PreambleIn many Irrigation Projects, crop yields are reduced due to water logging and salinization of the land.

In some cases, there is total loss of production and therefore the land is abandoned. Water logging

may also cause human health problems, particularly malaria, because of ponded water. Of the

estimated 235 million ha of irrigated land in the world, 10 to 15 percent has been affected by water

logging and salinization.

Two important causes of water logging and salinization are:

1. Excessive application of irrigation water

2. Lack of adequate drainage

Thus provision of adequate drainage is a solution to the water logging and salinization problems of

irrigated lands. Lack of adequate drainage has probably been the greatest single cause of failure of

irrigation projects throughout the world. History has repeatedly shown that the excess water and salt

must be removed from soils for long-term sustainability of the irrigated agriculture.Therefore,if

irrigation is considered to be the science of survival of mankind, drainage undoubtedly provides for

the survival of irrigation

The main objective of land drainage is to remove excess water in order to improve the profitability of

framing the land. The need for drainage in humid and semi-arid regions stems basically different

requirement. In humid areas, an effective drainage system prevents water logging by removing

excess rainfall and ensures easy and early access to the fields for carrying out agricultural activities.

The main objectives of a drainage system in semi-arid regions, on the other hand are to control the

water table and maintain the soil salinity in the root zone within acceptable limits for optimizing crop

yields.

Ever since the introduction of the gravity flow irrigation system in Indus Basin during the latter half

of the 19th century, the seepage of canal water into the sub soil strata has been a continuous process.

Mostly a flat topography with only a small gradient available for the natural drainage and inefficient

irrigation practices caused rise in the ground table to alarming levels. This produced major

environmental problems of water logging and salinity in the irrigated areas

Drainage

Definition“Drainage is the removal of excess water and dissolved salts from the surface and subsurface of the land in order to enhance crop growth.”

EnlightenmentDrainage can be either natural or artificial. Most areas have some natural drainage; this means that excess water flows from the farmers' fields to swamps or to lakes and rivers. Sometimes, however, the natural drainage is inadequate to remove the extra water or salts brought in by irrigation. In such a case, an artificial or man-made drainage system is required. A man-made drainage system is an artificial system of surface drains and/or subsurface drains, related structures, and pumps (if any) to remove excess water from an area.

Drainage is needed for successful irrigated agriculture because it controls Ponding, Water logging Salinity.

DRAINAGE TO CONTROL PONDINGTo remove ponding water from the surface of the land, Surface Drainage is used. Normally, this consists of digging shallow open drains. To make it easier for the excess water to flow towards these drains, the field is given an artificial slope. This is known as land shaping or grading (Figure 5).

Surface Drainage Surface Drainage is the removal of excess water from the surface of the land by diverting it into improved natural or constructed drains, supplemented, when necessary, by the shaping and grading of the land surface towards such drains.

DRAINAGE TO CONTROL WATERLOGGINGTo remove excess water from the root zone, subsurface drainage is used (Figure 6). This is done by digging open drains or installing pipes, at depths varying from 1 to 3 m. The excess water then flows down through the soil into these drains or pipes. In this way, the water table can be controlled.

Subsurface Drainage Subsurface drainage is the removal of excess water and dissolved salts from soils via groundwater flow to the drains, so that the water table and root-zone salinity are controlled.

DRAINAGE TO CONTROL SALINIZATIONTo remove salts from the soil, more irrigation water is applied to the field than the crops require. This extra water infiltrates into the soil and percolates through the root zone. While the water is percolating, it dissolves the salts in the soil and removes them through the subsurface drains (Figure 7). This process, in which the water washes the salts out of the root zone, is called leaching.

BENEFITS OF DRAINAGEOne of the benefits of installing a drainage system to remove excess water is that the soil is better aerated. This leads to a higher productivity of crop land or grassland because:

The crops can root more deeply. The choice of crops is greater. There will be fewer weeds. Fertilizers will be used more efficiently. The grass swards will be better. Other benefits of well-drained soils are: The land is more easily accessible. The land has a greater bearing capacity. The soil has a better workability. The period in which tillage operations can take place is longer. The soil structure is better, which also improves permeability. Soil temperatures are higher, so that crops (particularly horticultural crops) and grasses

can be grown earlier.Selection of Drainage System

Selection of drainage system depends upon the nature of the problem and physical characteristics of the area.The physical factors identified are topographic factor, soil factors and water factors. However when physical factors are equally favorable for the drains and tubewells then the deciding factor may be the relative economics.

THE NEED FOR DRAINAGE

Figure 2 shows the water balance in an irrigated area. Before irrigation water can be applied to a crop, it has to be diverted from a river or lake (1) or pumped from the groundwater reservoir (2). The amount of water needed has to be greater than the quantity required by the crop because some of it will leave the area in various ways: not only will it be used by the crop as evapotranspiration(3) but some of it will be lost as evaporation (4) as seepage (5) and operational spills (6) from the irrigation canal system, as tail water runoff from irrigated fields (7) and as deep percolation (8) In the field, irrigation water, together with any rainfall (9) will be partly stored on the soil surface (10)and will partly infiltrate into the soil (11) If rain or irrigation continues for long periods, pools may form on the soil surface. This excess water on the soil surface is called ponded water. It needs to be removed.

Drainage systemsCOMPONENTS OF A DRAINAGE SYSTEM

As shown in Figure 8, a drainage system has three components:

A field drainage system, which prevents ponding water on the field or controls the water table.

A main drainage system, which conveys the water away from the farm. An outfall, which is the point where the drainage water is led out of the area.

History & Orientation

Drainage Problems of Pakistan and Past InterventionsBefore the construction of extensive system, the groundwater table in the Basin was in the state of natural equilibrium. The water table was quite deep, ranging from 50 to 100 feet below ground level in different parts of the country. The groundwater level fluctuated during the annual hydrological cycle, it used to rise as a result of the monsoon rains, but world return to the normal levels during winter as a result of natural drainage.

Indus Basin irrigation system was initially developed without provision for drainage. Extensive irrigation without proper drainage in the alluvial soils of Indus plain disturbed the natural equilibrium as percolation from the unlined canals, watercourses and inefficient field application practices started to build up the recharge .As such the groundwater table started to rise gradually. In order to monitor the phenomenon a network of observation points was developed beginning 1870 and a schedule of their bi-annual observation was adopted. The rate of rise of water table varied from 0.5 ft to 1.5 ft per year depending upon the local environment.

The need for drainage investigations were realized for the first time in 1918 when a Drainage Board was created. In 1925 , a Water logging Enquiry Committee was constituted to advise the Govt. on the issue ,which was replaced by a Water logging Board in 1928. First Drainage Circle was established in 1932 and construction of seepage and seepage-cum-storm-water drains was started in Chaj and Rachna Doabs in 1933.After Independence two Drainage Circles were created in 1951 . After the independence two Drainage Circles were created in 1951.

On the basis of groundwater levels, various remedial measures were tried.

Closure of canal in monsoon season. Construction of seepage-cum-storm water drain, in water logged areas. Lowering the F.S.L of canals. Planting of phreatophytes along canals. Installation of tube wells along major canals.

However, none of the measures provided more than local or temporary relief and the regional problems of water logging and salinity continued.

Punjab Irrigation SystemThe Punjab Irrigation System is accompanied with drainage systems. Originally the drains were designed to collect the agricultural surplus water and flood water. Due to increase in population and industrialization the drains mainly collect the industrial and municipal effluents of varied nature. In general drains are creating pollution problems in the Irrigation channels. Much of the drainage effluent is either retained in the Indus Basin or disposed into the rivers and canals. In Punjab the length of total surface drains are 3883 km.

Chart 1 illustrates the change in depth to water table from preirrigated time to the early 1960s. The water table in the middle of the doabs has risen from 20 to 30 meters during this 80- to 100-year time period. This rise initially was at a constant rate until the water table approached the land surface As it became evident that the rising water table and the resulting threats of water logging and salinity threatened the future of irrigated agriculture in the Indus Plain, a number of studies were made to determine the root of the problem. Carlston (1953) carefully studied previous research and identified three main factors: leakage from the irrigation-distribution system; infiltration of applied irrigation waters, and, to a lesser degree, increased recharge from rainfall runoff due to obstruction of natural drainage courses.

Punjab Irrigation department is divided into six zones

1. Sargodha Irrigation Zone2. Bahawalpur Irrigation Zone3. Lahore Irrigation Zone4. Faisalabad Irrigation Zone5. Multan Irrigation Zone6. DG Khan Irrigation Zone

This report focuses on the drains which are under Multan Irrigation Zone, before going towards drain there is brief introduction regarding this zone .

Multan Irrigation ZoneIntroductionMultan Irrigation was created on 25.03.1968. The Zone is controlled by the Chief Engineer with help of the 04 Nos Superintending Engineers. This zone is consisting on 03 Canal Circles and 01 Development Circle namely, Haveli Canal Circle, at Multan, Mailsi Canal Circle, at Multan, Nili Bar Circle, at Sahiwal and Development Circle, Multan Zone, at Sahiwal. The circle is controlled by Superintending Engineer with help of Executive Engineer, Sub Divisional Officer, Deputy Collector, Zilladar, Sub Engineer and other technical and office staff. The Index Plan of Multan Zone is as under

The main sources of the supply of water are Mangla Command and Tarbela Command. The 04 Nos. Barrages/Head works are fall in this zone which are

Trimmu Barrage Sidhnai Barrage Sulaimanki Barrage Islam Barrage

Below is the OBS ( Organization Breakdown Structure ) of Multan Irrigation Zone.