Drainage basin, also called catchment area, or (in North America) watershed, area from which all precipitation flows to a single stream or set of streams. The boundary between drainage basins is a drainage divide: all the precipitation on opposite sides of a drainage divide will flow into different drainage basins.

Each drainage basin is separated topographically from adjacent basins by a perimeter, the drainage divide, making up a succession of higher geographical features (such as a ridge, hill or mountains) forming a barrier.

Large basins receive more precipitation than smaller basins, therefore they have a larger runoff. Basins with a higher drainage density (number of tributary rivers) collect rain water more quickly, therefore the lag time will be shorter.

A drainage basin is an area of land where all precipitation that falls will drain or flow downhill into a specific stream. Drainage basins are often surrounded by steep mountain ridges or hills and have a drainage divide, which is a line that separates two adjacent drainage basins.

Drainage patterns

• Dendritic drainage pattern.
• Parallel drainage pattern.
• Trellis drainage pattern.
• Rectangular drainage pattern.
• Radial drainage pattern.
• Centripetal drainage pattern.
• Deranged drainage pattern.
• Annular drainage pattern.

The Four Types Of Drainage Systems For Your Home

• Surface Drainage System.
• Subsurface Drainage System.
• Slope Drainage System.
• Downspout and Gutter Systems.
• Contact All Aspects Waterproofing For Your Drainage Needs!

dendritic drainage pattern

Basically, there are three drainage methods from which the designer can select being; surface drains, pumped tube wells and horizontal pipe drains. The selection between these techniques is not very straightforward and depends to a certain extend on the preferences of the designer.

open deep drainage

Drainage can be either natural or artificial. Many areas have some natural drainage; this means that excess water flows from the farmers’ fields to swamps or to lakes and rivers. There are two types of artificial drainage: surface drainage and subsurface drainage.

All above ground and below ground horizontal drainage pipes should be laid to an adequate gradient. Gradients from 1 in 40 to 1 in 110 will normally give adequate flow velocities. A gradient of 1 in 80 is suitable for commencing calculations for pipe schemes.

In order to carry the flow and to avoid blockages, the drain or sewer that you intend to connect to generally needs to be at least 0.8m lower than the ground floor level. If it is less than this, you should seek advice from a builder, architect or drainage engineer.

The rise may be set at a unit of one, so that, for example, a slope of 1:20 means that as each dimensional unit of height rises or falls, the dimensional unit of length runs out by 20 units.