On July 2nd the Hilo Bay Watershed Advisory Group presented a lecture and forum hosted by the U.S. Army Corps of Engineers (USACE).  Project team members for the U.S. Army Corps of Engineers were Tom Smith, Jessica Podoski, Ray Chapman, and Project Manager Milton Yoshimoto.  Dr. Tracy Weigner of University of Hawaii at Hilo’s Marine Science Department also spoke about a study she and graduate student Lucas Mead did on the food web and overall water quality of Hilo Bay and the Wailuku, and Wailoa rivers.  The lecture began with Smith summarizing USACE’s Hilo Bay Water Quality and Circulation Study.  According to Smith, the objective of the study was to investigate the flow of the current breakwater and modern breakwater alternatives and the wave height caused by the current and alternative breakwater structures. These alternatives include a version with pieces of the breakwater taken it out at equal spacing and one with pieces taken out at equal intervals, but with interferences placed a little ways away from the holes.

Podoski then discussed the models they used to predict water circulation and wave movement, which she first did by showing a model of water circulation for the whole Hawaiian Islands and then Hilo Bay.  These models were based on a grid, which showed wave and water circulation becoming smaller and smaller as they became closer to a particular location.  Hilo Bay was tested via these models for one month using the different alternative breakwater structures and the current structure and then the data was compared.

Weigner presented her study’s data and conclusions from Hilo’s water sources.  She and Mead studied eight sites in the Hilo Bay and the Wailoa and Wailuku rivers.  They studied many water quality parameters including temperature, salinity, conductivity, pH  levels, oxygen saturation, turbidity, and light penetration.  When they tested the sites during dry or storm conditions the Wailuku river had a higher level of turbidity than the Wailoa river.  None of these sites ever exceeded Department of Health (DOH) standards for turbidity.  Nitrate levels, though, did exceed DOH standards under conditions of storms and dry weather in the Wailoa river and at some point all the sites went above DOH standards.  The sites also exceeded DOH chlorophyll A levels with the river mouth of the Wailoa having the highest.  Chlorophyll A appeared to be highest during dry summer conditions.  These observations seemed to come with the pattern of rivers increasing in their turbidity levels during storms and then increasing in nitrate levels after storms.  Weigner and Mead’s study was funded by the Hawaii County Department of Public Works, NSFEPSCoR Program, NSF REU Program, and NSF Kealoha Program.

Further lecturing on USACE’s study was conducted.  They concluded that all potential changes to the breakwater would improve flow of sediment in the waters between the Wailoa and Wailuku rivers compared to the present rate of flow.  The current flushing (removal of sediment by water circulation and wave action) time for Hilo Bay is about fourteen days.  All of these alternatives will increase wave heights in the Federal Navigation Channel and varied in the estimated costs for making the changes.

An audience discussion followed.  One audience member, who grew up in Hilo and swam in Hilo Bay frequently, commented that removing the breakwater would eliminate Hilo Town and the black sand beaches.  Other questions included those about bacteria in these water sources and if there was potential that the wave height would increase enough for surfing in some beach areas (this was answered, yes).  The lecturers responded to questions regarding the study that the USACE study is ongoing, no project for changing the breakwall is planned, and the current draft report will come out in October for public viewing.  Weigner added in her response to a question on nitrite levels by saying that she would like to do future research on nitrate, but there is no funding for it right now.  Thanks to Tara Anderson for submitting this report.