Storm Hydrographs

What does ‘flash flooding’ mean?

What is a Storm Hydrograph?

Read through SUG 13-15 the next page ‘how and why do storm hydrographs vary’

Notes

Key terms you need to know:

Rising limb The time interval between peak rainfall and peak discharge

Peak discharge The normal day-to-day discharge of the river

Lag time The part of a storm hydrograph in which the discharge starts to rise

Falling/recessional limb The time when the rainfall reaches its highest

Base flow The time when the river reaches its highest flow

Peak rainfall The part of a storm hydrograph where the water in the river starts to decrease

Highlight the information below:

Storm Hydrograph

___________: the highest amount of rainfall per time unit______________: shows how quickly the discharge rises after a rain storm_______________: the highest recorded discharge following a rainfall event_______________: the time difference between peak rainfall and peak discharge_______________: shows the reduced discharge once the main effect of runoff has passed._______________: the normal flow of a river when its water level is being sustained by groundwater flow_________________: (does not always appear) marks the level of discharge above which flooding will occur.

How does the shape of the basin affect the shape of a storm hydrograph?

How does the steepness (relief) of the profile affect the shape of a storm hydrograph?

Using the table at the bottom of page 17 of Hodder

Answer the questions below

How does the drainage density affect the shape of a storm hydrograph?

How does geology affect the shape of a storm hydrograph?

How does the type of soil affect the shape of a storm hydrograph?

Notes

Different shapes of a storm hydrograph

‘FLASHY’- steep limbs, high peak discharge, short lag ‘FLAT’- gentle rising limb,lower peak discharge, long lag

Use the statements to complete the grid (on the previous page) showing how different factors determine the shape of a hydrograph

The shape of the storm hydrograph may vary from event to event on the same river (temporal variation) or one river can vary from another (spatial variation). The different factors in the table are PHYSICAL FACTORS which can’t be controlled.

Storm hydrographs which have a very gentle rising limb, a lower peak discharge and a long lag time are called delayed or attenuated hydrographs(FLAT HYDROGRAPHS)

The impact of urbanisation on hydrological processes

Using all of page 18 of Hodder to create a mind map to show the impact that urbanisation has on hydrological processes.

Why does urbanisation increase the risk of flooding (6 marks)___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Synoptic Themes (Highlight)

Through their control of land use and land-use changes in a considerable number of countries, planners are major players. Planning departments in both urban and rural areas, and landowners such as farmers, are important players in the management of flood risk. The decisions they make, for example about the location and amount of urban growth, can clearly affect the behavior of drainage systems. Their decision will impact most on run-off, water budgets and storm hydrographs.

Hydrographs are also likely to be affected by climate change, with a general prediction of more intense rainfall in many northern hemisphere areas which would create ‘flashy’ hydrographs and more flooding, while some tropical areas may become drier and hydrographs subdued (‘flat’ ‘subdued’ or ‘delayed’), with consequent navigation and water supply issues.

Review: Factors that affect the discharge of a river and the shape of the storm hydrograph.

On the left hand side of the table add the word ‘HUMAN’ or ‘PHYSICAL’ for each factor.