Prospects of Low Cost Recharge Tank to Augment Safe Water...
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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] Prospects of Low Cost Recharge Tank to Augment Safe Water Availability By Very Shallow Hand Tubewell in the Coastal Areas of Bangladesh
Transcript of Prospects of Low Cost Recharge Tank to Augment Safe Water...
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]
Prospects of Low Cost Recharge Tank to Augment Safe
Water Availability By Very Shallow Hand Tubewell in the
Coastal Areas of Bangladesh
• The development of groundwater resources for potable use has increased
substantially over the last decades.
• Bangladesh depends mainly on groundwater sources to meet its domestic
demand for potable water.
• Rural domestic water supplies are obtained mainly from tubewells fitted with
hand pumps and dug wells.
• Although groundwater is generally of better quality than surface water, it has the
drawback of being complicated and costly to treat once it becomes contaminated.
• By early 1990's, Bangladesh achieved almost universal (i.e. about 97%) drinking
water supply coverage until the success was overshadowed by the presence of
excessive arsenic in the shallow groundwater and saline water encroachment in
coastal aquifers.
• The national water coverage of safe water supply is about 86%. Further progress
in ensuring better water supply, particularly in hard to reach areas still remain a
big challenge. In HtR areas, the water supply coverage is only 24%.
• Additionally, changing climatic conditions may offer for more challenges on the
availability of safe and fresh water resources.
Status of water supply in Bangladesh
Increase in precipitation in monsoon
Increase in evaporation
Prolonged monsoon
Sea Level Rise: Increase in salinity intrusion
Drought
Impact on agriculture & fisheries
Increase in flooding intensity
Decrease in precipitation in dry season
Submergence of coastal areas
Increase in snow melt in the Himalayas
Water Resources Management Vulnerabilities
Physiographic Divisions and Groundwater Problems
• Water scarcity, unidentified deep aquifers and lowered
groundwater table (upto 35 m below ground surface)
below suction limit are the major limitations in Barind
drought prone area of Nizampur union under Nachole
upazila.
• Based on socioeconomic status of the inhabitants and
physiographic conditions force mode deep set hand
tubewells and groundwater based piped water supply
have been selected as best options for safe water supply.
• Suction mode shallow tubewells may be installed close
to the river periphery and where groundwater irrigation
is less i.e. groundwater table remain within the suction
limit of 7.5 m round the year.
• Considering thickness of upper Madhupur clay,
different technology for groundwater recharge e.g.
recharge basin, sand pile, recharge well and injection
well may be designed to augment groundwater storage in
the subsurface.
• Preserved pond may also be used for piped water
supply.
Water Supply Options for 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
• Haor areas of Shimulbak union under
South Sunamganj upazila are characterized
by lakes (beels) and swamps (haors) and
water logging for 6-8 months and arsenic
contamination in shallow groundwater are
the major problems for the population.
• Considering fresh water scarcity and non-
availability of dry lands in the studied union
as well as socio-economic condition of the
inhabitants, installed RWHS, deep
tubewells and multi outlet deep tubewells
are the major feasible options for safe water
supply.
• PSF can also be constructed for safe water
supply and eco-san latrine for sanitation.
Water Supply Options for Haor Areas
Hydrogeology of Floodplain and Chars
Hydrographs for wells (2nd Aquifer) in southern Kachua
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Water level (elevation) in meter
KH-22KH-25KH-34KH-36KH-55KH-56KH-60
• Shallow hand tubewell is the most popular water
abstraction technology in the flood prone char areas where
shallow groundwater is safe from arsenic contamination.
• Considering regular seasonal flood in the area, dual
platform tubewells have been installed which is feasible to
use during flood too.
• Dug wells, iron removal plants (IRP) and arsenic iron
removal plants (AIRP) have also been installed as useful
options whereever feasible based on hydrgeological and
physiographic conditions.
• Deep tubewells and rainwater harvesting system (RWHS)
may be installed in arsenic affected areas.
Water Supply Options for Char Areas
• Besides regular seasonal flood, arsenic contamination in
shallow groundwater is the major problem in the floodplain.
• Therefore shallow tubewell is no more useful technology
for safe water supply. Deep Tubewell is the sustainable
option for safe water supply in floodplains.
• Based on physiographic condition and water quality brick
made RWHS, dug wells, AIRP have been installed in the
area as feasible options.
• Deep tubewell may be installed using high capacity
mechanized drilling rigs to overcome the problem of
gravels encountered in aquifers in many places at depths of
about 100 m.
Water Supply Options for Floodplains
Pre-monsoon/Dry Season
Groundwater Salinity in Coastal Aquifers
Monsoon/Wet Season
• Saline water encroachment in both surface water
bodies and groundwater aquifers is the main
constraints for fresh water supply in the coastal area.
• Besides salinity problem, natural disasters are also
obstruct for providing safe WATSAN facilities.
• Considering physiographic conditions, water
quality as well as socio-economic condition of the
inhabitants, pond sand filters (PSF), both RWHSs,
with and without filter and community based
RWHSs, pond water based piped water supply and
desalinization plant have been installed as feasible
options for safe water supply in the area.
• Deep tubewells (>300 m deep) may also be
installed for community based piped water supply.
• Very shallow shrouded tubewells may be used to
withdraw recently recharged shallow groundwater
stored above arsenic and saline affected zone.
• Fresh precipitation water recharge may be
augmented by installing managed aquifer recharge in
very shallow subsurface that would improve the
quality of groundwater by reducing salinity
concentration level of shallow groundwater.
Water Supply Options for Coastal Belt
• 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).
• Construction of recharge technologies like
recharge tank removing the subsurface clay and
by filling sand and brick cheeps will contribute
additional storage of fresh water to the aquifer.
• The sand filled pit can be overlain by a brick
made tank i.e. reservoir without a bottom floor
having wall height of 1 to 1.5 m and same
diameter like the filled pit.
• From rooftop, rainwater through pipes can be
poured directly in the recharge tank.
• Where maintenance of the community level
water supply and artificial recharge technologies
are challenging, household level technology will
face this challenge less.
Recharge Tank
• In many areas local inhabitants are already using very shallow hand tubewells, but
without knowing the concentration levels of arsenic and salinity that needs to
monitor adequately.
• In all cases care must be taken to avoid any surface contamination including
bacterial pollution, salinity intrusion due to shrimp cultivation and storm surges and
to monitor arsenic contamination level.
• It needs to maintain a periodic maintenance of artificial recharge structures to
avoid rapid reduction of infiltration capacity due to clogging, silting, chemical
precipitation, and accumulation of organic matter.
• As the rain water will be used directly for recharge, the possibility of clogging will
be less and maintenance will be easier.
• 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
• It is necessary to expand and improve the water supply and sanitation services in
order to satisfy the basic needs of the people including the Hard to Reach areas.
• The need to expand these facilities is greater in the case of under privileged groups
and regions.
• Promotion of various technology options will be sustainable for both water supply
and sanitation keeping the needs of specific areas and socio-economic groups of
people within broader environmental considerations.
• Necessary measures needs to be taken to prevent damage of technologies during
natural disaster.
• Social mobilization needs to be developed through training of volunteers at village
level for maintenance of technologies.
• Adequate awareness programs are needed to habituate uncommon type of
technologies.
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