Winds, Waves, Tides, and the Resulting Flow

Patterns and Fluxes of Water, Sediment, and

Coral Larvae off West Maui, Hawaii

By Curt D. Storlazzi and Michael E. Field

Photograph of sediment plumes off Kahana, West Maui, by E. Brown (NPS)

Open-File Report 2008-1215

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

Dirk Kempthorne, Secretary

U.S. Geological Survey

Mark Myers, Director

U.S. Geological Survey, Reston, Virginia 2008

For product and ordering information:

World Wide Web: http://www.usgs.gov/pubprod

Telephone: 1-888-ASK-USGS

For more information on the USGS—the Federal source for science about the Earth,

its natural and living resources, natural hazards, and the environment:

World Wide Web: http://www.usgs.gov

Telephone: 1-888-ASK-USGS

Suggested citation:

Storlazzi, C.D. and Field, M.E., 2008, Winds, waves, tides, and the resulting flow patterns and

fluxes of water, sediment, and coral larvae off West Maui, Hawaii: USGS Open-File Report

2008-1215, 13 p. [http://pubs.usgs.gov/of/2008/1215/].

Any use of trade, product, or firm names is for descriptive purposes only and does not imply

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual

copyright owners to reproduce any copyrighted material contained within this report.

2
Contents 

Introduction ......................................................................................................................................... 4 

Meteorology ........................................................................................................................................ 4 

Tides ..................................................................................................................................................... 5

Waves................................................................................................................................................... 6 

Nearshore Circulation ....................................................................................................................... 6 

Coastal Transport ............................................................................................................................... 9 

Summary .............................................................................................................................................. 9 

References Cited .............................................................................................................................. 11 

Additional Digital Information ........................................................................................................ 13 

Direct Contact Information ............................................................................................................. 13 

Figures 

Figure 1. Map displaying topography and bathymetry of West Maui. ...................................... 5 

Figure 2. Map displaying surface water dispersal patterns during the 2003 coral 

spawning season................................................................................................................................ 7 

Figure 3. Schematic displaying the nature of flow and water column properties 

resulting in a front .............................................................................................................................. 9 

Figure 4. Schematic diagram of the dynamics of flow and turbidity along 

West Maui.. ....................................................................................................................................... 10 

 

3
Winds, Waves, Tides, and the Resulting Flow

Patterns and Fluxes of Water, Sediment, and

Coral Larvae off West Maui, Hawaii

By Curt D. Storlazzi and Michael E. Field

U.S. Geological Survey, Pacific Science Center, Santa Cruz, CA 95060 USA

Introduction

A series of recent studies has focused on the flow patterns and particle fluxes along the

coast of West Maui, Hawaii, USA, from Honolua south to Puumana (fig. 1). From those studies a

relatively good understanding has emerged of the physical processes that influence the relative

amount of suspended sediment in nearshore waters and the circulation patterns that transport

sediment and coral larvae along the coast and between islands. This report is a synthesis of our

existing knowledge on the nature of flow and transport off West Maui.

Meteorology of West Maui and its Impact on Coastal Processes

The northeast trade winds occur throughout the year but are most consistent from AprilNovember. These winds strike the northeast side of West Maui, are steered around the West

Maui volcanic cone and most often approach the shoreline obliquely from the north in the study

area (Fletcher and others, 2002). Insolation-driven heating and nocturnal cooling of the island

cause the general trade wind speeds in the vicinity of the islands to vary from almost negligible at

night to more than 10 meters/second in the afternoon, compared to about 5 meters/second in the

open ocean (Storlazzi and others, 2006b). The wind speeds in the channels between the islands of

Maui, Molokai, and Lanai are often 50-100% faster than those observed along west Maui due to

funneling between the islands’ large volcanic cones. These relatively rapid diurnal variations in

wind speed result in a very thin (<1 meter) wind-driven oceanic surface layer. It is important to

note that this thin surface layer is trade-wind controlled, and transport in the layer can be

significantly different in rate and direction than the rest of the water column.

Precipitation patterns on West Maui result primarily from orographic uplift of air masses

driven by the northeast trade winds. Due to orographic effects associated with the high (> 1400

meters) West Maui shield volcano, most of the precipitation (100-400 centimeters/year) falls on

the northern face of the volcano while the south and southwest sides of the volcano receive less

than 40 centimeters/year on average (Fletcher and others, 2002). This causes a north-south

gradient in both stream flow and terrestrial sediment discharge along West Maui, with greater

freshwater and sediment discharge to the north (between Honolua and Kahana) relative to the

coast south of

4
FIGURE 1. Map displaying topography and bathymetry of West Maui.

Honokawai. Most of the lower portions of the streams are perennial in nature, with flow occurring

only during periods of heavy rain, typically during the winter months (Soicher and Peterson, 1996).

Tides

The tides off West Maui are of the mixed, semi-diurnal type, with a mean daily tidal range

of 0.6 meter and minimum and maximum daily tidal ranges of 0.4 meter and 1.0 meter, respectively

(Storlazzi and Jaffe, 2003, 2008; Storlazzi and others, 2004; Storlazzi and others, 2006b).

5
Waves

The wave climate off West Maui is dominated by four wave regimes: the North Pacific

swell, northeast trade-wind waves, Southern Ocean swell and Kona storm waves (Moberly and

Chamberlain, 1964). North Pacific swells are generated by strong winter (November-March)

storms as they track from west to east across the North Pacific and have significant wave

heights (Hs) ~ 3-8 meters and peak periods (Tp) ~ 10-20 seconds. The northeast trade-wind waves

occur throughout the year but are largest from April through November when the trade winds

blow the strongest; these waves have Hs ~ 1-4 meters but have very short periods (Tp ~ 5-8

seconds). The Southern swell is generated by storms in the Southern Ocean during the Southern

Hemisphere winter; while the waves are typically small (Hs ~1-2 meters), they have very long

periods (Tp ~ 14-25 seconds). Kona storm waves occur when local fronts or extratropical lows

pass through the region and are neither frequent nor consistent in their occurrence. Kona storm

waves typically have Hs ~ 3-5 meters and Tp ~ 8-12 seconds.

Additional information on waves and their influence on coral distribution has been derived

from models (Storlazzi and others, 2005). Those authors found that maximum wave conditions

were dominated by the large (8+ meters), long-period (22 seconds) North Pacific winter waves

along the north shore of West Maui. Due to refraction, some of this wave energy wraps around

the west end of the island, generating very high wave-orbital velocities at Honolua and Napili that

rapidly decrease south towards Honokawai. The rest of the west shore of Maui is in the shadow

of Molokai and is protected from these large North Pacific waves, which exhibit low wave-orbital

velocities. Trade wind waves show a similar gradient in wave energy that decreases southward

from Honolua as the coastline is increasingly sheltered by the West Maui volcano. Most of West

Maui is sheltered from Kona storm waves and Southern Ocean swell, except for small windows

south of Olowalu and to the east of Thousand Peaks. These findings were reinforced by the later

work of Vitousek and others (2007), who modeled sediment transport along West Maui between

Black Rock and Hanakao’o Point; their model results compared favorably to in situ data collected

by Storlazzi and others (2004).

Nearshore Circulation off West Maui

Until recently, the only studies investigating currents off West Maui looked at large-scale

(order of 10s of kilometers) flow through the channels between the islands of Lanai, Molokai and

Maui (Flament and Lumpkin, 1996; Sun, 1996). Using satellite data and a numerical model, Sun

(1996) observed long-term mean flow through the channels driven by differences in sea-surface

height across the island chain. Flament and Lumpkin (1996) noted that the flow in the upper water

column out in the middle of the Pailolo Channel was primarily oriented east-west at 0-1.0

meters/second (mean = 0.04 meters/second) while the flow closer to the bed was oriented

southwest-northeast, roughly parallel to the isobaths, at 0-0.5 meters/second (mean = 0.04

meters/second). Flament and Lumpkin (1996) also calculated that the majority of the current’s

energy was in the diurnal and semi-diurnal tidal frequencies.

Hatcher and others (2004) and Storlazzi and others (2006b) showed that surface flow, and

likely coral larvae dispersal, offshore Honokawai during the 2003 summer coral spawning season

6
was net alongshore to the south and offshore to the west, causing net projected transport of

surface water to be to the south and offshore (fig. 2). The meteorologic and oceanographic data

FIGURE 2. Map of GPS drifter tracks displaying surface water dispersal patterns off West Maui during the 2003

summer coral spawning season. The colors denote different periods of spawning when the drifters were released.

From both of these and previous studies (Flament and Lumpkin, 1996; Storlazzi and Jaffe, 2003)

show that flow off West Maui in the Auau, Pailolo and Kalohi Channels is primarily controlled by

the winds and tides. The general flow patterns and seawater properties show greater

consistency during the summer months when the forcing by northeast trade winds is relatively

steady, storms occur very infrequently and nearshore surface wave-induced flows are at a

minimum. During the summer coral-spawning season (June-October), both the forcing (winds

and tides) and the resulting flow and environmental patterns were relatively consistent, with

northeast-southwest oscillating tidal currents with a superimposed net flow to the southwest and

offshore. Similar forcing and response across multiple spawning periods resulted in comparable

models of projected water and coral larvae pathways during the 2003 spawning season.

Furthermore, since Hawaiian corals always spawns at the same time relative to the phase of the

moon (Kolinski and Cox, 2003), these spawning events always occur during the transition from

spring to neap tides and thus the relative magnitude of the tidal current forcing during each

spawning period is relatively consistent. These consistent patterns, along with the similar paths

that the drifters followed over multiple deployments, suggest that the temporally limited drifter

trajectories from the study period are likely a good model for initial dispersal patterns off west

Maui during the summer months when many of the Hawaiian corals spawn.

7
Studies by Storlazzi and Jaffe (2003, 2008), Storlazzi and others (2003, 2004) and Storlazzi

and Presto (2005) measured tides and currents on the inner (< 30 meters) shelf and show that the

tidal wave propagated from south to north in the study area. Similar to the findings of Flament

and Lumpkin (1996), they observed that flow over the deeper portion of the fore reef was

dominated by diurnal and semi-diurnal tidal currents, and to a lesser extent by lower frequency

motions likely driven by wind-driven differences in sea level across the island chain, as modeled

by Merrifield and others (2002), and/or the impingement of mesoscale eddies on the island chain

as shown by Firing and others (2004). Over the reef flat, however, flows were primarily wind- and

wave-driven, and they were often oriented at an angle (> 90o) to the flows concurrently measured

out over the fore reef.

The summer months are characterized by consistent northeast trade winds and small

waves, and under these conditions high-frequency internal bores are commonly observed off

Kahana, there is little net flow or turbidity over the fore reef, and net flow on the reef flat is

downwind to the southwest and turbidity is high (Storlazzi and Jaffe, 2003; 2008). When the trade

winds wane or the wind direction deviates from the dominant northeast trade wind orientation,

strong alongshore currents flow to the northeast, into the dominant trade wind direction, and

lower turbidity is observed both on the reef flat and over the fore reef. During the winter, when

large storm waves impact Kahana, strong offshore flow and high turbidity occur on the reef flat

and the fore reef. Over the course of a year, trade wind conditions resulted in the greatest net

transport of turbid water due to relatively strong currents, moderate overall turbidity, and their

frequent occurrence. Near-surface current directions over the fore reef varied on average by

more than 41o from those near the seafloor, and the orientation of the currents over the reef flat

differed on average by more than 65o from those observed over the fore reef. This shear

occurred over relatively short vertical (order~meters) and horizontal (order~100s of meters)

scales, causing material distributed throughout the water column to be transported in different

directions under constant oceanographic and meteorologic forcing.

Wave- and wind-driven flows appear to be the primary control on flow over shallower

portions of the reefs while tidal and subtidal currents dominate flow over the outer portions of the

reefs and insular shelf (Storlazzi and others, 2003; 2006a). When the direction of these flows

counter one another, which is quite common, they cause a zone of cross-shore horizontal shear

and often form a front, with turbid, lower-salinity water inshore of the front and clear, highersalinity water offshore of the front (fig. 3). It is not clear whether these zones of high shear and

fronts are the cause or the result of the location of the fore reef, but they appear to be correlated

alongshore over relatively large horizontal distances (order~kilometers). When two flows

converge or when a single flow is bathymetrically steered, eddies can be generated that, in the

absence of large ocean surface waves, tend to accumulate material. Areas of higher turbidity

and lower salinity tend to correlate with regions of poor coral health or the absence of welldeveloped reefs, suggesting that the oceanographic processes that concentrate and/or transport

nutrients, contaminants, low-salinity water or suspended sediment might strongly influence coral

reef ecosystem health and sustainability.

8
FIGURE 3. Schematic displaying the nature of flow and water column properties resulting in a front along West Maui.

Higher turbidity and submarine groundwater discharge or freshwater runoff is typically found close to shore. Along the

 relatively straight sections of coast, net wave- and wind-driven flow close to shore is downwind. Flow farther offshore

 is upwind, causing zones of high cross-shore horizontal velocity shear and often fronts.

Coastal Transport

Eversole and Fletcher (2003) and Vitousek and others (2007) studied beach sand transport

along West Maui and characterized Kaanapali as an alongshore system. Approximately 3 X 104

cubic meters of sand is driven to the north by south swell during summer months; forced by north

swell the sand returns to the south in winter months. This volume of sand can result in dramatic

beach-width changes of more than 50 meters in a few weeks. Vitousek and others (2007)

suggested that rapid changes in beach width, such as those observed in the summer of 2003, are

likely due to unusually high sea levels (15-20 centimeters above normal) resulting from a series of

mesoscale eddies that arrived over spring and summer months (Firing and others, 2004). Seasonal

beach profile changes at Kaanapali beach are pronounced.

Summary

 These studies suggest the following conceptual model of meteorologic and

oceanographic processes over the inner shelf off West Maui (fig. 4). The northeast trade winds

striking the West Maui volcanic cone cause a strong north-south gradient in precipitation along

West Maui throughout the year. This precipitation gradient, along with the large area of plowed

agricultural lands on the uplands in this area causes, on average, more freshwater and sediment

to be discharged from streams between Honolua Bay and Kahana than farther south. This stream

discharge, along with submarine groundwater discharge, causes lower salinities and higher

concentrations of fine-grained suspended sediment close to shore. Trade wind-induced currents

transport the turbid, lower-salinity water south alongshore over the shallower reef areas. These

flows appear to keep the turbid, lower-salinity water coherent alongshore, reducing dissipation

by forcing these waters against the shoreline while the wave-generated turbulence tends to keep

the fine-grained sediment in suspension, offsetting sediment settling due to gravity.

9
FIGURE 4. Schematic diagram of the dynamics of flow and turbidity along West Maui. Higher turbidity and freshwater

effluence or runoff is typically found close to shore. Net wave-driven flow close to shore is to the south in the northern

part of the study area and to the north in then southern portions of the study area, causing convergence in the region

 between Mala Wharf and Kaanapali. Flow further offshore is typically the opposite of that observed inshore, with offshore

 flow to the north in the northern portion of the study area and to the south in the southern portion of the study area.

Together, these two factors persistently create relatively high levels (order of 10’s of NTUs) of

turbidity close to shore in the Kahana region. The turbid, lower-salinity, southward-flowing

inshore jet over the shallower portions of the reefs in the northern part of the study area appears

to veer offshore between Honokawai and Kaanapali. It is not clear, however, exactly where the

offshore veering of these turbid waters occurs due to the highly variable currents measured in

this area. The flow close to shore offshore of Lahaina heads north past Mala Wharf; its fate north

of there is unknown. The region between Mala Wharf and Kaanapali appears to be a zone of

eddy formation. These eddies, along with the lack of large ocean surface waves (due to

shadowing by the surrounding islands), help to retain fine-grained sediment in this area, causing

10
persistent high turbidity (order of 10’s of NTUs) despite the absence of fluvial discharge. In 

contrast, turbid freshwater water is likely not retained in Honolua Bay during the winter when 

stream discharge is the greatest due to the rapid flushing and mixing of the bay by large North 

Pacific storm waves. 

References 

Eversole, D., Fletcher, C.H., 2003. “Longshore sediment transport rates on a reef-fronted beach: 

Field data and empirical models Kaanapali Beach, Hawaii.” Journal of Coastal Research, 

vol. 19, no. 3, p. 649–663. 

Firing, Y.L., and Merrifield, M.A., 2004. “Extreme sea level events at Hawaii: Influence of 

mesoscale eddies.” Geophysical Research Letters, vol. 31, L24306 

Flament, P. and Lumpkin, C., 1996. “Observations of currents through the Pailolo Channel: 

Implications for nutrient transport.” In: Wiltse, W. (Ed.), Algal Blooms: Progress Report on 

Scientific Research. West Maui Watershed Management Project, p. 57-64. 

Fletcher, C.H., Richmond, B.M., Grossman, E.E. and Gibbs, A.E., 2002. Atlas of Natural Hazards in 

the Hawaiian Coastal Zone. USGS Geologic Investigations Series I-2716. 

http://pubs.usgs.gov/imap/i2761/

Hatcher, G.A., Reiss, T.E., and Storlazzi, C.D., 2004. “Application of GPS drifters to track Hawaiian 

coral spawning” U.S. Geological Survey Open-File Report 2004-1309, 14 p. 

http://pubs.usgs.gov/of/2004/1309/

Kolinski, S.P., and Cox, E.F., 2003. “An update on modes and timing of gamete and planula release 

in Hawaiian Scleractinian corals with implications for conservation and management.” 

Pacific Science, vol. 57, p. 17-27 

Merrifield, M.A., Yang, L., and Luther, D.S., 2002. “Numerical simulations of a storm generated 

island-trapped wave event at the Hawaiian Islands.” Journal of Geophysical Research, 

vol. 107, no. C10, 3169, doi:10.1029/2001JC001134. 

Moberly, R.M., and Chamberlain, T., 1964. Hawaiian Beach Systems. University of Hawaii. 

Soicher, A.J., and Peterson, F.L., 1996. Assessing Terrestrial Nutrient and Sediment Discharge to 

the Coastal Waters of West Maui, Hawaii. University of Hawaii, Honolulu, Hawaii, 98 p. 

Storlazzi, C.D., and Jaffe, B.E., 2003. “Coastal Circulation and Sediment Dynamics along West 

Maui, Hawaii, PART I: Long-term measurements of currents, temperature, salinity and 

turbidity off Kahana, West Maui: 2001-2003” U.S. Geological Survey Open-File Report 03-

482, 28 p. http://pubs.usgs.gov/of/2003/of03-482/

11
Storlazzi, C.D., Logan, J.B., McManus, M.A., and McLaughlin, B.E., 2003. “Coastal Circulation and 

Sediment Dynamics along West Maui, Hawaii, PART II: Hydrographic Survey Cruises A-3-

03-HW and A-4-03-HW Report on the spatial structure of currents, temperature, salinity 

and turbidity along Western Maui” U.S. Geological Survey Open-File Report 03-430, 50 p. 

http://pubs.usgs.gov/of/2003/of03-430/

Storlazzi, C.D., Field, M.E., Ogston, A.S., Logan, J.B., Presto, M.K., and Gonzales, D.G., 2004. 

“Coastal Circulation and Sediment Dynamics along West Maui, Hawaii, PART III: Flow and 

particulate dynamics during the 2003 summer coral spawning season” U.S. Geological 

Survey Open-File Report 2004-1287, 36 p. http://pubs.usgs.gov/of/2004/1287/

Storlazzi, C.D., Field, M.E., Rogers, K., Jokiel, P.L., Brown, E., and Dykes, J.D., 2005. “A model for 

wave control on coral breakage and species distribution in the Hawaiian Islands” Coral 

Reefs, vol. 24, p. 43-55. 

Storlazzi, C.D., and Presto, M.K., 2005. “Coastal Circulation and Sediment Dynamics along West 

Maui, Hawaii, PART IV: Measurements of waves, currents, temperature, salinity and 

turbidity in Honolua Bay, Northwest Maui: 2003-2004” U.S. Geological Survey Open-File 

Report 2005-1068, 34 p. http://pubs.usgs.gov/of/2005/1068/

Storlazzi, C.D., McManus, M.A., Logan, J.B., and McLaughlin, B.E., 2006a. “Cross-shore velocity 

shear, eddies and heterogeneity in water column properties over fringing coral reefs: 

West Maui, Hawaii.” Continental Shelf Research, v. 26, p. 401-421. 

Storlazzi, C.D., Brown, E.K., and Field, M.E., 2006b. “The application of acoustic Doppler current 

profilers to measure the timing and patterns of coral larval dispersal.” Coral Reefs, vol. 25, 

p. 369-381. 

Storlazzi, C.D., and Jaffe, B.E., 2008. “The relative contribution of processes driving variability in 

flow, shear, and turbidity over a fringing coral reef: West Maui, Hawaii” Estuarine Coastal 

and Shelf Science, vol. 77, p. 549-564. 

Sun, L.C., 1996. “ The Maui algal bloom: The role of physics.” In: Wiltse, W. (Ed.), Algal Blooms: Progress 

Report on Scientific Research, West Maui Watershed Management Project, 54-57. 

Vitousek, S., Fletcher, C.H., Merrifield, M.A., Pawlak, G., and Storlazzi, C.D., 2007. “Model 

scenarios of shoreline change at Kaanapali Beach, Maui, Hawaii: Seasonal and extreme 

events.” ASCE Coastal Sediments 2007 Meeting Proceedings, vol. 2, p. 1227-1240. 

12
Additional Digital Information

For an online PDF version of this report, please see:

http:// pubs.usgs.gov/of/2008/1215/

For more information on the U.S. Geological Survey Western Region’s Coastal and Marine

Geology Team, please see:

http://walrus.wr.usgs.gov/

For more information on the U.S. Geological Survey’s Coral Reef Project,

please see:

http://coralreefs.wr.usgs.gov/

Direct Contact Information

General Project Information

Dr. Michael E. Field (Project Chief): mfield@usgs.gov

Regarding this Report:

Dr. Curt D. Storlazzi (Lead Oceanographer): cstorlazzi@usgs.gov

13