gpa_east_africa_case.. - GRID Africa GeoPortal - UNEP

Public ServicesExisting services include schools, a home for the elderly and a district clinic. Their impact isincluded in the domestic requirements calculations presented further on in the document.Recreational SectorBeau Vallon is a very important zone for recreation not only for the tourists but also for thelocal community. Recreational activities include swimming, snorkelling, diving and watersports. The recreational sector provides additional employment and maintains a state ofholiday ambience in the area.Hydrology. Overlooking the Beau Vallon/Bel Ombre area are heights of up to 880 m inaltitude at the Morne Seychellois mountain group. There are two main rivers emptying into thebay, the Sullivan river and the Mare Anglaise river. These form the main estuaries in the area.There are also five smaller rivers in the study area. There is no in-depth seepage and virtuallyno groundwater reservoirs. In spite of the retarding effect of the very dense vegetation, therunoff water concentration times are very short (from 15 to 60 minutes). As a consequence,rainfall immediately causes flooding in certain areas. The land area of the catchment isbetween 1000 and 1100 hectares.Oceanography. The oceanographic data shows clear alternate phenomena depending onthe prevailing wind direction: during the trade wind period the currents veer counter clockwisein the bay, while it reverses in a clockwise direction during the Northwest monsoon. Thecurrent speed is in any case extremely week, making the bay a confined area. As the bay issheltered from strong Southeast swells, there is a net surplus input of fresh water from theland (SETOI, 1990).Geology and Soils. Low-lying areas of Beau Vallon are the coastal plain area and low-lyingareas around the main river mouths. The sediments of the former are dominantly calcareouswhilst the latter are characterised by sediments consisting of fine clays and quartz derivedfrom laterites. The coastal shorelands of Beau Vallon consist entirely of calcareous sands.The soil types in the mountainous areas behind the coastal plain comprise laterite andkaolinitc clays forming red earth giving a base of dense vegetation.Beach Characteristics. The sandy beach of Beau Vallon is approximately 1.8 kilometreslong with an average width of 30 metres at low tide. Sand dunes exist only in a few smallareas protected by beach debris and by Takamaka trees. The sand is yellowish-white incolour and fine to medium. The Beau Vallon Beach is the most built-up beach in Seychellesand sea walls and buildings on the high water mark are evident. The beach is very active andseasonal movement of sand takes place. However, there is definite evidence of beacherosion characteristic of such highly disturbed sandy coasts (Shah, 1998).Ecology. The ecological characteristics of the Beau Vallon coastal zone are numerous bothspatially and in biodiversity, which include brackish water marshes, coastal vegetation, coralreefs and other marine fauna and flora (Payet, 1995). There are eight areas that can beconsidered as special ecosystems:Table 3: Special EcosystemsArea In m 2 DescriptionNorthern Fringing Reef 700,000 Coral ReefSouthern Fringing Reef 260,000 Coral ReefNorthern Fringing Reef Flat 250,000 Inter-tidal and Littoral EcosystemSouthern Fringing Reef Flat 62,500 Inter-tidal and Littoral EcosystemMare Anglaise River Estuary 5,500 Ecosystems of Estuaries and Enclosed SeasSullivan River Estuary 3,900 Ecosystems of Estuaries and Enclosed SeasMare Anglaise River Wetlands 46,800 River and Stream EcosystemsSullivan River Wetlands 15,600 River and Stream EcosystemsSource: Grandcourt, 1995Final Draft Report – Cost Benefit Case StudiesGPA Strategic Action Plan on Sewage, October, 200043