Atty. Gloria Estenzo-Ramos
Last Saturday’s discovery of a two-meter wide sinkhole in the middle of the river in Barangay Banhigan in Badian, Cebu is not something to be taken lightly. It is potentially life-threatening.
Sinkholes are “pits in the ground that form in areas where water gathers without external drainage, according to the U.S. Geological Survey.
As water drains below ground, it can dissolve subterranean caverns, particularly in areas where the bedrock is made of water-soluble evaporate rocks such as salt or gypsum or of carbonate rocks such as limestone or dolomite.” (https://www.livescience.com/44123-what-are-sinkholes.html.)
In a Rappler report, it is estimated that “majority of the country’s municipalities – 1,171 out of the total 1,490 – sit on soluble rocks.
The presence of soluble rocks increase the hazard of sinkholes and subsidence. (https://www.rappler.com/nation/98681-sinkholes-ground-subsidence-assessment-philippines)
The news about the discovered sinkhole reminded me of my conversation a few days ago on the subject matter in relation to disaster risk reduction management (DRRM), with the tireless eco-steward, former Cebu City Councilor Nida Cabrera.
This columnist was informed of the existence of sinkholes and subsidence in more than half of the city’s barangays.
“Land or ground subsidence is the lowering of the ground surface due to excessive extraction of water from the ground.
Subsidence can harm a community by making it more susceptible to flooding.” (https://www.rappler.com/nation/98681-sinkholes-ground-subsidence-assessment-philippines)
The Mines and Geosciences Bureau of the Department of Environment and Natural Resources has presented to the Cebu City government and barangays an advance copy of the report by the MGB Central Office (MGB-CO) Sinkhole Assessment Team entitled “Karst Subsidence Hazard Assessment and Ground Penetrating Radar (GPR) Survey in the Upland and some Lowland Urban Barangay of Cebu City.”
The 249-page report was shared during a workshop last March 30, 2017 at the Sinulog Hall, Rizal Public Library.
Together with the printed report are the 49 files each labeled “Subsidence Threat Advisory,” representing advisory on specific locations, the type of hazard(s), and recommendations for 49 upland/rural and some urban barangays of Cebu City, including the specific letters addressed to concerned barangay heads.
One barangay was informed of 37 sinkholes in the area, ranging from “3 to 150 meters based on geological assessment, 90 to 140 based on IFSAR-DEM and 40 to 200 meters on LIDAR-DEM.” Recommendations include i) vigilant monitoring of signs of sinkhole/cave collapse, and subsidence in the areas identified by concerned barangay officials, ii) extra vigilance by residents during heavy, continuous rains brought by typhoon or monsoon rains, especially if areas with identified sinkholes are flooded, iii) in case of sinkhole and/or cave collapse, to cordon off the area and report situation to city authorities/City Disaster Risk Reduction and Monitoring Office, iv) monitor displaced, bulging and presence of tension cracks along national and barangay roads, with signages installed indicating the threat of subsidence, v) activate Barangay Disaster Risk Reduction and Management Council and establish an effective evacuation protocol, with evacuation and relocation sites being “geologically assessed” and suitable for the purpose and (vi) awareness campaign on subsidence hazards due to sinkhole collapse conducted to barangay officials and residents.
The letter from the MGB emphasized that the barangay concerned should advise the constituents “to initiate readiness and measures for this identified geohazard.” It adds that “increase in rainfall, lowering of water table, strong earthquake will increase subsidence activity.”
The barangay is exhorted to contact the City Disaster Risk Reduction and Management Office/Council “to plan for any emergency and pre-emptive evacuation as soon as possible. Adaptation measures for affected communities should also be upgraded.”
Since receiving the report from the MGB, did the barangay officials immediately call for a meeting among the residents and share with them the threat assessment? That should be a prelude to the much-needed DRRM planning which is required by RA 10121, the DRRM Act of 2010.
There is no substitute for preparedness. As Benjamin Franklin wisely noted, “By failing to prepare, you are preparing to fail.
Inaction is not an option, in the era we are in. In fact, it is a culpable act with serious consequences to both the constituents and the public authorities.
Our citizens have the right to be informed of hazards in their locality, thus massive public information and urgent action are needed to ensure their safety.
It is likewise important for us to be aware of our responsibility in ensuring that our actions do not impact our environment and the lives of those around us. “Although a natural process, the formation of sinkholes is often accelerated or triggered by human actions.
Broken land drains, water mains and sewerage pipes, increased rainfall, storm events, modified drainage and diverted surface water can all help wash sediment into the underlying limestone, causing subsidence.
There have been many well documented occurrences of sinkholes forming beneath broken water mains, unlined storm-water culverts and leaking swimming pools.” (https://www.bgs.ac.uk/ mendips/caveskarst/karst_3.htm)