Coastal Circulation and Sediment

Dynamics in Hanalei Bay, Kaua’i, Hawaii

PART II:

Tracking Recent Fluvial Sedimentation:

Isotope Stratigraphy Obtained in Summer 2005

U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2006-1125
Coastal Circulation and Sediment

Dynamics in Hanalei Bay, Kaua’i, Hawaii

PART II:

Tracking Recent Fluvial Sedimentation;

Isotope Stratigraphy Obtained in Summer 2005

Amy E. Draut, Michael E. Field, Michael H. Bothner, Joshua B. Logan, 

Michael A. Casso, Sandra M. Baldwin, and Curt D. Storlazzi

U.S. Geological Survey, Pacific Science Center, Santa Cruz, Calif.

U.S. GEOLOGICAL SURVEY

Open-File Report 2006-1125

2006
U.S. Department of the Interior

P. Lynn Scarlett, Acting Secretary

U.S. Geological Survey

P. Patrick Leahy, Acting Director

U.S. Geological Survey, Reston, Virginia 2006

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LIST OF TABLES

TABLE 1. Locations, lengths, and dates of sediment cores collected in June

and August 2005, and river-bed grab samples collected in August

2005.

TABLE 2. Inventory of 7Be, 137Cs, and excess 210Pb at all core sites.

LIST OF FIGURES

FIGURE 1. Location map of the main eight Hawaiian Islands.

FIGURE 2. Locations of sediment-core sites in Hanalei Bay.

FIGURE 3. Water and sediment discharge from the Hanalei River.

FIGURE 4. Sedimentary facies and isotope activity at Station A in June 2005

(Core K0605-1).

FIGURE 5. Sedimentary facies and isotope activity at Station A in August 2005

(Core K0805-7).

FIGURE 6. Sedimentary facies and isotope activity at Station B in June 2005

(Core K0605-2).

FIGURE 7. Sedimentary facies and isotope activity at Station B in August 2005

(Core K0805-1).

FIGURE 8. Sedimentary facies and isotope activity at Station C in June 2005

(Core K0605-3).

FIGURE 9. Sedimentary facies and isotope activity at Station C in August 2005

(Core K0805-3).

FIGURE 10. Sedimentary facies and isotope activity at Station D in June 2005

(Core K0605-4).

FIGURE 11. Sedimentary facies and isotope activity at Station D in August 2005

(Core K0805-4).

FIGURE 12. Sedimentary facies and isotope activity at Station E in June 2005

(Core K0605-5).
FIGURE 13. Sedimentary facies and isotope activity at Station E in August 2005

(Core K0805-6).

FIGURE 14. Sedimentary facies and isotope activity at Station F in June 2005

(Core K0605-6).

FIGURE 15. Sedimentary facies and isotope activity at Station F in August 2005

(Core K0805-2).

FIGURE 16. Sedimentary facies and isotope activity at Station G in June 2005

(Core K0605-7).

FIGURE 17. Sedimentary facies and isotope activity at Station G in August 2005

(Core K0805-5).

FIGURE 18. Photographs of sediment cores from Hanalei Bay.

FIGURE 19. Photograph of mottled texture attributed to bioturbation in sandy

sediment.

FIGURE 20. Inventory of 7Be at core sites in June and August 2005.

FIGURE 21. Inventory of 137Cs at core sites in June and August 2005.

FIGURE 22. Excess 210Pb inventory at core sites in June and August 2005.

LIST OF APPENDICES

APPENDIX 1. Sediment logs for cores collected in June 2005.

APPENDIX 2. Sediment logs for cores and river-bed samples collected in

August 2005.

ADDITIONAL DIGITAL INFORMATION

This report contains material related to the following Infobank Activity ID

numbers: A-1-05-KA (for June 2005 field work; ) and S-1-05-KA (for August 2005

field work):
http://walrus.wr.usgs.gov/infobank/a/a105ka/html/a-1-05-ka.meta.html

http://walrus.wr.usgs.gov/infobank/s/s105ka/html/s-1-05-ka.meta.html

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

http://pubs.usgs.gov/of/2006/1125/

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/

CONTACT INFORMATION

General Project Information

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

Regarding this Report:

Dr. Amy E. Draut (Research Geologist): adraut@usgs.gov

REPORT REFERENCE

Draut, A. E., Field, M. E., Bothner, M. H., Logan, J. B., Casso, M. A., Baldwin, S.

M., and Storlazzi, C. D., 2006, Coastal Circulation and Sediment Dynamics in

Hanalei Bay, Kaua’i, Hawaii, Part II, Tracking Recent Fluvial Sedimentation;

Isotope Stratigraphy Obtained in Summer 2005. U.S. Geological Survey OpenFile Report 2006-1125, 52 p.
ABSTRACT

Delivery and dispersal of fluvial sediment in Hanalei Bay, Kaua’i, Hawai’i,

have important implications for the health of local coral reefs. The reef

community in Hanalei Bay represents a relatively healthy ecosystem. However,

the reefs are periodically stressed by storm waves, and increases in sediment

and dissolved substances from the Hanalei River have the potential to cause

additional stress. Increased turbidity and sedimentation on corals during Hanalei

River floods that occur in seasons of low wave energy, when sediment would not

be readily remobilized and advected out of the bay, could affect the health and

sustainability of coral reefs and the many associated species.

Measurements of short-lived isotopes 7Be and 137Cs in sediment cores

have been used to trace the thickness and distribution of terrestrial sediment in

Hanalei Bay, in order to assess spatial and temporal patterns of sediment

deposition and remobilization relative to coral-reef locations. A third isotope,

210Pb, derived primarily from seawater, provides additional information about

recent sedimentary history. Isotope profiles and observations of sedimentary

facies from cores collected at multiple locations in June 2005, and again in

August 2005, indicate the presence of recent fluvial sediment and organic debris

in the east part of the bay near the mouth of the Hanalei River. Away from the

immediate vicinity of the river mouth, sediment in the uppermost 1 m below the

sea floor had not retained a significant quantity of fluvial sediment within the eight

months prior to either sampling effort. During the study interval in summer 2005

the Hanalei River had no major floods and there was relatively little sediment

input to the bay. Sediment away from the river mouth was dominated by

carbonate sand, although some terrestrial sediment was present in sub-sea-floor

horizons. Sedimentary facies and isotope inventories throughout the bay showed

substantial spatial heterogeneity.

Sediment cores will be collected again at the same sites discussed here

during early and late summer 2006. If possible, additional sites will be sampled in

the Black Hole depocenter near the river mouth. Major floods in winter and spring

2006 are expected to leave a significant new sediment signal in the bay that

should be detected in summer 2006.

INTRODUCTION

Analyses of terrestrial sediment delivery to the coral-reef community of

Hanalei Bay on the island of Kaua’i, Hawai’i, USA, were conducted as part of the

U.S. Geological Survey (USGS) Coastal and Marine Geology Program’s Coral

Reef Project. The field studies discussed in this report occurred concurrently with

measurements of waves, currents, temperature, salinity, and turbidity in Hanalei

Bay by (Storlazzi and others, 2006). Together, these studies are intended to

provide a detailed understanding of the oceanic and sedimentary processes that
directly affect the development and health of coral-reef communities and their

many associated species in the bay. The ultimate goal of the USGS Coral Reef

Project, which is actively involved in similar research in other areas of the

Hawaiian Islands, is to understand better the transport mechanisms of sediment,

larvae, pollutants, and other water-borne substances in coral-reef environments.

Assessing the oceanic and sedimentary processes that affect coral-reef

communities, such as those in Hanalei Bay, is a necessary step in identifying

potential threats to these reefs, which constitute an integral part of the Hawaiian

Islands’ ecosystem.

Delivery of fluvial sediment to Hanalei Bay has particularly important

implications for the health of the local coral-reef ecosystem. Deposition on and

burial of corals by fluvial sediment during floods of the Hanalei River in seasons

of low wave energy, when sediment would not be readily remobilized by waves

and removed by currents, could have substantial negative effects on the health of

coral reefs and the many other species associated with them. In addition to the

physiological stress imposed by sediment, the coral-reef and near-shore

ecosystems may potentially be affected by substances such as fertilizers and

other contaminants discharged into the bay during river floods.

Sediment cores were collected at seven locations within Hanalei Bay

during two sampling surveys in the summer of 2005. Observations of

sedimentary facies were then used together with measurements of short-lived

isotopes 7Be, 137Cs, and 210Pb in these cores to trace the thickness and

distribution of terrestrial sediment in the bay, and thus to assess spatial and

temporal patterns of sediment deposition and remobilization.

Project Objectives:

The goal of this component of the USGS Coral Reef Project is to identify

the spatial and temporal distribution of terrestrial sediment in and around the

near-shore coral-reef community of Hanalei Bay, Kaua’i, Hawai’i. Isotope and

sedimentary-facies data obtained from sediment cores will provide insight into

the potential effects of terrestrial sediment delivery patterns around the Hanalei

Bay coral reefs. These data are relevant to future watershed-restoration projects

proposed by the U.S. Coral Reef Task Force’s (USCRTF) Hawaiian Local Action

Strategy (LAS) to address land-based-pollution threats to coral reefs in the

Hanalei linked watershed-reef system. The work was conducted with the

collaboration of the Hanalei Watershed Hui, a local organization dedicated to

monitoring environmental quality in the Hanalei Bay watershed

(http://www.hanaleiwatershedhui.org/).

Study Area:

8
Sediment cores were collected in Hanalei Bay, on the north shore of the

island of Kaua’i, Hawai’i (figs. 1, 2). Hanalei Bay covers an area of approximately

4.4 km2. The 25-km-long Hanalei River, a designated American Heritage River, is

one of the largest rivers in the Hawaiian Islands in terms of water discharge. It

drains an area of 54.4 km2 before debouching into the bay. Its north-facing

drainage basin consists of steep-walled, heavily vegetated volcanic ridges and

fluvial gorges that drain the area of the island’s 1,500-m-high central mountains.

These mountains receive the highest recorded rainfall on Earth (>10 m yr-1). The

lowermost 12 km of the river channel pass through a broad floodplain consisting

of middle to late Holocene marine sands overlain by fluvial deposits (Calhoun

and Fletcher, 1996) that have now been developed for extensive agricultural use.

The potential for runoff of sediment and contaminants to affect coral-reef ecology

in the bay in the lower river basin is considered a subject of great concern by the

Hanalei Watershed Hui; agricultural development and soil erosion in the drainage

basin can increase the sediment load in the river. The steep topography of the

drainage basin is subject to landslides that deliver variable amounts of sediment

to the river, for an estimated total sediment yield of 140 ± 55 Mg km-2 yr-1

(Calhoun and Fletcher, 1999). Calhoun and Fletcher (1999) estimated that

approximately 30 percent of the annual fluvial sediment load is deposited on the

coastal floodplain, while 70 percent (1.76 x 104 Mg) is delivered to Hanalei Bay.

The Hanalei River enters Hanalei Bay from the east (fig. 1); the smaller

Waioli and Waipa Rivers and several small freshwater streams also discharge

intermittently into the bay’s south and west sides, and likely deliver submarine

groundwater discharge to the bay even in the absence of surface stream flow

(Storlazzi and others, 2006). The physical environment of the bay in summer is

dominated by northeast to easterly trade winds accompanied by low wave

energy. From June through August 2005 significant wave heights were <1 m

within the bay itself with periods 2.5–5.9 seconds, driven dominantly by northeast

trade winds (Storlazzi and others, 2006). Winter conditions, typically beginning in

October, are characterized by a North Pacific swell regime that produces wave

heights of 2–5 m with periods of 12–20 seconds (Moberly and Chamberlain,

1964) that approach the bay typically from the northwest. Occasional lowpressure systems, including hurricanes, approach Kaua’i but usually make

landfall on the south coast, away from Hanalei Bay.

Current meters deployed during the summer of 2005 (Storlazzi and others,

2006) indicated weak currents in the bay from early June through late August,

with net near-surface flow entering the bay in the east and flowing out of the bay

in the west. Near-bed current velocities indicated opposite, cyclonic (counterclockwise) flow. Waves and currents in the western part of the bay were more

energetic than in the east. Currents of 0.05 m s-1 were measured near the

surface at the CRAMP (Coral Reef Assessment and Monitoring Project, a study

site established by the University of Hawai'i) site compared to 0.02 m s-1 near the

surface at the offshore wall site; Storlazzi and others, 2006, see fig. 2), a

difference attributed to more direct exposure to trade winds at the western side of

the bay.

9
Ni’ihau

Kaua’i

O’ahu

Moloka’i

Lana’i

Kaho’olawe

Maui

Hawai’i

Figure 1. Location map showing the major Hawaiian Islands.

Hanalei Bay, on the north shore of Kaua’i, is shown in the red box.

10
The sea floor of Hanalei Bay consists of marine carbonate sediment and

terrigenous siliciclastic material derived from the basaltic highlands of the Hanalei

River basin (Calhoun and others, 2002). The center of the bay is largely free of

indurated coral-reef substrate, with a flat sea floor at typically 10–18 m water

depth. At the east side of the bay, 500 m offshore of the river mouth, is a broad

depression ~15 m deep known as the Black Hole because terrestrial sediment

and dark organic matter obscures visibility in the water column (fig. 2). The

fringing reef inside Hanalei Bay hosts ecological communities that were, in recent

studies of the bay’s marine biological diversity, considered to be relatively

healthy. Hanalei Bay is unusual among Hawaiian coral communities in having

increased its live coral cover since the mid-1990s (Friedlander and others, 1997,

2005).

Isotopes Used as Sediment Tracers:

This study utilizes three radioisotopes: 7Be, 137Cs, and 210Pb. These

isotopes have been used in previous studies of near-shore and inner-shelf

sedimentation to assess accumulation rates and sources. All are particle-reactive

and adsorb readily onto the surfaces of sediment grains. Beryllium-7 has been

shown to be especially useful for identifying episodic seasonal flood deposits

near shore (Allison and others, 2000). Lead-210 and 137Cs have been used

together in numerous coastal and lacustrine settings to estimate accumulation

rates and deposition age of sediment (Duursma and Gross, 1971; Nittrouer and

others, 1979; Smith and Ellis, 1982; Buesseler and Benitez, 1994; Allison and

others, 1998, 2000; Jaeger and Nittrouer, 1995; Kuehl and others, 1995;

Goodbred and Kuehl, 1998; Draut and others, 2005).

The first tracer, 7Be, is a naturally occurring isotope with a 53-day half-life

that forms in the atmosphere by cosmic-ray spallation of nitrogen and oxygen.

The production of cosmogenic 7Be is controlled by insolation, and so the flux of

7

Be from the atmosphere to the earth’s surface has a latitudinal and seasonal

dependence (Olsen and others, 1986; Baskaran and others, 1993). After it

becomes associated with airborne particles and is deposited on land, 7Be rapidly

becomes incorporated into vegetation and soil. In contrast to the slow rate at

which 7Be can be delivered to the sea floor via settling of particles through the

marine water column (which may take longer than its activity remains

measurable), 7Be is concentrated in terrestrial sediment carried to the coastal

ocean by river discharge. An appreciable inventory of this isotope can therefore

accumulate in fluvial deposits near shore (Canuel and others, 1990; Allison and

others, 2000). The presence of 7Be in near-shore sediment indicates that

sediment had been exposed to the atmosphere within the past eight months, or

approximately five half-lives; it is therefore particularly useful for detecting

recently deposited fluvial sediment.

Cesium-137 is an isotope with a 30-year half-life and a non-constant

source function: it was first introduced to the environment during nuclear-weapon

testing that began in the 1950s and peaked in 1963, then ceased to be added

11
0 250 500 METERS

159 31'0"W 159 30'0"W

22 13'0"N o

o o

A

B

C

D

E

F

G

CRAMP

N

RS4

RS3

Hanalei R.

Wai’oli R.

Waipa R.

“Black

Hole”

5 m

10 m

15 m

20 m

25 m

20 m

15 m

Figure 2. Locations of sediment-core sites in Hanalei Bay. Stations occupied in June and August 2005 for this study (yellow circles) identified by

station letter (A–G). River Sites 3 and 4 (RS3 and RS4) are also marked;

River Sites 1 and 2 are located out of this map area, ~4 km and ~2.5 km

upstream of the river mouth, respectively (locations listed in tab. 1). Red

circles indicate the locations of oceanographic instrument packages

deployed during summer 2005 (Storlazzi and others, 2006). Bathymetry in

this image has been interpolated from SHOALS lidar data; dark-blue areas

indicate no bathymetric data. The isobath interval is 5 m.

12
after the 1972 atmospheric nuclear testing ban with the exception of additions

caused by the 1979 and 1986 nuclear accidents at Three Mile Island and

Chernobyl, respectively. Because 137Cs has been almost entirely removed from

the atmosphere by rainfall, it is now introduced to the marine environment

primarily via sediment that has been eroded from land and discharged by rivers

into the ocean (for example, Smith and Ellis, 1982). As with 7Be, the supply of

137Cs to shallow marine settings is controlled largely by fluvial sedimentation.

Measurable activity of 137Cs indicates that some component of the sediment has

been in contact with an atmospheric or fluvial source more recently than the

1950s, when this isotope was first introduced to the environment. If sediment has

accumulated undisturbed since that time, 137Cs profile with sediment depth may

mirror the history of atmospheric fallout, and so can be used to infer

accumulation rates (Livingston and Bowen, 1979; Miller and Heit, 1986).

The third isotope, 210Pb, is a naturally occurring daughter product of 238U

with a half-life of 22.3 years. Excess 210Pb is defined as the 210Pb activity above

(in excess of) the equilibrium activity supported by concentrations of parent and

grandparent isotopes in the 238U decay series in the same sediment sample. The

excess 210Pb activity is the difference between the total 210Pb and the supported

210Pb. Supported 210Pb, that amount of 210Pb in sediment produced in situ by

continuous 226Ra decay (via 222Rn, with a 3.8-day half-life), is identified by

measurement of 214Pb (half-life 26.8 minutes), an intermediate daughter product

between 222Rn and 210Pb that is assumed to be in secular equilibrium with 210Pb.

Because the half-life of 226Ra is long (1,622 years), supported 210Pb is produced

in marine sediment by 226Ra decay for thousands of years after its deposition and

isolation from other 210Pb sources. In the coastal marine environment of the

Hawaiian Islands, adjacent to clear Pacific Ocean water, the primary source of

excess 210Pb is the decay of 226Ra dissolved in seawater. Other sources include

fallout to surface water following its production in the atmosphere from the decay

of 222Rn gas, and input by fluvial discharge. The presence of excess 210Pb

characterizes sediment deposited within the past ~100 years, or five half-lives. In

undisturbed sediment, the excess 210Pb-activity profile can be used to model

rates of sediment accumulation and mixing (for example, Nittrouer and others,

1979; Crusius and others, 2004).

METHODS

Sediment Collection and Sub-Sampling:

Sediment cores were collected with a diver-operated hand-held coring unit

at seven sites in Hanalei Bay (fig. 2). Core collection occurred in June and

August 2005, coincident with the times chosen by Storlazzi and others (2006) to

deploy and recover oceanographic instruments. Core sites were chosen to

provide representative spatial coverage around the bay; two of seven sites were

13
located in the Black Hole (Stations A and F), two along the coral wall at the east

side of the bay near the Hanalei River mouth (Stations C and G), two in the

central part of the bay (Stations B and E), and one along the coral wall at the

northwest side of the bay (Station D; fig. 2). The diver-operated corer uses a

slide hammer to drive a 10.7-cm-diameter polycarbonate core barrel into the sea

floor, and can collect cores up to ~0.8 m long depending on the consolidation of

the sediment. A check valve within the slide hammer-core barrel adapter

provides suction to retain sediment while the barrel is pulled out of the sediment.

The bottom of the core barrel is sealed as soon as possible by inserting a piston.

Core lengths recovered during this study typically ranged from 20–50 cm (tab. 1).

At sites of uniform unconsolidated sand, core recovery was often complicated by

the movement of water through the sediment during insertion of the piston.

After core collection, sediment was extruded from the core barrel using a

jack to push the piston and sediment through the barrel. Sedimentary facies and

textures were described qualitatively and sampled during extrusion. The top 22

cm of each core was sampled in 2-cm intervals; below 22 cm, sample

thicknesses alternated between 2 cm and 8 cm. Additional samples were

collected from any horizons with unusual facies variation. Sediment from the

edges of each sample was discarded to avoid sampling material that had been

smeared, obscuring its original depth, as the core barrel was driven into the sea

floor or extruded from the barrel.

In addition to sediment cores collected within Hanalei Bay, four sediment

grab samples (0–5 cm deep) were obtained from the river bottom in August 2005

(fig. 2). Facies at these four river sites were described, and, along with the core

samples, these were later analyzed on gamma counters to allow comparison of

isotope activity in the river sediment with that in the bay.

Isotope Analysis by Gamma Counting:

Gamma-ray activity provides a straightforward and efficient means to

measure the radioactive isotope content in sediment (Gäggler and others, 1976).

Each isotope emits gamma radiation at a characteristic frequency associated

with its decay. Because detection by this method allows detection of multiple

frequencies simultaneously, the activities of all desired isotopes are assessed in

one counting session.

Laboratory analyses were performed at the USGS laboratory in Woods

Hole, MA. The wet sediment samples were homogenized and sub-sampled.

Aliquots weighing approximately 100 g were freeze-dried and then

disaggregated. Samples were analyzed on planar germanium detectors

(Canberra Industries, Inc., model GS2020S) for 48–96 hours (until the 210Pb

standard error was within 3%). Activity levels of 7Be, 137Cs, and 210Pb were

measured using net counts of the 478, 661.6, and 46.3 keV peaks respectively.

Excess 210Pb activity was calculated from independent measurement of 214Pb at

352 keV (Livingston and Bowen, 1979; Joshi, 1987). The efficiency of the

detectors over the energy range 46.3–665 keV was calibrated using EPA

14
Site Latitude Longitude Core Date Water Depth Core Length Comments

A 22° 12.739' 159° 30.083' K0605-1 6/7/05 15.3 m 58 cm Black Hole

K0805-7 8/27/05 15.3 m 53 cm

B 22° 12.595' 159° 30.506 K0605-2 6/7/05 11.0 m 34 cm South-central bay

K0805-1 8/24/05 11.3 m 38.5 cm

C 22° 12.889 159° 30.196 K0605-3 6/7/05 13.1 m 52 cm NE side of bay

K0805-3 8/25/05 13.4 m 23 cm

D 22° 12.840 159° 30.764 K0605-4 6/8/05 13.4 m 21 cm NW side of bay

K0805-4 8/26/05 13.4 m 34 cm

E 22° 12.743 159° 30.474 K0605-5 6/8/05 12.2 m 21 cm Middle of bay

K0805-6 8/26/05 12.2 m 39 cm

F 22° 12.725 159° 30.087 K0605-6 6/8/05 14.6 m 4 cm Black Hole

K0805-2 8/25/05 15.6 m 58.5 cm

G 22° 12.807 159° 30.039 K0605-7 6/8/05 10.7 m 15 cm Reef wall near river mouth

K0805-5 8/26/05 8.5 m 28 cm

River Site 1 grab sample 8/28/05 1.2 m n/a 30 m upstream of stream gage

River Site 2 22° 12.649' 159° 28.547' grab sample 8/28/05 0.8 m n/a Under traffic bridge

River Site 3 22° 12.799 159° 29.489 grab sample 8/28/05 0.9 m n/a 0.8 km above river mouth

River Site 4 22° 12.825 159° 29.731 grab sample 8/28/05 0.5 m n/a Beach park at river mouth

Table 1. Locations, lengths, and dates of sediment cores collected in June and August 2005, 

and river-bed grab samples collected in August 2005.

15
1000

2000

3000

4000

O N D J F M A M J J A S

Water Year 2004 Water Year 2005

O N D J F M A M J J A S

20

40

60

80

100

Discharge (m /s) 3

Study

interval

Discharge (cfs)

Discharge (m /s) 3

200

400

600

800

5

10

15

20

160 170 180 190 200 210 220 230

Year Day 2005

June July August

Discharge (cfs)

Sediment load (t/day)

50

100

150

200

160 170 180 190 200 210 220 230

Year Day 2005

June July August

O N D J F M A M J J A S O N D J F M A M J J A S

1000

2000

3000

4000

5000

6000

7000

Water Year 2004 Water Year 2005

Study

interval

Sediment load (t/day

A )

C D

B

Figure 3. Water and sediment discharge from the Hanalei River. Data were measured at USGS gaging station number

16103000 (“Hanalei River near Hanalei”, located 9.2 km upstream from the river mouth) and were provided by the USGS Pacific

Islands Water Science Center in Honolulu, Hawai’i (http://hi.water.usgs.gov/). A. Hydrograph for water years 2004 and 2005

(10/1/03 through 9/30/05) with the study interval (June–August 2005) indicated. B. Fluvial sediment load (in metric tons per day)

for water years 2004 and 2005 based on a rating curve and suspended-sediment samples analyzed by the Water Resources

Division of the USGS. C. Hydrograph during the study interval in summer 2005, beginning with the start of the June coring work

(6/5/05; Year Day 156) and ending with the final day of August field work (8/27/05; Year Day 239). D. Fluvial sediment load during the summer 2005 study interval.

16
standard pitchblende ore in the same range of geometry as the samples.

Calibration of the detectors specifically for 137Cs (661.6 keV) was carried out with

a standard solution from Isotope Products Laboratory. The activities of 7Be,

137Cs, and excess 210Pb were decay-corrected to the date of core collection. A

correction for self-absorption on all of the isotopes was made using the method

of Cutshall and others (1983). The accuracy of these results was confirmed by

analyses of standard reference materials, which yielded excellent agreement with

certified results.

Isotope inventories (total activity beneath 1 cm2 of sea-floor area at the

core site) were calculated for the cores by multiplying the measured activity (in

disintegrations per minute per dry gram of salt-free sediment) in each depth

interval by the estimated bulk density (g cm-3) and by the core section thickness

(cm). The products were summed over the entire core length. Sediment bulk

density was estimated using a measured weight per unit volume of

disaggregated, freeze-dried sediment. This procedure assumes that the

unconsolidated sandy sediment was not compacted appreciably.

RESULTS

The hydrograph and sediment load for the Hanalei River during the study

interval, and for the two most recent complete water years, are shown in figure 3.

The Hanalei River flood event that most recently preceded the June core

collection occurred on 2/2/05, with a peak discharge of 95 m3 s-1 (3,370 cfs; fig.

3). The time between June and August core collection was a time of low fluvial

sediment input to Hanalei Bay when no major floods occurred.

Locations, dates, lengths, and sediment-sample depths for each core and

river grab sample are listed in table 1. Inventories of 7Be, 137Cs, and excess 210Pb

for each core site are reported in table 2. Complete descriptions of sediment from

all 14 cores (seven each in June and August 2005) are listed in appendices 1

and 2. Figures 4–17, ordered by core site name (locations shown in fig. 2), show

activity profiles for 7Be, 137Cs, and excess 210Pb in the 14 cores, as well as

sedimentary-facies diagrams. Isotope activities have been decay-corrected to the

time of sample collection, and are reported as disintegrations per minute per dry

gram of salt-free sediment. Facies showed substantial spatial heterogeneity

within the bay; examples of different sediment types observed are shown in the

photographs in figure 18.

Cores collected in the Black Hole (at Stations A and F; figs. 4, 5, 14, and

15) contained a thin layer of unconsolidated very fine-grained sediment and

organic debris at the surface, underlain by a mixture of carbonate sand and dark

mud. Rounded siliciclastic pebbles were found in the upper parts (within 15 cm of

the sea floor) of two of the Black Hole cores (Core K0605-1 from Station A in

June, and Core K0805-2 from Station F in August). Three of the four Black Hole

cores (From Stations A and F; cores K0605-1, K0805-2, and K0805-2) contained

dark, consolidated mud with wood and leaf debris that extended from a depth of

17
Station Core

Excess 

210Pb 

dpm/cm^2

Complete 

inventory 

recovered?

137Cs 

dpm/cm^2

Complete 

inventory 

recovered?

7Be 

dpm/cm^2

Complete 

inventory 

recovered?

A K0605-1 208 y, 56 cm 2.34 y 9.46 y

K0805-7 205 y, 40 cm 1.66 y 0.07 y

B K0605-2 243 n, but almost 0.33 y 0.00 y

K0805-1 262 n, but almost 2.38 probably 0.58 y

C K0605-3 293

n, but almost, 

53 cm 0.09 y 0.09 y

K0805-3 53 n. only 20 cm 0.03 y 0.00 y

D K0605-4 107 n. only 20 cm 0.02 y 0.05 y

K0805-4 135 n, 30 cm 0.00 y 0.34 y

E K0605-5 163 n. only 20 cm 0.01 y 0.32 y

K0805-6 168 n, 18 cm 0.00 y 0.00 y

F K0605-6 28 n, only 4 cm 0.40 n 0.31 n

K0805-2 128 y, 40 cm 1.33 y 0.79 y

G K0605-7 56 n. only15 cm 1.39 n. only15 cm 1.55 n

K0805-5 88 n, 18 cm 2.51 n 2.18 n? only 18 cm

Table 2. Inventory of 7 Be, 137 Cs, and excess 210 Pb in the sediment at all core sites. Inventories were 

calculated from gamma-counted activity. Units are disintegrations per minute (dpm) per cm 2 of sea-floor surface area.

18
15–20 cm below the sea floor down to the base of each core. The fourth Black

Hole core (Core K0605-6) was too short (4 cm) to allow much comparison

between its facies and that of the other three, although its consolidated mud and

sparse sand were similar to the upper 4 cm of the other three.

The June and August cores from Black Hole Station A contained facies

and isotope-activity profiles that differed somewhat (figs. 4 and 5). In June, Core

K0605-1 at this station contained appreciable 7Be activity down to a depth of ~20

cm below the sea floor, measurable 137Cs in the upper ~25 cm, and excess 210Pb

that ranged from 5–10 dpm g-1 in the upper ~25 cm. In contrast, at this same site

in August (Core K0805-7), only one sample (centered at a depth of 7 cm beneath

the sea floor) had any measurable 7Be. Measurable 137Cs was present in the

upper ~20 cm but displayed a very different profile from that of the June core,

and excess 210Pb in the upper 20 cm was higher than in June (up to 12 dpm g-1).

In both the June and August cores from Station A, the dark, consolidated mud

layer between ~20 cm and the cores’ bases was almost entirely inactive with

respect to the three isotopes analyzed. At Black Hole Station F, both cores

contained some 7Be in the upper 5 cm but the June core (K0605-6) was too short

to calculate inventory accurately for any of the three isotopes measured. In the

August core from Station F (K0805-2), low activity levels of 137Cs were detected

in the upper 10 cm (~0.1 dpm g-1) and excess 210Pb was a fairly constant 6–8

dpm g-1 in the upper 12 cm.

The cores from Station G, at the east side of the bay near the river mouth,

both contained carbonate sand immediately beneath the sea floor, underlain by a

horizon of mixed carbonate sand and dark mud 5–8 cm thick, which in turn was

underlain by more carbonate sand. Core K0605-7 (Station G in June) stopped at

a depth of 15 cm beneath the sea floor; below that depth, Core K0805-5 (from

the same Station G in August) contained unstratified sand, coral rubble, and

siliciclastic gravel. Beryllium-7 profiles from these two cores at Station G were

similar, within the analytical and sampling error, with both cores showing 7Be

activity in the upper 5 cm. Both cores displayed 137Cs peaks between 5 and 13

cm, allowing for sampling error. However, activity levels in the August core

(K0805-5) were more than twice as high as those in the June core (K0605-7).

Excess 210Pb in both cores was at or below 5 dpm g-1.

The remaining core site, Station C, located along the coral wall at the

northeast side of the bay, was dominated by carbonate sand in both the June

(K0605-3) and August (K0805-3) cores, although some silicilastic heavy-mineral

grains were visible in both. The longer of those two cores (K0605-3) contained

dark sand below a depth of 36 cm that was finer-grained than the overlying

dominantly carbonate layer. Both 7Be and 137Cs were not detectable in both

cores collected at Station C, with the exception of one sample from the June core

(K0605-3) that had very low activity (~0.03 dpm g-1) and a large error. Excess

210Pb in the June core decreased down-core from ~8 dpm g-1 to below 5 dpm g-1,

and was almost not detectable (<2 dpm g-1) at this site in August.

Cores from Station B, in the south-central part of the bay, were dominated

by carbonate sand although the core collected in August (K0805-1) had three

distinct horizons of darker sand with isolated clay patches. This August core had

19
0

10

20

30

40

50

60

Unconsolidated mud

Medium to coarse sand

Mud nodule

(rip-up clast?)

Dark, consolidated

mud

Plant matter and

woody debris

Medium to coarse sand,

sharp base

Medium to coarse sand with

mud patch; burrows

Medium to coarse sand;

rounded pebbles

Sedimentary Facies

137

Cs (dpm/g)

0

10

20

30

40

50

60

0.1 0.2

D

e

pth (c

m)

Excess

210

Pb (dpm/g)

0

10

20

30

40

50

60

5 10 15

0

10

20

30

40

50

60

0.5 1

7

Be (dpm/g)

Station A, June 2005 (Core K0605-1)

Figure 4. Sedimentary facies and isotope activity at Station A in June 2005 (Core K0605-1). Activities of 7Be, 137Cs,

and excess 210Pb, all decay-corrected to the date of sample collection, are shown in disintegrations per minute (dpm)

per dry gram of salt-free sediment. This site is located in the Black Hole, at the east side of Hanalei Bay, near the

mouth of the Hanalei River.

20
0

10

20

30

40

50

Unconsolidated mud

Carbonate sand

mixed with mud

Dark mud with

organic debris

Carbonate sand,

mud, and peaty

organic debris

Peaty mud

Peaty mud,

trace sand

Peaty mud

with leaves

Mottled, peaty

mud; leaves,

burrows

Sedimentary Facies

D

e

pth (c

m)

Excess

210

Pb (dpm/g)

0

10

20

30

40

50

5 10 15

137

Cs (dpm/g)

0

10

20

30

40

50

0.1 0.2

7

Be (dpm/g)

0

10

20

30

40

50

0.1 0.2

Station A, August 2005 (Core K0805-7)

Figure 5. Sedimentary facies and isotope activity at Station A in August 2005 (Core K0805-7). Activities of 7Be, 137Cs, and excess 210Pb, all decay-corrected to the date of sample collection, are shown in disintegrations per minute (dpm) per dry gram of salt-free sediment. This site is located in the Black Hole, at the east side of the bay, near

the river mouth.

21
Sedimentary Facies

0

5

10

15

20

25

30

35

Unconsolidated

mud

Homogenous

carbonate

sand

D

e

pth (c

m)

Excess

210

Pb (dpm/g)

0

5

10

15

20

25

30

35

5 10 15

137

Cs (dpm/g)

0

5

10

15

20

25

30

35

0.1 0.2

7

Be (dpm/g)

0

5

10

15

20

25

30

35

0.02 0.06 0.1

Station B, June 2005 (Core K0605-2)

Figure 6. Sedimentary facies and isotope activity at Station B in June 2005 (Core K0605-2). Activities

of 7Be, 137Cs, and excess 210Pb, all decay-corrected to the date of sample collection, are shown in

disintegrations per minute (dpm) per dry gram of salt-free sediment. This site is located in the southcentral part of the bay.

22
Sedimentary Facies

Fine- to mediumgrained carbonate

sand (gray to tan)

Darker gray

sand with

isolated

clayey patch

Alternating

darker and

lightercolored

sand with

occasional

isolated clay

patches.

Void space

at 29 cm.

0

5

10

15

20

25

30

35

40

D

e

pth (c

m)

Excess

210

Pb (dpm/g)

5 10 15

0

5

10

15

20

25

30

35

40

137

Cs (dpm/g)

0.2 0.6 1

0

5

10

15

20

25

30

35

40

7

Be (dpm/g)

0.1 0.2 0.3

0

5

10

15

20

25

30

35

40

Station B, August 2005 (Core K0805-1)

Figure 7. Sedimentary facies and isotope activity at Station B in August 2005 (Core K0805-1). Activities of 7Be, 137Cs, and excess 210Pb, all decay-corrected to the date of sample collection, are shown in disintegrations per

minute (dpm) per dry gram of salt-free sediment. This site is located in the south-central part of the bay.

23
Sedimentary Facies

Homogenous

yellowish

carbonate sand

Darker, finer

gray sand

compared to

overlying

horizon; isolated coral

pieces

0

10

20

30

40

50

60

Unconsolidated

mud

D

e

pth (c

m)

Excess

210

Pb (dpm/g)

0

10

20

30

40

50

60

5 10 15

137

Cs (dpm/g) 7

Be (dpm/g)

0

10

20

30

40

50

60

0.04 0.08

0

10

20

30

40

50

60

0.04 0.08

Station C, June 2005 (Core K0605-3)

Figure 8. Sedimentary facies and isotope activity at Station C in June 2005 (Core K0605-3). Activities of 7Be, 137Cs, and excess 210Pb, all decay-corrected to the date of sample collection, are shown in disintegrations per

minute (dpm) per dry gram of salt-free sediment. This site is located on the northeast side of the bay, ~8 m

away from the coral wall near the river mouth.

24
Sedimentary Facies

Unconsolidated

mud

0

5

10

15

20

25

Medium to coarsegrained carbonate

and terrigenous

sand

D

e

pth (c

m)

Excess

210

Pb (dpm/g)

0

5

10

15

20

25

5 10 15

137

Cs (dpm/g)

0

5

10

15

20

25

0.04 0.08

7

Be (dpm/g)

0

5

10

15

20

25

0.04 0.08

Station C, August 2005 (Core K0805-3)

Figure 9. Sedimentary facies and isotope activity at Station C in August 2005 (Core K0805-3). Activities of 7Be, 137Cs, and excess 210Pb, all decay-corrected to the date of sample collection, are shown in disintegrations per

minute (dpm) per dry gram of salt-free sediment. This site is located on the northeast side of the bay, ~8 m

away from the coral wall near the river mouth.

25
Surface ‘fluff’ layer

Homogenous

carbonate sand

0

5

10

15

20

25

Organic matter;

leaves and

twigs

Sedimentary Facies

D

e

pth (c

m)

Excess

210

Pb (dpm/g)

0

5

10

15

20

25

5 10 15

137

Cs (dpm/g)

0

5

10

15

20

25

0.04 0.08

7

Be (dpm/g)

0

5

10

15

20

25

0.04 0.08

Station D, June 2005 (Core K0605-4)

Figure 10. Sedimentary facies and isotope activity at Station D in June 2005 (Core K0605-4). Activities of 7Be, 137Cs, and excess 210Pb, all decay-corrected to the date of sample collection, are shown in disintegrations per

minute (dpm) per dry gram of salt-free sediment. This site is located on the northwest side of the bay, ~5 m

away from a coral wall near the location of the CRAMP (Coral Reef Assessment and Monitoring Project)-site

instrument package discussed by Storlazzi and others (2006).

26
Leaf litter

Homogenous

carbonate sand

Sedimentary Facies

0

5

10

15

20

25

30

35

D

e

pth (c

m)

Excess

210

Pb (dpm/g)

0

5

10

15

20

25

30

35

5 10 15

137

Cs (dpm/g)

0

5

10

15

20

25

30

35

0.04 0.08

7

Be (dpm/g)

0

5

10

15

20

25

30

35

0.04 0.08

Station D, August 2005 (Core K0805-4)

Figure 11. Sedimentary facies and isotope activity at Station D in August 2005 (Core K0805-4). Activities of 7Be, 137Cs, and excess 210Pb, all decay-corrected to the date of sample collection, are shown in disintegrations per

minute (dpm) per dry gram of salt-free sediment. This site is located on the northwest side of the bay, ~5 m

away from a coral wall near the location of the CRAMP (Coral Reef Assessment and Monitoring Project)-site

instrument package discussed by Storlazzi and others (2006). 27
Homogenous

carbonate sand

(core disturbed)

Sedimentary Facies

0

5

10

15

20

25

D

e

pth (c

m)

Excess

210

Pb (dpm/g)

0

5

10

15

20

25

5 10 15

137

Cs (dpm/g)

0

5

10

15

20

25

0.04 0.08

7

Be (dpm/g)

0

5

10

15

20

25

0.1 0.2 0.3

Station E, June 2005 (Core K0605-5)

Figure 12. Sedimentary facies and isotope activity at Station E in June 2005 (Core K0605-5). Activities of

7Be, 137Cs, and excess 210Pb, all decay-corrected to the date of sample collection, are shown in disintegrations per minute (dpm) per dry gram of salt-free sediment. This site is located in the middle of the bay.

28
Homogenous

carbonate sand

(core slightly

disturbed)

Sedimentary Facies

Mottling

(bioturbation?)

at 6 cm

0

5

10

15

20

25

30

35

40

D

e

pth (c

m)

Excess

210

Pb (dpm/g)

0

5

10

15

20

25

30

35

40

5 10 15

137

Cs (dpm/g)

0

5

10

15

20

25

30

35

40

0.04 0.08

7

Be (dpm/g)

0

5

10

15

20

25

30

35

40

0.04 0.08

Station E, August 2005 (Core K0805-6)

Figure 13. Sedimentary facies and isotope activity at Station E in August 2005 (Core K0805-6). Activities of

7Be, 137Cs, and excess 210Pb, all decay-corrected to the date of sample collection, are shown in disintegrations per minute (dpm) per dry gram of salt-free sediment. This site is located in the middle of the bay.

29
Consolidated mud

with

sparse

carbonate

sand

Sedimentary Facies

0

1

2

3

4

5

D

e

pth (c

m)

137

Cs (dpm/g)

0

1

2

3

4

5

0.04 0.08 0

1

2

3

4

5

5 10 15

Excess

210

Pb (dpm/g)

0

1

2

3

4

5

0.1 0.2

7

Be (dpm/g)

Station F, June 2005 (Core K0605-6)

Figure 14. Sedimentary facies and isotope activity at Station F in June 2005 (Core K0605-6). Activities of 7Be, 137Cs, and excess 210Pb, all decay-corrected to the date of sample collection, are shown in disintegrations per

minute (dpm) per dry gram of salt-free sediment. This site is located in the Black Hole.

30
Carbonate

sand and

mud

Sedimentary Facies

Fluid mud

Laminated

mud; gravel

Laminated mud

Peaty mud

0

10

20

30

40

50

60

Mud with

carbonate

sand, fining

upward

Wood at

40 cm

D

e

pth (c

m)

Excess

210

Pb (dpm/g)

0

10

20

30

40

50

60

5 10 15

137

Cs (dpm/g)

0

10

20

30

40

50

60

0.2 0.4

7

Be (dpm/g)

0

10

20

30

40

50

60

0.2 0.4

Station F, August 2005 (Core K0805-2)

Figure 15. Sedimentary facies and isotope activity at Station F in August 2005 (Core K0805-2). Activities of

7Be, 137Cs, and excess 210Pb, all decay-corrected to the date of sample collection, are shown in disintegrations per minute (dpm) per dry gram of salt-free sediment. This site is located in the Black Hole.

31
Sand

(dominantly

carbonate)

Sedimentary Facies

Mixed sand

and mud;

dark and

mottled

patches

0

5

10

15

Sand

(dominantly

carbonate)

D

e

pth (c

m)

Excess

210

Pb (dpm/g)

0

5

10

15

5 10 15

137

Cs (dpm/g)

0

5

10

15

0.2 0.4

7

Be (dpm/g)

0

5

10

15

0.2 0.4

Station G, June 2005 (Core K0605-7)

Figure 16. Sedimentary facies and isotope activity at Station G in June 2005 (Core K0605-7). Activities of

7Be, 137Cs, and excess 210Pb, all decay-corrected to the date of sample collection, are shown in disintegrations per minute (dpm) per dry gram of salt-free sediment. This site is located next to the reef wall on the

east side of the bay, near the river mouth.

32
Carbonate

sand

Sedimentary Facies

Poorly sorted

carbonate sand

Unstratified

coarse

sand, coral

rubble, and

terrestrial

gravel

0

5

10

15

20

25

30

Unconsolidated mud

Mud, some sand

Mixed carbonate

sand and mud

Coral clast

at 5 cm

Mixed carbonate

sand and mud

D

e

pth (c

m)

Excess

210

Pb (dpm/g)

0

5

10

15

20

25

30

5 10 15

137

Cs (dpm/g)

0

5

10

15

20

25

30

0.2 0.4

7

Be (dpm/g)

0

5

10

15

20

25

30

0.2 0.4

Station G, August 2005 (Core K0805-5)

Figure 17. Sedimentary facies and isotope activity at Station G in August 2005 (Core K0805-5). Activities of

7Be, 137Cs, and excess 210Pb, all decay-corrected to the date of sample collection, are shown in disintegrations per minute (dpm) per dry gram of salt-free sediment. This site is located next to the reef wall on the east

side of the bay, near the river mouth.

33
measurable 7

Be activity in its upper 4 cm, while the June core (K0605-2) had

none. Both exhibited a single-point peak in 137Cs, which was otherwise absent, at

14 cm in June (K0605-2) and at 29 cm in August (K0805-1), the latter

accompanied by a finer grain size than in the overlying and underlying horizons.

Both cores from Station B had excess 210Pb profiles that decreased steadily from

~8 dpm g-1 to below 5 dpm g-1.

At Station E, in the middle of the bay, both the June and August cores

consisted entirely of homogenous carbonate sand. The June core (K0605-5) was

disturbed by the motion of water through the sand during core recovery.

Beryllium-7 and 137Cs were not detectable in the cores collected at Station E

except for one sample in the June core (K0605-5) that contained 7Be activity on

the order of 0.1 dpm g-1 at a depth of 5 cm. Both cores exhibited excess 210Pb

profiles that decreased slightly down-core from ~7 dpm g-1 at the sea floor to ~5

dpm g-1 below 10 cm.

Cores from Station D, on the northwest side of the bay approximately 5 m

away from a coral wall, were dominated by a homogenous carbonate-sand facies

throughout much of the core in both June and August. During both sampling

visits, a surface fluff layer that contained leaf litter and other organic debris was

present. Divers observed that this material was readily mobilized by surge at the

sea floor, and may have been resuspended during core collection. The June core

at this location (K0605-4) contained a basal horizon of leaves and woody debris

with its upper contact ~18 cm beneath the sea floor. No similar horizon was

present in the August core at Station D (K0805-4) even though it extended 35 cm

below the sea floor. The August core contained 7Be in its upper ~5 cm, while

there was no detectable 7Be in the June core except for a very low activity with a

large counting error that occurred in the basal organic layer. Neither core

contained 137Cs; both cores from Station D contained excess 210Pb profiles that

remained constant at ~4 dpm g-1 throughout the core.

Isotope activities in the four sediment grab samples collected from the

surface of the Hanalei River bed in August 2005 provide a basis for comparison

of the August cores collected within the bay. The four samples spanned

approximately the lowermost 4 km of the river channel. The sample collected

farthest upstream is referred to as River Site #1 in table 1, and is located ~4 km

from the mouth and above most of the agricultural runoff in the Hanalei Valley.

Sediment from River Site #1 consisted of mud and organic debris; this sample

had 7Be activity of 0.22 ± 0.06 dpm g-1, 137Cs activity of 0.39 ± 0.02 dpm g-1, and

excess 210Pb activity of 0.09 ± 0.05 dpm g-1. Sediment at River Site #2, located

~2.5 km above the river mouth, consisted of mud and organic material with 7Be

activity of 0.06 ± 0.03 dpm g-1, 137Cs activity of 0.39 ± 0.02 dpm g-1, and excess

210Pb activity of 1.44 ± 0.09 dpm g-1. River Site #3 was located ~0.8 km above

the river mouth, in an area dominated by coarse sand; this sample had no

measurable 7Be, 137Cs activity of 0.15 ± 0.01 dpm g-1, and no measurable excess

210Pb. River Site #4 was located at the river mouth, where fine sand and mud

were collected on the left (southern) bank of the river by the Hanalei beach park.

Sediment from River Site #4 contained 7Be activity of 0.06 ± 0.03 dpm g-1, 137Cs

activity of 0.003 ± 0.002 dpm g-1, and excess 210Pb activity of 2.11 ± 0.08 dpm g34
1

. Because the river-sediment samples were grab samples from the bed surface

only, isotope inventories in the river bed beneath those sampling sites cannot be

measured.

DISCUSSION

Sedimentary Facies and Isotopic Signatures:

Carbonate sand was the dominant sediment type at many of the sampled

sites. Most cores also contained some material derived from a terrestrial source:

siliciclastic pebbles and gravel, heavy-mineral sand grains, and organic debris

such as leaves and wood. Terrestrial material was especially prevalent in cores

taken from the east side of the bay near the river mouth, and in the Black Hole

bathymetric depression. The thickest accumulation of recent fluvial sediment was

sampled at Station A in the Black Hole (Core K0605-1), where, in June 2005, the

7

Be profile showed that sediment that had been deposited within the past eight

months was present to a depth of 22 cm. This recent accumulation of terrestrial

sediment is inferred to have occurred during the Hanalei River flood event that

most recently preceded the June core collection: a flood on 2/2/05 with a peak

discharge of 95 m3 s-1 (3,370 cfs; fig. 3). Suspended-sediment concentrations

measured during that flood were sufficient to deliver a total sediment load that

exceeded 7,000 t d-1 (http://hi.water.usgs.gov/; fig. 3), making that the largest

flood, in terms of both water and sediment discharge, that occurred during

combined Water Years 2004 and 2005. Although this February 2005 event was a

substantial flood, traces of its sediment were scarce by the time we collected

sediment cores four months later.

The paucity of detectable terrestrial sediment in June 2005 is attributed to

energetic wave conditions that presumably dominated Hanalei Bay during late

winter and spring. Wave heights and currents were not measured within the bay

during that time (the USGS oceanographic instruments were deployed in June

2005; Storlazzi and others, 2006). The nearest buoy operated by the National

Oceanic and Atmospheric Administration, 270 km WNW of Kaua'i, recorded

conditions between February and June 2005 that could account for

remobilization and removal of substantial fluvial sediment from Hanalei Bay if

similar conditions prevailed within the bay itself. Data from that buoy indicate a

storm in mid-March 2005 with significant wave heights (Hsig) greater than 7 m

(http://www.ndbc.noaa.gov/station_page.php?station=51001). Such energetic

oceanographic conditions, common on Kaua'i’s north shore in winter months,

apparently removed most of the sediment delivered by the 2/2/05 flood from

Hanalei Bay.

At several core sites, sediment collected in August 2005 was markedly

different in composition from that collected in June. At Station A in the Black

Hole, the facies sampled in June and August were broadly similar (both

exhibiting the dark, consolidated mud with sparse sand and terrestrial-vegetation

35
debris below ~20 cm) but the June (Core K0605-1) and August (K0805-7)

isotopic profiles were substantially different. These differences in sediment

content and isotopic profiles are likely a result of having sampled slightly

different locations in August than in June, although attempts were made to return

to the very same stations using previously recorded GPS waypoints. It is not

possible otherwise to explain the disappearance, by late August, of all of the 7Be

that had been present at Station A in June. Too little time had elapsed between

collection of the June and August cores (83 days, or 1.6 half-lives) for all of the

June 7Be inventory to have been lost by radioactive decay. Wave and current

gages in the bay recorded no resuspension events between June and August

that could have removed the upper ~20 cm of 7Be-rich sediment (Storlazzi and

others, 2006).

The variety of sediment, and the variable thickness of recently delivered

fluvial material (as identified by the presence of 7Be) implies a spatially

heterogeneous sea floor, particularly at the east side of the bay near the river

mouth. It is likely that bioturbation disturbed most or all of the cored sediment and

isotopic profiles, altering their appearance in August from what it had been in

June; evidence for bioturbation was frequently observed, including burrows,

mottled texture (fig. 19), and the presence of live worms, small shrimp, and, in

Core K0805-7 from Station A in the Black Hole, a live 1-cm-diameter crab.

Bioturbation would be expected to mix the sediment and its associated particlereactive isotopes and to blur peaks in isotope activity, but would have little or no

effect on the total inventory of a particular isotope beneath the sea floor at a

given site.

Grab samples of sediment collected from the Hanalei River bed in August

2005 indicated a general pattern of river-bed 7Be activity that decreased by an

order of magnitude downstream (with the exception of the sample taken at River

Site #3, in which 7Be was absent; this is probably attributable to the coarse grain

size at that location). River Site #1, the farthest upstream of the four river

samples, contained 7Be activity of 0.22 ± 0.06 dpm g-1, almost the highest of any

marine or fluvial samples collected in August. This value is similar to the 7Be

activity measured in August 2005 at marine Stations F and G, both of which were

very near the river mouth. Activity of 137Cs decreased downstream by two orders

of magnitude along the lowermost 4 km of the river channel, from 0.39 (a value

much higher than was found in all but one of the marine sediment samples) to

0.003 dpm g-1. These down-channel decreases in 7Be and 137Cs activity are

consistent with the expected behavior of these isotopes, which tend to be

concentrated in terrestrial runoff. Excess 210Pb in the river-bed samples

increased by more than an order of magnitude down-channel from River Site #1

to the mouth, likely due to the availability of excess 210Pb in the marine water

column (the basaltic Hawaiian Islands, which are poor in the parent 238U

compared with granitic continental source rocks, correspondingly produce little

terrestrial 210Pb). It is noteworthy, though, that sediment samples from the lower

Hanalei River probably do not record a purely terrestrial sediment signal,

especially during summer low discharge. Calhoun and Fletcher (1999) recorded,

on three-fourths of their sampling days, a wedge of sea water under the traffic

36
A B

C D

Figure 18. Photographs of sediment cores from Hanalei Bay. A. Mixed mud and

sand overlie consolidated mud in sediment from the Black Hole (Core K0805-2, collected in August 2005 from Station F). B. Close-up view of the same core as in A,

showing detail of mud with carbonate sand that grades upward into laminated mud

containing peat and rare sand. A contact occurs at 15.5 cm, above which laminated

mud was present (see appendix 2 for a complete facies description). C. Alternating

sandy (lighter) and muddy (darker) horizons in Core K0805-1, collected at Station B

in the south-central part of Hanalei Bay. D. Example of the uniform, unconsolidated

sand that occurs in many of the cores, with a fine-grained surface ‘fluff’ layer (Core

K0805-3, from Station C on the northeast side of the bay).

37
Figure 19. Photograph of mottled texture attributed to bioturbation in

sandy sediment. This example is from Station B in the south-central

part of Hanalei Bay, Core K0805-1. The internal core diameter is

10.8 cm.

38
bridge (our River Site #2) with a thickness that typically occupied the lower half of

the river’s water column. With this saltwater wedge underlying fresh water in the

lower river channel, ocean-sourced 210Pb and suspended sediment of marine

origin could affect the terrestrial isotopic signal sampled at River Sites #2, 3, and

4.

The total inventory of 7Be, 137Cs, and excess 210Pb at each core site varied

slightly between the June and August 2005 sampling visits (figs. 20–22). It is

clear from the 7Be inventory calculations that the greatest accumulation of recent

fluvial sediment (that which had been delivered within the past ~8 months, likely

dominated by the 2/2/05 flood) is near the Hanalei River mouth on the east side

of the bay (fig. 20) and in the Black Hole. Cesium-137, which, like 7Be, is

concentrated primarily in terrestrial sediment, shows a similar pattern, with the

highest total inventories in the Black Hole and at Station G, although in August

2005 the south-central part of the bay (Station B) had a 137Cs inventory nearly as

high as that on the east side of the bay, at 2.38 dpm cm-2 (though based on a

single-point peak; fig. 21).

Excess 210Pb inventory in the marine sediment cores did not show

patterns as clear as those of 7Be and 137Cs (fig. 22). This is partially because

cores were not always long enough to include all of the down-core extent of

excess 210Pb (see tab. 1; for this reason, excess 210Pb inventory for several sites

have been omitted from fig. 22 and others are reported as minimum values).

High excess 210Pb inventory at core sites away from the river mouth (such as

Station B) suggests that a major source of excess 210Pb is scavenging from

seawater. It is probable that grain-size variation has affected some of the isotopic

profiles in the cores collected for this study (as substances that adsorb to particle

surfaces, all three isotopes will be present in higher activity levels in finer

sediment compared to the same mass of coarse-grained sediment). However,

none of the cores exhibited a ‘standard’ excess 210Pb profile (one with a well

defined surface mixed layer underlain by gradually decreasing activity and finally

by background or ‘supported’ activity) that would have represented undisturbed

sediment (Nittrouer and others, 1979). This is not surprising given the energetic

wave climate that prevails in Hanalei Bay during the fall and winter, which would

be expected to resuspend sediment frequently; resuspension events would

disturb any established 210Pb profile while also providing an opportunity for

sediment to scavenge additional 210Pb from the water column. Given the irregular 210Pb-activity profiles in these cores, it is not practical to try to estimate

accumulation rate by either the Constant Initial Concentration or the Constant

Rate of Supply geochemical models often applied for such purposes (Bentley

and Nittrouer, 1999; Noller, 2000; Draut and others, 2005).

Accumulation and Transport Patterns:

The summer of 2005 was an interval during which no major Hanalei River

floods occurred. Although this study interval was quiescent with respect to fluvial

sediment delivery to the bay (the most recent substantial flood having occurred

39
on 2/2/05), summer floods can and do happen on this river that are an order of

magnitude higher than the discharge during summer 2005. Recent examples

include a 27 m3 s-1 (962 cfs) event on July 12, 2000, and a 56 m3 s-1 (1,960 cfs)

event on July 26, 2003. Floods of these magnitudes have the potential to deposit

large quantities of sediment in the bay, by the combination of a large sediment

input with low summer wave and current energy. The weak, cyclonic, nearbottom currents, weak anticyclonic surface currents (0.02–0.05 m s-1), and low

wave heights (Hsig 0.2–0.8 m) measured in the bay by Storlazzi and others

(2006) during the summer of 2005 would likely not be efficient enough to flush a

major fluvial sediment input out of the bay quickly. A large summer flood could

therefore create substantial turbidity in the photic zone while quiescent conditions

would allow sediment to settle on reefs and the sea floor within the bay.

Based on the oceanographic data collected by Storlazzi and others

(2006), it is likely that the anticyclonic surface summer currents redistribute

sediment from the hypopycnal fluvial surface plume in a clockwise pattern around

the bay. This is supported by the low proportion of mud and organic terrigenous

material at Station C on the northeast side of the bay, which would be up-current

from the river mouth and Black Hole depocenter during the summer. It is inferred

that these fine-grained and low-density materials would have been winnowed out

of fluvial material while in suspension near that site and transported to the south,

leaving the coarser siliciclastic sand to settle downward where it would encounter

cyclonic near-bottom currents (Storlazzi and others, 2006). Siliciclastic sand, but

little to no terrigenous mud or organic debris, was found on the northeast side of

the bay within the sea floor at Station C (Core K0605-3). Terrestrial materials

may be transported south with the river plume by anticyclonic surface currents

toward the Black Hole. Sediment that settles to the sea floor in the Black Hole is

likely to remain there at least temporarily, because this bathymetric depression

forms a natural sediment trap.

Current patterns measured by Storlazzi and others (2006) are consistent

with the lack of terrigenous material in the middle of the bay (Station E). The

anticyclonic surface current may also have been responsible for transporting

terrestrial leaf litter from the Hanalei River mouth to the northwest side of the bay

(Station D). Alternatively, the organic matter on the sea floor and ~20 cm deep at

Station D (Core K0605-4) could have been delivered by the lesser flow of the

Waipa or Wai’oli Rivers and then transported north to that site by the current. It is

not known how winter sediment-transport pathways may differ from those

inferred from the summer data sets collected by this study and by Storlazzi and

other (2006). Additional oceanographic and sedimentologic studies planned for

the summer of 2006 will likely clarify patterns of sediment motion around the bay.

The core sites discussed in this report, and several planned new sites in

the Black Hole, which seems to act as an important sediment trap, will be

sampled again in June and August, 2006. The 2006 sampling plan is intended to

capture a record of several major river floods that have occurred during winter

and spring 2006, and to document the sedimentary signal of any floods that may

occur in spring and summer 2006. New core stations around the bay, in addition

to four new core sites currently planned for the Black Hole area, may be sampled

40
0 250 500 METERS

159 31'0"W o 159 30'0"W o

22 13'0"N o

9.46

0.09 >1.55

0

0.32

0.05

A

n/a

G

E

D

C

F

B

A

B 0 250 500 METERS

159 31'0"W o 159 30'0"W o

22 13'0"N o

0.07

0 >2.18

0.58

0

0.34

0.79

G

E

D

C

F

B

A

Figure 20. Inventory of 7Be, in dpm cm-2, at core sites in June (A) and

August (B) 2005. Where minimum values are given, cores were not long

enough to capture all of the inventory of this isotope (see tab. 2).

41
0 250 500 METERS

159 31'0"W o 159 30'0"W o

22 13'0"N o

2.34

0.09 >1.39

0.33

0.01

0.02

A

n/a

G

E

D

C

F

B

A

B 0 250 500 METERS

159 31'0"W o 159 30'0"W o

22 13'0"N o

1.66

0.03 >2.51

2.38

0

0

1.33

G

E

D

C

F

B

A

Figure 21. Inventory of 137Cs, in dpm cm-2, at core sites in June (A) and

August (B) 2005. Where minimum values are given, cores were not long

enough to capture all of the inventory of this isotope (see tab. 2).

42
0 250 500 METERS

159 31'0"W o 159 30'0"W o

22 13'0"N o

G

E

D

C

F

B

A

208

>293 n/a

>243

>163

>107

A

n/a

B 0 250 500 METERS

159 31'0"W o 159 30'0"W o

22 13'0"N o

205

>53 >88

>262

>168

>135

128

G

E

D

C

F

B

A

Figure 22. Excess 210Pb inventory in dpm cm-2 at core sites in June (A) and August (B)

2005. Where minimum values are given, cores were not long enough to capture all of the

inventory of this isotope (see tab. 2). Because excess 210Pb activity typically penetrates

deeper beneath the sea floor than that of 7Be or 137Cs, excess 210Pb inventory relies on

collection of longer cores. Values are not given (“n/a”) for sites at which cores were too

short to estimate the excess 210Pb inventory.

43
if the initial sampling efforts in June 2006 suggest that studying more sites would

be warranted. If the distribution of recent fluvial sediment can be quantified

shortly after a flood and again several months later, these isotope-geochemical

techniques can thus be used to compile a more complete picture of the sediment

dynamics in Hanalei Bay that affect local coral-reef communities.

CONCLUSIONS

Sedimentary facies and short-lived isotopes have been used to map the

distribution of recent fluvial sediment delivered to Hanalei Bay, Kaua’i. The

youngest and thickest terrigenous sediment is located on the east side of the bay

near the Hanalei River mouth and in the Black Hole bathymetric depression,

which apparently acts as a sediment trap. The thickest accumulation of recent

fluvial sediment was sampled in the Black Hole, where as much as 22 cm of

predominantly terrestrial sediment may have accumulated within the previous

eight months based on a 7Be-activity profile. Recent terrestrial sediment detected

in June 2005 may have been the remnant of a much more substantial flood

deposit from a Hanalei River flood in early February 2005. Core sites farther from

the river mouth, in the middle and western part of the bay, did not contain a

significant quantity of recent fluvial sediment during the spring and summer of

2005.

The coral-reef community in Hanalei Bay has the potential to be adversely

affected by the delivery of fluvial sediment. Deposition on and burial of corals by

sediment during summer floods, when wave and current energy are low and

sediment would not be readily remobilized, could have significant effects on the

reef ecosystem. Additional study in 2006 may clarify the spatial and temporal

patterns of sediment redistribution in the bay following substantial spring and

summer input of fluvial sediment. Sediment cores will be collected again at the

same sites discussed here during early and late summer 2006. If possible, up to

six sites will be sampled in the Black Hole depocenter near the river mouth

(Stations A, F, and four new sites). Major floods of the Hanalei River have

occurred in winter and spring 2006, some of which occurred late enough that

they are expected to have left a significant new sediment signal in the bay.

ACKNOWLEDGMENTS

This project was supported as part of the USGS Coral Reef Project. We thank

Carl Berg, Chief Scientist, Hanalei Watershed Hui, for valuable discussions and

guidance, and for logistical help in the field. Kathy Presto and Tom Reiss of the

USGS assisted with field work. Charles Bass and Garret Santos are thanked for

vessel operation and other logistical support. Reviewers Susan Cochran and

Renee Takesue provided helpful and timely feedback on this manuscript.

44
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47
APPENDIX 1: Sediment log for cores collected in June 2005

Station A (Core K0605-1; Black Hole):

0–0.5 cm: Fine-grained ‘fluff’ layer of surface sediment.

0.5–2 cm: Medium to coarse sand.

2–6 cm: Rounded pebbles up to 2.5 cm in diameter, in medium-coarse sand

matrix.

6–13 cm: Dominantly medium to coarse sand but with some fine, dark mud along

one side of the core. Several 1–2 mm-wide burrows occur from 10–13 cm.

13–17 cm: Medium to coarse sand with sharp base.

17–58 cm: Dark, very fine mud that is more consolidated than the overlying

horizon. Sediment is gray, black, or brown mud with some small plant

rootlets and pieces of wood in the lower part of this unit. A rounded clump

of mud was found that spanned from 30–35 cm depth, speculated to have

been a possible mud rip-up clast. Similar objects were observed on the

sea floor in this area of this core site at the time of its collection.

Station B (Core K0605-2; Middle-south part of bay):

0–0.5 cm: Thin surface fluff layer that is easily mobilized by surge on sea floor.

0.5–34 cm: Homogenous carbonate sand.

Station C (Core K0605-3; Northeast side of bay along coral wall):

This core was disturbed by water flowing through the unconsolidated sand during

collection.

0–0.5 cm: Thin surface fluff layer (organics and very fine sediment) that is easily

mobilized by surge on sea floor.

0.5–36 cm: Homogenous carbonate sand.

36–52 cm: Sand appears finer and has a grayer color than the overlying more

yellow sand. This is attributed to a higher heavy-mineral content in this lower unit.

Two coral fragments >1 cm across were present, at 40 cm and at 50 cm.

Station D (Core K0605-4; Northwest side of bay near CRAMP site):

0–0.5 cm: Thin surface fluff layer that is easily mobilized by surge on sea floor.

0.5–18 cm: Homogenous carbonate sand.

18–21 cm: Dark organic matter including leaves and twigs up to 5 cm long.

Station E (Core K0605-5; Middle of bay):

This core was disturbed by water flowing through the unconsolidated sand during

collection.

0–21 cm: Homogenous fine- to medium-grained carbonate sand.

Station F (Core K0605-6; Black Hole):

Only 4 cm of core recovery. Fluff / fluid-mud layer was present on the sea floor

initially but was lost or disturbed by core collection.

48
Station G (Core K0605-7; Along reef wall near Hanalei River mouth):

0–8.5 cm: Sand.

8.5–12 cm: Mixed sand and mud, mottled coloring, with some dark gray to black

patches.

12–15 cm: Sand.

49
APPENDIX 2: Sediment log for cores and river-bed samples

collected in August 2005

Station A (Core K0805-7; Black Hole):

0–0.5 cm: Fine-grained brown ‘fluff’ layer of surface sediment.

0.5–7 cm: Carbonate sand mixed with mud.

7–13 cm: Dark brown to black mud. Within that horizon is (from 10–12 cm) fresh

woody debris, other organics, worms, and less sand than the overlying horizon.

13–20 cm: Mixed carbonate sand, mud, and peaty organic debris.

20–22 cm: Brown, peaty mud with well preserved leaves and trace amounts of

wood.

22–30 cm: Brown peaty mud with well preserved leaves. Small amount of sand

but dominantly mud with leaves.

30–42 cm: Brown peaty mud with well preserved leaves.

42–49 cm: Brown peaty mud with well preserved leaves; mottled texture, no real

bedding. Sparse sand.

48 cm: Burrows visible; wood and plant debris within brown peaty mud.

49–53 cm: Plant matter.

Station B (Core K0805-1; Middle-south part of bay):

0–10 cm: Fine to medium-grained gray to tan-colored sand.

10–19 cm: Slightly darker gray sand compared to the overlying horizon. An

isolated clayey patch (1–2 cm wide) is present at 17 cm.

19–20 cm: Lighter-colored sand compared to the overlying horizon.

20–23 cm: Darker gray sand compared to the overlying horizon.

23–28 cm: Lighter-colored sand compared to the overlying unit; this horizon has

a sharp basal contact. An isolated clayey patch (1–2 cm wide) is present at 25

cm.

28–30 cm: Darker sand with void space ~1 cm wide.

30–38.5 cm: Grades gradually downward to lighter colored sand. An isolated

clayey patch (1–2 cm wide) is present at 33 cm.

Station C (Core K0805-3; Northeast side of bay along coral wall):

0–2 cm: Surface fluff / fluid-mud layer, mixing downward into fine carbonate

sand.

2–23 cm: Unconsolidated, homogenous mixture of medium- to coarse-grained

carbonate and terrigenous sand.

Station D (Core K0805-4; Northwest side of bay near CRAMP site):

0–0.5 cm: Small amount of leaf litter on sea floor but no real fluff layer.

0.5–34 cm: Homogenous, unconsolidated carbonate sand.

Station E (Core K0805-6; Middle of bay):

50
0–39 cm: Homogenous, unconsolidated carbonate sand; small amount of mixing

when core was collected. Mottled coloration was observed at a depth of 6 cm,

attributed to bioturbation.

Station F (Core K0805-2; Black Hole):

Several worms were present in this core.

0–0.5 cm: Surface fluff / fluid-mud layer, very fine sediment.

0.5–9.5 cm: Coarser sediment (unit coarsens upward) including carbonate sand

and mud.

9.5–12 cm: Laminated mud with occasional gravel-sized clasts. Dark brown to

black sand and mud. At 12 cm is a sharp basal contact.

12–14 cm: Laminated gray to brown mud.

14–15.5 cm: Gray laminated mud layer with an abrupt lower contact. This unit is

peaty.

15.5–32 cm: Brown to black mud with occasional carbonate sand grains. The

lower contact is gradational as this horizon grades down into sandier facies.

32–58.5 cm: Brown to black mud with some carbonate sand. At 40 cm was a

piece of wood that measured 4 cm long and 1 cm wide.

Station G (Core K0805-5; Along reef wall near Hanalei River mouth):

0–0.5 cm: Surface fluff / fluid-mud layer, dark brown.

0.5–4 cm: Medium to coarse-grained carbonate sand.

4–5 cm: Fine black mud mixed with carbonate sand.

5–12 cm: Mixed carbonate sand and black mud. A 2-cm-wide clast of coral

rubble occurs at a depth of 5 cm.

12–16 cm: Poorly sorted carbonate sand.

16–18 cm: Mixed carbonate sand and black mud.

18–28 cm: Unsorted, unstratified mixture of coarse-grained sand, coral rubble,

and terrestrial gravel.

River Site #1 (~4 km upstream of river mouth, near USGS gaging station

16103000): Sediment at this site consisted of mud and abundant organic debris,

including leaves and stems. Logs and branches are present underwater in the

river channel in the immediate area surrounding this sample location.

River Site #2 (under the traffic bridge where the access road between the

towns of Hanalei and Princeville crosses the Hanalei River, ~2.5 km above

the river mouth): Sediment at this site is dominantly mud with abundant organic

debris.

River Site #3 (approximately 0.5 km above the river mouth): Sediment at this

location is mixed sand and mud, dominated by dark, heavy-mineral, siliciclastic

grains.

51
River Site #4 (on river left at the mouth, adjacent to the Hanalei beach

park): Sediment at this site is fine sand and mud that forms a sandbar 5–15 m

wide.

52