River unfold

Anyone of us here often pass by the Cagayan de Oro River. Its still and majestic look quite gets our attention especially when we’re stuck in the middle of the busiest bridges during peak hours in the city.

But this seem to be still looking majestic river have once covered and enveloped the city in quagmire of disaster which claimed thousands of lives. And yes, I’m talking about Typhoon Sendong who battered the city in 2011.

That fateful day of December 17, 2011, a staggering 180mm of rain had fallen in the vicinity of Cagayan de Oro. Added up by the huge dump of water coming from Bukidnon had hastily made the river water rose from its normal level to almost five meters and higher in some areas. The ginormous amount of water overwhelmed the river which paved way to a very destructive flash floods.

A few years after the horrendous typhoon, experts have started to study the river system of CDO. A preliminary depth profiling of Cagayan de Oro River was started. It was headed by Dr. Edgar Alan Po from Xavier University College of Agriculture and was financed by Mr. Elpie Paras. The objective which concerns the general public is the creation of a 3-dimensional model of the river depth as well as the calculation of the areal coverage of the flooded area in the past typhoon Sendong. This was then followed by the creation of the aerial flood scenarios which will show the flood aerial coverage in some sections of the river in case of a continuous heavy rain.

Looking into the methodology

The study area was conducted along a segment of CDO River, from the junction of Bubonawan to the river delta in Brgy. Bonbon. The team was composed of two guides, a Global Positioning System (GPS) equipment handler, an operator of the echo sounder device, an overall support staff and a documenter.

A device called Trimble ProXRS (Trimble Navigation Ltd., Sunnyvale, California) was used as roving unit to determine the elevation data in the surface of the river.

To create an aerial flood scenarios, the researchers utilized the Digital Elevation Model (DEM) generated from ASTER GDEM (Advanced Spaceborne Thermal Emission and Reflection Radiometer- Global Digital Elevation Model; PhilGIS, 2012). The result generated by the device facilitate the development of sample flooded area estimation if CDO River rose up, from above normal level of 2-6 meters.

Delineating the location of the river from the surrounding landscape was needed to be able to generate a 3D representation of the river depth. Satellite image in 2m spatial resolution taken from JAXA ALOS satellite map image last Dec. 21, 2011 was used. By the use of the image a digitized and stored area of the river in polygon shapefile was created to trace the visible river edge.

Significant results and observations

A noticeable increase/decrease of sediment load was observed overtime. This would then call on the need to implement a dredging operation or river conservation program. This action can help in the mitigation of the impeding erosion and deposition of certain solid matter in the river which can affect its depth.

It has also been found in the study area that 78% of the river is less than two meters deep. Only a small portion which comprises 2.66% of the river area is more than five meters deep. These deep portions are mostly located from Bubonawan to Cagayan de Oro River junction to Pelaez Bridge.

The project’s contribution to CDO’s resiliency

“As the study at is lang siya it can’t help, the only thing it can do is to provide information for future intervention to be conducted”, Dr. Po said. This project would really make essential changes if it will be applied on the government precautionary measures against disasters. But as of the moment no government office had reached out the team to ask for the essential results.

“If you look at the results, you already know where the deep areas are, and the shallow areas are” Dr. Po pointed out. “So if the government wanted to mitigate disasters in the future by conducting dredging, then they already know where to go” he added. Dr. Po is certain that if the government would just reach out to them, they can give helpful information basing on the results of their study. He also believe that they are one of the pioneering researchers who made such study on the CDO river system.

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If asked on what will be the most effective way in mitigating effects of disasters, Dr. Po answered with conviction. “Ultimately nature is the one who is going to determine that!” He clarified that all of these precautionary measures against flood disasters like dredging and building of dikes are just based on assumptions. “If nature for some reasons decides to bring a larger flood than usual then the dike might just not be effective at all” Dr. Po exclaimed.