Accepted Papers - 3.pdf - UNESCO

some pumping. Where as in a recharge well the raw
water impurities smaller than screen slot is fed into
the gravel pack and is never pumped out but it
gradually chokes the gravel pack reducing its
permeability over a period of time.
� The raw water collected from rain or river
generally has higher mineral contents and hence
causes more incrustation which causes the blockage
of screen and gravel pack over a period of time.
Hence, it is recommended that double the
length of screen shall be used in a recharge well
as compared to a pumping well of the same size
to have higher cushion in screen length and to
control the entrance velocity to reduce
incrustation. The maximum entrance velocity
recommended for a recharge well is 0.015 Meters/
Sec.
Now, we cannot use length of the screens
higher than the thickness of available aquifer as there
will be no practical meaning of it. Therefore we must
use screen design that offers sufficiently large %
open area to restrict the entrance velocity within the
maximum limit with the available thickness of the
aquifer.
This makes V-Wire screens the ideal choice
for an efficient and long lasting recharge well.
Moreover to restore the permeability of screen
and gravel pack the recharge well shall be
redeveloped after every monsoon. The most
effective method of removing incrustation is acid
treatment. Hence if the material of construction for
screens is such that it allows acid treatment without
any mechanical failure than it significantly helps to
keep restoring the recharge capacity of the well and
ultimately increases the useful life of the recharge
well significantly.
Hence it is recommended that SS 304
Stainless steel, which allows acid treatment, shall
be used for screens.
� � �
370
Fine Gravel/ coarse sand pack-
Fine Gravel/coarse sand pack design can be
done in the same way as for a pumping well. The
particle size distribution for fine gravel/coarse sand
shall be decided based on the sediment size
distribution and screen slot.
� Conclusions :
� It is of utmost importance and priority to plan
systematic artificial recharge projects for identified
command areas and water drawal rates.
� Selection of recharge structure site shall be
carefully done to achieve optimum transport of
recharge water from the recharge point to the point
of usage on a sustainable basis keeping in view the
phenomena of diminishing recharge as explained in
this article.
� Selection of aquifers to be recharged shall be
carefully done based on the usage (high) ,
permeability (high) and hydrostatic pressure (Low).
� The recharge water collection structure shall be
designed to provide required head to achieve the
desired recharge rate.
� Design of all the elements of recharge well shall
be done so as to have optimum frictional losses and
reduction in raw water turbidity for higher recharge
rate for a longer duration.
� SS 304 Stainless steel V-Wire screen technology
be used in filter pit as well screen for minimal
frictional losses, lesser entrance velocity, reduced
incrustation, acid cleaning and longer corrosion life
for a long lasting efficient recharge well.
� This article is an attempt to provide guidelines
and approach in planning a recharge project which
shall be applied judiciously by the planner
depending upon the actual site conditions from case
to case. Further research work remains to be carried
out on the guidelines given in this article to arrive
at exact hydraulic expressions to estimate the
theoretical recharge rate and conduct laboratory
studies to verify the theory.