executive summary global study flooding

GLOBAL STUDY TO PROPOSE SPECIFIC INTERVENTIONS TO

REDUCE THE BELIZEAN ROAD NETWORK VUNERABILITY TO

FLOODING EVENTS

- DRAFT FINAL REPORT -

JULY, 2010

INDEX

1 EXECUTIVE SUMMARY...............................................................20

2 INTRODUCTION.........................................................................26

2.1 BACKGROUND....................................................................................................26

2.2 SCOPE OF WORK...............................................................................................27

3 DESCRIPTION OF BELIZE RIVER WATERSHED...............................29

3.1 DRAINAGE SYSTEM...........................................................................................29

3.2 TERRAIN AND LAND USE..................................................................................29

3.3 GEOLOGY............................................................................................................31

3.4 HYDROGEOLOGY...............................................................................................33

3.5 WATER RESOURCES.........................................................................................35

3.6 WATER QUALITY................................................................................................39

3.7 METEOROLOGY..................................................................................................40

3.8 ECOLOGY / BIODIVERSITY................................................................................42

3.9 SOCIO-ECONOMIC ENVIRONMENT..................................................................44

4 DESCRIPTION OF THE WESTERN HIGHWAY..................................48

4.1 LOCATION AND FUNCTION...............................................................................48

4.2 TOPOGRAPHY IN LOWER PART OF WESTERN HIGHWAY............................50

4.3 DRAINAGE...........................................................................................................51

5 DATA COLLECTED......................................................................59

5.1 MAPS....................................................................................................................59

5.2 REPORTS, PROJECTS AND PREVIOUS STUDIES..........................................62

5.3 CLIMATE DATABASE. RAINFALL, FLOW AND WATER LEVELS.....................63

6 BATHYMETRIC SURVEY OF BELIZE RIVER....................................66

6.1 INTRODUCTION..................................................................................................66

6.2 SURVEY PREPARATION....................................................................................67

6.3 GEODESY AND DATUM......................................................................................68

6.3.1 Geodesy........................................................................................................68

6.3.2 Datum............................................................................................................70

6.4 DATA ACQUISITION............................................................................................71

6.4.1 Singlebeam Echosounder.............................................................................71

6.4.2 Global Positioning System with differential corrections (dGPS)....................73

6.4.3 Data logging..................................................................................................75

6.5 POSTPROCESSING OF DATA AND MAPPING.................................................76

7 GIS CONFIGURATION.................................................................77

7.1 INTRODUCTION..................................................................................................77

7.2 STRUCTURE OF GIS..........................................................................................77

7.3 DIGITAL ELEVATION MODEL (DEM).................................................................78

7.4 CITIES AND INFRASTRUCTURES.....................................................................85

8 HYDROLOGY STUDY...................................................................88

8.1 INTRODUCTION..................................................................................................88

8.1.1 Objectives and Scope....................................................................................88

8.1.2 Review of Previous Hydrologic Studies.........................................................88

8.2 AVAILABLE DATA................................................................................................90

8.2.1 Drainage system............................................................................................90

8.2.2 Flow data.......................................................................................................90

8.2.3 Climate..........................................................................................................91

8.2.4 Precipitation...................................................................................................91

8.2.5 Temperature..................................................................................................93

8.2.6 Hydrometric stations......................................................................................95

8.2.7 Meteorological stations..................................................................................97

8.3 PROBABLE MAXIMUM FLOOD.........................................................................100

8.3.1 Most Intense Hurricanes in Belize and the Belize River Watershed Area...100

8.3.2 Main data for Belize River Watershed.........................................................105

8.3.3 Runoff modelling to be used........................................................................108

8.3.4 Probable Maximum Precipitation and Probable Maximum Storm...............114

8.3.5 HMS Model Calibration for Flooding...........................................................150

8.3.6 Rainfall-Runoff Model used for the Calculation of Flooding........................150

8.3.7 Estimating the Temporal Distribution of the PMP........................................155

8.3.8 Unit Hydrograph..........................................................................................156

8.3.9 Base Flow....................................................................................................157

8.3.10 Creating the HMS Model.............................................................................158

8.3.11 Transformation of the Probable Maximum Storm to Probable Maximum Flood172

9 RIVER MODELING....................................................................178

9.1 TIN ELABORATION...........................................................................................178

9.1.1 What is a TIN?.............................................................................................178

9.1.2 Create a TIN from the available cartography..............................................180

9.2 DEFINITION OF RIVER GEOMORPHOLOGY..................................................184

9.2.1 Stream centerline........................................................................................184

9.2.2 Bank lines....................................................................................................186

9.2.3 Flowpath......................................................................................................188

9.2.4 Cross sections.............................................................................................189

9.2.5 Manning definition.......................................................................................194

9.3 STRUCTURES...................................................................................................198

9.3.1 Major structures (bridges inventory)............................................................198

9.3.2 Minor structures (culverts inventory)...........................................................200

9.4 BOUNDARY CONDITIONS................................................................................206

9.5 HYDRODYNAMIC ANALYSIS............................................................................209

10 FLOODING ANALYSIS...............................................................216

10.1 METHODOLOGY............................................................................................216

10.2 AFECTED AREAS..........................................................................................217

10.2.1 Settlements at Risk of Flooding in Belize....................................................218

10.2.2 Flooding analysis by hydrodynamic modeling.............................................221

10.2.3 Inventory of areas prone to flood.................................................................225

10.2.4 Flood plain between Sibun and Belize rivers..............................................231

11 RECOMMENDATIONS................................................................232

11.1 IMPROVING THE QUALITY OF AVAILABLE DATA......................................232

11.1.1 Elevation data..............................................................................................232

11.1.2 Hydrometric data.........................................................................................236

11.1.3 Meteorological data.....................................................................................238

11.1.4 Belize river cross sections...........................................................................241

11.1.5 Other tributaries...........................................................................................242

11.2 DRAINAGE IN WESTERN HIGHWAY............................................................243

11.2.1 Improvements to bridges.............................................................................244

11.2.2 Improvements in existing culverts...............................................................245

11.2.3 New culverts................................................................................................256

11.3 WATERSHED REGULATIONS IN MOPAN RIVER.......................................258

11.3.1 General considerations................................................................................258

11.3.2 “El Camalote” hydroelectric project.............................................................259

11.4 LAND PLANNING IN BELIZE CITY................................................................264

11.4.1 Context........................................................................................................264

11.4.2 Geography...................................................................................................264

11.4.3 Institutional Arrangement.............................................................................265

11.4.4 Current Status of Belize City Urban Planning.............................................268

11.4.5 Description of the Belize City Development Plan........................................269

11.4.6 Current Status of Implementation................................................................273

11.4.7 Recommendations for Urban Planning.......................................................276

11.4.8 Recommendations Regarding Physical Issues...........................................276

11.4.9 Recommendations Regarding Institutional Issues......................................278

11.5 RISK MAPPING AND DAMAGE ASSESSMENT...........................................279

11.6 RIVER WALLING............................................................................................283

11.7 URBAN DRAINAGE IN BELIZE CITY.............................................................286

11.7.1 Historic Development of Belize City............................................................288

11.7.2 Existing Situation.........................................................................................288

11.7.3 Topographic and Natural Environment........................................................292

11.7.4 Drainage. Existing problems........................................................................295

11.7.5 Drainage performance and principles.........................................................296

11.7.6 Recommendations.......................................................................................297

11.8 SIBUN RIVER WATERSHED.........................................................................303

11.9 CROOKED TREE...........................................................................................307

11.10 MARINE STUDY.............................................................................................310

11.11 DREGDING THE BELIZE RIVER...................................................................314

11.12 CLEARING AND SNAGGING THE RIVER....................................................315

11.13 EVACUATION ROUTES.................................................................................319

11.14 REGIONAL INTEGRATED MANAGEMENT OF BELIZE-MOPAN WATERSHED

320

11.15 COLABORATION BETEWEEN ADMINISTRATIONS....................................321

12 GENERAL ENVIRONMENTAL EFFECTS........................................322

12.1 GENERAL EFFECTS......................................................................................322

12.2 EFFECTS OF SNAGGING.............................................................................322

12.2.1 Invertebrates................................................................................................322

12.2.2 Fish..............................................................................................................323

12.3 EFFECTS OF CLEARING..............................................................................323

12.3.1 Water Quality...............................................................................................323

12.3.2 Terrestrial Habitat........................................................................................323

12.3.3 Aquatic Habitat............................................................................................324

12.4 EFFECTS OF CHANNEL EXCAVATION.......................................................324

12.4.1 Channel Instability.......................................................................................324

12.4.2 Hydrologic and Hydraulic Effects................................................................324

12.4.3 Aesthetics....................................................................................................324

12.4.4 Recreation...................................................................................................325

12.4.5 Water Quality...............................................................................................325


12.4.7 Aquatic Habitat............................................................................................325

12.5 EFFECTS OF SIDE SLOPE PROTECTION...................................................326

12.5.1 Aesthetics....................................................................................................326

12.5.2 Recreation...................................................................................................326

12.5.3 Water Quality...............................................................................................326


12.5.5 Aquatic Habitat............................................................................................327

12.6 EFFECTS OF SEDIMENT CONTROL STRUCTURES AND CULVERTS.....327

12.6.1 Aesthetics....................................................................................................327

12.6.2 Recreation...................................................................................................328

12.6.3 Aquatic Habitat............................................................................................328

12.7 EFFECTS OF LEVEES AND FLOODWALLS................................................328

12.7.1 Aesthetics....................................................................................................328

12.7.2 Recreation...................................................................................................328


13 CONCLUSIONS.........................................................................330

ANNEXES.....................................................................................334

ANNEX 1. MAPS...........................................................................................................334

ANNEX 2. TECHNICAL SPECIFICATIONS FOR GAUGIN STATIONS.......................335

ANNEX 3. TECHNICAL SPECIFICATIONS FOR AUTOMATIC WEATHER STATIONS338

ANNEX 4. HYDRODYNAMIC RESULTS IN CROSS SECTIONS................................355

ANNEX 5. SOFTWARE FOR HYDRODYNAMIC MODELING. HEC RAS...................356

LIST OF FIGURES

Figure 1. Western Highway.................................................................................................48

Figure 2. Roads of Belize....................................................................................................49

Figure 3. Elevation in lower areas of Western Highway.....................................................50

Figure 4. Hector Creek and Sibun river...............................................................................51

Figure 5. Main bridges in Western Highway.......................................................................52

Figure 6. Culverts in Western Highway...............................................................................53

Figure 7. Tight canopy and tree branches..........................................................................66

Figure 8. Rocky outcrops and bypass of the More Tomorrow Falls....................................67

Figure 9. Survey area..........................................................................................................68

Figure 10. Bruttour Ceestar and 200kHz narrow beam transducer....................................71

Figure 11. Wooden frame mounted over the side of the survey vessel for the transducer and

dGPS antenna.............................................................................................................72

Figure 12. Trimble AgGPS 332...........................................................................................73

Figure 13. Panasonic Toughbook CF19.............................................................................75

Figure 14. Thumbnail of one of the river bed profile charts................................................76

Figure 15. Cartography from NASA (contours each 100 m)...............................................79

Figure 16. First DEM (no data between 100 and 0 m)........................................................80

Figure 17. Elevation data for river bed (bathymetric survey)..............................................80

Figure 18. Detail of elevation data for river bed and cross section (bathymetric survey). . .81

Figure 19. Detail of elevation data for river banks from river surface information (with GPS)

....................................................................................................................................81

Figure 20. Detail of elevation data for roads (with GPS).....................................................82

Figure 21. Elevation data from NASA contours (every 100 m)...........................................82

Figure 22. New Digital Elevation Model..............................................................................83

Figure 23. Details of new Digital Elevation Model...............................................................84

Figure 24. Details of new Digital Elevation Model...............................................................84

Figure 25. Cities and villages..............................................................................................85

Figure 26. Roads.................................................................................................................86

Figure 27. Belize City..........................................................................................................86

Figure 28. Bridges...............................................................................................................87

Figure 29. Culverts..............................................................................................................87

Figure 30. Flow Records at Cristo Rey Macal River...........................................................89

Figure 31. Monthly Distribution of Average Precipitation in Belize.....................................92

Figure 32. Monthly Maximum and Minimum Temperatures for Belize................................94

Figure 33. Location of Hydrometric Stations along the Belize River...................................96

Figure 34. Location of Meteorological Stations in Belize....................................................99

Figure 35. Pattern and eyewall of the Keith Hurricane in October 1, 2000.......................102

Figure 36. Pattern and eyeball of Tropical Depressión No. 16.........................................105

Figure 37. Belice River sub basins....................................................................................107

Figure 38. Land use in Belice River subcatchments.........................................................110

Figure 39. Isohyetal maps of accumulated precipitation for 24, 48, 72 and 96 hour periods for

Hurricane Keith.........................................................................................................121

Figure 40. Isohyetal maps of accumulated precipitation for 24, 48, 72 and 96 hour periods for

Tropical Depression No. 16.......................................................................................122

Figure 41. Accumulated area corresponding to average values of accumulated precipitation.

..................................................................................................................................125

Figure 42. Depth-Area-Duration curve for the country of Belize for Hurricane Keith Event.129

Figure 43. Depth-Area-Duration curve for the country of Belize for Tropical Depression No. 16

Event.........................................................................................................................129

Figure 44. Relationship Between Dew Point Temperature and Precipitable Water for 13,000

MASL and Sea-Level Elevations...............................................................................133

Figure 45. Final Depth-Area-Duration Curves for the Country of Belize...........................138

Figure 46. Design Storm Isohyetal Maps obtained from BOSS HMR52 for the Belize River

Watershed.................................................................................................................139

Figure 47. Estimation of Recession curve for Hydrograph...............................................154

Figure 48. Mass Curve for Tropical Depression No. 16....................................................155

Figure 49. Maximum Flood Hydrograph for the Sub Basin of Crooked Tree Wildlife Reserve.

..................................................................................................................................173

Figure 50. Maximum Flood Hydrograph for the Sub Basin of Labouring Creek...............173

Figure 51. Maximum Flood Hydrograph for the Sub Basin of Beaver Dam Creek...........174

Figure 52. Maximum Flood Hydrograph for the Sub Basin of Roaring Creek...................174

Figure 53. Maximum Flood Hydrograph for the Sub Basin of Iguana Creek....................175

Figure 54. Maximum Flood Hydrograph for the Sub Basin of Barton Creek.....................175

Figure 55. Maximum Flood Hydrograph for the Sub Basin of the Macal River.................176

Figure 56. Maximum Flood Hydrograph for the Sub Basin of the Chiqibul River.............176

Figure 57. Maximum Flood Hydrograph for the Sub Basin of the Mopan River...............177

Figure 58. The Delaunay criterion to create a TIN............................................................178

Figure 59. Nodes and edges of a TIN...............................................................................179

Figure 60. Contours map of Belize....................................................................................181

Figure 61. DEM of Belize..................................................................................................182

Figure 62. New DEM of Belize..........................................................................................183

Figure 63. Drawing the Stream Centerline of Belize River in HEC GeoRAS....................184

Figure 64. Map of Belize, Mopan and Macal rivers...........................................................185

Figure 65. Drawing the Bank Lines of Belize River in HEC GeoRAS...............................186

Figure 66. Drawing the Bank Lines of Belize River in HEC GeoRAS...............................187

Figure 67. Flowpath of Belize River in HEC GeoRAS......................................................188

Figure 68. Cross section in Double Run...........................................................................190

Figure 69. Drawing cut lines..............................................................................................191

Figure 70. Extrapolated cross-section...............................................................................191

Figure 71. Cross-sections for Belize River........................................................................192

Figure 72. Details of defined cross-sections for Belize River............................................192



Figure 75. Images of Belize River.....................................................................................196

Figure 76. Example of Flow Hydrograph as Boundary Condition.....................................208

Figure 77. .First longitudinal profile of Belize River...........................................................209

Figure 78. First Longitudinal profile of Macal River...........................................................209

Figure 79. Longitudinal profile of Mopan River.................................................................210

Figure 80. Shape and cross sections of Belize river under GeoRAS...............................211

Figure 81. Details of shape and cross sections of Belize river under GeoRAS................211

Figure 82. Shape and cross sections of Belize with georeferenced maps.......................212

Figure 83. 3D perspective.................................................................................................213

Figure 84. Hydraulic analysis under HEC-RAS................................................................213

Figure 85. Details of hydraulic analysis.............................................................................214

Figure 86. Details of hydraulic analysis. Longitudinal Profile............................................214

Figure 87. Details of hydraulic analysis. Longitudinal Profile............................................214

Figure 88. Details of hydraulic analysis. Cross Sections..................................................215

Figure 89. Settlements in the Belize district at risk flooding..............................................219

Figure 90. Settlements in the Cayo district at risk flooding...............................................220

Figure 91. General view of flooding areas........................................................................221

Figure 92. Flooding areas from hydrodynamic modelling.................................................221



Figure 95. Flooding areas from hydrodynamic modelling near Belmopan........................223

Figure 96. Flooding areas from hydrodynamic modelling near San Ignacio-Santa Elena223

Figure 97. Flooding areas from hydrodynamic modeling..................................................224

Figure 98. Flooding areas from hydrodynamic modelling near Belize..............................224

Figure 99. Inventory of areas prone to flood from Hattieville to Belize City......................225

Figure 100. Inventory of areas prone to flood near Belize City.........................................225

Figure 101. Inventory of areas prone to flood near San Ignacio-Santa Elena..................229

Figure 102. Inventory of areas prone to flood in Belize City.............................................230

Figure 103. Inventory of areas prone to flood near Belmopan..........................................230

Figure 104. Flood plain between Sibun and Belize rivers.................................................231

Figure 105. Illustration of How the LIDAR Sensing Instrument Captures Elevation Points.233

Figure 106. Example of Interpreting LIDAR Elevation Maps............................................235

Figure 107. Location of Hydrometric Stations along the Belize River...............................237

Figure 108. Location of Meteorological Stations in Belize................................................240

Figure 109. Floodplain between Belize and Sibun rivers..................................................243

Figure 110. Main bridges in Western Highway.................................................................244

Figure 111. Culverts in Western Highway.........................................................................245

Figure 112. Proposed culverts near Belize City................................................................256

Figure 113. Proposed culverts near Belmopan.................................................................257

Figure 114. Proposed culverts near San Ignacio-Santa Elena.........................................257

Figure 115. Dams in Macal River (Belize).........................................................................258

Figure 116. Location of proposed dam.............................................................................262

Figure 117. Location of proposed dam.............................................................................263

Figure 118. Belize City and Environs................................................................................265

Figure 119. Portions of Belize City Developed in Low Areas............................................270

Figure 120. Wetland Areas that may Protect Belize City..................................................271

Figure 121. Conservation Areas in Comprehensive Development Plan...........................275

Figure 122. Wetland areas Abutting Belize City Peninsula...............................................277

Figure 123. Flood risk.......................................................................................................279

Figure 124. Villages in risk area near Belize City.............................................................280

Figure 125. Villages in risk area between Belmopan and Cayo.......................................280

Figure 126. Villages in high risk area near Belize City......................................................282

Figure 127. Villages in high risk area between Belmopan and Cayo................................282

Figure 128. Banks erosion in Belize river.........................................................................283

Figure 129. Banks erosion in Belize river.........................................................................284

Figure 130. Detail of proposed gabion walls.....................................................................285

Figure 131. Detail of embedded gabion river wall.............................................................285

Figure 132. Actual drainage paths....................................................................................289

Figure 133. Existing canals in Belize City.........................................................................290

Figure 134. Existing canals in Belize City.........................................................................291

Figure 135. Topographic relief of Belize City....................................................................292

Figure 136. Dead and dying mangroves south of Faber’s Road area: May 2005............293

Figure 137. Wetlands in and southern area of Belize City, current mangrove and open water.

..................................................................................................................................294

Figure 138. Western Section of Lake Independence after heavy rainfall in August 2005 295

Figure 139. Belama area, prone to flood..........................................................................298

Figure 140. Satellite map of floodplain between Belize and Sibun rivers.........................306

Figure 141. Connection with Belize River under flooding conditions................................308

Figure 142. Possible canal to mitigate impact of flooding.................................................309

Figure 143. Proposed location of wave recorders............................................................310

Figure 144. Accumulation of woody vegetation and debris..............................................316




Figure 148. River section to clear.....................................................................................318

Figure 149. Proposed evacuation route............................................................................319

Figure 150. Mopan-Belize watershed...............................................................................320

LIST OF TABLES

Table 1. Bridges characteristics..........................................................................................52

Table 2. Culverts characteristics.........................................................................................53

Table 3. Capacity of culverts...............................................................................................57

Table 4. Average Monthly Flow of the Belize River, record at Double Run Station. Period 1966-

2005............................................................................................................................90

Table 5. Average Monthly Precipitation in Belize................................................................92

Table 6. Average Annual temperatures at Central Farm (Cayo), Philip Goldson Int’l Airport and

Cooma Cairn...............................................................................................................94

Table 7. Location of Hydrometric Stations in Along the Belize River..................................95

Table 8. Meteorological Stations in Belize River Watershed and near locations................97

Table 9. Characteristics of the Belize River Sub Basins...................................................106

Table 10. Land use in Belice River subcatchments..........................................................109

Table 11. Table of Runoff Curve Numbers (SCS, 1986)..................................................111

Table 12. SCS Curve Numbers for Hidrological Soil Group C for Sub Basins of Belize River.

..................................................................................................................................112

Table 13. CN Ponderados para Subcuencas del Río Belice............................................113

Table 14. CN for Belize River Watershed.........................................................................114

Table 15. Precipitation measured by AgroClimat Stations during period of Hurricane Keith.115

Table 16. Precipitation measured by AgroClimat Stations during period of Tropical Depression

#16............................................................................................................................116

Table 17. Accumulated precipitation 24, 48, 72 and 96 hour periods for Hurricane Keith.117

Table 18. Accumulated precipitation 24, 48, 72 and 96 hour periods for Tropical Depression

#16............................................................................................................................119

Table 19. Areas corresponding to values of average precipitation for 24, 48, 72 and 96 hour

periods for Hurricane Keith.......................................................................................123

Table 20. Areas corresponding to values of average precipitation for 24, 48, 72 and 96 hour

periods for Tropical Depression No. 16.....................................................................124

Table 21. Accumulated areas corresponding to values of average precipitation for 24, 48, 72

and 96 hour periods for Hurricane Keith...................................................................126

Table 22. Accumulated areas corresponding to values of average precipitation for 24, 48, 72

and 96 hour periods for Tropical Depression No. 16................................................127

Table 23. Monthly Maximum 12-hour Persisting Dew Point Temperatures for Hurricane Keith

and Tropical Depression No. 16................................................................................131

Table 24. 50 Year Return Period Dew Point Temperatures for Hurricane Keith and Tropical

Depression No. 16....................................................................................................132

Table 25. Persisting 12-hour and Storm Dew Point Temperatures for Hurricane Keith and

Tropical Depression No. 16.......................................................................................132

Table 26. Maximum Precipitable Water for Storm’s Reference Location.........................134

Table 27. Estimated Precipitable Water for Observed Storm...........................................135

Table 28. Moisture Maximization Factor, r, for Hurricane Keith and Tropical Depression No. 16.

..................................................................................................................................135

Table 29. Maximized Average Precipitation Values and Corresponding Isohyetal Areas for

Hurricane Keith and Tropical Depression No. 16......................................................136

Table 30. Envelope for the Relationship Between Area and Precipitation for Maximized

Precipitation..............................................................................................................137

Table 31. Final Depth-Area-Duration Precipitation Values for the country of Belize........138

Table 32. Rainfall Depth for Design Storm Isohyets Developed for the Belize River Watershed.

..................................................................................................................................140

Table 33. Design Storm Characteristics............................................................................141

Table 34. Design Storm Temporal Distribution for Crooked Tree Wildlife Reserve River Sub

Basin (1)....................................................................................................................141

Table 35. Design Storm Temporal Distribution for Labouring Creek Sub Basin (2).........142

Table 36. Design Storm Temporal Distribution for Beaver Dam Creek Sub Basin (3).....143

Table 37. Design Storm Temporal Distribution for Roaring Creek Sub Basin (4).............144

Table 38. Design Storm Temporal Distribution for Iguana Creek Sub Basin (5)..............145

Table 39. Design Storm Temporal Distribution for Barton Creek Sub Basin (6)...............146

Table 40. Design Storm Temporal Distribution for Macal River Sub Basin (7).................146

Table 41. Design Storm Temporal Distribution for Chiquibul River Sub Basin (8)............148

Table 42. Design Storm Temporal Distribution for Mopan River Sub Basin (9)................149

Table 43. Summary of Maximum Precipitation (mm) for Design Storm Temporal Distribution for

All Sub Basins...........................................................................................................150

Table 44. Historical Observations of Hurricane Keith and Tropical Depression No. 16 Maximum

Precipitation for the country of Belize........................................................................150

Table 45. Time of Concentration and Storage Coefficient for Belize River Watershed....156

Table 46. Base Flow values for each Sub Basin of the Belize River................................157

Table 47. Probable Maximum Flood Values for the Sub Basins for Belize River.............172

Table 48. Manning numbers.............................................................................................194

Table 49. Bridges inventory..............................................................................................198

Table 50. Culverts along the Western Highway: San Ignacio-Belize City.........................200

Table 51. Entering Initial conditions..................................................................................207

Table 52. Entering Boundary conditions...........................................................................207

Table 53. Entering Flow Hydrograph as Boundary Condition...........................................208

Table 54. Inventory of areas prone to flood......................................................................226

Table 55. Location of Hydrometric Stations in Along the Belize River..............................236

Table 56. Meteorological Stations in Belize River Watershed and near locations............238

Table 57. Bridges characteristics......................................................................................244

Table 58. Recommendations for existing culverts............................................................245

Table 59. Villages in high risk areas.................................................................................281

1 EXECUTIVE SUMMARY

Over the years, severe weather has resulted in great human hardship and economic loss to the

countryof Belize. These have ranged from the un-named hurricane of 1931 which killed over

1,000 people, to Hurricane Hattie which struck in 1961 and resulted in the moving of the capital

from Belize City to Belmopan, to Hurricane Iris which struck in 2001 and devastated Monkey

River and Placencia villages. On October 16, 2008, Tropical Depression 16 produced such

heavy rains over Belize, Guatemala and Honduras that the Mopan, Macal and upper Belize

Rivers overflowed their banks at various locations, impacting many communities in the Belize

and Cayo Districts. The flooding events caused significant damage to road infrastructure,

housing, and the agriculture and tourism sectors. Several communities remained under water

for extended periods.

In the wake of Tropical Depression 16, the Government of Belize, through its Ministry of Works,

commissioned a study aimed at analyzing the hydrological regime of the entire basin of the

Belize River, with a view to determining the vulnerability to various storm scenarios of the

adjacent communities and properties.

The specific objectives of the study were as follows:

I) to obtain a comprehensive understanding of why the affected areas were so

vulnerable;

II) identify effective measures that can be taken in the short term to mitigate this

vulnerability both in terms of physical interventions such as complementary

infrastructure, and in improved maintenance of drainage paths and waterways;

III) for the long term, to itemize a series of investments that can be put in place to

reduce the vulnerability due to flooding of villages along the banks of the Belize River

as well as to safeguard the integrity of the road network.

In order to achieve the objectives of the study, a scope of works was carefully detailed by the

Ministry of Works. This scope of works included a review of all available documentation on the

storm event as well as an assessment of water sources and potential storage areas from the

upper reaches of the Belize River to the sea; a review of previous reports, specifically the

Richards and Dumbleton Drainage Reports on “Surface Water Drainage for Belize City” and

“Miles 0 to 15, Western Highway” to examine the extent to which recommendations made in the

reports were adopted and their effectiveness, and make further/new recommendations to be

adopted; a critical look at land use practices in the affected areas to prescribe measures to be

adopted to reduce the risk of flooding in these areas; and the identification, prioritization and

recommendation of appropriate physical interventions, such as hydraulic structures, that can be

put in place for improved flood management in vulnerable areas and effective protection for the

integrity of the road network.

In carrying out the scope of works described above, some limitations had to be taken into

account. The key limitation was a lack of high quality information about the storm events

analyzed (including Tropical Depression #16 of 2008), particularly detailed rainfall data, which

then required a number of estimations and extrapolations based on the Consultant’s experience

as well as the local knowledge of the Ministry of Works. Additionally, there was an absence of

high resolution mapping at a level of detail allowing precise identification of all risk areas and

development of a more technical approach such as that required for the hydrological modeling

The key findings of the study can be summarized as follows:

1. The road runs through lowlying areas at an elevation of some few feet above sea level,

between the Sibun and Belize rivers. Both these rivers meander considerably in their

final reaches down to the sea and the surrounding drainage pattern is confused and not

well defined. Variations in rainfall patterns in the upper catchments of the rivers, together

with the different regimes, cause separate patterns of flooding in the two river basins.

2. Due to the very flat relief of the region, flood flows can thus move in a variety of ways

dependent upon prevailing hydraulic conditions and the highway can be inundated from

either or both sides

3. Nevertheless, the model does not allow rigorous analysis of flooding conditions beyond

the river banks modelled due to lack of information about ground elevation data. This

lack of rigor in the calculation has been offset by historical records and knowledge of the

behaviour of the basin.

4. The meandering nature of the river makes the elaboration of a one-dimensional study

such as this difficult

5. The hydrodynamic analysis of Belize River indicates a significant difference in flow

velocity in the same section. This is the source of erosion and sedimentation problems

that increases the risk of flooding

6. Some bridges have dimensional configuration that do not allow the proper flow of the

river in case of flood.

7. Extensive flooding areas have been identified on the Western Highway, where the

inventory of culverts indicates a deficit in the drainage capacity.

8. The accumulation of organic debris and refuse enhances the flooding in the rivers. This

is related to the lack of an adequate and coordinated maintenance (and clearing)

programme.

9. There are massive bank erosions in certain sections of the river. This erosion causes

uncontrolled material falling into the river causing loss of effective area of the river

channel and a subsequent rise in the river bed and overspilling into populated areas

10. Many populated centers are built in areas with high risk of flooding

11. In general, much of the lower Western Highway lies in a flood zone, between the Belize

and Sibun rivers. Flooding in this area cannot be avoided and therefore mitigation

measures are necessary in case of extreme events.

12. Urban planning studies have been done for Belize City, which identify a significant

increase in population growth in flood prone areas

13. Belize City is located in a flood plain. However, its urban drainage system has serious

deficiencies that ought to be improved

Based on the findings of this study, several key recommendations are made for reducing the

vulnerability of the road network to flooding events. These recommendations must first and

foremost be taken in the context of the afore-mentioned limitations of the study. The key

recommendations from the study can be summarized as follows:

1. Investment in improvements to bridges and culverts along the Western Highway in order

to improve flow of water from one side of the highway to the other. Recommendations

were made to replace the Hawksworth Bridge and increase the heights of bridges at Red

Creek and Unitedville; to clean-out or excavate some 29 culverts; to increase the

capacity of some 16 culverts; and to construct 42 new culverts.

2. New reservoir capacity could increase the ability to regulate flows in the Mopan River,

similar to the current situation on the Macal River due to the presence of the Chalillo

Dam, the Vaca Dam, and the hydroelectric facility at Mollejon. This approach has the

side benefit of providing electric power resources, but one big draw-back is that this

would have to be done in Guatemala. It is therefore recommended that close

coordination and cooperation be sought between the Guatemalan and Belizean

Authorities. It is recommended that the Belizean and Guatemalan authorities together

seek to complete the construction of the El Camalote Hydroelectric Project in Guatemala

near Melchor de Mencos, which would assist greatly in regulating flows in the Mopan

River. More generally speaking, it is recommended that a bi-lateral agreement be signed

between the Belizean and Guatemalan governments, creating a Watershed

Management Unit to address issues in the Mopan - Belize Watershed. (Kindly note here

that the proposed construction of a Hydroelectric Plant at the Camalote site on the

Mopan River would indeed help attenuate the floods in the Mopan and the Belize Rivers,

however, consideration should be given to the environmental impacts such an

infrastructure would have downstream of the proposed dam.

3. Adopt an urban planning strategy for Belize City which would stress conservation of

wetland areas west of the Belize City Peninsula between the Northern and Western

Highways, as well as halting development in some of the low areas of the City, such as

the Belama Area, the Port Loyola Area, and the Coral Grove Area. Additionally, it is

recommended that development not be conducted, or be seriously constrained, in the

Crooked Tree Lagoon and surrounding wetland areas. In order to create and implement

this strategy, it is recommended that a Belize City Urban Development Master Plan be

commissioned by the Belize City Council and the Housing and Planning Authority of the

Ministry of Housing and Urban Development. Elements of this plan are elaborated upon

in the body of this Report.

4. Address the problem of river bank erosion by construction of gabion walls along the

most vulnerable stretches of the Belize River, as detailed in the body of this Report.

5. It is recommended that a complete drainage masterplan be developed for Belize City

and Belmopan. Additionally, recommendations are made for improving drainage in the

Belama, Lake Independence, Port Loyola, and Collet areas.

6. It is very important that further studies be done. In particular, the following follow-up work

is recommended:

a. Aerial Survey of Belize River Watershed to obtain accurate topographic data in

order to allow deeper and more rigorous hydrodynamic analysis of the river and

more accurate flood vulnerability assessment.

b. Comprehensive study of the Sibun River, including hydrologic and hydrodynamic

studies and inventories of existing infrastructure (bridges, culverts, etc.).

c. Conduct a comprehensive Hydrologic study of the Crooked Tree Catchment

Area.

d. Analysis of the influence of the marine regime on the behaviour of the Belize

River hydrodynamics.

e. Conduct a complete Geophysical survey of the Belize River riverbed in order to

develop a comprehensive dredging proposal, starting with sections of the river

with severe sedimentation identified in the field investigations..

f. Acquire as soon as possible high resolution contour maps for the entire study

area, including the Belize and Sibun Rivers and the Crooked Tree Lagoon

System to be used in many applications including improved hydrological and

hydrodynamic modelling of the watersheds of Belize.

Strenghten the MOWs database Unit in an effort to consolidate all Civil Engineering,

Hydrological and other relevant data and information for easy access and future

application.

7. It is recommended that a Unit be created with responsibility for annual clearance and

snagging of the Belize River.8. Kindly note that the following were not provided;9. Designs for new proposed flood risk reduction works.

10. Maintenance plan(s) for existing flood control and protection infrastructure.

11.

12. Considering the Consultancy services to be provided i.e. to prepare and provide engineering designs

for prioritized flood protection works and using the draft FRRP 2013 as the basis for the proposal the following is submitted:

13.

14. A cursory review of the Draft Flood Risk Reduction Action Plan and Implementation Strategy for the RNA Belize District was made in

an effort to determine the scope of the works for the consultancy required.

15.

16. The flood mitigation works identified in chapters 7 and 8 of the Flood Risk Reduction Plan 2013 have been interpreted as follows;17. Chapter 7 Old Northern Road, Component 118. Infrastructure works on the Old Northern Road proper (no indication given of the extent of the works) and 5 additional farm roads (road lengths provided).19.20. Chapter 8 Belize River Valley, Component 121. Infrastructure works in the Belize River Valley Area to address consist of 3 farm roads (road lengths not provided) and a low river crossing.22.23. The FRRP 2013 provide an indication of the services to be provided for the Component 1 of each of the above. The services to be provided would be in the range

of 750,000 dollars.

24. The accuracy of the figure depends on the definition of the extent of the works. 25.

26. Submitted for your consideration.

executive summary global study flooding

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