How does human activity cause change

Nile delta

Great Yarmouth Outer Harbour (GYOH)

Mangawhai-Pakiri coastline of New Zealand

Happisburg

Bacton

Sea palling

Overstrand

Coastline management

Threats of coastline
1) coastal erosion, cliffs composed of rapidly eroding glacial deposits
2) wave energy, destructive waves remove sediment
3) tidal ranges of 5m increase flood risk
4) storm surges, increase erosion & flood risk
5) unintentional impacts of coastal development
6) climate change & sea level rise (6mm/yr)

Shoreline management plans (SMPs)
are documents that examine the risks associated with coastal processes and present a policy to manage those risks. they consider risks to local people as well as natural & build environment, the policy is drawn up with many local stakeholders.
The published SMP will
1) divide sub-cells into appropriate management units
2) identity economic & environmental assets, assess issues and conflicts, propose a defence plan
3) use DEFRA criteria for management
4) Intergrated Coastal Zone Management (ICZM), manage whole of coastal zone not just shoreline

DEFRA criteria
1) hold the line, maintain existing defences
2) advance the line, build new defences
3) managed re-alignment (retreat), allow flooding with managment
4) no active intervention, no investment

  • a reduction in human intervention in a natural processes
  • working with the natural processes rather than against them

Accessing the risks
1) Cost benefit analysis (evaluating the economic, social & environmental costs and benefits of the scheme)
2) Environmental Impact Assessment (assessing the impact of a project so damage can be minimised, will the environmental quality improve or decline based on the DEFRA strategy employed)

Sediment

Erosion rates
Pre-defences all of NE cliffs average 0.65-0.75m/yr (quite rapid)
Sea defences built in early 18th century

Sediment supply
Overstrand

  • sediment volume decrease & erosion rates increase
  • sediment trapping at Overstrand has caused sediment starvation downdrift
  • reduces sediment volumes has increased rates of erosion as sediment no longer protects the toe of the cliff - accelerating removal and cliff retreat rates by undercutting and landslides increase

Sediment budgets
Overstrand

  • beach at Overstrand is growing BUT beaches to the South are being starved of sediment which may lead to enhanced erosion rates

Summary of NE Norfolk coast

  • characterised by less resistant geology, high wave energy & high rates of LSD
  • coastal management (protection) is required to reduced the impacts of erosion and sea level rise
  • the natural processes in the sediment cell have been disrupted by human activity (coastal defences):
    1) cliff protection by coastal defences has reduced erosion rates in key locations
    2) BUT, in many areas erosion rates remain high
    3) sedimentary budget calculations indicate the defences have caused sediment starvation on many beaches downdrift which has the potential to expose cliffs to increased erosion rates
    4) further management is required to halt the natural processes of coastal erosion

Assets

  • property value £34.5m
  • B1159 (Walcott) liable to flooding
  • water treatment pumping effluent station cost to replace £1.6m
  • tourism jobs 6,000 (seasonal & full time)
  • tourism £4.17m per year
  • agricultural land £6,000 per hectare
  • cliffs 5551 sites
  • historical assets e.g. The Pleasance gardens and structures, erosion impact in 50-100 years, 1.500 value (£000s)

Overstand will be missing in the next 100 years if we do nothing

Threat of rapidly erosion on less resistant cliffs

  • steep cliff section at top failure plans
  • landslides
  • mudflows
    The mechanism of failure
  • small scale features at top of the cliff (fault scarps)
  • rotational slip plane
  • rotational slump slip planes (slumping

POLICY - hold the line

Hard engineering - building structures at the base of cliffs or on beaches
Soft engineering - work with natural processes in the coastal system as management

Hard engineering at Overstrand

  • timber revetments
  • timber groynes
  • rock filled revetments
  • concrete curved sea wall with toe
  • gabions
  • cliff drainage pipes
  • rip-rap

Why Overstrand needs protecting

  • beaches encourage tourism
  • recreational activity space, leisure
  • residential area
  • various hotels & guest houses
  • tourism based industries
  • tourism accommodation
  • heritage historic buildings

Predicted erosion losses of £34032k by 100 years

Rotational slumping
clays and sands absorb water increasing weight leading to failure. sandstone poorly cemented and porous, but clay beneath is impermeable. causes mudflows & landslides.

Summary
HTL - defences have intentionally the coastline
Flows of materials:
1) beaches are growing in volume, reducing gradients and increasing width
2) promontories (headlands: Cromer and Overstrand) are no long retreating due to protection yet reduce sediment inputs to the beach

  • slope failure means cliff recession still going
    Flows of energy
    1) defence strategies reduce wave energies

Sea wall
large walls constructed of concrete, protects cliff from upland erosion and is a barrier to flooding. however, water can erode wall & expensive to maintain.

  • Cromer & Overstrand, reduces sediment input, promotes beach starvation

Groynes
wooden fence-like barriers built at right angles to the beach, prevents longshore drift, flooding & erosion, allows beaches to build up. however, can create erosion further down, expensive, unattractive

  • Cromer, trap sediment and reduces wave energy enlarging beach
  • Overstrand, reduces LSD, traps sediment, builds beach, reduces sea wall undercutting

Gabions
bundles or rocks in metal mesh located at cliff bares, reduces impact of waves inexpensively. however, not very effective or attractive.

  • Overstrand, retraining wall protect slope

Revetments
slanted structures made of concrete, wood or rocks along a cliff, prevents cliff erosion by absorbing energy. however, expensive to implement & can create strong backwash

  • Cromer, protects cliff toe, build beach behind (raised)

Rip-rap (rock armour)
large boulders or rocks piled up on beach infant of a cliff or sea wall, absorbs energy of waves & helps build up beaches. however, expensive to implement & maintain

Slope drainage
plastic or clay pipes in the slope, reduce pore water pressure and reduce weight on slope. however, often blocked, destroyed in slumps.

  • Overstrand, reduce weight of cliff & reduces slumping and collapse

Storm surges
2m surge on high tide caused extensive flooding inland. Flooding of Broadlands caused environmental & economic (tourism) devastation.
Storm surges are caused by extremely high onshore winds, low atmospheric pressure and coastline shape

Sea wall
Sea palling has a curved and stepped sea wall so that it reflects wave energy thrown water into air (disrupts swash) and toes break wave energy up. the sheet piling also stops undercutting and increases stability. most effective type of sea wall

Info
a small seaside resort.

  • 14km sand dune ridge between Eccles and Winterton is only defence to Broadland
  • a gap occurs at Sea Palling
  • coast composed of rapidly eroding earths & glacial boulder clay
  • these factors mean that erosion rates along unprotected stretches of coastline are on average more than 2m/yr

Tidal range = over 5m, increases flood & erosion risk
Fetch = 1500 miles (high energy environment, frequent storms)

How groynes work

  • encourage sediment build up & dissipated wave energy
  • ratio of groin length to spacing is vital in their effectiveness, 1:4 seems to be most effective, 1:2 on shingle beaches

Terminal groyne syndrome

  • a similar process to flanking, wave refraction causes rip currents which increase erosion leading to landslide & cliff collapse
  • can see this in Sidestrand (increased erosion after last groyne is visible, undercutting leading to cliff instability)

1953 storm surge & flooding in Norfolk, earth embankment damaged after, rebuilt

POLICY - hold the line

  • flooding of Broadlands would be an environmental & economic disaster
  • 6000 hectares would be flooded

How is Sea palling defended

  • earth embankement
  • curved sea wall (added to embankment since 1954)
  • stepped toe
  • rip-rap (later addition due to undercut)
  • embankment has flood gates

Offshore reefs

  • management strategy, initially advance the line
  • constructed with aim of reducing wave energy & protecting the beach for tourism & recreation
  • medium term strategy, hold the line
  • construction, built in 2 stages (first 4 in 1995, North, £5.9m), 450m apart, 2.8m above sea level, 321,000 tonnes of rock
    Why?
  • built up beach reduces wave energy, safe tourism destination
  • waves break offshore & energy reduced
  • dissipates wave energy, reducing erosion
  • expensive & difficult to install

Info

  • handles 1/3 of the nations gas supply worth £1.7m per day
  • sea defences put in place coast an estimated £18m

Eccles - a problem
in addition to groynes built at Eccles to increase beach size caused by beach starvation at Sea palling, leading to sea wall undercutting & addition of rip-rap

  • 1.4m tonnes of sand added as beach norishment

Unexpected problem - Tombolos
soon after offshore reef construction, salients then tombolos formed behind the rock reefs. caused by offshore reefs being too far apart

Intentional change - more reefs
in 1996, 5 more reefs built

  • 180m long with gap of 160m to prevent erosion in gaps
  • only 1.2m high than sea level to allow waves to pass over the top, to prevent tombolos
  • used 220,000 tonnes rock & cost £10.5m

Summary
Intentional changes

  • flood defences (embankment, flood gates)
  • sea wall
  • beach norishment
  • offshore reeds
    almost all to reduce wave energy
    Unintentional
  • tombolo & salient formation, beach growth
  • reduction in LSD
  • sediment starvation down drift

POLICY - hold the line then retreat

Effectiveness overtime

  • pre-defences in 18th century, -0.65-075m/yr
  • 1885-1985, -01.05m/yr
  • 2005-2013, -0.28m/yr

Pre-2018 defences at Bacton

  • sea walls & revetments were built here in 1950s
  • rock armour & groynes are also resent to protect the terminal against erosion
  • hold the line policy now adopted, sea walls require regular maintenance
  • by protecting this area and not adjacent areas, Bacton will eventually develop into a headland
  • protection of the cliffs here creates problems, as sediment is no longer being supplied to villages to the south (Happisburg & Sea palling)

Bacton gas terminal located here

"Bacton to Wallcott" sandscaping scheme
2019 summer

  • manmade, taking sand from seabed & placing it on the shore
  • first product of its kind in the UK
  • completed beaches now protect home & industry
  • 1.8 million cubic metres of sand places & engineered, enough to fill Wembley Stadium
  • cost £22m and created 3 miles of new beaches
  • raised beach by up to 7 meters
  • should protect the stretch of coastline for up to 20 years, but sand expected to erode & move with storm currents

POLICY - managed retreat turned into now no active intervention

Has the project worked?
Overall effective, but not a long term investment as will be gone in around 20 years. In July 2021 wave action created a sand bar that breaks energy of the waves.

  • Beachfront cafe owner says in past 15 years, cafe has flooded twice casing major damage, but now he no longer worries about weather

A history of defences summarised
1959 - timber revetments & groynes built
1982 - damaged revetment & groynes partially rebuilt
1992-1995 - various schemes rejected or costs > benefits
2002 - another scheme rejected, lifeboat ramp collapses, 4000 tonnes of rock placed at foot of cliffs as short-term emergency measure
2003 - house dismantled before it collapses onto beach, metal staircase giving beach access opens
2004 - garages on cliff top demolished, EU experts say defences badly manages, new management plan suggest managed retreat only cost effective & sustainable plan, 99.6% consulted object to new plan
2008 - natural England plan o allow sea to flood the area
2019 - new rockbound constructed at base of cliff to try reduce erosion, local council

What is happening here?

  • a small promontory acts as a groyne & focuses erosion
  • sediment is deflected offshore causing starvation on downdrift beach
  • wide beach caused by enhanced erosion
  • shore platform, cliff, beach, scree / landslide
  • oxidation, landslide, wave erosion (undercutting), cliff retreat

Reasons for rapid erosion

  • rock type & structure, less resistant boulder clay which slumps when wet
  • naturally narrow beaches, less protection as dont reduce wave power
  • man-made structures, groynes have been installed to stop longshore drift & build up beach in certain places, narrows unprotected beaches elsewhere
  • powerful waves, long fetch, high energy
  • beach starvation, Bacton defences trap sediment further up coast promontory effect of the headland

Embayment formation (gullies)
non-uniform erosion process, involving the cyclic formation of a series of embankments that continually enlarge. this could infer land sliding processes involving block falls, mudflows & running sand.

  • in winter, erosion caused by groundwater is seen in the gullying of the cliff face, causing frequent, shallow land sliding in the Happisburg Sand Member. eventually cliff failure occurs. the beach surface is low and scouring of the supper face os the till extends the till platform
  • in summer, beach surface is higher and covers the winter 'platform', wave attack is the dominant form of erosion accompanied by land sliding in the Happisburg Sands

wave refraction around sea wall causes increases erosion & may lead to cliff erosion & landslides

Summary

  • the defending of Bacton Gas Terminal from erosion has had significant impacts on landscape system
  • traditional hard engineering methods have been used yet caused unintentional sediment starvation downstream
  • downdrift at Happisburg the promontory effect and starvation has lead to rapid erosion rate. here geology, wave energy and sediment supply are significant factors impacting cliff retreat
  • soft engineering method 'sandscaping' or beach nourishment has intentionally modified beach characteristics and reduced erosion rates. as predicted by models LSD has transported materials sediment down drift and increased sediment supply to protect villages

Economic development

  • sand is an essential material in the modern economy as it can be used in construction, glass & concrete making and beach norishment
  • a high-quality sand resource occurs in the nearshore zone at Mangawhai-Pakiri on the east coast of New Zealand's Northland Peninsula, it is suitable for the construction industry
  • located just 50km north of Auckland, New Zealand's largest and most economically metropolitan area (1.5m population - 1/3 New Zealand's total - 35% total GDP, tourism focused on the coastline with 2.3m foreign visitors in 2015)

sand mining / offshore dredging

Offshore sand mining and the sediment budget

  • nearshore sand dredging on the 20km coastline between Mangawhai and Pakiri has operated for over 70 years
  • between 1994-2004, 165,000 metres cubed /yr was extracted
  • mining ended in Mangwhai in 2005 but has continued at Pakiri beach
  • current extraction rates are 75,000 metres cubed /yr until 2020, this sand is used to replenish Auckland tourist beaches
  • sand is a non-renewable resource on the coastline, deposited during the Holocene (past 9000 years), coastal sediment budget is overall a closed system
  • extraction rates at Pakiri beach exceed inputs by a factor of 5, the effect will deplete total sand supply

Impact on coastal landforms

  • as closed sediment cell, current rates of sand extraction are unsustainable
  • beaches starved of sediment have become wider & flatter & less effective at absorbing waves
  • higher energy waves then erode the beaches
  • foredune ridges are undercut by wave action, developing steep, seaward-facing scarps. loss of vegetation cover makes them susceptible to wind erosion
  • 1978, storms caused 28-metre breach at the base of Mangawhai spit. this, and a second breach, altered tidal currents, leading to sedimentation of Mangawhai's harbour
  • shallower water in harbour also threaten Mangawhai community with flooding, subsequent dredging of the harbour & groyne construction on the spit has helped restore some equilibrium
  • coastal retreat is already evident & attributed partly to sand extraction

Reasons for economic development

  • deep water port
  • Euro trade
  • service offshore industry e.g. oil rig decommissioning
  • boat tourist trade 200,000 leave from the town, ferry links with Dutch towns
  • Crane construction allows building offshore turbine & services offshore aggregates industry
  • GYOH construction began 2007, completed spring 2009
  • £75 million
  • 2 breakwaters of 1,400m
  • 1,600,000 metres cubed of sand dredged from port & used to provide 17.6ha for development

Hopton Holiday Village

  • claimed it would have lost its first row of clifftop caravans & a second row in 2 years time had it not commissioned the work
  • at the time sand levels at Hopton-on-sea were reported to have dropped by up to 10ft (3m) in 5 years
  • 2014, Borne Leisure built 9 rock groynes at Hopton-on-sea with 54,000 tonnes of imported granite at a cost of more than £7m
  • coastal erosion expert Dr Phillip Barber studied damage & said port was to blame as it changed tidal flow & littoral drift
  • since 2010, Hopton beach lost between 20,000 to 40,000 cubic metres of sand each year

North increased accretion, rate decreasing after construction. above the GYOH

Goleston redistribution of sediment & bar formation, some accretion due to wave refraction & reduced flow

Hopton accelerated erosion caused by beach starvation

What is the delta like?

  • a wave dominated arcuate delta composed of promontories separated by embankments
  • beach forming a continuous coastal flat with dunes & lagoons at the distal end
  • the delta was built from 7 distributies, most silted up leave 2 active channels: Rosetta & Damietta branches

a low energy coastline

Evolution of Nile Delta
region was an alluvial plain with seasonally active braided river channels. sea level rise, transgression, submerged.

Delta = large areas of sediment found at the mouth of rivers, sediment is deposited by rivers and tidal currents

Deltas

3 delta landforms
upper delta - plain composed of river sediment, above tidal area
lower middle delta - inter-tidal zone composed of both river and marine sediment
submerged delta plain - below sea level and composed mainly or marine sediment

Factors for formation

  • river discharge / energy
  • large sediment load (supply) from a river
  • a shallow shelf or platform for sediment to accumulate
  • a low energy environment
  • sediment is deposited faster than it is removed, greater sediment leads to faster growth
  • low tidal ranges

Why does deposition occur?
1) a shallowing river gradient causes velocity & energy to drop
or 2) high energy river (fluvial) entering low energy sea (here)

  • decrease in volume of water channel
  • flocculation, mixing of salt & fresh water

Important processes
slowing flow, mixing of fresh and salt water aids flocculation meaning all the small silt/clay particles are depositied
lower density, the river water has lower density and floats above sea water due to lack of salinity, river beds load deposited close to coast, suspended load well offshore

How do deltas grow?
1) river meets low energy area, head of water spreads out, energy drops & sediment deposited. near source coarser material is deposited, finer offshore. delta lobe formed.
2) rivers flow across the delta, these cut new channels and lead to growth. towards of a new lobe (progradation). levees (raised banks on side of river) form on river sides
3) when a distrubary is blocked or sister up the river breaks through its levees to grow a new lobe (avulsion).
During flooding low lying areas between distrubries fill with flood plain deposits (interdistrubary bays, swamps)

Unintentional impact of development
transition from a fluvial dominated growing delta to an eroding wave dominated delta

  • the Aswan High Dam completed in 1964 to control flow of the nile, to generate electricity and to provide water for irrigation
  • but the dam impacted sediment flux
  • as result a great deal of effort has gone into constructing coastal defence struts to protect important sections of the coast of particular socio-economic importance

Sediment supply to the delta

  • Aswan dams & irrigation schemes reduced discharge & sediment entering delta, reduced from 40 to 5 x10^9 metres cubed per year
  • sediment load decreased from 200 million tonnes to 134 trapped in artificial resiviours
  • irrigration schemes 10,000km of canals, low velocities, deposition of muds, entrapping sediment
  • wetlands, swamps & lakes also trap sediment

Important factors for development of Nile Delta

  • geology & structure (limited impact, sands & gravels)
  • low wave energy (short fetch & swell window)
  • low tidal range (restricted circulation)
  • climate (semi-arid)
  • human impact
  • fluvial energy
  • currents & waves

Sidestrand erosion rate 1885-1985 = -1.52, 2005-20015 = 0.98

Erosion 1885-1985 = -0.30, 2005-2015 = -2.43