HUMAN RESPONS

E TO FLOOD

Flood management

Human response to flood

IMMEDIATE LONG TERM Provide boats to rescue

people

Supply medicines to treat and prevent spread of diseases

Supply clean water

Distribute food and temporary housing (tents)

Aids from foreign countries

Prediction Hydrograph analysis Real-time monitoring Studying past records

Hard Engineering

Soft Engineering

Prediction

a. Hydrograph Analysis:- analysing a series of storm hydrographs for a basin, it is possible to device estimates for the behavior of the river for storms of different sizes

b. Real time monitoring:1. A series of monitoring stations are set up along the rivers2. Automatic measurements are sent to a central flood control office3. allows hydrologist to follow the progress of flood waves down

rivers

4. It is expensive and difficult to set up esp in remote areas

c. Studying past records:5. Enables people to workout the likelihood of floods of

different sizes

Flood protection/ management

Involve in trying to lengthen the amount of time it takes for water to reach the river channel

increasing the lag time

Flood management techniques: Hard Engineering

options Soft Engineering

options

Flood protection/ management

• More expensive• Have greater impact on the river and

the surrounding landscape

Hard Engineering Options

• More ecologically sensitive

Soft Engineering Options

Hard Engineering options

• Dam Construction• River Engineering:

realignment / Channelisation

• Revetment, e.g River Yangtze, China

• (Refer pg 61-62 of yr booklet)

Soft Engineering options

•Afforestation•Ecological Flooding•Planning•Flood warnings•Public relief / Emergency action

Flood control

HARD ENGINEERING SOFT ENGINEERING

Dam Construction

River Engineering: realignment / Channelisation

Revetment, e.g River Yangtze, China

(Refer pg 61-62 of yr booklet

Afforestation

Ecological Flooding

Planning

Flood warnings

Public relief / Emergency act

Hard engineering strategies

•Store and control river discharge•Used to control tributaries of the Mississippi , e.g River Missouri

Dams

• By raising the height of river banks, water can be contained

• Flood walls in York (Nov 2000) contained record levels and saved many homes from flooding

Levees & retaining walls

•Increase the speed of flow and reduces the length of the river•(R. Mississippi has been shortened by over 24km)

Straightening meanders

• Provides additional channels alongside existing course of river

• Maidenhead, Windsor and Eton relief Channel removed 5500 homes from the threat of Thames floodwater

Flood relief channels

River revetment

Soft Engineering strategies

•Increase interception•Reduces run-off•E.G Tennessee river valley, a tributary of R. Mississippi

Afforestation

•Floodplain zoning•Allows certain areas to flood naturally•Land uses are limited to grazing and recreation

Planning regulations

•Reduce the amount of surface run-off•Reduce the liabilty to flooding

Contour ploughing in

Semi-arid area

• Protect the natural river channel & valley

• Maintained habitat and species diversity

• Arable land is returned to its former use as natural meadowland

Wetland and riverbank

conservation schemes

• In times of high discharge sluice gates are opened and water Is allowed to flood adjacent areas

• A new washland in Yorkshire saved many homes in Dorncaster from flooding in 2007

Washlands or Spillways

• In Bangladesh, the yearly floods which engulf most of the countryside cannot be prevented, but people are given enough warning they can take refuge in flood shelters

Forecasting floods and warnings

Case Study - Hard engineering:Three Gorges Dam, China

Largest hard-engineering project ever undertaken on a river

When: 2009

Location: Yangtze River

3 gorges: Qutang gorge Wu Gorge Xiling Gorge

The dam will enable China to:

Generate up to 22 500MW of power, reducing the country’s dependence on coal

Largest power station in the world

Supply Shanghai’s 13 million people with water

Protect 10 million people from flooding

Water level will be raised to allow shipping above the Three Gorges (formerly rapids)

Protest against the Three Gorges Dam

Most floods in recent years have come from rivers that join the Yangtze below the Three Gorges Dam

The region is seismologically active and landslides are frequent

Silting as a result of increased deposition and the development of a delta at the head of the lake.

Up to 1.2 million people have to be moved to make way for the dam

Landslide along the

river

Protest against the Three Gorges Dam

Much of the land available for resettlement is over 800m above sea-level, cold & infertile soils on steep slopes

Dozens of towns will be flooded e.g. Wanxian & Fuling

Dam will interfere aquatic life – the white flag dolphin is threatened with extinction

Archaelogical treasures wil be drowned, including the Zhang Fei Temple

White flag Dolphin

Zhang Fei Temple

Case Study-Soft Engineering strategies:Komadugu-Yobe river basin, NE Nigeria

Intense tropical rains bring floods in the Komadugu-Yobe river basin

Between June and August

Traditional farming focuses on the renewal of fertile silt deposits with the floodwaters

Soft engineering: a water conservation projectThe Nguru Wetlands Conservation Project

Approach: Conserves the value of wetlands both economically and

environmentally

Promotes sustainable development in the area for people and wildlife

Teaches local people about wetland management

Release large wet-season flows from Tiga and Chawalla dams into rivers

Impacts: Water and alluvium are distributed more fairly

Supports the traditional method of irrigation and farming

Marsh grazing land is maintained

Involves programme to monitor: The extent of flooding and the changes in vegetation and wildlife The use of water from village wells in order to check levels of the

water table Competition for land between animal herders and crop farmers

Distribution of fuel-efficient wood stoves was design to reduce wood consumption

people to resolve conflicts