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Property along the the world's beaches is beautiful and attractive to many. But there are dangers, too. Find out how you can check out property to avoid nasty surprises.
The sea fascinates us. Many people dream of owning a house at the shore of the ocean, or at the banks of a river. A villa at the beach stands, right or wrong, for a high quality-of-life. Living near to the water, however, comes along with risks – for one’s life, and the value of one’s property. Let me give you a few points worth watching, before buying expensive coastal property.
- Ground elevation. The land should be at a comfortable elevation above the water. I would argue that a minimum of seven feet above the maximum tidal level is a required minimum– particularly in view of a slowly rising sea level calculated for the next hundred years. Some coastal areas also suffer from subsidence. These are areas in marinas, where the artificial landfill hasn’t fully compacted yet. Clay, as a rule of thumb, compacts more and faster than sand. Areas such as the Mississippi Delta in Louisiana, Venice in Italy, Bangkok Thailand, Bangladesh etc are deltas that are gradually subsiding ‘naturally’. The rivers being encased with artificial levees, no new spillover sediment can counter the effect of natural sediment compaction in the subsurface. Massive extraction of groundwater, oil and gas enhances and accelerates subsidence. Combined with a rising sea level, many deltas are gradually drowning, and valuable properties and natural habitats are being lost.
- Ground elevation and catastrophic events. To be safe from a millennium storm surge, or tsunamis, only land higher than some fifty feet might offer some degree of protection.
- Land stability along the seashore. Long-shore currents carry sand and clay along the shorelines. Wherever a current strengthens, sediment is eroded. Wherever the current weakens, sediment is deposited and, with interaction of waves and tides new land emerges. Some land such as coastal mouth bars (Padre Island in Texas etc) have formed that way. A current’s direction changes over time- and long-shore currents have enormous erosive powers. Where land is today may be sea tomorrow.
- Living on a delta. Deltas are also can be short-lived. Aerial pictures of the Texas Gulf Coast taken over the last seventy years show the birth and death of several delta lobes. A changing long-shore current wiped out a delta that once reached far out into the sea. The entire erosion and removal of the delta was completed during a time span of a few years only. Note that any human building activity along the shore (marinas, industrial harbors, current breakers etc) affect the direction and strength of the long-shore currents. Which means that coastal currents are going to shift more rapidly than ever.
- Land stability along rivers. Living on natural levees of actively meandering rivers also presents dangers. These are seasonal flooding events after the winter/rainy season. The direction (vector) and strength of a naturally meandering river current is changing continuously. Meandering rivers migrate through their lowland like a sidewinder snake does in the desert. Just have a look at the Amazons River. Land located above a today’s levee may be eroded over a few years. Rivers with artificial man-made levees offers a degree of protection.
- Surface angle and slope stability. Slope angles higher than 5 deg are not problematic, if the property is located on hard, solid rock. Soft sediments however, particularly if soaked by rain, rising ground water or storm surge tend to start sliding. Crevasses appear on the surface, and the land slides on a scooping fault plane. You can observe this happening along natural and artificial levees in SE Texas.
- Settling on cliffs can be a dangerous business, too. Hi-shore cliffs endure day-in-day-out the power of breaking waves. These scour the cliff at the water level, which eventually will lead to a disintegration and collapse of the cliff’s frontal sections. An earthquake can also trigger a cliff’s collapse. A typical case for what I’m describing here is the beautiful hi-shore in areas of southern California.
- The underground. Solid rock reacts ‘benign’, when an earthquake strikes. Unconsolidated sediments, as used in ‘artificial’ land recovery projects (marinas etc) are transformed into liquid when the quake strikes. Examples from California and Japan have demonstrated that a house can easily 'drown' in quake-liquefied sediment. Some areas, that are located on limestone, may harbor underground cavities. These form, as water leaches the limestone away, and can collapse to form sizeable craters. Underground caves systems in area where salt and freshwater do mix, may be particularly at risks. Such areas exist in Florida, Meso-America, Thailand and Malaysia.
In a nutshell, good coastal property is characterized by:
- Being safely located above the water;
- Formed by solid, non-fractured rock (granite etc);
- Dipping with a gentle angle toward the sea
© 2005 by Franz L Kessler.
The author of this article holds a PHD in sedimentology, and has worked in the oil business for twenty years.
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