Bathymetry and its Influence on the Coastline

Barbados' offshore bathymetry (Fig. 2.5) demonstrates a veiy narrow shelf ranging between 1.5 to 3 km offshore except at its southwest comer near Needham’s Point where, because o f a narrow tongue like bulge, the shelf is about 6 km wide (Delcan 1995). Thereafter, it slopes off rapidly into deep water. This is consistent with the geologic origin o f the island, which is a peak on the Barbados Ridge20 (Speed 2001).

Parallel for much o f the coast, but, especially along the West and South coasts, is a series o f parallel bank reefs that are between 10 and 25 m below the sea surface. Fringe reefs are found at most headland locations along much o f the west coast, acting as natural wave barriers and beach sediment anchors, retaining beach sands within the respective beach cells.

Shelf and coastal processes around the island are dominated by trade wind-generated waves, which are consistent for most o f the year increasing in intensity in January and June (Delcan 1993). The waves refract over the nearshore reefs and transport beach and nearshore sediments along the coastline according to the prevailing longshore current direction. There is known to be seasonal variation in this, with current reversals occurring during the summer months from a north - south direction to a south - north direction (Proctor & Redfem 1983, Delcan 1994). Periodically, between December and April, the coastline is subject to swell waves generated in the far north western Atlantic Ocean. These swell events normally have durations o f 1 - 4 weeks but have been known to exceed this, depending on the extent o f penetration o f the cold front experience in the Atlantic Ocean (Colin Depradinepers. comm.).

20 According to Speed (2001) the Barbados Ridge is an extensive sub-sea mountain range between Tobago and a point east of Martinique The Barbados island peak is the only peak on the ridge currently above sea level. The Barbados Ridge descends eastward to the deep Atlantic Abyssal plain. To the west the ridge descends less steeply as it is bordered by the Tobago Trough.

Fig. 2.5 Offshore Bathymetry of Barbados (Source: Admiralty Chart 2485 (1987)).

18500mE 47300mE

94200mN 94200mN

Speightstovvn

Ragged Point

Holetown

North Point

O istins Bav

South Point

Atlantic Ocean

Cobblers R eef - offshore barrier reef

Nearshore area - varies between 500m - 3km

Bridgetown

18500mE 47300mE

There is a critical link between the wave energy experienced on the coast and the actual impact on the shore. This is controlled by the extent o f wave refraction o f the seabed and diffraction experienced by headlands (USACE 1984, Carter 1989). The wave generation mechanism for the island has been recently studied in detail as part o f the Coastal Infrastructure Programme being executed by Government o f Barbados. Three types o f wave condition have been identified (Fig 2.6) (Baird and Associates 2003):

• Locally generated seas - waves created by the north easterly trade winds blowing in the vicinity o f Barbados;

• Long period swells - generated by extra tropical cyclones originating in the mid latitudes o f the North Atlantic. These swell waves have the potential to wrap around the island;

• Hurricane and tropical cyclone waves - generated from small scale sever storm events that may be generated in the northern equatorial belt and generally pass in an east to northwest direction in the vicinity o f the island. These wave events frequently have large wave conditions and significant surge associated with them.

Fig. 2.6 Types o f W ave Generation M echanism s in the Caribbean Sea (Source: Baird and Associates 2003).

Figure 2.7 show a point rose plot o f individual hourly wave heights as a function o f wave direction. A comparison o f Figure 2.7 with Figure 2.8 shows the largest number o f waves approach from the North East but the waves with the largest wave heights tend to occur form the North-Northwest (Baird and Associates 2003).

Fig. 2.7 Plot o f Hourly W ave Heights as a Function o f W ave Direction (Source:

Baird and Associates 2003).

Fig. 2.8 W ave H eight Rose O ffshore Barbados (Source: Baird and Associates 2003).

ICZM requires application o f both planning and model usage in a range o f conditions from average to storm events. The average wave climate conditions have been used in this research as the storm events are generally o f low frequency and low magnitude in terms of damage done to the coast Recovery normally is seen within 2 - 4 weeks. This does not negate the potential devastating effects tropical depression or hurricane waves can impact on the coast. When such storms events are affecting the coast, there is no active use o f the recreational nearshore, given the high waves and associated energy and their potential dangers.

2.63 Barbados* Coastal Development Assets 2.6.3.1 Tourism, Human Settlem ent and Housing

Tourism is Barbados’ largest revenue earner, employing approximately 25% of the current available labour force. The tourism infrastructure consists of approximately 6000 hotel rooms distributed across 150 hotels. More than 90% o f this infrastructure is located on the West and South coasts, from Six Men's Bay, St. Peter in the North, to South Point, Christ Church in the South21 (Barbados Tourism Authority 2001).

Currently in excess o f 40% o f the island’s 276,000 population, live within 2 km of the coast. The population is concentrated in a continuous linear urban corridor, extending from May cocks Bay, S t Lucy in the North, to Ragged Point, St. Philip in the Southeast.

This corridor includes the four principal urban settlement nodes (Fig. 2.9). The distribution o f residential housing follows an equivalent pattern to that o f the population (TCPO 1999). Most coastal properties are high-income and very expensive real estate, with only a few remaining locations where traditional “Chattel style” housing22 (houses built o f wood or wood and concrete) can be found.

21 Of the 150 hotels only 12 are not located on or in dose proximity to a beach or coastline resource.

22 Chattel houses are traditionally wooden and transportable. Previously, homeowners used to rent the land they lived on and frequently it was necessary to move/relocate once the land lease had expired or if the land rent had been increased and it was no longer affordable to the laid occupant. These house types were constructed to be easily and quickly dismantled and transported on the back of a flat bed truck to the new land location. There they would be reassembled. The process would normally take a day.

2.6.3.2 Industry

Most coastal industrial facilities are located in and around the Greater Bridgetown Area (Fig. 2.9).

Fig. 2.9 Map of Coastal Industry Locations (Source: Original)

18500mE Bridgetown, St. Michael and Oistins, Christ Church.

2.6.4 Barbados' Natural Hazard and Vulnerability Issues

The following section outlines the major natural hazards experienced in Barbados.

2.6.4.1 Hurricanes and Tropical Storm Hazards

The destructive nature o f these hazards is associated with their extensive high winds, which, depending on the shoreline configuration, can produce storm surges in excess o f 6 metres, destroying coastal structures and ultimately reconfiguring coastlines. The torrential rains, frequently associated with such systems, compound their damage, significantly contributing to coastal flooding in low-lying areas. Historically, hurricanes and tropical storms have been the greatest hazard, although the island’s location (Section 2.6.1) has “spared" it from a devastating direct hit for more than 45 years as many systems develop into hurricanes once they pass Barbados’ latitude. Barbados has, however, had a series o f “brushes” and indirect hits resulting in the island having an average return interval o f 3.07 years between hurricanes (Hurricane City 2003). The island’s hazard records show that between 1898 and 2002 a total o f 35 tropical storms, eight hurricanes, six tropical depression and two major floods were recorded23 (Fig.

2.10). Although the number o f hurricanes per year can vary, their annual threat is ever present.

Fig. 2.10 M ajor M eteorological Hazard Types Affecting Barbados

F lo o d 4%

T o p ic a l d e p r e s s i o n

1 2 %

T rOpiv,ai s t o r m

6 7 %

H u r r i c a n e k 17%

N = 51

23 See Appendix 2.

39

It is generally acknowledged that climate change can influence the overall intensity of hurricanes. Granger (1997) reported that since Hurricane David and Allen in 1979, the major hurricanes with a Category 4 or 5 classifications (e.g. Gilbert, Hugo, Andrew, Frederick, Luis, Marilyn and Opal) have consistently had highly significant sustained wind speeds, central pressures and storm surge heights. They have consistently resulted in coastal inundation, loss o f life and extensive damage to residential, commercial and industrial infrastructure, and general devastation to the agricultural sector.