This is Eileen Wray-McCann for Circle of Blue. And this is What’s Up with Water, your “need-to-know news” of the world’s water, made possible by support from people like you.

Uzbekistan authorities say that they are investigating a dam failure in the country’s eastern region. On May 1, the Sardoba dam ruptured, forcing the evacuation of 22 villages and more than 70,000 people in the Sirdaryo region. An additional 5,000 people downstream in Kazakhstan also fled their homes to escape the flood waters. Radio Free Europe/Radio Liberty reports that the dam was completed in 2017 and that authorities will investigate whether construction standards were violated.

In western Kenya, meanwhile, flooding and landslides caused by torrential rain have displaced about 100,000 people. According to Reuters news service, Kenyan authorities told communities located downstream of two dams to evacuate. They warned that unusually high water levels might cause the dams to collapse. The Kenya Meteorological Department says that wet weather could continue for several weeks. The rainy season typically ends in May.

In the United States, industries across the spectrum are looking for federal aid in response to the coronavirus pandemic. That includes the Interstate Oil and Gas Compact Commission, a consortium of 31 oil-producing states. Reuters reports that the commission has requested stimulus funding in the next aid package. The money would pay laid off fossil fuel workers to plug abandoned oil and gas wells. Roughly 3 million wells are deserted across the United States, and about 2 million remain unplugged. Unplugged wells can leak pollutants into air and groundwater. The commission says that stimulus funding would help keep oil and gas workers employed during the Covid-19 crisis and provide a service that many states cannot afford on their own.

Also in the western U.S, a federal judge froze nearly 300 oil and gas lease sales in Montana, ruling that the federal Bureau of Land Management did not adequately analyze the leases’ potential impacts on groundwater. Two environmental groups and two Montana landowners filed the lawsuit, which applies to lease sales that occurred from December 2017 to March 2018. The Bureau could still proceed with the sales after redoing its analysis.

This week, a Circle of Blue report on a study pointing to groundwater as the biggest flooding threat to Honolulu as the seas rise.

Building a wall seems like an intuitive way to protect a coastal city from rising seas. Ocean barriers date back to ancient times. But the intuitive response can be the wrong response, say experts, when the obvious threat is not the greatest threat.

Shellie Habel is a coastal geologist with the Hawaii Department of Land and Natural Resources and Hawaii Sea Grant. She’s the lead author on a study that investigated three flooding pathways in Honolulu, all of which are a consequence of rising seas. The study is the first to give a sense of how much of the city’s flooded area is due to various flooding sources both individually and in combination. The higher the sea level, the greater the likelihood that floods will come from multiple pathways simultaneously.

Habel told Circle of Blue that if the plan to prevent flooding in a city like Honolulu was simply to block the ocean, “it’s not going to work.” Water has other, less obvious ways of invading, and that stealth movement has implications for water pollution and transportation in Hawaii’s largest city. In Honolulu’s case, a sea wall would be a losing strategy against sea-level rise because a wall would not address the most serious flooding problem.

The largest source of inundation for the city’s roughly 350,000 residents is not the ocean. It’s groundwater. Habel and her colleagues found that only 2 or 3 percent of flooded area in Honolulu’s urban core is solely due to overland marine sources. That range holds for the four sea-level elevations that the study considered. Groundwater flooding, by contrast, is the predominant individual source of flooding. This happens because groundwater in the coastal region is hydrologically connected to the ocean. When the Pacific swells, so does the inland water table.
A hypothetical wall on the Honolulu waterfront would fail to prevent flooding, Habel said, because water would still bubble up from underground and back up through the storm drains, which are the third flooding pathway. These days, groundwater swamps basements and roadways in low-lying areas and seeps into underground parking garages. Habel says that a solution that only considers marine flooding will not work because 97 percent of the total area that is projected to flood will still flood from rising groundwater and storm drain backups. Places like New Orleans and cities in the Netherlands, which also have groundwater flooding problems, use pumps as part of their solution.

The study was published in the journal Scientific Reports. It began by looking at a number of flooding scenarios and estimating how often the seas would exceed the thresholds they represent. Habel did the research while working on her Ph.D. at the University of Hawaii at Manoa. The lowest threshold reflects an event that has already occurred: a king tide in 2017 that pushed water levels abnormally high. King tides are the highest tides of the year and are seen as a sort of preview of the sea levels in store as the climate changes. The other three thresholds — called minor, moderate, and major — were based on a federal government data set.

As the sea level increases, so does the area of land that is flooded by water from all three pathways simultaneously — from ocean, groundwater, and storm drain backups. And that increase in flooded area rises substantially. It goes from 18 percent of the flooded land at the king tide threshold to 55 percent when sea levels reach the major flood threshold.

Kristina Hill is a professor at the University of California, Berkeley, who works on flooding and urban design. She said that the study is valuable because it attributes how much flooding comes from each pathway, and, she said, the amount that is linked to groundwater should be an eye-opener. Inspired by previous flooding studies in Honolulu and elsewhere, Hill is directing research in the San Francisco Bay Area on the connections between rising seas and rising groundwater. As in Honolulu, Hill has found that groundwater-related flooding in the Bay Area is an overlooked risk. It’s a region with shallow water tables, urban developments built on former wetlands, and rising waters. The areas in Honolulu that are among the most vulnerable to flooding are also those that are built on former wetlands that were filled in with dredged material.

Higher water is more than a nuisance. It causes real damage that increases the higher the waters rise. Besides flooding thresholds, the study also assessed current and future flooding threats to roadways, storm drains, and sewage ponds in Honolulu. Buildings and property are also at risk but were not a part of this research. More significantly, the study points to potential increases in water pollution.

In Hawaii, cesspools are frequently used as a means of sewage disposal. Cesspools are pits or wells that hold kitchen and bathroom wastewater from a house or business. To function properly, a cesspool needs several feet of unsaturated ground between its bottom and the water table, where microbes in the soil can process the waste. Rising seas and rising water tables eliminate this unsaturated space. Because they are underground, cesspools are among the lowest elevation infrastructure in Honolulu, and therefore at the highest risk for sea-level rise disruption.

Habel found that nearly 90 percent of roughly 700 cesspools in the study area would cease to work when the Pacific reaches the level of the 2017 king tide. In that scenario, 11 of the cesspools would be fully flooded. Cesspools are a known hazard, polluting rivers and marine waters with fecal waste. The U.S. Environmental Protection Agency required all large-capacity units in Hawaii to be shut down by 2005. These mostly served businesses and apartments. However, there are an estimated 88,000 cesspools in Hawaii still in use, mostly for households. In 2017, the state legislature passed a bill that requires owners to upgrade their cesspools to septic tanks or connect to a sewer system by 2050.

And that’s What’s Up With Water from Circle of Blue, which relies on your support for independent water news and analysis. Please visit and make a difference through your tax-deductible donation.