5 Reconnaissance Survey of Bohol
Bohol is one of the provinces in Region 7 included in the scope of USC Phil LiDAR 1 Project. There are about five major rivers in Bohol – Abatan, Loboc, Matul-id, Ipil, and Inabanga. The Hydrology team had a two-day ocular survey (August 12–13, 2014) on the five rivers mentioned. These rivers are located in the following respective municipalities – Maribojoc, Loboc, Candijay, Trinidad, and Inabanga, as shown in Figure 5.1.
5.1 Abatan River
The Abatan River is found in the Municipality of Maribojoc. During the Team’s visit, the group was able to communicate with the officer-in-charge, Oscar Fransisco Vallez. He cited the occurrence of landslide in Antequera (the upstream tributary of the Abatan River located in Brgy. Bungahan), scouring of rivers in Brgy. Busao, and siltation of the Abatan River. He also mentioned that the flood in Sitio Bato of Brgy. Kimbawan can reach to a depth of 1 meter, which is confirmed by a resident from that area (see Figure 5.2). Mr. Vallez also suggested the placement of a rain gauge in Brgy. Busao. The municipal engineer, Engr. Raul Bernard A. Jabines, and the DRRMC (Disaster Risk and Reduction Management Council) head, Ms. Paz “Pai” Celades, were also introduced to the Team. On the other hand, Engr. Ricardo Fornis discussed the objectives of the project, the necessary measurements and the needed support from LGU.
Automated Water Level Sensors (AWLS) were established on specific bridges of Bohol. One is found in the Abatan River Bridge shown in Figure 5.3. The left panel is a picture of Abatan River Bridge. This is actually a temporary bridge since the concrete bridge collapsed during the earthquake. The ruin of the concrete bridge can be clearly seen in the figure. The right panel shows the AWLS installed on the bridge. This bridge may be a site for hydrologic measurements. Abatan River is also popular for its “Maribojoc Mangrove Firefly”. The sites along the Abatan River visited by Team and their coordinates are shown in Table.
5.2 Loboc River
Loboc River is situated in the municipality of Loboc. It is famous for its floating restaurants and is a popular tourist destination. Figure 5.6 shows the floating restaurants in Loboc River.
It is found that there is a rain gauge outside the Loboc Municipal Hall monitored by the Department of Agriculture as shown in Figure 5.4. A rain gauge can also be found in a bridge over the Loboc River known locally as Jumbo Bridge. An AWLS is found in the bridge as shown in Figure 5.5. It is situated near the rain gauge. Jumbo Bridge is a possible site for hydrologic measurements in Loboc River. Figure 5.6 shows floating restaurants viewed from this bridge. Rich vegetation can also be observed in the river banks.
At the upstream portion of Loboc River, in situ measurements of physical parameters as well as the depth were conducted . Depth, pH, DO and temperature were determined to be 2.35 to 3 meters, 7.45, 8.0 mg/L and 27.50C, respectively. Table 5-2 displays the geographic locations of the sites visited by the Team along the Loboc River.
Another possible site for hydrologic measurements over Loboc River is Cuenco Bridge, where there is also an AWLS (see Figure 5.9).
5.3 Matul-id River
Matul-id River passes through the municipalities of Ubay, Pilar, Alicia, Candijay and Cogtong. This river is part of the big stretch of a protected area known as the Carood Watershed. Figure 5.10 shows part of Matul-id River in Candijay, Bohol. Upon the USC Phil LiDAR 1 Team’s visit to Candijay, the project was discussed to Municipal Engrs. Rey Caadlawon, Francisimo Estepia, and Martin J Olaco.
5.4 Ipil River
Ipil River is located in the municipality of Trinidad, which is situated in the northern part of Bohol. The morphology of the river is shown in Figure 5.11. A possible site for hydrologic measurements is identified at Trinidad Bridge where an AWLS is located as shown in Figure 5.12. To assess the water quality, dissolved oxygen (DO), pH, and temperature were measured and were found to be 4.9mg/L, 6.85, and 31.4o C. Velocity measurements were also conducted, which gave about 0.21m/s. This measurement was made on a bank near the Trinidad Bridge, as can be seen in Figure 5.13.
The Team had the chance to cruise along the river. The Team also conducted DO, pH, and temperature measurements downstream and upstream. The downstream measurement results were 5.6 mg/L, 6.92, and 30.9o C, respectively. The Team found a bridge, called Tugas Bridge, upstream (coordinates 10.08960 N latitude and 124.31330 E longitude) where DO, pH, and temperature are found to be 7.5 mg/L, 6.56 and 30.40C, respectively.
5.5 Inabanga River
The headwater of Inabanga River comes from 17 municipalities, one of which is Trinidad, where Ipil River is located. Inabanga River serves as the mouth of all the rivers found in the 17 municipalities. The whole stretch of the river is about 30 km. A screenshot of Inabanga River from Google Earth is shown in Figure 5.14. A possible site for hydrologic measurements is Quezon Bridge. An AWLS is found on the bridge as shown in Figure 5.15.
1. July 29 – August 1, 2014: Phil LIDAR 1 Training at the National Engineering Center, University of the Philippines – Diliman.
2. September 15 – 19, 2014: Mentoring on Data Processing at the University of San Carlos, Cebu City
3. September 18 – 19, 2014: Mentoring on Field Validation at the University of San Carlos, Cebu City
- At the time of the writing of this report, the flow meters have just arrived.
- Data processing is not yet included in this report.
- Mentoring on flood modeling is tentatively scheduled on October 27-31, 2014.
7 Works Cited
University of San Carlos, & DENR Region VII. (2000). Socio-Economic Planning and Environmental Study of the Four Protected Areas in Cebu Island (Vol. 1). Cebu City.