1. Flooding Case Study - Boscastle

2. Flood Hydrographs
LO: To describe what a flood hydrograph shows and how it can be affected by the drainage basin
bbc footage
All will be able to name the features shown on a flood hydrograph
Most will be able to read data from a flood hydrograph
Some will be able to describe how the stages in a flood hydrograph can affect people
2 hour hydrograph

3. Hydrograph
A hydrograph is a line that shows river discharge over a period of time.
Hydrographs of rivers in flood help show the link between rainfall and river level. This helps people to predict possible floods.

5. Hydrographs Label your copy of the hydrograph diagram.
Glue it in along with your definitions
Discharge (cumecs)
Peak Discharge
Falling Limb
Rising Limb
Peak Rainfall

6. Boscastle

7. Lagtime
Lag time is the amount of time it takes rain to get into a river.
It can be affected by lots of things including; rock type, steepness of hills, vegetation slopes and whether the area is built up.
1. What is the peak rainfall on the Boscastle hydrograph? What time did it occur? 2. What is the discharge of the river Valency before the rain (the baseflow)? 3. What time was the peak discharge at Boscastle? How much water was in the river then? 4. What is the lag time on the Boscastle hydrograph i.e. how long did it take the rain water to reach the river?

9. Boscastle Floods 16th August 2004
In the middle of their peak tourist season in 2004 Boscastle was
Boscastle

10. Factor Short lag time Long lag time Rock type Vegetation Hill slope
Land use
Put the statements into their correct spot in the table
Bare earth with few plants
Permeable (water soaks into it)
Steep valley sides
Rural farmland
Lots of trees and plants
Impermeable (water doesn’t soaks in)
Built up area – lots of tarmac
Gentle valley sides