Project context and challenge
In October 2015, Hurricane Joaquin tore across Long Island. It was the strongest October hurricane on record in The Bahamas since 1866. The island suffered over USD 35 million in damage, about a third of the national total. Storm surge breached the coastal barrier, flooded low-lying settlements and cut the Queen’s Highway, the island’s only main road. Long afterwards, floodwater stayed trapped around Deadman’s Cay airport and White Pond, cutting residents off from clinics and essential services.
As part of the Integrated Coastal Zone Management (ICZM) Bahamas Program, funded by the Inter-American Development Bank, the Ministry of Works & Utilities asked for two things: an environmental and socio-economic baseline for four flood-prone sites along 11 km of shoreline in Central Long Island, and a strategy and design to reduce flood risk in these communities.
The challenge: flooding driven by both storm surge and extreme rainfall, homes and infrastructure spread thinly along a low-lying coast, sensitive mangrove and coral habitats, and rising sea levels.
CDR’s approach and contribution
CDR led a consortium combining international modelling expertise with local knowledge, together with IHE Delft, Bahamian environmental firm Islands by Design, REBEL and Shore Monitoring.
Field, drone, marine and bird surveys mapped the island’s ecosystems, while interviews and community mapping showed which services and places matter most to residents. Satellite-derived bathymetry and local survey data were merged into a corrected elevation model of the island and its shallow surroundings.
CDR then generated thousands of synthetic hurricanes, based on historical storms such as Joaquin, for today, 2050 and 2100, including up to 78 cm of sea level rise. Two linked SFINCS models simulated regional surge and the combined effect of surge, tide and rainfall. They revealed that the most damaging surge builds up on the shallow banks to the northwest and breaks through the coastal barrier from the inside out. The resulting hazard maps fed a risk assessment covering damage, ecosystem impacts and loss of access.
Three strategies were tested through cost-benefit analysis and a multi-criteria workshop with stakeholders on Long Island. A large-scale dune barrier was ruled out in favour of a tailored mix of local protection and adaptation. CDR prepared preliminary designs and bills of quantities for the first phase works, concept designs for levees and an action plan for policy measures, supported by a knowledge transfer programme.
Result
The Ministry now has a phased Flood Risk Reduction Strategy, ready for implementation. It starts with improved drainage around Lower Deadman’s Cay and White Pond, followed by levees protecting the Deadman’s Cay and Petty’s and Hamilton’s settlements, and is supported by flood zoning, updated building codes and early warning.
The physical measures reduce expected annual flood damage by around 20% today and 25% by 2100. Floodwater drains much faster, so residents can reach clinics and critical infrastructure within five days of a hurricane.
