The University of the West Indies Organization of American States

PROFESSIONAL DEVELOPMENT PROGRAMME: COASTAL INFRASTRUCTURE DESIGN, CONSTRUCTION AND MAINTENANCE

A COURSE IN DESIGN OF MARINE STRUCTURES

CHAPTER 9 CASE STUDIES (1 & 2) By DAVID SMITH, PhD Smith Warner International Limited Consulting Engineers Kingston, Jamaica

Organized by Department of Civil Engineering, The University of the West Indies, in conjunction with Old Dominion University, Norfolk, VA, USA and Coastal Engineering Research Centre, US Army, Corps of Engineers, Vicksburg, MS, USA. Trinidad and Tobago, West Indies, September 24th – 28th, 2001

PresentedPresented byby DavidDavid A.Y.A.Y. Smith,Smith, Ph.D.,Ph.D., P.Eng.P.Eng. Managing Director, Smith Warner International Ltd.

September 28, 2001 Design brief for Port St. Charles (PSC) Marina included: Ø Excavation of a 10 acre land parcel adjacent to the sea; Ø Construction of a lagoon connected to the sea; Ø Construction of 145 condominium units on the perimeter of the lagoon; Ø Creation of an “Outer” marina for mega-yachts; Ø Creation of an enhanced beach area. Pre-construction

During construction l EIA carried out initially to facilitate planning approval; l Key regulatory agencies were TCPO and CZMU; l Issues addressed under EIA were: – Impact of project on adjacent shorelines; – Water circulation characteristics; – Impact of excavation on water table; – Impact on fisheries; – Social impacts l Wells were sunk and water tested at regular intervals; l Hydrodynamic computer modeling of lagoon was undertaken; zones of stagnation were identified and mitigative strategies were developed; l Wave analyses were carried out to define extreme conditions; l Detailed bathymetric surveys were conducted; l Drogue tracking was initiated; l A wave recorder was deployed; l A lee-side wave climate was synthesized. l Design of the inner wall treatment was developed; l Design of a water circulation system developed; l Preliminary evaluation of the optimum way to open the lagoon to the sea; l Preliminary design of nourished beach: – Specification of sand from excavation; – Extent of nourishment and need for structural protection; – Appropriate public access issues; l Preliminary design of artificial reefs; l Preliminary design of outer breakwater; l Sand bypassing specifications.

l Establishment of a comprehensive beach profile monitoring programme; l Water quality monitoring; l Far-field coastal process monitoring. 70.00

60.00 Six Mens HS01 HS02 HS03 50.00 HS04 HS05 HS06 HS07 40.00 AWS AM

Beach(m) Width AS Six Mens 30.00 HS01 HS02 HS03 HS04 20.00 HS05 HS06 HS07

10.00 AWS AM AS

0.00 10-Jan-00 29-Feb-00 19-Apr-00 8-Jun-00 28-Jul-00 16-Sep-00 5-Nov-00 25-Dec-00 l Algal blooms in lagoon; l Need to “fine-tune” dredging program to nourish adjacent beaches; l Post-construction modifications.

PresentedPresented byby DavidDavid A.Y.A.Y. Smith,Smith, Ph.D.,Ph.D., P.Eng.P.Eng. Managing Director, Smith Warner International Ltd.

September 28, 2001 l History of devastation in Belize from natural hazards; l Hurricanes; l Flooding; l Volcanic ash; l Landslides.

l Storm surge mapping carried out to identify areas most vulnerable to this phenomenon; l River flooding also mapped to indicate road linkages that could be affected; l Information from these investigations incorporated with multi-hazard mapping. l Unnamed hurricane in 1931 (Cat.3) resulted in estimated storm surge of up to 4 m in Belize City. Approximately 2000 people killed; l Hurricane Hattie (Cat.4) in 1961 was the defining event; l Storm surge estimates of 4.5-6.0 m in Belize City. Widespread damage occasioned; l Government capital moved to Belmopan; l Population relocated to Hattieville. Bata Building in Belize City – during Hurricane Hattie, eyewitnesses observed water levels as high as the dotted line shown here. Belize Wind Speed vs. Water Elevation

Data 7 Poly. (Data) HurricaneHattie1961 6 Linear (Data)

5 n 1931 hurricane 4

3 Water Elev atio

2

1

0 0 1020304050607080 Wind Speed l Storm surge computations carried out for other coastal towns: – Corozal – Dangriga – Punta Gorda l Category 5 storm surges predicted to be approximately 7 m; l Category 4 storm surge predicted to be approximately 5 m l Recent defining events were Hurricanes Mitch and Keith; l Visual observations made of flooding extents; l Extensive network of rainfall and storm gauges, however, storm gauges not referenced to national benchmark elevations; l Data collected in an analog format and requires conversion to digital; l From rainfall analysis, Keith was estimated to be a 1 in 50 year event. 1 View from the Hector Creek Bridge (1) immediately following Hurricane Keith, and (2) months later.

Note that this is the same sign

2 l Proper topographic and bathymetric data needed; l Bathymetric data obtained from charts (deep water seaward of the Cayes, shallow Inner Channel); l Surveys commissioned to give information on river cross-sections and longitudinal profiles; l Surveys provided data on shoreline and land profiles; l Ideal data would have been satellite derived DTM. l Hazard mapping carried out showing zones of shoreline that could be inundated by storm surge from Category 3, 4 and 5 hurricanes; l Flood plain mapping done to delineate zones of inundations from the 1 in 50 year flooding event; l Both events mapped on the same chart to give locus of “danger” area. l Best locations for shelters selected ; l Shelter sites have to be multi-purpose buildings; l Preferred access routes to and from shelters also proposed; l Access routes selected based on all-weather access capabilities; l Times for transit computed; l Shelter capacities for satellite villages examined; l Shelter capacities evaluated based on the evaluated needs of the community.