soft engineering Flashcards
how does beach nourishment work
-replaces beach sediment that may have been eroded/transported by LSD
-larger beach absorbs wave energy
advantage of beach nourishment
-uses natural sediments, looks natural
-provides amenity for recreation
-supporting local tourist industry
disadvantage of beach nourishment
-costs about 300,000 for 100 metres
-short life span so regular updates needed
-sediments dredged from offshore so changing sediment cell balance
-deeper offshore waves = more energy
what is cliff regrading
-the lithology of cliff may be unstable/prone to collapse
-engineers calculate stable slope angle based on rock characteristics
-cliff slope artificially cut back to stable angle
disadvantage of cliff regrading
-costs about 1 million
-some land and property will be lost
-engineers may miscalculate
-stabilisation measures like cliff drainage and planting may also be needed
advantage of cliff regrading
-creates natural looking slope
-reduce risk of sudden collapse
-give confidence to property owners on edge of slope as it shld remain stable
how does cliff drainage work
-when cliff lithology consists of permeable layer above impermeable it may be unstable after rainfall due to pore pressure
-to reduce pressure and mass movement, drains can be inserted into cliff
advantage of cliff drainage
-looks natural once completed
-reduce mass movement
-cost effective
-confidence of land and property owners
disadvantage of cliff drainage
-difficult to implement along whole cliff without disturbing cohesion of rock layers
-only reduces mass movement, doesn’t prevent it
how does managed retreat work
-areas can be set aside for sea to flood/erode
-e.g. former salt marsh like blackwater estuary
-variable cost depending on size of area
advantage of managed retreat
-allows natural process to take place
-extend current ecosystems
-cheaper than sea defences in the long term
disadvantage of managed retreat
-needs agreement w land and property owners
-doesnt prevent land being lost
-no compensation in the UK for land and property loss
-loss of archaeological or historic sites
whats dune stabilisation
-dunes act as natural barrier to sea level rise and storm waves
-fragile
-may have to repair with geofabric or replanting grass
advantage of dune stabilisation
-looks natural and effective to higher sea levels and tides
-provides natural ecosystem and recreational area
disadvantage of dune stabilisation
-may need to be fenced off reducing amenity in short term
-powerful storms mean its short term
-200-2000 for 100 metres
