Types of Drainage Patterns
Drainage systems vary and often a pattern is seen in the kind of drainage that an area presents on the topo sheet. An area drained by a single river is called its drainage basin or catchment area. It includes the various streams, tributaries and sub tributaries that join to create a network of the river. Thus the main river of an area along with its tributaries forms a drainage pattern. The pattern that is formed is dependent on the relief and the rocks that make up the surface of the area. It is logical that water will flow from higher to lower area and while doing so, it will cut through the surface of the land.
On the topo sheets the perennial water bodies are shown with blue lines. The seasonal streams are shown in black lines. Irregular streams are those which carry water for short spells, generally during and after rainfall, and then disappear or finish off. These are shown by dotted black lines.
Types of Drainage Patterns
The three main types of drainage patterns that can be identified are dendritic, trellised and radial. The disappearing streams indicate an area of inland drainage as in deserts or underground streams such as those in the limestone areas. Broken ground is also shown with black lines and found in ravines and badlands where lack of vegetation causes extensive erosion when the rivers flood.
Dendritic drainage pattern: The name is derived from the Greek word dendron which means a 'tree'. This drainage pattern is similar to a branching tree and hence the name. This pattern of flow of streams and rivers develops in an area which comprises rocks with a uniform structure. The direction taken by the river and its tributaries is largely dependent on the slope. The water channels thus flow through the valleys between the ridges and spurs resulting in the river and its tributaries making a pattern that resembles a tree and its branches.
Trellised drainage pattern: It is a rectangular shaped drainage pattern that develops where bands of rocks vary in resistance. In some areas there are alternate bands of hard and soft rocks. The flowing water can erode the soft rocks and thus flows along the bands of soft rock. Many such water channels form a trellis. The streams (called subsequent rivers) cut out the valleys (called vales) and join the main river (called consequent river) at right angles. The main river, by sheer force, cuts the hard rock and flows down the slope forming an escarpment and thus a river gap is created.
Radial drainage pattern: It is a 'spoke- like' pattern. Water channels flow from around the top if a hill or the top of a dome type feature in numerous directions like the spokes of a wheel. Such a pattern of drainage may develop from a volcano or conical mountain.
There are a few other drainage patterns as well, which are uncommon. The centripetal drainage pattern is the opposite of radial drainage pattern. The streams converge in an area which is either a depression or a basin.
In a parallel drainage pattern, a number of streams flow parallel to each other by following the slope of the region.
Many cities in the United States today have laws against changing the flow of water. Everyone from landscaping companies to State Department of Transportation designers have to keep this in mind. As cities build up, that means more and more cement and asphalt have taken over the natural soil and grasses. This causes the water to run off much more quickly.
To combat this flow of water and drainage, cities are creating flood drainage lakes. I have seen houses being sold to counties just so the county or city can build a drainage area for flood runoff. It is important as a homeowner to know the flow of water, and learning these patterns is important.