The drainage basin system

Question 1

Drainage Basin

Answer 1

An area of land drained by a rive and its tributaries
* Edge of basin is marked by boundary called watershed
* Vary in size e.g Missipssipi, Nile and Amazon
* Its an open system

Question 2

Stores and Transfers

Answer 2

1. Water enters basin as precipitation, some intercepted by vegetation, some drips as stemflow
2. Groundwater flow feeds river banks and beds, slow transfer
3. Infiltration occurs also. Infiltration capacity refers to what extent the soil is already saturated and is exceeded when soil is unable to absorb the water
4. Overland flow where water runs off the surface
5. Throughflow can occur where water is soil water until it reaches the water table

Question 3

Water Balance

Answer 3

• Helps hydrologists to plan for future water supply and flood control
• P = Q + E +/- S (precipitaion, total runoff, evapotranspiration, storage)

Question 4

Total runoff

Answer 4

A measure of the proporton of the total precipitation that makes its way into rivers and streams
* Varies with differences in soil water, rock type and vegetation cover
* Intensity of precipitation is also important

Question 5

Discharge

Answer 5

Volume of water passing through a certain point in a river
* Measured in cumecs
* Discharge (m^3 per second) = cross sectional area (m^2) x velocity

Question 6

Flood hydrograph

Answer 6

A graph showing the discharge of a river after a storm event
* It has 6 main features: falling + rising limb, peak discharge, peak rainfall, lag time and baseflow

Question 7

Lag time

Answer 7

Time taken between peak rainfall and peak discharge

Question 8

Rising + falling Limb

Answer 8

1. Rising limb- when the river discharge rises
2. Falling limb- where the river dicharge falls

Question 9

Baseflow

Question 10

Flashy hydrograph

Answer 10

Respond quickly to storm event
* Short lag time and high peak rainfall
* Small basins
* Impermeable rocks lead to overland flow
* Urbanisation encourages rapid water transfer
* Steep slopes lead to rapid water transfer
* Saturated soils leads to rapid overland flow
* Heavy rain exceeds infiltration capacity

Question 11

Subdued hydrograph

Answer 11

Responds more slowly with an attenuated hydrograph
* Large basins mean slow water transfer
* Permeable rocks encourage slow transfer
* Forests/interception slow down water transfer
* Gentle slopes slow down water transfer
* Dry soils soak up water and slows down its transfer
* Light rain