Accepted Papers - 3.pdf - UNESCO

particular command area in which the ground water
is to be recharged.
� Conduct a study of pumping wells under use
in the command area and find out total pumping
quantity per day and main aquifers used.
� Study the types of aquifers from the point of
view of their permeability and hydrostatic pressure
and select the aquifers needed to be recharged.
� It is a known fact that the aquifers form long
linkages to longer distances and may have different
elevations at different points. Map the linkages of
selected aquifers around command area.
� It is well known that the ground water
movements in the aquifer occur from a place where
the ground water has higher energy to the places of
low energy. Theoretically as per the Bernoulli
equation the energy contained in ground water
comprises of – Pressure, Velocity and Elevation. But,
practically the pressure remaining more or less same
at various points and the velocity energy being
negligibly small the significant one is the elevation
energy. As per this concept the ground water
movement will be more from a point of higher
elevation to a lower elevation and velocity of
movement is directly proportional to the difference
in elevations of the two points. According to this
argument select a recharge site location having
maximum possible elevation on the aquifer map as
compared to the average elevation of the same
aquifer at the pumping wells in the command area.
While doing this care must be taken not to increase
the distance to be traveled and care shall also to be
taken to avoid any blockage or drainage in the path.
� Basically a trade is to be achieved between the
elevation, distance and possibility of getting enough
rain water while making a final selection. If any dam
if available in the vicinity it may be a good idea to
make a diversion from dam at certain height to an
artificial recharge structure so that when the water
level rises above certain level in the dam during
monsoon the recharge collection pond is filled at
higher elevation.
� Having selected the site make an artificial
catchment for collecting the rain water. The storage
capacity shall be decided based on the data of water
drawal from the selected aquifers by the pumping
wells in the command area and availability of
recharge water.
� The design of the catchment shall be deeper
366
and narrower. We will study the reason later in the
article.
� Design of recharge well
Having selected the site to give optimum
ground water movement from recharge point to the
pumping point the next crucial step is to design a
recharge well to achieve optimum recharging
efficiency and make use of the natural water energy
to the maximum extent possible. To understand the
phenomena taking place let us first understand the
well hydraulics concept. (Please note that only the
concept is highlighted and not the exact calculations
to simplify the topic for ease of understanding the
basic concept before going into the intricacies of
calculations).
� Well hydraulics
The fundamental principle : Simplifying the whole
process the recharge is basically to inject water into
the aquifers by utilizing the static head of the water
above the aquifer level. It is a sort of Injection well
where no positive pumping is used to inject the
water. This means that the possibility and rate at
which the water will be injected into the aquifer is
basically a function of available static head above
the aquifer being recharged. This can be explained
as a short expression as follows –
The Rate of Recharge Q R á Effective Head H eff
………………(1)
The Effective Head H eff : The effective head is the
useful injection pressure available. In a recharge well
condition there is a head of recharge water collected
above the well which is the distance between the
top of the water level in the recharge structure and
the bottom of the aquifer being recharged
(henceforth termed as H R and there is a hydrostatic
pressure of water already available in the aquifer
acting opposite to each other and there are several
points of frictional head losses (henceforth termed
as H f ) which consume the available head. The
hydrostatic pressure of water inside the aquifer is
the distance between the static water level in the
well in absence of recharge water and the bottom of
the aquifer being recharged (henceforth termed as
H aq ). Fig. 1 clarifies the terminology. Accordingly
the effective head can be expressed as follows –