Usgs geologic Investigations Series i-2761, Oahu

60

Haleiwa

T

he Haleiwa coastline is dominated by the embayments associated

with the confluence of the Kiikii and Paukauila streams and the

Anahulu River.A long and narrow beach, bordered in many places by dete-

riorated seawalls and revetments, extends from Mokuleia to Kaiaka Bay.

Rocky outcrops of limestone compose both Kaiaka and Puaena points. To

the northeast, the coast toward Kawailoa Beach consists mostly of inter-

spersed sand beaches and 3-6-ft rocky escarpments of basalt or limestone.

Broad wave abrasion platforms extend offshore of Mokuleia Beach, but

narrow toward Kawailoa Beach. This is a high wave-energy coastline that

receives some of the largest breaking waves in the state. In 1969, for exam-

ple, wave heights of between 30 and 35 ft were recorded offshore of

Haleiwa, and in 1998 as high as 50 ft. It is also a low-sloping coast, and near

the stream mouths wetlands and ponds are found. The only boat harbors

along the entire North Shore of Oahu are found inside Kaiaka and Waialua

Bays.

The moderate to high (5) to high (6) Overall Hazard Assessment

(OHA) for the Haleiwa coast is largely influenced by the low coastal slope

and a history of high wave energy and stream flooding.Additionally, where

erosion is ranked high along Mokuleia, and Alii Beach Park in Haleiwa, the

OHA is ranked high (6). The tsunamis of 1946, 1952, and 1957 generated

flood heights of 11, 17, and 17 ft, respectively, along the Haleiwa coastline.

In 1932, between 26 and 30 in of rain fell in a 24 hr period, resulting in

extensive local flooding. Because of this history and the low coastal slopes

found here, hazards due to tsunami, stream flooding, and high waves are

ranked high along this coast. The storm hazard along this coast is moder-

ately high, except northeast of Kawailoa Beach where the threat from hur-

ricanes is reduced because of higher slopes and local sheltering. Erosion is

high along the western segment of the Mokuleia shoreline and at the

Anahulu River mouth, and moderately high along the eastern portion of

Mokuleia and between Puaena Point and Kawailoa Beach. It is reduced to

moderately low and low at three sites in Mokuleia, where the wide offshore

reefs and scattered rocky carbonate outcrops onshore help buffer the

coastline from wave energy. Sea-level rise is ranked moderately low

throughout this region compared to Maui and the Big Island. The hazard

due to volcanism and seismicity is also ranked moderately low as it is

throughout the northern half of Oahu.

Haleiwa

Narrow beaches and

wide fringing reefs line

the Mokuleia and

Haleiwa coastal areas.

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S

ome of the world’s best surf breaks are found along the Waimea Bay coastline, where

winter waves annually reach breaking heights of 20 to 25 ft. Small pocket beaches along

the Kawailoa Shoreline give way to a rocky basalt coast south of the beautiful wide beach and

stream mouth at Waimea Bay. Long, coarse-grained sand beaches extend between Sunset

Beach and Waialee. Isolated outcrops of basalt and reefrock harden the shoreline near

Pupukea, Sunset Point, and Waialee Point. The coastal slope is steeper near Waimea Bay, but

gradually decreases toward Sunset Beach where it coincides with a low coastal terrace that

reaches northeast to Kahuku (see Kahuku map). Fringing reefs (mostly fossil) cover most of

the offshore region of this coast.

The Overall Hazard Assessment (OHA) for the Waimea coast is moderate to high (5),

which is primarily a result of the susceptibility to high wave energy and stream flooding. In

1946, 1952, and 1957, tsunami runup of 19, 20, and 22 ft, respectively, inundated Waimea Bay.

Stream flooding, especially in the flash flood prone Waimea River Valley, historically has been

significant, and high wave events annually overwash the coastal road and cause damage to

coastal property. For these reasons, the hazard due to tsunami, stream flooding, and high

waves are ranked high. While storms like Hurricane Iwa have been known to produce 50-55

mph winds along this coast, the hazard due to storms is ranked moderately low relative to

other areas in Hawaii. Erosion is ranked moderately low in Waimea Bay and along hardened

coastlines, and moderately high for most of the long sandy beaches to either side of Waimea

and along Pupukea Beach to Sunset Beach. It is also ranked high at the sandy beaches along

the coastal terrace near Waialee. The hazard due to sea-level rise is ranked moderately low

here as it is for most of Oahu, which is experiencing only moderate rates of rise. The vol-

canic/seismic hazard is also ranked moderately low here in the northern half of Oahu.

61

Waimea Bay

Waimea Bay

The Waimea coast looking southwest toward Kawailoa.

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62

Kahuku

R/B

frw

Bfr

e

Rfr

Hazar

d 

Type:

G    CS           

T  SF  

W  S  E  SL 

V/S       OHA

Bfr

Rfr

Bfr

e

R/B

frew

Rfr

Rfrw

R/Bfrw

R/B

frw

B

fre

Rfr

R/B

fr

no

data

1

4

4

2

2

2

2

2

4

Rfrw

Island of Oahu

Coastal Hazard Intensity

158°00'W

Hazard Intensity:

EXPLANATION

[For explanation of hazard types, see

 “Notes on Specific Hazards” in the Introduction]

Overall Hazard Assessment  (OHA)

G - Geology:

fr-fringing reef;  br-barrier reef;  e-embayed coast;  w-wetland

B-Beach;  S-Stream;  R-Rocky;  H-Headland;  D-Developed

Low - 1       2          3        4 - High

<20% -1      2       3 - >45%

W - High Waves

SF - Stream Flooding

S - Storms

E - Erosion

SL - Sea Level

V/S - Volcanic/Seismic

- No Data

T - Tsunami

CS - Coastal Slope

1         2          3         4          5         6          7

Low

High

Base Credit:  USGS 1:50,000 Kaena Point, Hawaii5321  II  W733 Edition 1-DMA and USGS 1:50,000 Laie, Hawaii  5421  III  W733  Edition 1-DMA

Prepared in cooperation with Hawaii Coastal Zone Management Program, Hawaii Office of Planning and the National Oceanic & Atmospheric Administration

K

ahuku

21°43'N

SCALE:  1:50,000

Contour Interval = 40 meters

0

0.5

1 mile

0

0.5

1.0

1.5 km

Cartography by Manoa Mapworks, Inc.

T

he northernmost tip of Oahu reaches around Kahuku Point where

low coastal terraces host one of the most extensive wetlands in the

state. Relict and modern dune fields lie seaward of mixed-use aquaculture

ponds and a wildlife sanctuary that provides habitat for birdlife. Rocky

limestone cliffs encircle the embayments at Kawela and Kuilima bays.

Lithified outcrops of eolianite along Kahuku and Makahoa points are

scoured by solution weathering, intertidal bioerosion, and the relentless

trade winds, creating a sharp and jagged surface that makes access to the

shoreline difficult. Extensive ridges of beachrock on the foreshore are

found along the entire area and are evidence of recent coastal erosion and

retreat. Spectacular wind-swept sand formations mark much of the wind-

ward coast and have left limestone outcrops and islets offshore. Sand

beaches are perched on benches of eolianite and old reefrock or beachrock

between Kahuku Point and Makahoa Point. Here some active dunes also

exist seaward of vegetated Holocene dunes. The fringing reefs widen east

of Kahuku Point due to the decreased wave energy away from the winter

swell of the north shore.

The Overall Hazard Assessment (OHA) is moderate to high (5) from

Waialee around Kahuku Point to just north of Kahuku town, while south to

Makahoa Point, where the wave energy is lower, it is reduced to moderate

(4). The tsunami and stream flooding hazards are ranked high along the

entire Kahuku coastline. During the 1946 and 1957 tsunamis, flood inun-

dation heights of 27 and 23 ft were recorded at Kahuku Point. The hazard

associated with high waves is ranked high around the entire Kahuku Point,

but is reduced to moderately low southeast of the Point where the coast is

partly sheltered from north swell. The storm threat is ranked moderately

low along the Kahuku coast because it is partly sheltered from the impact

of the majority of tropical storms that historically track to the west and

south of Oahu. Erosion is ranked moderately low for the small embay-

ments lining the western portion of Kahuku Point, except along the rocky

point immediately northeast of Kawela Bay beach where it is low.Along the

northeast side east of Kahuku Point there are no available data, except at

the town of Kahuku, where erosion is ranked high, but is then reduced to

low along Makahoa Point. The hazard due to sea-level rise here is moder-

ately low. The volcanic/seismic hazard here in the northern half of Oahu is

also ranked moderately low.

Kahuku

Sand dunes and

perched beaches

along Kahuku Point

are continuously

reshaped by the

persistent trade

winds.

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