Can Jalaur megadam contain massive floods?

By Joseph B.A. Marzan

 

An Ilonggo engineer warned of possible risks from a megadam project in Iloilo if national and local government entities do not take action to examine the status and the conditions on which the structures under the project were built.

Engr. Edgar Mana-ay issued the warning after the flooding in Cagayan province and surrounding areas in the northeastern parts of Luzon island at the height of Typhoon Ulysses.

At that time, the National Irrigation Administration (NIA) advised several provinces that it would release water by opening the sluice gates of the Magat Dam, located in between the towns of Alfonso Lista, Ifugao and Ramon, Isabela, to prevent the water from reaching spilling levels.

Mana-ay said the same episode could happen in the Jalaur River Multipurpose Project II in Calinog, Iloilo.

Mana-ay explained to Daily Guardian on Air last Friday that what happened to Luzon was a 60-year flood, a flood that has a one-in-sixty chance of happening depending on weather conditions.

Geological experts measure the probability of flooding in years. The floods in Iloilo City caused by Typhoon Frank in 2008 was considered a 100-year flood.

Mana-ay said that flooding should not be blamed on the decision to open Magat Dam’s sluice gates because the situation would have been worse if these were not opened.

But Mana-ay said the same may happen to Iloilo province if the situation and the conditions surrounding the Jalaur River Multipurpose Project Stage II (JRMP II) are not scrutinized.

The geotechnical investigation of the environmental conditions was done by a Korean firm, Dasan Consultants, which declared the areas of the construction as safe.

He suggested that the NIA and the Iloilo provincial government should take a second look into the results of the investigation made by Dasan.

He said he already appealed to Iloilo Governor Arthur Defensor Jr. to check on the conditions of the dam with the NIA and Dasan in a Nov. 4, 2019 column published in Daily Guardian.

He likewise mentioned one previous incident with the Three Gorges Dam in China, which resulted in a 50-year flood after opening its sluice gates, causing damage to “an area bigger than Mindanao”.

“In a 60-year flood which may happen, will the reservoir be able to control the flow and absorb the water with a slow area going downstream? These must be answered by [Dasan Consultants]. Even in a 60-year flood, [Dasan] should show that Jalaur’s dam system can hold the water coming down from the fields,” Mana-ay said.

He added that Dasan and NIA should make it clear to everyone that the dams under the JRMP can hold floods.

“[Dasan] and NIA should be able to explain in layman’s terms to the public if the [JRMP system] can handle at least maybe a 40-year flood. There should be a public hearing with everyone interested that indeed the dams can mitigate flood. We need to be assured that what happened in Luzon will not happen here when a 60-year flood comes,” he added.

The engineer suggested cleaning of the waterways. Quarrying may be encouraged but in a controlled manner.

Quarrying is the removal of earth-based materials such as soil and rock for use in construction or other purposes.

“Our waterways need to be cleaned. In fact, quarrying should be encouraged but controlled. Because of mechanical weathering or chemical weathering, rocks from the land break down and go down to the water, and that makes the river levels rise. Quarrying would be one of the good solutions, but it has to be planned and controlled,” he added.

 

 

JRMP II DEVELOPMENTS

JRMP II is the second phase of the developments in the Jalaur River which passes through multiple towns in the province.

It was initiated in 1960 when President Carlos Garcia signed Republic Act No. 2651 on June 18, 1960, aiming to rehabilitate and modernize irrigation systems in Iloilo province.

Physical works under JRMP Stage I, however, started only in the 1980s.

JRMP II started in 2012, but construction on the dam started only in recent years, with full completion to be expected by 2023.

This stage of the project has three components, namely: Irrigation Development, Environmental and Watershed Management and Institutional Development.

The four main projects under this stage include the 109-meter Jalaur High Dam, the 38-meter Jalaur Afterbay Dam, the 10-meter Alibunan River Catch Dam, and the 80.74-kilometer high line canal.

The Jalaur High Dam, which is a water harvesting reservoir dam, will have the capacity to store up to 219 million cubic meters of water for irrigation, hydroelectric power, and bulk water supply.

Recently, the High Dam has had a cofferdam which is 30 meters high with an area of approximately 422.4 square meters and a 310-meter long, 5.5 meter wide horseshoe-type river tunnel, to divert the water to the project’s construction site, so it can continue with its downstream flow into the Jalaur River Basin.

The Alibunan River Catch Dam is an augmentation dam which will add irrigation water to portions of Calinog town and other neighboring municipalities.

The high line canal will be the main conveyance of the water towards the main and lateral canals going to the farm lots.

All of the dams are made through roller-compacted concrete or RCC, which are found mostly in South Korea.

The Jalaur High Dam will be the Philippines’ first concrete dam, unlike other dams in the country which were developed with earth materials such as soil or rock.

JRMP II’s spokesperson, NIA Watershed Management Head Steve Cordero, told Daily Guardian on Air last Friday that the JRMP II is at 39.43 percent of its completion as of October 2020.

Cordero said it was ahead of their 2020 target of 27.83 percent, despite the coronavirus disease 2019 (COVID-19) pandemic and a change in their project management.

He added that watershed management is also part of the project, through the Upper Jalaur-Alibunan Sub-Watershed, which is also part of the Jalaur River Basin.

Reforestation activities and forest land management are being done in this area according to Cordero, in partnership with the Department of Environment and Natural Resources (DENR), through funding by the Japan International Cooperation Agency (JICA).

Cordero said that the forest-related activities are also important to the longevity of the dams and continued watershed management.

“That is the most important part of the project, because our dam exists but there are no forests, there will be no water flowing and stored. The reforestation activities also help the longevity of our project because if there are forests planted in our watershed area, we can avoid quick erosion of the soil or what we call siltation. So if there isn’t much silt deposited in our dam, we can store more water for multipurpose use. So we definitely need this aspect of the project,” Cordero said.

Another project is the Barotac Viejo Small Reservoir Impounding Project, which is a small-scale fisheries project with the Bureau of Fisheries and Aquatic Resources (BFAR) in Barotac Viejo town.

The Small Reservoir constitutes around five percent of the total reservoir area, dedicated for livelihood programs of the indigenous peoples who will be affected by the JRMP II.