Managing floods and Boscastle Case Study

Hard engineering

Using man-made structures to prevent or control natural processes from taking place

Hard engineering examples

• Dams and reservoirs

• Channel straightening

• Embankments

• Flood relief/bypass channels

Dams/Reservoirs

During periods of high rainfall, water is stored in the reservoir and can be released when rainfall is low

Channel straightening

Cutting through menders to speed up water flow, can be lined with concrete

Embankments

Raised banks which allow the river to hold more water before flooding occurs

Flood relief channels

Man-made river channels to bypass an urban area

Soft engineering

Working with natural river proceses to manage the flood risk. It doesn’t involve building artificial structures or trying to stop natural processes

Soft engineering examples

• Wetlands and flood storage areas

• Floodplain zoning

• River restoration

• Afforestation

Wetlands and flood storage areas

Allowing areas of land to flood deliberately to store more water and reduce flooding downstream

Floodplain zoning

Restricting land uses to certain locations on the floodplain

River restoration

Where the purse of the river has been changed artificially, river restoration uses the natural processes and features of a river to slow down the flow and reduce flooding downstream

Afforestation

Re-planting trees to obstruct the flow of water and slow down the transfer to river channels

Boscastle location

• Small village located in North Cornwall between Bude and Polzeath

• At a confluence of the Valency, Jordan and Paradise Rivers

Boscastle flooding date

August 2004, 2 months worth of rainfall in 2 hours

Boscastle flooding effects

• Over 1000 homes, cars and businesses swept away and damaged

• 90% of its industry is tourism, which was disrupted for many months after

Boscastle flooding human factors

• Trees cut down, limiting interception

• More building on the drainage basin

• Arch bridges formed a dam which then burst

Boscastle flooding physical factors

• Heavy, localised rainfall

• At a confluence of three rivers

• Saturated ground fro previous rainfall

• Steep valley upstream Acted as a funnel

• Impermeable rock

• Rapid overland flow

• Narrow river channel in village

Boscastle flood defences installed

• Widening and deepening the river channel

• Removing low bridges and replacing them with wider ones to prevent dams forming

• Raining car parks using a permeable surface

• Removing dead trees and planting new ones

• Installing gauges to monitor the river’s water levels

• Overall cost: £10 million managed by the Environment Agency