Environment and development in coastal regions and in small islands

Coastal management sourcebooks 1
Chapter 2

What to look for when investing in coastal land or property

The prospect of owning a coastal property on a Caribbean island is a dream for many people. Those who seek to make their dream come true would be well-advised to consider very carefully the potential hazards of living near the ocean before selecting and evaluating a particular site.

All residents of Caribbean islands, and especially those in coastal areas, should be aware of and prepared for the following natural events:

• Tropical storms and hurricanes occur each year and the evidence indicates that we are entering a twenty-year active hurricane cycle. (See Case 2 in Chapter 1.)
• Coastal erosion may have several causes, including winter swells, hurricanes and sand mining. (See Cases 1, 2 and 6.)
• Sea levels are rising globally. As a result, greater beach erosion is likely over the coming decades.
• Heavy rains and flooding have serious consequences, expecially in low-lying areas inland and near the coast.
• Landslides and rockfalls commonly occur on steep volcanic islands and on coastal cliffs. These are often triggered by heavy rainfall.
• Tsunamis are extremely high waves also known as tidal waves. They are very rare events caused by underwater earthquakes or huge undersea landslides. Several have been experienced in the Caribbean within historic times and have caused death, flooding and damage to coastal areas. During tsunamis, low-lying coastal areas, in other words those below the 6 m (20 ft) contour, may be flooded. Tsunamis can travel at speeds of 800 km/hr (500 mph), which means that an earthquake off the coast of Venezuela could result in a tsunami reaching the Caribbean islands within a matter of minutes. At present, there is no tsunami warning system in the Caribbean region. However, there is one piece of information that could save a life: if you are at the beach and see the water suddenly recede a considerable distance, leaving parts of the seabed dry, this could be the forerunner of a tsunami. Run for higher ground!

Prospective home buyers should also consider the consequences of corrosion in salt air, which affects everything from cars and electronic equipment to nuts and bolts. The salt-laden air also influences the type of plants that can be grown around a beachfront property. Another factor to consider is that almost all beaches in the Caribbean are public. On holidays and weekends, a secluded getaway may become a noisy open-air party. It pays to check out the site very carefully.

Global climate change and sea level rise: proceed with caution

There is evidence that the increased rate of global warming experienced over the past century is the result of human activities, for example the increased use of fossil fuels like coal and oil. There is further concern that warmer air temperatures will accelerate the melting of ice sheets. Warming will also result in the expansion of ocean waters. Both effects will result in an increase in ocean volume, which may in turn be reflected in rising sea levels.

Sea level varies according to the tidal state and weather conditions, so accurate measurements have to be recorded over a number of years to determine mean sea level. In the coming decades, there will be considerable variability in the extent of sea level rise at the regional and local level. A few islands rising tectonically may actually experience falling sea levels. Sea level is being monitored in the Caribbean region; the highest rate of sea level rise measured historically in the eastern Caribbean is 1–2 mm per year.

Day-to-day wave and current action at the shoreline and the availability of sediment in a beach system are far more important to beach stability than rising sea levels. However, over a period of two to three decades, rising sea level will elevate the ocean surface, thereby allowing waves to reach farther up the beach. Beaches will adjust to this situation by changing shape. On developed shorelines where beaches have little space to adjust, there is a possibility of increased erosion.

Land that is at, or close to, sea level will be susceptible to submergence and flooding wherever sea level is rising. Occupants of coastal land should be aware that the water table below the ground surface is linked directly with the sea surface. Hence, in the long term, a change in the sea level is likely to result in a rising water table. A rising water table can lead to ground saturation.

If building close to the ocean, sea level rise is an important factor to consider. While the impacts will not be immediate, most houses are expected to last for more than thirty years. The best response is to ensure that there is as much setback as possible between the building and the beach. Do not settle for the minimum setback, but rather allow as much distance as possible.

On a larger scale, the magnitude of the impact can be reduced by ensuring that governments are fully committed to international conventions designed to control such problems, like the International Convention on Climate Change.

P R E P A R I N G
A   C H E C K L I S T

It is often useful to prepare a checklist to assess the vulnerability of a particular site to coastal erosion. Use the blank checklist in Appendix I to evaluate the vulnerability of the site you plan to purchase. To guide you in filling it in, the various features of the checklist are explained below and a completed checklist for a beach site on the north coast of Tortola in the British Virgin Islands is given in Table 4.

Elevation of the site

The higher the land, the safer the site from seawater inundation, especially during storms and hurricanes. Recent hurricanes resulted in seawater extending more than 100 m (328 ft) inland at some low-lying sites only 1–2 m (3–7 ft) above mean sea level.

For the checklist, the following elevation categories may be used to determine site vulnerability:

• less than 3 m (10 ft) above mean sea level = high vulnerability;
• 3–5 m (10–16 ft) above mean sea level = medium vulnerability;
• more than 5 m (16 ft) above mean sea level = low vulnerability.

Landforms behind the beach

Solid bedrock is more resistant to wave energy than sandy terraces and dunes; thus, rocky shores and cliffs represent safer sites. However, even solid cliffs experience erosion and their vulnerability varies according to their geology. Harder rocks, such as granites, basalts and limestones, are more resistant to erosion than softer rocks, such as clays and sandstones.

Sand dunes are accretionary features formed by wind. Vegetated dunes are a sign of stability. However, it is important to realize that dunes are temporary features that can be completely destroyed by a hurricane. (See also Cases 2 and 7.) For example, in Anguilla during Hurricane Luis in 1995, low dunes were cut back 30 m (98 ft) and dunes more than 8 m (26 ft) high were cut back 10 m (33 ft). Building on the primary dune should always be avoided.

Bearing this in mind, the following categories may be used for the checklist:

• where there is an extensive dune system with more than one row of dunes, the site should be given a low vulnerability index;
• where there is only one line of dunes present, the site should be given a medium vulnerability index.

The following list represents the major types of landforms found behind the beach and their vulnerability index for the purposes of the checklist:

• low land composed of soil formations = high vulnerability;
• low land composed of a sand terrace = high vulnerability;
• single dune line behind the beach = medium vulnerability;
• multiple dune system (more than one line of dunes behind the beach) = low vulnerability;
• sloping land (soil over rock) covered with vegetation = low vulnerability;
• low rocky shore (soft rock) = medium vulnerability;
• low rocky shore (hard rock) = low vulnerability;
• cliff (soft rock) = medium vulnerability;
• cliff (hard rock) = low vulnerability.

Wave exposure

The fetch, or distance, of open water a shoreline faces can provide an indication of the likely size of potential storm waves. For instance, many of the eastern shores of the Caribbean islands face the Atlantic Ocean, with more than 3,200 km (2,000 miles) of open sea stretching before them. Thus, these coasts are likely to experience very large waves during storms and hurricanes. On a local scale, another island or a small offshore cay might shelter a particular bay or part of a bay.

For the checklist, the following categories may be used:

• fetch greater than 160 km (100 miles) = high vulnerability;
• fetch 16–160 km (10–100 miles) = medium vulnerability;
• fetch less than 16 km (10 miles) = low vulnerability.

Photograph 37. Tombolo, Scotts Head, Dominica, 1994. This narrow strip of land made up of  sand and stones has been formed by waves  and joins the small islet of Scotts Head  (foreground) to the main island of Dominica  (background).

Proximity of site to vulnerable accretionary feature

Accretionary features like those shown in Figure 5 (Case 1, Chapter 1) include spits, bars, tombolos and cuspate forelands. While these features are formed by the process of accretion, or sand build-up, they are nevertheless very vulnerable to sudden change, particularly during tropical storms and hurricanes. Spits, bars and tombolos should be avoided as building sites. Development on coastal lands within 100 m (328 ft) of these features should take into account the likelihood of possible major coastline changes. Similarly, cuspate forelands are vulnerable to sudden, major changes after extreme weather and, while the land behind these features may provide suitable sites for development, caution should be exercised in siting new development schemes and maximum setback distances should be adopted.

For the checklist, the following categories may be used:

• on a bar, spit or tombolo = extremely high vulnerability, on no account build here;
• within 100 m (328 ft) of a bar, spit or tombolo = high vulnerability;
• behind a cuspate foreland = low vulnerability;
• if none of these features exist, record the category as not relevant (NR).

Photograph 38. Sand dunes, Rendezvous Bay,  Anguilla, 1994. These vegetated dunes,  together with the newly forming low dunes at  their base, indicate stability. However, dunes  are merely sand reservoirs and may be  completely eroded in a hurricane.

Proximity to river mouth or tidal inlet

During heavy rainfall and floods, coastal river mouths often shift their positions and there may be considerable erosion of the beach near these features. It is important to check the proximity of the site to both small and large river mouths. Be aware that, even if the channels are dry for most of the year, there is the potential for considerable beach and coastline changes during heavy rainfall. As a guide for the checklist, ‘proximity’ is defined as 10 times the channel width, e.g. if the channel width is 2 m (7 ft), avoid building within 20 m (66 ft) either side of the channel mouth.

Some beaches separate ponds from the sea. These ponds may be wet or dry; if wet, they usually contain brackish water. They fulfill important functions, such as filtering sediment and pollutants from the water before it reaches the sea. They are not recommended sites for any type of construction.

Inlets between islands, particularly narrow tidal inlets as exist in the Turks and Caicos Islands and the Bahamas, are influenced by waves and tidal currents. Beaches near such inlets may experience rapid and significant changes. Rates of change may be several times greater than at other beaches on an island. (See also Case 9.) Proximity to a tidal inlet may be defined here as being within 1 km (0.6 miles) of the inlet.

For the checklist, the following categories may be used:

• within a distance of less than 10 times the width of the river mouth = extremely high vulnerability, avoid building here;
• within a distance of 1 km (0.6 miles) of a tidal inlet = high vulnerability;
• if neither of these conditions exist, record the category as not relevant (NR).

Presence of coral reef

Offshore coral reefs, whether patch, fringing or barrier reefs, often come to within 1–2 m (3–7 ft) of the sea surface. They may therefore act as natural breakwaters and cause the incoming waves to break before they reach the shore. Thus, the existence of such features will help to reduce the size of storm waves. (See also Case 10.) Local fishermen and -women, the fisheries department, dive operators and bathymetric maps are all good sources of information on reefs.

For the checklist, the following categories may be used:

• absence of any reef structure at all = high vulnerability;
• presence of an offshore coral reef, but the waves are not breaking on it = medium vulnerability;
• presence of an offshore coral reef, waves are seen breaking on it = low vulnerability.

Beach size

A wide beach, which is essentially a flexible barrier, is the best form of coastal protection. The back beach, which is the section from the high water mark to the tree line, building line, dune line or land edge, is an important feature. A wide back beach covered with grass and vines indicates stability. However, always view the site during both summer and winter, since the state of the beach may change dramatically and some coastal vegetation, like vines, can grow very quickly.

For the checklist, the following categories may be used:

• minimum back beach width less than 5 m (16 ft) = high vulnerability;
• minimum back beach width 5–10 m (16–33 ft) = medium vulnerability;
• minimum back beach width more than 10 m (33 ft) = low vulnerability.

Erosion indicators

There are several visual indicators of erosion. Dead trees and exposed tree roots indicate where wave action is concentrated, particularly during high seas. Buildings in the sea may be picturesque, but with no protective beach, they are extremely vulnerable to high seas and were probably built when there was a wide beach. Sea defences, seawalls, rock revetments, groynes and offshore breakwaters, all indicate erosion or the potential for erosion.

Photograph 39. Beach erosion, Josiahs Bay,  British Virgin Islands, 1990. These exposed tree roots and the fallen tree indicate the waves had reached the land behind the beach recently.

It is important to check both in the immediate vicinity and farther along the beach. Steep bluffs and slopes at the back of the beach separating the land or dunes from the beach are usually formed by waves. A gentle vegetated slope indicates stable conditions. Breaks in the dune line may also indicate areas where the waves have eroded and broken through the dune line in the past. Beachrock forms within the body of the beach and, wherever exposed, indicates erosion. (See also Case 10.)

On shorelines bordered by cliffs, signs of instability include wave-cut notches at the base of the cliff, landslides and slumping rock material, and springs issuing from the cliff face.

For the checklist, the cumulation of indicators present may be used to determine the site’s vulnerability to erosion:

• 3 indicators or more = high vulnerability;
• 2 indicators = medium vulnerability;
• 1 indicator = low vulnerability;
• no erosion indicators = not relevant (NR).

Most recent hurricane

Tropical storms and hurricanes cause major changes to the beach and coastline that sometimes prove semi-permanent in that they last for decades. (See also Case 2 in Chapter 1.) Tropical storms and hurricanes may cause beach instability for several years afterwards as beaches and offshore systems, including coral reefs, slowly recover.

For the checklist, the site’s vulnerability to change as a result of the most recent hurricane may be determined as follows:

• hurricane occurred within 1 year = high vulnerability;
• hurricane occurred 1–5 years ago = medium vulnerability;
• hurricane occurred 6–10 years ago = low vulnerability;
• hurricane occurred eleven or more years ago = not relevant (NR).

Information from neighbours

When preparing a checklist, always try to obtain local information from your prospective neighbours. A space has been left on the checklist for this kind of information, since this will help in assessing the vulnerability of some of the other features.

Calculating the overall vulnerability index

Once the nine features described above have been evaluated in terms of extremely high, high, medium or low vulnerability, an overall vulnerability index can be calculated. Each ‘high’ index is given a score of 3, each ‘medium’ index a score of 2 and each ‘low’ index a score of 1. Note that if any feature has been given an ‘extremely high’ index (See Proximity to an accretionary feature and/or river mouth or tidal inlet.), no building at all should be considered on this site. Any feature recorded as not relevant (NR) should be given a value of zero. Add together the values for all features to determine the overall index.

Making an assessment

In making your overall assessment, use the following guidelines:

• overall index value of 19 or greater equals high vulnerability; if at all possible, look for alternative sites to build. However, if this is not feasible, utilize such planning mechanisms as elevating the building onto piles or implementing very high setback distances;
• overall index value of 12–18 equals medium vulnerability; a prospective buyer might wish to take special care at this site, perhaps by ensuring there is space for setbacks between the building and the beach that are above the minimums recommended by planning authorities;
• overall index value of 11 or less equals low vulnerability; this would be a suitable site for development.

Consult other information sources on beach erosion.

If you wish to take your investigation further, you may like to consult relevant reports that have been done on coastal erosion on the island. These can usually be read at planning or environmental agencies or at non-governmental organizations (NGOs) like the National Trust. Planning and environmental agencies are likely to have information about the different beaches on an island. They can provide data from regular beach monitoring programmes or other studies and their own professional expertise and experience. Another information source are the historical aerial photographs of the particular beach, which are usually stored at the government agency dealing with land survey. Local fishermen and -women and regular beachgoers are sometimes knowledgeable sources of information. A little time spent in the local bar or rum shop may also produce useful information.

Consult local insurance companies.

Always ask about insurance rates before you buy coastal property. Since the end of the 1980s, insurance premiums have been rising rapidly. On occasion, insurance has been difficult to obtain. A primary reason for rising insurance rates is the damage inflicted by recent hurricanes.

Consult planning and legal authorities about public rights to the beach.

While, in some Caribbean islands, private ownership of land may extend to the high water mark, this is not always the case. Even when private ownership covers the dry sandy part of the beach, it does not mean that a private land owner has the right to restrict public access or use across this part of the beach. It is wise to consult the local legal and planning authorities to determine the accepted practices on a particular island. It is understood in most of the Caribbean islands that beaches are always available for public use. The more detailed your investigation, the greater chance you will have to enjoy your coastal property for many years to come.

Determine the planning guidelines for the site.

Planning guidelines will include setbacks, building density (the ratio of the built area to the unbuilt area on the lot), height of the building (number of stories permitted) and other essential criteria. Based on your own vulnerability assessment using the form in Appendix I, you may wish to increase the setback from the active wave zone to a distance farther than that recommended by the planning authority. Advice from a coastal specialist may influence your final decision with regard to the siting of structures.

Coastal development setback guidelines.

Coastal development setbacks are especially important in the tourism-orientated islands. They provide buffer zones enabling beaches to move naturally without the necessity for seawalls and other structures; they reduce damage to beachfront property during high wave events like hurricanes; they improve the view and access along the beach; and they provide privacy for the occupants of coastal property and for beachgoers.

The use of a fixed setback for all beaches on an island has proved difficult to implement. Beaches behave differently. Some are eroding, others are accreting. The nature of the change may also vary over the short and long term. As a result of these characteristics, recently proposed guidelines (Cambers, 1997) develop specific setbacks for individual beaches based on a combination of different parameters:

• historical changes over the last 30 years;
• changes over the past five years, as determined from beach monitoring data;
• changes in the position of the dune line or land edge likely to result from a major hurricane;
• coastal retreat likely to occur as a result of projected sea level rise over the next 30 years;
• the existence or absence of offshore features, such as coral reefs or beachrock ledges. These provide protection during high wave events;
• factors linked to human activities, among which beach and dune mining;
• such planning considerations as lot size, marine park designations and special types of development, for example beach bars.

The actual setback for a specific beach has been determined as follows:

Using this methodology, specific setbacks can be determined for each beach.

In all cases, setbacks should be measured from the line of permanent vegetation or the tree line.

T A B L E 4
Prospective buyer's checklist for site vulnerability to erosion
Sample checklist for Josiahs Bay, Tortola, British Virgin Islands (site shown above).

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