Streamflow and Erosion Response to

Prolonged Intense Rainfall of November 1–2

2000, Island of Hawaii, Hawaii

By Richard A. Fontaine and Barry R. Hill

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 02-4117

Honolulu, Hawaii

2002
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

The use of firm, trade, and brand names in this report is for identification purposes

only and does not constitute endorsement by the U.S. Geological Survey.

For additional information write to: Copies of this report can be purchase

from:

District Chief U.S. Geological Survey

U.S. Geological Survey Branch of Information Services

677 Ala Moana Blvd., Suite 415 Box 25286

Honolulu, HI 96813 Denver, CO 80225-0286

U. S. DEPARTMENT OF 

MARCH 3, 1
Co

CONTENTS

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Purpose and Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Study Area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Waiakea High-Rainfall Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Kapapala High-Rainfall Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Storm Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Rainfall Amounts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Rainfall Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Description of Flood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Peak Flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Waiakea High-Rainfall Area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Kapapala High-Rainfall Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Peak-Flow Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Waiakea High-Rainfall Area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Kapapala High-Rainfall Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Rainfall-Runoff Relations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Waiakea High-Rainfall Area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Kapapala High-Rainfall Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Erosional Features in the Kapapala High-Rainfall Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

References Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

FIGURES

1–3. Maps showing:

1. Study areas and total rainfall, November 1–2, 2000 flood, island of Hawaii, Hawaii . . . . . . . . . . . . . . . . 

2. Waiakea high-rainfall area and data-collection sites, island of Hawaii, Hawaii. . . . . . . . . . . . . . . . . . . . . 

3. Kapapala high-rainfall area and data-collection sites, island of Hawaii, Hawaii . . . . . . . . . . . . . . . . . . . . 

4. Graph showing hourly rainfall totals for November 1–2, 2000 at Waiakea Uka and Kapapala Ranch,

island of Hawaii, Hawaii. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

5. Photograph showing site of destroyed Highway 11 bridge over Keaiwa Stream near Pahala, Hawaii,

November 3, 2000, island of Hawaii, Hawaii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

6–7. Maps showing:

6. Total rainfall in the Waiakea high-rainfall area, November 1–2, 2000 flood, island of Hawaii, Hawaii . . 

7. Total rainfall in the Kapapala high-rainfall area, November 1–2, 2000 flood, island of Hawaii, Hawaii. . 

8. Scatterplot of peak-flow recurrence interval and area-weighted storm rainfall, November 1–2, 2000 flood,

island of Hawaii, Hawaii. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

9–10. Graphs showing:

9. Piihonua hourly rainfall totals and Honolii streamflow data, November 1–2, 2000 flood, island of Hawa

Hawaii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
iv Streamflow and Erosion Response to Prolonged Intense Rainfall of November 1-2, 2000, Island of Hawaii, Hawaii

10. Relation between peak unit runoff and drainage area, November 1–2, 2000 flood, island of

Hawaii, Hawaii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

11–12. Photographs showing:

11. Hillslope erosional feature at site 47 along Kaoiki Pali, showing evidence of both fluvial

and mass-wasting erosion, island of Hawaii, Hawaii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

12. Headcut on Waihaka Stream between Kapapala Ranch and site 13, showing effect of

resistant cap of lava above ash deposits, island of Hawaii, Hawaii . . . . . . . . . . . . . . . . . . . . . . . . . . . 

TABLES

1. Maximum rainfall totals and recurrence intervals for selected durations, November 1–2, 2000 flood,

island of Hawaii, Hawaii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

2. Peak-flow and erosion measurement sites for November 1–2, 2000 flood, island of Hawaii, Hawaii . . . . . . . . . . . 

3. Peak flows and associated recurrence intervals for November 1–2, 2000 flood, and previous record peak flows,

island of Hawaii, Hawaii. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

4. Rainfall and runoff data for November 1–2, 2000 flood, island of Hawaii, Hawaii . . . . . . . . . . . . . . . . . . . . . . . . . 

5. Critical rainfall durations associated with peak flows for November 1–2, 2000 flood, island of Hawaii, Hawaii . . 

6. Hillslope erosional features along the Kaoiki Pali resulting from the November 1–2, 2000 flood,

island of Hawaii, Hawaii. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

7. Dimensions of selected hillslope erosional features along the Kaoiki Pali resulting from the November 1–2,

2000 flood, island of Hawaii, Hawaii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

8. Shear stresses exerted by peak flows upstream of hillslope erosional features along the Kaoiki Pali,

November 1–2, 2000 flood, island of Hawaii, Hawaii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
Introdu

Abstract

A combination of several meteorologic and

topographic factors produced extreme rainfall over

the eastern part of the island of Hawaii on November 1–2, 2000. Storm rainfall was concentrated in

two distinct areas, the Waiakea and Kapapala

areas, where maximum rainfall totals of 32.47 and

38.97 inches were recorded. Resultant flooding

caused damages in excess of 70 million dollars,

among the highest totals associated with flooding

in the State’s history. Storm rainfall had recurrence

intervals that ranged from 10 years or less for maximum 1-hour totals to 100 years or more for maximum 24-hour totals.

As part of this study, peak flow and/or erosion

data were collected at 41 sites. Analyses of these

data indicated that peak discharges of record

occurred at 6 of 12 sites where historic data were

available. Peak flows with estimated recurrence

intervals from 50 to over 100 years were recorded

at 4 of 11 sites. Peak flows were poorly correlated

with total storm rainfall. Critical rainfall durations

associated with peak flows ranged from 1 to 12

hours and were about 3 hours at most sites. Rainfall-runoff computations and field observations

indicated that infiltration-excess overland flow

alone was not sufficient to have caused the

observed flood peaks and therefore saturationexcess overland flow and subsurface flow probably

contributed to peak flows at most sites.

Most hillslope erosion associated with the

storm took place along or near the Kaoiki Pali in

the Kapapala area. Hillslope erosion was pr

nately caused by overland flow.

INTRODUCTION

During November 1–2, 2000, prolonged an

intense rain fell in two separate areas of the isla

Hawaii: the Waiakea area and the Kapapala are

1). Storm rainfall totals exceeded 30 in. within 

high-rainfall areas, and ranged from 5 to 25 in. w

larger surrounding area encompassing most of t

ern half of the island (Paul Haraguchi, consultin

orologist, written commun., 2001). The resultan

flooding caused millions of dollars in damages t

bridges, homes, businesses, and farms. No hum

ities resulted from the storm, and only one injur

reported. This study was done by the U.S. Geol

Survey (USGS), as part of the USGS Office of 

Water’s national program to document the effec

extreme floods in the United States.

Purpose and Scope

This report describes the streamflow respo

the storm of November 1–2, 2000, and docume

geomorphic effects of the storm and flood. The

descriptions are based on (1) determinations or 

mates of peak streamflows at selected locations 

the Waiakea and Kapapala high-rainfall areas, (2

minations of the recurrence intervals of the floo

at gaging stations with adequate data, (3) comp

of peak streamflows at different locations on th

of area-weighted rainfall and drainage area, and 

descriptions of hillslope erosional features relate

storm and flood in the Kapapala area. Detailed 

tions of storm meteorology, rainfall distribution 

Streamflow and Erosion Response to Prolonged Inten

Rainfall of November 1–2, 2000, Island of Hawaii, Ha

By Richard A. Fontaine and Barry R. Hill
2 Streamflow and Erosion Response to Prolonged Intense Rainfall of November 1-2, 2000, Island of Hawaii, Hawaii

intensity, and geomorphic effects in the Waiakea highrainfall area are provided by Haraguchi (Paul Haraguchi, consulting meteorologist, written commun., 2001),

and are not included in this report. Large-scale mass

movement on the Kilauea Volcano that may have

occurred during the storm (Cervelli and others, 2002)

also is not described here.

During the period October 28–29, 2000, strong

thunderstorms brought rainfall, estimated to be as great

as 24 to 27 in., to localized areas of eastern Maui (Kevin

Kodama, National Weather Service, written commun.,

2000). Runoff from this storm overflowed bridges,

prompting the closure of several roads. Numerous tourists and local residents were temporarily stranded as a

result of the storm although no fatalities occurred.

Although flooding was significant, analysis of the October 28–29, 2000 storm on Maui was not included in the

scope of this report.

Acknowledgements

The assistance of Kevin Kodama, National

Weather Service, Paul Haraguchi consulting meteorologist, and Sterling Yong, State of Hawaii Flood Coordinator, in obtaining information is gratefully

acknowledged. Mr. and Mrs. Gordon Cran of the Kapapala Ranch were kind enough to allow us access to

ranch lands for fieldwork and provided directions to

sites of interest. Saku Nakamura of the Natural

Resources Conservation Service provided data on soil

properties and Michael Lisowski of the U.S. Geological

Survey provided valuable insights regarding geomorphic processes associated with the storm.

STUDY AREA

The high-rainfall areas of Waiakea and Kapapala

(fig. 1) are located on the windward (eastern) slopes of

the island of Hawaii. The study area includes parts of

the volcanoes of Mauna Kea, Mauna Loa, and Kilauea.

These volcanoes are of Pleistocene or Recent age;

Mauna Loa and Kilauea are active volcanoes (Stearns

and Macdonald, 1946). Surface and subsurface rocks

include basaltic and andesitic aa and pahoehoe lava

flows and the Pahala Ash (Stearns and Macdonald,

1946). The climate is generally warm and humid. Prevailing winds are northeast trades, and orographic

effects imposed by the high, broad, volcanic mountains

of the island have a major effect on annual and 

rainfall distribution (Paul Haraguchi, consulting 

rologist, written commun., 2001). Historically, 

plantations have dominated land use at altitudes 

3,000 ft. Diversified agriculture, cattle ranching

forestry expanded after the closure of the planta

the 1990’s but much of the former sugar lands r

fallow. At altitudes above 3,000 ft, most of the 

forest, park, military reservations, or hunting ar

Waiakea High-Rainfall Area

The Waiakea high-rainfall area (figs. 1 and 

includes the city of Hilo and extends from abou

Papaikou on the north to Glenwood on the sout

from sea level to an altitude of approximately 4

(Paul Haraguchi, consulting meteorologist, writ

commun., 2001). Mean annual rainfall in this a

ranges from 118 in. along the coast to 236 in. at a

near 3,000 ft (Giambelluca and others, 1986). E

for the urban areas near the ocean, land cover is 

ally dense, tropical, native, and introduced fore

tation, with some agricultural activity on extens

former sugarcane lands.

The Waiakea high-rainfall area includes th

windward slopes of both Mauna Kea and Maun

Mauna Kea lies to the north of the Wailuku Riv

2), and its slopes are formed of moderate to hig

meable aa and pahoehoe basaltic and andesitic 

flows of the Hamakua Volcanics capped with P

Ash (Stearns and Macdonald, 1946) (updated g

names used are from Langenheim and Clague, 

South of the Wailuku River, the area includes h

and prehistoric basaltic aa and pahoehoe lava fl

the Kau Basalt and basaltic flows of the Kahuku 

capped by Pahala Ash (Stearns and Macdonald

Although all of the surficial geologic mater

highly permeable, the differing permeabilities of 

flows, pahoehoe lava flows, and ash are likely t

infiltration and runoff during rainfall. Stearns an

donald (1946 p. 159) considered the Pahala Ash 

generally less permeable than the lava flows of 

Hamakua Volcanics, and suggested that the ash 

increase runoff during storms. Sato and others (

p. 27) considered pahoehoe lavas to have low p

ability in comparison to surrounding soils, altho

they noted that aa lava flows act as ground-wat

recharge areas (Sato and others, 1973, p. 34) an
Study 

Figure 1. Study areas and total rainfall, November 1–2, 2000 flood, island of Hawaii, Hawaii (rainfall lines from

consulting meteorologist, Paul Haraguchi, written commun., 2001).

2

20 ̊

156 ̊

PA IFIC OCEAN

Oahu Molokai

L

Kah

Hawaii

HAWAII

156 ̊

155 ̊30'

55 ̊

19 ̊3

19

Keaau

Hilo

Papaikou

H

Honokaa

H

in Cook

Pahala

MAUNA LOA

KILAUEA

MAUNA KEA

WAIAKEA

HIGH-RAINFALL

AREA

KAPAPALA

HIGH-RAINFALL

AREA

HUALALAI

Upol

Honuapo Bay

O

Papa Bay

KealaB

Hono

B

Kawaih

B

0

0

5 10 MILES

5 10 KILOMETERS 10 KILOMETERS

EXPLANATION

LINE OF EQUAL RAINFALL, IN INCHES

RAIN GAGE AND NAME

Piihonua Hilo Airport

Waiakea Uka

Mountain View

Kapapala Ranch

Kapapala Ranch

Hawaii Volcanoes

National Park

Pahoa

5

10

15

20

25

35

35

25

30
4 Streamflow and Erosion Response to Prolonged Intense Rainfall of November 1-2, 2000, Island of Hawaii, Hawaii

Figure 2. Waiakea high-rainfall area and data-collection sites, island of Hawaii, Hawaii.

EXPLANATION

TOPOGRAPHIC CONTOUR, IN FEET ABOVE MEAN SEA LEVEL

STREAMFLOW-GAGING STATION AND ABBREVIATED NUMBER

MISCELLANEOUS DISCHARGE MEASUREMENT 

 SITE AND NUMBER

Gl

0

0

5 

5 KILOM

13000

600

7000

5000

9000

8000

6000

7000

7000

3000

0

10000

10000

12000

8000

9000

9000

4000

12000

1000

7176.5

014

7000

52

MAUNA LOA

155 ̊30' 155 ̊20' 155 ̊10'

19 ̊40'

19 ̊30'

19 ̊5
Storm Character

presumably contribute little or no surface runoff. For

most soils, surface permeability is 2.0 to 20 in/hr (Sato

and others, 1973; Saku Nakamura, Natural Resources

Conservation Service, written commun., 2001). Most

soils overlying ash or pahoehoe lavas have decreases of

two orders of magnitude in permeability at depths ranging from 8 to 72 in. below land surface (Saku Nakamura, Natural Resources Conservation Service, written

commun., 2001). Soils overlying aa lavas have

increases in permeability with depth (Saku Nakamura,

Natural Resources Conservation Service, written commun., 2001). The parts of the study area underlain by

ash or pahoehoe lavas therefore are more likely to generate shallow subsurface flow during heavy rainfall,

owing to their decreases in permeability at shallow

depths on steep slopes (Freeze, 1974), than are parts of

the area underlain by aa lavas, which have increases in

permeability at depth.

Kapapala High-Rainfall Area

The Kapapala high-rainfall area (figs. 1 and 3)

includes the Kapapala Ranch, the community of Wood

Valley, and the town of Pahala, and extends approximately from altitudes of 1,000 to 7,000 ft (Paul Haraguchi, consulting meteorologist, written commun., 2001).

Mean annual rainfall ranges from about 39 in. near the

7,000-ft elevation to 118 in. at the 3,000-ft elevation

(Giambelluca and others, 1986). From 3,000 ft to sea

level, annual rainfall decreases to about 40 in. (Giambelluca and others, 1986). Until the end of plantation

agriculture in 1995, much of the area below an altitude

of 3,000 ft to the southwest of the Kapapala Ranch was

used for sugar cultivation. Most of the former sugarcane

lands now are used for macadamia nut orchards, pasture, or are left fallow. The land to the northeast of the

Kapapala Ranch has been used for pasture for many

years. Forests cover most of the area above an altitude

of about 3,500 ft.

The Kapapala high-rainfall area is located mostly

on the slopes of Mauna Loa, but extends onto the southwestern slopes of Kilauea as well. Surficial geology on

Mauna Loa include primarily basaltic lava flows of the

Kau Basalt, with smaller exposures of ash-capped

basaltic lava flows of the Kahuku Basalt and a large

landslide deposit in the Wood Valley area (Stearns and

Clark, 1930; Stearns and Macdonald, 1946). On

Kilauea, the surficial geology consists of historic and

prehistoric basaltic lava flows (Stearns and Macdonald,

1946). Several major landforms related to struc

deformation or large-scale mass movement on b

Mauna Loa and Kilauea are within the Kapapal

rainfall area, including fault scarps called pali in 

and numerous fissures and extensional cracks (

and Macdonald, 1946).

As in the Waiakea high-rainfall area, differe

the permeabilities of surficial geologic material

affect rates and process of storm runoff in the K

high-rainfall area. Stearns and Clark (1930, p. 1

Stearns and Macdonald (1946, p. 76–77) conside

Pahala Ash exposed on the Kahuku Basalt to be 

permeable than the surrounding Kau Basalt. So

developed on ash have permeabilities ranging fr

to 6.0 in/hr, whereas soils developed on lava ha

face permeabilities ranging from 6.0 to 20 in/hr 

and others, 1973; Saku Nakamura, Natural Res

Conservation Service, written commun., 2001). 

tion-excess overland flow therefore will occur a

fall intensities of 2.0 to 20 in/hr. Soils develope

both types of parent material have decreases of 

two orders of magnitude in permeability at dept

ing from 4 in. below land surface for soils develo

lavas to 48 in. below land surface for ash soils (

Nakamura, Natural Resources Conservation Se

written commun., 2001). Such significant decre

permeability at shallow depths on steep hillslop

likely to result in shallow subsurface storm flow 

intense rainfall (Freeze, 1974).

STORM CHARACTERISTICS

Haraguchi (Paul Haraguchi, consulting me

gist, written commun., 2001) identified four pri

conditions whose simultaneous convergence du

November 1–2, 2000 contributed to the extreme 

of the storm. The conditions included (1) the up

topography of eastern Hawaii, (2) the location of 

upper level trough 500 mi southwest of Kauai, 

pattern of southeasterly trade winds in the area, 

the location of the remnants from tropical storm 

Total rainfall amounts for the storm of No

1–2, 2000 were historical maximums at many lo

and exceeded 30 in. at some gages (Paul Harag

consulting meteorologist, written commun., 200

However, in some parts of eastern Hawaii, the m

mum rainfall totals from the November 1–2, 200

were not significantly greater than those record
6 Streamflow and Erosion Response to Prolonged Intense Rainfall of November 1-2, 2000, Island of Hawaii, Hawaii

Figure 3. Kapapala high-rainfall area and data-collection sites, island of Hawaii, Hawaii.

EXPLANATION

TOPOGRAPHIC CONTOUR, IN FEET ABOVE MEAN SEA LEVEL

STREAMFLOW-GAGING STATION AND ABBREVIATED NUMBER

MISCELLANEOUS DISCHARGE MEASUREMENT 

 SITE AND NUMBER

EROSIONAL FEATURE SITE AND NUMBER

H

P

Piikea

Gulch

Kaalaala Gulch

Keaiwa Gulch

0

0

5 MILES

5 KILOMETERS

155 ̊40' 155 ̊20'

19 ̊20'

19 ̊10'

155 ̊30'

Kapapala

Ranch

KILAUEA

7000

27

50

MAUNA LOA

13000

8000

12000

10000

11000

7000

11000

6000

000

9000

8000

10

5000

3000

see fig. 3 --

continued
Storm Character

Figure 3. Kapapala high-rainfall area and data-collection sites, island of Hawaii, Hawaii--Continued.

EXPLANATION

TOPOGRAPHIC CONTOUR, IN FEET ABOVE MEAN SEA LEVEL

MISCELLANEOUS DISCHARGE MEASUREMENT 

 SITE AND NUMBER

EROSIONAL FEATURE SITE AND NUMBER

3000

4500

5000

5500

6000

6500

4000

3500

6500

155 ̊20'

19 ̊20'

19 ̊25'

155 ̊25'

Kaoiki

Pali

29

35

34

36

47

39 38 37

41

42

40

45

46

28

50

50

51

30

33

31

34

36a,b,c,d

32

29

0

0

1

1

2 MILES

2 KILOMETERS

HIGHWAY 11
8 Streamflow and Erosion Response to Prolonged Intense Rainfall of November 1-2, 2000, Island of Hawaii, Hawaii

during other storms. Several previous 24-hour rainfall

totals recorded on the island of Hawaii have been in

excess of 25 in. (Stearns and Clark, 1930; Paul Haraguchi, consulting meteorologist, written commun., 2001).

Storms with rainfall equal to or greater than the storm of

November 1–2, 2000 probably occurred before the historical period of record in Hawaii and are likely to occur

periodically in the future.

Rainfall Amounts

According to provisional data from the National

Weather Service (NWS) hydronet network (internet site

http://www.prh.noaa.gov/hnl/pages/hydrology.html),

the mean rainfall during October 2000 at six rain gages

in the Waiakea high-rainfall area was 182 percent of

normal, whereas year-to-date (January through October

2000) totals averaged 92 percent of normal. In the

Kapapala high-rainfall area, rainfall during October

2000 averaged 63 percent of normal at two rain gages.

January through October 2000 rainfall totals at the two

gages averaged 51 percent of normal. Thus, antecedent

soil moisture was probably higher in the Waiakea highrainfall area than in the Kapapala high-rainfall area.

During the November 1–2, 2000 storm, rainfall

totals of as much as 38.97 in. in the Kapapala high-rainfall area and 32.47 in. in the Waiakea high-rainfall area

were recorded (Kapapala Ranch and Mountain View

NWS gages). Lines of equal rainfall shown in figure 1

(Paul Haraguchi, consulting meteorologist, written

commun., 2001) depict the spatial distribution of total

rainfall for the November 1–2, 2000 storm. Haraguchi

(consulting meteorologist, written commun., 2001)

summarized daily rainfall totals at 39 gages and hourly

rainfall totals at 11 gages that were used to develop the

rainfall map. Two distinct storm centers with greater

than 30 in. of rainfall can be seen in figure 1. The

Waiakea high-rainfall area 30-in. rainfall line extends

southwest from near Hilo Airport to Glenwood. The

Kapapala high-rainfall area 30-in. rainfall line is centered near Kapapala Ranch.

One of the distinguishing characteristics of the

November 1–2, 2000 storm was that most of the rain fell

in periods of only 24 hours in duration. Plots of provisional, hourly rainfall data from the NWS Kapapala

Ranch and Waiakea Uka stations depict the temporal

pattern of rain during this storm (fig. 4). The most

intense rainfall at the Kapapala Ranch station (in the

Kapapala high-rainfall area) was during a 6-hou

that extended from 0600 to 1200 hours on Nove

During this 6-hour period, hourly rainfall totals 

from 3.02 to 4.15 in. The most intense rainfall a

Waiakea Uka station (in the Waiakea high-rainfa

was during a 4-hour period from 2200 hours on 

ber 1 to 0200 hours on November 2. During this 

period, hourly rainfall totals ranged from 2.57 t

in.

The temporal distribution of storm rainfall 

tinctly different in the Waiakea and Kapapala h

rainfall areas. Peak-rainfall intensities occurred 

later in the Kapapala high-rainfall area. As a res

amount of rain that fell prior to the period of ma

intensity was much greater there. In the Waiake

rainfall area, as represented by the data for the W

Uka station (fig. 4), the 4-hour period of most i

rainfall occurred 14 hours after the beginning o

storm. A total of 6.65 in., or 21 percent of the to

storm rainfall of 30.89 in., fell prior to the perio

most intense rainfall. A total of 12.83 in., or 42 

of the total-storm rainfall, fell after the period o

intense rainfall. In the Kapapala high-rainfall ar

represented by the data for the Kapapala Ranch 

(fig. 4), the 6-hour period of most intense rainfa

occurred 22 hours after the storm began. A tota

13.73 in., or 35 percent of the total-storm rainfa

38.97 in., fell prior to the period of most intense r

A total of 2.99 in., or 8 percent of the total-stor

fall, fell after the period of most intense rainfall

Maximum rainfall totals and recurrence in

for selected durations for the November 1–2, 20

storm are summarized in table 1. Rainfall frequ

data are discussed in the next section. The maxi

rainfall totals shown in table 1 can be used to fu

contrast the Waiakea and Kapapala high-rainfal

The only rain gage in table 1 that is located in th

pala high-rainfall area is the Kapapala Ranch g

Maximum rainfall totals for durations of 1, 3, 6, 

24-hours at the Kapapala Ranch gage were high

all but one value recorded at each of the other g

table 1, the exception being the maximum 1-ho

fall total of 4.56 in. at Hilo Airport. The maxim

and 6-hour rainfall totals of 12.25 and 22.25 in. a

pala Ranch were 25 and 48 percent greater than 

mum totals for those durations at any of the othe

These data indicate that, for the most part, max

rainfall intensities were greater in the Kapapala 
Storm Character

Figure 4. Graph showing hourly rainfall totals for November 1–2, 2000 at Waiakea Uka and Kapapala Ranc

island of Hawaii, Hawaii. (Provisional data from the National Weather Service)

8 10 12 14

NOVEMBER 1 NOVEMBER 2

16 18 20 22 24 2 4 6 8 10 12 14 16 18

DATE AND TIME IN HOURS

Waiakea Uka

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

8 10 12 14

NOVEMBER 1 NOVEMBER 2

16 18 20 22 24 2 4 6 8 10 12 14 16 18

DATE AND TIME IN HOURS

RAINFALL, IN INCHES

Kapapala Ranch

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

RAINFALL, IN INCHES
10 Streamflow and Erosion Response to Prolonged Intense Rainfall of November 1-2, 2000, Island of Hawaii, Hawaii

rainfall area than they were in the Waiakea high-rainfall

area.

Rainfall Frequency

The severity of rainfall events, both in terms of

total rainfall and intensity, can be quantified through the

use of rainfall-frequency data. Frequency data are commonly expressed in terms of recurrence intervals in

years. The recurrence interval is approximately the

average period of time between events that are greater

than or equal to a specified value. For example, an event

with a recurrence interval of 50 years is one that has a

rainfall total expected to be equaled or exceeded, over

the long term, an average of once every 50 years. Recurrence intervals are computed for rainfall totals that fall

within specified durations or time intervals.

Recurrence intervals associated with maximum

rainfall totals for selected durations of time for the

November 1–2, 2000 storm are summarized in table 1.

Recurrence interval data in table 1 were based on analyses contained in Technical Paper 43 published by the

U.S. Weather Bureau (1962).

Recurrence interval data summarized in table 1

indicate that for durations of 1-hour, the maximum rainfall intensities recorded during the November 1–2, 2000

flood were not extreme. With the exception of the

Kapapala Ranch and Hilo Airport data, where 5 to 10

year recurrence intervals were found, maximum 1-hour

rainfall totals were of a magnitude that would be

expected to occur every 1 to 2 years on average. The

severity of the November 1–2, 2000 storm, as measured

by rainfall recurrence interval, increased as the d

of the time interval increased. Twenty-four hour 

totals had recurrence intervals greater than or e

100 years at six of the eight rain gages included 

table 1.

DESCRIPTION OF FLOOD

Rainfall intensities of greater than 10 in/day 

expected at least once a year somewhere in the 

Hawaii (Lee and Valenciano, 1986, p. 201). Floo

therefore common throughout the State, particu

areas such as the Waiakea and Kapapala high-r

areas (Harris and Nakahara, 1980; Haraguchi, 1

and Haraguchi, 1980b). In these areas, intense ra

common and most streams have small watershe

than 50 mi2

) with very steep slopes. In combina

these factors produce significant volumes of run

short response times.

Total flood damages associated with the N

ber 1–2, 2000 storm were estimated to be in exc

70 million dollars (Paul Haraguchi, consulting 

rologist, written commun., 2001). Travel in and 

the Waiakea and Kapapala high-rainfall areas w

brought to a standstill as numerous bridges and 

crossings were destroyed. Most notable among 

damaged crossings were the four bridges along 

way 11 near Pahala and the Komohana Street B

over Alenaio Stream. Figure 5 is a picture taken 

site of the former Highway 11 Bridge over Kea

Stream, just north of Pahala, on November 3, 2

Table 1. Maximum rainfall totals and recurrence intervals for selected durations, November 1–2, 2000 flood, islan

Hawaii, Hawaii

[Provisional data from the National Weather Service, Honolulu, Hawaii; >, greater than; rain gage locations are shown in figure 1]

National Weather

Service rain gage

Depth (inches)/Recurrence interval (years)

1 hour 3 hours 6 hours 12 hours 24 hours

Piihonua 3.35/1 8.67/10 14.15/25–50 20.44/50–100 24.73/50–1

Hilo Airport 4.56/5–10 9.78/50–100 13.21/50–100 22.55/>100 26.89/>100

Waiakea Uka 3.24/1 8.78/10–25 15.02/50–100 23.90/>100 29.11/>100

Mountain View 3.31/2 8.56/25–50 13.24/50–100 19.28/>100 29.75/>100

Glenwood 2.32/1 6.24/5–10 10.78/25 17.51/100 26.60/>100

Pahoa 2.76/1 5.73/2–5 9.90/25 14.33/50 16.03/25

Hawaii Volcanoes

 National Park

2.10/1 5.40/5 7.00/5 13.80/25–50 20.80/100

Kapapala Ranch 4.15/10 12.25/>100 22.25/>100 28.73/>100 37.02/>100
Description of 

In response to the extreme flooding and level of

damage, the Governor of Hawaii declared the island of

Hawaii a disaster area on November 4, 2000. Within a

week the island was declared a federal disaster area. In

the sections that follow are summaries of the peak-flow

discharge and frequency, and rainfall-runoff data for the

November 1–2, 2000 storm in the Waiakea and Kapapala high-rainfall areas.

Peak Flows

As part of this study, the U.S. Geological Survey

collected peak flow and/or erosion data at 41 sites to aid

in the description of the flood. These 41 sites are listed

in table 2 and their locations are shown in figures 2 and

3.

Waiakea High-Rainfall Area

Peak flow and/or peak stage data were collected at

11 sites in the Waiakea high-rainfall area. These sites

are listed in table 2 and their locations are shown in figure 6. Included among the 11 sites are 8 active streamgaging stations, 2 discontinued stream-gaging s

and 1 miscellaneous site. Of the eight active gag

tions, only two are continuous record sites wher

and discharge data are collected at 15-minute in

ments, and of the two, only one operated during 

flood. The six remaining active stations are cre

gages where only measurements of peak stage a

discharge are available for the storm. Data colle

activities at the one miscellaneous and two disco

sites were undertaken specifically for the study 

flood.

Peak flow and stage data for the Novembe

2000 flood in the Waiakea high-rainfall area ar

marized in table 3. Also included in table 3 are t

ods of record at the gaging stations and the date

magnitudes of the previous peak flows of record

rence interval data in table 3 is discussed in the 

ing section of the report.

A variety of hydraulic models and hydrolog

niques were utilized to compute peak stages an

at the 11 sites in the Waiakea high-rainfall area

peak stage at site 7000 was determined by using

Figure 5. Photograph showing site of destroyed Highway 11 bridge over Keaiwa Stream near Pahala, Hawa

November 3, 2000, island of Hawaii, Hawaii. Note person (circled) for scale.
12 Streamflow and Erosion Response to Prolonged Intense Rainfall of November 1-2, 2000, Island of Hawaii, Hawaii Table 2. Peak-flow and erosion measurement sites for November 1–2, 2000 flood, island of Hawaii, Hawaii Site number (figs. 2 and 3) USGS station number Station name Peak flow data Erosion data Station type Remarks 7000 16700000 Waiakea Stream near Mountain View No No abandoned continuous-record streamgage peak stage measurement 7013 16701300 Waiakea Stream at Hilo Yes No crest-stage gage peak discharge from slope-area measurement 7014 16701400 Palai Stream at Hilo Yes No crest-stage gage peak discharge from slope-area measurement 7016 16701600 Alenaio Stream at Hilo Yes No crest-stage gage bank erosion near gage; peak dis- charge from slope-area measure- ment 7040 16704000 Wailuku River at Piihonua Yes No active continuous-record streamgage peak discharge from rating 7130 16713000 Wailuku River at Hilo Yes No abandoned continuous-record streamgage peak discharge from rating; streambank landslide near gage 7170 16717000 Honolii Stream near Papaikou Yes No active continuous-record streamgage peak discharge from rating 7174 16717400 Kalaoa Mauka Stream near Hilo Yes No crest-stage gage peak discharge from flow through culvert measurement 7176 16717600 Alia Stream near Hilo Yes No crest-stage gage peak discharge from rating 7176.5 16717650 Kapehu Stream near Pepeekeo Yes No crest-stage gage peak discharge from flow through culvert measurement 7700 16770000 Hionamoa Gulch at Pahala Yes No abandoned crest-stage gage peak discharge from critical-depth measurement 7705 16770500 Paauau Gulch at Pahala Yes No active continuous-record streamgage bank erosion at gage; peak discharge from flow through culvert measurement

2 191822155281601 Waihaka Stream at altitude 3,230 feet near

Pahala

Yes No miscellaneous bank erosion upstream; peak discharge from critical-depth measurement

13 191702155271301 Waihaka Stream at altitude 2,290 feet near

Pahala

Yes No miscellaneous above channel headcut; peak discharge from critical-depth measurement

18 191744155273001 Waihaka Stream at altitude 2,740 feet near

Pahala

Yes No miscellaneous peak discharge from critical-depth

measurement

21 191616155282601 Waiakaloa Gulch at Wood Valley Camp Yes No miscellaneous peak discharge from critical-depth

measurement

27 191209155282301 Paauau Stream below Highway 11 at Pahala Yes No miscellaneous peak discharge from critical-depth

measurement

28 none none No Yes miscellaneous29 192228155224201 Unnamed Gulch above Peter Lee Road near

Wood Valley

Yes No miscellaneous upstream of site 30; peak discharge

from critical-depth measurement

30 none none No Yes miscellaneous downstream of site 2931 none none No Yes miscellaneous downstream of site 3532 none none No Yes miscellaneous
Description of 

34 192326155215101 Unnamed gulch at altitude 3,530 feet

Kaoiki Pali near Volcano

Yes Yes miscellaneous peak discharge from critical-depth

measurement

35 192314155215901 Unnamed gulch at altitude 3,470 feet

Kaoiki Pali near Volcano

Yes No miscellaneous upstream of site 31; peak discharge

from critical-depth measurement

36a none none No Yes miscellaneous36b none none No Yes miscellaneous36c none none No Yes miscellaneous36d 192400155212101 Unnamed gulch at altitude 3,460 feet Kaoiki Pali near Volcano Yes Yes miscellaneous peak discharge from critical-depth measurement37 none none No Yes miscellaneous38 none none No Yes miscellaneous39 none none No Yes miscellaneous40 none none No Yes miscellaneous41 none none No Yes miscellaneous42 none none No Yes miscellaneous45 none none No Yes miscellaneous46 none none No Yes miscellaneous47 192507155210401 Unnamed gulch at altitude 4,000 feet near

Volcano

Yes Yes miscellaneous peak discharge from critical-depth

measurement

50 none none No Yes miscellaneous51 none none No Yes miscellaneous52 193940155073901 Waiakea Stream above Hoaka Stream at

Waiakea

Yes No miscellaneous peak discharge from critical-depth

measurement

Table 2. Peak-flow and erosion measurement sites for November 1–2, 2000 flood, island of Hawaii, Hawaii--Continued

Site

number

(figs. 2 and 3)

USGS

station number Station name Peak flow data Erosion data Station type Remarks
14 Streamflow and Erosion Response to Prolonged Intense Rainfall of November 1-2, 2000, Island of Hawaii, Hawaii

Figure 6. Total rainfall in the Waiakea high-rainfall area, November 1–2, 2000 flood, island of Hawaii, Hawaii (rainf

from consulting meteorologist, Paul Haraguchi, written commun., 2001).

Gl

hi

7000

52

EXPLANATION

LINE OF EQUAL RAINFALL, IN INCHES

STREAMFLOW-GAGING STATION AND ABBREVIATED NUMBER

MISCELLANEOUS DISCHARGE MEASUREMENT 

 SITE AND NUMBER

WATERSHED BOUNDARY

155 ̊30' 155 ̊20' 155 ̊10'

19 ̊40'

19 ̊30'

19 ̊50

0

0

5 

5 KILOM

5

10

15

25

7176.5

6

3

7014

10

MAUNA LOA

MAUN
Description of 

differential leveling techniques to refer a flagged highwater mark to the stage datum used at the gage. Criticaldepth techniques (Barnes and Davidian, 1978, p. 189)

were used to compute the peak flow at site 52. Use of

the critical-depth technique to compute peak flows was

validated by Jarrett and England (2002). Slope-area

techniques (Fulford, 1994) were used to compute peak

flows at sites 7013, 7014, and 7016. A calibrated stagedischarge rating curve (Rantz and others, 1982) was

used to compute peak flows at sites 7040, 7130, 7170,

and 7176. Flow-through culvert computations (Fulford,

1998) were used to compute peak flows at sites 

and 7176.5.

Record peak flows and/or stages were reco

4 of the 11 sites including Waiakea Stream near 

tain View (site 7000), Waiakea Stream at Hilo 

7013), Palai Stream at Hilo (site 7014), and Ale

Stream at Hilo (site 7016). The four sites with n

peaks of record are all located in or close to the 

enclosed by the 30-in. rainfall line shown in figu

the Waiakea Stream near Mountain View gage, t

Figure 7. Total rainfall in the Kapapala high-rainfall area, November 1–2, 2000 flood, island

of Hawaii, Hawaii (rainfall lines from consulting meteorologist, Paul Haraguchi, written

commun., 2001).

7705

27

0

0

5 MILES

5 KILOMETERS

EXPLANATION

LINE OF EQUAL RAINFALL, IN INCHES

STREAMFLOW-GAGING STATION AND ABBREVIATED NUMBER

MISCELLANEOUS DISCHARGE MEASUREMENT 

 SITE AND NUMBER

WATERSHED BOUNDARY

155 ̊40' 155 ̊20'

19 ̊20'

19 ̊10'

155 ̊30'

5

5

10

25

13

8

34

47

15

KILAUEA

MAUNA LOA
16 Streamflow and Erosion Response to Prolonged Intense Rainfall of November 1-2, 2000, Island of Hawaii, Hawaii

discharge was not determined; however, the peak stage

from this flood (6.44 ft) was 1.97 ft higher than the peak

stage for the period of record (1930 to 1995). Peak flow

at the Waiakea Stream at Hilo gage (site 7013) was 57

percent higher than any peak there since 1968.

Peak flow at the Palai Stream gage (site 7014) was 25

percent higher than any peak there since 1965. These

findings were based on both published and unpublished

USGS data collected at the gages.

The peak flow for the Alenaio Stream at Hilo gage

(site 7016) was significantly higher than the previous

peak of record; however, records have been collected at

this site for only 5 years. Peak flows during the November 1–2, 2000 storm at three sites north of Hilo (sites

7174, 7176, and 7176.5) were on average 44 percent

lower than their previous peak flows of record 

ary 20, 1979 flood; Harris and Nakahara, 1980)

Kapapala High-Rainfall Area

Peak flow data were collected at 12 sites in 

Kapapala high-rainfall area. These sites are list

table 2 and shown in figure 7. The 12 sites inclu

active stream-gaging station, 1 discontinued cre

gage, and 10 miscellaneous sites. No continuou

records of discharge are available in the area be

site 7705 (Paauau Gulch at Pahala) was inopera

ing the November 1–2, 2000 flood. Data collec

activities at the one discontinued site and the 10 

laneous sites were undertaken specifically for th

of this flood.

a

 Site number refers to the site numbers from table 2

b

 Peak stage associated with the peak flow was 4.47 feet c

 Peak stage during the November 1-2, 2000 flood was 6.44 feet

Table 3. Peak flows and associated recurrence intervals for November 1–2, 2000 flood, and previous record peak

flows, island of Hawaii, Hawaii

[ft3/s, cubic feet per second; --, not available; >, greater than; P, operational as of 2002]

Previous record

peak flow

(ft3/s)

Date of

previous peak

November 1–2, 2000

Site

numbera Period of peak-flow record

Peak flow

(ft3/s)

Recurrence

interval (year

7000 310b 08/26/70 1930-95 --c >100

7013 3,670 08/12/94 1968-75, 1979, 1993-P 5,760 70

7014 1,260 02/20/79 1965-71, 1979-80, 1994, 2001-P 1,580 50

7016 1,010 07/30/97 1997-P 6,300 --

7040 80,200 08/11/40 1928-40, 1940-1947, 1948-P 40,700 10

7130 79,800 12/13/87 1977-79, 1980-95 75,000 10

7170 22,600 05/23/78 1911-13, 1967-P 14,300 5

7174 400 02/20/79 1963-67, 1973-76, 1978-79, 1985,

2001-P

228 15

7176 2,850 02/20/79 1962-72, 1979, 1986, 1994-P 1,520 80

7176.5 3,320 02/20/79 1963-68, 1975, 1979, 1985-86,

1994-P

1,900 30

7700 10,400 02/20/79 1963-80, 1985-86, 1994 11,400 25

7705 3,600 01/05/69

01/08/75

1963-79, 1994-98, 2001-P 4,480 15

2 -- -- none 7,150 --

13 -- -- none 11,600 --

18 -- -- none 8,920 --

21 -- -- none 5,500 --

27 -- -- none 7,180 --

29 -- -- none 530 --

34 -- -- none 54 --

35 -- -- none 229 --

36d -- -- none 145 --

47 -- -- none 262 --

52 -- -- none 6,420 --
Description of 

Peak-flow data for the November 1–2, 2000 flood

in the Kapapala high-rainfall area are summarized in

table 3. Also included in table 3 are the periods of record

at the gaging stations and the dates and magnitudes of

the previous peak flows of record. Recurrence interval

data in table 3 is discussed in the following section.

Note that for the 10 miscellaneous sites in table 3, only

peak flow data for the November 1–2, 2000 flood are

included because there are no historical data for these

sites.

Several hydraulic models were used to compute

peak flows at the 12 sites in the Kapapala high-rainfall

area. The peak flow at site 7705 was determined using

a combination of culvert and road overflow analyses

(Fulford, 1998). Critical-depth techniques (Barnes and

Davidian, 1978. p. 189) were used to compute peak

flows for the remaining 11 sites.

Record peak flows took place at both of the stations in the Kapapala high-rainfall area with historic

information, Hionamoa Gulch at Pahala (site 7700) and

Paauau Gulch at Pahala (site 7705). Peak flows at the

Hionamoa and Paauau gages were 10 and 24 percent

higher than the previous peaks of record at the gages

since 1963. These findings were based on both published and unpublished USGS data collected at the

gages. The two sites with new peaks of record are close

to the area enclosed by the 30-in. rainfall line shown in

figure 7.

Attempts were made to determine peak flows for

Keaiwa, Kaalaala, and Piikea Gulches near Highway 11

(fig. 3). At each of these locations, bridges were heavily

damaged or destroyed during the flood. Unfortunately

no suitable sites were found where flood hydraulic

models could be applied. At each of these locations the

flow broke into multiple channels and in many places

created new ones. Peak flow determinations of 7,360

cubic feet per second (ft3

/s), 6,460 ft3/s, and 6,920 ft3/s

were made at Keaiwa, Kaalaala, and Piikea Gulches,

respectively, after the February 20, 1979 flood (Harris

and Nakahara, 1980, p.12). Given that (1) maximum

storm total rainfall in this area during the 1979 flood

was 26.80 in. (Harris and Nakahara, 1980, p. 8) while

the maximum recorded during the November 1–2, 2000

flood was 38.97 in. and (2) peak flows at the two historic stream gages in the area (sites 7700 and 7705) had

significantly higher flows in 2000 compared with 1979,

it is probably reasonable to assume that peak flows at

these sites during the November 2000 flood were higher

than those determined for the February 20, 1979 flood.

Peak-Flow Frequency

As explained in the section on rainfall freq

the recurrence interval of a given peak flow is a m

of the average number of years between floods 

flows that equal or exceed it. For example, the 1

peak flow is one that would be equaled or exce

over the long term, an average of once every 10

This does not imply that floods will take place at 

intervals: two 100-year floods could take place 

the same year, or 100 years could pass without 

100-year flood. Another way to view the recurr

interval is to take its reciprocal (for example 10

becomes 1/100 or 0.01), which yields the annua

exceedance probability. In this case, a 100-year 

has an annual exceedance probability of 0.01, or 

cent chance of occurring or being exceeded in an

year.

In this study, Log Pearson type III procedu

described by the Interagency Advisory Commit

Water Data in Bulletin 17B (1982) were used to 

pute frequency curves for each of the data colle

sites (table 3) that have a minimum of 10 years 

record. These frequency curves were then used 

mate recurrence intervals for the November 1–2

flood. When computing frequency curves, the s

skew was weighted with a generalized skew coe

of –0.05 (Interagency Committee on Water Data

p. 12) and where available, historic information 

used to extend the effective length of record (In

agency Committee on Water Data, 1982, app. 6

toric record lengths were based on published an

unpublished USGS records available for the sit

well as those for adjacent sites. When available

November 1–2, 2000 peak discharge was includ

the frequency analyses. None of the sites where 

quency analyses were run have peak discharges a

by reservoirs. No trends were detected in any o

annual peak flow series; therefore, all were trea

being homogeneous. In general, the higher a giv

flow is relative to the historic peak flows at a si

higher the recurrence interval. In this respect, re

rence intervals computed for the November 1–2

flood are also a reflection of the past flooding hi

a site.
18 Streamflow and Erosion Response to Prolonged Intense Rainfall of November 1-2, 2000, Island of Hawaii, Hawaii

Waiakea High-Rainfall Area

Sufficient historic records were available for 9 of

the 11 data sites in the Waiakea high-rainfall area to

compute recurrence intervals for the November 1–2,

2000 flood. The recurrence interval data are shown in

table 3. The recurrence interval for the November 1–2,

2000 flood on Waiakea and Palai Streams (sites 7000,

7013, and 7014) ranged from 50 to greater than 100

years. An exact recurrence interval was not shown for

site 7000 because the peak flow for the November 1–2,

2000 storm could not be determined. The peak flow was

known to be significantly greater than that associated

with the highest point on the stage-discharge rating

curve in effect when the station was last in operation

(5.00 ft gage height is equivalent to 473 ft3

/s) because

the peak stage for the November 1–2, 2000 flood was

6.44 ft and the stage-discharge rating was unlikely to

have changed significantly since 1995. The peak-flow

frequency curve computed for site 7000 indicated that a

100-year flood has a discharge of about 440 ft3

/s, thus a

greater-than-100-year recurrence interval shown in

table 3. No recurrence interval was shown for site 52

because this is a miscellaneous site with no historic

data. No recurrence interval was shown for site 7016

because there are only 5 years of historic data available.

On the basis of the locations of sites 52 and 7016 and the

recurrence interval computed for adjacent sites, the

November 1–2, 2000 flood probably had a recurrence

interval between 50 and 100 years at those locations.

At sites on the Wailuku River and Honolii Stream

(sites 7040, 7130, and 7170) the recurrence intervals

were 5 to 10 years. At each of these sites there were several historic peak flows that were greater than the

November 1–2, 2000 flood. For example, in 73 years of

record at site 7040, the November 1–2, 2000 peak flow

of 40,700 ft3

/s was exceeded by five annual peak flows,

with the highest being 80,200 ft3

/s in August 1940.

At sites on three small streams north of Hilo, (sites

7174, 7176, and 7176.5) the recurrence intervals were

15, 80, and 30 years, respectively. The recurrence interval of 80 years for Alia Stream (site 7176) appears to be

somewhat of an outlier; however, given the data collected over the 40-year historic period of record at the

site, the computation is reasonable. At Alia Stream the

two highest peaks of record are 2,850 ft3

/s and 1,520

ft3

/s (February 1979 and November 2000 floods) while

the third highest peak was only 560 ft3

/s (April 1986

flood). The 1979 and 2000 peak flows are 5.1 and 2.7

times greater than any previous peak flow recorded at

Alia Stream in 40 years. As noted earlier, the hi

given peak flow is relative to the historical peak 

the higher the recurrence interval. At Alia Strea

the 1979 and 2000 floods are significantly high

the other historic peak flows, therefore the stati

frequency analyses show them to have high rec

intervals.

Kapapala High-Rainfall Area

Only 2 of the 12 sites in the Kapapala high-

area had sufficient historic data to compute recu

intervals for the November 1–2 flood. These we

7700 on Hionamoa Gulch at Pahala and site 77

Paauau Gulch at Pahala. Recurrence intervals w

sonably consistent and were 25 years for site 77

15 years for site 7705 (table 3). The remaining 

were miscellaneous sites with no historic data.

Rainfall-Runoff Relations

The relations between the rainfall that fell 

the storm of November 1-2, 2000, and the runo

responses of streams in the Waiakea and Kapap

high-rainfall areas are examined in this section 

report. Improving our understanding of floodin

cesses in these areas is important for those living 

and for county, state, and federal officials who 

plan for the recurrence of damaging floods.

The process of flood generation or product

involves a complex interaction of atmospheric i

geology and geomorphology, vegetation and so

human influences (Pilgrim and Cordery, 1992, 

The relatively young and evolving nature of the b

(Stearns and Macdonald, 1946) and the extreme 

variation of rainfall (figure 1) in the study area 

complicate the process.

A simplistic, yet useful way to consider ra

runoff relationships can be found in the structur

rational method formula (Pilgrim and Cordery, 

p. 9.15),

q = F C i A, 

where:

q is the flood peak flow,

F is a unit’s conversion factor, which in E

units equals 1.008 and is

 generally omitted from the formula,
Description of 

 C is a dimensionless term that relates runoff to

rainfall,

 i is the rainfall intensity, and

A is the drainage area of the basin.

The rational formula is widely used to estimate

flood flows in small basins and can be considered “an

approximate deterministic model representing the flood

peak” (Pilgrim and Cordery, 1992, p. 9.15). In this simplistic model, the C term incorporates most of the complexities referred to above. However, flood peak flow in

this model is directly correlated to drainage area of the

basin and rainfall intensity. The rainfall intensity term

has a time frame, which is considered to be the time of

concentration for the basin or the time it takes water to

travel from the most remote point in the basin to the

point of interest. The rational method is not used for

computations in this report. The implication for 

study, derived from the rational method formula

while total rainfall for a storm is an important f

affecting total storm runoff, peak flows are mor

enced by rainfall that fell over shorter periods o

To evaluate rainfall-runoff relations in the 

area, peak-flow and recurrence-interval data fro

3 along with rainfall-runoff data shown in table 

used. Table 4 includes the drainage area, peak u

off, area-weighted storm rainfall, the most prox

NWS hourly rain gage and the maximum hourly 

recorded at the gage during the November 1–2, 

storm, and peak runoff ratios for each of the 22 

where peak-flow data were collected. Watershe

boundaries were digitized and geographic infor

system (GIS) techniques were used to compute

a

 Site numbers correspond to sites listed in table 2 and shown in figures 2 and 3 b

 Values greater than 100 are considered unreasonable and likely result from errors in drainage area, rainfall intensities, or peak flow estimates c

 Averages were computed from peak hourly rainfall at the Kapapala Ranch and Hawaii Volcanoes National Park gages

d

 Computed drainage area has a high degree of uncertainty owing to poorly defined drainage area boundaries e

 Peak unit runoff is subject to error owing to the uncertainty in the computed drainage area

Table 4. Rainfall and runoff data for November 1–2, 2000 flood, island of Hawaii, Hawaii

[mi2, square mile; ft3/s/mi2, cubic feet per second per square mile]

Site

numbera Drainage area(mi2)

Peak unit

runoff

(ft3/s/mi2)

Peak hourly

rainfall

(inches)

Rain gage used

for peak rainfall

Peak-runoff ratio

(peak unit runoff

as percentage of

peak hourly

rainfall)

Area-weighte

storm rainfa

(inches)

7000 17.4 -- -- -- -- 23.1

7013 35.8 161 3.24 Waiakea 8 25.8

7014 5.08 311 3.24 Waiakea 15 30.0

7016 8.62 731 3.24 Waiakea 35 28.2

7040 230 168 3.35 Piihonua 8 8.9

7130 256 293 3.35 Piihonua 14 10.0

7170 11.6 1,230 3.35 Piihonua 57 17.1

7174 0.24 950 3.35 Piihonua 44 22.5

7176 0.58 2,620 3.35 Piihonua b121 22.5

7176.5 1.09 1,740 3.35 Piihonua 81 22.5

7700 9.31 1,220 4.15 Kapapala 46 26.9

7705 1.74 2,780 4.15 Kapapala 96 33.4

2 6.54 1,090 4.15 Kapapala 40 28.1

13 7.97 1,460 4.15 Kapapala 54 29.4

18 7.45 1,200 4.15 Kapapala 45 29.0

21 2.50 2,200 4.15 Kapapala 82 34.8

27 7.41 969 4.15 Kapapala 36 31.6

29 0.30 1,770 3.12 caverage 91 32.5

34 d0.01 e5,400 3.12 caverage b277 27.5

35 0.37 619 3.12 caverage 32 29.3

36d d0.05 e2,900 3.12 caverage b149 27.5

47 0.43 609 3.12 caverage 31 26.0

52 31.3 205 3.24 Waiakea 10 25.2
20 Streamflow and Erosion Response to Prolonged Intense Rainfall of November 1-2, 2000, Island of Hawaii, Hawaii

watershed drainage areas in square miles. The watershed boundaries are shown in figures 6 and 7. Peak unit

runoff is simply the peak flow rate at a location divided

by the drainage area upstream from it.

Area-weighted storm rainfall values were based on

the application of the isohyetal method (Linsley and

others, 1982, p. 71). Lines of equal storm precipitation

were overlain on a map showing watershed boundaries

(figs. 6 and 7). The area-weighted rainfall was then

computed for each site in table 4 by weighting the average precipitation between successive rainfall lines by

the area between them, adding these values, and dividing the total by the total watershed drainage area (Fontaine and Nielsen, 1994, p. 28). Average precipitation

within the innermost rainfall lines was assigned the

value of rainfall associated with the highest line.

The peak-runoff ratio was computed as the peak

runoff rate (in cubic feet per second converted to inches

of runoff per second) divided by the peak rainfall rate

(in inches per second) and is expressed as a percent. The

peak rainfall rate was taken to be the maximum hourly

rainfall from the closest NWS rain gage (provisional

data from the NWS). The selected rain gages and their

peak hourly rainfall intensities are shown in table 4. The

peak rainfall rate used in these computations sh

optimally correspond to the time of concentrati

the watershed in question. In small (less than ab

mi2

), intermediate (about 1–10 mi2), and large (

than about 10 mi2

) watersheds, the optimum pe

fall rates would be less than 1 hour, 1 to 3 hour

hours or more, respectively. In this analysis, the 

peak rainfall rate was used for all sites, without 

nificant loss of accuracy because rainfall during 

November 1–2, 2000 storm was characterized b

extended periods of uniform, high intensity rainf

example, rainfall intensities for the maximum 3

durations, at the four index stations used in the 

computations, averaged 90 percent of the intens

the maximum 1-hour durations. In addition, rai

intensities for durations of less than 1 hour wer

available.

To explore the relationship between peak f

and rainfall data, a scatterplot of peak-flow recu

interval (table 3) compared with area-weighted 

rainfall (table 4) was prepared (fig. 8). As can be 

figure 8, peak-flow recurrence intervals show li

relation with storm-total area-weighted rainfall 

lation coefficient is 0.335). For example, the fo

with area-weighted storm rainfall totals of betw

Figure 8. Scatterplot of peak-flow recurrence interval and area-weighted storm rainfall, November 1–2, 

flood, island of Hawaii, Hawaii.

0

20

40

60

80

100

120

0 15 20 25 30 35 45 10

AREA-WEIGHTED RAINFALL, IN INCHES

PEAK-FLOW RECURRENCE INTERVAL, IN YEARS

Correlation coefficient = 0.335
Description of 

and 25 in. have recurrence intervals that range between

15 and greater than 100 years. The lack of a correlation

between peak-flow recurrence intervals and storm-total

rainfall indicates that peak flows are more strongly

influenced by shorter-duration rainfall totals.

Perhaps the best way to evaluate the relations

between peak flows and short-duration rainfall totals is

to compare streamflow hydrographs with short-duration rainfall that fell on the watershed area upstream

from the streamflow recording station. Unfortunately,

during the November 1–2, 2000 flood, only one USGS

continuous-record gaging station was in operation and

hourly rainfall data are currently only available for

selected rain gages in the study area. Watershed-wide

rainfall intensity data from the NWS are not available

for the November 1–2, 2000 flood at this time. Streamflow data collected at 15-minute increments for Honolii

Stream (site 7170) are compared with the most 

mate NWS hourly rain-gage data (Piihonua) in f

The data in figure 9 indicate that initially there w

streamflow response to rainfall. Between 1300 

1500 hours on November 1, 1.06 in. of rain fell

ing in the initial rise in the flow hydrograph wh

peaked between 1 and 2 hours later. The next ra

peak was the 1.58 in. of rain, which fell betwee

and 2000 hours on November 1. Again the flow

hydrograph started to rise about 2 hours later. A

point rainfall intensity and streamflow continue

increase with both the rainfall and flow rates pe

between 2400 hours on November 1 and 0100 h

November 2. After 0100 hours, both the rainfal

streamflow rates fell significantly. The rainfall b

0100 and 0200 hours on November 2 was 1.94 i

ever, this rate was not sufficient to continue to i

streamflow. This implies that the peak flow and

Figure 9. Piihonua hourly rainfall totals and Honolii streamflow data, November 1–2, 2000 flood, island of Hawaii, 

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

RAINFALL, IN INCHES

0

2000

4000

6000

8000

10000

12000

14000

16000

RAINFALL, PIIHONUA

STREAMFLOW, SITE NUMBER 7170

0 4

NOVEMBER 1 NOVEMBER 2

8 12 16 20 24 4 8 12 16 20 24

DATE AND TIME
22 Streamflow and Erosion Response to Prolonged Intense Rainfall of November 1-2, 2000, Island of Hawaii, Hawaii

response time at site 7170 was associated with the

4-hour period of time that rainfall rates were greater

than 1.94 in/hr (between 2100 hours on November 1

and 0100 hours on November 2). The earlier response

times of 1 to 2 hours and this 4-hour duration of intense

rainfall prior to a drop in the flow hydrograph implies

that the time of concentration or critical rainfall duration, for the November 1–2, 2000 storm, is somewhere

between 1 to 2 and 4 hours for this watershed. Again,

given the limitations in the rainfall data, this is only an

approximation.

According to Benson’s (1962, p. 32) study of the

correlation of peak flows and rainfall intensities, the

best results come from using rainfall intensities having

the same recurrence intervals as the peak flows. Therefore, it could be assumed that another measure of time

of concentration or critical rainfall duration would be

provided by comparing the peak flow and maximum

rainfall recurrence intervals from tables 1 and 3. For

each site with a peak-flow recurrence interval in table 3,

the most proximate rain gage was selected (table 4). The

minimum rainfall duration with a recurrence interval

(table 1) that most closely matches the peak-flow recurrence interval was then determined and summarized in

table 5. For example, for site 7170, the critical rainfall

duration is 1 to 3 hours while the analysis of the

hydrograph (fig. 9) indicates the critical rainfall duration was between 1 to 4 hours.

To compare peak-flow rates at a variety of 

with differing drainage areas, it is best to use th

unit-runoff rate (the peak flow rate divided by th

age area, table 4). A scatterplot of peak unit-run

compared with drainage area is shown in figure 

Data for sites 34 and 36 were not included in fi

because of uncertainties in their computed drain

areas. Data for sites 7040 and 7130, although co

with the generalized trend line shown, were not

included in figure 10 because their drainage are

an order of magnitude greater than those for the 

ing sites. Data in figure 10 indicate that the pea

runoff rates generally decline with increasing d

area. High-intensity rainfall is more likely to ex

over entire watersheds when those watersheds a

small. In larger drainages, the timing and spatia

bution of high rainfall intensities are more likely 

throughout the watersheds, therefore leading to 

runoff rates that are not synchronized. Although 

trend of declining peak unit-runoff rates is clear

relation is not strong enough (correlation coeffi

-0.444) to allow use of the data in figure 10 to m

mates of peak unit-runoff rates at sites where pe

calculations were not made for the November 1–

flood.

Peak runoff ratios (table 4), in conjunction 

soil permeability data (Sato and others, 1973; S

Nakamura, Natural Resources Conservation Se

written commun., 2001), indicate that infiltratio

excess (Horton) overland flow did not account f

proportions of the peak flows. Peak streamflow

sented between 8 and 96 percent of peak rainfall 

19 sites where reasonable comparisons could be 

that is, at sites where peak-runoff rates were les

100 percent of peak-rainfall rates (table 4). The 

peak-runoff ratio for the 19 sites was 43 percen

streamflow was more than 50 percent of peak ra

6 sites and more than 80 percent of peak rainfal

sites (table 4). These peak-runoff ratios are high 

of the high infiltration rates in the study area. P

ability data for soils in the study area indicate th

fall intensities of at least 2.0 and up to 20.0 in/h

necessary to exceed infiltration rates and cause 

Horton overland flow. For many of the soils in th

area, permeability data indicate that rainfall inte

of 6.0 in/hr are required to generate Horton ove

flow. Actual maximum hourly rainfall intensitie

ranged from 2.10 to 4.56 in. (table 1), so some 

overland flow probably was generated during th

a

 Site numbers are listed in table 2 and shown in figures 2 and 3. b Minimum rainfall duration with a recurrence interval matching

the peak flow recurrence interval.

Table 5. Critical rainfall durations associated with peak

flows for November 1–2, 2000 flood, island of Hawaii,

Hawaii

Site numbera Critical rainfallduration (hours)b

7000 12

7013 6

7014 3–6

7040 3

7130 3

7170 1–3

7174 3

7176 12

7176.5 6

7700 1–3

7705 1–3
Description of 

on soils with permeabilities between 2.0 and 6.0 in/hr.

However, the large areas with permeabilities greater

than 6.0 in/hr probably contributed no Horton overland

flow because rainfall intensities were less than infiltration rates. Therefore, the generally high peak-runoff

ratios (table 4) for watersheds with highly permeable

soils indicate that saturation overland flow and subsurface stormflow probably contributed to peak flows.

This conclusion is supported by field evidence of

restricted areas of overland flow, and by subsurface permeability data that indicate sharp decreases in permeability at shallow depths.

Waiakea High-Rainfall Area

In the description of the study area it was noted that

the watersheds north of the Wailuku River lie on the

slopes of Mauna Kea with its older, Hamakua Volcanics

lava flows and the remaining sections of the Waiakea

high-rainfall area lie on the slopes of Mauna Loa with

its younger and often historic Kau Basalt lava flows.

This geologic distinction is readily apparent when viewing the rainfall-runoff data in table 4. Sites located on

the slopes of Mauna Kea have peak unit-runoff rates

and peak-runoff ratios that are four to five times 

than those for sites located on the slopes of Mau

Six sites have rainfall-runoff data for wate

on the slopes of Mauna Loa (sites 52, 7013, 7014

7040, and 7130). Peak unit-runoff values for th

sites range from 161 to 731 cubic feet per secon

square mile (ft3

/s/mi2) and average 311 ft3/s/mi

runoff ratios range from 8 to 35 percent and ave

percent.

Four sites have rainfall-runoff data for wat

on the slopes of Mauna Kea (sites 7170, 7174, 

and 7176.5). Peak unit-runoff values for the fou

range from 950 to 2,620 ft3

/s/mi2 and average 1

ft3

/s/mi2. The peak-runoff ratio for site number 

(Alia Stream near Hilo) was computed to be gre

than 100 percent, which implies that the maxim

off rate from the watershed was greater than the 

mum rainfall rate that fell on it. With the excep

unusual circumstances, such as dam failures, thi

a physical possibility and implies that one or m

the computations for this watershed were in err

Piihonua hourly rain gage, while located a sign

Figure 10. Relation between peak unit runoff and drainage area, November 1–2, 2000 flood, island of H

Hawaii.

0

500

1000

1500

2000

2500

3000

3500

0 10 20 30 

DRAINAGE AREA, IN SQUARE MILES

PEAK UNIT RUNOFF,

IN CUBIC FEET PER SECOND PER SQUARE MILE

generalized trend line
24 Streamflow and Erosion Response to Prolonged Intense Rainfall of November 1-2, 2000, Island of Hawaii, Hawaii

distance from the Alia Stream watershed, was still the

closest site with hourly rainfall data for use in computing the peak-runoff ratio. It is likely that differences in

rainfall between that recorded at the Piihonua rain gage

and that falling on the Alia Stream watershed exist

which would therefore render computations using the

Piihonua rain gage data incorrect. Another possibility is

that there were errors in the computation of the peakflow rate for the Alia Stream site. Excluding data for

site 7176, peak-runoff ratios for the three remaining

sites range from 44 to 81 percent and average 61 percent.

The estimates of critical rainfall durations (table 5)

for sites in the Waiakea high-rainfall area do not show

any clear patterns. Critical durations for five of the nine

sites located in the Waiakea high-rainfall area are

approximately 3 hours. The values of 12 and 6 hours

computed for sites 7176 and 7176.5 do not appear reasonable and this could be attributed to the lack of a

proximate hourly rain gage for these watersheds. Values of 12 and 6 hours computed for sites 7000 and 7013

in the Waiakea Stream watershed could be a function of

the lower rates of runoff from that area. Watershed

response time will be slower when higher percentages

of rainfall infiltrate into the ground.

Kapapala High-Rainfall Area

Rainfall-runoff data were computed for 12 sites in

the Kapapala high-rainfall area (table 4). Peak unit-runoff and peak-runoff ratios determined for sites 34 and

36d were found to be unreasonable. As noted above,

peak-runoff ratios greater than 100 percent are not probable in this area. Watersheds in the vicinity of sites 34

and 36d are extremely poorly defined and errors in the

measurement of drainage areas for these sites are likely.

Sites 34 and 36d were determined to have very small

drainage areas (0.01 and 0.05 mi2

) and therefore any

measurement errors would lead to large percentage differences in the computations of areas and therefore peak

unit-runoff and peak-runoff ratios. Rainfall-runoff data

for these sites are not used in the summary provided

below.

Unlike the Waiakea high-rainfall area, no clear

trends were apparent in the rainfall-runoff data computed for the 10 sites in Kapapala high-rainfall area

(table 4). Peak unit-runoff values range from 609 to

2,780 ft3

/s/mi2 and average 1,390 ft3/s/mi2. Peak

ratios range from 31 to 96 percent and average 

cent. Peak unit-runoff and peak-runoff ratios co

for the Kapapala high-rainfall area are similar t

slightly lower than those computed for the area n

the Wailuku River in the Waiakea high-rainfall 

Estimates of critical rainfall durations (tab

were computed for only two sites in the Kapapa

rainfall area (sites 7700 and 7705). For both site

puted durations were 1 to 3 hours indicating the 

response of peak-flow rates in these streams to 

of peak-rainfall intensities. One factor that migh

contributed to this rapid response, noted in an e

section of this report, is that the periods of max

rainfall intensities in the Kapapala high-rainfall 

took place much later in the storm and after sign

amounts of antecedent rainfall had already falle

2). This fact coupled with the higher rainfall int

recorded in the Kapapala high-rainfall area (tab

could have contributed to faster response times

An interesting pattern in computed peak un

off was noted for sites 2, 18, and 13 along Waih

Stream near Kapapala Ranch. As can be seen fr

data for these sites in table 4, proceeding down

from site 2, with a drainage area of 6.54 mi2

, to 

with a drainage area of 7.45 mi2

, to site 13, with 

age area of 7.97 mi2

, peak unit runoff increased 

1,090 to 1,460 ft3

/s/mi2. This trend contrasts wi

normal pattern of declining peak unit runoff rat

increasing drainage area (fig. 10). At these sites 

Waihaka Stream, the increasing peak unit-runo

are directly correlated to the fact that the area o

mum storm rainfall, and most likely intensity, w

closer to site 13 and Kapapala Ranch. Another f

likely to be land use in the area. As noted in the 

tion of the study area, most of the land above an 

of about 3,500 ft is forested. Site 2 on Waihaka 

is at an altitude of 3,230 ft and therefore downs

from that altitude the percentage of non-foreste

area in the watershed increases. Runoff from th

forested lands would be higher because infiltrati

there would be lower (Dunne and Leopold, 197

p. 167).
Erosional Features in the Kapapala High-Rainfal

EROSIONAL FEATURES IN THE

KAPAPALA HIGH-RAINFALL AREA

Erosional features attributed to the storm of

November 1–2, 2000 included both channel and hillslope features. This report focuses on the hillslope features because of their relation to surface runoff

generation processes (overland flow).

Hillslope erosional features included mass-wasting and fluvial (caused by flowing water) features, and

some features that showed evidence of both massmovement and fluvial erosion (table 6). Hillslope features were observed along the Kaoiki Pali, between the

Kapapala Ranch and Kilauea Volcano (fig. 3). A few

small features also were noted above Wood Valley. No

hillslope features were observed southwest of Wood

Valley or northeast of site 47 (fig. 7) in Hawaii Volcanoes National Park.

Field visits were made to all hillslope features

along the Kaoiki Pali to collect information on the processes and materials contributing to the hillslope failures and to measure representative dimensions of the

failures. These features had a variety of forms, but in

general, the features had well-defined headscarps below

the top of the pali, steep sides, or banks, highly irregular

scar surfaces, and deposits on the gentle slope at the foot

of the pali. Erosional features on ash deposits typically

had lobe-shaped lateral scarps along their banks that

appeared to be the result of mass wasting following

undercutting by fluvial erosion (fig. 11). Locations were

determined by altimeter, compass bearings to mapped

features, and from examination of topographic maps.

Except where precluded by steep slopes or unstable

landslide deposits, the headscarp of each failure was

examined for signs of overland flow, including debris

deposits, rill or channel cutting, and flattened leaves of

grass oriented in the presumed direction of flow. Deposits were examined to infer the extent to which they were

transported after the initial failures by flowing water.

Failure scars were also examined for evidence of subsurface flow, including macropore openings, deposits

of fine sediment at ash-basalt contacts, persistent moisture, or moss growth at headscarps. Topographic slopes

were measured with an Abney level. Dimensions were

measured with a range finder or fiberglass tape.

Hillslope erosional features included debris slides,

debris flows, slumps, gullies, and features having characteristics of both gullies and landslides (table 6

tudes at the tops of the erosional features range

2,640 to 4,020 ft. Topographic slopes at the top

features ranged from 11 to 100 percent. Measur

lengths ranged from 20 to 668 ft, average widths 

from 2.3 to 157 ft, and average depths ranged fr

to 9 ft (table 7). Measured volumes ranged from 

12,400 cubic yards (table 7). Of the 21 features 

in the field, 8 occurred in ash deposits, 11 invol

basalt interlayered with ash, and only two failur

occurred in basalt without interlayered ash. Fiv

features did not have discernible evidence of ov

flow at their upslope ends. Evidence of overlan

was found for the other 16 features.

Shear stresses computed for peak flows at 

hillslope erosional features ranged from 2.47 to 

pounds per square foot (lb/ft2

) and are summari

table 8. Shear stress was computed as:

T = γds 

Where T is shear stress, in pounds per square fo

γ is the specific weight of water, in poun

cubic foot,

d is maximum flow depth, in feet, and

s is the topographic slope of the channel 

feet per foot (Leopold and others, 19

p. 157).

Depths were determined from cross-sectio

veys. Slopes were determined from cross-sectio

veys and measurements of distances between cr

sections (sites 36 and 47), or were calculated fr

ues of discharge (Q), in ft3

/s, and conveyance (

ft3

/s, computed for critical-depth flow measurem

(sites 29, 34, and 35):

. 

Slopes (S) computed using (3) are energy slope

underestimate the bed slopes to an unknown de

The computed shear stresses are at or abov

critical shear stresses required to initiate channe

ungrazed grass-covered valley floors (Prosser a

Slade, 1994; Prosser and Dietrich, 1995; Prosse

Abernathy, 1996) and are substantially higher t

critical shear stresses required to erode grassy v

floors under simulated grazing that would be m

resentative of actual field conditions along the K

S Q

K

---     2

=
26 Streamflow and Erosion Response to Prolonged Intense Rainfall of November 1-2, 2000, Island of Hawaii, Hawaii

Pali (Prosser and Slade, 1994; Prosser and Dietrich,

1995; Prosser and Abernathy, 1996). The peak flows

along the Kaoiki Pali, therefore, appear to have exerted

sufficient shear stresses to initiate the observed hillslope

erosional features.

Previous studies (Prosser and Slade, 1994; Prosser

and Dietrich, 1995; Prosser and Abernathy, 1996) have

shown that a shear stress of about 0.52 lb/ft2 is sufficient

to erode a grazed grass-covered valley floor. Substituting a value of 0.52 lb/ft2 in (2) and rearranging to solve

for d at the sites listed in table 8 gives a range of 0.04 to

0.76 ft of depth corresponding to the critical shear

stress. Flow depths less than this range would not be

likely to initiate erosion. Thus, the maximum flow

depths at locations where erosion did not occur were

likely less than 0.76 ft, even in swales and other topographic depressions that would tend to concentrate

flow. Substantial amounts of overland flow therefore

were probably restricted to locations where erosion was

observed. Widespread overland flow with depths of

greater than a few tenths of a foot probably did 

occur. This observation supports the peak runof

analysis presented earlier, which indicated the p

ity of major contributions of subsurface storm f

peak flows.

Collapse features above lava tubes were no

several locations at the foot of the pali. Field ev

indicates that many of these features intercepted 

runoff. No evidence of discharge of subsurface 

from lava tubes was found.

Evidence of previous erosional episodes al

Kaoiki Pali was found in a few locations. Near 

(fig. 3), previously unmapped alluvium was fou

exposed at one of the collapse features described 

indicating possibly two earlier periods of fluvial 

and deposition in the unchanneled area. A tree e

in the landslide scar at site 36 (fig. 3), had two 

sets of roots, one about 4 ft higher than the othe

cating burial in an earlier erosional episode and 

quent exhumation in the storm of November 1–2

a

 Site numbers are listed in table 2 and shown in figure 4.

Table 6. Hillslope erosional features along the Kaoiki Pali resulting from the November 1–2, 2000 flood, island of

Hawaii, Hawaii

[--, not determined]

Site

numbera Type of feature

Altitude at

headscarp

(feet)

Hillslope gradient

(percent) Geologic materials

Evidence fo

overland flow

28 debris flow 3,030 40 basalt/ash Yes

30 debris flow/gully 3,250 29 basalt/ash Yes

31 debris slide 3,350 12 basalt Yes

32 debris slide 3,440 50 basalt/ash No

33 debris slide 3,410 80 basalt/ash No

34 debris flow/gully 3,530 75 basalt/ash Yes

36a slump/gully 3,360 25 ash Yes

36b gully 3,420 33 ash Yes

36c slump 3,430 33 ash Yes

36d gully 3,460 17 basalt/ash Yes

37 slump/gully 3,880 33 ash Yes

38 gully 3,890 11 ash Yes

39 gully 4,020 18 basalt/ash Yes

40 gully 3,740 14 basalt/ash Yes

41 slump/gully 3,720 20 basalt/ash Yes

42 debris slide 3,590 -- basalt No

45 debris flow/gully 3,810 17 ash Yes

46 debris flow 3,810 18 basalt/ash No

47 gully 4,000 27 basalt/ash Yes

50 debris slide 2,640 100 ash No

51 gully 2,640 100 ash Yes
Erosional Features in the Kapapala High-Rainfal

Figure 11. Hillslope erosional feature at site 47 along Kaoiki Pali, showing

evidence of both fluvial and mass-wasting erosion, island of Hawaii,

Hawaii.

fluvial

mass-wasting

a

 Site numbers are listed in table 2 and shown in figure 4

Table 7. Dimensions of selected hillslope erosional features along the Kaoiki Pali resulting from the

November 1–2, 2000 flood, island of Hawaii, Hawaii

[--, not determined; (e), estimated; max., maximum width reported in place of average width]

Site

numbera Horizontal length(feet)

Average width

(feet)

Average depth

(feet)

Volume

(cubic yards)

28 306 72 9 7,340

30 668 -- -- --

30.1 262 2.3 2.3 51

31 163 105 8 5,070

32 355 157 6(e) 12,400

33 180 40 -- --

34 420 20 5(e) 1,560

36a 131 72 (max.) -- --

36b -- -- -- --

36c 91 66 (max.) -- --

36d 142 75 (max.) -- --

37 253 -- -- --

50 20 35 -- --

51 -- 8 -- --
28 Streamflow and Erosion Response to Prolonged Intense Rainfall of November 1-2, 2000, Island of Hawaii, Hawaii

a

 Site numbers are listed in tables 1 and 2 and shown in figure 3; site

29 is upstream of site 30 b Channel bed slope estimated from hydraulic model computations

c Channel bed slope measured in the field

Several fissures or cracks were observed near site

35 along the top of the Kaoiki Pali. These cracks are not

necessarily related to the storm of November 1–2, 2000,

but they appear to be recent based on “bridges” of live

grasses that span the cracks. These cracks indicate the

possibility of future large and rapid mass-movement

failures along the Kaoiki Pali. Hummocky deposits near

site 36 (fig. 3) may have resulted from earlier such failures.

In addition to the hillslope failures associated with

the storm, major channel widening and deepening

occurred on many streams in the Kapapala high-rainfall

area, and many completely new channels were cut

where existing channels lacked the capacity to convey

the storm runoff owing to low channel conveyance or

blockage by debris or engineered structures. One such

channel, Waihaka Stream at the Kapapala Ranch, was

eroded to a depth of about 40 ft. Channel deepening and

widening followed a pattern similar to that of the discontinuous gullies described in the southwest U.S. by

Leopold and others (1964); headcuts and plunge pools

were created where resistant lava prevented downcutting upstream but easily-eroded ash allowed downcutting downstream (fig. 12). Downstream from headcuts,

channel depth and bank height decreased until peak

flows were able to overtop banks, leading to cutting of

more new channels on previously unchanneled hillslopes. Channel cutting was apparently enhanced both

by the low resistance of the Pahala Ash to erosion by

surface water and the youthful age of the landscape,

which has poorly developed drainage and only minor

topographic divides between stream basins.

A detailed investigation of the extent and m

tude of channel erosion related to the storm of N

ber 1–2, 2000, is beyond the scope of this repor

However, near site 2 (fig. 3), an attempt was m

estimate the amount of channel widening by me

the maximum lengths of the roots of ohia trees e

along the channel banks. These measurements in

about 20 ft of erosion on each bank. This estim

consistent with anecdotal information on the wi

of the channel at the nearby ranch pipeline cros

which was destroyed during the storm and rebu

December 2000 (Gordon Cran, Kapapala Ranch

commun., 2001).

Channel erosion appeared to be much mor

sive during the storm of November 1–2, 2000, t

other recent storms that were of only slightly sm

magnitude. The extensive channel erosion durin

storm of November 1–2, 2000, may have been 

of the long duration of intense rainfall and high 

flow (fig. 9), as suggested by Costa and O’Con

(1995) for study sites on the U.S. mainland.

Fewer erosional features were documented 

Waiakea high-rainfall area (Paul Haraguchi, con

meteorologist, written commun., 2001). These f

included several landslides on coastal cliffs and 

banks. Hillslope erosional features and channel 

did not occur to the same degree as in the Kapa

high-rainfall area possibly because the thick ash 

its that are easily eroded by surface water do no

in the Waiakea area.

SUMMARY AND CONCLUSIONS

The unique convergence of the upslope top

phy of eastern Hawaii, the location of a large up

level trough and remnants from tropical storm P

the pattern of tradewinds in the area combined 

duce extreme rainfall over parts of the island of 

on November 1–2, 2000. Two distinct storm ce

received rainfall in excess of 30 inches: the Wa

and the Kapapala high-rainfall areas. Most of th

fell in a 24-hour period and maximum-recorded 

for the entire storm in the Waiakea and Kapapa

was 32.47 inches at Mountain View and 38.97 in

Kapapala Ranch. The severity of the November 

2000 storm, as measured by the recurrence inte

the rainfall, increased as the duration of the tim

val increased. Maximum 1-hour rainfall totals h

Table 8. Shear stresses exerted by peak flows upstream of

hillslope erosional features along the Kaoiki Pali, November

1–2, 2000 flood, island of Hawaii, Hawaii

Site

numbera Depth(feet)

Channel

bed slope

(feet per foot)

Shear stress

(pounds per

square foot)

29 3.6 b0.011 2.47

34 3.9 b0.015 3.64

35 5.1 b0.012 3.81

36 2.6 c0.125 20.5

47 3.1 c0.220 42.6
Summary and Conclu

recurrence intervals of 10 years or less while most maximum 24-hour rainfall totals had recurrence intervals

equal to or greater than 100 years.

Peak flow and/or erosion data were collected at 41

sites to aid in the description of the flooding associated

with the November 1–2, 2000 storm. New peak discharges of record occurred at six of the 12 sites where

historic data were available. The recurrence intervals

associated with the peak discharges ranged between 50

and 100 years for streams south of the Wailuku River in

the Waiakea high-rainfall area. The majority of the

remaining streams in the study area had recurrence

intervals between 5 and 30 years. Peak unit-runoff rates

computed for 22 sites ranged from 161 to 5,400 

feet per second per square mile of watershed are

unit-runoff rates averaged 311 cubic feet per sec

square mile for the Wailuku River and streams 

south, in the Waiakea high-rainfall area. Peak u

runoff rates in the remainder of the Waiakea an

Kapapala high-rainfall areas were comparable a

aged 1,635 and 1,390 cubic feet per second per 

mile.

Analysis of rainfall-runoff relationships in 

study area was complicated by the complex and 

ing nature of the geology and the extreme spati

tion of the storm rainfall. Peak flows were foun

Figure 12. Headcut on Waihaka Stream between Kapapala Ranch and site 13,

showing effect of resistant cap of lava above ash deposits, island of Hawaii,

Hawaii.

lava

ash
30 Streamflow and Erosion Response to Prolonged Intense Rainfall of November 1-2, 2000, Island of Hawaii, Hawaii

poorly correlated to area-weighted storm rainfall and

were therefore more strongly influenced by shorterduration rainfall totals. Comparison of peak streamflow

and rainfall recurrence interval data indicated the critical rainfall durations for the generation of peak flows

ranged from 1 to 12 hours and were about 3 hours at

most sites. Peak-runoff rates divided by peak-rainfall

intensities were found to average 43 percent at 19 sites.

While maximum hourly rainfall intensities exceeded

infiltration rates in parts of the study area, the overland

flow generated would not have been sufficient to

account for the high peak-runoff rates. This finding

indicates the saturation overland flow and subsurface

flow probably contributed to peak flows at most sites.

Most hillslope erosion related to the storm

occurred along or near the Kaoiki Pali in the Kapapala

high-rainfall area. The erosion was mostly caused by

overland flow and was associated with thick ash deposits of the Kahuku Basalt.

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