Human actions and coastal recession

Coastal recession refers to the gradual wearing away and retreat of coastlines due to erosion processes. Human activities can disrupt natural coastal systems, often accelerating this recession by interfering with sediment movement and supply.

Understanding sediment cells

A sediment cell is a section of coastline that functions as a relatively self-contained system, where sediment (such as sand and shingle) is sourced, transported, and deposited. These cells can achieve dynamic equilibrium, a state where inputs and outputs of sediment are balanced, maintaining a stable coastline over time without human interference.

Human actions can upset this balance, leading to increased or decreased rates of coastal recession. This occurs because interventions alter the natural flow of sediment within the cell.

Ways human actions disrupt sediment cells

• Building dams on rivers - Dams trap sediment upstream, reducing the amount that reaches the coast. This limits the material available for longshore drift, the movement of sediment along the coastline by waves at an angle. As a result, beaches downstream receive less sediment, leading to higher erosion rates as waves directly attack the coast without a protective buffer.
• Constructing coastal defences - Structures like groynes, which are barriers built perpendicular to the shore to trap sediment, prevent longshore drift from distributing material evenly. This builds up beaches on one side but starves those further along, causing smaller beaches and faster recession in unprotected areas.
• Dredging activities - Dredging involves removing sediment from offshore bars, harbours, or beaches for uses such as construction materials, deepening shipping lanes, or beach nourishment (adding sand to eroded beaches). This permanently removes sediment from the cell, reducing natural buffers against waves and increasing recession rates.

These disruptions highlight how human interventions, intended to solve local problems, can create broader issues along the coastline by altering natural sediment dynamics.

Human activities in the Nile Delta

The Nile Delta in northern Egypt serves as a key example of how human actions exacerbate coastal issues in a low-energy coastal environment, where wave and tidal forces are relatively weak.

Key features of the Nile Delta

This delta covers about 22,000 km² and includes the final stretch of the River Nile before it meets the Mediterranean Sea. It supports around 50% of Egypt's population, making it a densely populated area. Major cities like Alexandria, with over 5.4 million residents, are located here.

The delta faces threats from rising sea levels in the Mediterranean and high erosion rates, compounded by human modifications.

Impacts of rising sea levels and erosion

• Saltwater intrusion - This occurs when seawater infiltrates the soil from below, increasing salinity in low-lying areas. Floods deposit salt on the land, reducing soil fertility and making farming difficult.
• Effects on agriculture and fishing - Increased salinity affects freshwater lakes and lagoons, rendering them unsuitable for irrigation. Some fish species cannot survive in these saltier conditions, threatening the local fishing industry.
• Coastal retreat - The delta is retreating by up to 140 metres per year in some places due to a combination of erosion and minimal sediment replacement.

Role of the Aswan Dam

The construction of the Aswan Dam in 1970 significantly reduced sediment transport down the Nile. Before the dam, about 9.5 million tonnes of sediment reached the delta annually, helping to build and maintain it.

Effects of the dam on sediment supply:

• The dam traps over 98% of this sediment in Lake Nasser, preventing it from replenishing eroded coastal areas.
• Without this fluvial sediment (material carried by the river), the delta cannot counteract erosion from waves and rising seas, accelerating retreat.

This case illustrates how large-scale human engineering, while providing benefits like flood control and hydroelectric power, can disrupt natural coastal processes and lead to long-term environmental and economic challenges.

Economic losses from coastal recession

Coastal recession can result in significant economic impacts, particularly in areas with valuable land and infrastructure. These losses vary based on land use and location, affecting individuals, businesses, and governments.

Variations in land value and protection

Land values differ greatly depending on their purpose, influencing decisions about coastal protection.

Agricultural land is often left unprotected, leading to loss of farmland and reduced income for farmers. In contrast, high-value residential areas are more likely to receive defences.

Impacts on industry and businesses

• Heavy industry - Such facilities are rarely built on rapidly receding coasts to avoid costly relocations. Planning permissions consider recession risks, preventing developments that could lose value.
• Small businesses - Enterprises like hotels on eroding coasts may be abandoned, causing job losses and ripple effects on local economies. This can lead to reduced investment and limited employment opportunities in coastal settlements.
• Property market - Homes on receding coasts are hard to sell and often uninsurable, leading to rapid devaluation. This can affect entire villages, lowering property values even in less risky areas.

Infrastructure challenges

Receding coasts require rerouting roads, rail lines, or other infrastructure, which imposes high costs on local authorities or national governments. These expenses can strain budgets and divert funds from other services.

Overall, economic losses from coastal recession create long-term challenges, including reduced investment and uncertainty for future development.

Social losses from coastal recession

Beyond economic impacts, coastal recession can disrupt communities, leading to social challenges that affect residents' quality of life and wellbeing.

Effects on communities and relocation

• Forced relocation - People living on receding coastlines may need to move, breaking up communities and causing depopulation. This is particularly common in densely populated low-lying areas.
• Isolation and stress - Those who remain may feel cut off if infrastructure is lost, leading to disconnection from services and other places. Uncertainty about the future can cause significant stress for residents and business owners.

Loss of amenity value and services

Amenity value refers to the benefits a landscape provides through its cultural, aesthetic, and wellbeing aspects.

Consequences of coastal recession for amenity value and services:

• As areas recede and become abandoned, they lose their character and become visually unattractive, diminishing amenity value.
• Local services, such as shops or schools, may close as people leave, disproportionately affecting low-income or less mobile individuals. This can also result in job losses for local workers.

Safety risks

Although rare, coastal recession poses physical dangers.

Examples of safety risks:

• Cliff collapses can cause fatalities, especially for people walking on unstable paths.
• Falling debris, particularly after storms, can injure beachgoers.

These social losses compound economic issues, creating a cycle of decline in affected coastal areas.