In areas of heavy rainfall or low soil percolation, it is necessary to employ surface drainage systems to get rid of surplus surface water from the land. Commonly used surface drainage systems include shallow ditches, open channels, grassed waterways and sloped banks. These drainage systems drain away surface water quickly and efficiently, but do not make much of a difference to groundwater. If there are land drainage problems due to groundwater, they will need other solutions.
Surface drainage needs to be carefully planned by taking into account the land's topography, the amount of rainfall received, and the type of soil. In some cases, shallow ditches following the land contour may be enough, in others the ditches may need to be deeper or the land may need to be graded or sloped to facilitate soil drainage. The ditches may follow a random pattern or a parallel pattern.
Large fields with a good many depression areas do well with randomly patterned field ditches. These shallow ditches follow the land contours, do not impede the movement of farm machinery and drain away water from depressed areas. Parallel field ditches are excellent for agricultural drainage on flatter types of lands, and are also used as to prevent erosion on sloping farm lands. Water from the field ditches is drained away into side ditches. The side ditches then carry water to an outlet channel.
Other methods for effective surface drainage include land grading and smoothing. Both of these involve using soil moving equipment like tractors, scrapers and land levelers to alter the land surface to make it easier for the surface water to run off. The land is first graded to give it a proper slope and it is then smoothed to remove any depressions or obstructions.
Open drains and ditches need to be regularly maintained to keep them free from silt deposits and vegetation growth. They also need to be monitored for signs of erosion. Sometimes the open ditches, if they happen to be rather deep, may require to be fenced to prevent animals and people from falling into them accidentally.
Surface drainage is important in farm areas as it prevents many water-related land problems and ensures that crops do not become waterlogged. Having a proper surface drainage system also prevents the topsoil from being washed away. The drained water is usually carried away to a stream, river, dam or another drain.