Dealing with environmental threats on Luyang Watershed

CEBU, Philippines - Luyang Watershed is one of the important watersheds in the Province of Cebu because of its ecological and economic significance. Currently, there are existing and proposed development initiatives within the catchment and in order to ensure sustainable development of this area, there is a need to generate information on areas vulnerable to natural and man-made hazards as inputs to the watershed management plan.

In support to the new research thrust of the department, the project on the vulnerability assessment of characterized watersheds in Central Visayas has been conceptualized and formulated. Vulnerability assessment is an approach in identifying and determining areas susceptible or vulnerable to natural hazards and man-made or anthropogenic hazards.

The conceptual framework in the conduct of vulnerability assessment of characterized watersheds includes assessment of the biophysical and socio-economic parameters, hazard identification and analysis, critical factor analysis, GIS-based analysis and mitigation measures.

What the project is aiming for?

The project aims to identify and determine natural/man-made hazards in Luyang Watershed, Carmen, Cebu; to identify critical factors affecting the vulnerability of the watershed to natural/man-made hazards such as soil erosion, landslide and flooding; to determine and map out the vulnerability levels of the watershed to natural/man-made hazards using GIS-assisted methodologies; to formulate specific mitigating measures to reduce damage caused by natural/man-made hazards as well as improve the current conditions of the watershed; and to formulate policy recommendations as inputs to the sustainable management of Luyang Watershed.

The components of the project are the GIS-assisted approach in soil erosion assessment of Luyang Watershed; landslide assessment and zonation of Luyang Watershed; and flood hazard assessment of Luyang Watershed.

Vulnerability level on soil erosion, landslide and flooding

The GIS-assisted models on soil erosion, landslide and flooding have been developed and applied in Luyang Watershed, Carmen, Cebu (as shown by the graphics). In the process, the capability of GIS-assisted methodology has been confirmed to be a valuable tool in watershed planning. In predicting soil erosion, the Universal Soil Loss Equation was used. Generally the location of areas vulnerable to soil erosion is along areas of steeper slopes with poor vegetation. These are noted in some upland barangays such as Lower Natimao-an, Lanipga, Cantukong, Upper Natimao-an, and Ipil which have high to severe soil erosion with 237.66 hectares, 209.16 hectares, 175.79 hectares, 123.59 hectares and 121.78 hectares, respectively.

Any changes in land use or farming systems leading to loss of vegetation cover and the subsequent increase in surface runoff will eventually result in higher potential soil erosion. Therefore, there is a need to increase the vegetation cover through reforestation in grasslands and brushlands, agroforestry development with soil and water conservations, planting of fruit trees in built-up areas, adoption of improved cropping systems such as multiple cropping, intercropping, and crop rotation. Organic farming is also recommended.

Areas vulnerable to landslides are those located in steeper slopes, unstable geology and near fault lines. This may be triggered further by high precipitation or rainfall that causes the saturation of soil and some ground disturbance which may lead for mass movement.

It was predicted that about 282.68 hectares, 269.40 hectares, 185.20 hectares, 172.24 hectares, and 163.08 hectares of barangays Caurasan, Santican, Sac-on, Corte, and Upper Natimao-an, respectively, have low landslide vulnerability. For areas with moderate landslide vulnerability, Santican has been predicted with the largest area about 270.52 hectares. Corte is predicted to rank second with 267.38 hectares. This has been followed by Lanipga with 263.45 hectares, Caurasan with 228.77 hectares, Sac-on with 215.95 hectares, Lower Natimao-an with 206.36 hectares, and Cantukong with 194.90 hectares. Thus, it is recommended that infrastructures and settlements must be avoided in areas with moderate to high landslide vulnerable. Upper slopes of roads constructed in steeper slopes must be supported with ripraps. This can be implemented with legislation support from the local government unit.

The flood-prone areas were generated by calculating areas with elevations below the elevation of the highest flood water mark. It was noted that some portions of Luyang, Fuente, and Cogon West are flood-prone areas.

Based on the results, it is recommended that settlements within flood-prone areas especially with higher water level must be relocated to higher grounds or be advised to elevate the construction of houses. If not, LGU to install early warning system, escape route clearly marked evacuation plan disseminated. Moreover, river dikes must be constructed. —/MEEV   (FREEMAN NEWS)