IS 13939: Farm Drainage--Interceptor Drains for Steep Hill Slopes Under Plantation Crops--Guidelines for Laying

12 Pages·1994·1.3 MB·English

by  Bureau of Indian Standards (BIS)

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IS 13939 (1994, Reaffirmed 2009): Farm
Drainage--Interceptor Drains for Steep Hill Slopes Under
Plantation Crops--Guidelines for Laying. UDC 626.861 :
631.62
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( Reaffirmed 1998 )
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Indian Standard
FARM DRAINAGE-INTERCEPTOR
DRAINS FOR STEEP HILL SLOPES UNDER
PLANTATION CROPS-GUIDELINES
FOR LAYING
C BIS 1994
BUREAU OF INDIAN STANDARDS
MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG
NEW DELHI 110002
February 1994 Price Group 4
Farm Drainage Equipment and System Sectional Committee, F ADC 28
FOREWORD
This Indian Standard was adopted by the Bureau of Indian Standards, after the draft finalized by the
Farm Drainage Equipment and System Sectional Committee had been approved by the Food and
Agriculture Division Council.
Influence of high rainfall, steep slopes and complex nature of the underlying rocks present at shallow
depth, result~ in drainage problem of special nature in soils with plantation crop in areas like Darjeeling,
some parts of Dooars, Terai of Nortn Bengal, Cachhar of Assam and Tea areas of South India. High rain
fall on tine textured soils results in soils of low permeability which becomes suscepetible to and are
aggravated by com paction, surface capping and natural. and chemical cultivation pans. These soil~ often
develop structureless layers at depth which makes natural drainage of subsoil excess water Vf'ry djfficult.
The soil strata of different permeability give rise to springs along their outcrops some of which are merely
seasonal whilst others flow throughout the year. A spring Or spring hoe often adversely affects a considera
ble area of land under plantation crop in different parts of the. country.
The seepage flow at shallow depths in the rootzone causes serious water logging that decays tea roots and
restricts the uptake of essential nutrients required for optimum growth of test The subsurface seepage flow
under exc~ssive hydrostatic pressure causes land slide problem at places. Well designed interceptor drain
age system have been found useful in reducing the problenl of water logging and land slide by releasing
the hydrostatic pressure of the soil. The true interception occurs when the hydraulic gradient of the
undisturbed water table is 1 percent or greater.
In view of the importance of such drains, a need was felt to preplre this standard for providing guidelines
for designing and laying of interceptor drains.
In preparation of this standard, assistance has been derived from Tocklai Experimental Station, Tea
J
Research Association orhat.
IS 13939 c 1994
Indian Standard
FARM DRAINAGE -INTERCEPTOR
DRAINS FOR STEEP HILL SLOPES UNDER
PLANTATION CROPS- GUIDELINES
FOR LAYING
1 SCOPE 5.2 Nature ( phreatics or artesian) and direction
of groundwater flow shall be determined.
This standard provides guidelines for designing
5.3 Lateral extension, thickness, slope, hydraulic
and laying interceptor drains in hill sloping lands,
conductivity and drainable porosity of the water
with plantation crops.
bearing strata shall be determined.
2 REFERENCE
5.4 Water table and hydraulic head shall be
The following Indian Standard is a necessary measured. The observation wells for water table
adjunct to this standard: measurements and piezometers for the pressure
head should be installed in phreatic and semi
IS No. Title
confined or confined aquifers. Spacings of 50
IS 9979 : 1981 Code for design and laying of
metres are suggested. Hydraulic head may be
mineral filters for tile drain
obtained by adding appropriately gravitational
system
head and pressure head. The readings should be
used to draw water table contour maps as well a<;
3 TERMINOLOGY
hydraulic head difference maps.
3.0 For the purpose of this standard, the foHowing 5.5 The depth of impe rvious Jayers shall be
definition shall apply. obtained. Physical (auger hole/soil profile
exposition) or geophysical (geoelectric or
3.1 Interceptor Drain
seismic) method shall be applied to determine the
The drain in which all ground water flow enters depth of impervious layer.
from the upslope side.
6 INTERCEPTOR DRAINAGE SYSTEM
NOTE - True interception occurs when the hydraulic
gradient of the undisturbed water table is 1 percent or 6.1 Type of System
more.
Interceptor drain should be installed to collect
4 SOURCES OF EXCESS WATER lateral or horizontal flow coming from known
upland areas, thus preventing it from reaching the
4.1 The major source of exce3S water may be as
area to be protected. In many instances, a single
follows:
interceptor line proves to be an adequate remedial
a) Seepage from Up-land - Foreign ground measure. The interceptor usually should be placed
water inflowing from adjacent land or from at the upper boundary of the wet area. Intercep
a river or from an irrigation canal whose tor drain should be planned as single random
water level is higher than the water table drain or as a series of parallel drains. They are
in the area under plantation. required where soils are relatively permeable and
b) High rainfal1 received in the area under table where the gradient of the water table is
plantation. reJatively steep
4.2 It is important to estimate the amount of 662 Location of Drain
excessive seepage from upland and identify the
The location of an interceptor drain, as they are
locations.
observed quite commonly in the areas with
5 FIELD INVESTIGATION plantation crops, are given below.
5.0 Before starting the designing and laying of 6.2.1 Abrupt Change in Topography
the interceptor drains, the following investigations
This is a situation of large valleys where the land
shall be made.
is subject to seepage from upland. An abrupt
5.1 Delimitation of the waterlogged area by field change in land is subject to seepage from upland.
inspection and the use of aerial photographs, if An abrupt change in land slope from steep to flat
available, shall be made. causes a rise in water table at the base of the slope
1
IS 13939 : 1994
or a terrace. In such cases, the water table surface corrective measure is to lower the water table in
is found close to a straight 1ine or fiat curve this area bY'an interceptor drain instaUed at the
extending from the water surface in the stream to base of the hill land or at the base of a higher
some distant point beneath the terrace. The' terrace ( su Fig 1 ).
G.L
HIGH WT AREA
~I
-----.WT A-FTE-R -DRA-INA-GE- _
..... .......
INTERCEPTER DRAIN
FlO. 1 LOCATION OF INTERCEPTOR DRAIN VVHERE SLOPE CHANGES ABRUPTLY
FEOM STEEP TO FLAT
6.2.2 Impervious Layer Close to Ground at the foot of the slope. An interceptor drain shall
be provided at the foot of the slope to control the
At points, the impervious layer rises close to the
water table in the lower reaches ( see Fig. 3 ).
ground surface under natural conditions. It causes
the hydrualic grade line or water table surface to 6.2.4 Morl! Permeable Layer Sandwitched Between
rise to near the ground surface. This situation is Poor(v Pervious Layers
often found in alluvial flood plains where ancient
channel changes have built up barriers of fine In some situations the permeable layer outcrops
gained sediments. The corrective measure may he and causes a seep affecting a considerable area
an jnterceptor drain just upslope from the barrier below. This occurs when soil is highly stratified
(see Fig. 2). with exposed outcrop. Such permeable layers
carry a considerable groundwater with hydraulic
6.2.3 Seepage at the Foot of a Slope grade line that intercept the ground surface at
s;);ne point in the outcrop area causing a natural
A commonly observed situation in hills is a sudden seep. An interceptor drain should be located at
drop in ground elevation. The land slope mayor the base of the permeable material to collect the
may not remain the same. It causes water tables flow from the aquifer and prevent seepage at the
to rise close to ground surface in the lower reaches ground surface ( see Fig. 4 ).
2
IS 13939 : 1994
G.L
INTERCEPTER DRAIN
HIGH W'T AREA
---.I:::""!-_
WT BEFORE DR-AIN-A-GE ------ ---
WT AFT ---___
ER Dr. ...... ....
ltAINAGE ................
'-..,.
IMPERVIOUS LAYER
FIG. 2 LOCATION OF INTERCEPTOR DRAIN WHERE IMPERVIOUS LAYER COMES CLOSE
TO GROUND SURFACE
6.2.5 Seepage from Water Channel almost equal. On steeper slopes there is a bridging
over effect produced by the flow of foreign water
A considerably high amount of seepage flow
in the capillary fringe above the phreatic water
occurs into the lower areas from water channels
surface. This bridging effect may not occur in an
and causes waterlogging. An interceptor drain
open drain. The escape of lateral flow over the
constructed some distance below the water
top of the pipe drain line may range from 5 to
channel can take care of waterlogging and control
20 percent depending on the nature of soil and
water table below the rootzone ( see Fig. 5 ).
slope.
6.3 Drain Type
6.4 Drain Depth
The choice between an open drain and a pipe
drain depends on soil profile characteristics and An interceptor drain should be placed as deep as
slope of 1and. The soil profile characteristics it is practical to install, preferably along the top
should be given more weightage in making the of the impervious layer so as to intercept the
decision. Underlying soil having loose formation maximum amount of seepage flow. In case of pi pe
should not be cut open and requires only close drains, the trench of the drain shall not be cu t
systems. Open system should be used if a mini into the impervious layer otherwise a significant
mum depth of stable soil is available after 60 cm percentage of lateral flow will bridge over the
below the designed depth of the drain. In land drain line and continue on down slope. The pipe
with slope upto 3 percent or so, the efficiency is drains shall be installed with suitable envelopes
3
IS 13939 : 1994
G.L
G.L
---
-
--
....... ..... ,
,
...... ,... ... ..............
....
....... ,
..... HIGH W.T. AREA
,
" .....
"
"'-
"
"
'"
'-, -
INTERCEPTER DRAIN
.......
Fro. 3 LOCATION OF INTERCEPTOR DRAIN AT THE FOOT OF A SLOPE
resting on the impervious layer so that maximum installed progressively accomplished by digging
amount of water is intercepted. the first drain to protect the higher portion of the
wet area and lower drains can be dug after
6.5 Filter
evaluating the effect of the first drain.
Organic, mineral and synthetic filters may be
6.7 Amount of Flow Intercepted
used ( see IS 9979 ; 1981 ).
The quantity of lateral flow intercepted by a drain
6.6 Drain Spacing
is dependent on the position of the drain. About
Proper location of interceptor drain is very 50 percent of the flow is intercepted if the drain
important. In many instances, a single interceptor is placed at the mid point between the water
line may prove to be adequate. They can be table and impervious layer. If the drain is placed
effective for a considerable distance downslope three fourths of the way down about 75 percent
from the drain but the upslope effect is usually of the flow will be intercepted. If it is possible to
very small and can be ignored. The spacing of install drain at impervious layer, nearly 100 per
interceptor drains ranges between 60 and 150 m cent of the foreign groundwater can be intercep.
based on practical experience. The spacing, how ted. It is desirable to estimate the amount of water
ever, shall depend upon land slope(s), soil hydrau. . flowing past the point of interception. By position ..
lie conductivity(k). thickness of soil layer being ing the drain device in the profile, the probabJe
intercepted for seepage flow, relative position of quantity of water to be drained can be measured.
interceptor drain with respect to impervious layer Roughly, the quantity varies directly with the
and amount of seepage flow. The system shall be depth of flow intercepted.
4
IS 13939 : 1994
G.L
WT RECEPTO~ DRAIN
POORLY HIGH WT AREA 1
~-T -BEFORE DRAINAGE
'PERVIOUS LAYER
~------------
POORLY PERVIOUS LAYER
Flo. 4 LOCATION OF INTERCEPTOR DRAIN WHERE PERVIOUS LAYER IS SANDWICHED
BETWEEN POORLY PERVIOUS LAYERS
7 DRAWDOWN tangency with the original water table
level,
7.1 Under the situation when all the flow ongm
ates from various sources upland and the soil is H = thickness of hori zontal flow of soil water
homogeneous, slope is uniform, Dupuit-Forchhen. . being intercepted, and
mer ( D-F ) assumptions are valid, the impervious
layer exists at certain depth below the drain, the s = the slope in metres per metre of original
water table surface.
impervious layer and the initial water table have
a slope fS' with horizontal base line existing under 7.1.2 Drawdown Downslope
this situation the drawn down shall be calculated
This is approximately equal to the height of the
in accordance with the following procedure.
water in the drain provided the radial resistance
7.1.1 Drawn Down Upslope is negligible i.e., h is approximately equal to Do
( see Fig. 6 ).
Glover's formula, given below, in simplified form
can be used under such conditions to calculate 7.1.3 The discharge of the interceptor drain per
the drawdown ( see Fig. 6 ): unit length shall be expressed by the following
formula ( see Fig. 6 ):
4 H
x= 3·-s- H-h
Q= H ql
where
where
X = distance in metre upslope where the Q = discharge of the interceptor drain per
drawdown curve approaches significant unit length ( mS/day ),
5
IS 13939 : 1994
H = thickness of horizontal flow of water below the rootzone of ten. The design details of
upslope being intercepted (m), the system are as follows~
h = water table . height above impervious Drain type Open ditch
layer down side of the drain (m), and
Shape Half trapezium
ql = flow rate per unit length from
Depth 150cm
upslope ( rns/day ).
Top width 120 to 150 em
NOTE - The shape of the drawdown curve Bottom width 30 to 45 em
upslope is independent of hydraulic conducw Bed gradient 2 percent
tivity of the soil aDd quantity of flow becomes
a function of the slope. Location Along the upper boun
dary of the wet area
7.2 Water Table Control
as observed during
In areas where water table was recorded to be rainy season.
fluctuating between 30 and 45 cm depth below Spacing 60 to 150 m depending
ground level throughout the year before drainage upon specific condi
a systematically designed interceptor drainage tions of the area and
system was instal1ed to control the water table piezometric data.
WATER CHANNEL
HIGH WT AREA
WATER CHANNEL
HIGH WT AREA
--
INTfnCEPTER DRAIN
LJ -_
"r AFTl':'R DRAINAG-E - - - - __ _
C'..
FIG. 5 LOCATIoN OF INTSRCEPTOR DRAIN WHERE SEEPAOE FROM WATER CHANNELS OCCUR
INTO FLOW LANDS
6