Coastal management -geo 101

Storm surge
Storm surge
high water level brought by a cyclone that swamps low-lying areas
Sea wall
Sea wall
To build a large wall to protect the land behind the beach
Rubble is often placed in front of wall to pre-break the waves-thus reducing dynamic loading
Sea walls come in a variety of shapes
-Could be a pile of rocks
-concrete walls
Sea walls work by reflection destructive wave energy away from the coast
Beach loss
A well constructed seawall will work (in that it will protect the land behind it), but beach loss is common.

Sea walls:
-cause erosion during high energy conditions
• reduce (through beach loss) the deposition of sediment during normal conditions
• lock up sediment behind the wall (prevent beach-dune interaction)

Groyne
Groyne
-Often working with sea walls
-The construction of a structure perpendicular to the shore designed to catch sediment moving alongshore
-Groynes are often used in fields & commonly associated with sea walls
-Groynes slow the longshore currents that carry sand
• Slow moving water can carry less sediment, thus sand is trapped and deposited on the updrift side -There are different types of groynes: ANCHOR & TERMINAL

Groynes can also create problems
-While sand collects on the updrift side, the downdrift side is deprived of sand
-Preventing sediment from leaving one area will have implications for other areas – the coastline is a linked system

Anchor Groynes
capture a portion of sediment (so some sediment allowed around)
Terminal Groynes
captures all sediment
Breakwater
Breakwater
To protect the shorline by creating a structure that reduces incident wave energy
-Often used in association with beach re-nourishment programs
-A breakwater is also the name given to structures used to create artificial harbours or provide safe berthing for boats
Other variations of breakwater
Artificial surfing reefs=designed to make the perfect wave and to preserve the beach

Reef balls= concrete, moveable balls designed to mimic reefs which creates a habitat for marine life on accident

Beach replenishment
Beach replenishment
To replace lost sediment by placing new sediment on the beach
Have they solved the problem with beach replenishment
-Beach nourishment is only a temporary solution
• The processes that removed the sediment in the first place are still operating
• Often beach replenishment needs to be carried out periodically
Problems with beach replenishment
It is expensive
• The sand has to come from somewhere
• Where (in the coastal zone) do we find a regular supply of sand?
• Estuaries are excellent sediment traps
• Often dredging is required to deepen them again
• Beach replenishment can be cost effective when linked to existing dredging programmes (Dahm 2003)
Dune rehabilitation
Remember sand dunes are important:
• Sand dunes act as flexible barriers
• During storms sand is eroded from beach-dune system and is deposited offshore
• This sand is (normally) returned during calm weather
• Sand dunes are NOT permanent structures, instead they act as reservoirs of sand
• Constant cycle of dune erosion, dune rebuilding and stabilisation

Dune rehabilitation involves:
• replanting sand dunes to help recreate natural dune systems
• the construction of fences & access tracks to protect dune vegetation

Two key elements:
Vegetation: without vegetation the sand will blow away and no dunes will be formed
Protection: Many sand dune systems are being destroyed, minimising this destruction is essential

Dune rehabilitation is popular with coastal managers
Cheap
Natural
Long term
Involves people/communities resulting in people being loyal to the beach which means they will come back and take care of it in the future
Accomodation (in the coastal management)
Accommodation means learning to live with sea level rise and coastal inundation (elevating building, warning systems etc..)
Set back zone
a zone where you cannot build (enforced by the council) due to room for beach processes to occur
Which means if you want to build a house there you cannot because the council establishes a zone where the beach processes like erosion will take place and eventually erode that zone away
How have we responded to coastal erosion in the past?
-In short-badly
-In the past we failed to realise that coastlines are dynamic and this are constantly changing
-Shorelines are not fixed
-Coastal environments are dynamic
-Management solutions are often static
-All coastal management methods involve modification of this model
-In the past we built hard structures designed to protect the coast – today there is a
shift away from this engineering approach to more integrated “softer” options
Responding to coastal erosion
In the past the answer to coastal erosion was to build a hard structure – to protect the land behind the beach
Today we see a shift from this engineering approach to a more integrated approach
Softer management options have emerged
We have moved away from static options to more dynamic options
What are the management options to deal with coastal erosion?
-Hard structures
-soft options
-relocation or retreat
-do nothing
Coastal erosion itself is natural
Coastal erosion only becomes an issue when it impacts upon people and infrastructure
Hard structures
sea wall
groynes
breakwaters
Soft options
These options are more natural and do not require hard structures
• Beach replenishment
• Coastal dune rehabilitation
Relocation or retreat
Move existing infrastructure and buildings away from the coast
• Establish set back zones
• This is difficult to do in on land already developed
• And its not a popular option
-Sometimes retreat is a viable option when there is space to do so
Which option is the most suitable?
The management option adopted for any given stretch of coastline will be influenced by both socio-economic (population, business etc..) and physical factors (location, processes etc..)
• Haslett (2000) argues that the relationship between the value of a coast to society and the cost of protecting that coast dictates the management option chosen
If the cost of protecting coastal land is high but the value of the land is low which option would be the most suitable?
Retreat
What causes coastal erosion?
Remember the THREE causes & that coastal erosion is a natural process – it only
becomes a problem when it impacts upon people