ABSTRACT
Worldwide, most beaches are suffering from serious and accelerating erosion (Pilkey and Young 2009)� Major factors responsible for this erosion include rising sea levels, sand mining, regional subsidence from tectonic causes (amplified in many places by oil and gas extraction), increasing tropical storm intensity driven by global warming, use of groynes that block long-shore sand transport (stealing sand from the neighbors), and seawalls that are built too close to the shoreline (to protect buildings that should never have been permitted so near the water’s edge) due to lax or irresponsible planning (Pilkey and Wright 1988; Pilkey and Dixon 1996)� The only beaches that show clear net growth are a few yellow or brown quartz sand beaches, made up of mineral grains washed into the sea from erosion of rocks on land� These are growing in a few places where massive deforestation has greatly increased erosion of soils and rocks, causing increased transport of sand to beaches near river mouths�
In the tropics, the major factor is death of reef-building corals from global warming, new diseases, pollution, soil erosion, physical damage from human activities, or unsustainable fishing practices� In cooler waters, massive loss of oyster reefs from overharvesting is causing the same result; loss of biological reef structures that protect and build beaches� This results in loss of the organisms whose dead skeletons make up white beach sand grains, and concomitant loss of growing protective
CONTENTS
Global Shore-Erosion Crisis ������������������������������������������������������������������������������������������������������������ 11 Global Warming, Sea-Level Rise, and Erosion ������������������������������������������������������������������������������� 12 Hard-Shore Protection ��������������������������������������������������������������������������������������������������������������������� 13 Soft-Shore Protection �����������������������������������������������������������������������������������������������������������������������20 Biorock: A Superior Marine Construction Material ������������������������������������������������������������������������22 Biorock Shore Protection in the Maldives ���������������������������������������������������������������������������������������25 Biorock Shore Protection in Indonesia ��������������������������������������������������������������������������������������������27 References ���������������������������������������������������������������������������������������������������������������������������������������� 33
reefs shielding the shore from waves� Consequently, beaches suffer from two effects simultaneously: sand erodes faster due to higher wave energy, while less new sand is available to replace it� The massive worldwide destruction and degradation of coral reefs in the last two decades have resulted in most white limestone sand beaches suffering serious net erosion, shown clearly by trees, buildings, roads, and airport runways collapsing into the sea�
When reefs become degraded and need to be replaced by seawalls in order to keep the beach from washing away, the typical costs for concrete or rock seawalls are about $10-15 million per kilometer� A standard estimate of global coastline length is 350,000 km (although this surely ignores the fine-scale details), so protecting all of that could cost up to $5�25 trillion� These estimated costs are for a sea-level rise of about 1 m, but runaway greenhouse warming owing to unabated, increased CO2 levels that melts the ice caps could result in ultimate sea-level rises of up to 100 m!
