m)
Total roof
area (sq.
km)
Yearly total
volume of
rainwater
(ML)
Daily Total Volume
Of Rainwater (MLD)
370
2
740,000
6,78,000*
110
74.58
149160
408.65
If 30 % of this water can be collected, then
more than 100 MLD water will be available
to recharge the aquifer artificially.
Production well
Production
well
Abandoned
well
Number of abandoned wells of DWASA.
R1
R2
R3
R4
R5
Total
175
47
21
15
6
264
Other Options
Dredging and re-excavation of
khals
Avoid construction along faults
River dredging and Bank filtration
Systematic Clay Mining
Site Specific Artificial Recharge
Technique Map
Rules for selecting sites of
definite artificial recharge methods
No of
Locatio
ns
Clay
thickness
(m)
6
10 – 15
Trench pit
6
40 – 50
Injection well
2
3–7
Dug well
3
1
2
5 – 15
0 – 10
20 – 25
Method
Lateral trench with
vertical shaft
Spreading Technique
Retention pond with
well
2
25 – 35
En-echelon Dam
2
15 -30
Check dam
Dhaka has high potential for
Artificial Recharge
Workshop on
ACTION RESEARCH ON GROUNDWATER BUFFERING IN BANGLADESH
24 February, 2011
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