Environment - TU Delft OCW · Environment Chapter 12 ct 4310 bed, bank and shoreline protection...
Transcript of Environment - TU Delft OCW · Environment Chapter 12 ct 4310 bed, bank and shoreline protection...
Vermelding onderdeel organisatie
June 3, 2012
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Environment Chapter 12
ct 4310 bed, bank and shoreline protection
H.J. Verhagen
Faculty of Civil Engineering and Geosciences Section Hydraulic Engineering
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Introduction
• Ecologists stress that for a healthy environment there should be a good connection between land and water
• So shorelines are multifunctional elements in the landscape
• Main issues:
• use of vegetation
• allow animals to migrate from land to water and vice versa
• use of sustainable materials
• So:
• vertical walls are certainly not good
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Other material
• Powerpoint presentation MilVriOev
• CUR manuals Natuurvriendelijke Oevers:
• 200 Aaanpak en toepassingen
• 201 Belasting en sterkte
• 202 Oeverbeschermingsmaterialen
• 203 Fauna
• 204 Vegetatie langs grote wateren
• 205 Water- en oeverplanten
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ecological infrastructure
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river as ecological connection with stepping stones
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comparison
Space requirements versus
• discharge capacity,
• nautical possibilities, ect.
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species and dynamics
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food chain relations in a bank
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hardly any exchange of life is possible between land and water
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crossing location for mammals
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planning and execution of steps
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load and strength
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Basic types of shoreline protection
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filter tests for nature friendly fascine mattress
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Reed and waves
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Damping of wave loads
0.81 1 exp 0.001cos
TT
I
H BK N
H
N = number of stalks per m2
B = width of vegetation
= angle of incidence
0 for windwaves
55 for ship waves
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wave damping and roughness in reed
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roots as an armour against sliding
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permissible flow duration on grass cover
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reinforced vegetation
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Vegetation growing through rock
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Armorflex with vegetation
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Roots in jute
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Roots and Enkamat
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exchange of water in strip due to passage of a ship
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Berm along a shore
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erosion between groynes
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cross section of a coast with mangroves
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wave transmission through mangroves (100 m)
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Load reduction over a dam
0.31
1 exp( 0.5 )Tdam
I I
H BF
H H
B = crest width of the dam
Fdam: 0.64 rock
0.70 gabions
0.80 closed (asphalt, blocks)
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wave transmission dams
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water exchange possibilities
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grass
• Grass is a flexible, renewable slope protection
• Grass can withstand quite some load
• Environmentalists do not like “monocultures”
• Fortunately from an engineering point of view, variation is also better
• Hydraulic engineers like roots, farmers like leaves
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grass and clay layer
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Texture formation in the clay body
Texture formation =
structuurvorming
Textured =
gestructureerd
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“Maintenance”
Cattle and light fertilising
No cattle, removal of grass
Fertilising, and no removal of grass
Cattle, fertilizer and herbicides
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load and strength of grass under wave attack
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results of erosion tests
Fertilised +
cattle
Non-fertilised
after 25 yrs
Non-fertilised
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erosion speed as function of wave height
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Erosion speed of a grass turf
Quality cE
good 0.5 - 1.5
moderate 1.5 - 2.5
bad 2.5 - 3.5
max 2
E s
d dt
E c H
safety coefficient
E erosion speed
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permissible duration of wave load and grass quality
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Inner slope problems
Bosman, 2007
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Inner slope erosion without cover
ComCoast, 2007
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Reinforced grass
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Conclusions
• Good grass cover does not show damage, even with very high overtopping discharges
• Grass with damages shows erosion with high overtopping rates
• Reinforced grass shows less damage in case of damage
• After removal of the grass cover, damage is considerable
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Vetiver nursery
Agricultural University, Ho Chi Minh city, Vietnam
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Vetiver as run-up reductor
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Results of the experimental work
Algera, 2006 Vu, 2007
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Bank protection with Vetiver
Jaspers Focks, 2006
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Cumulative loss of bank materials Cumulative loss of bank material soil type C
0
1000
2000
3000
4000
5000
6000
7000
0 150 300 450 600 750 900 1050 1200 1350 1500 1650 1800
Number of cycles
Lo
ss
of
ma
teri
al (c
m^
3)
Soil C with Vetiver 1Soil C with Vetiver 2Soil C with Vetiver 3Soil C, fallow 1Soil C, fallow 2Soil MX with Vetiver 1Soil MX with Vetiver 2Soil MX with Vetiver 3
Jaspers Focks, 2006