ASEANO Project Report: Mapping and Characterization of the Imus River Watershed
PUBLICATION DATE:
Tuesday, April 19, 2022
PUBLICATION TYPE:
Reports
STATUS:
Only Available Online
DESCRIPTION:
River systems have been identified as major pathways and transporters of wastes, including plastics, that ultimately end up in the oceans. The Imus River Watershed (IRW) is located in the Philippine Province of Cavite, one of the provinces in the CALABARZON Region of southern Luzon. This study delineated and mapped the physical boundaries of the Imus River watershed and determined the topographic features, stream characteristics, geomorphology, political subdivisions, barangay communities, population distribution, land use and land cover, and hydro-climatic characteristics of the watershed. Both primary and secondary data sources were used in making comprehensive land use maps, population maps, and hydroclimatic data analyses.
The boundary of the Imus River Watershed was initially established through an unsupervised delineation process using a digital elevation model of Cavite with a 5-meter resolution in ArcGIS. Sangley Point Synoptic Station in Cavite City and the CvSU-PAGASA Agrometeorological Station in Indang were used to define the general hydroclimatic condition of IRW due to their close proximity to the watershed. The total drainage area of IRW is 11,259.80 hectares, covering portions of Tagaytay City, Amadeo, Silang, Dasmariñas, Imus City, Bacoor City and Kawit. Elevation within the watershed ranges from 0 to 655 meters above sea level. The lowland area covers parts of Kawit, Imus City, and Bacoor City; a central hilly area covers parts of Imus City, Bacoor City, and the majority of communities in Dasmariñas and Silang. The upland area covers parts of Silang, Amadeo, and Tagaytay City. There were 56 perennial streams identified with a total length of 186.15 km and 36 river segments. The Imus river system is a combination of headwaters and medium-sized streams. The sub-watersheds, labeled A, B, and C, have drainage densities of 1.15 km/km2, 1.95 km/km2, and 1.41 km/km2, respectively. The sub-watersheds A and C have stream frequencies of 0.20/km2 and 0.25/km2 while sub-watershed B has a stream frequency of 0.39/km2. In alphabetical order, these sub-watersheds have bifurcation ratios of 5, 3.31, and 2.5, elongation ratios of 0.33, 0.26, and 0.43, and circulatory ratios of 0.18, 0.11, and 0.26.
A total of 222 barangay communities are located within the boundaries of the watershed with a total population of 1,351,057 in 2015. 90.67% of the province is classified as alienable and disposable land, while the remaining forest land represents only 9.33%. Alienable and disposable lands are further classified as production land (55.24%) and built-up areas (44.76%). The Sangley Point Synoptic Station has a normal mean temperature of 28.53°C while the CvSU-PAGASA Agromet Station has a normal mean temperature of 26.20°C. The average total annual rainfall recorded at Sangley Point Synoptic station and CvSU Agromet Station were 2,265.69 mm and 2,483.05 mm, respectively. The average flow during wet season was 1,601.84 liters per second, while the average flow during dry season was 1,337.42 liters per second.
RELATED PUBLICATIONS
IRBM Project 3rd RSC Meeting Proceedings
Held back-to-back with the 25th Meeting of the ASEAN Working Group on Water Resources Management (AWGWRM), the Third Regional Steering Committee (RSC) Meeting of the GEF/UNDP/ASEAN Project on Reducing Pollution and Preserving Environmental Flows in the East Asian Seas through the Implementation of Integrated River Basin Management (IRBM) in ASEAN Countries was held on 4 June 2025 through a hybrid format,. i.e., in-person at Haliday Inn Resort Baruna in Bali, Indonesia and online via Zoom.
Hosted by the Government of Indonesia through the Ministry of Environment (MOE), the meeting was co-chaired by Mr. Oudomsack Philavong, AWGWRM Chairperson and Mr. Gerd Trogemann, Manager of United Nations Development Programme-Bangkok Regional Hub of Asia and the Pacific (UNDP-BRH). The meeting was attended by the National Focal Points (NFPs) of the AWGWRM from nine (9) ASEAN Member States (Cambodia, Indonesia, Lao PDR, Malaysia, Myanmar, Philippines, Singapore, Thailand, and Vietnam), the East Asian Seas Executive Committee, the ASEAN Secretariat, and UNDP-BRH.
The Regional Project Management Unit (RPMU), hosted by PEMSEA Resource Facility and MOE Indonesia served as Secretariat to the RSC meeting.
Proceedings of the Training on Marine Spatial Planning (MSP) Application in the Scaling-up of Integrated Coastal Management (ICM)
PEMSEA, in partnership with the Fujian Institute for Sustainable Oceans (FISO) and supported by the China Oceanic Development Foundation (CODF), conducted a training workshop on Marine Spatial Planning (MSP) Application in the Scaling-up of Integrated Coastal Management (ICM) last April 2025 in Xiamen, China. The workshop convened participants from 10 East Asian countries including Brunei Darussalam, Cambodia, Indonesia, Lao PDR, Malaysia, Philippines, Singapore, Thailand, Timor-Leste, and Vietnam. Through lectures, field visits, simulation, and peer-to-peer exchanges, the training aimed to build a regional pool of ICM-MSP trainers and contribute to the development of a standard course for regional adaptation.
The proceedings details:
- Concepts and tools for ICM and MSP implementation
- Regional experiences on integrating ecosystem-based spatial planning into policy and practice
- Field demonstrations from Xiamen's coastal transformation under ICM
- Practical strategies for developing ICM-MSP curricula and training delivery
The training supports the operationalization of the SDS-SEA Implementation Plan, particularly on capacity development and area-based management.
Integrated River Basin Management Project Newsletter - Edition 7
Now in its third year, the IRBM Project enters a pivotal phase in advancing integrated river basin management across Southeast Asia. “Midpoint Momentum”, the seventh edition of the project’s newsletter, highlights key developments – notably the review of the implementation progress at the Third Regional Steering Committee Meeting, including the completion of the Mid-term Review, the conduct of the orientation workshop on the REWEFe Toolkit for the ASEAN Member States, the official project launch in Viet Nam and the development of solutions templates to support IRBM pilot project planning and implementation.
This issue also features field stories, such as the Women of the Wetlands in the Pasac-Guagua Watershed, and announces the launch of the IRBM e-Portal on PEMSEA’s Seaknowledge Bank.
From establishing coordination mechanisms at the local, national, and regional levels to designing scalable solutions template for river basin-level implementation, the IRBM Project continues to accelerate momentum – strengthening regional collaboration, deepening stakeholder engagement, and enhancing capacity and knowledge sharing across the ten ASEAN Member States.
Workshop Report_Regional Orientation on ReWEFE Toolkit
The GEF/UNDP/ASEAN Integrated River Basin Management Project convened a Regional Orientation Workshop on the Development of Water-Energy-Food-Ecosystem (WEFE) Toolkit for River Basins in Southeast Asia on 3 June 2025 in Bali, Indonesia to introduce and demonstrate the applications of the toolkit in selected river basins of the project.
Proceedings of the 2nd Blue Carbon Technical Working Group Meeting
The PEMSEA Resource Facility (PRF), in partnership with the National Marine Hazard Mitigation Service, Ministry of Natural Resources (NMHMS/MNR), convened the 2nd Blue Carbon Technical Working Group Meeting on 5–6 June 2025 in Haikou, Hainan Province of China. The meeting was attended by nearly 60 experts and stakeholders on blue carbon from 11 countries in the EAS region and beyond. The PRF Secretariat served as the Secretariat for the meeting. Online participants included members of the PEMSEA Network of Learning Centers and other Blue Carbon experts from the region.
The meeting aimed to:
- Draw consensus on the governance framework of an innovative Blue Carbon Ecosystem Services Management Mechanism (Draft 0) and the requirements to operationalize a regional blue carbon certification program.
- Improve understanding and consensus building among BC-TWG members on the draft regional blue carbon accounting protocol.
Expected outcomes of the meeting include:
- Refined concept of a Blue Carbon Ecosystem Services Management Mechanism, including a blue carbon stock monitoring network.
- Refined regional blue carbon accounting protocol.
- Refined workplan for 2025 and 2026 for review, guidance and/or approval at the 17th EAS PC in July 2025.