Hydrology and fluvial geomorphology 1.2

Question 1

What is an annual hydrograph and a storm hydrograph?

Answer 1

A graph that shows change in river discharge

• over the course of year
• during a rainfall event

Question 2

Explain these key terms of a storm hydrograph:

• Rising limb
• Falling limb
• Lag time
• Peak
• Storm flow
• Base flow

Answer 2

• Rising limb: discharge increasing
• Falling limb: discharge decreasing
• Lag time: time between maximal rainfall and peak discharge
• Peak: highest level a river reaches
• Storm flow: additional discharge from storm
• Base flow: normal discharge

Question 3

What are the climate influences on hydrographs?

Answer 3

• Precipitation: increased rainfall leads to flashier hydrograph.
• Temperature: increased temp leads to more evaporation.
• Antecedent moisture: increased soil moisture leads to more surface runoff and more discharge.
• Seasons: more discharge in winter months vs summer months

Question 4

What ways can drainage basin characteristics influence hydrographs?

Answer 4

• Size: larger basins increase lag time and more water
• Density: more streams carrying water to river channel
• Porosity and permeability of soil: if more infiltration takes place, less river discharge
• Landuse: less permeable surfaces such as urbanisation will increase surface runoff

Question 5

Examples of how land use can affect hydrographs?

Answer 5

Two drainage basins of equivalent sizes in Washington USA in 2000.

• Newaukum Creek is a rural drainage basin that reached a daily average of 10 cumecs
• Mercer Creek is an urbanised drainage basin that reached a daily average of 25 cumecs