Forever flooding in Metro Manila? An expert weighs in

Prominent flood control engineer Dr. Guillermo Tabios shares a harsh reality — some densely populated areas of Manila may no longer be livable.

In a wide-ranging conversation with Howie Severino triggered by recent devastating flooding, the UP professor emeritus of civil engineering explains that the low-lying metropolis could be facing unstoppable flooding.

Climate change, clogged waterways, and the lack of major infrastructure spell regular disasters for millions of residents. Unless large floodways are built to carry water to the sea, Tabios says certain residential areas need to be abandoned to avoid the certainty of worsening floods and regular evacuations and fatalities. Current flood control projects are a patchwork that hasn’t solved the problem. He calls for a new cabinet-level Department of Water Resources that will coordinate government efforts and focus on comprehensive solutions.

Tabios cites Iloilo City as an urban center that has built effective flood control systems by diverting water away from the city center.

In Metro Manila, such an approach may require tunneling from Laguna Lake to the Pacific Ocean. According to Tabios, the reclamation projects in Manila Bay only exacerbate the situation by blocking the flow of water to the sea.

HOWIE: Magandang araw, podmates! Si Howie Severino muli na nagpapaalala na nakakatalino ang mahabang attention span.

Ang paksa natin ngayon ay ang pagbabaha sa Metro Manila at marami pang bahagi ng Pilipinas.

At ang ating panauhin ay si Dr. Guillermo Tabios, isang civil engineer, flood control systems expert, at professor emeritus sa University of the Philippines. Magandang araw sa inyo, Professor Tabios.

DR. TABIOS: So magandang araw sa inyo rin, Howie.

HOWIE: Prof., wala ng baha sa kalsada, as we speak. So humupa na 'yung tubig pero kadaraan ko lang sa ibang bahagi ng Maynila, tambak pa rin ang basura. A vivid reminder kung ano 'yung pinagdaanan ng marami nating kababayan. So, Doc, as a scholar of flood control, you must be so frustrated that flooding is still a regular occurrence.

It's not like this is such a surprise for us. May mga lumang litrato ng baha sa Maynila noong colonial era pa. 2024 na ngayon. Bakit hindi natin masolusyunan ang pagbabaha?

DR. TABIOS: Well, geographically or topography-wise bale, Metro Manila is a city built on swamplands. I mean, the big part of Metro Manila 'yung low-lying areas, especially 'yung old Manila, and of course, somewhere in Sampaloc, Tondo, Binondo, you name it, Pasay, that's the floodplain or not really a floodplain but it's the delta ng Marikina River Basin or Tullahan River Basin, even parts of Valenzuela and Obando.

Those are mountains, coming from Sierra Madre and then going down. And then it ends up, like, after few kilometers, then it's a flatland siya. And when you reach a flatland, definitely that will be a, what's called a delta. You'll have a network of channels that form like a delta towards the sea.

Now you build a city on that, that's why we have esteros, 'yung mga Paco esteros, all those esteros in Manila, so it's really flood prone to begin with.

Then, you have these developments where you modify the channel network in a delta. So magtayo ka ng mga housing doon o magtayo ka ng mga daan, mawawala 'yung natural na waterways.

Kahit even the 1500s, 1600s, mayroon tayong mga swamp noon, mayroon tayong mga estero, mayroon tayong mga canal that bring out water from Marikina River Basin or Tullahan, all the way down. Wala namang tao, walang flood disaster. Now you put people, so nagkaroon ng disaster.

HOWIE: Okay, Doc. Let's just pause there and think about what you just said. So Maynila is basically part of a low-lying area of Luzon kaya talagang prone to flood din 'yan. Tapos nilagyan natin ng maraming developments at daming population dito dahil nga may strategic value rin 'yung kaniyang location.

Pero, Doc, we're not the only low-lying urban center in the world. I mean, nagbabasa kami ngayon tungkol sa kasaysayan ng flooding sa ibang bahagi ng mundo. You're very aware of the experience of Holland, low-lying din po sa Europa. At nagkaroon din sila ng devastating flooding noong 1953, the Great North Sea Flood na ang dami rin namatay. 1953 na 'yun, more than 50 years ago.

And nagkaroon sila ng whole of society approach. Gumawa sila ng mga dike, levees, boulders, kung ano-anong mga infrastructure. And now, they are considered a global leader in flood risk management.

So why can't we do the same thing? What is preventing us from managing flood risk na other societies have done that at tayo ay paulit-ulit tayo nagdudusa nang ganito?

DR. TABIOS: One of the features of tropical countries, it's really a humid, tropic country where you can get lots of rains. Typhoons in our case. We also have monsoons. We have even the inter-tropical convergence zone. And when the trade winds converge, then you have these rains and so on.

Now in Europe it's also the same. There are areas that are low-lying and in fact, in Spain or even in Rome, and then in Paris but they have big rivers along those big cities. We also have a big river, Pasig River, which is maybe, we patterned it from those European cities. But I think the big difference is that we are in a humid, tropic country. Lots of rain. So that's a big difference.

Now, when you think about flood management or flood risk management, it's so difficult to just kind of do this, do that because there are so many components as far as flood control. Structural measures and non-structural measures.

But one of the things that I've been noticing in the Philippines, we're very good in master planning. But the problem with the master planning, it's dependent on mga foreign technical assistant. That's one. So once na ginawa 'yung study, 'pag tapos na 'yun, ginawa na, and then umalis na 'yung mga foreign consultant, wala nang follow-up.

Now, if I look at flood dynamics, flood disasters, it's a very evolutionary in nature. Very dynamic because you have, of course, land use change.

When you change the land use, you'll have different pervious and impervious areas. You have mga encroachment. Kung mayroon mga land development, nawala na 'yung mga waterway that will bring water from the inland towards the rivers and then towards the sea.

And you have all kinds of modifications and even unwanted like garbage, like even in local drainage. Nawala 'yung capacity kasi napuno ng garbage. Now, how do you bring water all the way to the river and so on?

Now, the other thing with the flood control, we can always do master planning but then, 'yung investments does not come right away. I mean, there was in 2012 'yung Metro Manila Flood Master Plan. P350 billion. 'Yung P350 billion, maybe P100 billion or so 'yun ang nagawa pa. But that was 10 years ago, 15 years ago. Ang dami ng nagbago. Nagkaroon ng bago subdivision dito, nagkaroon ng mga condominium, nawala na 'yung mga waterway, nagkaroon ng dumi. So it's overtaken by that, 'yung mga change bale.

So should we keep on updating or revising our plan which is no longer master planning but really adaptive planning. You retrofit or you adapt because nagbago na 'yung river landscape or 'yung landscape, so to speak.

HOWIE: I just want to ask you specifically about Typhoon Carina kasi 'yan ang recent experience ng maraming tao. And in the wake of that disaster, ang daming mga factor nga 'yung nabanggit. 'Yung Pangulo mismo, nabanggit niya climate change, ang basura. Ang ibang tao naman, pati mga senador, sinasabi malaking factor itong reclamation project sa Manila Bay.

Ang daming nagtuturuan, pasaway kasi mga tao. Nabanggit ninyo rin 'yung basura, nabanggit n'yo rin 'yung master planning. Sabi ng iba eh wala nga master plan puro mga malilit na projects. And of course, there's the issue of deforestation at kulang sa reforestation.

How do these fit together? Ano 'yung pinakamalaking factor? Kasi given na 'yung low-lying tayo. Given na 'yan. Hindi naman puwedeng i-evacuate 'yung Metro Manila, nandiyan na 'yan. So what's the best way of adapting? Should we, for example, stop the reclamation projects?

DR. TABIOS: You know, reclamation is a different story. But when you look at flood control, definitely you have to start from the headwaters, sa uplands, watersheds, all the way down. Now, that's what we always say holistic approach to flood risk management.

Now, one of the things that really reduces the capacity of the river is 'yung sediments. So how do you control sediments? 'Pag upstream pa, mayroon ka ng mga control, maybe a forest that will minimize 'yung sediment yield from the watersheds and then gets into your river it, then shallows the river. Imagine-in mo, during Typhoon Ondoy, that area in Loyola Grand Villa, there was a Tumana Bridge doon.

And if you're aware of that, that crosses 'yung from Loyola Grand Villa or diyan sa Balara, you go down there and then you go across to San Mateo or Marikina. Tumana. That is an overflow bridge. So nakakadaan doon. On top, mayroon kang concrete, mayroon kang culvert sa bottom and then 'pag mataas ang tubig, tatapon lang doon. So hindi puwedeng dumaan du'n.

But during Ondoy. it must have been filled up mga 2 to 3 meters of sediment, over a period of mga 7 hours. So imagine-in mo 'yung that area siyempre, na-bury siya 2 to 3 meters.

But think along the river, 2 to 3 meters, nawala 'yung depth na 'yun. So it will reduce that so much capacity. So that's one. So that's why you have to have controls upstream. Now ...

HOWIE: Excuse me, excuse me, Doc. Saan naman nanggaling 'yung sediment na nagbara ng ilog? Dahil ba na walang puno sa gubat?

DR. TABIOS: That's one. Because if you have really a lot of rain, mahirap i-control 'yung sediment na mag-erode from your watersheds. Archipelagic countries, ganu'n talaga ang problema. Whether you're quarrying along the river banks and so on, but the the bulk of the sediment comes from the 'yung overland flow planes ng watersheds.

I mean not in the river but on the sides, you know. So because you just have so much rain, we were talking about humid tropic rains which are like 400-500 millimeters in one day. That's a lot of rain, if you think about it.

Anyway so you go down to the downstream. So napuno ng sediment, nawala na 'yung capacity river mo. Now, you also have some debris coming from the mountains, maybe mga log or maybe some of these na-uprooted na mga vegetation. They will also contribute to, we call it a rate roughness or friction bale because you have this mga roughness element and so on.

So those are things. Now if you think about those kinds of rains na na-experience natin, Ondoy, Carina, Ulysses, 'yung Habagat or 'yung sudden onset na mga typhoons or storms, it's just so much rain that you are experiencing bale. So it's not quite easy to control that as far as all. So that's the problem. You can't do this.

But one of the things that I've noticed na, I mean in the Philippines and that's where we don't really have a dedicated body to look at this flood risk management or flood planning or adaptive planning for flood control on a daily basis or when I say daily, it's like maybe you do a study every day but good for the next three months or six months. Because a year ago, ito na nga ang nangyari.

And if you look at Metro Manila, you have different sub-basins where you have Marikina, Tullahan, Valenzuela, nandu'n sa Zapote, Bacoor, and those areas.

You have to, as an academic bale, you have to run simulation models. Different scenarios, you change the land use, what will happen? If you do this kind of a structural measure or non-structural measures, what happens? Will it work? Maybe it works here but doesn't work another place.

And then, you think in terms of floods na generating mechanism. Typhoons are so much different from Habagat.

In fact, if you look at the master plan na ginawa noong 2010, World Bank 'yung nag-fund noon, all the design flood parameters, we call it, based on a two-day rainfall. Based on 1:50, 1:100, like one shot over the next two days. But we can have multiple peaks in our floods, our rain.

And then, it can even last for five days. Like the Habagat of 2012, August, that was seven days. Ulan nang ulan. Mahina 'yung intensity pero over seven days, you have more than what you got from Ondoy or Ulysses. Same thing with Carina. You got in three days time, you got more than what fell during Ondoy over almost 24 hours. 455 [mm] 'yung Ondoy 24 hours. Carina about 600 [mm] over almost three days. Almost 65 hours. So it's a prolonged by the...

HOWIE: Nabanggit ninyo 'yung Ondoy, 'no, 2009. Maybe some of our listeners may be too young to even remember. But that was a defining disaster for many. Ang daming na-traumatize 'yung mga mulat na noon. Grabe, ang lalim ng baha noon, nakakatakot 'yung taas ng tubig, et cetera.

What should have happened after that? Sabi n'yo nga, naglabas na 'yung gobyerno ng master plan nu'ng 2010. One year later, may nag-improve ba mula nu'ng Ondoy nu'ng 2009? That was 15 years ago. You would think, may mga plano na in place to prevent a Carina from causing the same kind of disaster.

DR. TABIOS: Yeah. So they were running the models to look at the performance of mga different flood component, flood control component here and there, structural, non-structural, based on a two-day, 50-year or 100-year, because Ondoy was about 80-year return period of flood.

So you have over two days, mayroong peak na ganu'n. Tapos. But Carina or Habagat 2012, it's a prolonged multi-peak, although mas mababa 'yung intensity. So that's a different scenario as far as flood dynamics is concerned.

I want to mention during the time 2009, a week after that, from October 2 to October 10, there was a Typhoon Pepeng in Agno River Basin in Pangasinan. That one is a single peak typhoon. Every time, kaya lang tatlong beses dumaan doon. Pumasok siya, lumabas. Pagkatapos, pumasok ulit, lumabas. Pumasok ulit, third time, doon ang pinakaraming rainfall. But during the time, the affected na big flood structure, 'yung San Roque Dam, napuno 'yun.

So on October 9, that was after five days, they have to release 5,000 cubic meters [of water] per second. That's like maybe 21 to 22 meters high sa Santo Niño na amount of flow. Pero doon binaha 'yung Carmen Rosales hanggang second floor ng SM Rosales during the time.

So that was not Habagat, but it's three times pabalik-balik. So that's the difference. That's what you call Fujiwara effect na during that time, mayroon typhoon dito. A litle bit in Taiwan, mayroon typhoon. Hindi siya makapasok doon. Hindi siya makapunta roon 'yung Pepeng kaya pabalik-balik siya sa Pangasinan.

We can have a similar situation in Metro Manila like that. It could be like a multi-peak typhoon over a span of four, five days. We haven't experienced that but that's another scenario na 'pag nangyari 'yun, delikado. Parang magkaroon ka ng Ondoy three times. That's a possibility sa atin.

HOWIE: Yeah, so Doc, is there a way of preventing flooding then? Parang lumalabas inevitable halos, e. These are acts of nature, 'no? Obviously. So is there something we can do to prevent this kind of suffering of people?

DR. TABIOS: Yeah, in flood studies bale, what we do is really, if you have a sort of what we call a digital twin, like a mathematical model of the entire Metro Manila, you can run scenarios. Different typhoon, multiple peak typhoons, Habagat, et cetera.

And then look at what you do in Marikina, what you do in Pasay, what you do in Tullahan. All these together. You look at all the possible scenarios as far as the weather. You look at the possible scenarios as far as nagkaroon ng land use na ganito or maybe these kinds of sediment na nagbago 'yung river landscape mo, maybe nagkaroon ng debris, and then look at the performance.

But you can always do all kinds of simulations and then, look at the possible solutions and assess the performance of these different solutions because you're looking at a very complex, very big... If you look at flood problem, it's what we call a wicked problem. It's a highly non-linear, large scale, complex, unpredictable, uncertain, and you name it.

I'll give you an analogy, very simple maybe. You look at the traffic problem in let's just talk about Quezon City area, bounded by EDSA, and then, you have this Ortigas doon sa side na 'yun, and then C5, and then maybe somewhere in Commonwealth.

So the C5, I mean, this area, this quadrangle na 'to, marami kang mga pumapasok, lumalabas na vehicles. Tapos mayroon ng mga mall na parang magpa-parking 'yan, parang mga reservoir 'yan, pagkatapos 'yung pinaka-waterway mo, 'yung mga road network.

Some roads will be small, some become big, and then you have these mga vehicle tumatakbo na mayroon mga driver na behavior na paganito, paganyan, paganyan-ganyan. And you look at the traffic flow and then, you have this MMDA 'yung mga traffic enforcer. Stop dito, go doon, pero the traffic enforcer in Katipunan does not know the traffic enforcer dito sa Commonwealth, sa C5 Commonwealth. They don't coordinate. They don't talk to each other.

Basta stop, go, and so on. As far as their eyes can see, Stop. As far as they can see is Go. It's really a lot of chaos, 'di ba? We see it like that. And the road network is just like the intricate network of the roads. It's just an intricate network of flood channels.

If you look at the city of... even Quezon City, the waterways from San Juan and so on, Araneta, galing dito sa Marikina, galing doon, 'pag mag-meet sila sa Pandacan, parang ganoon lang 'yun. Now, you think about a reservoir, you can store water like a detention pond, like a parking lot, papasok 'yung mga vehicle, and then at certain time, lalabas na naman sila, maybe it's rush hour, lalabas sila lahat. These are very intricate.

If you look at the discrete particles tumatakbo, the difference of water is just continuum na materials. But it's as complex, as uncertain, as a large-scale wicked problem as that.

HOWIE: Okay. So if you were to recommend a infrastructure solution, what would it be?

DR. TABIOS: It depends where you are. Parati lang pinapag-usapan 'yung sa reclamation. They always make the terminology na if you have this water coming from doon na sa Roxas Boulevard. So if you have the sea right away along Roxas Boulevard, maybe that was way back in the 60s, wala pa 'yung reclamation sa SM MOA and CCP, wala pa 'yun, 'yung tubig, 'pag tumalon doon sa Roxas Boulevard, there's a very wide river that gets to Manila Bay. So nakatalon na agad.

Now you reclaim. Nagkaroon ka ng reclamation. So in a flatland, it takes more time and farther away from the sea para tatakbo 'yung tubig. So magkaroon sila mga waterway this way. Parang mga finger of channels.

But some reclamations don't do it that way. If you go to Florida, if you go to even San Francisco or San Jose, mayroon mga reclamation doon. Ang reclamation nila, kung ito 'yung coast i-reclaim na dito na area pero dito na part channel pa rin. Pagkatapos to go across that, mayroon mga bridge. So 'yung main channel mo, ay 'yung pinaka-waterway mo, connects the reclaimed area, which is an island, to the mainland.

Do we do that? We don't do that, 'di ba? If you go to Holland, it's the same thing. Some of those. You go to 'yung kay Donald Trump na Mar-a-Lago, ganu'n 'yun. Nakausli kaya in between, tatakbo 'yung tubig. Walang problema because it goes to the sea.

HOWIE: Yes, sa madaling salita, Doc, the way the Manila Bay reclamation is being done will worsen flooding sa palagay ninyo?

DR. TABIOS: Yes. Because 'yun ang sinabi ni [DENR Secretary Maria Antonia Yulo] Loyzaga during the hearing. Kasi nga kinut mo na 'yung natural waterway na it's an open, big, big, wide Roxas Boulevard. Pero kung lagyan mo ng kanal doon, mag-bridge ka papunta sa kabilang side, parang hindi ganu'n 'yung reclamation mo, it will not impact, adversely impact 'yung pag-discharge ng tubig from the inland to the sea.

HOWIE: Dapat ang design ng project may daanan 'yung Pasig River.

DR. TABIOS: May daanan 'yun paano. It could be like an island.

HOWIE: Doon sa gitna ng reclaimed area.

DR. TABIOS: Oo, makaroon naman ng island doon. At 'yung reclaimed area is an island. Tapos meron mga bridge. You look at some areas sa Louisiana, sa Florida, ganu'n ang pag-reclaim nila. Naiwan doon sa gitna, pagkatapos nakalabas papunta ng sea.

So in other words, ito 'yung Roxas Boulevard, dito mayroon kang reclamation. Sa gitna, open 'yun na canal towards the sea. About a year ago, I think, there was flooding in Roxas [Boulevard] after they built 'yung whatever 'yung dolomite na beach. Tapos mayroon daw problema 'yung pumping and so on. Kasi nga, na-reclaim mo na 'yung area na 'yun, pero dapat nilagyan mo ng waterway in between. Parang cut-off channel all the way to the sea. So walang problema kung na ganu'n.

HOWIE: So bakit nga hindi kinonsider 'yun, e, matagal na 'yung problema natin ng pagbabaha?

DR. TABIOS: If I were to think about flood control, those are things that if you run a digital twin nu'ng area na 'yan, you could see the scenario. If you do this, if you do that, what happens? So walang mga ganu'n sa atin. We don't do that. We don't vet it, so to speak, kung ano 'yung mangyari sa flood dynamic.

Now, if you look at other areas, one of the things I've been advocating dito sa Marikina River, where the water coming from Sierra Madre and then going down to Marikina City all the way to Pasig River all the way to Manila, it's just so much because here are humid tropics.

So how do we control that? Can you move the water from the mountains all the way to the other side right away? Which is in the case of Kuala Lumpur, they diverted the water. This is the Klang River and Watershed. Instead of going to Kuala Lumpur, dinivert nila rito.

Sa Iloilo, we have this Jaro River or Jaro River. Dumaraan du'n 'yan sa Iloilo City. They diverted this way. They put a channel, goes right to the sea. We can do that. In fact, I've been suggesting in Cagayan de Oro, same thing. There's an area there na puwede mo i-divert. Coming from Mount Kitanglad in Bukidnon, goes down to Cagayan River, Cagayan de Oro City. Instead na pupunta sa Iponan River dito. So it will avoid the big city na wala ka na magawa kasi nandu'n na 'yan. Ang dami na talagang developments. You cannot remove that.

Now, there are schemes in Marikina River where, of course, in 1982, we built the Manggahan Floodway 'di ba, where from Marikina River, we diverted through Manggahan Floodway to be temporarily stored sa Laguna Lake.

And part of that suppose we offer on a flood control scheme is that because you have now put so much water in Laguna Lake and Napindan is a very small channel to evacuate the waters right away, mag-ano ang Parañaque spillway. Pero hindi na nagawa 'yan kasi very urban na 'yung area na 'yan.

So mayroong scheme ngayon 'yung World Bank na study in 2010. Somewhere in Muntinlupa, you dig a hole all the way down 30 meters below, a tunnel, and then 30 meters na hole na naman, parang butas 'yan to pump it out to Manila Bay. But definitely that's a very, you know, not a good idea because sediments will come in, garbage can get in, and then you have to pump it on the other side. That's very expensive.

So that's that. And then part of the World Bank plan is to put a spillway, they call it also a spillway, somewhere in Pakil, Pangil-Pakil, that area, right at the back of... If you look at the lake, merong three lobes na ganito. This is the west lobe, mayroon kang central, pagkatapos 'yung east lobe, which is somewhere here sa Jala-Jala, and then dito sa... Lagyan lang ng kuwan, all the way to Pacific Ocean. But that's Laguna Lake level, maybe it can go up mga 3-4 meters of sea level, move it almost 22 kilometers to the right side. It will hardly move the water from that point all the way 22 kilometers away.

Kaya inisip ko, somewhere in Marikina, a little bit upstream or Marikina down, put a tunnel all the way to Kaliwa River. Somewhere in Kaliwa low. That's about 25 kilometers, 26 kilometers. 'Yun mga ahead of mga... So puwedeng ganu'n sana. Isang scheme 'yun.

HOWIE: What would this be, Doc, this would be a tunnel, parang spillway din galing sa watershed heading to the Kaliwa River and then, ang exit niya Pacific na?

DR. TABIOS: It will be in Kaliwa River, Kaliwa River. Kaliwa River goes to... Agos hanggang goes to Pacific Ocean.

HOWIE: Okay. So parang diversion. Ida-divert mo 'yung floodwaters, 'yung agos ng tubig.

DR. TABIOS: Just like Jaro River, we diverted it. Or 'yung River Klang na river which is the smart tunnel, storm water and road tunnel sa Kuala Lumpur, dinivert mo lang. Pinadiretso mo instead of dadaan pa ng Marikina. Pero sa atin na case, i-divert natin 'yung other side instead of on the other sideways lang bale. Sa atin, opposite way.

HOWIE: So itong proposal, this idea to divert water to the Pacific Ocean rather than allow that same water to flood Metro Manila, pinag-uusapan ba 'yan ngayon? Ginagawa bang priority 'yung mga ganoong klaseng suggestions?

DR. TABIOS: I always thought there was a little bit of politics behind that. In 2010, when the World Bank study must have been finished, and then it was approved by the ICC yung the Infracom of NEDA, DPWH, and so on, under Secretary Singson then, 2012 'ata 'yun, wala pa 'yun sa study na 'yun.

And I was telling Secretary Babes Singson, he was DPWH [secretary] then, and the water czar. That's a good idea. So sabi niya, "Why don't you ask students to do a study?"

So I asked students to do the study but it was never really picked up seriously by the government. A lot of the flood control, especially in Metro Manila, it's like dominated by mga JICA consultant. If that's not really the idea, I hope I'm not controversial here, maybe they will not really entertain. So if you want to do that, do it to your own. But who am I to be influencing 'yung kuwan? There's a JICA office in DPWH 'di ba. So maybe that's not really going to be entertained because they were insisting na "Oh, you have the Parañaque spillway where in 2018... Imagine, 2018, 2014, or 2012, I already started talking about this one. 2018, nagkaroon sila ng another study doon sa Parañaque spillway. I know the details of that. It's about P60 billion.

And then they put dikes sa Laguna Lake, which is another mga, basta umabot ng P140 billion because you diverted water from Marikina to Laguna Lake. But you could have avoided that by spending maybe P60 or P40, P60 billion to put the tunnel that I'm talking about.

And on top of that, mayroon nga silang another tunnel from Pakil which is lake level ng Laguna all the way to Pacific Ocean. That was in the 2010 study ng World Bank. That is why I mentioned the Japanese there because it was a Japanese consulting firm who did the World Bank study.

HOWIE: So nabanggit n'yo 'yung sa Iloilo, balikan natin 'yun.

DR. TABIOS: Oo, sa Jaro River.

HOWIE: So would that be an example of a flood control project that has been effective para sa inyo?

DR. TABIOS: Definitely, yeah. It has been working. I think the Iloilo River promenade na ganu'n. Ang ganda. They were able to build mga restaurant. Maganda na kuwan. Hindi na binabaha. Maganda na bale. Imagine-in mo, kung na-divert natin, magkaroon tayo ng riverbanks diyan sa Marikina, which was I think suggested by Architect Palafox noon. Hindi na sana binabaha 'yun, 'yung riverbanks na 'yun. Hindi ba?

HOWIE: So what would need to happen sa Marikina River para hindi na magbaha?

DR. TABIOS: That's my suggestion. It was a Marikina River Basin bale. Of course, in the other areas like dito sa San Juan River that joins Pasig in somewhat sa Pandacan where we have this big parang depressed area around Rodriguez and Araneta and then, even part of 'yung Quezon Ave, hindi ba, in between that, 'yung mayroong De Los Santos Hospital doon sa may E. Rodriguez, hanggang one... nasa first floor 'ata 'yung mga binabaha roon. That's a low-lying area.

So either, you just have to abandon 'yung lower area for housing or anything, mga tindahan, tataas 'yung mga... So that's a non-structural measure. You have to remove the people there.

HOWIE: Abandon! You have to abandon low-lying areas na. Kasi parang...

DR. TABIOS: No, it's not abandon but do not use it as a housing or a shelter. Maybe parking lot or whatever para pagbaha, puwedeng umalis doon. You cannot put a hospital there. Hindi ba 'yung hospital binaha riyan that time.

HOWIE: Yes. Oo.

DR. TABIOS: What I'm saying is that those are non-structural measures. In fact, in the World Bank study again, there's about like... estimate there are priority areas, about 700,000 people, they have to be removed in those low-lying areas. CAMANAVA, diyan sa may San Juan River, some areas in Marikina, almost three-fourths of a million people you remove.

HOWIE: And this was back in 2010.

DR. TABIOS: That's 2010. Now maybe ngayon...

HOWIE: Oo, siguradong dumami na 'yung tao roon. So ang sinasabi niyo, Doc, no infrastructure project can save these low-lying areas dahil nga babaha lang nang babaha 'yan. I mean, no matter what we do, talagang hindi talaga siya fit for human habitation.

DR. TABIOS: Yes. In other words, if we keep on, if we run simulation models, again, I keep on talking about that, 'yung scenario na ganito, Carina, Ondoy, and it could happen again and again, what will be the socio economics of that? Do you still want to live there?

In the flood disaster management, you have these five or seven suits from mitigation, prevention, you have this adaptation, early warning, response recovery and so on. Ang ginagawa natin, parang response recovery lang, 'di ba? Can we prevent? Can we mitigate? Maybe walang mitigation doon so we prevent.

Now, kung baguhin natin 'yung use noon, hindi siya titira, or gusto nang tumira, mayroon bang adequate flood warning? O sige, mag-siren ka para tumakbo na sila, which is what we do in Marikina. But can you really tolerate that? Pero mayroon coping mechanism mga tao, maybe. Wala silang choice. Okay lang sa kanila na umalis uli sila. But you have the risk na mayroong ayaw umalis. Then, namatay. And all these gastos, pag-rescue and so on, is that economic? We keep on rescuing people.

HOWIE: Yes, yes. So balikan natin itong sinasabing kailangan ng tanggalin 'yung population, ano?

DR. TABIOS: Oo. Doon sa World Bank, yeah, there are areas.

HOWIE: Yeah, which areas are these? Nabanggit niyo E. Rodriguez sa Quezon City.

DR. TABIOS: Oo, that's one. There were areas in Marikina that I know na natanggal, even sa may Pasig. Somewhere near the lakeshore, that area of in Taytay, in Malabon there were some... It's in the World Bank study.

HOWIE: Yeah, so those are very densely populated areas.

So itong Iloilo na sinasabi niyo, ano 'yung ginawa roon na puwede nating tularan dito sa Luzon, dito sa Metro Manila...

DR. TABIOS: Okay.

HOWIE: ...Na ginawa nila? Sabi n'yo nga, effective 'yung ginawa nila.

DR. TABIOS: Yeah. Ito 'yung sa Iloilo, ganu'n and this like north, and then this south. Ito 'yung city. Instead of 'yung river goes this way pa sa city, they diverted here towards the southeast bale instead of going north to south. It was going down from north to southeast.

HOWIE: So basically, naghukay sila? Naghukay sila ng bagong daanan ng ilog?

DR. TABIOS: Yes. They created a Manggahan Floodway so to speak. Manggahan Floodway is a man-made channel that connected that lower Marikina around Rosario area, Circulo Verde, all the way to Laguna Lake.

HOWIE: So was the Manggahan Floodway effective? Effective ba? Kasi malaki rin 'yung ginastos doon.

DR. TABIOS: Yeah. The idea behind that is that you move the waters instead of going down to lower Marikina and Pasig sa Napindan, you temporarily store sa Laguna Lake. And then, later on...

HOWIE: Pero ang Laguna Lake din, Doc, hindi naman ganoon kalalim ang Laguna Lake.. Umaapaw rin, e.

DR. TABIOS: Ang nangyari, you transferred the problem to Laguna Lake. Kasi, like during, if you, 'yung mga town ng Santa Cruz or even parts of Bae, Los Baños, and then parts dito sa Binangonan and so on, 'pag 'yung water elevation niya, DPWH datum which is 10.4, 10.5 meters above sea level 'yung pinaka-zero niya, ganu'n.

Anyway, if you say 14 meters bale, as opposed to 11.5. 'Pag 11.5 minus 10.5, that's only 1 meter above sea level. 'Yan ang meaning nu'n. 'Pag 14 minus 10.5, that's 3.5 meters above sea level. During Ondoy, umabot ng 14. Mga 12.5 or more, babahain na 'yung mga Santa Cruz na 'yan, and so on.

Ngayon, during Ondoy, umabot ng 14. It took 90 days, a little bit over 3 months, to move the water from 14 back to mga 12. Pero you were able to put from 12 to 14 during Ondoy lang bale. Ganu'n karami 'yung ulan na 'yun. Napuno 'yung lake. And it took 9 months bago, I mean 3 months bago humupa sila na ganu'n because you diverted water du'n.

So essentially, you transferred the flood problem to them, to the Laguna towns. You did not... you were able to alleviate flooding in Pasig River along Makati or maybe along Malacañang or Pandacan, pero 'yun nag-suffer 'yung mga taga-Laguna.

HOWIE: Nilipat mo lang sa Laguna Lake, 'no?

DR. TABIOS: Nilipat mo roon.

HOWIE: So ang pinakamagandang solusyon, ilipat ang tubig sa dagat talaga?

DR. TABIOS: Sa dagat talaga. That's the reason dapat mayroong Parañaque spillway para mabilis tumakbo roon pero hindi nga nagawa.

HOWIE: Papuntang Manila Bay.

DR. TABIOS: Papuntang Manila Bay.

That's the reason we need a dedicated body to be able to do all of this, 'yung Department of Water Resources, part and parcel of that department to look at this problem every day. Hindi puwede 'yung after 5 years, after 10 years, may mangyari na malaki.

HOWIE: You mean a department? A department.

DR. TABIOS: Yeah, the Department of Water Resources. It already passed Congress third reading, being entertained by Senate na ngayon. Big part of that is to look into 'yung adaptive planning na sinasabi ko and it will have a division to have planning, operation studies, scientific support to see all these kinds of problems on a continuous basis. It cannot be like reactive lang tayo parati.

HOWIE: Hindi sapat 'yung DPWH ngayon? Kasi 'yan ang tinuturo ng marami.

DR. TABIOS: The DPWH, if you look at the flood control na ginagawa nila, first of all, along national waterways, highways. They don't really look at the local flooding. These are LGU issue. So mayroon mga subdivision, magtatayo ka, mayroon kang mga supposedly local na flood studies, what's the impact of that. Pero ginagawa ba talaga? Walang tumitingin sa kanila na ganu'n.

And then, even na lumabas na subdivision na 'yung tubig, papunta roon sa national drainage which is DPWH. Mayroon bang national drainage na adequate enough to move all the way to the rivers, to Manila Bay? Wala. And then, if you look at flood control in holistic manner, dapat tingnan mo rin sa watershed. Pero the watershed is done by the DENR.

Are they really looking at flood control? They try to look at flood control but more into landslides and things like that. Hindi talaga 'yung flood disasters. So walang coordination.

So during the Senate hearing, they were talking about coordination, collaboration. But without the digital twin I'm talking about, because flooding is a wicked problem, it's a large-scale, complex, uncertain, unpredictable and so on, kailangang vehicle to be able to see this. You draw simulation, then visualize. Anong mangyari kung gawin natin ito, gawin natin 'yan? What happens in time, in space?

For a prolonged storm, as supposed to a sudden onset storm, change in land use, change in mga behavior, garbage, and so on. All those things, to be able to see in a very big picture, holistic manner, you have that kind of digital twin. Otherwise, 'yung mga taga-DENR, 'yung mga taga-DPWH, 'yung mga LGU, hindi nila makikita 'yun.

That's what it takes to solve problem like this. And then, you have to time the investments. Investments are really parang ang hirap na makakuha ng pera. So if you are not able to do this, you're not able to do that, can you improvise? Can you retrofit?

HOWIE: You've given us a lot of food for thought now. Maraming salamat sa inyong oras.

DR. TABIOS: Okay. Thank you very much, Howie. And nice to meet you.

HOWIE: Yes. It was a great conversation. We want to thank you for educating us and we hope more of our policymakers listen to people like you, Dr. Guillermo Tabios, isang expert sa flood control systems. Maraming salamat po at mabuhay po kayo.

DR. TABIOS: Thank you very much, Howie.