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Sea Level Monitoring

The Pointe La Rue tide gauge was installed on 11th January 1993 and located at 04° 40.3S and 055° 31.7E.   GLOSS No. 273, Toga I053, NODC II 30054502 and in fact it has replaced Port Victoria as the GLOSS station (Fig. 1, 2, 3 & 4 ).
Instrument type: float/well, Handar 436-A, Encoder 436-B.   The gauge was a contribution of the University of Hawaii Sea Level Center in Honolulu, and was installed by personnel from the University of Hawaii. It is now under the responsibility of the Meteorological Office of the Directorate of Civil Aviation. The Survey Division of the Ministry of Land Use and Habitat in 1992 established the benchmark for that particular station.
The University of Hawaii technicians were using the following benchmarks as the references (Table 1) for installation.

Table 1. Tidal Benchmarks Levelling Record at Pointe La Rue, Mahe

Tide gauge Station Reference Point Year of installation Responsible  height      (m) Description Pointe La Rue BMTOS 1993 UHSL and SMS 2.002 above the zero of the staff Top of a 2-meter fibreglass staff mounted on the west tide well.   BMSWW 1993   1.053 A stainless hex head bolt on top of the black/grey end cap mounted on the west tide well.   BMSWE 1993   1.061 A stainless hex head bolt on top of the black/grey end cap mounted on the east tide well.   BMUH1 1993   3.064 A stainless one-inch plate mounted in white epoxy in between the two tide wells on top of the concrete deck.   BMUH2 1993   2.979 A stainless one-inch plate mounted in white epoxy at the Southwest corner of the T.G. concrete slab and about 15 feet South of BMUH1.   BMUH3 1993   2.269 A stainless one inch plate mounted in white epoxy in the South corner of the top step of the boat launch access steps (20ft west of gauge)   BMGS     2.370 A stainless BM indented with a 1/4" hole and painted yellow, located at the Rawindsonde Station on the path to the instrument area used by German Researchers.   BM37     1.959 This is a standard Survey Division BM which is a pin on the main road at Glacis, Pt. La Rue.   TP1 1993   2.731 A section of 1/2" stainless rod mounted in white epoxy on the North breakwater wall at the start of the jetty access road.   TP2 1993     A section of 1/2" stainless rod mounted in white epoxy on the North breakwater wall and 50ft East of the start of the jetty access road.   TP3 1993     A section of 1/2" stainless rod mounted in white epoxy on the North breakwater wall and about 120 ft East of the start of the jetty access road on the curved lookout.   TP4 1993     A section of 1/2" stainless rod mounted in white epoxy on the North breakwater wall and about 40 ft before the start of the jetty. A section of 1/2" stainless rod mounted in white epoxy on the North breakwater wall and about 40 ft before the start of the jetty.   TP5 1993     A section of 1/2" stainless rod mounted in white epoxy on the South breakwater wall of the jetty access road at the outcrop, which is mid-way to the jetty.

Sensitivities to Sea Level Rise

Seychelles is particularly vulnerable to sea level in that it would affect almost all of the economic sectors on which the country depends on, tourism and fisheries. This sensitivity is further enhanced by the fact that the main granitic islands, which rise up to more than a thousand feet, have steep hill slopes prone to landslides, and a very narrow strip of coastal plain. Both the Port and Airport of the country were built upon reclaimed land and will be severely impacted by a rise in sea level. On the other hand most of the coral islands will eventually disappear from the surface of the earth. A rise in sea level in the Seychelles will most probably affect Seychelles in the following manner:

1.       Destruction to property and infrastructure located on the coastal plains and reclaimed land:

2.        Inundate potential agricultural areas and displace wetlands and the coastal plains;

3.       Cause several low-lying islands, especially the sand cays to disappear;

4.       Erode the shorelines and tourist beaches;

5.       Enhance coastal flooding especially during severe rainstorms and high tides;

6.       Increase salinity of mangrove swamps and raise groundwater level affecting plant growth;

7.       Threaten potability of groundwater aquifers and coral island lens;

8.       Alter tidal ranges in the rivers and bays;

9.       Alter sediment deposition patterns;

Reduce light penetration required by coral reefs to survive.

Frequently asked questions on sea level within the Seychelles

Are sea levels around Seychelles rising?

Yes.

At what rate?

The trend shows an increase of sea level of around 20 cm by 1998 and stabilized by 1999 to 2000 due to the effect of La Nina (see figure below). But the linear trend shows it is rising.

Are they rising faster than anywhere else in the world?

Don't Know.

Why are they rising faster here?

We do not know if they are rising faster here but what we know is that Global Greenhouse gas emissions, anthropogenic climate change is liable to adversely impact on sea level rise; both of these effects have direct impacts on critical coastal zone of Seychelles. Therefore it is a global issue that should be tackle by the international community as a whole.

How worried are you about the future sea level rises in Seychelles?

Very worried.

What are the predictions for how much higher the sea level will rise in Seychelles?

Tide predictions are performed by the University of Hawaii (http://www.soest.hawaii.edu/UHSLC).The predicted tides are obtained with the use of a harmonic analysis program, which is executed on a year of apparently good data for a given station (see figure below).

Data from the Pointe La Rue tide gauge are sent automatically by satellite to the University of Hawaii and the tide staff readings and floppy disk are sent through the post. Data obtainable are hourly, daily & monthly. The datasets can also be remotely access using the Internet. This allows datasets to be available on-line and does away with inconvenience and delay in writing letters and in sending tapes and floppy disks by airmail

Pointe Larue

Has Seychelles lobbied the international community on this issue?

For more than a decade, Seychelles through the Alliance of Small Islands State has been urging the international community to reduce Green House Gases (GHG) emissions. This is because many islands developing states are extremely vulnerable to potential impacts of climate change, short-term variability in weather patterns, and sea level rise. Our concern has been conveyed to the international community at every opportunity. We have been given strong support to a range of international agreement, such as, Agenda 21, Barbados Plan Of Actions, the UNFCCC and the Kyoto Protocol. Seychelles and other small island states are very disappointed that global emissions of GHG have continued to grow.

Has that campaigning had any effect?

Not quite. But we are still pressing.

Are any schemes being introduced in Seychelles to combat further rises in sea levels?

We have been taking steps to meet our obligations through a series of coordinated projects and activities related to sea level monitoringand Institutional Strengthening. Developed a greenhouse gas inventory, take climate change into account in such matters as activities involving marine and coastal areas, agriculture, energy and the natural environment of Seychelles