Feature:

The Marine Geological Survey Division of the Mines and Geosciences Bureau (MGSD-MGB) conducted Coastal Geohazard Assessment in the Province of Camarines Sur.

"Discourage construction of dwelling units along the immediate corridors of the coasts to protect properties against coastal erosion," suggested the technical teams.

This statement forms part of the numerous recommendations in their reports that revealed the coastal strips of 20 barangays in the province to be critically threatened by coastal erosion.

The said reports had enumerated barangays in seven municipalities that are highly at risk to coastal erosion. These are: Barangay Cirilo in Pasacao; Barangay Tinalmud Nuevo in Libmanan; Bulalacao, Bagong Sirang and Buenavista in Presentacion; Barangays Tagbac and San Rafael in Ragay; Barangay Siramag in Balatan; Barangay Bagacay in Tinambac; and Barangay Sabang in Calabanga.

The others which were considered to be moderately susceptible to erosion were identified in the coasts of 17 barangays namely: Barangay Gibgos, Gata, Tabgon, Haponan and Oring in Caramoan; Barangay F. Simeon in Ragay; Barangays Pararao, Luluasan and Duran in Balatan; Barangays San Antonio, Bagolatao, Salinggogon and Hamoraon in Minalabac; Barangays Liwacsa and Balinguian in Presentacion; Barangay Bahao in Libmanan; and Barangay Manzana in San Jose.

The extent of delineated eroded coastal peripheries in the study areas ranges from 30 meters to as much as 160 meters, in Barangay Sabang, Calabanga Municipality, or an equivalent of about 0.5 - 2.0 meters (most extensive) of land lost per year. This figure is appraised with a conjecture of having a uniform rate of wearing-away of lands based on a 50-year period gap.

The results of the surveys determine that the severity of potential of coastal erosion in the aforementioned barangays are controlled by a combination of the geology, presence of natural and man-made coastal defense structures, effects of surrounding bodies of water and exposures to monsoon winds.

Most of the assessed coasts high for erosion, are composed of sand and in some places, mud, which are naturally prone to constant change; some places are building sand seaward and in other areas eroding landward. In most areas, the beaches were found to have undergone natural processes, while in others, there are interferences of human activities. Apparently, sand is eroded during the monsoon and typhoon seasons, but seems to regenerate in the summer months.

The reports indicated that by nature, unconsolidated or loose sediments are highly susceptible to erosion, against the interplay of waves, tides and currents coming from the open seas of the Pacific Ocean, Ragay Gulf, San Miguel Bay and Lagonoy Gulf.

Moreover, man-made coastal defense structures have also affected the rate of erosion process in the coastlines of Camarines Sur. It was accounted to, that these structures were either able or unable to respond to the dynamic beach changes considering these structures usually serve as conduit or barrier to land-sea sediment exchange.

Sometimes these defenses can even exacerbate further erosional problems which usually occur near the ends of seawalls, especially if they are not properly tied into the adjacent shoreline. Waves erode ends of seawalls forming embayment concentrating wave energy and aggravating erosion at the protected backshore. These breached or damaged hard structures were the bases of the teams to rate some barangays to be critical to coastal erosion.

The proximity of the coastal areas to bodies of water such as Kilbay, Rabel, Ovacosoc, Pagatpatan, Lagonoy, Sabangcawayan, Punis and Masilite rivers and their geographic locations in relation with the usual path of the most typhoons in the Philippines, have likewise affected the susceptibility of the beachfronts in the province to erosion and flooding.

Through interviews, the MGB team gathered that the local residents had observed that the growing trend of inundation occurred at highest tide regimes during typhoons, which are critical to houses and infrastructures such as roads and seawalls.

Beaches along the Municipality of Caramoan are well exposed to severity of coastal inundation. These are recorded in Barangays Tabgon, Oring, Oroc-oroc, Cagnipa, Guijalo, Pandanan, Daraga, Cogon, Haponan, Maqueda, Gibgos, Toboan, Bikal, Mampirao, Cabcongan, San Vicente, Pagolinan and Paniman.

Other barangays that are highly susceptible to precipitation-induced and storm surge flooding were identified in the following municipalities: Barangay Siramag in Balatan; Barangay Tinalmud Nuevo in Libmanan; Barangay Payak in Bato; Barangays Sta. Rosa del Sur, Caranan and San Cirilo in Pasacao; Barangays Itangon and Caorasan in Bula; Barangays Liwacsa, Sta. Maria, Cagnipa, Lagha and Bitaogan in Presentacion; Barangay Apad in Ragay; Barangays Sto. Niño and Patitinan in Sagnay; Barangay Pinamasagan in San Fernando; Barangays Sabang, Tagas, Telegrafo and Manzana in San Jose; Barangay Casuna in Tigaon; Barangays Castillo and Pandan in Cabusao; and Barangays Sabang and Sabang East in Calabanga.

Moderately prone to coastal flooding are located in the following: Barangays Camangahan, Pararao, Luluasan, Coguit and Duran in Balatan; Barangay Pagatpatan and Palo in Bato; Barangays Magais, Sabang, San Juan, Sinagawsawan, Sinuknipan II and Pasay in Del Gallego; Barangays Bahao and Villadima in Libmanan; Barangays San Antonio, Salinggogon, Hamoraon and Bagolatao in Minalabac; Barangays Balogo and Dalupaon in Pasacao; Barangays Balinguian, Maangas, BagongSirang, Patrocinio and Bulalacao in Presentation; Barangays San Rafael, Catabangan and Lower Omon in Ragay; Barangays Turague, Nato and La Purisima in Sagnay; Barangays Cotmo, Bical and Gnaran in San Fernando; Barangays Dolo and Adiangao in San Jose; Barangay Bagacay in Tinambac; Barangay Caima in Sipocot; and Barangay Huyonhuyon in Tigaon.

The reports also indicated that the nearness to headlands and promontories can protect an area to coastal erosion. This is best exemplified in Brgys.Siramag and Payak which are adjacent to Bedal Point in Caramoan Municipality. These two barangays are both facing the Ragay Gulf and are covered by unconsolidated and non-cohesive sandy deposits interspersed with tuff, coral and shell fragments. Yet, the coasts are rated low to erosion. Here, the headland and promontories act as protection/shield against the onslaught of monsoon winds.

As a whole, coastal erosion in Camarines Sur is diverse and a complicated problem to some areas. To propose effective measures for preventing and controlling coastal erosion, proper evaluation and understanding of its causes should be done first. It is within this context that the MGSD-MGB had focused on the assessment of coastal geohazards all over the country.

It is further recommended that continuous coastal erosion or accretion monitoring to be done to highly prone and low lying areas, measuring sand supply and replenishment offshore and onshore especially nowadays wherein there is growing intensity of weather patterns and impending sea level rise brought about by climate change.

By: Marine Geological Survey Division