Ocular surveys of the rivers covered in the project were done during the start of the project. Other flood-prone locations were also visited during these surveys.
Banica and Ocoy Rivers
During the ocular survey conducted last December, 2014 in Negros, Banica and Ocoy rivers were also visited. These rivers were identified by local government units to be flood-prone. Weather stations such as automatic rain gauge (ARG) and water level monitoring sensors (WLMS) were already installed by DOST-7 in these rivers.
Banica River has upper tributaries in Tejero and Apulong. Tejero and Apulong are both located in the town of Valencia. The main source of water is the Casaroro Falls in Valencia. Tejero, a tributary of Banica, can be observed in Tejero Forest Camp. Locals have called this tributary as Tejero and will be referred to as such in this report. Forest Camp is a developed tourist attraction in Valencia.
Figure 3 1 is a photograph taken at the bridge in Tejero Forest Camp. A Water Level Monitoring System (WLMS) installed by DOST-7 can also be observed in the figure. A blow-up photograph of the river bed is also presented.
The photograph was taken on a sunny morning of December 18, 2014. Even with the fair weather, a turbulent flow was observed. Rocks were also observed to be deposited on both the upstream and downstream side of the bridge. The locals reported that the bridge was damaged during Typhoon Sendong because of the very turbulent and rapid flow of water carrying large rocks and boulders.
Problems on the installed WLMS in Tejero Forest Camp were reported. During the survey the team discovered that the sensor was situated right above the river bed with extreme rock deposits. During the verification of the values displayed by the sensor, a distance of approximately 4m was recorded from the sensor to the water level. Comparing this with the values displayed in the ASTI website of DOST, the values were not consistent. It turns out that the source of the inconsistency is the calibration of the level measurement. The sensor detects the protrusion of the boulders below it. Thus it appears that the water level is high even though there is no water below.
During the ocular survey, the team attempted to look for other possible locations for the WLMS. However, issues on the security and safety of the sensors arise if the sensor will be moved upstream. This leaves the current location of the sensor as the most suitable location. Changing the orientation of the sensor by turning it 90 degrees counterclockwise might solve this issue. This could avoid the part of the river bed with extreme deposits of boulders.
The other upper tributary of the Banica River is still in Tejero but is popularly called by the locals as Apulong. This will also be referred to as such in this report. Error! Reference source not found. is a photograph taken in Apulong. No WLMS was installed in the said location. Apulong can be observed to be very similar to Tejero. Large rocks were also deposited in the banks of the river. The bridge was also damaged during Typhoon Sendong.
Downstream of the Banica River in Brgy. Balugo, is the City Pound Bridge. A Water Level Monitoring Sensor of DOST was installed in this bridge. No problem was reported on the data displayed by this sensor. The water in the said location now takes into account the water flowing in Tejero and in Apulong. 4 shows the WLMS in the City Pound Bridge.
Ocoy River in Dumaguete City is another river causing noticeable damage. The team was able to conduct an ocular survey in Calabnugan – Camanjac Bridge. Damages on the bridge were observed and can be seen in 5. A WLMS was also installed in this bridge and there were no problems reported in ASTI.
Due to the damage caused by this river the team thinks that there is a need to include these two rivers in Phil-LiDAR 1. This concern was raised up to the program leader. It was then included in the rivers covered by the project but will be of least priority as they will only replace the previously eliminated Matul-id and Cauitan rivers in the list of rivers to be covered by the team.
During a separate trip last January 20-22, 2015, the other rivers of Negros Oriental were surveyed. The team divided into two. One team commenced their trip by going directly to Basay while the other conducted courtesy visit to the Governor’s office. Team 2 was accommodated by the PDRRMC Executive Officer, Mr. Adrian Sedillo, since the Governor was not around at that time. The team acquired contacts to different city and municipal designated disaster and rescue teams to contact during the ocular visit.
During the conversation, Mr. Adrian discussed about the different river systems that are flood-prone in Negros Oriental. We stated the river systems included on our project but he recommended other river systems should be incorporated to our project due to the disasters caused by flooding. He cited that some of the included rivers have no record of casualties in the past years and yet was included in the scope. He mentioned the rivers in Jimalalud, Tayasan, Sta. Catalina, and Dumaguete City is worth including on our project coverage.
One of the local rescue responder showed us where the previous flood level and it was approximately 3.5 meters above the river bed. The flood plain extended to the banana plantation beyond the right bank (see Figure 3-7). This portion of the river will be selected as the location for data acquisition and extreme events for the reason that the local responders live on the river bank and it would be easy for them to react during extreme events.
Figure 3-8 presents a photograph of the chosen study area in Libertad river. The photo was taken while facing downstream.
Tanjay River was recently flooded during the Typhoon Sendong hit the country. The water level rose up just below the roof of the Novallas Elementary School as can be seen in Figure 3-9.
This location is suitable for doing flow measurements since the location is far from the convergence of fresh water and seawater. There are also many local people who can work with us during extreme events living near the river banks. The team did not go further upstream because of mobile networks scarcity. It would be difficult for the team to communicate with the local hire during extreme events and for safety purposes.
This river also suffered flooding when Typhoon Lawin ravaged the country. The flood level extended to the nearby houses located approximately 150 meters from the river channel and is about 2.5 meters elevation from the river bed. This location would a suitable spot for data acquisition and extreme events measurement since there are local people who are settling near the river banks and can be hired for data acquisition.
Siaton River was also damaged by the Typhoon Lawin on September 25, 2012. The river changed its course due to small islets that were obstructing the path of the river. The original river banks were damaged and the width of the river expanded since the rage of the water scoured the banks. This location is our prospect on doing the flow data measurements and for extreme event data gathering because there are local residents dwelling near the river banks making it easy for them during extreme events to collect data
Establishment of ground location for data gathering was not achieved due to the difficulty of terrain since the rented vehicle has low ground clearance and cannot maneuver over the road moving toward the prospect location on the map. The team decided to only do measurements on the bridge that was accessible to the vehicle. The width of the river was 138 meters and its water level clearance from the bottom of the bridge was 9 meters. The bridge has an installed Automated Water Level Sensor (AWLS). Final location of study area is presented in the next sections.
Coordination with the local government unit was first done by the team. The field survey was done with the assistance of Mr. Ricky Subito. Discussion of the purpose of the visit and ocular survey were done in the Mayor’s Office with Mr. Jay Oliver Abing.
The team then went to the Tiabanan Bridge found at the coastal part of Basa, Negros Oriental. People residing near the mouth of the river are the ones greatly affected during flooding events. Determination of suitable locations for flow measurement was done afterwards. The proposed study area is located in Brgy. Bungalunan, Sitio Sandig, Basay and right before the small dam. The river at that location is approximately 60m wide and 1m deep at the lowest point during normal flow. This would be the most probable site that we would get our flow velocity data.
Bayawan River is located at the City of Bayawan. The location at Sitio Mantapi, Barangay Nangca is the place we propose to conduct measurements. The place is not affected by the tides, has GSM signal, and above the residential area. The width is 45m and 1.3m in depth at the lowest point during normal flow. However, the river at this point has no bridge. In fact, in order to cross the river, the residents make a make-shift hand railing using ropes tied to both sides of the river. Bamboo rafts are also used as means of transportation in going down stream as can be seen in Figure 3-13.
Pagatban River is located between the Municipality of Basay and the City of Bayawan. Access to the area is either from the mouth of the river with a motorboat as a means of transportation or by a steep foot trail from Brgy. San Miguel to the river. It was inaccessible at the time of the visit due to heavy rainfall. Engr. Kenneth S. Artes, the Demographic Officer of the Bayawan City Planning Office, told us that residents along the river have been relocated to a higher and safer place. Their mandate is to leave no residents behind near the river banks. This implies that it is difficult to find local hires who can conduct the base flow and extreme event measurements. In addition to the difficult access to the area, he added that GSM signal is difficult in the area. Based on this information, Pagatban River may not be suitable for flood modeling.