What Lies Beneath? Questions Raised About Infrastructure Below

Quoted in Gina Mangieri's "Always Investigating" extensive coverage of the problems with underground cavities and sinkholes in Kakaako, What lies beneath? As Kakaako develops up, questions raised about infrastructure below.

This broken culvert was discovered in spring 2017 and required emergency repairs.

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Driving through Kakaako lately has meant navigating a maze of emergency road work after underground near-collapses and even sink holes have popped up in the area.

“We have so many streets,” explained Panos Prevedouros, a University of Hawaii civil and environmental engineering professor, “so many likelihoods of a potential sinkhole.”

That’s because Kakaako was once a low-lying marsh, perfect for fishponds, salt, rice, and taro, but trickier for roadways and urban development we see now.

UH experts Always Investigating spoke with say the buckling roads are giving us signs of three things to watch out for:

Age of infrastructure like underground drainage culverts;
Rising sea levels and groundwater; and
Soil problems common to coastal areas.
“We have clay and sand, things that are easy to dissolve,” said Prevedouros, “and then because we have intrusion of sea water, or perhaps pipes, storm drains, and even sewers breaking, all that has the effect of diluting the soil and creating all kinds of cavities which pose a major threat to public safety.”

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Experts agree the new structures are built to last and take all coastal-zone geographical challenges into account.

“The newer the buildings, the safer they are,” Prevedouros said. “The older buildings, they may start having problems with their foundations and they may have some tilting. Eventually they will have to have significant repairs and eventually demolition and reconstruction.”

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“One of the side benefits of the rail project is they can help us with the geo-technical investigations they have done,” Prevedouros said, “and actually they can inform the neighborhood as to the stability of the soils, because they have to do it for their own foundations. Unless you plan to put a big rail or a big road in the area, you cannot simply start poking holes. It’s simply too expensive.”

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The Flooding in Mapunapuna?

Quoted in Alexander Zane's story on KHON about the repeated flooding in Mapunapuna.

Several years ago, the city installed a duckbill drainage system to get storm water out and keep ocean water from coming in.

But according to Panos Prevedouros, chair of the UH Manoa Dept. Of Civil and Environmental Engineering, anything more would come with a hefty price.

“Basically you’d need to have a storage system and a pump system to pump the storm water out of it. Essentially close the connection. You have to cut the cord with the ocean so the ocean never comes in,” Prevedouros explains.

As for the option of installing a pump system to get water out of the area, Panos Prevedouros says it probably won’t happen.

“I’m pretty sure that the area does not generate significant county taxes to justify a huge investment. That’s probably what the problem has been all this time. If the area was upgraded with more expensive real estate so that the county can collect more taxes than a more sophisticated solution could be put in place, so it’s a trade-off kind of thing,” Prevedouros said.

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A couple more things to add here:

Duckbills can get clogged by debris and then they remain open allowing ocean water to intrude. In all likelihood they do not work as City claims because the area flooded during king tides in July this year.

Given the relatively low property value of this area, it makes sense to provide incentives for small businesses to relocate and return this large parcel to nature. That is, treat this area as a small estuary:  The Mapunapuna pond.

In addition, Charles Hunt saw this story and contacted me with the following important perspective and information:

An added perspective that occurs to me is that such systems will become increasingly necessary, what with progressive sea-level rise, so the City will eventually have to start installing some. Mapunapuna could be an early prototype for the City to gain experience with system designs, learning which systems and consultants have “proven out” in other locales, which systems offer best cost/reliability characteristics, etc. Or – if tax-base is an overriding consideration – perhaps another locale like Waikiki or Downtown will become the first prototype.

Here’s a link to the gateway page for my report, there’s a full PDF of the report available at the page. We installed some instrumentation to record water levels and the pump on-off duty cycle and were able to tell a few stories about drainage from the watershed and how the pump-out system operated during a couple of rain storms over the year of study:

Hunt, Charles D., Jr.; De Carlo, Eric H., Water-Resources Investigations Report 99-4171: Hydrology and Water and Sediment Quality at James Campbell National Wildlife Refuge near Kahuku, Island of Oahu, Hawaii, 2000.

Hunt also suggested that a camera system can be used to monitor the operation of the duckbills.

Residents calls for emergency repairs to crumbling Hauula highway

Quoted in this news story by Allyson Blair of Hawaii News Now.

Transportation engineering expert Panos Prevedouros says that with the amount of erosion that's already occurred, the Department of Transportation should schedule emergency repairs.

"This is a site that needs immediate work right now," he said. "The holes are too close to the travel lane. At this point, they need to do some inspection with wave technology to find out if there are any cavities under the road."

[Pictures by A. Blair -- click to enlarge]

Hawaii's Coastal Highways

Sea level rise and extreme weather events can wash out portions of coastal highways.  This has happened several times on Oahu and many other locations.  With increasing population and traffic volume, the temporary loss of lanes or entire roadway cross sections becomes a major threat to public health and safety, let alone a threat to daily life and long term economy. Coastal roadway segments must be made more resilient to weather effects and reliable for operations regardless of storm surges.

As I outlined in a report that was the top story on Hawaii News Now (on Feb. 17, 2016--also see note 1) "Long-term solution for erosion along Kamehameha Highway won't come cheap", in general terms, the solution may come in three options, each one more suitable to various coastal highway segments (i.e., not one size fits all.)

1. Maintain the location of the current highway and elevated it by, say, 10 ft. This is a land protection option similar to those in low lying countries such as The Netherlands.
2. Relocate the highway several hundred feet inland and at a higher elevation.
3. Keep the highway largely as is and add jetties, lagoons and breakwaters to widen the coastline and isolate the highway from the forces of the ocean.

The first option requires no transportation work, but it has tremendous impacts by separating the community from the coast and a host of drainage issues. However, this "walling" option may be necessary for the effective protection of property and lives along specific sections, and at locations were current and other ocean forces make the deployment of option 3 impractical.

The second option attempts to develop a new highway in mostly agricultural, Hawaiian homestead or pristine nature areas, all of which are likely to generate insurmountable community and environmental impacts. However, there may be short segments where this option is economical and the impacts are small or moderate. For example a re-alignment of Kam. Hwy. away from Turtle Bay has been outlined in Hawaii DOT plans. Also for this option, the highway may be elevated which minimizes the disruption to lands underneath but it increases costs and reduces accessibility. Low height elevated segments may be necessary for wetland protection.

The third option, jetties and artificial ponds, is the most attractive because it protects the highway and communities, substantially reduces beach erosion and at some places adds beach or ocean recreation space. Its downside is some destruction of marine environment but some of this may be offset by the creation of traditional Hawaiian fishponds. This option also has the potential to be combined with wave action or high/low tide power generation by devices at key locations of the ponds (i.e., tidal power plants). An approximation of the proposed ponds is the lagoons at Ko'olina pictured below.

Notes
1: Two weeks later, on February 29, 2016, another segment of the same road failed due to waves, as covered in: Contraflow to last another week as crews shore up second stretch of crumbling highway.