Source document: https://docs-lawep.s3.us-east-2.amazonaws.com/1697800361580.pdf (Dominica)
GOVERNMENT OF THE COMMONWEALTH OF DOMINICA MINISTRY OF PUBLIC WORKS, ENERGY AND PORTS Disaster Vulnerability Reduction Project Proposed Rehabilitation Of Roads And Drainage Structures In The Eastern Part Of Dominica Ministry of Public Works, Energy and Ports Technical Services Division Government Headquarters, Roseau Commonwealth of Dominica Tel: (767) 266-3026/3231 Fax: (767) 440-4799 Website: www.dominica.gov.dm 27 May 2013 Ministry of Public Works, Energy and Ports Disaster Vulnerability Project – Pilot Program for Climate Resilience 27 May 2013 1.
Introduction/Background The island of Dominica, like many of its Caribbean sister islands, is particularly vulnerable to the effects of natural hazards such as hurricanes, earthquakes, floods and landslides.

Over the past several years, such disasters have not only impacted the physical environment but have had particularly major negative impacts on the county’s economy.
The Government of Dominica is collaborating with the World Bank to develop a disaster vulnerability reduction project (DVRP) with the aim of reducing the vulnerability to natural hazards and the adverse impacts of climate change in Dominica.

In particular, sections of the main road in the eastern parts of the island has shown to be particularly vulnerable under conditions of heavy rainfall.
Figure 1 – Map of Dominica and showing vulnerable area under consideration for project Page 2 of 26 Ministry of Public Works, Energy and Ports Disaster Vulnerability Project – Pilot Program for Climate Resilience 27 May 2013 The sections of road (43.3km) as highlighted in Figure 1 above comprise four (4) major road links as follows: Link Number Description 31104 Pond Casse - Bois Diable 31201 Bois Diable - Castle Bruce 31202 Castle Bruce - Petite Soufriere 31301 Castle Bruce - Hatton Garden (through the Carib Territory) Figure 2 – Roads for consideration under DVRP Length of Link (km) 4.5 9.5 8.8 20.5 The indicated sections of road have shown to be particularly susceptible to flooding and landslides.
Page 3 of 26 Ministry of Public Works, Energy and Ports Disaster Vulnerability Project – Pilot Program for Climate Resilience 27 May 2013 Figure 3 – Map showing further detail of project Page 4 of 26 Castle Bruce Proposed road network to be considered under Disaster Vulnerability Reduction Project and Pilot Program for Climate Resilience Link 31301 = 20.5km Link 31202 = 8.5km Link 31201 = 9.5km Link 31104 = 4.5km Ministry of Public Works, Energy and Ports Disaster Vulnerability Project – Pilot Program for Climate Resilience 27 May 2013 2.
General Objective of the Project The main objective of the project is the rehabilitation of infrastructure taking into account the effects of climate change and adopting a design and construction methodology to build in sufficient robustness/resilience to help such structures function under extreme environmental forces.

In the affected region, the main areas of concern and our observation of structures most impacted include: 1.
High embankments immediately adjacent to the existing roads – Increased frequency of landslides 2.

Hydraulic structures/Pipe culverts – High failure of structures due to construction method and in cases, lack of sufficient discharge capacity 3.

Bridges – Many of the existing structures show signs of severe scour at the piers/abutments and also suffer the effects of a general lack of regular maintenance 4.
Road infrastructure – Road pavement has deteriorated due to insufficient drainage and the effects of increased traffic 3.

Preliminary Assessment of Existing Site Conditions Using the area of the Pond Casse roundabout as a reference, the following locations have been highlighted.

3.1 Link 31104 – Pond Casse Roundabout to Bois Diable Failure of hydraulic/culvert structure at chainage 1.6km – Following heavy rains from 17 – 19 April 2013, a section of the main road 25m long by 15m deep was washed away.
Proposal – Replace by a new rectangular reinforced concrete hydraulic box structure and retaining wall.
Cost – EC$1.2M (US$0.45M) Page 5 of 26 Ministry of Public Works, Energy and Ports Disaster Vulnerability Project – Pilot Program for Climate Resilience 27 May 2013 Figure 4 – Resulting gap in road caused by failure of culvert Further to the above, there are fifty one (51) circular concrete pipe culverts (See Figure 20) along that road link which were constructed about the same time (1950’s and 1960’s) and using the same construction methodology as the failed structure.
A recent inspection has shown a high level of deterioration (separation between pipe joints, scouring near inlet causing ingress of water into the fill, etc.)

for the main structures.

Thus, an urgent and detailed inspection regime is proposed.
Page 6 of 26 Chainage 1.6km - New reinforced concrete drainage structureItem No.DescriptionQuantityUnitRate (EC$)Amount (EC$)1General items1 sum235,130 235,130 2Demolition/Site clearance1 sum6,125 6,125 3Retaining walls/Box culvert1 sum900,000 900,000 4Road surfacing/Guard rails1 sum74,340 74,340 1,215,595 Ministry of Public Works, Energy and Ports Disaster Vulnerability Project – Pilot Program for Climate Resilience 27 May 2013 3.2 Link 31201 – Bois Diable to Castle Bruce i) Landslide at chainage 5.2km – Approximate size of landslide is 25m long by 20m high.
Figure 5 – Landslide being cleared Proposal – Embankment stabilization, drainage, road and safety measures.
Cost – EC$0.25M (US$0.1M) Page 7 of 26 Chainage 5.2km - Typical landslide mitigation measuresItem No.DescriptionQuantityUnitRate (EC$)Amount (EC$)1Clearing and grubbing of site1 ha20,000 20,000 2Excavation for stabilisation of embankment, incl disposal2,500 m350 125,000 3Drainage; concrete section 1mx1m50 m500 25,000 4Base/Subbsae100 m3100 10,000 5Wearing course; 50mm asphalt surfacing325 m2110 35,750 6Grassing/Seeding - Replanting of slopes1,500 m210 15,000 7Guard rails - Provision of safety measures50 m300 15,000 245,750 Ministry of Public Works, Energy and Ports Disaster Vulnerability Project – Pilot Program for Climate Resilience 27 May 2013 ii) Subsidence in road pavement as a result of culvert failure – The observed failure can be linked to a failure in the culvert structure Figure 6 – Subsidence in road showing direction of movement Proposal – Replace existing culvert structure with new.
Overall cost for new structures is provided in Figure 19. iii) Bridge at chainage 8.2km – Scour along abutments and missing safety railings.

Single lane bridge 18m span by 5m wide and of typical composite construction.

Recommended for replacement.


Figure 7 – Missing railings to narrow single lane bridge Page 8 of 26 Ministry of Public Works, Energy and Ports Disaster Vulnerability Project – Pilot Program for Climate Resilience 27 May 2013 Figure 8 – Scour to bridge abutments due to high flows of river Proposal – Existing bridge is of an aged construction and replacement is recommended.

Overall cost for new structures is approximately EC$1.5M (US$0.55M).
iv) Bridge at chainage 8.2km at Castle Bruce – The structure as shown in Figures 9 and 10 indicates a compromised structure.

In particular, the channel under the 34m span and 5m wide structure has suffered significant siltation.

The clearance between the bridge soffit and river is only 1m.
Figure 9 – Damaged safety rails to bridge Page 9 of 26 Ministry of Public Works, Energy and Ports Disaster Vulnerability Project – Pilot Program for Climate Resilience 27 May 2013 Figure 10 – Heavily silted river channel Proposal – Existing bridge is of an aged construction and replacement is recommended.

In addition, significant upstream/downstream dredging and river training measures are required.

Overall cost for new structures is approximately EC$2.5M (US$0.92M).
3.3 Link 31202 – Castle Bruce to Petite Soufriere i) Causeway at Castle Bruce – Existing structure at chainage 14.1km with twelve (12) 0.9m diameter culvert pipes are frequently blocked with debris.

Consideration to be given to the provision of an adequate structure across the affected location.

In addition, the road level may need raising.


Figure 11 – Causeway at Castle Bruce Page 10 of 26 Ministry of Public Works, Energy and Ports Disaster Vulnerability Project – Pilot Program for Climate Resilience 27 May 2013 Proposal – Given the frequency of overtopping due to obstruction with debris, the construction of a wide span crossing structure/bridge is recommended.
In addition, consideration must be given to raising the existing road by at least 1m (for 50m before and after crossing structure) to obtain sufficient clearance between the stream and soffit of the proposed structure.

Overall cost for new structures is approximately EC$1.0M (US$0.37M).

ii) Bridge at chainage 14.5km – Calixte bridge 24m span by 4.5m wide structures at Castle Bruce in good condition but abutment walls require attention to mitigate the effects of adverse river flows.
Figure 12 – Single lane bride Figure 13 – Both upstream and downstream abutments flanked/scoured Page 11 of 26 Ministry of Public Works, Energy and Ports Disaster Vulnerability Project – Pilot Program for Climate Resilience 27 May 2013 Proposal – Abutment walls need to be extended to mitigate the effects of flanking.

If not addressed, sustained high river flows may cause undermining and thus, compromise the main structure.
The bridge is also narrow and may need widening to accommodate two (2) lane traffic.

Overall cost for new structures is approximately EC$1.0M (US$0.37M) iii) Landslide location – Situation at chainage 16.5km at Castle Bruce after heavy rains in 2012.

Affected section approximately 20m high by at least 500m long.

Slope stabilisation required.

Figure 14 – Unstable slopes after landslide at Castle Bruce Proposal – Embankment stabilization, drainage, road and safety measures.
Cost – EC$0.25M (US$0.1M) Page 12 of 26 Ministry of Public Works, Energy and Ports Disaster Vulnerability Project – Pilot Program for Climate Resilience 27 May 2013 iv) Hydraulic structure at chainage 19.2km – Two (2) streams flow into existing structures.

The capacity of that structure appears inadequate for the levels of discharge and replacement advised.

Figure 15 – Culvert structure with compromised Proposal – Replace existing culvert structure with new.
Overall cost for new structures is provided in Figure 20.
Page 13 of 26 Chainage 16.5km - Typical landslide mitigation measures (Castle Bruce; Dipax,Tranto)Item No.DescriptionQuantityUnitRate (EC$)Amount (EC$)1Clearing and grubbing of site1 ha20,000 10,000 2Excavation for stabilisation of embankment, incl disposal3,000 m350 150,000 3Drainage; concrete section 1mx1m50 m500 25,000 4Base/Subbsae100 m3100 10,000 5Wearing course; 50mm asphalt surfacing350 m2110 38,500 6Grassing/Seeding - Replanting of slopes2,000 m210 20,000 253,500 Ministry of Public Works, Energy and Ports Disaster Vulnerability Project – Pilot Program for Climate Resilience 27 May 2013 v) Bridge at chainage 20km – Existing single lane 12.5m by 4m bridge at San Sauveur has severely scoured/undermined.
Replacement of structure recommended.

Figure 16 – Small bridge at San Sauveur near shoreline Proposal – Existing bridge is of an aged construction and replacement is recommended.

In addition, the structure is near an aggressive marine environment.

Overall cost is approximately EC$0.8M (US$0.3M).

structures for new vi) Unstable slopes at chainage 21km – San Sauveur slopes.

Stabilisation measures recommended.


Figure 17 – Unstable slopes at San Sauveur Proposal – Embankment stabilization, drainage, road and safety measures.

Cost – EC$1.9M (US$0.7M) Page 14 of 26 Ministry of Public Works, Energy and Ports Disaster Vulnerability Project – Pilot Program for Climate Resilience 27 May 2013 3.4 Link 31301 – Castle Bruce to Hatton Garden (through the Carib Territory) Like the rest of region, that 20.5km section of road has suffered from many landslides.
However, the scale of such occurrences are less severe but must be considered for investigation.

In addition, there are at least two (2) areas where slow creeping landslips have been observed.

At one location, the main road has been traversed by the slip and in another, a school building is at risk.

There are strong suspicions that such occurrences are related to subsurface is strong recommendation for geotechnical water.

In that regard, there investigation across the entire region.
Further, preliminary assessments have shown that many of the existing culverts/hydraulic structures (100 nos.

crossing structures) are showing signs of a structural failure.

As such their integrity and discharge capacity are compromised.

As a result, there is the need to carry out detailed assessments on all the structures, with a view to complete replacement, if necessary.
The existing road has also deteriorated rapidly and considerably due to increased traffic from Pond Casse to Marigot, as a result of heavy construction works on the Airport Road Upgrade Project (Seen in figure 3 as the AFD Pond Casse – Marigot Page 15 of 26 Chainage 21.0km - Typical landslide mitigation measures (San Sauveur)Item No.DescriptionQuantityUnitRate (EC$)Amount (EC$)1Clearing and grubbing of site1 ha20,000 20,000 2Excavation for stabilisation of embankment, incl disposal20,000 m350 1,000,000 3Drainage; concrete section 1mx1m600 m500 300,000 4Base/Subbsae1,200 m3100 120,000 5Wearing course; 50mm asphalt surfacing3,900 m2110 429,000 6Grassing/Seeding - Replanting of slopes2,500 m210 25,000 1,894,000 Ministry of Public Works, Energy and Ports Disaster Vulnerability Project – Pilot Program for Climate Resilience 27 May 2013 Lot2).
Some rehabilitation is recommended in order to maintain satisfactory performance of that road.

Further, at the end of that road link, chainage 20km, is the Hatton Garden Bridge.

The steel girders of that composite structure (2 spans of 12m) are severely corroded due to exposure to the marine climate.

Figure 18 – Hatton Garden Bridge at chainage 20km Figure 19 – Corrosion to steel girders of bridge Proposal – Rehabilitation and widening of existing bridge is recommended.
Overall cost for rehabilitated structure is approximately EC$2.0M (US$0.74M).

Page 16 of 26 Ministry of Public Works, Energy and Ports Disaster Vulnerability Project – Pilot Program for Climate Resilience 27 May 2013 3.6 Proposal for the replacement of culverts The following figures (20 – 22) summarize the replacement costs for culvert structures in the affected 43km region.
Figure 20 – Link 31104 Pond Casse to Bois Diable Figure 21 – Link 31201 Bois Diable - Castle Bruce Figure 22 – Link 31202 Castle Bruce - Petite Soufriere Page 17 of 26 TypeDiameter/Height (m)NºConcrete Pipe0.6115,000 15,000 Concrete Pipe0.93220,640 660,480 Concrete Pipe1.21527,338 410,070 Concrete Box3.02250,000 500,000 Concrete Box4.01400,000 400,000 Total number of culvert structures in link51Total1,985,550 Replacement cost per structure (EC$)Total cost (EC$)Link NºLink NameLength (km)Av.
Width (m)Details31104Pond Casse - Bois Diable4.55.6TypeDiameter/Height (m)NºConcrete Pipe0.62215,000 330,000 Concrete Pipe0.93420,640 701,760 Concrete Pipe1.21427,338 382,732 Concrete Box2.41150,000 150,000 Concrete Box3.02250,000 500,000 Concrete Box5.02500,000 1,000,000 Total number of culvert structures in link75Total3,064,492 9.55.3Link NºLink NameLength (km)Av.
Width (m)31201Bois Diable - Castle BruceDetailsReplacement cost per structure (EC$)Total cost (EC$)TypeDiameter/Height (m)NºConcrete Pipe0.61515,000 225,000 Concrete Pipe0.92020,640 412,800 Concrete Pipe1.2527,338 136,690 Concrete Box4.02400,000 800,000 Total number of culvert structures in link42Total1,574,490 Replacement cost per structure (EC$)Total cost (EC$)31202Castle Bruce - Petite Soufriere8.84.5Link NºLink NameLength (km)Av.
Width (m)Details Ministry of Public Works, Energy and Ports Disaster Vulnerability Project – Pilot Program for Climate Resilience 27 May 2013 Figure 23 – Link 31301 Castle Bruce - Hatton Garden (through the Carib Territory) From the above, the total replacement cost of the culvert structures (figures 21 to 23) is estimated at EC$8.7M (US$3.2M).

3.7 Summary of other infrastructure costs The following figure 24 summarizes the cost of infrastructure for consideration.
Considered are:  Stabilisation of slopes affected by landslides  Upgrade of bridges Page 18 of 26 TypeDiameter/Height (m)NºConcrete Pipe0.4315,000 45,000 Concrete Pipe0.63815,000 570,000 Concrete Pipe0.92520,640 516,000 Concrete Box1.22027,338 546,760 Metal (Armco) Pipe1.21227,338 328,056 Metal (Armco) Pipe1.8140,000 40,000 Concrete Box2.0145,000 45,000 Total number of culvert structures in link100Total2,090,816 Total cost (EC$)31301Castle Bruce - Hatton Garden (through the Carib Territory)20.55.1Link NºLink NameLength (km)Av.
Width (m)DetailsReplacement cost per structure (EC$) Ministry of Public Works, Energy and Ports Disaster Vulnerability Project – Pilot Program for Climate Resilience 27 May 2013 Figure 24 – Summary of infrastructure upgrade costs Page 19 of 26 Item No.DescriptionCost (EC$M) Link 31104 – Pond Casse Roundabout to Bois Diable1Hydraulic/culvert structure at chainage 1.6km 1,215,595 2Landslide at chainage 5.2km 245,750 3Bridge at chainage 8.2km 1,500,000 4Bridge at chainage 8.2km at Castle Bruce 2,500,000 Total in link5,461,345 Link 31201 – Bois Diable to Castle Bruce1Landslide at chainage 5.2km 245,750 2Bridge at chainage 8.2km 1,500,000 3Bridge at chainage 8.2km at Castle Bruce 2,500,000 Total in link4,245,750 Link 31202 – Castle Bruce to Petite Soufriere1Causeway at Castle Bruce 1,000,000 2Bridge at chainage 14.5km 1,000,000 3Landslide at chainage 16.5km - Dipax253,500 4Bridge at chainage 20km - San Sauveur800,000 5Unstable slopes at chainage 21km – San Sauveur 1,894,000 4,947,500 Link 31301 – Castle Bruce - Hatton Garden (through the Carib Territory)1Bridge at chainage 20km 2,000,000 Total in link2,000,000 Total infrastructure cost16,654,595 Ministry of Public Works, Energy and Ports Disaster Vulnerability Project – Pilot Program for Climate Resilience 27 May 2013 3.9 Roads and safety Worthy for consideration are the sections of roads listed in the following figures.
Considerable damage was done by the action of overflowing rivers and streams.

Figure 25 – Proposal for the upgrade of 5km of affected road Figure 26 – Proposal for the upgrade of 15km of affected road From figures 22 and 23, at least EC$21.9M is required for the noted upgrade.
3.10 General summary of costs As a general summary, a sum of at least EC$47.3M (US$17.5) is required to address the issues related to infrastructure of deficient standard, with a view to improving the integrity and long term performance.
Page 20 of 26 Item No.DescriptionQuantityUnitRate (EC$)Amount (EC$)Link 31202 – Castle Bruce to Petite Soufriere1Drainage; small rectangular concrete section 5,000 m300 1,500,000 2Base/Subbsae9,000 m3100 900,000 3Wearing course; 50mm asphalt surfacing30,000 m2110 3,300,000 4Guard rails - Provision of safety measures5,000 m300 1,500,000 7,200,000 Item No.DescriptionQuantityUnitRate (EC$)Amount (EC$)Link 31301 – Castle Bruce - Hatton Garden (through the Carib Territory)1Drainage; small rectangular concrete section 5,000 m300 1,500,000 2Base/Subbsae20,000 m3100 2,000,000 3Wearing course; 50mm asphalt surfacing75,000 m2110 8,250,000 4Guard rails - Provision of safety measures10,000 m300 3,000,000 14,750,000 Ministry of Public Works, Energy and Ports Disaster Vulnerability Project – Pilot Program for Climate Resilience 27 May 2013 Figure 27 – Total cost of rehabilitation of infrastructure Page 21 of 26 Item No.DescriptionCost (EC$M)1Rehabilitation of culverts8.7 2Other infrastructure; Landslide stabilisation/bridges16.7 3Roads and safety22.0 Total47.3 Ministry of Public Works, Energy and Ports Disaster Vulnerability Project – Pilot Program for Climate Resilience 27 May 2013 APPENDIX 1 SUMMARY OF CULVERT INVENTORY IN AFFECTED REGION Page 22 of 26 Ministry of Public Works, Energy and Ports Disaster Vulnerability Project – Pilot Program for Climate Resilience Inventory of culverts in region under consideration 10 May 2013 Page 23 of 26 TypeDiameter/Height (m)NºConcrete Pipe0.61Concrete Pipe0.932Concrete
 Pipe1.215Concrete Box3.02Concrete Box4.01Total number of culvert structures in link51Link NºLink NameLength (km)DetailsAv.
Width (m)5.64.5Pond Casse - Bois Diable31104 Ministry of Public Works, Energy and Ports Disaster Vulnerability Project – Pilot Program for Climate Resilience Inventory of culverts in region under consideration 10 May 2013 Page 24 of 26 TypeDiameter/Height (m)NºConcrete Pipe0.622Concrete Pipe0.934Concrete Pipe1.214Concrete Box2.41Concrete Box3.02Concrete Box5.02Total number of culvert structures in link75Link NºLink NameLength (km)Av.
Width (m)Details31201Bois Diable - Castle Bruce9.55.3 Ministry of Public Works, Energy and Ports Disaster Vulnerability Project – Pilot Program for Climate Resilience Inventory of culverts in region under consideration 10 May 2013 Page 25 of 26 TypeDiameter/Height (m)NºConcrete Pipe0.615Concrete Pipe0.920Concrete Pipe1.25Concrete Box4.02Total number of culvert structures in link42Link NºLink NameLength (km)Av.
Width (m)Details31202Castle Bruce - Petite Soufriere8.84.5 Ministry of Public Works, Energy and Ports Disaster Vulnerability Project – Pilot Program for Climate Resilience Inventory of culverts in region under consideration 10 May 2013 Total number of culverts in region (43.3km) = 268 Page 26 of 26 TypeDiameter/Height (m)NºConcrete Pipe0.43Concrete Pipe0.638Concrete Pipe0.925Concrete Box1.220Metal (Armco) Pipe1.212Metal (Armco) Pipe1.81Concrete Box2.01Total number of culvert structures in link100Details5.120.5Castle Bruce - Hatton Garden (through the Carib Territory)31301Link NºLink NameLength (km)Av.
Width (m)