Helicoidal Flow

Helicoidal Flow is the cork-screw like flow of water in a meander.

It is a contributing factor to the formation of sli off slpoes and river cliffs in a meandering section of river. The helicoidal motion of the flow aids the processes of hydraulic action and corrasion on the outside of the meander, and sweeps sediment across the floor of the meander towards the its inside.

The Genesis of a Meander

Pools are are areas of deeper calmer water with greater erosion and where the river flows faster due to reduced friction.

Riffles are wide shallow areas of the river where water 'ripples' over pebbles beds with protruding rocks.

As these pools and riffles enlarge, the river will be propelled by centripedal force to twist round the riffles thus starting the side to side flow of the river. Erosion occurs on the outside of the bend, while deposition occurs on the inside.

All rivers take the path of least resistance to maintain theire maximum velocity (thalweg).

Outside of the bend:

• Fastest flow
• Lateral erosion
• Hydraulic action
• Undercutting of the alluvial materials of the river's floodplain
• Abrasion
• Deeper
• River cliff

Inside of the bend:

• Deposition
• Shallow
• Slowest flow
• Slip off slope/point bar
• Low energy

Flood Management Schemes: Realignment/Diversion

Realignment/Diversion

Description:

A river is either diverted through a relief channel or given a straighter route by removing meanders or slower sections of the river.

Advantages:

• Provides alternative route
• Straighter and shorter course
• Steeper gradient
• Aids navigation
• Reduces flood risk
• Habitats may survive
• Allows some control

Disadvantages:

• Totally artificial environment
• Destruction of most river habitats
• May cause greater flood risk downstream

Soft Engineering!

Soft Engineering is the use of ecological principles to stabilize the river banks, while improving aesthetics, enhancing habitats and saving money. It uses vegetation and other materials to soften the land-water surface.

• Flood Abatement
• Improved flood Predictions and warnings
• Floodplain zoning
• Designing Building that can cope with being flooded

Flood Abatement includes:

          -Afforestation

          -Contour ploughing

          -Riverbank Conservation

  

Floodplain Zoning

 

Improved Forecasting and Warnings

   Frrom the Environmental Agency in the UK.

Designing buildings that can cope with being flooded

- Waterproof coatings and coverings

-Windows elevated above flood level

-Concrete bottom step so it drys quicker

-Lime based plaster or cement walls means that they dry quicker

-Stainless steel kitchen appliances

-Moveable barriers to seal openings like doors

-Raising electricity sockets

River Quaggy Restoration Scheme

The river Quaggy is 1.7km long and paases through many South London boroughs like Bromley, Greenwich and Lewisham.

The scheme replaced an artificial channel that was fenced off to the public. The hard engineering approach didn't work.

In 1990 the Friends of the Quaggy suggested that it should run through Sutcliffe Park again.

Local people were consulted on the development and design, and were involved extensively in the remodeling.

This renewal took place between 2003 and 2007, and it not only improved the environment, but also created recreational activities for the residents.

Since the flood plain was restored there has been no flooding, and Sutcliffe Park is now the floodplain and the diverging lake, whereas the land was covered in buildings which prohibited infiltration.