A.2.1: Hydrograph Characteristics

Question 1

Hydrographs

Answer 1

Shows how a river channel responds to the key processes of the hydrological cycle

Measures the speed at which rain falling on a drainage basin reaches the river channel

Graph of river discharge plotted against time

Question 2

Rising limb

Answer 2

Indicates amount of discharge and the speed at which it is increasing

Very steep in a flash flood or in small drainage basins where the response is rapid

Generally steep in urbanised catchments

Question 3

Peak flow or discharge

Answer 3

Higher in larger basins

Steep catchments have lower infiltration rates

Flat catchments have high infiltrates rates, so more throughflow and lower peaks

Question 4

Lag time

Answer 4

Time interval between peak rainfall and peak discharge

Influenced by basin shape, steepness, stream order

Question 5

Run-off curve

Answer 5

Illustrates relationship between overland flow and throughflow

If there is low infiltration, high antecedent moisture, impermeable surfaces and strong rainfall, overland flow will dominate

Question 6

Base flow

Answer 6

The seepage of groundwater into the channel - very important where rocks have high pore space

A slow movement, and the main, long-term supplier of the river’s discharge

Question 7

Recessional limb

Answer 7

Influenced by geological composition and behaviour of local aquifers

Larger catchments have less-steep recessional limbs, likewise flatter areas

Question 8

Hydrograph size (area under the graph)

Answer 8

The higher the rainfall, the greater the discharge

The larger the basin size, the greater the discharge

Question 9

Influence of geology on hydrographs

Answer 9

Different rock types and structures influence how quickly rainwater reaches the river channel.

Impermeable rocks (and soils) generate more overland flow, so a shorter lag time and a higher peak flow

Permeable surfaces allow more water to percolate through the ground, leading to a more moderated and delayed river response.

Question 10

Influence of seasonality on hyrographs

Answer 10

Variations in a river’s flow depend on:
- The amount and nature of precipitation
- Seasonal variations in temperature and evapotranspiration
- Changes in vegetation cover
- Variations in rock types, soil types and the shape and size of the drainage basin

Seasonal changes in climate generally have the greatest impact on changes in river flow

Question 11

Draw a hydrograph

Answer 11

Check book