Managed Aquifer Recharge for Artificial Storage (MARAS) of...

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: anwarzahidb@gmail.com

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

anwarzahidb@gmail.com

Hydrogeology of Barind

Example:

The Barind

• 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.

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Managed Aquifer Recharge for Artificial Storage (MARAS) of

Water to Improve Groundwater Conditions in Vulnerable

Climatic Areas of Bangladesh