“If it will not take place up-stream, the areas downstream will suffer,” Siringan stressed. Long shore sediment drift affects the river mouth’s discharge flow, worsening flooding and sedimentation.
The city’s official website lists sixty three of the city’s 80 barangays as urban and 17 rural. It further lists that geomorphologically, Cagayan de Oro has three broad landforms: lowlands, level up-lands, and hills/mountains.
The lowlands consists of sandbars, tidal flats found mainly between the mouths of Cagayan river and Iponan river, a narrow strip of level area described as a coastal alluvial plain from Puerto in the southeast to the center of the city, a broad alluvial plain in a limited patch around a small hill south of the city and the main river flood plain formed the Iponan and Cagayan rivers that coalesced north of the Cagayan-Iligan highway which is most susceptible to flooding.
Its uplands consists of three distinct plateaus, the most extensive of which occupies the southeastern region; another situated west of Cagayan river along the road to Lumbia and Talakag, Bukidnon and a third is in the south-central region just north of Barangay Indahag.
Close up of landslide slumps or slips in the Iponan Watershed show the threshold for landslide occurrence in both forested and denuded areas were exceeded.
Siringan noted that floods in Cagayan de Oro have become more frequent and higher, in large part due to the 2,000 hectares of forest cover from its watershed which were converted to agriculture and other uses and never replaced. As a result, riverside areas suffer from poor water retention and contribute to the high sediment loads of rivers, constricting waterways and shallow river mouths.
Lagmay also urged the city stakeholders to conduct further research and zone flood prone areas. The team noted that rainfall data is not readily available and records are relatively recent. They urged the city to coordinate with Namria (National Mapping & Resource Information Authority) to have tide gauge stations installed to monitor the mean sea level and determine if it is getting higher or lower through time.
“Records are needed,” Siringan stressed. “We need to start recording.”
Lagmay said low-cost technology which recently became available in the market can empower city planners to do flood simulations using aerial photography with relatively inexpensive commercial digital still cameras and digital photogrammetry software in conjuction with field data, (end of Geological Assessment Report).”