Long Philip Burn Natural Flood Management
Consider reduce stocking
density for grazing sheep to
encourage the grass to grow
longer for a slightly enhanced
period during the year
Gully planting in steep cleuchs
to provide more natural channel
roughness, dissipating energy
and slowing down flow velocities
In upper catchment, consider
options to reduce the amount of
muir burning to reduce the rate at
which water runs off the hillside
Increase vegetation cover in runoff
sensitive zones to improve
interception rate and improve the
ability of the soil to soak up rainfall
Increased riparian planting to create
opportunity for woody debris dams ,
slowing down velocities in the channel
and reducing scour rates
Increase boggy areas in flatter, wetter
parts of the plateau above the
reservoir to increase the potential to
store run off before entering the
watercourse
Restoration of straightened sections to
a more natural meandering form
further slow the flow velocities in the
channel and provide significant
environmental enhancement
Remove constrictions to flow in
the flatter parts of the catchment
Build on the success of the
sedimentation ponds (installed
November 2009) to consider
provision of other sediment
traps further upstream
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Natural Flood Management (NFM) can be defined as working with existing natural processes to adapt the way in which a river system responds to rainfall for the purposes of flooding
or erosion protection
The fundamental principle behind NFM is to generally reduce the rate at which water arising from a rain storm enters the watercourse
Slowing down the rate of runoff means all of the water which falls on the catchment doesn't enter the burn at the same time, reducing the flood levels in the burn.
The Long Philip Burn suffers from fast run off rates at various locations where the ground is bare and steep. This run off erodes the soil which washes into the burn, ultimately choking
the channel and increasing flood risk
Many of the proposals involve increasing the area and diversity of local vegetation cover. This will have a positive impact on the biodiversity of the river corridor and beyond.
NFM on its own can't prevent flooding downstream, but it can be seen to reduce flood defence extents and levels or increase the level of protection provided by an exisitng set of flood
defences.
Halcrow and SBC are currently working to determine the exact nature and extent of NFM measures which will have the most positive impact on flood risk within the catchment.
In higher parts of the catchment,
reduce muir burn and grazing
stock density to promote thicker
vegitation cover
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Coniferous planting on steep
slopes to help bind the soil and
reduce erosion if run off does
occur
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Deciduous planting and
shrubbery on flatter riparian area
to increase ability of soil to soak
up rainfall, increase interception
rate and bind the soil to reduce
erosion
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Hillside with minimal
vegetative growth
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Heavy rain in the catchment falls onto sparsely or close cropped vegetated hillside
Lack of significant vegetation means soil moisture levels are high and ground quickly becomes saturated
As ground becomes saturated, rainwater begins to run directly over the surface
On steeper sections, flow speed increases, eroding the soil and transporting sediment
High volumes of rapid runoff converge quickly on the watercourse, increasing levels very quickly (flash flood)
High volumes of sediment entering the burn and eroded from the sides of the burn choke the channel, reducing its
capacity to convey flow and increasing the flood risk.
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Before
Heavy rain in the catchment falls onto more densely vegetated hillside - presence of leaves and branches intercepts
raindrops and slows down the rate at which rain hits the ground surface
More vegetation means the soil will have a lower moisture content and become saturated less rapidly
Onset of direct run off is delayed due to enhanced "sponge" effect of vegetated soils
On steeper sections, deep rooted vegetation will limit erosion and slow down flow velocities when run off does occur
Delay in onset of runoff entering the watercourse means main channel flood level rises more slowly and to a lower peak
level
Lower volumes of sediment entering the burn and lower flow velocities in the burn (leading to lower erosion risk to the sides
of the burn) mean the risk of choking the available channel capacity is reduced
After