Exactly a year ago, September 2024, I wrote a column “Learning from Japan’s solution to floods,” in Palawan Daily News (PDN) which was about my experience and exposure to the Japan International Cooperation Agency’s (JICA) flood control structure built in 1998 in Ormoc City in Leyte. I worked briefly in the Department of Public Works and Highways (DPWH) 4TH Leyte Engineering District sometime in 2007.
I find this topic relevant this time, because this Japan-funded flood control project implemented almost three decades ago in my home province is still intact, durable, robust and enduring unlike the national government-funded flood control projects since 2022 until present that dominates our headlines today because some of these flood control projects are substandard, poorly implemented and collapsed easily.
Until now, the 27-year-old Ormoc flood control structure has indeed surpassed the test of time and is expected to protect and safeguard Ormocanons from catastrophic storms and floods. Besides this is the most impressive flood control project that I have seen in my entire life.
Its concrete reinforced floodwalls, dikes and levees are massive and sturdy. So massive that it safeguards nearby communities from a 50-year return period of floods.
What also impressed me was the project’s A-Type Steel Slit Dam and hydraulic drops with environmentally desirable features.
What is A-Type Steel Slit Dam? It is a three-meter steel slit which they said suited against strong colliding force and big boulders. In flood control, slit dam serves to capture destructive debris such as branches of trees and other driftwood during floods, while allowing normal sediment, sand and water to pass through unimpeded. The work of removing the deposited floating logs and maintenance of the A-Type Steel Slit structure is also easier than those of other types of steel slit because it has no cross beam.
From this project I have learned some basic concepts introduced by Japanese engineers.
I have observed that in JICA flood control project like this, rivers were widened. Widening the channel and setting the high-water level in almost the same elevation as the ground level of both banks, help safeguard the nearby community from floods of a 50-year return period.
The river channel width was also widened, and the meandering stretches in the downstream to avoid problems caused by the water level raising of meandering flood flow and the scouring of channel bed.
JICA said that their structural design was made based on the careful study on the topographical, geological and hydrological characteristic of the basin and river channel, cause of the previous flood damage, adaptable construction materials and construction method, conservation of sustainable river environment and operation and maintenance after project completion, as well as other social and economic aspects.
I have also learned that the unique feature of this flood control project in Ormoc is its application of nonstationary extreme value analysis to design flood control structures that account for the impact of climate change. This is unlike the traditional methods that assume stationary flood events.
This specialized methodology, nonstationary extreme value analysis ensures that infrastructure is built to endure and survive the increasing frequency and harshness of extreme weather events evident in the changes in rainfall patterns, urbanization and many other factors in many cities in the country.
This methodology also recognizes that the return period of an extreme weather event can change over time due to factors like urbanization and climate change. For instance, a storm that might have had a 50-year return period could now have a 15-year return period under nonstationary conditions, indicating a likelihood or probability of occurrence.
The nonstationary extreme value analysis, as an advanced statistical method treats extreme flood events as non-static meaning moving or changing, recognizing that climate change is altering rainfall patterns in the pasts.
What is the purpose? The goal I have learned is to accurately determine the design parameters for flood control structures such as the ideal height of levees and capacity of drainage systems, so that the flood control structure can manage more frequent and severe storms that previously projected.
This definitely differs from the traditional or stationary analysis, which is fixed or steady, assuming that future weather events would follow the same statistical patterns.
This approach enhances the climate resilience of flood control measures, making our infrastructure more robust against changing environmental conditions.
This is also an accurate and dynamic basis for designing and construction flood control projects, ensuring they are acceptable and enough for current and future flood risks, meaning they can withstand and endure the pressures of the natural calamity and can protect the people from hazards.
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