GW

1. GROUNDWATER MANAGEMENT
This topic extends the ideas of groundwater development in addressing questions of how
a groundwater resource as a whole is managed and some of the important tools and
strategies.
Water is a resource that can be readily transported to achieve a better balance between the
location of its supply and the demand for its use. Unlike petroleum, groundwater is not a
minority fluid in the substance environment and its value is not normally determined by
the market place. However, groundwater can be non renewable, at least when viewed
with in human time frame, and its exploitation is subject to supply and demand. In areas
with abundant surface water, groundwater is frequently an under exploited resource.
Conversely, in areas without surface water supplies, groundwater is almost always our
exploited. In areas between these extremes, the development of total water resource
depends on the demand for water. How the total water resource system, in both cases is
developed and the manner in which it is operated depends not only on the availability of
supply but on legal, political, and socio economic precedents and constraints.
Groundwater Management Strategies
This section explores in more detail some of the issues related to the management of
groundwater basins. The California State department of Water Resource (1980)
describes groundwater basin management in the following terms.
Groundwater basin management includes planned use of the groundwater basin yield,
storage space, transmission capability and water in storage. It includes
1. Use of artificial recharge
2. Planned variation in amount and location of pumping over time
3. Use of groundwater storage connectively with surface water from local and
in ported sources, and
4. Use of groundwater dams
5. Protection and planned maintenance of groundwater quality
A) Artificial Groundwater Recharge
Groundwater recharge may be described as the process whereby the amount of water,
either present in or flowing through the interstices of the subsoil, increases by natural or
artificial means. Considering the aquifer in the figure below, natural recharge may be
subdivided into:
Sub divided into:
a) Downward percolation of rainfall through permeable strata to the groundwater
body

2. b) Infiltration of surface water through the permeable beds of a river or lake
c) Inflow of groundwater from adjacent water bearing formations into the aquifer
under the consideration.
Fig. Groundwater cycle
At the same time, however, the aquifer loses groundwater, its natural components
being:
d) Evaporation
e) Discharge by springs and subsurface outflow into effluent streams
f) Percolation to neighboring aquifers through the boundaries.
In the long run, natural recharge equals natural discharge and a near-stationary water
table occurs with seasonal fluctuations around an average level.
Fig. water table variation in a strip of land as a result of residual rainfall during rainy
Season
Artificial abstraction of groundwater from an aquifer, however, lowers the groundwater-
table, increasing natural recharge and decreasing natural discharge in its turn. Natural
Artesian aquifer
Residual rainfall
Influent river
Discharge
aquiclude
aquifer
Level in summer
Level in winter
Winter summer winter

3. recharge is increase by a shift of the water divide, which enlarges the catchment area and
by increased infiltration of surface water from influent streams.
The discharge is decreased by reduction of evapotranspiration losses, by a smaller return
of groundwater to the surface and by reduced percolation to adjacent aquifers. As long as
the amount of artificial recovery is limited, the resulting increase in recharge together
with decrease in discharge, will balance this abstraction and a new equilibrium situation,
or steady state is reached. In order to study these phenomena in more detail the figure
below shows a simplified case of an unconfined aquifer above an impervious base. Only
one river intersects this basin. This river receives the major part of the recharge by
rainfall, while a minor part is discharged by a spring at the right.
Fig. Normal groundwater cycle Fig. artificial groundwater
abstruction of limited capacity
Fig. artificial groundwater abstruction Fig. maximum artificial groundwater
with bank infiltration abstruction
Precipitation minus evapotranspiration
Water divide
Water divide
Artificial abstructionn

4. For artificial abstraction of groundwater, a line of wells is set at some distance parallels to
the river. As a result of abstraction of even a small magnitude, an appreciable draw down
of the groundwater table occurs, drying up the spring at the right and decreasing the
overflow of groundwater into the river. When more water is abstracted than balanced by
the recharge by rainfall, a further draw down of the water table occur. Yet a stationary
situation is still possible, the balance being made up of river water entering the aquifer
through the riverbanks. Due to clogging of the riverbed, however, the amount of bank
infiltration will decrease to a certain limit. The maximum possible amount of bank
infiltration can be reached if further larger abstraction of groundwater is there, to lower
the water-table. Then further increase in artificial abstraction will not induce an increase
of this recharge. The deficit is to be taken from storage, inducing a further and
continuously proceeding draw down of drawdown of the groundwater-table and
permitting such abstraction for a limited period only. From these observations it may be
clear that under the given geohydrological conditions the maximum possible groundwater
abstraction reduces the outflow to zero and maximize the amount of water entering the
aquifer. Especially in more complicated situations the determination of the physical
maximum possible abstraction is not easy, but it is otherwise a straightforward process,
depending on the meteorological and geohydrologic considerations only.
The maximum permissible groundwater abstraction abstraction, the so-called safe yield
of the formation, is the only part of the maximum possible one. It occurs when the
pertaining drawdown of the groundwater-table becomes objectimable, or when the
increase in catchment area, together with a reversal of outflows, attracts water of
undesirable chemical or bacteriological quality, that may endanger the quality of the
water to be abstracted. It will there fore be clear that next to physical factors, like climatic
and geohydrologic factors, the magnitude of this maximum permissible abstraction
depends on subjective consideration regarding the environment, legislation, politics,
aesthetics, etc. This makes the determination of the safe yield of a catchment very
difficult if not impossible.

5. Fig: influence of groundwater abstraction on the position of the water divide.
The safe yield of an aquifer, as defined above, is rather low and commonly lies between
20 and 80% of the recharge by residual rainfall. In its turn this residual rainfall varies
from near zero in desert areas to values of 1000mm/year and more in wet climates where
a pervious soil and a flat topography is present. Fortunately there is a way to improve the
groundwater recharge, namely by increasing the amount of natural recharge by artificial
means.
Artificial recharge may be defined as the planned activity of man by which surface water
from stream and lakes is made to infiltrate the ground, usually at rates and in quantities
many times in excess of natural recharge, giving a corresponding increase in the
magnitude of the safe yield. There are many methods by which groundwater supplies
may be artificially increased. Yet they may be classified into broad groups, as follows.
1) Indirect method
2) Direct method.
Indirect artificial groundwater recharge methods.
The indirect methods, also known as induced groundwater recharge methods, are the
methods by which increased recharge is obtained by locating the means of groundwater
abstraction as close as practicable to areas or sources from which the natural discharge
may be diverted and tapped.
The most common method of induced recharge consists of
-Setting galleries or a line of wells at a short distance- say 50m parallel to the bank
of a river or lake.
When a small amount of groundwater are abstracted from the galleries parallel to the
river, the groundwater discharge into the river will decrease, while the water abstracted
by the gallery will entirely consist of natural groundwater, originating from rainfall on the
area to the right of the river. Each groundwater abstraction, however, is accompanied by
a draw down of the water table. With high rates of abstraction, the abstracted water
consists for a small part of natural groundwater and for a large part of artificial
groundwater originating from the river if the permeability of the streambed is high. That
is, if the aquifer has a large value for the coefficient of permeability, enormous amounts
of groundwater may be abstracted from the galleries, without serious adverse effect on
the water table more inland or on the discharge of other rivers crossing the area.
The most serious threat of the applicability of the induced recharge for public water
supplies today is the always-present danger of catastrophic pollution of river water by
mistaken industrial discharges, colliding ships, crashed lorries etc. For a short time, the

6. water in the river may contain outright poison then that cannot be withheld by
underground flow.
It goes without saying that this asks for an immediate cessation of groundwater
abstraction when the treatment works cannot cope with this type of pollution, even when
this leaves population and industry within the supply area without water.
Direct artificial G, W. Recharge methods
These are methods by which water from surface sources is conveyed, over considerable
distances, to suitable aquifers where it is made to percolate in to a body of groundwater.
Compared with the induced recharge of the preceding section, this scheme has many
advantages of which most important are:
a) Before the water enters the aquifer, it may be cleaned by treatment, removing
suspended matter, in order to prevent as much as possible clogging of the
infiltration basins, and removing or changing other substances [e.g. phosphates,
Nitrates] which could pollute or react unfavorably with the water and soil
particles present in the aquifer, or cause unfavorable environmental conditions in
the infiltration basin (e.g. Algae), on the banks of infiltration basins and
abstraction ditches and in the abstraction diches, or in zones with out flowing
groundwater.
b) In case clogging of the recharge basins occurs, they can be easily cleaned and
restored to their original capacity by draining, drying and scraping.
c) During (short)periods with an unfavorable quality of the river water, recharge
may be interrupted while abstraction continue, the abstracted water coming form
the stock of groundwater built up in the aquifer by infiltration during the
preceding periods of good river water quality.
The direct recharge methods may be classified into three groups
1) Artificial recharge by flooding or infiltration basins.
- It is applicable when the aquifer reaches or nearly reaches the ground surface.
2) Artificial recharge by means of pits and shafts

7. - It is applicable when the aquifer is situated at a moderate depth below the ground
surface.

8. Fig: direct recharge to shallow aquifer using ditches and drains.
3) Artificial recharge by injecting wells.
- It is applicable when the overburden has a large thickness, or when environmental
objections impede the application of artificial surface infiltration.
Artificial recharge by injection well has the greatest versatility as it can be applied
for all aquifers, confined or unconfined, situated at any depth below the ground
surface. Pits and shaft suffer from danger of clopping, necessitating an intensive and
often expensive pretreatment of the water to be recharged, together with the used of
special well construction that allows easy and thorough cleaning.
Objectives of artificial Recharge of G.W.
In management of water resources, the man made increase of the amount of surface water
entering an aquifer is practiced, in order to allow for a larger rate of groundwater
abstraction. The underlying reasons for this procedure are quite varied. Most important
are:
a) Storage
b) Equalization of water quality
c) Transportation of water
d) Maintenance and restoration of groundwater levels.
Storage

9. In case an unconfined aquifer has its water table at a great depth, artificial recharge may
raise the phreatic level, thus increasing the stock of groundwater, with out the danger of
flooding low-laying areas.
This under ground storage does hardly do any damage to the environment, while in flat
and densely populated countries, in particular, it is much easier and cheaper to provide
this type of storage than surface.
Maintenance and restoration of groundwater level:
The draw down of the groundwater-table as mentioned in the preceding paragraphs may
also be objectionable by it self, as it may injure the environment (flora, fauna) harm the
agricultural use of the lands concerned, damage buildings, and other civil engineering
works by soil subsidence or the rotting of wooden pile foundations. It may also cause
attraction of water from neighboring areas. In case this water is of low quality, salt water
for instance, mixing with native water will make the aquifer unfit as a source for drinking
water supply. Again artificial recharge may be practiced to prevent these negative effects.
Equalization of water quality & purification
When water from river or lake is made to flow through a fine grained aquifer, filtration
will occur, removing the major parts of the suspended and colloidal load, reducing the
number of bacteria and other organisms and brining about important change in the
chemical quality of the infiltrated water. The aquifer acts as a slow sand filter, the water
will be clear and free from pathogenic organisms provided that distance and time of
travel are not too small say more than 50m and 2 moth respectively, allowing its direct
use as drinking water in many instances.
Transport of water:
In many urban and industrialized regions, over pumping may deplete groundwater
reservoirs, and dry up wells and force consumer to look for other sources of water,
usually drinking water from a public supply system. This is expensive for the community
concerned, and it may be avoided when artificial recharge of aquifer is possible for
instance at a local outcrop (fig). The aquifer serves as a conduit to bring river water from
the intake to the various points of abstraction. Only under favorable circumstances,
however, adequate supply may be obtained.

10. B) Conjugative Use
Connective use involves the coordinated use of surface and ground water to meet some
specified water demand in a given area.
The following questions are associated with conjunctive use.
1. What system has to be built to minimize the discrepancy (in time, space and
quality) between the natural supply of water and the demand for it.
2. To what extent should the water resource system be developed and how extensive
should the region serviced be?
3. How should the system be operated so as to achieve a given set of objective in the
best possible way.
The conjunctive use can be operated on the basis of
1. Interconnected stream –aquifer system
- the hydraulic connection between the two sources plays a major role.
- the objective this basis might be to use the total resource in such a way as to
maximize benefits.
2. Marginal value rule
the importation should take place when the cost of importation equals the cost of
mining groundwater or less.
3. Issues of riparian protection
to maintain the ecological health of riparian ecosystems through the management
of groundwater and surface water systems

11. C ) Groundwater Dams
Conventional dams for water storage are built across a river or stream to collect water in
open reservoir upstream of the dam. But a groundwater dam is constructed to obstruct the
flow of groundwater and store it below the ground surface. It may serve as a collecting
structure that diverts groundwater flow, for instance to recharge adjacent aquifer or to
raise the water table in an aquifer to make it accessible for pumping.
Ground water dams may be of two types, subsurface dams and sand -storage dams. A
subsurface dam is constructed below the ground level to arrest the groundwater flow in
the natural aquifer, whereas a sand-storage dam is constructed to impound water in
sediments caused to be accumulated by the dam itself.
A groundwater dam can also be a combination of the two types described above.
The advantages of using the groundwater dams:
The advantages of using groundwater dams instead of common storage are many. Some
of them are the followings.
 Evaporation losses are reduced or even completely avoided.
 It is not subject to the reduction of the design storage capacity by siltation and
vegetal growth
 The water stored is less susceptible to pollution and health hazards such as
mosquito breeding and spreading of the snail fever.
 The land above the stored water can be used for other purposes.
Design considerations of groundwater dams
1) Physical conditions
a. Climate: The need to dam the ground water is basically caused by an
irregularity of rain fall distributions over time. Every drop of water from rain
fall should be saved in all dry, monsoon, and tropical wet-and-dry climate
areas of the world.
b. Topography:
Topographical conditions govern to large extent the technical possibilities of
constructing the dams as well as achieving large storage reservoirs with
suitable recharge conditions and low seepage losses. The basin in which water
is to be stored may be underlain by bedrock or unconsolidated formation of
low permeability.
It is generally preferable to site groundwater dams in well defined and narrow
valleys or river beds to reduce cost and possible seepage losses. On the other

12. hand, storage volumes have to be maximized. In mountainous areas with very
high surface gradient, it might be difficult to find acceptable storage volumes.
The gradient of water table mostly coincides with the ground surface gradient.
This fact indicates that the construction of groundwater dams is feasible only
bat certain minimum topographical gradient, which will vary according to the
local hydrogeological conditions. Generally the gradient has to be 0.2- 4% .
But in extreme cases construction has been made on slopes of 10-16%.
The topography of the impervious beds or bedrocks underlying storage
reservoirs also determines the storage efficiency and method of dam
construction
c. Hydrogeology:
The most favorable aquifers for construction of subsurface dams are river
beds made up of sand or gravel
In situ weathered layers and deeper alluvial aquifers have also been dammed
with success, even if such aquifers generally have less favorable storage and
flow characteristics
d. Sediments:
For sand-storage dams, the type of parent materials in the catchments from
where sediments originate, determines the amount of coarse particles in the
total sediments which in turn determines the storage capacity of the formation.
The most favorable rocks are coarse granite, quartzite and sand stones.
The areas where the dominant rocks are basalts and rhyolites tend to be less
suitable for sand- storage dams.
2) User aspects
a. Water use alternatives:
The user alternatives (domestic or irrigation) are determined by the volume of
the water that can be stored.
3) Organizational aspects
4) Economical aspects