2020.02.24 MGB MIMAROPA identifies river dredging zones in OrMin

River dredging zone in Balete River. The left side features a wide accumulation of sediments, while island bars are also present.


Technical personnel from the Mines and Geosciences Bureau (MGB) MIMAROPA Region began the identification of river dredging zones (RDZs) of nine priority rivers in Oriental Mindoro, February 18-23, in line with the implementation of the Department of Environment and Natural Resources’ (DENR) River Restoration Project through dredging activities in the heavily-silted river channels in the province.

Following an inter-agency meeting earlier this year, the MGB MIMAROPA Region, as task force member, was tasked to deploy a team which will form part of the technical working group to assist the Provincial Government of Oriental Mindoro in determining strategic zones where river dredging could help alleviate flood hazards for exposed communities.

This is in line with the efforts to mitigate flood risks in the province where river dredging was identified as a safety measure that can reduce water levels in flooding events.

It also aims to survey possible economic minerals in these rivers which may correspond to the payment of additional taxes by the proponent in accordance with Section 1, Article III of DAO 2019-14, “Rationalizing Dredging Activities in the Heavily-Silted River Channels within the Province of Oriental Mindoro Pursuant to the DENR-DPWH- Department of the Interior and Local Government (DILG)- Department of Transportation (DOTr) Joint Memorandum Circular No. 1 Series of 2019.”

The study and evaluation were conducted in the following rivers as endorsed by the Provincial Engineering Office: Mag-asawang Tubig River in Naujan leading to Brgy. Estrella and San Antonio, Naujan; Bucayao River in Calapan leading to Brgy. Silonay, Calapan; Alag River leading to Brgy. Water, Baco; Baco River leading to Brgy. San Andres, Baco; Balete River in Gloria leading to Brgy. Balete, Gloria; Bongabong River in Bongabong leading to Brgy. Anilao, Bongabong; Wasig River leading to Brgy. Wasig, Mansalay; Mansalay River, Mansalay leading to Brgy. Poblacion, Mansalay; and Cagankan River in Mansalay leading to Brgy. Don Pedro, Mansalay.

The study was limited to the downstream portion of these rivers, not exceeding seven kilometres from the deltas.

The team, joined by DENR and Provincial Environment and Natural Resources Offices and Engineering Office, conducted  mapping of target rivers using remote sensing; on-site verification and mapping of sediment accumulation zones through ocular inspection and use of drone; site-specific flood and bank erosion hazard assessments; morphological analysis of the target river systems; application of the prescribed buffer zone for river dredging activities based on Consolidated DENR Administrative Order for the Implementing Rules and Regulations of Republic Act No. 7942 (Philippine Mining Act of 1995), and DPWH Order No. 139, Series of 2014; and delineation of the proposed river dredging zone.

Segments of the target river system with vast high flood-susceptible areas and with road networks and communities residing on their immediate vicinity were prioritized as river dredging zones, including the identified sediment accumulation zones.

Significant sediment accumulation and erosion of riverbanks were observed in some areas where regular flooding is experienced during continuous rainfall and even without any extreme weather disturbances.

The identified RDZs by the MGB MIMAROPA team will only be supplementary to the DPWH dredging masterplan as stipulated in Article I Section 2 of DAO 2019-14.

Moreover, the volume of dredging materials present was not indicated, hence, qualified technical personnel should undertake studies concerning allowable depths and volume for excavation.