To facilitate the acquisition of discharge data during rainfall events, the cross-sectional areas of all the other rivers must be acquired. Hence, the USC PhilLiDAR1 team conducted cross-section surveys to the remaining rivers in Negros that was not yet surveyed by UPD-DVBC.
The USC Phil-LiDAR 1 Team conducted cross-section measurements on the study areas in Negros Oriental on August 17-22, 2015. Two teams were formed for simultaneous river cross-section measurements. One team, comprised of four research associates, used the total station instrument to measure distance and elevation as seen in Figure 3-38. The other team, comprised of three research associates and our Senior Science Research Specialist, used the dual-frequency GNSS receiver as seen in Figure 3-39.The team with total station instrument marked a control point prior to the measurement. The team with GNSS receiver determined the elevation of the point. NAMRIA (National Mapping and Resource Information Authority) points were used as reference to determine the elevation and the Global Positioning System (GPS) coordinates.
The rivers whose cross-sectional areas were measured include Tiabanan River in Basay, Bayawan River in Bayawan, Sicopong River in Sta. Catalina, Siaton and Canaway River in Siaton, Banica and Ocoy River in Dumaguete, Tanjay River in Tanjay and La Libertad River in La Libertad.
Sitio Sandig, Brgy. Bungalunan, Basay
The team paid a visit to the Municipality of Basay and requested for assistance to reach the study area in Tiabanan River Bridge, Sitio Sandig, Brgy. Bungalunan. A service dump truck was provided due to the very rough road going to the area. NAMRIA benchmark with station name NGE-94 is located at the mouth of Tiabanan River Bridge. The rover was set on the known point and was moved to the study area for cross- sectioning. For satisfactory signal coverage, the base was set at a higher ground as seen in Figure 3-41.
The river had strong currents due to long duration of moderate rain showers which made it difficult to cross. For safety reasons, the cross section area of the river was not determined. A control point was established for a more accessible elevation point and GPS coordinates reference.
Bayawan River in Bayawan
Sitio Mantapi, Brgy. Nangka
A NAMRIA point with station name NGE-97 is located at the mouth of Bayawan River Bridge. The rover was set on the known point as the base was set on an unknown point of higher elevation. The rover was transferred to measure the cross section of the study area.
The Bayawan River was not flooded during the site visit but the river is usually deep. Two Research Associates got on the raft with two local hires for the cross sectioning (see Figure 3-42).
A bamboo pole was dipped into the river and water level at the surface was marked simultaneously. Using a steel tape, river depth was determined by measuring the length of the bamboo pole immersed into the water. Elevation of the water surface was determined using a rover. The cross section points of the river were determined by subtracting the measured length from the water surface elevation.
Sicopong River in Sta. Catalina
The team gathered at the Municipal Hall of Sta. Catalina asking for assistance to Sicopong River. NAMRIA point with station name NGE-98 is located on Sta.Catalina-Pamplona Roadside where the base was set. Accompanied by a guide, the team hiked from the base to the selected study area. With the rover, the river was cross sectioned as presented in Figure 3-43. Because the river was shallow, the rover pole was immersed. Hiring of locals for flow data measurements will commence on the nearest next visit.
Siaton River in Siaton
Sitio Pilapil, Brgy. Caticugan
NAMRIA point with station name NGE-115 is located on Barangay Albiga roadside. With the base set on an unknown high elevation point, signal obstructions such as canopy and high terrain were eliminated. Rover was set on NAMRIA point and transferred to the study area for river cross sectioning. The rover pole was immersed due to shallow waters as presented in Figure 3-44. One day of extreme flow data were gathered by the local hires.
Canaway River in Siaton
Sitio Cambuay, Brgy. Canaway
On initial survey, the base was set on NAMRIA point with station name NGE-115 which is located on Barangay Albiga Roadside. The rover, however, received a poor signal due to high terrain and thick canopies. Moving the base to a higher unknown point while setting the rover on a NAMRIA point, eliminated the signal obstructions. Rover was transferred to the study area for river cross sectioning. With shallow waters, the rover pole was immersed as presented in Figure 3-45.
Banica River in Dumaguete
The team was assisted by one of the volunteers from the Dumaguete Rescue Team. The study area is located at Barangay Balugo specifically at Balugo Bridge. Cross-sectioning was performed using a total station. A certain point was considered zero elevation since no established NAMRIA point on the bridge. Every point within the cross section was geotagged in order to obtain the coordinates. Next day, the team returned to the site with the dual frequency to obtain the coordinates and elevation of the zero elevation point. A NAMRIA point of station name NGE-106 was referred to obtain the exact elevation of each point of the cross sectioned area.
Ocoy River in Dumaguete
The study area for Ocoy River is located at Barangay Calabnugan specifically Calabnugan-Camanjac Bridge. Ocoy River is larger compared to Banica River. Ocoy River cross sectioning method performed was same as to Banica River by using total station. A certain point was considered as zero elevation and every point of the river cross sectioning was geotagged. The downstream side of the bridge was the cross sectioned area as seen in Figure 3-46. No local hires were trained since no barangay official was available at that time.
Tanjay River in Tanjay
Sitio Odiongan, Brgy. Novallas
Since the river was cross sectioned earlier this year using a Total Station, marked points on a basketball court near the study area was left. NAMRIA point with station name NGE-86 is located on a concrete ramp East of Negros Oriental Electric Cooperative (NORECO) building. High terrain obstruction was eliminated with the base set on high elevation. Rover was set from NAMRIA point and moved to the marked points. Elevation of the four corners of a basketball court was determined as seen in Figure 14.
La Libertad River in La Libertad
Sitio Bluke 1, Brgy. Solonggon
La Libertad River was cross sectioned earlier this year using the Total Station where marked points were left in Solonggon Elementary School basketball court. NAMRIA point with station name NGE-69 is located in the Municipal of Jimalalud on top of a concrete seawall. Base was set on an unknown point located on a jetty inside Lalimar. The rover was set on the control point and moved to Sitio Bluke 1 stage where acceptable signal range was reached as seen in Figure 16. Base was transferred to the school. With base set in the school basketball court, the rover was positioned to determine the elevation of the four corners of the court.