THESEN ISLANDS: INNOVATIVE ENVIRONMENTAL ADVANCEMENTS IN MARINA DEVELOPMENT

摘要

Thesen Islands development is an ambitious and technically complicated projectwhere the 96-hectare Thesen Island in Knysna, South Africa, is master planned into anestate of 19 islands surrounded by wide tidal waterways linked by bridges. Fifteen kilometersof pristine water front property need to be protected in the most environmentally friendly waypossible against the erosive forces of fluctuating tide levels and associated wave action toensure that the islands will be developed in harmony with the Knysna Estuary environment.After thorough site trials and investigations, hexagonal woven mesh products: Renomattresses, gabions and Terramesh? were found to be the only alternative in achieving theonerous standards and criteria as set out in the project specifications, i.e., environmentalcompliance, durability under aggressive marine environments, ease of installation andvegetation establishment, and cost effectiveness.The chosen solution is able to protect each idyllic island against scour arising frominter-tidal action and can also ensure the stability of the bank especially under rapid drawdown conditions. As a result, the tidal flow around the islands is completely natural withexcellent circulation, water quality and minimal silting. A state of the art modeling systemdeveloped by The Danish Hydraulic Institute was used to assist with the design and layout of the waterways. Hydraulic and hydrological modeling, which even accounts for climatechange, should ensure that the Islands are completely safe from flooding.A bioengineering approach is being used in the development of Thesen Islands.Indigenous salt marsh plants are being used in conjunction with the inert materials in theinter-tidal zone. Small fish and marine life find food and shelter in the plants and natural rockalong the edges of the waterways, which in turn, attract a diversity of birds and larger fishresulting in habitat improvement. The rock filled gabions provide surfaces for growth of algalmicrobialfilms, which may contribute to nitrogen and phosphorus uptake from the tidal flow,thus reducing phytoplankton growth potential in the canals.The Deputy Minister of Environmental Affairs and Tourism, Minister Ms. R. T.Mabudahfhasi has commended the developers “for the most responsible manner in whichthey conducted, supported and financed the environmental research, which probablyrepresents the most comprehensive, professional and detailed Environmental ImpactAssessment ever undertaken in South Africa.”