Drainage system [Types, Objective, Factors controlling method of drainage]
Agricultural drainage is the removal of excess water, known as free water or gravitational water, from the surface soil or below so as to create favourable soil condition for plant growths. Drainage also deals with the lowering dove a of the ground water table (GWT) below the root zone of the crops to improve the plant growth in some cases or to reduce the accumulation of salt in the crop root zone.
Irrigation and drainage are equally important for successful crop production. Irrigation and drainage cannot be separated from one another and they should go hand to hand. Excess water in the soil even for a short period may cause severe damage to crop and soil. Irrigation provides sufficient moisture in the soil for satisfactory growth of plant whereas drainage is important for avoiding excess moisture in the root zone. The excess moisture may originate from excess rainfall, over irrigation, seepage from canal or reservoirs or ditches. A land having high water table or water stand on the land surface for a long period, excessive soil moisture content, humid or super humid regions with continuous or intermittent rainfall or flat land with fine textured soil may need drainage for high agricultural productivity.
Following are the two types of drainage
1. Surface drainage
The process of removing the excess water from the land surface is known as surface drainage. Adequate arrangement for surface drainage in heavy rainfall areas is essential for speedy disposal of water. Rainfall, snowmelt, waste run off, seepage from adjoining higher land, overflow from stream channel etc. are the sources of surface water. Surface drainage system may be required in either humid or in irrigated areas which is usually an integrate part of irrigation system on slowly permeable soils or in areas of high precipitation rates. It is therefore told that irrigation and drainage are like the two faces of a coin.
2. Sub-surface or internal drainage
The process of removing the water from sub-surface or soil profile is known as sub-surface or internal drainage. There should be subsurface drainage in high water table areas. In either case, the system is conveniently divided into the following three functional parts:
a. Collection system: Budding, surface field ditches, row ditches or divers; Jri ditches are the integral part of the system that first pick up water from the land.
b. Disposal system: This is a part of the system that receives water from the collection system and conveys it, usually in an open channel to the outlet.
c. Outlet:This is the end point of the drainage system. The first step in the design of any drainage system is to locate the outlet, because most of the drainage systems fail due to failure of outlet. The most economic outlet is a natural water way, such as rivers, streams, ditches, municipal drains etc. Sub-surface drains are underground artificial channel through which excess water of a land may flow to a particular outlet.
Objective of drainage
Objectives of drainage are stated below:
i. Removal of excess water from the soil.
ii. Arrangement for good aeration in the soil.
iii. To control the loss of plant nutrients.
iv. To enhance the activity of soil organism.
v. To improve the soil structure.
vi. To control soil erosion.
vii. To prevent the salt accumulation on surface soil.
viii. To develop favourable conditions for the growth of plant root.
ix. To lower down the water level below the root zone.
Factors controlling method of drainage
Drainage system/method depends on the following factors:
i. Topography and gradient of the land.
ii. Type of the soil.
iii. Permeability of the soil.
iv. Crop and its water tolerance capacity.
v. The quantity of water to be disposed and its speed.
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