Erosion threatens Guyana’s coastal mangroves

 

Mangroves, they are our natural defence against the raging tide and rising sea level; however this unique ecosystem is threatened by the cyclic erosion/accretion that occurs along Guyana’s coastline.

The National Research & Extension Institute, Mangrove Department is currently monitoring the effects of erosion on coastal mangroves in Region 3, 4 and 6.   The erosion process, which occurs in 20-30 year cycles, is impacting several naturally regenerated and planted restoration sites at Hope Beach, Wellington Park, Greenfield and several villages along West Coast Demerara.

 

The coast of Guyana is part of a 1600 km-long muddy coastal system dominated by massive mud banks that migrate from the mouth of the Amazon River to that of the Orinoco in Venezuela. According to a study completed by Professors Antony and Gardel in 2013, the dynamics of the Guyana coastline are strongly hinged on pulses of mud abundance or scarcity embedded in multi-year cycles of mud-bank activity and inter-bank phases. The cyclic mud-bank phases regulate mangrove regeneration by providing a substrate for extremely rapid and large-scale colonization from older mangrove colonies and vigorous tree growth.

 

According to Ranata Robertson, Coastal Engineer at the University of Guyana, erosion can be caused by this natural process and by human or man-made interventions. For example, building structures beyond the seawall/within the sea defence area alters or disrupts the natural movement of sediments, hence, resulting in erosion.

 

Robertson noted that it is important for Guyana to conduct ongoing research to determine the movement of these mud banks and the associated erosion cycle.  Studies to map and model coastline retreat and advance are critical areas of research that needs to be integrated into a long term coastal zone management program. Collaborative studies have been ongoing with the University of Guyana Civil Engineering Department, NAREI’s Mangrove Restoration Programme and Sea & River Defence Division to better understand and model this cyclic process, she noted.

 

Robertson related that Mangroves are considered as primary sea defence. The role of coastal mangroves in Guyana is to dissipate or reduce wave energy along the coastline. They not only complement hard coastal defence structures but help with the environmental conservation and cost of maintaining hard structures.

 

While mangroves are subjected to cyclic erosion, studies conducted on Guyana’s coastal mangroves have proven that a mangrove bandwidth of 50m-80m is required to reduce a 3m high wave to approximately 0.01meters. In the areas where mangroves are not present, severe over-topping occurs (along Kingston and Sheriff Street) which results in increase cost for maintenance works over a period of time, she added.

 

According to Kene Moseley, head of NAREI’s Mangrove Department, erosion of the shoreline is a natural process that affects mangrove forests. However, once the forest has adequate width, the mangroves have the potential to naturally restore itself when the cycle changes and there is accretion and deposition of sediments.  This natural regeneration is however only possible provided that there are no other stress on the system.

 

The most recent example of the effect of erosion on mangroves was noted along of the West Coast Demerara, Region 3 shoreline.  NAREI started monitoring the erosion along this stretch of shoreline in 2014 to assess the changing conditions and the impact on the status of the mangrove forest.

Moseley noted that during that period the monitoring team observed and documented extensive rapid erosion along the shoreline. Windsor Forest, Ruimzeight, Rotterdam and Crane were regarded as critical areas. The erosion had totally cleared mangroves from sections at Windsor forest, while the remaining sections of the forest continued to thin as trees were uprooted.

 

Last Thursday, NAREI and SRDD met with the La Jalousie/ Nouvelle Flanders Neighbourhood Democratic Council. The discussion centered on the loss of mangroves within the NDC and the current rip-rap sea defence project being constructed by Ministry of Public Infrastructure.  Moseley presented an overview of the monitoring conducted by NAREI since 2014 showing the extent of the erosion and impact of the loss of the mangroves.  She noted that the situation was also further impacted by excessive garbage dumping and harvesting by fishermen for fishing poles. SRDD District Engineer, Mr. Dennis Ramsingh, briefed NDC Councilors on the status of the rip-rap project and reassured that the works were being completed to reinforce the sea defence due to the loss of the mangroves.  Due to the nature of the works, the remaining mangroves were cleared to facilitate placement of the boulders.  NAREI will continue to work with SRDD to monitor changes in the cycle and elevation along this stretch of coastline.

 

With respect to the other sites, Moseley noted that this is the first time Hope Beach is experiencing erosion since the mangroves were restored in 2010. Meanwhile at Greenfield, the erosion of the mangrove forest is being monitored and research is being conducted on the implementation engineering projects that may reduce the impact of the erosion and save the remaining forest.