Disclosure to Promote the Right To Information

Whereas the Parliament of India has set out to provide a practical regime of right to information for citizens to secure access to information under the control of public authorities, in order to promote transparency and accountability in the working of every public authority, and whereas the attached publication of the Bureau of Indian Standards is of particular interest to the public, particularly disadvantaged communities and those engaged in the pursuit of education and knowledge, the attached public safety standard is made available to promote the timely dissemination of this information in an accurate manner to the public.

इंटरनेट मानक

“!ान $ एक न' भारत का +नम-ण”Satyanarayan Gangaram Pitroda

“Invent a New India Using Knowledge”

“प0रा1 को छोड न' 5 तरफ”Jawaharlal Nehru

“Step Out From the Old to the New”

“जान1 का अ+धकार, जी1 का अ+धकार”Mazdoor Kisan Shakti Sangathan

“The Right to Information, The Right to Live”

“!ान एक ऐसा खजाना > जो कभी च0राया नहB जा सकता है”Bhartṛhari—Nītiśatakam

“Knowledge is such a treasure which cannot be stolen”

“Invent a New India Using Knowledge”

है”ह”ह

IS 14632 (1999): Farm Drainage System - PerformanceEvaluation of Horizontal Subsurface Drainage - Guidelines[FAD 17: Farm Irrigation and Drainage Systems]

IS 14632:1999

d ~2m-m w xyg-km - wkihIndian Standard

FARM DRAINAGE SYSTEM - PERFORMANCEEVALUATION OF HORIZONTAL SUBSURFACE

DRAINAGE - GUIDELINES

ICS 65.060.35

0 BIS 1999

B U R E A U O F I N D I A N S T A N D A R D SMANAK BHAVAN, 9 BAHADUR SHAH Zl\FAR MARG

NEW DELHI 110002

Price Group 8

Irrigation and Farm Drainage Equipment and System Sectional Committee, FAD 54

FOREWORD

This Indian Standard was adopted by the Bureau of Indian Standards, after the draft finalized by the Irrigationand Farm Drainage Equipment and System Sectional Committee had been approved by the Food and AgricultureDivision Council.

Drainage is an essential element to the sustainability of agriculture. A rational approach to drainage planningdemands that information is collected through reconnaissance survey, laboratory analysis and through fieldinvestigations by means of visual observations/measurements. The data so collected, however, may suffer frommany infirmities. The major difficulties are experienced due to-large spatial variability in the soil properties andas a result of small sample size in estimating soil properties. In the absence of any worthwhile tools to circumventthese difficulties is to rely upon these data sets to design an optimal combination of the drain depths and spacing.Once the drain or the system is installed, performance evaluation tests are conducted to confirm the datasets/design. Normally two kinds of tests are made: namely (i) single drain line tests, and (ii) testing of drainagesystem in test plots.

In order to conduct these performance evaluation tests as a means to rationalize the drainage design and establishan efficient system, a need was felt to prepare this standard. Normally the test procedure as outlined in thisstandard would yield following information:

a) Data on soil hydraulic/hydrological qualities such as hydraulic conductivity, drainable porosity andthickness of phreatic aquifer. As the ‘sample size’ is extremely favourable compared to the sample sizeinvolved in laboratory samples or field measurements in auger holes; it is presumed that more accurateaverages of these parameters would be available to extend the design; and

b) A check on the water table regime as induced by the experimental depths and spacing of the drains.

Thus, before the design could be extended to cover large areas, it is often desirable to lay test lines and test plotsto confirm the accuracy of drainage design parameters.

In the preparation of this standard considerable assistance has been derived from Water Technology Centre,Indian Agricultural Research Institute, New Delhi and Central Soil Salinity Research Institute, Karnal.

IS 14632 : 1999

Indian Standard

FARMDRAINAGESYSTEM- PERFORMANCEEVALUATIONOFHORIZONTALSUBSURFACE

DRAINAGE-GUIDELINES1 SCOPE

This standard lays down guidelines for performanceevaluation of the horizontal subsurface drainagesystem (pipe and tile drains).

2 REFERENCES

The following standards contain provisions whichthrough reference in this text, constitute provision ofthis standard. At the +ime of publication, the editionsindicated were valid. All standards are subject torevision and parties to agreements based on thisstandard are encouraged to investigate the possibilityof applying the most recent editions of the standardsindicated below:

IS No. Title

9696 : 1980 Code of practice for installation offarm drainage tile or pipe system

10907 : 1984 Code for design of farm drainagetile or pipe system

11493 : 1986 Glossary of terms retating to farmdrainage

3 DEFINITIONS

For the purpose of this standard following definitionsin addition to those given in IS 11493 shall apply.

3.1 Drainable Porosity

The drainable porosity also known as effectiveporosity or the specific yield is defined as the volumeof water released or taken into storage in anunconfined aquifer per unit cross-sectional area perunit decline or rise of water table as a fraction of totalvolume of the soil.

3.2 Drainage Coefficient

Design rate at which water is to be removed from adrainage area. It may be expressed in depth or volumeunits per day.

3.3 Hydraulic Conductivity

The proportionality factor in the Darcy flow law,which states that the effective flow velocity isproportional to ~the hydraulic gradient. Hydraulicconductivity, therefore, is the effective flow velocity

at unit hydraulic gradient and has the dimensions ofvelocity (LT-‘).

3.4 Equivalent Depth to Impermeable Layer

In drainage, the depth assigned to the actual depth toimpermeable layer to take into account the extraresistance caused by the radial -flow in cases wheredrains do not reach the impermeable layer.

3.5 Observation Well

A tube installed or a hole bored to a desired depthbelow the ground surface, used for observing the watertable level.

3.6 Pefiormance Evaluation

The evaluation of the functioning of the drainagesystem compared with established design criterion andto identify -the cause(s) of malfunctioning (ifapplicable).

3.7 PIezometer

A tube for measuring the combined position andpressure (Piezometric) head or potential of a fluid.

4 TEST CONDITIONS

4.0 Drainage system is tested for the following twoconditions:

a) Steady state, andb) Non-steady state.

For the purpose of this standard, guidelines relate tothe performance evaluation using test plots only.

4.1 Steady State Flow

Steady state conditions occur whenever for asufficiently long period -of time the position of thewater table does not change (remain static) and thedrain outflow is constant. This implies that, during thetests, irrigation water or rain must recharge the-groundwater reservoir at a rate that is approximately constantfor at least a few days and equal to the outflow rate.Such condition rarely occur under field conditions. Itmay,_however, be simulated with sprinkler system orcould occur during periods of steady rain. In spite ofthis, the procedure has found favour with thedesigners.

1

IS 14632 : 1999

4.1.1 The performance evaluation test under steadystate conditions (see Fig. 1) is based on the Hooghoudtequation which for a homogeneous isotropic mediumcould be written as:

8 Kdh 4 Kh=4=

7- + --F(1)

where

4 = discharge rate per unit surface area(m/day).

A drain outflow rate of 0.6 litre per second (that is,0.6 x 10m3 x 86 x 400 m3/day) for a drainage area of1.2 ha (drain spacing of 60 m and drain length of200 m) gives:

q = 0.6 x low3 x 86 x 400 m3/day1.2 x lo4 m2

= 0.004 3 m/day or 4.3 mm/day;h = hydraulic head (m) or water table elevation

above drain level midway between thedrains;

K = hydraulic conductivity (m/day). Subscript1 and 2 denotes the hydraulic conductivityof the layer above and below the drainsrespectively;

S =

d =drain spacing (m); andthickness of the so-called equivalent layer,which depends on the distance DO from draindepth to impervious base, the drain spacingS and the wetted perimeter of the drain.

4.1.2 If the drains are placed on an impervious layer,then DO as well as d is zero. For this case Equation (1)is written as:

4 Kh=4=

3. .‘. (2)

It then refers to flow which is from above the drainsonly. If on the other hand DO and~d are large such thatthe second term on the right hand side of Equation (1)will be relatively small compared to the first term sothat it could then be neglected:

8Kdh4’

S2. . .

Thus, equation (3) expresses flow below the level ofthe drains.

Equation (1) in a general form could also be written as

q=Ah+Bh=or . . . (4)

qlh=A+Bh . . . (5)

A 8 Kd and=-9

. . .

Equation (5) states that a plot between h and q/h willyield a straight line such that the intercept will yieldthe value of A while the slope of the straight line wouldyield the value of B. .

4.1.3 The above procedure would be valid for a twolayered medium provided the soil profile could bedescribed in two layers, one layer above the axis of thedrain while the other layer below the axis of the drain.In that event Equation (1) could be written as:

8 K2dh 4 Klh=q=-+_sz sz

. . . (8)

Here, Kl and K2 are the hydraulic conductivities of thelayer above and below the drain axis respectively.

4.1.4 If the boundary of the two layers is locatedbelow or above the drain axis and if it is not possibleto express these in two layers with their interface at thedrain level, Equation (8) would not be applicable.Where an impervious or a poorly pervious layer isfound above the drain level, a perched water table maydevelop (see Fig. 2). This may result in groundwaterflow towards the drain trenches over the boundary.Under these conditions also the theory asdescribed in4.1.1 should not be applied.

FIG. 1 SYMBC& USED IN ROW F~QUATION (1)

2

IS14632 : 1999

FIG. 2 PERVIOUS SOIL OVERLYING POORLY PERMEABLE BASIN CLAY GIVING RISE TO PERCHED WATER

TABLFF, AND WATERFLOW OVER BOUNDARY TO DRAIN TRENCH

4.2 Non-steady State Conditions

4.2.1 Ground water movement in -irrigated landsfollowing an event of irrigation or during dry spellsfollowing a rain storm would be fast enough thatsteady state theory will not be applicable. Under theseconditions non-steady state theory could be preferred.It is strongly recommended that data for both watertable heights and drain outflow should be processedwhenever possible. In cases, where data on any of thetwo parameters is unreliable, only then one of theparameters be used. It may be noted that a case ofrising water table is not the same as the case of a fallingwater table.

4.2.2 The relation between hydraulic head anddischarge rate differs from the case when there isdrop in the water table (see for example, the watertable positions in Fig. 3). Thus the theory as suchwould not be applicable for case of rising watertable.

4.2.3 Theory

The most commonly used equation for the purpose ofperformance evaluation is the equation of Glover andDumm as reported by Dumm. The equation is writtenas

2

” = flog ;l?hc,/hJ. . . (9)

wheret =

ho;ht =

f =

duration during which the water tabledrops from position h, to ht (days);hydraulic head at beginning (t = 0) andend (t = t) of any selected observationperiod (m); anddrainable pore space, also termed aseffective porosity, in the zone offluctuating water table.

(See 4.1.1 for the definitions of the other factors).

To take care of the convergence of flow towardsdrains, actual depth to impermeable layer, D isreplaced by equivalent depth to impermeable layer, d.Equations for non-steady state flow also require thatthe thickness of the aquifer through which water flowstoward the drains is constant. This implies that animpervious layer, if any, should be at a considerabledepth below the drain or, more accurately, that thetransmissivity (product of hydraulic conductivity andthickness) of that part of the aquifer which is belowthe drains should exceed by far that which is above thedrains. In case, it is not the case than one shouldreplace D with (d + hd2) in Equation (9).

Subsequent equat~ions are written with thesemodifications. However, if permissible by siteconditions one may use only d instead of (d + hd2).Equation (9) is written as:

S2lt2K (d + h,/2)t

= flog, (t.16 hdht). . . (10)

FIG. 3 SHAPE OF WATER TABLE-DURING RECHARGE (1) AND DURING MOST OF THE RECESSION (2)

3

IS 14632 : 1999

Commonly, drainage intensity factor (days-‘) isdefined as follows:

a=x2K(d + ho/2)

fS2. . . (11)

4.2.4 At a certain time t after cessation of the recharge(see Fig. 4) equation (10) will become approximatelyconstant and using equation (ll), followingexpression is applicable to subsequent stages of thefalling water table:

at = 2.3 log hdht . . . (12)

An additional and useful equation that follow fromexpressing q in h is:

q=2 +I?! . .P

(13)

q =2 p&f + ho/2)h

S2. . . (14)

It could be shown that similar to hydraulic heads givenby equation (1 l), discharge equations could also Abewritten as:

where

at = 2.3 log qdqt . . . (15)

qO, qt are the drainage rates at beginning (t = 0) and-end (t = t) of the observation period.

WATERJABLEH E I G H T (ml

DAYS

bERIO OF RECHARGE

F I G. 4 W ATER TABLE R ISE AND RECESSION

Itshould be noted that the point of time in a water tablerecession below which equation (12) through equation(15) holds could be calculated with the followingexpressions:

tA = 0.4a

. . .

For example, if a = 0.2 days-’ which is not uncommonin irrigated areas, then the usable period ofobservations after completion of irrigation or aftercessation of rain may be obtained as follows:

h = 2 =, 2 days . . . (17)V.L

Since the determination of the value of a is one of testobjectives and a; therefore, is unknown at thebeginning of the test, intensive measurements shouldstart immediately following the end of waterapplication.

5 TEST PROCEDURES

5.0 The important preliminary steps for irrigated aswell as for non-irrigated conditions are given below.

5.1 Preparatory Activities

a>

b)

c)4d

Select a test site that is representative of thesoils to be drained and their hydrologic condi-tions (climate, surface water, groundwater).Examine soil and water conditions of the testarea in detail; soil texture and structure, etc.

NOTES

1 The soil of the testsite should he homogeneous froma pedological and hydrological point of view.Heterogeneity complicates the evaluation of test results.

2 The test site should be accessible in all seasons.

Select drain depths and spacing to be tested.~Prepare layout of test plots.Provide necessary instrumentation for observ-ing drain discharge and hydraulic heads.

5.2 Measurements

Following steps should be followed:4

b)

c)

4

e)

f-l

b9

Measure water table heights prior to waterapplication.Apply irrigation water uniformly to as large apart of the test area as possible. One test unitcontaining 3 or more drains, being a minimumfor irrigation at the same time. The volume ofwater to be applied should-be large~enough tocause the water table to rise to the groundsurface at the midpoint between the drains.Turn off thewater supply and measure waterlevels (in all piezometers and observationwells) and drain discharges.Measure water levels (in all observation wells)and drain outflows daily during the recessionperiod, that is the period (normally l-2 weeks)in which the water table at the midpointbetween the drains falls uninterruptedlywithout any recharge due to irrigation/rainfallfrom close to the ground surface to about halfof drain depth.Install the drainage system in accordance withIS 9696.Process the data while discontinuing fieldmeasurements.After having checked the functioning of theobservation wells, repeat the test, if necessary,

4

adjust the frequencies of observations, if theconclusions of the first test indicate its need.NOTES1 If a high water table can not be reached following onewater application, or if the fall in the water table isinterrupted by rainfall, then observations need to bespread over a longer period of time so as to obtainsufficient data for processing. It is important to includeboth high and low water tables and correspondingdischarge rates in the series of observations.2 The evaporation has a tremendous effect on thelowering of the water table. This effect should beminimized as much as possible. The tests should,therefore, be conducted at a time when evaporationeffects are minimum.

5.3 Non-irrigated Conditions

The water table rise is governed by rainfall and thechances of having a quick rise to the ground surfacefollowed by an uninterrupted fall, are small. Thoughit remains important to measure dropping water tablesas accurately as possible, it will be of equal importanceto obtain a wide range of water table elevations andcorresponding outflow rates from a series of rainfallevents in one season. On-the-spot measurements ofrainfall is recommended.

6 LAYOUT OF TEST PLOTS

6.1 Both the test site and layout of test plots should,for maximum results, meet following requirement:

a) The soil of the site should be representative ofthe area that is to be drained. If there aredifferences in water transmitting properties

BUFFER PLOTSt I 1

3 4 de

IA

11

C

I-11 12 13 14 IS 16 17 18 1) 20

Q

b)

cl

IS 14632 : 1999

between parts of the area, then the betterdrainable should be selected in the first in-stance. Specific problem soils are to be in-cluded in testing programmes only if their areaextent warrants it. If it is considered that thesoil will not greatly interfere with themethodology, the results are consideredapplicable.The soil of the test site should be homogeneousfrom a pedological and hydrological point ofview. Heterogeneity complicates the evalua-tion of test results.The test site should be accessible in all seasons.

6.2 Number of Test Drain Lines

The minimum number of test drain lines in any testunit is three. This would permit the measurementsfrom one drain line only (the middle one). The mostpractical number of drains is 4 or 5, permitting themeasurement in at least 2 or 3 drains (see Fig. 5).

6.3 Number of Test Units _.

The number of test units for one soil type depends onthe number of depth-spacing combinations proposedto be tested as well as on the number of replicates. Thenumber may also depend upon other test combinationssuch as drain materials or envelop material to be-tested.For example, three spacings, one depth combinationwould require three (3 x 1) units. For two replications,the number of plots would be six. Similarly for thesame depth and spacing, if there are two pipe materialsand two envelop material then for two replicationsthere would be 8 test plots.

BUFFER PLOTS

I 1

b-

F IG. 5 PART OF AN EXPERIMENTAL SE T-UP, CONSISTING OF UNITS A, B, C AND D

5

IS 14632 : 1999

6.4 Replicates

Replicates in any test are necessary but actual numberwould depend on the amenability of results tostatistical analysis. In practice, however, variations insoils and hydrologic conditions within one plot areoften so large that even in seemingly homogeneoussoils, the statistically required number of replicateswould be large enough to make it impracticable. Alarge number of replicates implies a larger area which,in turn, would increases the differences in soilconditions for various test units. A still greater numberof replicates would be needed. Therefore, in actualpractice replicates are often limited to 2 or 3, and thetest results are not to be considered statistically proved.Rather, they provide indications of what may beexpected.

6.5 Dimensions of Plots

The flow to the drain lines should be as uniform aspossible over the length of the drain. Irrigation,therefore, should as much as possible be uniform sothat water table ele-vations are the same atcorresponding points in the field. End effects, that arecaused by special conditions near the ends of the plotssuch as the presence of a deep collector dram, deepwater table due to absence of irrigation, presence of aleaking irrigation ditch, could be reduced by designingplots that are long compared to their width. Alength-width ratio of 4 is considered a minimum. Forexample, if the width, that is, the drain spacing is30 m, the length of the drain should be at least 120 mand preferably 150-m or over.

6.6 Selection of Drain Depth

Drain depth is selected in accordance with IS 10907.In test units, normally one or a maximum of two depthsare sufficient. Differences between such depths as1.8 m and 2.0 m are unlikely to become apparent inshort term testing.

6.7 Selection of Drain Spacing

For relatively close drain spacings, test spacingsshould include that are at least one hundred percentwider and smaller than the theoretically calculatedspacing. If, for example, the calculated or otherwiseestimated spacing is 40 m, include both 20 m and80 m spacings. Normally, three tests spacings aresufficient. Wide plots having spacing-of 100 m or moreshould be avoided as these are unlikely to yield shortterm design information. The reason is that the size ofover 4 ha (100 m x 400 m) would make it difficult toirrigate at least two of them at about the same time(see 6.5).

Irrigation of one plot should be avoided because itpromotes the movement of groundwater to adjaGentnon-irrigated plots which may lead to inaccuracies. It

is, therefore, recommendable~that a spacing of about75 m could be the most practical upper limit forperformance evaluation studies. Once adequateinformationand understanding of the hydraulic of thearea have been developed on such plots, extrapolationto wider spacing (if needed) is possible.

6.8 Hydrologic Interference

To reduce the hydrologic interference betweenadjacent plots, the following precautionary measuresare suggested:

a)

b)

c)

Introduction of a buffer plot between adjacentunits (see Fig. 5);Differences in drain depth between adjacentunits, if any, should be kept small, for examplenot more than 30 to 40 cm; andDifferences in drain spacings betweenadjacent units should correspond to the smal-lest step. If, for example, test spacings are25 m, 50 m and 75 m, then units of -25 m and50 m spacings or of 50-m and 75 m spacingsshould be adjacent rather than those of 25 mand 75 m.

7 INSTRUMENTATION AND MEASURE-MENTS

7.1 Instrumentation

The basic observations required are the drain outflowrates and the elevations of the water table.Observations wells of depths at least equal to the depthof the drains are needed (see Fig. 6) at followinglocations:

a) Midway between drains to measure thehydraulic head at the mid point;

b) Near one or more of the drains of each unit, toobserve the shape of the water table; wellspreferably to be placed at distance of about0.5 m, 1.5 m and 5 m from the drain. Wheredrain spacings are over 75 m, one more well ata distance of 10 to 15 m from the drain isrecommended;

c) On top of the drain pipes, to check thefunctioning of the drains; and

d) At the upper and/or lower ends of some of theunits, to observe border effects.

7.1.1 Number and arrangements of wells in Fig. 6 isonly illustrative. They refer to ‘average’ conditionsand the first tests will show whether more observationwells are needed to suit local conditions. As anexample, more wells may be needed when there is alarge variation in readings between correspondingwells. Or the frequency of observations of some wellsmay Abe reduced when readings are highly uniform.

7.2 Measurement of Drain Discharge

The drain discharge is measured in drains 2, 3, 4 ofunit A,min drains 7,8,9 of unit B, etc [see Fig. 5(a)] or

6

IS 14632 : 1999

-I 1.I

II

l*

FIG. 6 EXAMPLE OF NETWORK OF OBSERVATION WELLS IN A TEST UNIT

at the end drains [see Fig. 5(b)]. The drain dischargeis measured by any one of the following methods:

a) Time-volume approach using a container anda stopwatch,

b) Weirs, andc) Discharge recorders.

Note that the discharge capacity of the collector drainshould be large enough to keep its water level belowthe field drain pipes during periods of high discharge.If the field drains are submerged back pressure willdevelop in the pipes and outflow measurements can nolonger be made.

It is recommended that a few recorders for observinghydraulic head as well as to measure drain be installedin any experimental set-up. They will help interpretand extrapolate data observed~with means that do notprovide continuous records.

7.3 Frequency of Observations

The frequency depends on such local conditions asclimate, soils, and also on the purpose of the test. Nostrict rules can therefore be given. In any case, thenumber of observations must be adequate for theprocessing of steady and non-steady state conditions.

The following guidelines should help to decidedischarge measurements:

a) At least three times a day during periods ofhigh discharge say during first 3 to 5 daysfollowing irrigation or heavy rains.Observations should be well distributed over a24-hour period;

b) Twice daily during the remaining daysbetween two irrigations or, in rainy climate,during periods of distinct increases ordecreases in discharge rates; and

c) Once daily in periods of low discharge or whenthe discharge is more or less stabilized.

For water table heights the suggested frequency inirrigated areas is:

a) One measurement just before irrigation,b) One measurement at the end of water

application, andc) Measurements should usually follow the same

guidelines as for discharge measurements.

It should be noted that once the shape of the water tableis known, the measurements could be concentratedmore on the wells half way between the drains in casefunds or human resource is limited.

7

IS 14632 : 1999

8 PROCESSING OF DATA -WORKEDEXAMPLES

8.1 Steady State Conditions

8.1.1 Procedure

4

b)

cl

Convert the observed discharge rate intomm/day or m/day and plot these versus timeand draw visually a ‘best fit’ line through thepoints (see Fig. 7A).Convert the observed depths to water table intohydraulic head values (mm or m), plot theseversus against time and draw visually a best fitline through the points (see Fig. 7B).Using these curve tabulate q versus h data. Plotdischarge rates versus hydraulic heads.

Note that Fig. 7C can also be constructed without theaid of Figs. 7A and 7B. The latter, however, are helpfulin showing the degree of regularity and accuracy ofmeasurements. Furthermore, if q and h have not beenmeasured on the same date, interpolations can bemade via Fig. 7A and 7B.

8.1.2 Analysis

Going back to Equation (4), it is seen that the qhrelation will be a straight line only if the value of Bfr2is small compared to the value of Ah (see Fig. 7C,curve 1). A straight line relationship between q and hillustrate that the contribution of the layer above thedrain to flow is relatively small compared to that of thesoil layer below the drainlevel. As a result, the greater

A

I I I I I I 1

. tI II I DAYS

l

0

1 I 8 I

0I I 1

2I

4 6 0DAYS

part of the drainage water will pass through the layersbelow the drains.

When flow above the drain level is not negligiblysmall, the qh line will be curved. Its actual shape willdepend on the relative contribution made by each ofthe two component of the right hand side. The greaterthe share of the layers above the drains the stronger thecurvature will be.

Equation (5) on the other hand reveals that q/h versush plot would always be a straight line. Thus, tofacilitate the interpretation of the data, it may behelpful to plot q/h versus h curves (see Fig. 8). Theresulting straight line makes an angle with thehorizontal axis, such that:

tan a = B . . . (18)

when the value of Bh2 is relatively small, then q/hversus h relation will be horizontal line parallel tox-axis.

Example:

Consider an experimental homogeneous and isotropicsoils field being drained by pipes of radius r = 0.05 m,placed at 2 m depth and at a lateral drain spacing of100 m. Drain discharge rate and water table depth havebeen measured frequently during periods when therewas little change in water table position. -Theobservations have been plotted [see Fig. 7A and 7B)and the corresponding values derived are given inTable 1. Use these data for performance evaluation ofthe system using steady state theory.

Qm/day A

h in metres

FIG. 7 PLOTS OF DISCHARGE VERSUS TME (A), HYDRAULIC HEAD VERSUS TIME (IQ, THE RESULTING

DISCHARGE VERSUS HEAD (C)

8

IS 14632 : 1999

q/hdOYS -1 a 10-a6+

D I I I I r P I I r 1 10 0.2 0.4 0.6 0.6 I.0

h(m)

FIG. 8 RELATION q/h-h, YIELDING STRAIGHT LINEN

Table 1 Discharge Rates and CorrespondingHydraulic Heads Based on Fig. 7

(Clause 8.1.2)

4 h cl/h(m.day-’ x 1 O-3) (ml (days-' x 10w3)

(1) (2) (3)4.23 1.8 2.353.60 1.6 2.253.00 1.4 2.142.52 1.2 2.102.00 1.0 2.001.53 0.8 1.911.10 0.6 1.830.70 0.4 1.750.33 0.2 1.65

Figure 9 provides a plot of q versus h and of q/h versush. The q-h relation is a slightly curved line. Althoughone would be tempted to draw a straight line throughthe points; it is better to draw q/h versus h line to arriveat more accurate results. With this plot tangent is readas tan a = 0.4 x 10s3. This then is the value of B inEquation (5). Applying Equation (S), the hydraulicconductivity is found to be:

K_sZtanu_ 100*x0.4x10”4 4 = 1 m/day . . . (19)

The value of A = 8Kd/s2 is read from the intersectionpoint on the vertical axis as 1.6 x 10s3. Since the soilsare homogeneous and isotropic KI = K2 = 1 m/day. Itfollow, therefore, that d = 2 m. It may be noted that ifKI is not equal to K2 then Kl and d can not be separatedout unless the value of d is explicitely known.

With known values of the drain spacing (S = 100 m),drain radius (r = 0.05 m) and the equivalent depth toimpermeable layer (d = 2 m) we can find the actualdepth to the impervious layer from the nomograph inFig. 10. Working backwards on the graph, and using

wetted perimeter u = m = 3.14 x 0.05 = 0.16 m, theproblem is to find a D, value on the left hand verticalaxis that is about six times the Do value on the righthand vertical axis. This appears to be 2.3 m such thatD, = 2.3 m.

In practice the value of the wetted perimeter oftenincludes the thickness of the filter material in drainradius. Thus the wetted perimeter is usually larger thanthe one that would follow from the drain radius alone.For example, if in the above case, a filter of thickness10 cm is placed all round the drain then the wettedperimeter would be about 0.48 cm. The D, valuewould then be about 2.2 m below the drains.

8.2 Non-steady State Conditions

The procedure and analysis is demonstrated by thefollowing example.

Consider an experimental field that has been drainedby pipes at a spacing of 30 m. The pipes with a radiusr = 0.05 m have been placed at a depth of 1.80 m(Fig. 11).

Soil investigations show a thick layer of clay with aplastic consistency whose upper boundary is at a depthof 4.8 m below ground surface. From hydraulicconductivity measurements and additionalobservations on the seasonal fluctuations of thewatertable it is concluded that the transmissivity of thislayer is very small compared to that of the overlyingsoil and the layer therefore may be considered animpervious floor.

The volume of water applied in an irrigation is140 mm, of which, according to design assumptions,40 mm percolate below the root zone. It is assumedthat all of it recharges the phreatic aquifer on the sameday. During the day of recharge and the following days

9

Is 11632 : 1999

q * 1o’3

m/day10

1

q/tLlo-3

days"

6-

FIG.~ PLOTSOF~ VERWS~ AND@Z VERSUS ~-IN THE~ALCULATIONOF K AND Kd

the water table depth and the discharge rate aremeasured several times a day (later on plotted as Fig.12). Using the data carry out the performance analysisof the system using non-steady state theory.

8.3 Calculation of the~Drainage Intensity Factor

To arrange the field observations and calculatedrainage intensity factor proceed as follows:

a)

b)

c>

Convert the observed discharge rates in mm orm per day, plot these versus time and drawvisually a ‘best fit’ line through the points(Fig. 12).

Convert the observed water table height intohydraulic head values (mm or m), plot theseversus time and draw visually a ‘best fit’ linethrough the points (Fig. 12).

Read from Fig. 12 the corresponding values atthe end of the days and compose Table 2.

Table 2 Recharge (R), Discharge (Q)and Corresponding Hydraulic Heads (H)

Based on Fig. 12

t= 1 2 3 4 5 618 daysR=40 _ - - - - _ - m mq= 14.4 5.9 4.4 3.4 2.6 2.0 1.6 1.2 mm/dayhi= 495 430 340 265 205 160 125 100 m m

d)

e>

Plot qt and/or ht values from this table versustime on semilog paper and obtain the lines ofFig. 13. Note that, according to Equations (12)and (15) which apply to tail recession theselines should be straight and parallel to oneanother;Calculate the drainage intensity factor. Apractical way of calculating is by using equa-tions (12) and~( 15) which may also be writtenas:

a = 2.3 (log ho - log ht)t

and

a = 2.3 (log qo - log qt)t

. . . (21)

In both cases this results in

a = 2.3 tan a .., (22)

It may be noted that ht, qt and ho, q. are points of thestraight part of the lines. They can be selected freely,taking into account that ho, qo presents an earlier datethan ht, qt. To obtain tan a it is practical to select onefull logarithmic cycle on the h or q axis, for examplefrom 700 to 70 (log 700 - log70 = log 10 = 1).

1The value of tan a is then found from tan a = -

tz - t1

10

IS 14632 : 1999

FIG. 10 NOM~GRAPH FOR HOOGHOUDT’S d VALUE

11

IS 14632 : 1999

FIG. 11 DRAINAGE CONDITIONS OF WORKED EXAMPLE ON NON-STEADY STATE FLOW

MY ORAULIC HEAD DISCHARGE RATEmm mm / DAYS

FIG. 12 WATER TABLE POSITION AND DISCHARGE RATJZS OBSERVED AND CONVERTED INTO

HYDRAULIC HEADS (mm) AND DISCHARGE RATES (mm/day)

It appears from Fig. 13 that

tan a = l/9.5 = 0.105

and therefore,

a = 2.3 x 0.105 = 0.242 days-’

Note that the lines of Fig. 13 become straight lines atthe time tA = 0.4 days after the recharge. The value oft.4 cannot be calculated at the time the lines must bedrawn, since a is then still unknown. In the case ofFig. 13 this does not present a problem since theposition and direction of the straight part is clear from

the points obtained between the-third and eighth day.It often happens, however, that the observationsappear somewhat scattered in the lower region of thelines where discharge rates are low and water tablesmove slowly. The inaccuracy of the observations maythen have a ‘considerable impact on the results. Theuncertainty about the beginning and the end of thestraight line calls for frequent and accurateobservations during, say, the period between thesecond and the sixth day after water application. Sinceu = 0.242 days-‘, it follows that tA = 0.410.242 = 1.7days. Thus in Fig. 13 where tA refers to a point of timeafter the cessation of recharge the line will be straight

12

lo! , I ‘ , , I’ I I I I I I 1 .

0 1 23456?99 10 11 12 13 14TIME IN DAYS

FIG. 13 PLOTS OF DISCHARGE AND HEAD VERSUS TIME

from t = 2.1 or-say t = 3 days after the start of irrigationallowing one day for irrigation.8.4 Calculation of Hydraulic Conductivity andTransmissivity

To calculate the hydraulic conductivity K, plot qcversus ht values from Table 2 and find q/h = 0.012 7(see Fig. 14). The q/h relationship yields a straight linewhen most~of the water flows to the drains through thesoil below the drain level. The variations in the watertable position will then have only a minor effect on theactual thickness of the phreatic aquifer (0) and non-steady state flow equations are applicable. Neglectinghd2 and applying Equation (14) which aftertransposing reads,

Kd = q/h (S2/2x) . . . (23)

there results, with S* = 900, Kd = 1.8 m*/day. To obtainthe hydraulic conductivity K from the Kd value findHooghoudt’s d value from the graph of Fig. 10.For 10. For u = 0.30m, S = 30m and D=3m(see Fig. 1 l), there results d = 1.97 m and consequentlyK = 0.9 m/day.

The transmissivity Kd = 0.9 x 3 x 2.7 m21day.

8.5 Calculation of the Effective_Porosity

The effective porosity f may be calculated from theexpression for a (Equation 11). After neglecting &/2,

IS 14632 : 1999

we get:

n;*Kd

a=F

if a, S and Kd are known, or from Equation (13)

q/h = 2afht

if a, q and h are known.

Substituting, in the first expression, the values for aand Kd, we find with S = 30 mJ= 0.8. The same valueis obtained from the second equation by substitutingq/h = 0.012 7 and a = 0.242.

8.6 Presentati_w-The data shall be presented in the sheets asgiven inAnnexes A, B, C and D.

9 INTERPRETATION

9.1 Once the data on hydraulic conductivity,drainable pore space and depth to impermeable layerare obtained with actually operating test units, thevalues are compared with those that were used in theinitial design. En all probabilities, new values are morenearer to reality because:-

-

these values are spatial average of a larger samplethan were used in the initial estimates.some processes that are ignored in drainageinvestigation and design find their influence while

13

IS 14632 : 1999

.DISCHARGE RAT E

4t= l where 1q:14,4 1

:

HYDRAULIC “7;

FIG. 14 DISCHARGE RATE VISAS HYDRAULIC HEAD

inverse technique is used to calculate theparameters.

With these values, a check is -made whether theexisting design would meet the,design criterion or not.If not, a new design is prepared with these values.

9.2 Performance of the Drainage Materials

Performance of thefunctioning of the drains is judgedon the basis of head loss fraction (!z.J&~) and theentrance resistance as calculated from the data of waterlevels in the observation wells. Following guidelinesare used:

Head Loss Fraction

Head loss fraction(h&tot)

Drain line performance

Smaller than 0.2 Good0.2-0.4 Moderate0.4-0.6 PoorMore than 0.6 Very poor

Entrance Resistance

Entrance resistance(re days/m)

Drain line performance

Smaller than 0.75

0.75-1.50

1.50-2.25

More than 2.25

Good

Moderate

Poor

Very poor

NOTE - These guidelines are normally applicable fordischarge rates in the range of 4 mm.

14

Is 14632 : 1999

ANNEX A

(Czuuse 8.6)SHEET FOR RECORDING BASIC SITE DATA SIZE, SOILS, TEST PREPARATION

Qhmw’sn~e: _________________________Date: ___________________

Locationofsite: __________________________Appr~ximatesize: _____________

Topography : Flat/uniform slope/shallow depression

Soils: Information on Texture StNChlE

upper 4 meters:Colour Mottling

A - - -

- - - -

Othercharacteristics ____________________-___-_------------------__-

Particle size Layer < 2-20 20-50 50-100 >looDistribution - - - - -(micron): - - - - -

Salinity : Layer Soluble salt content (mel-‘) EC (ds”‘-‘)Na+ K’ Ca” MgfC Sod’-- cl- HCO3-

- - - - - - - - -

PH: Hydraulic conductivity ---------(m day-‘)

Soilmoisturecontentatdraindepth ______________

Soilinformationbelow4mdepth _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Depthtoimpermeablelayer _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Climate:arid/semi-arid/sub-humid/humid___________

Specifyannualrainfalldistribution ______________

OBSERVATIONS ON DRAINAGE INSTALLATION

DateofdziMion _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Conditionsduringinstallation _____‘___________

Weather ____________________-------

Soil moisture profile

Watertableelevation _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Drainspacing _ _ _ _ - _ _ - - - - - _ - - _ - - _ - _ _ ( m )

Averagedepth ____________________-- (m)

Operations:

- Type of machine ------ Trench width ---------- Shape of the trench bottom -------- Stability of thetrench -----Binding material used __ ____ -__---__-_-I___ Was backfill compw@d -------- if ~0, how ?General evaluation: Well/Pairly/Poorly installed --------

Layout of test plots

IS 14632 : 1999

ANNEX B

(Clause 8.6)SHEET FOR RECORDING BASIC OBSERVATION WELL DATA

Drainlines ____________________----____

Typeofpipe ____________________--------____--outer

Diameterofpipe~_-_____-__-__---__----_-__---

Typeofenvelope________________________________

T h i c k n e s s o f m a t e r i a l _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ a n d d i s t r i b u t i o n a r o u n d p i p e

Levelof topofobserva t ionwel l s (m+sealevel) _ _ _ _ _ _ _ _ _ _ _ _ _ _

Enve lopeg rad ingc r i t e r i au sed_________________________

Levelofoutletpipe(m+sealevel) ___:____________---___

Dateofinstallationofobservationwells ___________T_______

Lengthofthedrain ____________________----__---- (m>

Areadrained ____________________--------___--- (ha)

Drain Line No.Distance of observation well from outfall

Row I (m)

Row II (ml

Row III (m)

Row Observation Levels with respect to top of observation wellNo. Well A/ \

Distance Bottom Land Crest of Mid Remarksfrom of sur- drain- of draindrain o.well face pipe pipe .(m> (m) (ml (ml (m)

At A2 A3 A4 A5 A6’ As

123

I 456678

II 910111112

III 13141516

.

IS 14632 : 1999

ANNEX C

(Chse 8.6)SHEET ON FIELD RECORDING AND COMPUTING

WATER LEVELS IN THE OBSERVATION WELLS

EXPERIMENTALDATA

FieldDrain line No.Date and hour of observationDate of last irrigationDuration of last irrigationSoil surface conditions:Drain outfall conditions:

days after irrigation

moist/dry/wetfree/submerged

Name of the observerRow Obs. W. Depth Observations of Water Level (W.L.)No. Well

Bl B2

onLaid , A 3Surface W.L. in W.L. in W.L. he re = h&

0. Well 0. Well Abovefrom Top from Mid h tot

Surface DrainB3 B4 B4-A5 k-B4

I

123 drain45h

II

678 drain9

10

1112

III 131415

htot = Head difference between observation wells at drain line and the mid point between drains.he = Head difference between observation wells at the drain and to the one placed just near the drain.r, = Entrance resistance.

Calculations of qUoutflow Observationtime

(s)B5

/ \Volume Time

(cm3) (s)B6 I37

V/t = Q Q 9u = en SpecialObskvation

(cm3/s) (m3/day) ( m / d a y )Bs= B9= Blo =

(Bfj/B7) (Bs X 0.086) (B9lL)1.2.3.L = length of the drain

17

IS 14632 : 1999

ANNEX D

(Clause 8.6)CALCULATION SHEET FOR DRAIN PERFORMANCE DATA

Days Drain No. Drain No.After A A, \ / \irrig- h&tot re = Wqu he/h tot re = he/q*ation /------h-----\~~Y

Row Row Row Avg Row Row Row Avg Row Row Row Avg Row Row Row AvgI II III I II III I II III I II III

1 (1) Read(2) Read

2 (1) Read(2) Read

3 (1) Read(2) Read

4 (1) Read(2) Read

5 (1) Read(2) Read

6 (1) Read(2) Read

7 (1) Read(2) Read

8 (1) Read(2) Read

9 (1) Read(2) Read

10 (1) Read(2) Read

Same data sheet shall be prepared for all drains.

18

Bureau of Indian Standards

BIS is a statutory institution established under the Bureau of lndian Standards Act, 1986 to promoteharmonious development of the activities of standardization, marking and quality certification of goodsand attending to connected matters in the country.

Copyright

BIS has the copyright of all its publications. No part of these publications may be reproduced in any formwithout the prior permission in writing of BIS. This does not preclude the free use, in the course ofimplementing the standard, of necessary details, such as symbols and sizes, type or grade designations.Enquiries relating to copyright be addressed to the Director (Publications), BIS.

Review of Indian Standards

Amendments are issued to standards as the need arises on the basis of comments. Standards are alsoreviewed periodically; a standard along with amendments is reaffirmed when such review indicates thatno changes are needed; if the review indicates that changes are needed, it is taken up for revision. Usersof Indian Standards should ascertain that they are in possession of the latest amendments or edition byreferring to the latest issue of ‘BIS Handbook’ and ‘Standards: Monthly Additions’.

This Indian Standard has been developed from Dot : $0. FAD 54 ( 4118 ).

Amendments Issued Since Publication

Amend No. Date of Issue Text Affected

BUREAU OF INDIAN STANDARDS

Headquarters:

Manak Bhavan, 9 Bahadur Shah Zafar Marg, New Delhi 110 002 Telegrams : ManaksansthaTelephones : 323 01 31, 323 33 75, 323 94 02 (Common to all offices)

Regional Offices : Telephone

Cent ra l : Manak Bhavan, 9 Bahadur Shah Zafar MargNEW DELHI 110 002

Eas te rn : l/l4 C. I.T. Scheme VII M, V. I. P. Road, KankurgachiCALCUTTA 700 054

Northern : SC0 335-336, Sector 34-A, CHANDIGARH 160 022

Southern : C. I. T. Campus, IV Cross Road, CHENNAI 600 113

Western : Manakalaya, E9 MIDC, Marol, Andheri (East)MTUMBAI 400 093

Branches l’\HMADABAD. BANGALORE. BHOPAL. BHUBANESHWAR. COIMBATORE.FARIDABAD. GHAZIABAD. GUWAHATI. HYDERABAD. JAIPUR. KANPl!R.LIICKNDW. NAGPUR. P,“\TNA n~~NE.RAJROT.Tl~IR~JVAN~~NTHAPUi~hM.

- - - -

1

323 76 17323 38 41

I

337 84 99,337 85 61337 86 26,337 91 20

1

60 38 4360 20 25

235 02 16, 235 04 42235 15 19.23523 15

8379295 832785XX327891:8327892

I’rinted at Printogxq~li. Nm Dclh, ‘ph.: 5726847