ISO/TR 13973:2014

TECHNICAL ISO/TR
REPORT 13973
First edition
2014-11-15
Artificial recharge to groundwater
Recharge artificielle des eaux souterraines
Reference number
©
ISO 2014
© ISO 2014
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ii © ISO 2014 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope .1
2 Normative references .1
3 Terms and definitions .1
4 Artificial recharge techniques .1
4.1 Surface spreading techniques . 2
4.2 Subsurface techniques .18
4.3 Combination of surface and sub-surface techniques .27
5 Environmental impact assessment .28
5.1 Monitoring of recharge structures .28
5.2 Water level monitoring .28
5.3 Water quality monitoring .29
Bibliography .32
Foreword
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The committee responsible for this document is ISO/TC 113, Ground water.
iv © ISO 2014 – All rights reserved

Introduction
Excessive extraction/use of ground water for various applications has resulted in marked lowering of
ground water levels. Ground water levels are depleting very fast in various areas threatening ground
water sustainability and causing adverse environmental impacts. Artificial recharge to ground water
provides augmentation of ground water resources using surplus surface water available. Artificial
recharge techniques can be applied to address the following issues:
a) enhance the sustainability of ground water resources in an area where over-development has
depleted the aquifer;
b) conservation and storage of surplus water for future requirements;
c) improve the quality of existing ground water through dilution.
The following are basic requirements for recharging the ground water reservoir:
a) availability of surplus water of suitable quality in space and time;
b) suitable hydrogeological environment;
c) identification of sites for augmenting groundwater;
d) cost effective and appropriate artificial recharge techniques and structures.
Availability of source water of suitable quality is one of the prime requisites for ground water recharge.
This can be assessed by analysing the water resources available as runoff and rainfall. The physical,
chemical, and biological quality of the recharge water is important in planning and selection of recharge
method. Age of water used for recharge is also considered important in certain cases.
The hydrogeological situation in each area needs to be appraised with a view to assess the recharge
capabilities of the underlying geological formations. Detailed knowledge of geological and hydrological
features of the area is necessary for proper selection of site and type of recharge structure. In particular,
the input on geological boundaries, hydraulic boundaries, inflow and outflow of waters, storage capacity,
porosity, hydraulic conductivity, transmissivity, natural discharge of springs, water resources available
for recharge, natural recharge, water balance, lithology, depth of the aquifer, and tectonic boundaries
features such as lineaments, shear zones, etc. are required for effective and efficient artificial recharge
to ground water.
The aquifers best suited for artificial recharge are those that can hold large quantities of water and do
not release them too quickly. The evaluation of the storage potential of sub-surface reservoirs (aquifers)
is invariably based on the knowledge of dimensional data of permeable material in floodplain (alluvial),
reservoir rock which includes their thickness and lateral extent. The availability of sub-surface storage
space and its replenishment capacity further govern the extent of ground water recharge.
Artificial recharge techniques envisage integrating the surface water resources to ground water
repositories resulting in changes in the ground water regime, like
a) rise in water level,
b) increment in the total volume of the ground water reservoir,
c) availability for extended period, and
d) quality of ground water.
The upper part of the unsaturated zone is not considered for recharging since it can cause adverse
environmental impacts like water logging, soil salinity, dampness, etc.
Artificial recharge projects are site-specific and replication of the techniques even in similar areas is
to be based on the local hydrogeological and hydrological environments. Artificial recharge to ground
water is generally supported by the remote sensing studies, hydro-meteorological studies, hydro-
geological studies, hydrological studies, soil infiltration testing, geophysical studies, hydro-chemical
studies, etc. The studies bring out the potential of unsaturated zone in terms of total volume, which can
be recharged.
Artificial recharge of ground water is normally undertaken in the following:
a) areas where ground water levels are continuously declining;
b) areas where substantial volume of aquifer has already been de-saturated;
c) areas where availability of ground water is inadequate in lean months;
d) areas where studies indicate scope for improvement of quality of ground water or areas where salinity
ingress into fresh water aquifers has already taken place or is likely to happen in the near future.
vi © ISO 2014 – All rights reserved

TECHNICAL REPORT ISO/TR 13973:2014(E)
Artificial recharge to groundwater
1 Scope
This Technical Report provides details of methods aimed at augmentation of ground water resources
by modifying the natural movement of surface water as a general guide. This Technical Report does
not cover the process of deciding and planning artificial recharge within an overall water resource
management scheme.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 772, Hydrometry — Vocabulary and symbols
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 772 apply.
4 Artificial recharge techniques
A wide spectrum of techniques are used to recharge ground water reservoirs. Artificial recharge
techniques are broadly categorized as
a) surface spreading techniques,
b) sub-surface techniques, and
c) combination of surface and sub-surface techniques.
Aquifer disposition plays a decisive role in choosing the appropriate technique of artificial recharge of
ground water as illustrated in Figure 1.
Key
1 and 2 surface spreading techniques
3, 4, and 5 sub-surface techniques
6 indication of water table/piezometeric head
NOTE Local regulations might exclude certain artificial recharge options, such as aquifer to aquifer
interconnection, as shown in item 4.
Figure 1 — Recharge techniques for increasingly deep permeable materials.
4.1 Surface spreading techniques
These are aimed at increasing the contact area and residence time of surface water over the soil to
enhance the infiltration and to augment the ground water storage in phreatic aquifers. The important
considerations in the selection of sites for artificial recharge through surface spreading techniques
include the following:
a) the aquifer being recharged should be unconfined, permeable, and sufficiently thick to provide
storage space;
b) the surface soil should be permeable and have high infiltration rate;
c) vadose zone should be permeable and free from clay lenses;
d) ground water levels in the phreatic zone should be deep so as to accommodate the recharged water
without water logging;
e) the aquifer material should have moderate hydraulic conductivity so that the recharged water
is retained for sufficiently long periods in the aquifer and can be used when needed as natural
repositories.
The most common surface spreading techniques used for artificial recharge to ground water are
flooding, ditch and furrow, recharge basins, runoff conservation structures, and stream modifications.
2 © ISO 2014 – All rights reserved

4.1.1 Flooding
This technique is ideal for lands adjoining rivers or irrigation canals in which water levels remain deep
even after monsoons and where sufficient non-committed surface water supplies are available. The
schematics of a typical flooding system are shown in Figure 2. To ensure proper contact time and water
spread, embankments are provided on two sides to guide the unutilized surface water to a return canal
to carry the excess water to the stream or canal.
Flooding method helps reduce the evaporation losses from the surface water system, is the least
expensive of all artificial recharge methods available, and has very low maintenance costs.
4.1.2 Ditch and furrows method
This method involves construction of shallow, flat-bottomed, and closely spaced ditches or furrows to
provide maximum water contact area for recharge from source stream or canal. The ditches should
have adequate slope to maintain flow velocity and minimum deposition of sediments. The widths of
the ditches are typically in the range of 0,30 m to 1,80 m. A collecting channel to convey the excess
water back to the source stream or canal should also be provided. Figure 3 shows a typical plan of
a series of furrows originating from a supply ditch and trending down the topographic slope toward
the stream. Though this technique involves less soil preparation when compared to recharge basins
and is less sensitive to silting, the water contact area seldom exceeds 10 % of the total recharge area.
Three common patterns viz. lateral ditch pattern, dendritic pattern, and contour pattern are detailed as
follows and shown in Figure 4:
a) Lateral ditch pattern: the water from the stream is diverted to the feeder canal/ditch from which
smaller ditches are taken out at right angles. The rate of flow of water from the feeder canal to
these ditches is controlled by gate valves. The furrow depth is determined in accordance with the
topography and to ensure that maximum wetted surface is available along with maintenance of
uniform velocity. The excess water is routed to the main stream through a return canal along with
the residual silt.
b) Dendritic pattern: water from the stream can be diverted from the main canal into a series of smaller
ditches spread in a dendritic pattern. The bifurcation of ditches continues until practically all the
water is infiltrated into the ground.
c) Contour pattern: ditches are excavated following the ground surface contour of the area. When a
ditch comes close to the stream, a switch back is made to meander back and forth to traverse the
spread repeatedly. At the lowest point downstream, the ditch joins the main stream, returning the
excess water to it.
Key
1 stream
2 direction of flow
3 return flow
4 delivery canal
5 sheet flow
6 embankment
Figure 2 — Schematics of a typical flood recharge system
4 © ISO 2014 – All rights reserved

Key
1 stream
2 diversion structure
3 gate and measuring device
4 various recharge ditches
5 supply ditch
6 alternate diversion
7 supply ditch
8 wire bound check dam
9 collecting ditch
10 measuring device
11 prevailing ground slope
12 ditch
Figure 3 — Schematics of a typical ditch and furrows recharge system
Key
1 stream
2 diversion structure
3 control ditch
A lateral ditch pattern
B dendritic ditch pattern
C contour ditch pattern
Figure 4 — Common patterns of ditch and furrow recharge systems
4.1.3 Recharge basins
Artificially recharged basins are commonly constructed parallel to ephemeral or intermittent stream
channels and are either excavated or are enclosed by dykes and levees. They can also be constructed
parallel to canals or surface water sources. In alluvial areas, multiple recharge basins can be constructed
parallel to the streams (see Figure 5), with a view to increase the water contact time, reduce suspended
material as water flows from one basin to another, and to facilitate periodic maintenance such as
scraping of silt, etc. to restore the infiltration rates by bypassing the basin under restoration.
6 © ISO 2014 – All rights reserved

Key
1 stream
2 diversion structure
3 cut fall
4 fence as required
5 intake structure
6 sediment retention basin
7 main entrance road on levees as required
8 recharge basin
9 interbasin control structure
Figure 5 — Schematics of a typical recharge basin
In addition to the general design guidelines mentioned, other factors to be considered while constructing
recharge basins include the following:
a) area selected for recharge should have gentle ground slope;
b) the entry and exit points for water should be diagonally opposite to facilitate adequate water
circulation in individual basins;
c) water released into the basins should be as sediment-free as possible;
d) rate of inflow into the basin should be slightly more than the infiltration capacity of all the basins.
The water contact area in recharge basin is normally high and may range from 75 % to 90 % of the total
recharge area. It is also possible to make efficient use of space by making basins of different shapes to
suit the terrain conditions and available space.
4.1.4 Runoff conservation structures
These are normally multi-purpose measures, mutually complementary, and conducive to soil and
water conservation, afforestation, and increased agricultural productivity. They are suitable in areas
receiving low to moderate rainfall mostly during a single monsoon season and having little or no scope
for transfer of water from other areas. Different measures applicable to runoff zone, recharge zone,
and discharge zone are available. The structures commonly used are bench terracing, contour bunds,
contour trenches, gully plugs, check dams, and percolation tank.
4.1.4.1 Bench terracing
Bench terracing involves levelling of sloping lands with surface gradients up to 8 %and having adequate
soil cover for bringing them under irrigation. It helps in soil conservation and holding runoff water on
the terraced area for longer durations, leading to increased infiltration and ground water recharge.
For implementing terracing, a map of the watershed should be prepared by level surveying and suitable
benchmarks fixed. A contour map of 0,3 m contour interval is then prepared. Depending on the land
slope, the width of individual terrace should be determined, which, in no case, should be less than 12 m.
The upland slope between two terraces should not be more than 1:10 and the terraces should be levelled.
The vertical elevation difference and width of terraces are controlled by the land slope. The soil and
weathered rock thickness, elevation difference, and the distance between the bunds of two terraces for
different slope categories are furnished in Table 1.
In cases where there is a possibility of diverting surface runoff from local drainage for irrigation, as
in case of paddy cultivation in high rainfall areas, outlet channels of adequate dimensions are to be
provided. The dimensions of the outlet channels depend on the watershed area as shown in Table 2. The
terraces should also be provided with bunds of adequate dimensions depending on the type of soils as
shown in Table3.
Table 1 — Soil thickness, vertical difference and distance between bunds of two terraces for
different slopes
Land slope Thickness of soil and Vertical separation Distance between
% weathered rock m bunds of two terraces
m m
1 0,30 0,30 30
2 0,375 0,45 22
3 0,450 0,60 20
4 0,525 0,75 18,75
5 0,600 0,90 18
6 0,750 1,05 17,5
7 0,750 1,20 17
8 0,750 1,20 15
[1]
Source: Manual on Artificial Recharge of Ground Water, Central Ground Water Board, India, 2007.
Table 2 — Dimensions of output channels for different watershed areas
Area of watershed Channel dimensions (m)
ha
Base width Top width Depth
<4 0,30 0,90 0,60
4 to 6 0,60 1,20 0,60
6 to 8 0,90 1,50 0,60
8 to 10 1,20 1,80 0,60
10 to 12 1,50 2,10 0,60
[1]
Source: Manual on Artificial Recharge of Ground Water, Central Ground Water Board, India, 2007.
8 © ISO 2014 – All rights reserved

Table 3 — Dimensions of terraces in different soil types
Soil thickness Base width Top width Height Side slope
cm m m
m
7,50 to 22,50 1,50 0,30 0,60 1:1
22,50 to 45,00 1,80 0,45 0,65 1:1
45,00 to 90,00 2,25 0,45 0,75 1:1
>90,00 2,50 0,50 0,80 1:1
[1]
Source: Manual on Artificial Recharge of Ground Water, Central Ground Water Board, India, 2007.
In areas where paddy is cultivated, water outlets of adequate dimensions are to be provided to drain out
excess accumulated water and to maintain water circulation. The width of the outlets may vary from
0,60 m for watersheds up to 2 ha to 3,0 m for watersheds of up to 8 ha generally for rainfall intensity
between 7,5 cm and 10 cm. All the outlets should be connected to natural drainage channels.
4.1.4.2 Contour Bunds
Contour bunding is a watershed management practice which is aimed at building up soil moisture
storage involving construction of small embankments or bunds across the slope of the land. They derive
their names from the construction of bunds along contours of equal land elevation. This technique is
generally adopted in low rainfall areas (normally less than 800 mm per annum) where gently sloping
agricultural lands with very long slope lengths are available and the soils are permeable. They are not
recommended for soils with poor internal drainage e.g. clayey soils. Schematic of a typical system of
contour bunds is shown in Figure 6.
Key
1 bund
2 trench
A plan view
B section view
Figure 6 — Schematics of a contour bund
Contour bund is a construction of narrow-based trapezoidal embankments (bunds) along contours to
impound water behind them, which infiltrates into the soil and ultimately augment ground water recharge.
Field activities required prior to contour bund include levelling of land by removing local ridges and
depressions, preparation of map of the area through level surveying and fixing of bench marks. Elevation
contours, preferably of 0,3 m interval are then drawn, leaving out areas not requiring bunding such as
habitations, drainage, etc. The alignment of bunds should then be marked on the map.
The important design aspects of contour bunds are
a) spacing,
b) cross section, and
c) deviation freedom to go higher or lower than the contour bund elevation for better alignment on
undulating land.
10 © ISO 2014 – All rights reserved

4.1.4.2.1 Spacing of bunds
Spacing of contour bund is commonly expressed in terms of vertical interval (V.I), which is defined as
the difference in elevation between two similar points on two consecutive bunds. The main criterion for
spacing of bunds is to intercept the water before it attains the erosive velocity. Spacing depends on slope,
[1]
soil, rainfall, cropping pattern and conservation practices.
Spacing of contour bunds is normally calculated using Formula (1):
Vertical IntervalV.I =+0,305 XS Y (1)
() ()
where
X is the rainfall factor;
S is the land slope (%);
Y is the factor based on soil infiltration and crop cover during the erosive period of rains.
The rainfall factor “X” is taken as 0,80 for scanty rainfall regions with annual rainfall below 625 mm, as
0,60 for moderate rainfall regions with annual rainfall in the range of 625 mm to 875 mm and as 0,40 for
areas receiving annual rainfall in excess of 875 mm. The factor “Y” is taken as 1,0 for soils having poor
infiltration with low crop cover during erosive rains and as 2,0 for soils of medium to good infiltration
and good crop cover during erosive rains. When only one of these factors is favourable, the value of
Y is taken as 1,50. Vertical spacing can be increased by 10 % or 15 cm to provide better location and
alignment or to avoid obstacles.
The horizontal interval between two bunds is calculated using Formula (2):
Horizontal IntervalH.I =×V.IS100 lope (2)
()
4.1.4.2.2 Cross section of contour bund
A trapezoidal cross section is usually adopted for the bund. The design of the cross section involves
determination of height, top width, side slopes, and bottom width of the bund.
The height of the bund depends on the slope of the land, spacing of the bunds, and the rainfall excess
expected in 24 h period for 10 year frequency in the area. Once the height is determined, other dimensions
can be worked out depending on the nature of the soil.
Height of the bund can be determined by the following methods:
a) Arbitrary Design: The depth of impounding is designed as 30 cm. 30 cm is provided as depth flow
over the crest of the outlet weir and 20 cm is provided as free board. The overall height of the bund
in this case will be 80 cm. With top width of 0,50 m and base width of 2 m, the side slope will be 1:1
and the cross section, 1 m .
b) The height of bund to impound runoff from 24 h rain storm for a given frequency can be calculated
[1]
by Formula (3):
Re×V.I
H= (3)
where
H is the depth of impounding behind the bund (m);
Re is the 24 h rainfall excess (m);
VI is the vertical interval (m).
To the height so computed, 20 % extra height or a minimum of 0,15 m is added for free board and another
15 % to 20 % extra height is added to compensate for the settlement due to consolidation.
Top width of the bund is normally kept as 0,3 m to 0,6 m to facilitate planting of grasses. Side slopes of
the bund are dependent on the angle of repose of the soil in the area and commonly range from 1:1 for
clayey soils to 2:1 for sandy soils. Base width of the bund depends on the hydraulic gradient of the water
in the bund material due to the impounding water. A general value of hydraulic gradient adopted is 4:1.
The base should be sufficiently wide so that the seepage line should not appear above the toe on the
downstream side of the bund.
Size of the bund is expressed in terms of its cross-sectional area. The cross sectional area of bunds depends
2 2
on the soil type and rainfall and may vary from 0,50 m to 1,0 m in different regions. Recommended
contour bund specifications for different soil depths are shown in Table 4.
Table 4 — Recommended contour bund specifications for different soil depths
Soil type Soil depth Top Bottom Height Side Area of
m width width m slope Cross section
m m m
Very shallow soils <7,5 0,45 1,95 0,75 1:1 0,09
Shallow soils 7,50 to 23,0 0,45 2,55 0,83 1,25:1 1,21
Medium soils 23,0 to 45,0 0,53 3,00 0,83 1,50:1 1,48
Deep soils 45,0 to 80,0 0,60 4,20 0,90 2:1 2,22
[1]
Source: Manual on Artificial Recharge of Ground Water, Central Ground Water Board, India, 2007.
The length of bunds per hectare of land is denoted by the bunding intensity, which can be computed
using Formula (4):
100 S
Bunding Intensity= (4)
V.I
where
−1
Bunding is the length of bunds per hectare of land (m );
Intensity
S is the land slope (%);
V.I is the vertical interval (m).
The earthwork for contour bund includes the main contour bund and side and lateral bunds. The area
of cross-section of side and lateral bunds is taken equal to the main contour bund. The product of
cross sectional area of the bund and the bund intensity gives the quantity of earthwork required for
bunding/hectare of land.
12 © ISO 2014 – All rights reserved

Deviation Freedom: Strict adherence to contours while constructing bunds is a necessary prerequisite
for ensuring maximum conservation of moisture and soil. However, to avoid excessive curvature of
bunds, which makes agricultural operations difficult, the following deviations are permitted:
a) maximum of 15 cm while cutting across a narrow ridge;
b) maximum of 30 cm while crossing a gully or depression;
c) maximum of 1,5 m while crossing a sharp, narrow depression not exceeding 5 m in width.
4.1.4.3 Contour Trenches
Contour trenches are rainwater conservation structures which can be constructed on hill slopes, as well
as on degraded and barren waste lands in both high and low rainfall areas. Cross section of a typical
contour trench is shown in Figure 7.
Key
1 stone or vegetative barrier
2 trench
3 berm
4 spoil bank
Figure 7 — Schematics of a contour trench
The trenches break the slope at intervals and reduce the velocity of surface runoff. The water retained
in the trench will help in conserving the soil moisture and ground water recharge.
2 2
The size of the contour trench depends on the soil depth and normally 1 000 cm to 2 500 cm cross
sections are adopted. The size and number of trenches are worked out on the basis of the rainfall
proposed to be retained in the trenches. The trenches may be continuous or interrupted and should be
constructed along the contours. Continuous trenches are used for moisture conservation in low rainfall
area whereas intermittent trenches are preferred in high rainfall area.
The horizontal and vertical intervals between the trenches depend on rainfall, slope, and soil depth. In
steeply sloping areas, the horizontal distance between the two trenches will be less compared to gently
sloping areas. In areas where soil cover is thin, depth of trenching is restricted and more trenches at
closer intervals need to be constructed. In general, the horizontal interval may vary from 10 m in steep
slopes to about 25 m in gentle slopes.
4.1.4.4 Gully plug and check dam
These structures are constructed across gullies or streams to check the flow of surface water in the
stream channel and to retain water for longer durations in the pervious soil or rock surface. As compared
to gully plugs, which are normally constructed across first order streams, check dams are constructed
across bigger streams and in areas having gentler slopes. These can be temporary structures such as
brush wood dams, loose/dry stone masonry check dams, Gabion check dams, and woven wire dams
constructed with locally available material or permanent structures constructed using stones, brick,
and cement. Competent civil and agro-engineering techniques are to be used in the design, layout, and
construction of permanent check dams to ensure proper storage and adequate outflow of surplus water
to avoid scours on the downstream side for long-term stability of the dam.
The site for check dam should have permeable soils or weathered material underneath to facilitate
recharge of stored water within a short span of time. The water stored in these structures is mostly
confined to the stream course and height is normally less than 3 m. These are designed based on stream
width and excess water is allowed to flow over the wall. In order to avoid scouring from excess runoff,
water cushions are provided on the downstream side. To harness maximum runoff in the stream, a series
of such check dams can be constructed to have recharge on a regional scale. The design particulars of a
cement plug are shown in Figure 8.
The following parameters should be kept in mind while selecting sites for check dams.
a) Total basin area of the stream should normally be between 40 ha and 100 ha. Local situations can,
however, be a guiding factor in this regard.
b) Rainfall in the basin should be preferably less than 1 000 mm/annum.
c) Stream bed should be 5 m to 15 m wide and at least 1 m deep.
d) Soil downstream of the bund should not be prone to water logging and should have a pH value
between 6,5 and 8.
e) Area downstream of the Check dam should have irrigable land under well irrigation.
f) Check dams should preferably be located in areas where contour or graded bunding of lands have
been carried out.
g) Rock strata exposed in the impounded area should be adequately permeable to cause ground
water recharge.
Check dams are normally 10 m to 15 m long, 1 m to 3 m wide and 2 m to 3 m high, generally constructed
in a trapezoidal form. Detailed studies are to be made in the watershed prior to construction of the
check dam to assess the current erosion condition, land use, and water balance. The community in the
watershed should also be involved in the planning and selection of the type and location of the structure.
For construction of the check dam, a trench, about 0,6 m wide in hard rock and l,2 m wide in soft
impervious rock is dug for the foundation of core wall. A core brick cement wall, 0,6 m wide and raised at
least 2,5 m above the stream bed is erected and the remaining portion of trench back filled on upstream
side by impervious clay. The core wall is buttressed on both sides by a bund made up of local clays and
stone pitching is done on the upstream face. If the bedrock is highly fractured, cement grouting is done
to make the foundation leakage free.
14 © ISO 2014 – All rights reserved

Key
(A) Vertical section of stream (C) Vertical section of bund
1 stream bed 1 wind wall
2 depth 2 main wall
3 excavation 3 side wall
4 highest flood level 4 header wall
5 full supply level 5 apron
(B) Horizontal section of bund 6 copping in 1:2:4
1 wing wall 7 stream bed
2 main wall 8 projection
3 side wall 9 foundation wall
4 head 10 water cushion
5 key wall (D) Plan
6 outlet 1 crip length
7 top
8 water cushion
9 toe wall
Figure 8 — Design of a check dam
4.1.4.5 Percolation tank
A percolation tank is an artificially created surface water body submerging a highly permeable land
area so that the surface runoff is made to percolate and recharge the ground water storage. They
differ from bunds in having larger reservoir areas. They are not provided with sluices or outlets for
discharging water from the tank for irrigation or other purposes. However, they may be provided with
arrangements for spilling away the surplus water that might enter the tank, so as to avoid over-topping
of the tank bund.
A basin may have more than one percolation tank if surplus runoff is available and the site characteristics
are also favourable for artificial recharge through such structures. In such situations, each tank
intercepts a share of the yield of the whole basin above it, which can be classified as
a) “free basin”, which is the basin area that only drains into the tank under consideration, and
b) “combined basin”, which is the area of the whole basin above the tank.
The difference between the combined basin and free basin gives the area of the basin intercepted by the
tanks located upstream of any tank. The whole basin of the highest tank on each drainage shall be its
free basin. Moreover, each tank will receive the whole runoff from its free basin, but from the remainder
of its basin, it will receive only the balance runoff that remains after the upper tanks have been filled.
4.1.4.5.1 Site selection criteria
The important site selection criteria for percolation tank include the following.
a) The strata in the area of submergence of the tank should have high permeability. The soils in the
basin area of the tank should be sandy to avoid silting up of the tank bed.
b) The availability of non-committed surplus runoff should be sufficient to ensure filling of the
tank every year.
3 2
c) As the yield of basins in low rainfall areas generally varies between 0,4 million m /km to 0,6 million
3 2 2 2 2
m /km , the basin area can be up to 5,0 km for small tanks and between 5,0 km and 8,0 km for
larger tanks.
d) Size of a percolation tank should be governed by the percolation capacity of the strata, as well
as basin yield. In order to avoid loss of water through evaporation, larger capacity tanks should
be constructed only if percolation capacity is proven to be good. If percolation rates are low to
moderate, tanks of smaller capacity may be constructed. Percolation tanks are normally designed
for storage capacities of less than 1 million m .
e) The depth of water impounded in the tank provides the recharge head and hence, it is necessary to
design the tank to provide a minimum height of impounded water column of 3 m to 6 m and rarely
6 m above the bed level. This would imply construction of tanks of large capacity in areas with
steep gradient.
f) The purpose of construction of percolation tanks is to ensure recharge of maximum possible
surface water runoff to the aquifer in as short a period as possible without much evaporation losses.
Normally, a percolation tank should not retain water beyond February.
g) The percolation tank should be located downstream of runoff zone, preferably toward the edge of
piedmont zone or in the upper part of the transition zone. Land slope between 3 % and 5 % is ideal
for construction of percolation tanks.
h) There should be adequate area suitable for irrigation and sufficient number of ground water
abstraction structures within the command of the percolation tank to fully utilize the additional
recharge. The area benefited should have a productive phreatic aquifer with lateral continuity up
to the percolation tank. The depth to water level in the area should remain more than 3 m below
ground level during post-monsoon period.
4.1.4.5.2 Investigations required
An area, preferably the entire watershed, needing additional ground water recharge is identified on
the basis of declining ground water level trends increase in the demand of ground water and water
scarcity during lean period, etc. Areas having scarcity of water despite incidences of flood may also be
considered for artificial recharge through percolation tanks.
A base map, 1:25 000 or detailed scale showing geological, physiographical, hydrogeological, and
hydrological details along with land use, cropping pattern, etc. is a pre-requisite for the scientific
16 © ISO 2014 – All rights reserved

planning. Topographic maps, aerial photographs, and satellite imagery of the area may be consulted
to gather preliminary information about the area under study. The nature of basin with regards to the
general slope, land use, forest cover, cropping pattern, soils, geology, etc. should be understood to assess
their influence on runoff.
The rainfall data of rain gauge stations located in the watershed or in its immediate vicinity is to be
collected during the preliminary investigations. The intensity and pattern of rainfall, number of rainy
days, and duration of dry spells during the monsoon are to be analyzed. The dependability of normal
monsoon rainfall and the departure of actual rainfall from normal rainfall are also worked out along
with other weather parameters.
Percolation tanks are to be normally constructed on second or third order streams, as the basin area
of such streams would be of optimum size. The location of tank and its submergence area should be
in non-cultivable land and in natural depressions requiring lesser land acquisition. There should be
cultivable land downstream of the tank in its command with a number of wells to ensure maximum
benefit by such efforts. Steps should be taken to prevent severe soil erosion through appropriate soil
conservation measures in the basin. This will keep the tank free from siltation which otherwise reduces
the percolation efficiency and life of the structure.
Micro-level geological/hydrogeological map is required in the area of submergence, at the tank site, and also
downstream of the site to find out the permeability of vadose zone and aquifer underneath. The potential of
additional storage and capacity of aquifer to transmit the ground water in adjoining areas is also assessed
based on aquifer geometry. Infiltration rates of soils in identified area of submergence are determined
through infiltration tests. Aquifer parameters of water-bearing formations in the zone of influence are also
determined to assess the recharge potential and number of ground water structures in the area.
Periodic water level measurements and ground water sampling for water quality are required before
and after the construction of percolation tanks. Detailed geological investigations are carried out to
study the nature and depth of formation at the bund (dam) site for deciding the appropriate depth of
cut off trench (COT). It helps in reducing the visible seepage and also ensures safety and long life of the
structure. The depth of foundation and its treatment should be considered on the basis of nature of
formation while designing and constructing the dam wall and waste weir.
4.1.4.5.3 Engineering aspects
A percolation tank is commonly an earthen structure with a masonry spill way. It is designed for
maximum capacity utilization, long life span, cost-effectiveness, and optimum recharge to ground water.
Storage capacity, waste weir, drainage arrangements, and COT are the important features of percolation
tank that need proper design. The overall design of the percolation tank is similar to that of a small
earthen dam constructed for irrigation.
Detailed topographical survey to demarcate the area of submergence in natural depression and alignment
of dam line in the valley is to be taken up prior to construction of the structure. A number of sections
along and across the drainage are prepared and the best suitable site is identified. The land availability
and possibility of land acquisition is explored during the survey. The spillway site is demarcated and is
designed in such a way that it allows the flow of surplus water based on single day maximum rainfall
after the tank is filled to its maximum capacity. The depth of foundation for masonry work of waste weir,
etc. is decided depending on the nature of formation. COT is provided to minimize the seepage losses
across the streambed. The depth of COT is generally 2 m to 6 m below ground level depending upon the
subsurface strata. In order to avoid erosion of bund due to ripple action, stone pitching is provided in the
upstream direction up to high flood level (HFL). The sources for availability of constructional material,
especially clay and porous soil for earthwork and stone rubble for pitching, are to be identified.
4.1.4.5.4 Design of Storage Capacity
The storage capacity of a percolation tank may be defined as the volume of water stored in the tank
up to the full tank level (FTL). The storage capacity can be computed by using the contour plan of the
water-spread locale of the tank. The total capacity of the tank will be the sum of the capacities between
successive contours. The smaller the contour interval, the more accurate the capacity computation will
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