can be either natural or artificial. Most areas have some natural drainage
where excess water flows from homes to lakes or rivers. However, natural
drainage is inadequate in removing extra water at times, so an artificial or
man-made drainage system is required. A man-made drainage system is an
artificial system of surface drains or subsurface drains, related structures
and pumps to remove excess water from an area. To remove stagnant water from
land surface, surface drainage is employed. This usually consist of digging
shallow open drains. To facilitate the ease of excess water to flow towards
these drains, the drains are built with bed slopes. Surface drainage is the
removal of excess water from land surface by diverting it into enhanced natural
or constructed drains, supplemented by the shaping and grading of land surface
towards these drains when necessary.
and hydrological factors under which the drainage system will have to function
need to be known to predict the effects of changes in the natural conditions
after installation of a drainage system. For the design of a drainage system,
the drainage requirement of the drainable surplus has to be known. This is the
quantity of water that must be removed from an area within a certain period to
avoid any unacceptable rise in the levels of the groundwater or surface water.
Removing drainable surplus is advantageous because it prevents waterlogging by
artificially keeping the water table sufficient deep. The drainage requirement
is the quantity of water that must be removed from an area within a certain period
to avoid unacceptable rises in the levels of the groundwater or surface water.
drainage requirement is a major problem because the natural conditions in these
areas are diverse so different water resources may be involved in the
calculations. Therefore, field work has to be carried out to find out what the
general features of the groundwater regime are. A proper understanding of these
regimes allows the drainage engineer to how they will be affected by drainage.
To calculate the drainage requirement, an analysis has to be made on the
overall water balance of the study area. Water balances are often assess for an
average year. However, waterlogging is neither the same duration nor frequency
every year. Therefore there is often a need to assess water balances, not only
for an average year but also for specific years like a very dry year or a year
with extreme rainfall.
The field drainage
system is a network that gathers the excess water from the land by means of
field drains, possibly by measures to promote the flow of water to these
drains. The main drainage system is a water-conveyance system that receives
water from the field drainage systems, surface runoff and groundwater flow and
transports it to the outlet point. The main drainage system consists of some
collector drains and a main drainage canal. A collector drain collects water
from the field drains and carries it to the main drain foe disposal.