Systems of Drainage

Surface Drainage

• A common type of drainage -- especially in arid and flat areas -- is surface drainage. Surface drainage entails making small furrows that lead to larger ditches around the land's outskirts. These ditches feed into streams and other tributaries, eventually into larger rivers and out to sea. There is some seepage of water through the soil to the ditches. Smoothing and flattening of land are beneficial for this type of drainage, which is important in flat areas where no natural sloping aids drainage.

Subsurface Drainage

• Subsurface drainage systems usually are needed in conjunction with surface systems. Subsurface systems comprise pipes and drains laid under soil. Using gravity, water flows into smaller pipes at the higher end of the water table and into increasingly larger pipes and drains until it reaches the main drains, a sump or a water-receiving body like a river or lake.

Secondary Drainage

• Secondary measures can be taken to improve drainage efficiency. With low-permeability soils, methods including sub-soiling, tillage and mole drainage can be employed. Tillage is the breaking up of surface soil by methods like troweling or plowing. Sub-soiling breaks up soil at much deeper levels than tillage. Mole drainage is the creation of small channels between rows. Biological methods include cropping with deep-rooted legumes and crop rotation. Deep-rooted trees can also be used to lower the water table.

Benefits

• Effective drainage systems' main benefits include increased health and well-being of humans, animals and crops. Effective soil drainage means increased crop yields, increased productivity and profitability for farmers and healthy management of soil and water tables. In addition, the drainage of wetlands decreases the breeding grounds of mosquitoes -- a major cause of malaria -- and provides fruitful land. Drainage also promotes beneficial soil bacteria activity. With less surface run-off comes less erosion and fewer land cave-ins. Higher-value crops can be planted and crop quality increases.