Drainage refers to the distribution of water features such as rivers, streams, oceans, natural or man-made lakes, etc.
Drainage pattern can be defined as the shape taken by a river and its tributaries. Hence, it is usually shown on topographic maps as drainage features. On the other hand, drainage pattern is the whole process of carrying ground water away, from the moment it falls on the earth surface as rain water to the time that some of it reaches the sea. Drainage can be on the surface and this happens when rivers actually flow on the surface and empty the water into a much bigger water body. When drainage is formed under the ground, it is called underground drainage.
TYPES OF DRAINAGE PATTERN
It is very important for the user to properly understand and identify the various patterns that occur along the course of a river. There are about 30 different types of drainage patterns. Among these are Anastomosing, Sub dendritic, Contorted, Dichotomic, Yazoo, Lacunate, Phantom, Kettle hole, etc. The most common types of drainage patterns are Dendritic, Radial, Trellis, Annular and Centripetal.
- Dendritic Drainage Pattern: In this pattern, there is irregular branching of the tributaries or streams in many directions like the branches of a tree. This pattern is usually found in areas of relatively homogenous rock where there is the same degree of resistance to erosion. The insequent streams normally join the parent river called consequent at an oblique angle. The resulting drainage pattern assumes a tree form and it branches, therefore its name is from the Greek word “Dendron” which means a treeg. Orange River in South Africa.
- Radial Drainage Pattern: Radial drainage pattern tends to develop in areas of large conical hill or area of volcanic cones. The drainage radiates from the conical point. The many rivers, streams and their tributaries diverge from a central elevated highlands and flow away to different directions.
- Trellis Drainage Pattern: This drainage pattern is found or developed in areas where there is alternate band of hard and soft rocks. The streams or tributaries flow almost parallel to each other in line with the nature of the rock materials of the soil. These tributaries follow the soft rock and join the main stream at right angle.
- Annular Drainage Pattern: The tributaries or the main river almost form a concentric ring around a highland as a result of interruption of the former stream channels by the formation of crater occupied by the lake. In other words, the main stream almost flows round or encircles a hill.
- Centripetal Drainage Pattern: Many rivers or streams flow from different directions into a lake.
A settlement is defined as a place having one or more buildings with people living in them.
Factors which may favour any settlement depend on the features, economic activities or resources available within that settlement.
People choose to settle in an area because of some of the following reasons:
- Availability of drinkable water.
- Presence of communication routes e.g. roads, railways, etc.
- Presence of economic resources like minerals.
- Presence of fertile soil for farming purposes.
- Presence of commercial activities e.g. markets.
Types of Settlement
There are three main types of settlement and these are:
- Nucleated or Dense Settlement: In this type, the buildings are very close to each other or are concentrated in a small area with many social amenities. This settlement is common in urban centres and also in some rural areas.
- Dispersed or Scattered Settlement: The buildings are scattered or far from each other with few social amenities.
- Linear Settlement: In this type, buildings are located along the roads, railways or even rivers in a linear form.
Other types include:
- Nodal Settlement: This is the settlement around the meeting point of roads or railways.
- Confluence Settlement: This is the settlement around the meeting point of two rivers e.g. Lokoja in Nigeria.