Bathymetric and validation surveys are joint fieldworks with the Data Validation and Bathymetric Component (DVBC) of the University of the Philippines Diliman. Before starting with the validation and bathymetric survey control points are established on points near the river to be surveyed. A static survey is done to carry this out. This survey enables determining the coordinates and elevations of unknown points from known NAMRIA benchmarks and NAMRIA control points. Figure 3-35 is an example of the established control point in Jumbo Bridge in Loboc.
Validation points are acquired to calibrate the LiDAR DEM to obtain elevations referred from the mean sea level. The processing in ArcGIS of these data is discussed in the previous section. The points are acquired by using a dual frequency GPS mounted on vehicles. The vehicle will then run at speeds ranging from 20-30kph on any built-up surfaces or roads along the floodplain. Continuous data of elevations are obtained during the survey. The data should be gathered at a line perpendicular to the LiDAR flight lines.
Bathymetric data are acquired from the mouth of the river upto the designated study areas in each river basin. These study areas separate the floodplain and watersheds of the river basins. In other words, bathymetric data are acquired throughout the entire floodplain of the river. These data can be acquired manually or by the use of echosounder.
In parts where the depth is shallow, manual survey will be done and in the parts where it is navigable by boat, an echosounder was used. Figure 3-36 presents the set-up of the echosounder and rover used in bathymetric survey. Figure 3-37 on the other hand presents the manual bathymetric survey done on the shallow stretch of the river.
Kotkot and Mananga Rivers
Bathymetric and validation survey of Kotkot and Mananga was done during the first month of 2015. A total length of 9.1 for Mananga and 10.8 for Kotkot River was surveyed.
Loboc, Inabanga and Abatan Rivers
Loboc, Inabanga and Abatan Rivers were surveyed last June 4-13, 2015. A bathymetric survey extending to 11km was done for Loboc, 18.9km for Inabanga and 17.9km for Abatan.
Sapangdaku, Balamban and Guinabasan Rivers
Last December 7-21,2015, Sapangdaku, Balamban and Guinabasan Rivers were surveyed to obtain validation and bathymetric data. These are the remaining three rivers in Cebu that are included in the 17 priority river basins of the project. A total bathymetric length of 3.5km, 8.8km, and 3.9km were acquired for Sapangdaku, Balamban and Guinabasan, respectively.