The Mines and Geosciences Bureau (MGB) of the Department of Environment and Natural Resources (DENR) said beach nourishment is “not a permanent remedy” to combat erosion and increase the beach width of Manila Bay.
Citing previous studies and scientific researches, the MGB explained that “mechanically placed sand on beaches moves as affected by waves, currents, tides and wind and other potential impacts of anthropogenic and natural events.”
In one study conducted by the Scripps Institution of Oceanography at the University of California at San Diego, “they found out that added coarser sand to the beach stayed on despite of energetic waves (but) in one case, the sand moved both north and south along the coast that later contributed to the closure of a river estuary causing concentrated pollution and hypoxia.”
In the case of the dolomite sand spread along the beach of Manila Bay, it said it is necessary to have a systematic monitoring of monsoon or seasonal currents to follow the general pattern of the direction of movement and deposition of piles of sediments in the bay.
“The process will take for some time but regular monitoring and studies will enable DENR to predict or model on how the nourished sand will evolve,” MGB said.
MGB experts from the Marine Geological Survey Division have been also conducting coastal geohazard assessments across the country and found that most beaches in the Philippines are prone to erosion, “which cause adverse changes in the shape and position of coasts.”
It pointed out that beach nourishment, or beach replenishment, which is the practice of adding sand or sediment to beaches aims to combat erosion and increase beach width.
“Beach nourishment is a soft engineering alternative to hard structures like seawalls, groins on the shore used to create a natural beach environment for the bay, eliminating detrimental effects of shore protection structures by burying them, and retaining sediment volumes to respond to sea level rise brought about by climate change,” the MGB explained.
After the dredging and clean-up of the Manila Bay, members of the different agencies involved in the rehabilitation of the bay have agreed that the initial beach nourishment to be implemented will be applied in the segment between the area fronting the US Embassy and the Manila Bay Yacht Club to mimic a “pocket beach.”
The DENR earlier said that beach nourishment was applied as part of the bay rehabilitation because “Manila Bay is not considered prone to coastal erosion as it is mostly protected by seawalls, but the beaches are very narrow.”
However, the MGB noted that “beach nourishment does not stop erosion, rather, it merely prevents erosion for a short time.”
The DENR has began laying out “white sand” made from crushed dolomite rocks early this month as part of the P389 million Manila Bay rehabilitation that started in 2018.
Due to criticisms with the use of dolomite as potential hazard to public health, the DENR clarified by citing the Grain Size Classification from the United States Geological Survey Open-File Report 2006-1195 dated 2011 that sand grains spread in Manila Bay is classified as coarse-grained sand to fine pebbles.
It said it was 2 millimeters to 5 millimeters in size or equivalent to 2,000 microns to 5,000 microns, and therefore almost 100 times bigger than dust. It is not “dust” which is 2.5 microns to 50 microns in size, according to the DENR.
They even cited the famous islands known for their fine sand such as Panglao and Boracay becoming world-renowned for their “powdery sugary sand,” which were derived from weathered coralline limestone and dolomitic limestone, and no health complaint has been filed by tourists and swimmers.
“In response to these clamor it is important that DENR had conferred the activity with other agencies before the implementation of the project,” the MGB said.