Embed Size (px)
Citation preview
Anwar Zahid, Ph.D.Deputy Director, Bangladesh Water Development Board
Faculty (Part-time), Department of Geology and
Department of Disaster Science and Management, University of Dhaka
E-mail: [email protected]
Marta Faneca SànchezDeltares, Netherlands
Managed Aquifer Recharge for Artificial Storage (MARAS) of
Water to Improve Groundwater Conditions in Vulnerable
Climatic Areas of Bangladesh
• Artificial recharge needs to be carriedout for overstressed aquifers and aquifers
suffer from water quality e.g. salinity problem.
• Areas where groundwater is either already over-exploited like Dhaka city and
drought-prone Barind area or saline prone, like in the coastal areas, recharge
enhancement has potential to store excess runoff and to reduce salinity.
• Impact of climate change i.e. changing precipitation pattern and rising sea-level
would augment the importance of artificial recharge.
• Traditional approaches of watershed development that stress enhancing managed
aquifer recharge for artificial storage of groundwater do not pay adequate attention in
developing countries like Bangladesh.
• The objective of this study is to select the appropriate and potential recharge
technologies for different climatological and physiographical areas of Bangladesh
considering appropriate variables.
Status of water supply in Bangladesh
Artificial Recharge AR
Infiltration Interception
Spreading methods Induced bank
infiltration
Wells, shafts &
boreholes
In-channel Runoff harvesting
Wells & shafts
Recharge Technologies
After Dillon, 2005
The identified variables that define the Physical Potential are:
•• Precipitation intensity and duration
•• Evaporation loss
•• Surface geology
•• Thickness of the aquitard
•• Groundwater depth below the surface in the middle of the Monsoon (June)
•• Wells contaminated with Arsenic
•• Inundation land type
The variables that define the Demand Urgency are:
•• Population density
•• Depth of the groundwater table below the surface (in April)
•• Poverty
•• Absence of perennial rivers close by
•• Irrigation demand
Variables Considered to Select Recharge Technologies
Example 1: Precipitation
Criteria: areas with high precipitation intensity and long duration of the precipitation are most
suitable than areas with low precipitation as rainwater needs to be harvested for infiltration. The
chosen criteria are:
The precipitation is 100mm/month or more during less than 4 months = suitability 0
The precipitation is 100mm/month or more during 4 to 7 months = suitability 0.5
The precipitation is 100mm/month or more during at least 7 months = suitability 1
Example 2: Thickness of the Aquitard
If the thickness of the aquitard is less than 5 meters, Infiltration Wells are less suitable as water can
infiltrate directly.
Data: thickness of the aquitard Map (Reference to paper)
Method: digitize the areas with a thickness inferior to 5 meter, those areas get a suitability of 0 while
the other areas get a suitability of 1.
Example 3: Arsenic Contamination
Criteria: If the aquifer is contaminated with arsenic, the suitability of ASR is low as infiltrated water
will mix with already contaminated water. In this case, the infiltration should be done at a deeper
aquifer or other methods should be applied.
– If > 20% of the wells contaminated by arsenic = suitability 0
– If <20% of the wells contaminated by arsenic = suitability 0.5
– If Arsenic safe = suitability 1
The final total potentiality has been calculated by first normalizing the Total Physical Potential and
the Total Demand Urgency, and then adding them up.
Total Potential
Proposed Technologies
• Infiltration wells with rain or river water as source (e.g. for Barind, coastal belt
etc.)
• Infiltration ponds with rain or river water as source (e.g. for coastal areas, Dhaka
etc.)
• Recharge basin (dig out the clay and fill it with sand and connect with the aquifer)
(e.g. for coastal areas etc.)
• Artificial subsurface reservoir (dig out the clay and fill it with sand, no connection
with aquifer) (e.g. for Barind, Haor areas, hilly areas etc.)
• Injection well with rainwater or river water (e.g. for Dhaka city, Barind etc.)
Ideas for pilots
• Subsurface infiltration drain
• use canals to infiltrate fresh water through infiltration wells below the canals (e.g.
in polder areas, under irrigation projects etc.)
Proposed Recharge Technologies
• Technology is comparatively simple and not
require high skilled labor for installation, as well
as operation and maintenance.
• Underground storage space is required and
existing roofs of houses are used as catchment
area.
• No evaporation losses due to underground
storage as high temperature prevail in summer.
• Early aquifer recovery and contributing to
protect declining trend of groundwater level.
• Applicable methods i.e. infiltration wells,
recharge basin etc. are easy to install and
operate.
• Recharge can degrade the aquifer unless
quality control of the injected water is adequate.
• Clogging may reduce recharge rate and needs
to be repaired.
Managed Aquifer Recharge
Recharge Well
Pre-monsoon/Dry Season
Groundwater Salinity in Coastal Aquifers
Monsoon/Wet Season
Example: Coastal Area
Recharge Tank/Basin
• Recharge Tank is proposed to augment storage
of fresh rainwater to shallow subsurface in order
to increase fresh water discharge by reducing
salinity level of nearby very shallow hand
tubewell (upto 6-8 m).
• This small scale very shallow hand tubewell
with the recharge tank is feasible in areas where
the thickness of the surface clay is within the
excavated range (<10m), groundwater salinity
level is low (Chloride concentration <1000 mg/l
or Electric conductivity <3000µS/cm) and depth
to groundwater table is also very shallow and
remain within 5-8m from the ground surface.
Recharge Tank
Recommendation
•Areas where groundwater is either already over-exploited like Dhaka city and Barind
etc. or saline prone, like in the coastal areas, recharge enhancement has potential to
store excess runoff and to reduce salinity.
• Infiltration wells, Infiltration ponds, Recharge basin, Artificial subsurface reservoir,
Injection well have the potential to install in different areas of Bangladesh with rain or
river water as source.
• Relevant hydrogeological and physical variables needs to be considered carefully to
select potential sites and site-specific recharge technologies.
15
Managed Aquifer Recharge for Artificial Storage (MARAS) of
Water to Improve Groundwater Conditions in Vulnerable
Climatic Areas of Bangladesh
