How polluted is the Ala Wai Canal?
According to one study published by the Mamala Bay Study Commission (MB-3), during an eight-hour storm in January 1995, the Ala Wai loaded as many enterococci bacteria into the bay as were discharged in the same period by Sand Island and Honolulu wastewater treatment plants combined.
Water quality in the canal is so bad, in fact, that many of the scientists who participated in the series of studies of Mamala Bay suggest the Ala Wai be treated as a “point source” of pollution — that is, like a pipe or an outfall — rather than the more diffuse “non-point source,” which is the category into which most natural streams are placed. A frequent recommendation, in fact, is that the water in the Ala Wai be disinfected before entering Mamala Bay.
All Wet
The Ala Wai is not a natural stream. Rather, it was dug in the 1920s to drain the wetlands of Waikiki and allow more intensive development of the area.
Before the canal was built, drainage from Manoa and Palolo entered the waters off Waikiki via a stream that had its mouth at the northern end of Kapi`olani Park. Charles Howard Edmonson, a scientist writing in 1928 of his research on corals off Waikiki, described the impact of Manoa Stream on the reef during times of heavy rain. “Previous to the construction of the Waikiki drainage canal (about three years ago),” Edmondson wrote, “the small stream opening near [Kapiolani Park] drained a large area extending to the upper limits of Manoa Valley. During periods of heavy rainfall, usually in the winter months, it carried immense volumes of silt-laden fresh water outward over the reef platform. At such times the turbidity of the water over the section of reef surveyed reached a high degree, a week or more being required for the water to regain normal clearness.”
Edmondson noted a correlation between siltation dumped by streams and limited coral growth. Silt “carried by fresh water has in past years been a very influential agent in controlling the distribution of corals on the section of Waikiki reef surveyed,” he observed. Still, Edmondson found near the stream mouth corals of the type “most resistant to both dilute sea water and to silt.”
(In 1925, Edmondson found 23 species, varieties, and forms of corals in his study of the reef in the area now known as Queen’s Beach. In 1995, University of Hawai`i scientists surveying the area for the Mamala Bay Study Commission reported finding just four species there. Edmonson provides an exhaustive list of corals, as well as a map indicating where they were found. The UH scientists provide neither, making difficult any effort to determine trends in coral density or species makeup over time.)
A Lost Buffer
Before the Ala Wai Canal, wetlands made up a large part of Waikiki. These served not only to absorb much of the drainage from upstream valleys, but also acted as a buffer and filter for upslope runoff. It is reasonable to think that even as Manoa, Mo`ili`ili, and Kaimuki were making the transition from rural to urban development, Waikiki wetlands continued to capture much of the soil burden in the runoff.
When the canal was dug, the wetland filter was lost. What’s more, Waikiki itself began to contribute to the runoff. Wetlands, by their very definition, soak up water. By contrast, urbanized areas, where paved surfaces and built-up lands are impervious to rainfall, deflect far more runoff into drainage than do unimproved lands. That runoff carries with it whatever happens to have fallen to the streets — petroleum products, antifreeze, and rubber from vehicles, excess pesticides and fertilizers from landscaping, trash, leaves, and the like.
Not only did Waikiki lose its natural ability to serve as a drainage basin, the areas around Manoa and Palolo streams also were developed, further diminishing the ability of the land around the streams to slow the runoff and hold back the soil carried with it. To eliminate the self-inflicted flood wounds brought about by building too near naturally flowing streams, the streams themselves were punished and forced into artificial channels.
By this point, which occurred about the same time as the construction of the Ala Wai Canal, the streams were little more than storm drains. Their ability to support native aquatic life was all but destroyed. Pollutants borne in the runoff caused by rains had a straight shot to the ocean, and as the upland areas became more and more urbanized, those pollutants became more and more abundant and complex.
Paying the Price
According to one study of sources of pollutants to Mamala Bay, the Ala Wai Canal discharges 23,350 acre-feet per year of runoff into ocean waters. This quantity is only slightly behind the volume of effluent discharged by the Honouliuli sewage treatment plant (26,884 acre-feet per year), and is third-ranked overall as a pollutant source, with the Sand Island plant in first place, with 80,651 acre-feet per year. (An acre-foot is the quantity of water needed to cover an acre of land at a depth of one foot.)
The Ala Wai acts as a settling basin of sorts, with about half of the suspended solids in the water that flows into it thought to settle out in the sediment of the canal before the water reaches the sea. Still, not all pollutants — nor even the worst ones — drop out of the soup. A study of alternative management measures for discharges to Mamala Bay (MB-10A, by Joseph O’Connor and Katherine Courtney) noted, “The small percentage of particles that are assumed to escape the existing settling basins will, in all likelihood, be the finer particles and colloidal matter that have a very high affinity for adsorbing a variety of pollutants, including metals, nutrients, pesticides, and sparingly soluble industrial chemicals.”
In any case, it is possible that measures proposed for cleaning up the Ala Wai might actually increase pollutant loading into Mamala Bay. As O’Connor and Courtney point out, “restoring water quality [to the Ala Wai] using acceptable options will not reduce pollutant loading [to the bay], and optimizing the function of the Canal as a settling basin will not help to improve water quality.”
Options?
O’Connor and Courtney briefly describe five possible approaches to cleaning up the Ala Wai. The first is to increase flushing of the canal by adding flows of either freshwater or seawater or some combination. Drawbacks to this option include the increased load of pollutants to the bay as well as possible subsidence of Waikiki, if the source of groundwater for flushing were wells in the area.
A second approach considered is “coagulation” of solids in the water, achieved by means of adding chemical flocculents — the same agents used in sewage treatment plants to enhance the coagulation of solids in raw sewage. But because of the extremely flashy nature of stream flows in Hawai`i, this approach faces “engineering obstacles,” the authors note. Also, they write, the flocculents “would have an adverse effect on aquatic biota in the Canal.”
Erecting a “salt-water barrier” is a possible third option. This approach is not well described in the study, but would involve the creation of “a one-way flow” of saltwater into the Ala Wai. “The effect,” O’Connor and Courtney write, “would be to improve water quality with the increased circulation and flushing in the canal.” Such a system has been effective in American Samoa, they note, adding: “The idea is under consideration by the Ala Wai Task Force.”
If further studies determine that the Ala Wai is a significant source of pathogens to recreational waters, disinfection of the Manoa-Palolo Stream by ultraviolet radiation might be appropriate, the authors suggest.
The fifth alternative involves placement of “artificial, constructed wetlands … that might be combined with chemical coagulation and increased flushing of the Canal.” This approach led to improved water quality in “another confined coastal system (Flax Pond, Long Island),” the authors write. If it is appropriate for the Ala Wai, “it could well lead to a substantial reduction in discharge of solids, nutrients and bacteria from the Ala Wai to Mamala Bay at the same time that it served to increase the water quality in the Canal and assisted in the restoration of beneficial uses.”
Another Committee
As a result of a lawsuit filed by the U.S. Environmental Protection Agency and the state Department of Health against the City and County of Honolulu for still more violations of the federal Clean Water Act, the city has agreed to finance a project intended to improve water quality in the Ala Wai Canal watershed.
Estimated cost of the project is $150,000. As described in a summary made available for public comment, goals of the project include making “measurable progress” in the next five years and beyond “toward meeting state water quality standards for the Canal and the streams.” A short-term goal is “to improve the aesthetic and recreational values of the waters (e.g., remove and prevent litter and dumping into and next to the waters).”
A “management coordinator” is to be selected jointly by the city and the state Department of Health. The DOH is to pay the salary with money from an escrow fund set up by the city under court order. Tasks spelled out in the agreement call for the coordinator to establish a steering committee, which is supposed to decide upon what “best management plans” (BMPs) for pollution control will be implemented and where.
The steering committee, the agreement says, “will be a focal point for a long-term, community-based, public-private program of non-point source management activities in the watershed.” Its chairman is to be the management coordinator. Members “shall consist of representatives from relevant state, city, and federal agencies, the University of Hawai`i, environmental groups, the regulated community, interested community groups, and the public.”
For more information on the Ala Wai Canal Watershed project, readers may wish to see a copy of the agreement between the city and the Department of Health. Copies are available for review at the DOH Clean Water Branch in Honolulu (919 Ala Moana Boulevard, Room 301).
Postscript
The City and County of Honolulu, together with the state Department of Transportation, are planning to dredge the Ala Wai Canal. A draft agreement calls for spending an unspecified amount of federal funds available to the state through the Intermodal Surface Transportation Efficiency Act (ISTEA), state funds of up to $500,000, and city funds of like amount on the project.
Before the dredging occurs, it is to be preceded by an environmental impact assessment, including tests for toxicity and contaminants in the dredged spoils that might preclude their on-land disposal.
— Patricia Tummons
Volume 6, Number 6 December 1995
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