Drainage
Drainage is the removal of excess water from the soil surface or root zone. Without it, roots lack oxygen, harmful salts build up, field operations are delayed and crops yellow and wilt. Waterlogging is common in canal-irrigated areas with seepage, low-lying land and heavy clay soils.
Methods
- Surface drainage: open ditches or shallow channels remove excess water from the land surface; land smoothing and grading help water move to them.
- Sub-surface drainage: removes water from below the surface and lowers the water table. Types include tile drains (perforated clay or plastic pipes laid underground), mole drains (unlined channels made in clay subsoil by a bullet-shaped mole plough) and vertical drainage (pumping from wells).
- Bio-drainage: planting trees with high transpiration, such as eucalyptus, to lower the water table.
Drainage is also essential when reclaiming saline soils, because salts leached by water must be carried away.
Watershed management
A watershed (catchment) is an area of land from which all rainwater drains to a common outlet such as a stream, river or reservoir. Ridges form its boundary.
Watershed management is the planned, integrated use of land, water and vegetation in a watershed to conserve soil and water, increase productivity and improve rural livelihoods.
Components
- Soil conservation: contour bunds, terraces, gully plugs, vegetative barriers.
- Water harvesting: farm ponds, check dams, percolation tanks, nala bunds to recharge groundwater.
- Afforestation and pasture development on upper slopes.
- Suitable crops and agroforestry for each land class.
- People's participation through user groups and watershed committees.
Treatment proceeds from ridge to valley: upper slopes are treated first so that runoff and silt are controlled before structures are built downstream.
Key points
- Surface drains remove ponded water; sub-surface drains lower the water table.
- Mole drains suit clay subsoils.
- A watershed is bounded by ridges and drains to one outlet.
- Watershed works follow the ridge-to-valley approach.
- Community participation is central to success.
Common mistakes
- Thinking watersheds are only river basins of large size; small micro-watersheds of a few hundred hectares are planned too.
- Treating drainage as needed only in rainy areas; irrigated canal areas also suffer waterlogging.