Textbook of Drainage Engineering

(

Textbook of

Drainage Engineering

f

Technical Editors RANVIR KUMAR Professor Department of Soil and Water Engineering College of Agricultural Engineering and Technology CCS Haryana Agricultural University Hisar 125 004

JOGINDER SINGH Professor Department of Soil and Water Engineering College of Agricultural Engineering and Technology CCS Haryana Agricultural University Hisar 125 004

ICAR

Published by Directorate of Knowledge Management in Agriculture Indian Council of Agricultural Research New Delhi 110 012

PRINTED REPRINTED

Project Director (DKMA) Incharge (English Editorial) Assistant Editor Associate

Chief Production Officer Technical Officer (Production)

DECEMBER 2005

FEBRUARY 2013

Dr Rameshwar Singh

Dr R P Sharma C S Viswanath D Pati V K Bharti Punit Bhasin

Š 2013, All Rights Reserved Indian Council of Agricultural Research New Delhi

ISBN : 81-7164-049-4

Price: ?400

Published by Dr Rameshwar Singh, Project Director (DKMA), Directorate of Knowledge Management in Agriculture, Indian Council of Agricultural Research, Krishi Anusandhan Bhavan, Pusa, New Delhi 110 012 and printed at M/s Chandu Press, D-97, Shakarpur, Delhi 110 092.

Contents Preface 1. Introduction to Land Drainage

'

v

1

2. Soil and Physics of Soil Moisture

16

3. Groundwater Hydraulics

58

4. Survey and Investigation

87

5. Water Balance

121

6. Surface Drainage Systems

151

7. Sub-surface Horizontal Drainage

185

8. Vertical Drainage

244

9. Salt Balance and Leaching Requirements

270

10. Management of Drainage System

301

11. Drainage Effluent Disposal Options

321

12. Socio-economic Impact of the Drainage System

326

Contributors Index

341 342

1

r-

Introduction to Land Drainage NEED

Drainage of agricultural land is the natural or artificial removal of excess water from, in or on the soil. Excess water adversely affects the production of crops by reducing the soil volume accessible to roots (DPA 1979). Excessive soilmoisture also prevents the carbon dioxide formed by plant roots and other organisms from being exchanged with oxygen from the atmosphere, a process known as aeration. In the absence of aeration, root development and uptake capacity for water andnutrients of most plants is reduced. Drainage also affects physical soil condition, cultivation, production, nutrient supply, soil salinity or alkalinity and disease or pests.

Land or agricultural drainage, a combination of irrigation and land drainage is one of the most important factors in maintaining or improving yield of farmers’ lands.

The development of irrigationproject in arid and semi-arid regions has invariably led to development of waterlogging and salinity problems in irrigation commands (Fig. 1.1).

—5S

&

mrr *r ' -r

..

-...

.

Fig. 1.1 Waterlogging and salinity problems in irrigated commands

This has created the necessity of agricultural drainage for the control of excess surface or sub-surface water for salinity control in addition to its relevance in humid regions. In monsoonic regions with humid climate, irrigation is needed for multicropping system adopted during different seasons of the year due to seasonal

2

TEXTBOOK OF DRAINAGE ENGINEERING

variability ofrainfall. Therefore, both irrigation and drainage are required for arid as well as humid regions of the monsoonic climate. So far the irrigation and drainage systems managed by different agencies have been planned, designed and executed separately. However, the optimal and sustainable use of irrigated agricultural lands requires irrigation and drainage system to be designed, constructed and managed as an integral unit. The irrigation projects provide water for the crops during dry spells frequently observedinmonsoonic climate. The excess use of irrigation water or rainfall in excess of agricultural water requirement creates a situation in which drainage becomes inevitable. In arid and semi-arid regions with low monsoonic annual rainfall, irrigation causes environmental degradation of valuable soil resources affected by water idgging and soil salinity problems. The potential gains of irrigation may be offset or reduced considerably if these problems are not tackled by providing land drainage along with irrigation. Irrigation and drainage management activities in a combined manner should attempt to narrow down the gaps between water supply and the crops water requirement in the project area without causing environmental problems. The combined performance of irrigation and drainage system is influenced by many factors, which are of engineering, hydrological, agricultural and organizational in nature. It is of paramount importance to integrate the management of irrigation and drainage systems in order to bring about a harmonious interaction.

HISTORICAL BACKGROUND OF DRAINAGE

Greeks and Romans are known to have installed field drains in reclamation projects 2000 to 2500 years ago. Reclamation projects especially of coastal marshlands including surface, subsurface and arterial drainage improvements have been implemented in many European countries for several centuries in the middle ages.

Records from the old Indus civilization (i.e., the Mohenjo-Daro and Harappa) show that around 2500 BC the Indus valley was formed. Using rainfall and floodwater, the farmers cultivated wheat, sesame, dates and cotton. Irrigation and drainage, occurring as natural process, were in equilibrium: when the Indus was in high stage, a narrow strip of land along the river was flooded at low stage, the excess of water was drained. Although salinity problems may have contributed to the decline of old civilization (Maierhofer 1962), in irrigated agriculture the importance of land drainage and salinity control was understood very early. In Mesopotamia, control of water table was based on minimizing inefficient use of irrigation water in the cropping practice of weed-fallow in alternate years. The deep rooted crops ‘shoq’ and ‘aguT created a deep dry zone. This prevented the rise of salts though capillary action (Jacobsen and Adams 1958). During the period from 1122 BC to 220 AD, saline-alkali soils in the north China plain and Wei-Ho plain were reclaimed by using a good irrigation and drainage system by leaching, rice planting and silting from periodic floods (Wen and Lin 1964). In the second century BC, Roman Cato referred to the need to remove water from wet fields (Weaver 1964) and during the Roman civilization subsurface drainage was also known. Lucius lnunius Moderatus, who lived in Rome in the first century, wrote twelve books entitled, “De Re Rustica” describing the procedure for making degraded lands suitable for agriculture (Vucic 1979). During the middle ages, in the countries around North-Sea, the swamps and lacustoure and

INTRODUCTION TO LAND DRAINAGE

<

3

maritime low lands were reclaimed by draining the water through a system of ditches.

Landreclamation by gravity drainage was also practised in the Far-East, for instance, in Japan (Kaneko 1975). The windmill was used to pump water for turning deeper lakes into polders, for example, the 7000 ha Beemster Polder in the Netherlands in 1612 (Leeghwater 1641). The word ‘polder ’ inDutch language is used internationally to indicate a ‘low lying area surrounded by a dike’, in which the water level can be controlled independently of outside water. During the 16th, 17th and 18th centuries, drainage technique spread over Europe including Russia (Noseko and Zonn 1976), and to the USA (Wooten and Jones 1955). In the 17th century, the removal of excess water by closed drains was introduced in England. In 1810, clay tiles started to be used and after 1830 concrete pipes made with portland cement (Donnan 1976). The production of drain pipes was first mechanical in England and then it spread over Europe and USA in the mid-19th century (Nosenko and Zonn 1976). Excavating and trenching machines driven by steam engines came into the limelight in 1890 followed in 1906 by the dragline in the USA (Ogrosky and Mockus 1964).

In the 20th century, with the invention of the fuel engine, the trenching or trenchless machine for high-speed installation of subsurface drains was developed. The thickwalled smooth, rigid plastic pipes replaced clay tiles in 1940 followed by corrugated PVC and polyethylene tubing in the 1960’s. Modem machinery regulates the depth of a drain with a laser beam. The high speed installation of subsurface drains is important in waterlogged areas where the number of workable days is limited due to cropping throughout the year. The development of new drainage machinery since 1960 was accompanied by the development of new drain envelope material. The pre-wrapped synthetic filters replaced traditional filters like coconut fiber, gravel (Metzger et al.

1992, Kumbhare 1992 and Honeyfield and Sial 1992).

LAND DRAINAGE FROM ART TO ENGINEERING SCIENCE

Thus, it is very clear that land drainage for centuries was based on local experience and gradually developed into an art with more general applicability. The theories were developed after Darcy’s experiments in 1856 and land drainage became an engineering science (Russell 1934, Ernst 1962, Kirkham 1972). Although these theories form the basis of modem drainage system, there has always been an element of art in land drainage. It is not possible to give beforehand a clearcut theoretical solution for each and every drainage problem. Sound engineering judgment on the spot is still needed and will remain so.

INFLUENCE OF IRRIGATION ON LAND DRAINAGE

Irrigation in agriculture is by far the greatest use of water on earth. More than 70% water is used for irrigation and the rest for domestic water supply, industry and other uses. Irrigation being a human intervention has a two-fold effect on the natural environment: • It changes the land surface of the area and its vegetation.

• It affects the area’s regime of soil moisture, solutes, and ground water: Water and solutes are brought to the area by irrigation canals.

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TEXTBOOK OF DRAINAGE ENGINEERING

Irrigation presently is practised on about 260 million hectares in the world, about . half of this in arid or semi-arid regions. It was particularly in these zones that special drainage measures required were recognized over the years. The considerable areas in these zones were degraded as a result of canal water irrigation. The irrigationproject involving inter-basin transfer of water without adequate drainage has disturbed the equilibrium between the groundwater recharge and discharge resulting in losses to the aquifer system. The water is mainly lost to the aquifer system through water conveyance in the canals and water courses and field application due to poor on-farm water management. The irrigation water even of excellent quality is a major source of soluble salts. The percolation of water causes the water table to rise followed by secondary salinization in irrigated area due to capillary rise. As ground water is often somewhat saline, even a small amount of capillary rise can add Considerably to the salinity of root zone. Thus irrigation results in the twin problems of water-logging and salinization. The aim of drainage in humid area is to control soil water for better aeration, higher temperature and workability. Its primary aim in irrigated land is to control soil salinity.

The discharge capacity in drainage as a result of irrigation should correspond to the quantity of irrigation water supplied in excess of crop water requirements (DPA 1983). The discharge capacity consists of two componentsâ&#x20AC;&#x201D;surface runoff and the subsurface discharge. The subsurface discharge must be corrected with a minimum depth to ground water table, or a maximum rise of the ground water table above the drain pipes of the water surface in the drains. The excess supply of irrigation water is primarily needed to cover losses occurring in conveyance or during field application.

In zones of limited rainfall, a further surplus may be required to maintain an acceptable salinity level in the root zone depending upon quality of irrigation water.

The drainage discharge over a given irrigation season and for the entire area is - - - (11) DA = V-E where, DA = drainage discharge of irrigation area V = total irrigation supply E = evapotranspiration The overall efficiency of the irrigation system ep, is the ratio between the quantity effectively used for evapotraspiration and the total quantity supplied. . . . (1.2) ep = E/V The overall efficiency may be expressed as the product of the conveyance efficiency, ec (the ratio of the quantity reaching the fields and the total water supply) and the field application efficiency (ratio of evapotranspiration of the crop and the quantity reaching the fields). ...(1.3) ep = ec'ea From equations (1.1) and (1.2) ...(1.4) DA =(l-ep)V and be can V E in mm given of time. period for expressed Da, The field losses, both as surface and subsurface discharge, will be more or less evenly distributed over the area, but within a single field they may show flow concentrations during and after application. The conveyance losses cause additional drainage discharge in the vicinity of canals only. The field drainage requirements

ea

•V

INTRODUCTION TO LAND DRAINAGE

5

excluding the effects of canals can be expressed as D =(l-e)eV ...(1.5) where, Da = field drainage discharge of sub area ecV = the relevant volume reaching the sub area.

The overall irrigation efficiency as givenby the equation indicates the effectiveness of the irrigation and drainage systems. In arid and semi-arid zones, the parts of losses are regarded beneficial for maintaining acceptable salinity level in the root zone.

«

Conveyance Losses Conveyance losses consist of losses by percolation and operational losses in the operation system. Percolation losses from unlined canals depend on the permeability of the soil and the depth to ground water \ table. If the ground water table is far below . phreatic the canal bed, a predominantly vertical flow A hi ,/ \\ plane develops under mainly saturated conditions.

If the soil surrounding the canal contains -Adifferent layers, or if, pervious or semiless_ permeÿble_ lining is applied and the flow is pervious, l i governedby the least permeable layer (Fig. \ 1.2). boundary afs* capillary flow / In case of shallow water table near the canal, the flow is governed by the available Fig. 1.2 Canal seepage with deep ground headbetween the groundwater and the water water table surface in the canal and by the horizontal permeability of the soil (Fig. 1.3). In such a case, the groundwater tends to reach the ground surface at the outer slope of the embankment which results in stagnation of water or surface runoff due to seepage. With a deep ground water table, the seepage losses will be more than the shallow water table in the same soil. But shallower water table has much more severe effect on the top soil and the crops.

nAh

-=t=r

cap zone surface \ /run off

/

'groundwafer / table

y i Fig. 1.3 Canal seepage with shallow ground water table at different depths

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TEXTBOOK OF DRAINAGE ENGINEERING

Table 1.1 Seepage losses per mz of wet canal parameter (Poiree and Ollier 1968) Surrounding Soil

Loss (m3/m2/day)

Loss per km canal length as percentage of flow (%)*

Clay Loamy clay Sandy clay Sand Sand gravel Gravel

0.09 0.18 0.20-0.40 0.50 0.75 1.00-1.80

0.07 0.14 0.15-0.31 0.38

0.58 0.77-1.39

•Assumed average water depth: 1.50 m; assumed average stream velocity: 1 m/sec.

Serious salinity caused by capillary rise from water table and evaporation along main canals is generally found in arid climate (Table 1.1).

Field Water Application The main purpose of irrigation is to replenish soilmoisture to a level (field capacity) so that evapotranspiration takes place at the potential level. The interval between irrigation depends on the day-to-day evapotranspiration and the rainfall/irrigation during that period (Israelson and Hansen 1962).

In the process of applying irrigation to replenish soil moisture for achievingpotential evapotranspiration more water is generally applied at the upstream of the surface irrigation thanthe water holding capacity of the soilresultingin deep percolation losses.

The overall irrigationefficiency at the farmers’ fields is seldommore that 50% and water application efficiency 70%. These losses result in the rise of groundwater table in areas underlain with saline groundwater. The moment the water table reaches within 3 m of the ground surface, serious water-loggingproblemis encountered which is accompanied by secondary soil salinization due to capillary rise from shallow ground water table.

The water-logging problem can to a great extent be minimized by adopting efficient on-farm water management practices, which include water application by properly designed surface irrigationmethods (wherever feasible using sprinkler and drip irrigation method), proper lining of conveyance systems and their periodic maintenance, proper irrigation scheduling, land development, conjunctive use of canal and saline groundwater. These measures will not only help in saving of water thus increasing irrigation command, but will also reduce the extent of rise of water table and minimize the risk of water-logging and salinity.

PLANT GROWTH IN RELATION TO DRAINAGE Water and Air in the Soil Roots require oxygen for respiration and other metabolic activities. They absorb water and dissolve nutrients from the soil and produce carbon dioxide, which has to be exchanged with oxygen from the atmosphere. This aeration process, a combination of diffusion and mass flow, requires open pore space in the soil. For proper development of roots, water, nutrients and air must be available simultaneously. If the pore space is mainly occupied with water for a considerable length of time, the soil is said to be water-logged causing deficiency of oxygen. Both soil texture and structure describe the size of pores—both capillary and non-capillary. The capillary pores are small and

7

INTRODUCTION TO LAND DRAINAGE

-v

important for storage of water. The non-capillary pores which are large and can be emptied easily, function under adequate drainage conditions as channels for the exchange of gases.

The field capacity and permanent wilting point are two important soil moisture contents. The difference between the two indicates the availability of soil moisture for plant growth. Field capacity is the upper limit of soil moisture and is the amount of water which under gooddrainage is retained against the force of gravity (Majumdar 2000). At field capacity the capillary pores are filled with water and the non-capillary pores with air. In most soils, aeration is sufficient at this point. In some heavy soils, however, although the pore space may be 60% or more, almost all pores are of capillary dimensions and can be readily drained, resulting in water-logged conditions (Fig. 1.4) (Daubenmire 1959). non capillary pore space

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Fig. 1.4 Distribution of rootlets; a, unfavourable soil; b, favourable soil.

Sandy soils often have too little capillary porosity and thus have a low moisture availability for the plant. The wilting point is the lower limit of available soil moisture that results in wilting of plants. , Plants are differently adapted to the availability of water in the environment. Natural vegetation reacts sharply to different soil moisture regime (Baron 1963) (Fig. 1.5).

Urt?caedioica

reed grass Glyceria maxima

hairy willow herb Epilobium hirsutum

100 cm

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2

4

6

8

m

Fig. 1.5 Effect of soil moisture regimes on plant growth.

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TEXTBOOK OF DRAINAGE ENGINEERING

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hydrophytes mesophytes xerophytes (e-f

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field capacity wilting point

time Fig. 1.6 Relation of growth of hydrophytes, mesophytes and xerophytes to moisture conditions in loam soil

Various ecological classes of plants are distinguished e.g. hydrophytes, xerophytes and mesophytes, denoting plants of wet, dry moist habitats (White 1956) (Fig. 1.6).

The plants belonging to mesophytes can not inhabit water or wet soil nor can they survive in low soil moisture condition (Daubenmire 1959). The majority of crops having moderately deep root fall in this category. Mesophytes and xerophytes occur under conditions indicated by points ‘c’ to ‘d’ (Fig. 1.6). Mesophytes die at moisture contents, below point ‘d’ and xerophytes become semi-dormant or dormant. In arid regions, besides xerophytes, some specially adopted mesophytes, the phreatophytes and ephemerals are also found. Ephemerals, in contrast with phreatophytes have a rather shallow and diminutive root system. Their main physiological adaptation lies in there ability to complete their life cycle during the brief rainy season. In case of water-logged conditions, the development of roots and growth are suppressed.

Good aerationandmoisture conditions throughout the soil profile stimulate growth and development of roots in all directions. The resulting extensive deep root system explores a large soil volume for water and nutrients. In a well-drained soil, the deep root system is able to withdraw water from the capillary fringe of the groundwater.

The highest point to which this capillary fringe extends depends on the depth of groundwater table and the texture and structure of the soil. In the capillary fringe, both aeration and water supply are favourable and the water requirements of the plant may be partly or totally fulfilled by this source.

Plants that develop a shallow root system due to water-logging during the initial growth phases may suffer form water shortage at later periods of drought, although the groundwater table may not be very deep. The average depth to which the roots of a number of field crops penetrate is given in Table 1.2. The deviations from the average values may be due to soil type and crop variants. For most of the crops, especially annuals, about 70% of the volume is found in the first 30 to 60 cm below soil surface.

Drainage and physical soil conditions: Physical soil conditions influenced by drainage are structure, aeration, organic matter and temperature.

INTRODUCTION TO LAND DRAINAGE

9

Table 1.2 Average depth of root penetration of crops under optimum soil moisture conditions Crops

Depth

Bulb crops, onion, lettuce Pasture grasses, cabbage, spinach, beans, strawberries, potatoes, carrots, egg plants Capsicum species, squash Coconut, oilpalm, datepalm Cotton, lima beans Maize, flax, small grains, sugar beet, melons Alfalfa, sorghum, sudan grass, steppe grasses, sugarcane, deciduous orchards, citrus orchard

(feet)

(cm)

1 -2 2

30-60 60

2-3

60-90 60-120 120 150-180 150-210

2-4 4 5-6 5-7

Soil Structure

Good structure results in favourable conditions for simultaneous aeration and storage of soil moisture and reduction in the mechanical impedance to root growth. In soil with a groundwater table at 40 to 60 cm below the soil surface, the deterioration of soil structure leading to a more compact and sticky top soil that the deeper ground water (Hooghoudt 1952). In surface layer of poorly drained soils, many large clods are found, whereas in the well-drained soils small crumbs dominate (Hooghoudt, 1952, Nicholson and Firth 1958). Drainage also the pore space promoting the cracking and aeration of soil (Wesseling and Van Wijk 1957). The percentage of large pores decrease with a shallow water table and hydraulic conductivity of the 50-90 cm large decrease (Van Hoorn 1958). The maintenance of soil water level at deeper depth has a positive influence on structure and related properties (Fig. 1.7). vol

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3 50

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80

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Fig. 1.7 Influence of water table depth on water and pore distribution

Soil Aeration In a well-drained soil, air not only penetrates into the deeper soil layer but the volume of air in the surface layer is also much greater (Fig. 1.7).

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TEXTBOOK

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DRAINAGE ENGINEERING

Soil Organic Matter Organic matter is important for soil structure as well as for the supply of nutrients.

During the decomposition of organic matter, important substances for the build-up of soil aggregates are formed and plant nutrients are released. The loss of organic matter has adverse effect on soil structure impeding internal drainage and thus root penetration.

Soil Temperature Drainage results in lowering of specific heat of soil and warming up of soil. In drained soil, climate is favorably changed making early planting possible in areas with cold winters. In soils with high water table freezing may cause root damage of crops that cover the soil during winter.

DRAINAGE AND CULTIVATION PRACTICES

Tillage With adequate drainage, the moisture content of the surface soil layer does not exceed field capacity. This is important because there is a narrow range of soil moisture content, suitable for tillage operations. The optimum soil moisture content is below field capacity. Therefore, the tillage of soil should be avoided soon after rainfall or irrigation. The tillage operations at higher moisture contents in many clayey soils cause breakdown of aggregates, dispersion of soil particles and to some extent puddling of soil (Me George 1937). In extreme cases the almost complete destruction of aggregates may result in a compacted soil, i.e., soil devoid of pore space. As a result of compaction and crust formation, both the infiltration rate and hydraulic conductivity are low, impeding internal drainage and improper functioning of subsurface drainage system. To derive maximum benefit from drainage, the soil should receive an adequate level of tillage to avoid differences in relief.

Weed Control Good drainage reduces both the need for tillage and the hazard of soil structure deterioration. Most crops are mesophytic, showing their best growth and development in soils with moderate moisture contents. The weeds associated with these crops are predominantly broad-leaved plants in well-drained soil and some grass species in poorly drained soils. Broad-leaved weeds are more easily eradicated than the grasses.

Weed growth can be effectively controlled by careful tending of the crop and application of rotations possible in well-drained soils. With adequate drainage, besides the disappearance of grasses, the vigorous growth of alfalfa controls the growth of broad leaved weeds.

Drainage and Nutrient Supply Various processes activated by bacteria, fungi or other micro and macro organisms depend on good aeration and drainage. The deeper the roots penetrate, the more nutrients are available for absorption. The advantage of drainage and consequent deep root zone is even more pronounced when the nutrients (N, P, K, Ca and Mg) are displaced to the deeper layers (Fig. 1.8). Good drainage also increases the microbiological decomposition of organic matter releasing and making available plant nutrients like nitrogen and phosphate. Good drainage prevents the production of

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