Human Interference with Coasts (Leaving Cert Geography): Revision Notes
Human Interference with Coasts
Human activities along coastlines can have both positive and negative effects on natural coastal processes. When people try to solve one coastal problem, they often create unexpected consequences elsewhere. Understanding these impacts is crucial for effective coastal management.
Coastal management requires understanding how human interventions interact with natural processes. Even well-intentioned solutions can create new challenges in different locations along the coast.
Case study: Dublin Bay
The original problem
Dublin Bay provides an excellent example of how human intervention can produce unintended results. In the past, natural coastal processes caused significant problems for Dublin's shipping industry. Sand and silt deposits regularly blocked the mouth of the River Liffey channel, forcing ships to run aground when entering Dublin Harbour. This created major difficulties for importing and exporting goods, which was essential for the city's economy.
Longshore drift is the natural process that moves sand and sediment along coastlines. While this is a normal coastal process, it can create problems for human activities like shipping when sediment accumulates in harbours.
Human intervention - the Bull Walls
Authorities initially tried to solve this problem through dredging - scooping mud and sediment from the harbour bottom. However, this approach proved ineffective as the sediment quickly accumulated again.
Dredging is the process of scooping mud and sediment from the bottom of a river, harbour, or sea.
To prevent longshore drift from depositing more sand and silt in the harbour, engineers constructed two major sea walls between 1818 and 1825. The North Bull Wall and South Bull Wall were built on either side of the Liffey channel to block sediment from entering the harbour area.
Formation of Bull Island
The walls had an immediate positive effect on shipping, allowing vessels to enter and exit the harbour more easily. The harbour depth increased by 3 metres over 50 years as tides and currents washed away accumulated silt. However, the walls created an unexpected consequence.
This case study demonstrates a key principle in coastal management: solving one problem often creates new challenges elsewhere. The Bull Walls successfully protected Dublin Harbour but led to the formation of an entirely new island.
Since sand and silt could no longer enter the harbour, these materials began accumulating on the north side of the North Bull Wall. This sediment built up rapidly, eventually forming a new island. Bull Island has now grown to an impressive size of 5 kilometres long and 700 metres wide, and continues expanding as more sand becomes trapped.
This island represents a 'gift from the sea' - an unplanned result of human interference with natural coastal processes.
Advantages of Bull Island
The unexpected island creation brought several benefits to Dublin:
Recreation and tourism: Bull Island became a valuable amenity for Dublin residents and visitors. Two of Dublin's most prestigious golf courses, Royal Dublin and St Anne's, were constructed on the island. The high sand dunes provide ideal conditions for links golf courses.
An amenity is a service or facility that benefits the local community.
Wildlife conservation: The island supports diverse flora and fauna, becoming officially recognised as a bird sanctuary in 1930 and a wildlife sanctuary in 1986. A visitor centre now provides information about the island's unique ecosystems.
Disadvantages of Bull Island
Despite its benefits, human activity has created problems for the island's natural structure:
Human recreational activities can damage the very coastal features that make an area attractive. This creates a management challenge between public access and environmental protection.
Sand compaction: Vehicles driving and parking on the beach compress the sand, reducing the amount blown inland by wind. This significantly slows down natural sand dune formation and growth.
Dune instability: People walking and playing on sand dunes damage the Marram grass that anchors them. When dunes become unstable due to trampling, they become much more vulnerable to wind erosion.
Coastal management approaches
Ireland has approximately 3,171 kilometres of coastline, with roughly half at risk from flooding and erosion. Coastal management strategies aim to protect these vulnerable areas using two main approaches: hard structures and soft structures.
Coastal protection strategies must balance effectiveness, cost, environmental impact, and long-term sustainability. The choice between hard and soft engineering often depends on the specific location and the level of protection required.
Hard structures
Hard coastal defences aim to prevent erosion using permanent, resistant materials. These structures are typically built from reinforced concrete or resistant rock and rarely require removal once constructed. Hard structures prove particularly popular in coastal towns where they protect buildings and infrastructure from wave damage.
Sea walls
Sea walls provide robust protection for coastlines against destructive waves. Engineers construct these barriers from concrete reinforced with steel, designing them with curved tops that deflect breaking waves back towards the sea. This curved design reduces the energy of incoming waves, making them less likely to overtop the protective wall.
Example: Lahinch Sea Wall
The coastal town of Lahinch in County Clare uses sea walls to protect businesses built along the shoreline from wave damage. The curved design deflects wave energy back to sea, reducing the risk of flooding.
Gabions
Gabions consist of steel mesh cages filled with stones, designed to reduce the energy of incoming waves. When waves hit a line of gabions, the water breaks up as it philtres through the stones in the mesh. This spreads out the wave's energy and reduces its erosive power.
Although gabions work effectively, they require more maintenance than sea walls. The mesh wire can break during storms, and stones may wash away over time. Many coastal engineers prefer sea walls for their durability and lower maintenance requirements.
Groynes
Groynes are low walls made of cement or wood, built at right angles to the shoreline. These structures trap sediment moving along the coast through longshore drift, allowing material to accumulate and preventing beach erosion.
Example: Youghal Beach
Several groynes have been constructed along Youghal Beach in County Cork to maintain the beach's width and prevent erosion through sediment trapping.
However, groyne construction creates negative effects downstream. By trapping sediment in one location, groynes deprive nearby coastal areas of natural sediment supply, potentially increasing erosion in those areas.
Rock armour
Rock armour provides a basic but effective form of coastal protection. Large boulders placed along coastlines absorb wave energy when waves crash against them, reducing their erosive power and preventing coastal retreat.
Despite their effectiveness, rock armour installations are not popular choices for coastal defence. They appear bulky and take up considerable space on beaches, reducing the area available for recreation and tourism.
Soft structures
Soft coastal protection methods offer more environmentally friendly alternatives to hard engineering. These approaches are not permanent and focus on repairing damage caused by destructive waves rather than preventing it entirely.
Soft structures are environmentally friendly, temporary coastal protection methods that repair damage rather than prevent it.
Beach nourishment
Beach nourishment involves adding new sand to beaches to increase their thickness and width. Sand is dredged from offshore locations and transported to the target beach. This process helps prevent erosion whilst increasing the beach's recreational value.
Example: Rosslare Beach Nourishment
Beach nourishment was successfully implemented in Rosslare, County Wexford during the 1960s. The project increased beach width and provided better protection against coastal erosion.
Although effective, this method proves very expensive and labour-intensive, requiring ongoing maintenance and sand replacement.
Sand dune repair
Sand dunes can be protected from erosion by planting Marram grass. The grass's extensive root system binds sand particles together, making dunes more resistant to wind erosion. Marram grass is particularly suitable for coastal protection because it tolerates salt spray and harsh coastal conditions.
Sand dune repair represents the most environmentally friendly form of coastal protection, as it works with natural processes and doesn't negatively affect other coastal areas.
Case study: Coastal protection at Lahinch, County Clare
Location and background
Lahinch sits in the Liscannor Bay area of County Clare, featuring a long sandy beach and excellent surfing conditions that attract many tourists. Since the early 19th century, coastal development has required protection from erosion and flooding through various hard engineering solutions.
Hard engineering solutions
A hydro-dynamic sea wall was constructed from concrete and reinforced with steel. The wall's curved top serves two important functions:
- It deflects wave hydraulic power back out to sea
- It reduces the amount of seawater getting over the wall
Rock armour was strategically placed at the base of local cliffs and in front of the curved sea wall. This prevents coastal erosion by breaking the hydraulic power of incoming waves before they reach the coastline.
Soft engineering solutions
The area combines hard structures with environmentally friendly soft engineering approaches:
Example: Integrated Coastal Protection at Lahinch
Marram grass planting: This salt-resistant vegetation has been planted on vulnerable sand dunes to trap and stabilise wind-blown sand. The grass's deep root system also reduces wind speed over dune surfaces while allowing sand to accumulate and hold sediments in place.
Gabions: Wire cages filled with stones were placed in the upper beach area, in front of sand dunes. These flexible, porous structures trap wind-blown sand whilst allowing vegetation to grow under favourable conditions.
Storm Darwin impact (2014)
Storm Darwin severely tested Lahinch's coastal defences in 2014. The original protective works proved inadequate against the storm's powerful waves, which overtopped existing defences and caused over €6 million worth of damage.
The storm damage included:
- Major destruction to buildings, wall cappings, footpaths, and promenade signage
- Complete collapse of metal fencing along the shorefront
- Severe flooding, with seawater reaching almost 500 metres inland
- Buildings adjacent to the car park submerged under 1.5 metres of water
- Flooding of low-lying areas of Lahinch Golf Course
Recent improvements (2017)
Following Storm Darwin's devastation, major protective works costing €2.85 million were completed in 2017:
- The existing sea wall was strengthened with additional concrete apron and more rock armour
- Gabions were removed from in front of sand dunes and replaced with rock armour during extended coastal protection works
- The improvements extended further along the coastline to provide more comprehensive protection
The rock armour replacement was necessary because the gabions proved insufficiently durable to withstand regular direct wave action. The new rock armour will help prevent future erosion from destructive waves, especially during major storm events, whilst stabilising the disturbed dune system.
Remember!
Key Points to Remember:
- Human coastal interference often produces unintended consequences, as shown by Bull Island's formation in Dublin Bay
- Hard structures (sea walls, gabions, groynes, rock armour) provide permanent protection but can be expensive and environmentally disruptive
- Soft structures (beach nourishment, sand dune repair) offer environmentally friendly alternatives but require ongoing maintenance
- Effective coastal management often combines both hard and soft engineering approaches, as demonstrated at Lahinch
- Climate change and extreme weather events like Storm Darwin continue to challenge existing coastal defences, requiring ongoing investment and adaptation