Down the Tubes

Storm-drain pollution prompts the city to take action.

photo: courtesy of the Department of Environmental Services

It’s easy to forget that almost everything flowing into our storm drains goes out to our streams and ocean without any treatment. Sediment, pesticides, oil and trash enter our water, not only affecting its quality, but also the health of marine life.

To reduce this pollution (and comply with the city’s municipal storm-water permit) the city’s Department of Environmental Services has identified high-priority areas across O‘ahu where special devices and structures will be installed over the next three years.

These include catch basin filters, which look like metal baskets installed inside curb openings to capture trash and sediment and absorb oil and other pollutants before they go down the storm drain; hydrodynamic separators—large, underground structures that swirl water around so sediment and pollutants are captured; and detention basins. Detention basins are large, grassy areas that act like sponges, soaking in storm water and sediment, and trapping trash, before another drainage pipe takes the excess water out to the ocean or stream.

“We picked four drains that go out into the Waikiki coast, because the area is such an important part of our economy,” says Gerald Takayesu, head of the storm- water quality branch in the Department of Environmental Services.

The next target area is a given. “The Ala Wai has been damaged by pollutants,” says Takayesu. “We are installing measures at the beginning of the canal, where there is little circulation.” Another area of the Ala Wai, at the bottom of University Avenue, is also on the list. Finally, drainage lines that discharge to Salt Lake (Ka‘elepulu Pond), Enchanted Lake, Kuapa Pond in Hawai‘i Kai, and the Wahiawa Reservoir (Lake Wilson) are flagged for their poor circulation.

These measures aren’t a panacea. “We have more than 2,000 pipes going to streams and oceans on O‘ahu, and we are only putting these into a few dozen high-priority areas—and these devices don’t catch everything,” says Takayesu. “If everyone did their part, that would be a big help in stopping the pollutants from ever reaching the system.”