Beach erosion describes the loss of sand and land along coastlines. It is a natural process, but various factors can intensify it, leading to significant changes in coastal environments. The removal of beach material occurs through both natural phenomena and human activities.
The Power of Waves and Currents
Waves and currents are primary drivers of beach erosion, directly impacting the shoreline. Wave energy, particularly during powerful storms, directly removes sand from the beach face. The characteristics of waves, including their height, direction, and frequency, determine their erosional impact. Larger waves, especially those generated during high-energy events like hurricanes or nor’easters, carry more energy and can displace much sand.
Waves approaching the shore at an angle generate longshore currents, which flow parallel to the coastline. These currents transport sand along the shore in a zigzag pattern, a process known as longshore drift. This continuous movement can lead to erosion in some areas where sand is carried away and deposition in others where it accumulates. Rip currents, which are strong, narrow channels of water flowing offshore, also contribute to localized sand movement, pulling sediment away from the beach.
Long-Term Environmental Changes
Natural processes operating over longer timescales also contribute to beach erosion. Sea level rise is a major factor, as higher water levels allow waves to reach further inland, eroding areas that were previously stable. Even a small increase in sea level can result in a disproportionately large amount of shoreline retreat.
Changes in natural sediment supply also influence erosion rates. Rivers naturally deliver sand and other sediments to coastal areas, replenishing beaches. However, natural geological shifts or changes in coastal ecosystems can reduce this supply, leading to sediment starvation. When less sand reaches the coast, beaches become more vulnerable to the erosive power of waves and currents, resulting in a net loss of beach material over time.
Human Contributions to Erosion
Human activities often accelerate beach erosion, sometimes inadvertently. Coastal development, involving the construction of buildings and infrastructure close to the shoreline, removes natural protective barriers like dunes and vegetation. These natural features stabilize sand and absorb wave energy, and their removal leaves beaches more exposed to erosion.
Coastal structures, such as groins, jetties, and seawalls, are built to protect specific areas but can disrupt natural sediment transport processes. Groins, structures built perpendicular to the shore, trap sand on their updrift side but starve the downdrift side of sediment, leading to increased erosion there. Jetties, often constructed at harbor mouths, can block the natural flow of sand, causing accumulation on one side and severe erosion on the other. Seawalls can also reflect wave energy, intensifying erosion at the base of the structure and leading to beach loss.
Direct removal of sand through sand mining from beaches or nearshore areas depletes the sediment needed to maintain shorelines. This practice directly contributes to localized erosion and makes beaches more susceptible to other erosive forces. The damming of rivers also plays a role, as dams trap sediment upstream, preventing it from reaching coastal areas and replenishing beaches downstream. This reduction in natural sediment supply starves beaches of new sand, exacerbating erosion over time.