Click anywhere on the screen to move on Click the text button to view text Reduce river flow by storing water naturally in blanket bogs Blocking ditches on moorlands slows the rate of flow into ID: 656317
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Slide1
River Conwy- flood management
Click
anywhere
on the screen
to
move
on.
Click the text button to view text.Slide2
Reduce river flow by storing water naturally in blanket bogs.
Blocking ditches on moorlands slows the rate of flow into
streams
and rivers, increasing the lag time between rainfall and river peaks. As moorlands are generally found in the uplands – the areas that receive most of the rainfall, storing the water there can be very cost effective. We rely on the moorlands for a constant drip feed of water in the summer months to sustain our rivers and fill our reservoirs;
for recreation
(kayaking, fishing, sailing) and
for animals such as otters
, water voles,
and fish.Slide3
Using the floodplain as a natural store for water.
The flood scheme allows the water to flow over man-made flood banks onto the natural flood plain of the valley floor. It is then stored and drains away over a few days.
Schemes usually involve lowering
flood
embankments, creating spillways to provide an alternative route for flood flows thus reducing water levels in towns and villages upstream.
Farmers are compensated for letting their fields become natural storage
.
Environment AgencySlide4
Build concrete
embankments.
One
way to keep water out is to set up an embankment such as that along the Thames in London or the Seine in Paris. Often recreation facilities and walkways will be added as amenities on top of the embankment. A
ny
water pipes which flow outside the embankment need to be closed manually or be equipped with check valves so that no leakage occurs inside the
barrier.
© Copyright N Chadwick and licensed for reuse under this Creative Commons Licence. Slide5
Use temporary flood defences e.g. Dutchdams or height adjustable
walls.
An alternative to permanent
walls is
a structure that is put in place in the event of a flood or raises automatically as the water level
rises.
Environment AgencySlide6
Build
flood defences.
One way to keep water out is to set up a defence which looks more natural. The base and centre of the defence is often reinforced with concrete or stone to combat the flow of water, whilst it’s often covered with soil and turfed to provide a natural looking defence.
© Copyright
Dave Dunford
and licensed for
reuse
under this
Creative Commons Licence
.Slide7
Limit development on floodplains.
Most rivers
don’t
flood
every
year. In fact many rivers won’t flood for years. F
lood
plains are flat land,
so their potential for development has resulted in them being built
on in the past. Building on floodplains reduces their ability to be used as stores for river floods. Any buildings on the floodplain are prone to flooding, and the cost of insuring the property will increase with every flood.
The easiest way to stop building being flooded on flood plains is to stop building on them
.Slide8
Straighten and deepen
channels.
Straightening
the river channel aims
to get the water through the system, or the town, as quickly as possible. Often the fast moving water will impact on settlements lower downstream unless they also have protection.
Deepening the
channel
removes
river
load
that has
been deposited over time. The load can be used to build natural embankments along the rivers. Over time, there will be a further build
up
sediment deposited in the river.Slide9
Reduce
river flow by planting trees
.
Planting more
trees
intercepts
rainfall and helps take water from the soil -
although
large
areas must be reforested to make a real difference.
Shelter belts of trees along small streams can also slow down and reduce the flow of water into
rivers. Felled
trees can also be laid across streams in
wooded
areas. They help to hold back the water and release it slowly into the river’s system. Trees
take time to grow, and any change must be well managed working in partnership with
landowners.Slide10
Control river flow by building dams.
Dams are expensive to build but can hold back a huge amount of water. This water can be used to supply water to homes for drinking or to farms for irrigation. Reservoirs can also be used for recreation. Once built they must be managed so that there is enough room in the reservoir for rainfall events during the winter months. Water must be released slowly during drought events to avoid reservoirs running dry. Water flowing from the dams can be used to produce electricity.