- Flow obstruction and change in river course to :- Earthquakes
– Falling of trees
- Heavy rains that persists for days
- Rivers have poor natural drainage system such as :- Absorbsion capacity
– Obstruction of natural drainage
- Soil erosion due to deforestation, agriculture and construction
i. Over grazing:
When people graze too many animals on the land, and the pasture is eaten away quickly, this results in lesser vegetation cover which would lead to soil washing into the rivers easily.
When a piece of land has been used for farming for a long period of time, the soil has become so infertile that no vegetation can grow on it. Because the land is less fertile than before, the soil washes into rivers more easily.
This causes landslides in the slopes of hills and mountains which may result in the unintentional damming of rivers and streams. Some of these rivers and streams might flow into existing rivers and overflow them.
Construction of temporary dams. This produces an obstruction to the flow of a river or stream which then results in an overflow. Also, possible dam failures as the dams may have been poorly constructed or maintained and could easily collapse and this would result in flooding.
i. Failure of hydraulic structures:
Accidents like the breaking of a reservoir may result in the entry of an enormous quantity of water in an area.
ii. Mismanagement of hydraulic structures:
Control structures like dams which are used for various purposes are usually operated according to what is known as an “operation rule” and mismanagement which results in the violation of the rule may necessitate an untimely and sudden release of large amounts of excess water which might flow into adjacent rivers and overflow them.
- Flow obstruction and change of river course
-in the river bed
-beside the river
-in the river bank
High rate of urbanization
Pressure on drainage system