Lessons Learnt from The

LESSONS LEARNT FROM THE

GRANDE RIVIERE RIVER SHIFTING EVENT OF 2012

REPORT SUBMITTED TO THE IMA BOARD OF GOVERNORS

Prepared by:

ADAM JEHU

Research Officer Remote Sensing Section - Geomatics Unit

JUNIOR DARSAN

Senior Research Officer Environmental Research Programme

HAMISH ASMATH

Research Officer GIS Section - Geomatics Unit

January, 2013

INSTITUTE OF MARINE AFFAIRS

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Tel.: (868) 634-4291/4

Fax: (868) 634-4433

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Institute of Marine Affairs

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1.INTRODUCTION ...... ERROR! BOOKMARK NOT DEFINED.

1.1 AREA OF INTEREST...... 1

1.2 BACKGROUND - BEACH CHANGE...... 3

2.ISSUES IDENTIFIED ...... ERROR! BOOKMARK NOT DEFINED.

2.1 SAND DAM CONSTRUCTION...... 5

2.2 CALLS FOR INFILLING THE EROSION CHANNEL...... 6

3.THE NATURAL RECOVERY...... ERROR! BOOKMARK NOT DEFINED.

4.DISCUSSION AND RECOMMENDATIONS...... ERROR! BOOKMARK NOT DEFINED.

5.CONCLUSIONS ...... ERROR! BOOKMARK NOT DEFINED.

LIST OF FIGURES

FIGURE 1: GRANDE RIVIERE, TRINIDAD2

FIGURE 2: COMPARISON OF BACKSHORE CHANGE BETWEEN 2011 (A) AND 2012 (B)3

FIGURE 3: CONSTRUCTED SAND DAM4

FIGURE.4: BEACH PROFILE PLOT ILLUSTRATING THE COMPARISON BETWEEN 2003

& 2012 RIVER SHIFTING EVENTS4

EXECUTIVE SUMMARY

Within the second quarter of 2012, changes in the hydrologic and oceanographic regimes which influence Grande Riviere beach have lead to the shifting of the Grande Riviere River course causing damage to turtle nesting areas and coastal infrastructure. Subsequent to this, the Turtle Management Committee instructed the Institute of Marine Affairs to provide a rapid assessment of the current state of Grande Riviere Bay.

The rapid assessment revealed that 4,843.419m3 of sand was required for full beach rehabilitation (Jehu et al, 2012). While the potential for sand relocation from the western end of the beach was possible for infilling the channel - the opportunity cost of sand translocation was high and is presented. It was then suggested that regarding remedial action for restoration of the backshore area encompassing the erosion channel - a no action plan should be adopted; allowing the depression to be in-filled naturally as had been observed in the past.

1. INTRODUCTION

1.1 AREA OF INTEREST

The village of Grande Riviere located on the north coast of Trinidad, between Toco and Matelot has been at the forefront of national and international concern, since July 2012. Grande Riviere's importance lies in the fact that it is a prime nesting site for the endangered Leatherback Turtle. The local community benefitted from the advent of ecotourism, which created numerous jobs ranging from tour guides, souvenir merchandisers and hospitability business as a result of nesting Leatherback Turtles State funded environmental preservation programmes also account for a substantial proportion of village employment. As such, Grande Riviere Bay presents an interrelated dynamic of socio-economic and ecological facets.

The Bay is approximately 970 m long and arcuate in shape with varying beach widths. The beach at the eastern section is much wider than at the western region with a well- defined berm and low backshore topography. The gradient at this section has a relatively gentle backshore with a moderate to steep beach face, while the central to western regions have a moderate slopes and are backed by steep cliffs.

Four monitoring stations were established on this beach in 2000 as part of a project to investigate the beach dynamics and risk posed to the leatherback egg clutches during the nesting season (Lee Lum, 2002). Figure 1 is an IKONOS (2007) image of Grande Riviere Bay showing the location of the four IMA stations at this bay.

FIGURE 1: GRANDE RIVIERE, TRINIDAD

The Institute of Marine Affairs (IMA) has been monitoring this beach since 2000 as part of a project to investigate the beach dynamics and risks posed to the leatherback egg clutches during the nesting season. The study showed that this small pocket beach was efficiently used by turtles during the nesting season. Results indicate that at the start of the nesting season in March, the majority of leatherback nests were deposited on the eastern section of the beach. After May, there was a continued westward shift in nest distribution that coincided with sand accretion (deposition of sand) in a westerly direction as the season progressed until August. As such, the seasonal erosional and accretionary cycles on this beach supported the distribution of nests as the nesting season progressed.

1.2 BACKGROUND - BEACH CHANGE

In April, 2012, it was observed that the course of the Grande Riviere River had been shifting westward - deviating from its normal path through the berm in a northerly direction the effect of which can be seen in Figure 2. Progression of this shift continued producing a backshore erosion channel of approximately 110 m in length. Expansion of this channel persisted until the intervention by the Drainage Division (Ministry of Works and Infrastructure, Government of the Republic of Trinidad and Tobago) in early July, 2012 where a sand dam was constructed to arrest the westward flow of the Grande Riviere River (Figure 3).

FIGURE 2: COMPARISON OF BACKSHORE CHANGE BETWEEN 2011 (A) AND 2012 (B)

FIGURE 3: CONSTRUCTED SAND DAM

Infrastructural damage was caused as a result of this river shifting event, which had previously occurred in 2003 and recorded by the Geology Section of the Environmental Research Programme, IMA (Figure 4).

FIGURE.4: BEACH PROFILE PLOT ILLUSTRATING THE COMPARISON BETWEEN 2003 & 2012 RIVER SHIFTING EVENTS

2. ISSUES IDENTIFIED

2.1 SAND DAM CONSTRUCTION

As a product of the river shifting event, damages were sustained to the Mt. Plaisir Estate Hotel - located on the Grande Riviere beachfront. Subsequent to this, the Drainage Division was contacted to assist in arresting the flow of the river into the backshore area - causing the damage to the hotel. The Drainage Division through the employ of heavy machinery, removed sand from the eastern side of the bay for the construction of a sand dam perpendicular to the beach, across the flow and thus diverting the river channel. An assessment of the sand dam constructed by the Drainage Division revealed that approximately 2,035m3 of sand was used for its construction.

Issues identified with this action:

Sand mining is not recommended in small pocket beaches especially where the sediment budget is uncertain as this can lead to severe coastal erosion in the mined areas.
Hindcast data at the IMA indicates that the beach on the eastern side of the river has been shown to have the highest nesting density for this period of nesting - coincident with larger beach widths and volumes. The sand translocation lead to the destruction of turtle eggs and emergent hatchlings (BBC World News July 10, 2012)
Following these actions, negative media in both national and international forums highlighted the 'massacre' of an IUCN Red-list species. These media houses carried this event with blame being placed upon the government ministries and organizations

responsible for the dam construction. The sensitivity of this event, highlighted the need for caution in moving forward with work in protected areas.

The use of heavy machinery on a protected beach is not advised. This led to compaction of the beach sand, which had negative implications for successful turtle nesting and hatching success.

2.2 CALLS FOR INFILLING THE EROSION CHANNEL

On 19th October 2012, representatives from the IMA met with the Turtle Management Committee to discuss options for remedial action at Grande Riviere. The main focus of the meeting was to decide on the best practice for infilling the backshore erosion channel left in the wake of the river shifting event and intervention by the Ministry of Works and Infrastructure in July, 2012. The IMA representatives informed the committee on the following:

Sand mining was not recommended as it may adversely impact the beach dynamics
The volume of sand required had not been established
An adequate source of sand could not be identified at this point in time
There was a need for proper evaluation of the bay before remedial works could commence

The committee acknowledged the issues raised and a rapid assessment was requested by the Minister of State of the Ministry of the Environment and Water Resources - to be conducted by the IMA.

The rapid assessment report by Jehu et al. (2012) suggested a no action plan be adopted based on historical data. Following this, the national media, NGOs and members of the

Grande Riviere Community insisted that the relevant authorities infill the channel - in fact on 06/01/2013, the Chairman of the IMA, Professor Indar Ramnarine, had to intervene in plans to unlawfully shift the berm from its then current location into the erosion channel.

3. THE NATURAL RECOVERY

As of Sunday 13th January 2013, the backshore erosion channel persisted and the calls for intervention heightened. However, based on an extensive data set, the IMA advised that the winter swells during the months of December to February would superimpose higher energy waves on the beach system which would return the eroded beach sediment from offshore back onto the beach. While an exact time-frame for beach recovery was not given (since these marine conditions are based on meteorological conditions), it was noted that the beach will recover naturally over time.

On Monday 14th January, high swell waves were experienced on the north coast of Trinidad emanating from a large frontal system positioned off the North American continent. This meteorological system produced the swell waves needed by Grande Riviere beach to facilitate its recovery. By the morning of Tuesday 15th January, 2013, the erosion channel in-filled naturally.

The maintenance of the stance taken by the IMA for no mechanical alteration of the beach proved to the best decision. Although full recovery of the beach has not yet been attained, it is well on its way to attaining its natural characteristics.

4. DISCUSSIONS AND RECOMMENDATIONS

The IMA hypothesized two possible scenarios which could have lead to the river shift:

1. The interaction between a significant high tide and high river flow caused increased hydraulic pressure at the mouth - forcing the water into the backshore area

2. An elevated berm at the mouth of the river - formed when the beach is in its accretionary phase - caused the path of least resistance to shift to the backshore area

Both premises however may have been avoided if the spillway - which joins the river to the eastern end of the bay - was functional for the release of hydraulic pressure within the river. The determination of factors which contributed to the Grande Riviere River shifting event are still undetermined with the need for further investigation encompassing the interactions between the oceanographic, hydrologic and hydrometeorological conditions of the watershed and bay area.

Beach sand mining in most respects is viewed as littoral destruction with potential impacts on both physical and ecological facets of the bay area. The burden of impact of this activity is not only held by the source area where beach sand is removed but also on areas targeted for nourishment. Grande Riviere Bay is a site of international importance for its acclaimed contribution to population enhancement of the critically endangered (IUCN Redlist Category) Leatherback Turtle. Prevalence of sound investigative science into the potential for deleterious impacts on the beach from remedial works must be explored prior to anthropogenic alterations of the beach.

5. CONCLUSIONS

Success and miscarriages were both present in the handling of the impacts of the river shifting event as it relates to both the anthropogenic and ecologically important physical environment. The following guidelines must therefore be adhered to in the event of future occurrences both at Grande Riviere and other regions of Trinidad and Tobago:

1. Events of this nature are usually not sudden - but however is the product of progressive natural changes to the river morphology and mouth location. It is therefore important for early reporting of such events in order to minimize impacts as those witnessed at Grande Riviere.

2. Once brought to the attention of relevant authorities, an initial assessment should be mandatory in order to advise on the best course of action taking into account the ecological importance and physical condition of the impacted environment.

3. The use of heavy machinery and construction of features not native to the receiving environment is not advised.

4. Removal or translocation of sediment is not advised as this has the potential for deleterious impacts on beach geomorphology.

5. Information dissemination and discussion with stakeholders is essential for the success of any intervention for arresting existent or potential impacts from riverine erosion.

6. There is a need for in-depth assessments prior to remedial or preventative measures being implemented in order to advise on the best course of action.

7. Once thoroughly assessed, the proper procedure must be followed for any active intervention through the application of a Certificate for Environmental Clearance in accordance with existing legislature.

6.REFERENCES

Jehu, A., Darsan, J., Asmath, H., 2012. Rapid Assessment: Grande Riviere beach- backshore erosion channel. Institute of Marine Affairs.

Lee Lum, L., 2002. Report on the project to monitor beach dynamics and the risk posed to leatherback turtle egg clutches at Grande Riviere Beach, Trinidad, West Indies. Institute of Marine Affairs, pp. 24

The IUCN Red List of Threatened Species 2013. Wallace, B.P., Tiwari, M. and Girondot,