Hathaway, C B Jr.

Maciolek, J.A.

Norton, S.E.

Parrish, J.D.

Timbol, A.S.

English

ScholarSpace at University of Hawai'i at Manoa

83STATUS OF STREAM CHANNEL MODIFICATIONIN HAWAII AND ITS EFFECTS ON NATIVE AQUATIC FAUNAJames D. Parrish, John A. Maciolek, Amadeo S. Timbol,Charles B. Hathaway, Jr. and Susan E. NortonHawaii Cooperative Fishery Research UnitUniversity of Hawaii2538 The MallHonolulu, Hawaii 95822A three-year, statewide study·was made of the occurrence andconsequences of channelization in Hawaiian streams. The 366pe~ennial streams of the State were inventoried for the firsttime, and some basic information was catalogued on their physicalcharacteristics, complete status of channel alteration, andmacrofaunaI communities. Fifteen percent of the State's streamshave channels altered in at least one of six forms. There are151 km of altered channel, 89% of which is on Oahu. Fortypercent of the modified channel length is concrete lined--theform of alteration found to be most ecologically damaging.Field measurements showed that channel alterations commonlycaused large changes in environmental parameters. Whereas theaverage pH value in natural streams was 7.2, the yearly meanmid-afternoon pH in lined channels was as high as 9.9.Conductivity and dissolved oxygen were significantly increased.The range of daily temperatures in lined channels was 17.8 -36.2oC as compared to 19.5 - 26.8 oC in natural channels. Thediel insolation cycle of exposed, artificial channels causedextreme diel change in all these environmental parameters. Thenative species tested in the laboratory had less tolerance ofhigh temperatures than exotics, and some native had upper lethaltemperature limits within the temperature range measured inchannelized streams.Twenty-five species of fish and decapod crustaceans werecollected statewide, of which only eight were native. Nativespecies were not abundant in most areas intensively surveyed;they appeared to thrive only in areas remote from development.Certain introduced species, notably poeciliid fishes, wereabundant in the most hea~ily channelized sections, whereas nativespecies were almost entirely absent.Channelization in its various forms (1) increases turbidity; (2)destroys natural substrate habitat; (3) creates wide, shallow,unnatural flows; (4) causes excessive illumination, watertemperatures, and pH levels; and (5) creates topographicaldifficulties for upstream migration. Effects (2) and (4) arebelieved to create especially serious problems for the nativemacrofauna that is benthic/demersal, cryptic, and obligatelydiadromous. As a result, present channelization practices appearto be damaging the quality of extensive stream habitat for nativespecies and contributing to their r~placement by hardy, uselessexotics.84Mitigation should include (1) minimizing channelization projects;(2) maintaining the natural length of channels; (3) maintaining(replanting) the vegetative canopy; (4) maintaihing naturalbottom material wherever possible; (5) using intermittentsections of natural bottom between minimum sections where linedchannel is unavoidable; (6) building a narrow, low-flow notchinto the bottom of flat lined channels; (7) installing minimumlength culverts in ways that will avoid downstream elevationsabove stream level (waterfalls).

Status of stream channel modification in Hawaii and its effects on native aquatic fauna

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Status of stream channel modification in Hawaii and its effects on native aquatic fauna

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