Flood Mitigation Using Large Diameter Krah Pipes in the Philippines
Philippines is indeed blessed with abundant resources. We are first in terms of marine biodiversity which comprises of more than 2,500 underwater species, we are third in geothermal energy coming next to US and Indonesia and third in terms of having the longest coastlines. And yet, on the other side, we are also bombarded by an average of 20 typhoons per year, five of which are fatally destructive. The geographical location of the Philippines is one of the major factors that causes flooding in its cities and communities, but it is not the only.
It is a common knowledge that there’s always two sides in every coin. Yes, climate change is something that we all have been hearing for many years now, and its publication makes it all the more real. But have we considered that on the other side, these effects are also brought to us by our own making? Architect Felino Palafox, Jr., a renowned Filipino-Catalan urban planner, opened an unresolved issue in one of his books regarding his observation on “acts of man and man’s acts of omission” that causes fatal flooding in the Philippines—the failure to plan and execute preparations for such expected hazards like typhoons.
Here’s a timeline of the most devastating typhoons in the recent history of the Philippines. I specifically, wanted to highlight a perfect example of what Ar. Palafox have mentioned about failing to plan. The first entry, Ondoy in 2009 and Ulysses in 2020 both infiltrated Manila area, particularly, Marikina City. It is a valley next to Luzon’s natural typhoon shield, the mountain ranges of Sierra Madre where in the old days, it is a lush ground for farming and marshlands. But in time, its population rises which greatly influenced the need for urbanization and suburbanization. Meaning, the old areas of natural soil are now being converted to concrete paved areas, communities and structures. Inspite of Marikina’s knowledge of their topographic situation and history of typhoons, they were still unprepared when another big typhoon hit them in 2020.
Full water cycle and half water cycle
An ideal rainfall cycle could be described as a full water cycle where the rain from the clouds will be absorbed by the soil and will be lagged as it seeps through underground back to the rivers, lakes and sea; and then up again to the clouds; but instead, we are now experiencing a half water cycle. In a half cycle, we skip the seepage through the natural soil due to concrete pavements and structures that covers the natural soil, and the water goes directly into the drainage and to the bodies of water. This phenomenon shortens the cycle of rainfall which contributed to the drastic increase of rainfall volume recorded since then up to now. According to data from Worldbank, the annual average precipitation in the Philippines has increased to 2826.17 mm in 2021 from 2529.66 mm in 2020.
Yes, there are hazards and natural risks and disasters like hurricanes from the north, typhoons from the east, earthquakes and tsunamis, and we can name more, but there are necessary preparations and risk mitigating solutions that we can do. Some countries have already been successful and now, it is our turn to follow suit.
Thus, major flood mitigation measures were established last 2021 to cater the excess runoff of heavy rains in the main cities of the Philippines. Spearheaded by the government agencies such as Department of Public Works and Higways in the National Capital Region and Region XI and together with their respective local government units, a stormwater retention tank using Krah pipes of diameters DN/ID 3000mm by 300m and DN/ID 3500mm by 2.4km length, respectively were designed to resolve flooding.
300 linear meter in 2 weeks
Last December 2022, we have completed the installation of DN/ID 3000mm pipeline along the main road of Tagum Davao Del Norte in Mindanao. The laying of the pipeline of 300 linear meter was done in a span of 2 weeks which drastically improved the duration of construction comparing to the conventional way of using concrete box culverts.
As for the Marikina city stormwater retention project, a DN/ID 3500mm pipeline is to be used at 2.4 km length from an original design of a 4m by 4m box culvert. According to the lead engineer designer of the project, the decision to shift from reinforced concrete box culvert (RCBC) to a Krah pipe is due to the significant difference of construction speed. Based on their recorded history of constructing RCBC along Boni Avenue, a 500m length of 4mx4m took them 2.5 years to finish due to the laborious process and existing heavy traffic in city areas.
But with the Krah pipe system, and they have high hopes that the construction time would be 6 months for the first phase of 600 linear meter.
Further projects with large diameters
After the success of the DN/ID 3000mm Krah pipe installation, we are now expecting similar projects that will be using large diameters such as what Marikina City has adopted since flooding problem is shared by most of the big provinces in the north and central of Luzon such as Pampanga, Nueva Ecija, Bulacan, Pangasinan and Tarlac.
Meanwhile, Cebu City in Visayas have already been planning their city’s master drainage design together with Zamboanga City in Mindanao.
Jen Lansangan,
Krah Asia, Inc.