Glossary Terms
Near-shore currents along the Wai‘anae coast are influenced by local and regional oceanographic and climatic conditions. Tides, trade winds, and large-scale ocean currents, together with island mass effects, create distinct oceanographic conditions along the leeward sides of the Hawaiian Islands, including the Wai‘anae coast.
The horizontal movement of water that accompanies the rising and falling of the tide is called the tidal current. Tides are very long-period waves that move through the oceans in response to the forces exerted by the moon and sun. Tides originate in the oceans and progress toward the coastlines, where they appear as the regular rise and fall of the sea surface (National Oceanic and Atmospheric Administration [NOAA] 2004). When the highest part, or crest, of the wave reaches a particular location, high tide occurs; low tide corresponds to the lowest part of the wave, or its trough. The difference in height between the high tide and the low tide is called the tidal range.
The incoming tide along the coast is called a flood current; the outgoing tide is called an ebb current. The strongest flood and ebb currents usually occur before or near the time of the high and low tides. The weakest currents occur between the flood and ebb currents and are called slack tides.
‘Olelo No‘eau
Malolo kai e! Malolo kai e!
Tide is not high! Tide is not high!
Said of threatening disaster. Robbers once lived at a place in Wai‘anae now known as Malolo-kai. Their spies watched for travelers to kill and rob. When there were only a few that could be easily overcome, the spies cried, "Low tide!" which meant disaster for the travelers. But if there were too many to attack, the cry was, "High tide!"
– Hawaiian saying
Hawai‘i's semi-diurnal tidal cycle is characterized by two high waters and two low waters of each tidal day. Along the Wai‘anae coast, this tidal regime results in changing current patterns. During normal trade wind conditions on a rising or flood tide, current flow is from the northwest toward the southeast, parallel to the coastline, with a velocity of about 1 knot (Bienfang and Brock 1980). This current reverses during falling or ebb tide conditions, flowing from the southeast to northwest at somewhat higher velocities, about 1.5 knots.
Typical tidal cycle from Honolulu, Hawai‘i.
Source: NOAA Center for Oceanographic Products and ServicesThe mass of the Hawaiian Islands interacts with large-scale trade-wind conditions and ocean currents. This interaction causes winds and currents to slow and create calmer areas on the leeward sides of each island, known as Hawai‘i's wake. Water movement along the Wai‘anae coast is influenced by these regional oceanographic phenomena, which create eddies, or swirls of water, where marine larvae and fish tend to concentrate. The existence of a warm-water countercurrent flowing from Asia toward the Hawaiian Islands has been attributed to Hawai‘i's wake (National Aeronautics and Space Administration [NASA] 2002), resulting from the interaction between the islands and regional current and trade-wind conditions (see figure).
Bienfang, P.K., and R.E. Brock. 1980. Predevelopment Reconnaissance of the Water Quality and Macrobiota Conditions Affronting the West Beach Coastline, Oahu, Hawaii. Technical Report Submitted to Environmental Communications, Inc.
National Aeronautics and Space Administration (NASA). 2002. Hawaii's Wake. http://science.nasa.gov/headlines/y2002/10apr_hawaii.htm
National Oceanic and Atmospheric Administration (NOAA). 2004. National Tidal Datum Epoch 1983-2001 Update. National Ocean Service Center for Operational Oceanographic Products and Services. http://www.co-ops.nos.noaa.gov/datum_update.shtml
Flament, P., S. Kennan, R. Lumpkin, M. Sawyer, and E.D. Stroup. 1996. Ocean Atlas of Hawaii. Department of Oceanography, School of Ocean and Earth Science and Technology, University of Hawaii. http://radlab.soest.hawaii.edu/atlas/
Pukui, M.K. 1983. ‘Olelo No‘eau: Hawaiian Proverbs and Poetical Sayings. Bishop Museum Press. Honolulu, HI.
URS, Inc. 1973. Marine Environmental Impact Assessment Report, Kahe Point Facility, Oahu Hawaii. URS 7220-03. Prepared for the Hawaiian Electric Company, Inc. 280 pp.
