Presentation on theme: "Flooding Case Study - Boscastle"— Presentation transcript:
1 Flooding Case Study - Boscastle
2 Flood HydrographsLO: To describe what a flood hydrograph shows and how it can be affected by the drainage basinbbc footageAll will be able to name the features shown on a flood hydrographMost will be able to read data from a flood hydrographSome will be able to describe how the stages in a flood hydrograph can affect people2 hour hydrograph
3 HydrographA 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 definitionsDischarge (cumecs)Peak DischargeFalling LimbRising LimbPeak Rainfall
7 LagtimeLag 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 wasBoscastle
10 Factor Short lag time Long lag time Rock type Vegetation Hill slope
Land usePut the statements into their correct spot in the tableBare earth with few plantsPermeable (water soaks into it)Steep valley sidesRural farmlandLots of trees and plantsImpermeable (water doesn’t soaks in)Built up area – lots of tarmacGentle valley sides
· In 2005, a new £800,000 flood defence scheme opened in Boscastle which includes a new, larger culvert on the river Jordan which will be able to carry double the amount of floodwater.
· In August 2006, construction started on the river Valency flood defence scheme, see Figure 9. In order to increase its capacity the river has been widened and deepened and the lower bridge replaced. A new car park has been built which is raised and set back from the river and a new tree management scheme has been introduced to reduce the chances of tree blockage. Two new sewing pumps and stations and a new sewer pipe to assist with flood flows have also been introduced.
·Flood defence works together with the regeneration scheme cost £10 million and were officially opened in October 2008.
(Environment Agency, 2012).
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BBC, 2004b. The Boscastle Floods 2004 [image online] Available at: <http://www.bbc.co.uk/cornwall/content/image_galleries/boscastlefloods2004_gallery.shtml?26> [Accessed 27 January 2012].
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