Environment and development in coastal regions and in small islands

Hurricane impact on beaches in the eastern Caribbean Islands 1989 - 1995

6.  EFFECTS OF HURRICANE HUGO ON THE BEACHES OF DOMINICA, NEVIS AND THE BRITISH VIRGIN ISLANDS

In 1989 two major hurricanes passed close to the eastern Caribbean Islands.  Between 3-5th September, 1989, Hurricane Gabrielle passed 640 km (400 miles) east of Dominica.  This was a large, well developed, category 3, hurricane which generated swells which affected the windward coasts of most of the northeastern Caribbean Islands.  Hurricane Gabrielle did not make landfall in the Caribbean. 

Less than two weeks later, between 16-18th September, 1989, Hurricane Hugo, a huge category 4 hurricane, with sustained winds of 140 mph (224km/hr) passed through the Leeward Islands.  The centre of this hurricane passed over northern Guadeloupe, Montserrat, St. Croix and the northeastern part of Puerto Rico, see Figure 5, before continuing north to hit Charlestown in South Carolina, USA.  Fourteen lives were lost and direct losses to the island states of Dominica, Montserrat, Antigua-Barbuda, the British Virgin Islands and St. Kitts Nevis were estimated at US$ 365 million, (UNDRO, 1989).

Figure 5. Track of Hurricane Hugo in 1989

Previous to Hurricane Hugo, beach monitoring programmes had been established in Dominica, Nevis and the British Virgin Islands.  The monitoring was continued after the hurricane, thus it is possible to quantitatively evaluate the impacts of these two hurricanes on the beaches of these three countries.

The centre of Hurricane Hugo passed 80 km (50 miles) north of Dominica, 20 km (13 miles) west of Nevis and 70 km (44 miles) south of Tortola in the British Virgin Islands.

6.1  Dominica 

Dominica is a mountainous volcanic island with very rugged, steep terrain and a narrow coastal plain where most of the population live.  The coastal shelf is narrow, less than 1 km wide, particularly on the west coast.  The beaches are generally narrow and consist of stones and black volcanic sand.  They exist mainly in embayments, separated by lengths of steep cliffs.  The south and west coasts consist of straight sections or gentle embayments, while the north and east coasts are more indented.  Coral reefs are limited mainly to the southwest and north coasts.  On the north coast, between Hampstead and Woodford Hill, the beaches consist of a mixture of coral sand and volcanic sand.

The centre of Hurricane David, a category 4 hurricane, passed over Dominica  in 1979, causing catastrophic damage to the country’s infrastructure and the environment.  No quantitative data relating to the beaches exist before or after this hurricane.  However, information does exist in a descriptive form.  For instance, the 300 m long isthmus joining Scotts Head Point to the mainland used to be at least 30 m wide with many trees and space for a cricket pitch.  During Hurricane David the isthmus was breached, and although it re-formed after the hurricane, it was much lower and narrower, only about 15 m wide.  The sand beach on the Caribbean side was replaced by stones and Dominicans had lost a popular picnic spot.

When the beach monitoring programme was established in Dominica in 1987, twenty three sites were established round the coast and an attempt was made to monitor every major beach in Dominica.  Appendix I shows the location of the monitoring sites in Dominica.

Hurricane Gabrielle caused severe erosion along the north and east coasts, but there was little damage on the west coast (Cambers and James, 1994).  The reverse was the case for Hurricane Hugo.  The southwestern quadrant of Hurricane Hugo was the most intense, while this sector was influencing Dominica the winds were from the north and the west, hence the damage was most severe along the west coast of Dominica.

Beach measurements taken in August 1989, one month before the hurricanes, were compared with beach measurements taken at the end of September 1989, approximately two weeks after Hurricane Hugo.  Firstly the area of the profile was compared before and after the hurricane, this was calculated as a percentage change.  Then the change in profile width was calculated as an absolute value in metres.  In some cases the hurricane waves eroded the edge of the land or sand dune, this was determined from the profile plots and is recorded in the fourth column in Appendix I.  The data are summarized in Table 2.

The most severe erosion was on the west coast.  On average all the beaches narrowed by 4.4 m (14 ft).  The land edge retreated inland 1.7 m (6 ft).  This later parameter is regarded as a permanent loss, since although the beaches recover after a hurricane, the actual position of the beach will be further inland, see also Section 3.1.

In order to try and assess the extent of beach recovery, the pre hurricane data for August 1989, have been compared with the data for August 1990, or the nearest month for which data are available.  The profile area for August 1990 has been calculated as a percentage of the value for August 1989.  Similarly the profile width for August 1990 has been calculated as a percentage of the value for August 1989.  Thus these values show the amount of recovery as a percentage of the pre-hurricane values.  The profile width has also been calculated in absolute terms.  The data are summarized in Table 3 and the individual data for each beach are contained in Appendix I.

Table 3 shows that one year later there had been some considerable recovery of the beaches.  The profile area and profile width values showed that the beaches had recovered to within 93% of their pre-hurricane levels.  However, a comparison of absolute values shows that on average the beaches were still 3 m (10 ft) narrower than before the hurricanes.

6.2  Nevis

Nevis is a small volcanic island with a central peak, Nevis Peak, and a gently sloping coastal plain, approximately 1 km wide.  The major beaches exist on the west and north coasts, the most famous of which is the 4 km long Pinney’s Beach on the west coast.  The coastline is fairly straight with few embayments.  The sand beaches consist of a mixture of coral sand (especially on the north coast) foraminifera sand and volcanic sand. 

In 1988 a beach monitoring programme was established in Nevis, seventeen sites were initially set up and, as in Dominica, the goal was to monitor all the major beaches.  Appendix II shows the location of the monitoring sites in Nevis.

There is no record of the effects of Hurricane Gabrielle in Nevis.  Presumably this impacted the east (windward) coast most severely, where there are few beaches.  However, there were severe impacts to the island’s infrastructure and environment following Hurricane Hugo, which passed 20 km (13 miles) to the southwest of Nevis.

Beach measurements taken in July 1989, two months before the hurricane were compared with measurements taken in October 1989, one month after the hurricane.  The data were compared using the same methodology as for Dominica, see Section 6.1.  The comparisons for each beach are shown in Appendix II and are summarized below in Table 4.

As in Dominica, the most severe erosion was on the west coast.  On average all the beaches narrowed by 5 m (17 ft).  The land or dune edge retreated inland 4 m (13 ft).  This is considered a permanent loss, for although the beaches recovered after the hurricane, the actual position of the beach was further inland, see also Section 3.1.

The extent of beach recovery was calculated in a similar manner to Dominica.  The data for July 1990 were compared with the pre-hurricane data for July 1989.  The individual data for each beach are recorded in Appendix II, while Table 5 below presents a summary.

The recovery was less extensive in Nevis than in Dominica.  One year later the beaches had only recovered to 76% of their pre-hurricane levels.  Indeed many of the beaches had continued to erode after the hurricane, particularly along Pinneys Beach.  Also some of the north coast beaches which showed little change or even accretion immediately after the hurricane, were showing erosion one year later.  One year after the hurricane, the beaches were on average 6.4 m (21 ft) narrower than before the hurricane.

6.3  British Virgin Islands

The British Virgin Islands (B.V.I.) are a group of about 40 islands, islets and cays located on a shallow bank which also includes the U.S. Virgin Islands.  The B.V.I. are a group of volcanic islands with steep terrain and a narrow coastal plain.  (The island of Anegada is the exception, this is a low coral cay north of the main island group).  In the main island, Tortola, there has been considerable reclamation along the coast.   The coastline is very indented and there are extensive reefs throughout the islands.

A beach monitoring programme was established in the B.V.I. in February - April 1989, just before the 1989 hurricanes.  Monitoring was concentrated on the major islands of Tortola, Virgin Gorda, Anegada, Beef Island, Peter Island and Jost Van Dyke.  In the three large islands of Tortola, Virgin Gorda and Anegada an effort was made to cover all the major beaches, in the other three islands certain beaches were selected.  A total of forty three sites  were monitored.  Appendix III shows the location of the monitoring sites in the B.V.I.

The B.V.I. were affected by Hurricanes Gabrielle and Hugo in 1989.  The effects of Hurricane Gabrielle were particularly noticeable on the north coast of Tortola, (Cambers et al., 1993).  Hurricane Hugo passed to the south of the B.V.I. so the island group luckily did not experience the strong southwest quadrant of the hurricane.

Beach measurements taken in July 1989, or as near to this as possible, were compared with those taken in late September and October 1989, a few weeks after the hurricanes.  The same methodology was used as for Dominica except no calculations have been made of the change in land/dune edge.  The data for each beach are contained in Appendix III and Table 6 contains a summary by island.

In the B.V.I. the effects of the hurricanes were more variable than in Dominica and Nevis, perhaps because of the number of different islands in the B.V.I. all with differing coastal topography and reef protection.  The most serious erosion was experienced on the north coasts of Tortola and Peter Island and the northwestern coast of Virgin Gorda.  When all the data for the B.V.I. are averaged, then the level of erosion was considerably lower than in Dominica and Nevis.  On average the beaches narrowed by 1 m (3 ft) in the B.V.I., this compares with 5 m in Nevis and 4 m in Dominica.

6.4  Comparative Assessment of the Effects of the 1989 Hurricanes

Figure 6 compares the average changes in beach profile width and the average retreat of the land/dune edge for Dominica, Nevis and the B.V.I. in 1989.  (No data were available for dune edge retreat in B.V.I.).  The graph shows that Nevis sustained the most serious damage to its beaches and its dunes, closely followed by Dominica.  The average data show that the damage to the beaches in the B.V.I. was low by comparison to the other two countries.

Figure 6. Comparative Impacts of Hurricane Hugo in 1989

Of the three countries, Nevis was the island closest to the hurricane centre (20 km), in addition Nevis was impacted by the strong southwestern quadrant of the storm.  Thus this accounts for the fact that the beaches in Nevis received the most severe damage.  The beaches in Dominica were also severely damaged especially on the west coast which would also have been impacted by the strong southwestern quadrant of the storm.  Conversely the storm passed 70 km (44 miles) south of the B.V.I., which therefore did not experience the full brunt of the southwestern section, this possibly explains why the damage was less and much more localized in the B.V.I.

Beach recovery was calculated only for Dominica and Nevis, see Figure 7.  One year after the hurricane, the beach recovery was greater in Dominica whose beaches had recovered to 93% of their pre-hurricane volume.  In Nevis, one year after the hurricane, beaches had only recovered to 76% of their pre-hurricane volume.  Actual profile width in Dominica was 3 m (10 ft) less than before the storm, while in Nevis actual profile width was 6.4 m (21 ft) narrower than before Hurricane Hugo. 

Figure 7. Beach Recovery from Hurricane Hugo in Dominica and Nevis

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