Drainage Basins

Surface runoff, is really rare.

Bank full condition- maximum amount of water that a river can hold.

Discharge is the velocity of the river times its volume. It is the amount of water in the river passing a given point at a given time, measured in Cumecs.

Velocity is the speed of the river. Measured in metres per second

Volume is the amount of water in the river. It is the cross sectional area of the rivers channel measure in square metres.

FACTORS AFFECTING THE RESPONSIVENESS OF A RIVER

1. RELIEF- the steeper the slopes the lower the rate of infiltration and the faster the rate of runoff when the soil is saturated.
2. ROCK TYPE- run off will occur quickly where the impermeable rocks are exposed at the surface or quickly when they underlay soils. Soils with large amounts of clay do absorb moisture but only very slowly – therefore their permeability is low.
3. SOIL TYPE- the deeper the soil the more water can be absorbed. Soils which have a larger particle sizes have larger infiltration capacities.
4. VEGETATION- interception caused by roots, trees have larger and deeper root systems that thin grass Mooreland and thus absorb more moisture.
5. LAND USE- urbanisation- impermeable road surfaces, sloping roofs, guttering and underground drainage systems transfer water very quickly to rivers. The increase of house building in towns and villages as people have opted to from large settlements especially on river flood-plains has contributed to the increase responsiveness of river systems.
6. RIVER USE- building dams and creating reservoirs in flooded valleys behind acts to slow down the rate of discharge at peak times as water is held back to protect the low lying land downstream. Water extracted for industry, domestic use and irrigation.
7. DRAINAGE DENSITY- the length of river course per area of land. The larger the amount of streams and rivers per area the shorter distance water has to flow and the faster the rate of response.
8. NATURE OF PRECIPITATION- rainfall intensity- the greater the rate of rainfall per unit of time, the more likely that overland flow, will take place. Snowfall- this will result in less run-off initially but a sharp rise in temperature may result in quick thaw and flooding.
9. SEASON ANS TIME OF YEAR- in summer similar amounts of rainfall may not lead to flooding as more of the water will be evaporated back from leaf surfaces, tarmac or from river itself.