U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with the State of Hawai‘i Commission on Water Resource Management

Low-Flow Characteristics of Streams from Wailua to 

Hanapēpē, Kaua‘i, Hawai‘i

Scientific Investigations Report 2020–5128
Cover. View of Wai‘ale‘ale and the Līhu‘e-Moloa Forest Reserve on the island of Kaua‘i, Hawai‘i. 

Photograph by Chui Ling Cheng, U.S. Geological Survey, 2017.

(inset). View of North Fork Wailua River at an altitude of about 1,100 feet on the island of Kaua‘i, 

Hawai‘i. Photograph by Alan Mair, U.S. Geological Survey, 2015. 
Low-Flow Characteristics of Streams from 

Wailua to Hanapēpē, Kaua‘i, Hawai‘i

By Chui Ling Cheng

Prepared in cooperation with the State of Hawai‘i Commission on Water Resource Management

Scientific Investigations Report 2020–5128

U.S. Department of the Interior

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

DAVID BERNHARDT, Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2020

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as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Cheng, C.L., 2020, Low-flow characteristics of streams from Wailua to Hanapēpē, Kauaʻi, Hawaiʻi: U.S. Geological 

Survey Scientific Investigations Report 2020–5128, 57 p., https://doi.org/10.3133/sir20205128.

ISSN 2328-0328 (online)
iii

Acknowledgments

The author is grateful to the many individuals, landowners, and agencies that provided the support 

needed to conduct this study. This study was conducted in cooperation with the State of Hawai‘i 

Commission on Water Resource Management. Landowners that graciously allowed access to 

their properties include Grove Farm, Eric A. Knudsen Trust, McBryde Sugar Company, Gay & 

Robinson, and Lāwa‘i Valley Nursery. The author is especially thankful to the following individuals 

for arranging access to streams in the study area: Linda Inouye of Grove Farm, Allen Reis and Dan 

Sargent of McBryde Sugar Company, Howard Greene of Gay & Robinson, Will Pavao of Pāohia 

area, and Keith Silva of Lāwa‘i Valley Nursery. Brad Rockwell of Kaua‘i Island Utility Cooperative, 

Leslie Milnes of East Kauai Water Users’ Cooperative, Adam Killerman of Grove Farm, Canen 

Ho‘okano of the Eric A. Knudsen Trust, Allen Reis of McBryde Sugar Company, and Howard 

Greene of Gay & Robinson shared their knowledge and insight of the study area and provided 

information on access to the discharge-measurement sites. The following U.S. Geological Survey 

(USGS) personnel conducted discharge measurements and planned the seepage-run analyses: 

Benjamin H. Shimizu, Alan Mair, Sarah N. Rosa, Lhiberty Pagaduan, Rylen Nakama, and Joseph 

J. Kennedy. USGS personnel Timothy Brunetto, Casey Rita, Anela Whisenhunt, and Madison 

May expedited analysis of hydrologic data at continuous-record stream-gaging stations for use in 

the study. USGS personnel Ronald Rickman, Richard Fontaine, Julie E. Kiang, and Kenny Eng 

provided valuable technical support throughout the study.
iv

Contents

Acknowledgments............................................................................................................................................... iii

Abstract................................................................................................................................................................1

Introduction ..........................................................................................................................................................1

Previous Low-Flow Investigations..............................................................................................................2

Purpose and Scope ....................................................................................................................................2

Description of the Study Area ..............................................................................................................................3

Climate and Rainfall....................................................................................................................................3

Hydrogeology..............................................................................................................................................3

Surface-Water Use .....................................................................................................................................6

Historical Surface-Water Availability...........................................................................................................8

Methods .............................................................................................................................................................11

Data-Collection Sites ................................................................................................................................11

Short-Term Stations.........................................................................................................................11

Partial-Record Sites.........................................................................................................................11

Seepage-Run Discharge-Measurement Sites ................................................................................14

Flow-Duration Statistics............................................................................................................................14

Record Augmentation...............................................................................................................................14

MOVE.1 Technique..........................................................................................................................15

Graphical-Correlation Technique.....................................................................................................15

Index Stations and Selection of Base Period..................................................................................15

Analysis of Low Flows at Different Types of Measurement Sites...................................................17

Short-Term Stations................................................................................................................17

Partial-Record Sites................................................................................................................18

Results and Discussion .....................................................................................................................................18

Natural Low-Flow Duration Discharges....................................................................................................18

Short-Term Stations.........................................................................................................................18

Partial-Record Sites.........................................................................................................................22

Streamflow Gains and Losses..................................................................................................................28

North Fork of Wailua River ..............................................................................................................28

South Fork of Wailua River..............................................................................................................30

Hanamā‘ulu Stream.........................................................................................................................38

Nāwiliwili Stream..............................................................................................................................38

Hulē‘ia Stream.................................................................................................................................43

Waikomo Stream.............................................................................................................................43

Lāwa‘i Stream..................................................................................................................................47

Wahiawa Stream.............................................................................................................................47

Hanapēpē River...............................................................................................................................47

Limitations of Approach .....................................................................................................................................53

Suggestions for Future Work.............................................................................................................................54

Summary and Conclusions................................................................................................................................54

References Cited ...............................................................................................................................................55
v

Figures

1. Map showing locations of study area, active and inactive continuous-record stream-gaging 

stations, and partial-record measurement sites in southeast Kaua‘i, Hawai‘i..............................4

2. Map of mean annual rainfall in study area, southeast Kaua‘i, Hawai‘i.........................................5

3. Plot of annual rainfall totals at rain-gaging station 220427159300201 on Wai‘ale‘ale near Līhu‘e, 

Kaua‘i, Hawai‘i, for water years 1961–97 and water years 1998–2019 ..............................................6

4. Hydrogeologic settings in the study area, southeast Kaua‘i, Hawai‘i...........................................7

5. Map showing locations of major surface-water diversion systems and associated intakes, and 

U.S. Geological Survey ditch-flow gaging stations in the study area, southeast Kaua‘i, Hawai‘i.....9

6. Map showing discharge, in cubic feet per second, that is equaled or exceeded 90, 70, and 50 

percent of the time during 1961–2019 at active stream-gaging stations and partial-record sites 

in the study area, southeast Kaua‘i, Hawai‘i ..............................................................................23

7. Plots showing the graphical relation between measured discharges at short-term continuousrecord and partial-record sites and concurrent daily mean discharges at index stations, 

southeast Kaua‘i, Hawai‘i...........................................................................................................24

8. Map of measurement sites and results for the February 2017 seepage run on North Fork 

Wailua River, Kaua‘i, Hawai‘i .....................................................................................................29

9. Map of measurement sites and results for the September 1982 seepage run on North Fork 

Wailua River, Kaua‘i, Hawai‘i .....................................................................................................31

10. Map of measurement sites and results for the September 2017, December 2019, and January 

2020 seepage runs on South Fork Wailua River, Kaua‘i, Hawai‘i.................................................32

11. Map of measurement sites and results for the March 1983 seepage runs on South Fork Wailua 

River, Kaua‘i, Hawai‘i..................................................................................................................35

12. Map of measurement sites and results for the October 1996 seepage run on Hanamā‘ulu 

Stream, Kaua‘i, Hawai‘i..............................................................................................................39

13. Map of measurement sites and results for the September 1973 seepage runs on Hanamā‘ulu 

Stream, Kaua‘i, Hawai‘i...............................................................................................................40

14. Map of measurement sites and results for the September 2019 seepage run on Nāwiliwili 

Stream, Kaua‘i, Hawai‘i..............................................................................................................41

15. Map of measurement sites and results for the October 1996 seepage run on Nāwiliwili Stream, 

Kaua‘i, Hawai‘i............................................................................................................................42

16. Map of measurement sites and results for the November 2019 seepage run on Hulē‘ia Stream, 

Kaua‘i, Hawai‘i............................................................................................................................44

17. Map of measurement site and results for the October 1996 seepage run on Hulē‘ia Stream, 

Kaua‘i, Hawai‘i ...........................................................................................................................45

18. Map of measurement sites and results for the January 2020 seepage run on Waikomo Stream, 

Kaua‘i, Hawai‘i............................................................................................................................46

19. Map of measurement sites and results for the September 2019 seepage run on Lāwa‘i Stream, 

Kaua‘i, Hawai‘i............................................................................................................................48

20. Map of measurement sites and results for the October 1996 seepage run on Lāwa‘i Stream, 

Kaua‘i, Hawai‘i ...........................................................................................................................49

21. Map of measurement sites and results for the November 2019 and January 2020 seepage run 

on Wahiawa Stream, Kaua‘i, Hawai‘i..........................................................................................50

22. Map of measurement sites and results for the September 2017 seepage run on Hanapēpē 

River, Kaua‘i, Hawai‘i .................................................................................................................51

23. Map of measurement sites and results for the October 1996 seepage run on Hanapēpē River, 

Kaua‘i, Hawai‘i............................................................................................................................52
vi

Tables

1. Low-flow duration discharges at inactive continuous-record streamflow and ditch-flow gaging 

stations in the study area, southeast Kaua‘i, Hawai‘i.................................................................10

2. Low-flow duration discharges at active long-term continuous-record stream-gaging stations and 

short-term continuous-record low-flow gaging stations established in the study area, southeast 

Kaua‘i, Hawai‘i............................................................................................................................12

3. Results of the Mann-Kendall test for trends in annual flows from 1961 to 2019 at six active 

long-term stations monitoring natural flow, Kaua‘i, Hawai‘i........................................................17

4. Summary of record-augmentation methods, regression equations, and selected regression 

statistics for partial-record sites in the study-area streams, southeast Kaua‘i, Hawai‘i..............19

5. Estimated flow-duration discharges at partial-record sites in the study-area streams, southeast 

Kaua‘i, Hawai‘i, for base period 1961–2019 ................................................................................21

6. Measured discharges at partial-record site 220346159280601 on North Fork Wailua River and 

concurrent daily mean discharges at stream-gaging station 16019000 on Wai‘alae Stream, 

southeast Kaua‘i, Hawai‘i............................................................................................................25

7. Measured discharges at partial-record sites 220326159275401 on north fork Waikoko Stream and 

220325159275401 on south fork Waikoko Stream and concurrent daily mean discharges at 

stream-gaging station 16057900 on Waiahi Stream, southeast Kaua‘i, Hawai‘i................................25

8. Measured discharges at partial-record site 220224159282301 on ‘Ili‘ili‘ula Stream and 

concurrent daily mean discharges at stream-gaging station 16097500 on Hālaulani Stream, 

southeast Kaua‘i, Hawai‘i...........................................................................................................25

9. Measured discharges at partial-record sites 220054159244001 on north fork Hanamā‘ulu 

Stream, 220037159242901 on south fork Hanamā‘ulu Stream, and 215923159235601 on 

tributary of Hanamā‘ulu Stream, and concurrent daily mean discharges at stream-gaging 

station 16068000 on east branch of North Fork Wailua River, southeast Kaua‘i, Hawai‘i .........26

10. Measured discharges at partial-record site 215853159281801 on Pāohia Stream and 

concurrent daily mean discharges at stream-gaging station 16052400 Lāwa‘i Stream, 

southeast Kaua‘i, Hawai‘i...........................................................................................................26

11. Measured discharges at partial-record site 215851159273901 on Kamo‘oloa Stream and 

concurrent daily mean discharges at stream-gaging station 16052400 Lāwa‘i Stream, 

southeast Kaua‘i, Hawai‘i............................................................................................................26

12. Measured discharges at partial-record site 215751159283901 on Ku‘ia Stream and concurrent daily 

mean discharges at stream-gaging station 16052400 Lāwa‘i Stream, southeast Kaua‘i, Hawai‘i.......27

13. Measured discharges at partial-record sites 215751159311801 on Wahiawa Stream and 

215754159311601 on left branch Wahiawa Stream, and concurrent daily mean discharges at 

stream-gaging station 16097500 on Hālaulani Stream, southeast Kaua‘i, Hawai‘i....................27

14. Measured discharges at partial-record site 220423159235501 on right branch ‘Ōpaeka‘a 

Stream and concurrent daily mean discharges at stream-gaging station 16071500 on left 

branch ‘Ōpaeka‘a Stream, southeast Kaua‘i, Hawai‘i................................................................27

15. Measured discharges at partial-record site 215822159282601 on Ku‘ia Stream and concurrent 

daily mean discharges at stream-gaging station 16071500 on left branch ‘Ōpaeka‘a Stream, 

southeast Kaua‘i, Hawai‘i............................................................................................................28

16. Measured discharges at partial-record site 215833159232601 on Nāwiliwili Stream, southeast 

Kaua‘i, Hawai‘i............................................................................................................................28

17. Measured discharges at partial-record site 215737159230301 on Pū‘ali Stream, southeast 

Kaua‘i, Hawai‘i ...........................................................................................................................28

18. Measured discharges at partial-record sites 215608159285801 on ‘Ōma‘o Stream and 

215538159292301 on Pō‘ele‘ele Stream, southeast Kaua‘i, Hawai‘i.........................................28
vii

Conversion Factors

U.S. customary units to International System of Units

Multiply By To obtain

Length

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

yard (yd) 0.9144 meter (m)

Area

acre 4,047 square meter (m2)

acre 0.004047 square kilometer (km2)

square foot (ft2) 0.09290 square meter (m2)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

gallon (gal) 0.003785 cubic meter (m3) 

million gallons (Mgal) 3,785 cubic meter (m3)

cubic foot (ft3) 0.02832 cubic meter (m3) 

cubic mile (mi3) 4.168 cubic kilometer (km3) 

Flow rate

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

cubic foot per day (ft3/d) 0.02832 cubic meter per day (m3/d)

cubic foot per second (ft3/s) 0.64636 million gallons per day (Mgal/d)

gallon per day (gal/d) 0.003785 cubic meter per day (m3/d)

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3/s)

Leakance

foot per day per foot ([ft/d]/ft) 1 meter per day per meter ([m/d]/m)

inch per year per foot ([in/yr]/ft) 83.33 millimeter per year per meter ([mm/yr]/m)

Seepage rate in cubic feet per second per mile of stream reach [(ft3/s)/mi] may be converted to cubic 

meter per second per kilometer of stream reach [(m3/s)/km] as follows:

m3/s/km = 0.01759 x [(ft3/s)/mi]

Datum

Vertical coordinate information is referenced relative to local mean sea level.

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.
viii

Abbreviations

ADV Acoustic Doppler Velocimeter

CWRM State of Hawaiʻi Commission on Water Resource Management

ft3/s cubic feet per second

(ft3/s)/mi cubic feet per second per mile

IVE Interpolated Variance Estimator

Mgal/d million gallons per day

MOVE.1 Maintenance of Variance Extension Type 1

MSE mean square error

RMSE root mean square error

USGS U.S. Geological Survey
Low-Flow Characteristics of Streams from Wailua to 

Hanapēpē, Kaua‘i, Hawai‘i 

By Chui Ling Cheng

Abstract

The purpose of this study is to characterize streamflow 

availability under natural (unregulated) low-flow conditions for 

streams in southeast Kaua‘i, Hawai‘i. The nine main study-area 

basins, from north to south, include Wailua River, Hanamā‘ulu, 

Nāwiliwili, Pūʻali, Hulēʻia, Waikomo, Lāwaʻi, and Wahiawa 

Streams, and Hanapēpē River. The results of this study can be used 

by water managers to develop technically sound instream-flow 

standards for the study-area streams.

Low-flow characteristics for natural streamflow conditions 

were represented by flow-duration discharges that are equaled 

or exceeded between 95 and 50 percent of the time. Shortterm continuous-record stream-gaging stations that monitored 

low flows on Waiahi and right branch Lāwaʻi Streams were 

established to serve as potential index stations for partial-record 

sites in the study area. Continuous-record stream-gaging station 

on Hanapēpē River monitored natural flow during calendar year 

2017 and the streamflow record during that period was used to 

estimate low-flow characteristics at the station. Partial-record 

sites were established on 3 main streams and 15 tributary streams, 

upstream from existing surface-water diversions. Low-flow 

characteristics were determined using historical and current 

streamflow data from continuous-record stream-gaging stations 

and miscellaneous sites, as well as additional data collected as 

part of this study. Low-flow-duration discharges for the following 

streams were estimated for the 59-year base period (water years 

1961–2019) using two record-augmentation techniques: right 

branch ʻŌpaekaʻa Stream, North Fork Wailua River, north and 

south fork Waikoko Streams, ‘Ili‘ili‘ula Stream, north and south 

fork Hanamāʻulu Streams, Kamo‘oloa Stream, Pāohia Stream, 

Ku‘ia Stream, Lāwa‘i Stream, Wahiawa Stream, and Hanapēpē 

River. The 95-percent flow-duration discharges (Q95) ranged from 

0.018 to 42 cubic feet per second (ft3/s). The 50-percent flowduration discharges (Q50) ranged from 1.1 to 69 ft3/s. Upper-bound 

estimates of low-flow duration discharges at partial-record sites 

on south fork Hanamāʻulu, Hanamāʻulu tributary, ʻŌmaʻo, and 

Pōʻeleʻele Streams were estimated based on the highest discharges 

measured as part of this study during Q95 to Q50 flow conditions, 

which were 0.44, 0.40, 0.19, and 0.22 ft3/s, respectively. Measured 

discharges on Nāwiliwili, Pū‘ali, and left branch Wahiawa Streams 

do not correlate with data at any active long-term continuousrecord stream-gaging stations (10 or more complete water years 

of natural-flow record) and therefore low-flow duration discharges 

could not be estimated.

This study also estimated streamflow gains and losses 

using seepage-run discharge measurements in eight of the nine 

study basins (Pūʻali Stream basin was excluded). A majority 

of the streams gained flow downstream from the uppermost 

diversions. Measured seepage-gain rates ranged between 0.03 and 

24.3 ft3/s per mile of stream reach. Seepage gains are presumed 

to originate mainly from groundwater discharge in the Wailua 

River, Hanamā‘ulu Stream, Nāwiliwili Stream, Hulēʻia Stream, 

Lāwa‘i Stream, Wahiawa Stream, and Hanapēpē River basins. 

Under natural-flow conditions and flow conditions of the seepage 

runs, a majority of the study-area streams flow continuously from 

the mountains to the ocean. Where a stream discharges into a 

reservoir––Hanamā‘ulu and Wahiawa Streams––a dry reach may 

occur immediately downstream from the reservoir to the point of 

seepage gain in the stream. 

Introduction

Hawai‘i’s surface water is a valuable resource that is 

critical for economic, ecological, and cultural beneficial 

uses. Traditionally, local communities depended on streams 

for drinking water, growing crops such as taro, supporting 

vegetation that provided materials for medicine and shelter, and 

other cultural practices. Streams can support unique species 

of endemic freshwater fauna, such as ‘o‘opu (freshwater fish), 

‘ōpae (freshwater mountain shrimp), and hīhīwai (freshwater 

snail). As the sugar industry became established in Hawai‘i, 

large, engineered diversion and irrigation systems were built 

to transport water across drainage basins, resulting in reduced 

streamflow downstream of diversion intakes. As sugarcane 

cultivation had ceased in many areas of the Hawaiian Islands in 

the 1990s, some diversion systems were abandoned, whereas 

others continued to divert water from streams for agricultural, 

industrial, and municipal uses. Many diversion structures have 

been constructed to capture a majority of the flow in the streams 

during low-flow conditions, leaving some reaches downstream 

from the diversion structures dry. Consequently, the diversion 

of surface water during low-flow conditions greatly influences 

water availability for ecosystems, aquatic biota, and other 

beneficial uses.

Insufficient water supply to meet both offstream and instream 

uses has been, and continues to be, a major issue in Hawai‘i. 

Conflicts have led to costly litigation over rights to the water 

between those currently diverting the water and those desiring 
2

Low-Flow Characteristics of Streams from Wailua to Hanapēpē, Kaua‘i, Hawai‘

sufficient flow in the stream for instream uses. On Kaua‘i, 

interim instream-flow standards for Waimea River and several 

of its tributaries, located adjacent to the study area (fig. 1), were 

amended in April 2017 as a result of a mediation agreement 

between Pō‘ai Wai Ola (West Kaua‘i Watershed Alliance), Kehaha 

Agriculture Association, Kauaʻi Island Utility Cooperative, 

the Hawai‘i State Department of Hawaiian Home Lands, and 

Agribusiness Development Corporation regarding the diversion of 

water into the Kōke‘e and Kekaha Irrigation Systems (fig. 1; State 

of Hawai‘i, 2017b).

The State Water Code mandates that the State of Hawai‘i 

Commission on Water Resource Management (CWRM) establish 

a statewide instream-use protection program (State Water 

Code, Hawai‘i Revised Statutes, chapter 174C, section71)

The principal mechanism that CWRM implements for the 

purpose of protecting instream uses is establishing instreamflow standards that describe flows necessary to protect the 

public interest in the stream with consideration of existing and 

potential offstream water use, including the economic impact of 

restricting such use (State Water Code, Hawai‘i Revised Statutes, 

chapter 174C, section 71[1][C]). The instream uses recognized 

by CWRM include (1) maintenance of fish and wildlife 

habitat; (2)outdoor recreational activities; (3) maintenance o

ecosystems;(4)aesthetic values, such as waterfalls and sce

waterways; (5) maintenance of water quality; (6) the conveyance 

of irrigation and domestic water supplies; and (7) the protection 

of traditional and customary Hawaiian rights.

Recognizing the complexity of establishing permanent 

instream-flow standards for all perennial streams in Hawai‘i, the 

CWRM originally established interim instream-flow standards at 

status quo levels in 1988–89. An interim instream-flow standard 

is originally defined as the amount of water flowing in each 

stream, considering the natural variability of streamflow, without 

further amounts of water being diverted offstream through new or 

expanded diversions existing at the time the administrative rules 

were adopted in 1988 and 1989 (Hawai‘i Administrative Rules, 

chapter 169, section 13-169-48). The CWRM first adopted interim 

instream-flow standards for all streams in southeast Kaua‘i on 

June 15, 1988 (Hawai‘i Administrative Rules, chapter 169, section 

13-169-45). These interim instream-flow standards did not have 

quantitative flow values and allowed diversions existing at the 

time of the adoption to continue operating. Additional information 

could be filed with CWRM to reduce or increase diversion, through 

a modification of the interim instream-flow standards. Upon 

reviewing a CWRM decision related to interim instream-flow 

standards for streams in eastern O‘ahu, the Hawai‘i Supreme Court 

deemed “status quo” interim instream-flow standards inadequate 

and required quantitative interim instream-flow standards to be 

established (State of Hawai‘i, 2000). Within the last two decades, 

the CWRM has compiled the best available information––

hydrology, and instream and offstream uses––on streams of 

concern to develop quantitative interim instream-flow standards 

upon receipt of a petition to amend an existing interim instreamflow standard. Quantitative interim instream-flow standards that 

account for economic, domestic, cultural, ecological, recreational, 

and aesthetic needs have not yet been established for streams in 

southeast Kaua‘i, Hawai‘i. 

Previous Low-Flow Investigations

Previous low-flow studies of Hawaiian streams have 

been largely conducted on a basin-scale basis, with a focus on 

computing a selected range of low-flow duration discharges 

and examining the effects of surface-water diversions on low 

flows and habitat availability for native stream fauna. Few 

studies were conducted to characterize low-flow availability 

in streams on Kaua‘i. Cheng and Wolff (2012) characterized 

availability and distribution of low flow in Anahola Stream and 

assessed flow availability for agricultural use under a variety 

of potential interim instream-flow standards established for the 

stream. In an effort to understand the occurrence and movement 

of groundwater in the Līhuʻe basin, Izuka and Gingerich (1998) 

conducted base-flow analysis of continuous stream-gaging 

station records and collected additional discrete streamflow 

measurements to quantify the magnitude of gains and losses in 

the measured stream reaches. These streamflow measurements 

are summarized in this report. Statewide analysis of low flows 

includes studies by Yamanaga (1972), Fontaine and others 

(1992), Bassiouni and Oki (2013), Cheng (2016), and Clilverd 

and others (2019). The application of record-augmentation 

methods for estimating low-flow characteristics at sites with 

either short-term records or partial-records of streamflow data 

is well documented in many of the aforementioned studies.

Purpose and Scope

This report presents the results of a study conducted 

during 2016–20 (study period) by the U.S. Geological Survey 

(USGS), in cooperation with CWRM, to provide information 

that could be used by CWRM to develop technically sound 

instream-flow standards for streams in southeast Kaua‘i. The 

objectives of the study were to quantify natural low-flow 

characteristics upstream of surface-water diversions and 

characterize the seepage gains and losses on selected reaches 

of a subset of streams in the study area. For the purposes of 

this report, low-flow characteristics are represented by flowduration discharges equal to and less than the median flow. 

The nine main study-area basins, from north to south, include 

Wailua River, Hanamā‘ulu, Nāwiliwili, Pūʻali, Hulēʻia, 

Waikomo, Lāwaʻi, and Wahiawa Streams, and Hanapēpē 

River. The scope of this investigation involved analyzing 

historical and current (study period) streamflow data at 

continuous-record stream-gaging stations and miscellaneous 

sites and the collection of additional data, including (1) 

streamflow records at continuous-record low-flow stations 

established on Waiahi and Lāwaʻi Streams; (2) discharge 

measurements at 18 partial-record sites established upstream 

from all surface-water diversions; and (3) seepage-run 

discharge measurements at selected sites in the study-area 

basins. This report includes descriptions of study-area streams 

that flow from the mountains to the ocean during low-flow 

conditions, estimates of selected flow-duration discharges (95 

to 50 percent exceedance values) on 13 streams, and estimates 

of seepage gains and losses on selected reaches of 11 streams.
Description of the Study Area 3

Description of the Study Area

The study area is situated on the island of Kauaʻi, the fourth 

largest (553 square miles [mi2]) and one of the geologically oldest 

of the eight main Hawaiian Islands (Stearns and Macdonald, 

1942). The topography of the island ranges from coastal beaches 

and the 2,700-foot (ft) sea cliffs of the Nāpali Coast in the 

northwest to the highest altitude of 5,243 ft above mean sea 

level at Kawaikini Peak, a mile south of Waiʻaleʻale (fig.1

The population on the island is more than 72,000, which is 5 

percent of the State’s 2018 population estimate (State of Hawaiʻi, 

2018), with Līhuʻe as the main population center. The study 

area includes nine stream basins––from Wailua in the north 

to Hanapēpē in the south––that drain the southeastern part of 

the island. The streams in the study area consist of the North 

Fork Wailua River; South Fork Wailua River and its tributaries 

Waikoko, ʻIliʻiliʻula, and Waiahi Streams; Hanamā‘ulu Stream; 

Nāwiliwili Stream; Pūʻali Stream; Hulēʻia Stream and its 

tributaries Kamoʻoloa, Pāohia, and Kuʻia Streams; Waikomo 

Stream and its tributaries ʻŌmaʻo and Pōʻeleʻele Streams; Lāwaʻi 

Stream; Wahiawa Stream; and Hanapēpē River. Drainage areas 

delineated by the study-area streams range from 1.5 to 52.5 mi2, 

with Pūʻali being the smallest and Wailua the largest. Low-flow 

characteristics of the study-area streams are mainly affected by 

(1) climate and rainfall; (2) the physical attributes of the valleys 

such as topography, land cover, land use, and hydrogeology; and 

(3) regulation and withdrawal of streamflow.

Climate and Rainfall

The topography of Kauaʻi and the position of the North 

Pacific subtropical anticyclone relative to the island produce a 

climate characterized by mild and uniform temperatures, cool and 

persistent trade winds, and seasonal and geographic variability 

in rainfall (Blumenstock and Price, 1967; Schroeder, 1993). 

Rainfall is generated from the rising and cooling of moistureladen trade winds along the windward slopes of the island. During 

the dry season (May–September), persistent northeasterly trade 

winds blow 80–95 percent of the time. During the rainy season 

(October–April), other migratory weather systems that affect the 

island reduce trade-wind frequency to 50–80 percent of the time. 

Heavy and intense rainfall can be caused by low-pressure systems 

from the northwest and those accompanied with southerly winds 

(Kona storms), cold fronts associated with mid-latitude cyclones, 

and tropical cyclones from the eastern Pacific Ocean (Giambelluca 

and Schroeder, 1998). Dry coastal areas receive most of their 

annual rainfall amounts from these storms.

Orographic rainfall on the island is characterized by steep 

spatial gradients with increasing altitude (fig. 2). Mean annual 

rainfall within the study area ranges from about 400 inches (in.) 

at Waiʻaleʻale to less than 25 in. in the coastal areas (Giambelluca 

and others, 2013). Within 1 mi of Waiʻaleʻale, mean annual 

rainfall can vary spatially by more than 150 in. During the study 

period, annual rainfall varied from 299 in. in water year 2017 to 

530 in. in water year 2018 (fig. 3)—about 24 percent below and 

35 percent above the mean annual rainfall for water years 1961–

2019, respectively—at rain-gaging station 220427159300201 

on Waiʻaleʻale (station 1047.0 in fig. 2). For water years 2016, 

2017, and 2019, the month of June was consistently one of the 

wettest months during the study period. In water year 2018, the 

month of August had the highest rainfall total of 76 in. out of all 

months in the water year, which is more than double the mean 

monthly rainfall total of 32 in. for water years 1961–2019. About 

34 in. of rain from the August 2018 rainfall total recorded at the 

Waiʻaleʻale rain-gaging station was generated from Hurricane 

Lane. A water year is a 12-month period that extends from 

October 1 to September 30 of the following year and is named 

according to the year during which the period ends. For example, 

the “2019 water year” is the period from October 1, 2018, to 

September 30, 2019. 

The basin of Wailua River receives the highest maximum 

rainfall of about 400 in. per year in the study area. Hanapēpē 

River basin receives a maximum rainfall of about 250 in. per year. 

The basins of Hulēʻia and Wahiawa Streams receive a maximum 

rainfall of about 200 in. per year. The basins of Waikomo and 

Pūʻali Streams receive the lowest maximum rainfall in the study 

area of less than 120 in. per year.

Bassiouni and Oki (2013) analyzed trends in streamflow and 

base flow for long-term continuous-record stations in Hawai‘i. 

Downward trends in base flow and low-streamflow characteristics 

occurred during the 1943–2008 period. The detected trends may 

be related to regionwide changes in climatic and land-cover 

factors. Statistically significant (5-percent significance level) 

downward trends in low flows were detected on east branch of 

North Fork Wailua River during 1943–2008.

Hydrogeology

Hydrogeology, as it relates to the composition and 

permeability of the aquifer and the position of the water table 

relative to the streambed, is an important physical characteristic 

affecting low flows because the natural low flow in a stream 

is mainly from groundwater sources. Groundwater in the 

study area occurs in three principal hydrogeologic settings 

(fig. 4): (1) dike-impounded-groundwater setting, (2) thickly 

saturated setting, and (3) freshwater-lens setting (Izuka and 

others, 2018). The following discussion summarizes the three 

principal hydrogeologic settings and where these settings occur 

relative to aquifer systems in the study area. Aquifer systems are 

hydrologic units established by the CWRM to provide a basis 

for managing groundwater resources and the aquifer systems 

may not reflect hydrogeologic conditions. 

Dike-impounded-groundwater settings occur where 

low-permeability dikes intrude lava flows and other rocks 

to form compartments in which groundwater can be 

impounded to hundreds or thousands of feet above sea level. 

Water flows from compartments with higher water levels 

to compartments with lower water levels, and eventually to 

adjacent groundwater bodies—such as freshwater lenses—or 

discharges to springs, streams, and submarine seeps. Dikeimpounded groundwater maintains perennial flow in streams 
4

Low-Flow Characteristics of Streams from Wailua to Hanapēpē, Kaua‘i, Hawai‘

men20-4010_fig01

Wailua

Waikomo

Hanamā‘ulu

Nāwiliwili

Pū‘ali

Hulē‘ia

Hanapēpē

Wahiawa

Aepo Lāwa‘i Kalāheo Māhā‘ulepū ʻEleʻele Kōloa

Līhuʻe

0 4 2 KILOMETERS

0 4 2 MILES Base modified from U.S. Geological Survey digital

data. Universal Transverse Mercator projection,zone 4, North American Datum 1983.

Altitude above mean sea level, in feet

5,243>0

Hydrologic-unit boundary—From State of Hawai‘i (2017a)StreamDiverson systemStreamflow-measurement location

Inactive stream-gaging station and number—Monitored 

natural-flow conditions

Stream-gaging station and number—Station in operation 

during base period from 1961 to 2019aStation monitored regulated flowbStation monitored natural flow from January to 

December 2017 and these records were used for record augmentation

Stream-gaging station and number—Station established for 

this study and monitors natural low-flow conditions only 

Partial-record measurement site and map identifier—

See table 5 for map identifier description

EXPLANATION

16053000

16068000

16052400

P18

159°20' 159°30' 159°40'

22°10'

22°00'

21°50'

16010000

16019000

16068000 16071500

16097500 16108000

Study

area

PACIFIC OCEAN

KAUA‘I

Kōke‘e Ditch

Kekaha Ditch

Waimea River

16049000 16060000

P1

16052400

16057900

P2

P3

P5

P6

P7

P8

P9

P11

P12

P13

P14

P15

P16

P17 P18

P1P2P3P4P5P6P7P8P9P10P11P12P13P14P15P16P17P18

Right Branch ‘Ōpaeka‘a

North Fork WailuaNorth Fork WaikokoSouth Fork Waikoko‘Ili‘ili‘ulaNorth Fork Hanamā‘ulu

South Fork Hanamā‘ulu

Hanamā‘ulu TributaryNāwiliwiliPū‘ali

PāohiaKamo‘oloaKu‘iaKu‘ia Tributary‘Ōma‘oPō‘ele‘eleWahiawaLeft Branch Wahiawa

Partial-record site identifierand stream name 16010000

16019000160490001605240016053000160540001605790016060000

KawaikōīWai‘alaeHanapēpēLāwa‘i

Kamo‘oloaKu‘iaWaiahiSouth Fork Wailua

Stream-gaging-station number and stream name

16071500

16068000

16049000b

Wai‘ale‘ale

Kawaikini Peak

16053000

16054000

P4

P10

16060000a

16068000160715001609750016108000

East Branch North Fork WailuaLeft Branch ‘Ōpaeka‘a

HālaulaniWainiha

22°00'

159°32'

22°04'

21°56'

159°28' 159°24'

159°20'

North

Fork Wailua River

So u t h Fork

Wa i ul aRiver

Hanamā‘ulu Stream

Hulē‘ia S t re am

Nāwiliwili Str eam

Pū‘ali

Stream

Lāwa‘i S tream

Wah ai wa Stream

Han ēpa ēp vi R re

Waiko mo Stream

Figure 1. Map showing locations of study area, active and inactive continuous-record stream-gaging stations, and partial-record measurement sites in southeast Kaua‘i, Hawai‘i. 
Description of the Study Area 5

men20-4010_fig02

Wailua

Waikomo

Hanamā‘ulu

Nāwiliwili

Hulē‘ia

Hanapēpē

Wahiawa

Aepo Lāwa‘i Kalāheo

Māhā‘ulepū Pū‘ali

22°00'

159°32'

22°04'

21°56'

159°28'

159°24'

159°20'

0 42 KILOMETERS

0 4 2 MILES

Base modified from U.S. Geological Survey digitaldata. Universal Transverse Mercator projection,zone 4, North American Datum 1983.

EXPLANATION

Mean annual rainfall, in inches—Modified from 

Giambelluca and others (2013)

394350300250200160120805017

Hydrologic-unit boundary—From State of 

Hawai‘i (2017a)

Windward-leeward area boundary

—

Modified from Yamanaga (1972)

StreamRain-gaging station and numberStreamflow-measurement location

Stream-gaging station and number—Station in 

operation during base period from 1961 to 2019aStation monitored regulated flowbStation monitored natural flow from January 

to December 2017 and these records were used for record augmentation

Stream-gaging station and number—Station 

established for this study and monitors natural low-flow conditions only

Partial-record measurement site and map 

identifier—See table 5 for map identifier description

16068000

16052400

P18

1047.0

P1

16052400

16057900

P2

P3

P5

P6

P7

P8

P9

P11 P12

P13

P14

P15

P16

P17 P18

P1P2P3P4P5P6P7P8P9P10P11P12P13P14P15P16P17P18

Right Branch ‘Ōpaeka‘aNorth Fork WailuaNorth Fork WaikokoSouth Fork Waikoko‘Ili‘ili‘ulaNorth Fork Hanamā‘uluSouth Fork Hanamā‘uluHanamā‘ulu TributaryNāwiliwiliPū‘aliPāohiaKamo‘oloaKu‘iaKu‘ia Tributary‘Ōma‘oPō‘ele‘eleWahiawaLeft Branch Wahiawa

Partial-record site identifierand stream name

160490001605240016057900160600001606800016071500

HanapēpēLāwa‘iWaiahiSouth Fork WailuaEast Branch North Fork WailuaLeft Branch ‘Ōpaeka‘a

Stream-gaging-station number and and stream name

16071500

16068000

16049000b

1047.0

1051.0

P4

P10

Wai‘ale‘ale

16060000a

Windward Leeward

 North

Fork Wailua River

So u t h Fork

Wa i ul aRiver

Hanamā‘ulu Stream

Hulē‘ia S t re am

Nāwiliwili Str eam

Pū‘a l i Stream

Lāwa‘i S tream

Wah ai wa Stream

 Han ēpa ēp vi R r e

Waikomo Stream

159°20' 159°30' 159°40'

22°10'

22°00'

21°50'

Study

area

PACIFIC OCEAN

KAUA‘I

Figure 2. Map of mean annual rainfall in study area, southeast Kaua‘i, Hawai‘i.
6

Low-Flow Characteristics of Streams from Wailua to Hanapēpē, Kaua‘i, Hawai‘

men20-4010_fig03

0

100

200

300

400

500

600

700

800

19611962196319641965196619671968196919701971197219731974197519761977197819791980198119821983198419851986198719881989199019911992199319941995199619971998199920002001200220032004200520062007200820092010201120122013201420152016201720182019

Annual rainfall, in inches

Mean annual rainfall for water years 1961–2019—Water years 

1961–97 from Giambelluca and others (2013); water years 

1998–2019 from U.S. Geological Survey (2020a)

393

393

Water year

EXPLANATION

Study

period

Figure 3. Plot of annual rainfall totals at rain-gaging station 220427159300201 (State key number 1047.0) on Wai‘ale‘ale near Līhu‘e, Kaua‘i, 

Hawai‘i, for water years 1961–97 (Giambelluca and others, 2013) and water years 1998–2019 (U.S. Geological Survey, 2020a).

in some parts of the Wailua, Hulēʻia, Lāwaʻi, Wahiawa, and 

Hanapēpē aquifer systems. 

Thickly saturated settings occur in low-permeability lava 

flows situated in an area with wet climate, where groundwater 

saturates nearly to the land surface and may discharge to the 

streams rather than as submarine groundwater discharge. This 

groundwater flow maintains perennial flow in most reaches 

of North Fork and South Fork Wailua Rivers and Hulēʻia 

Stream, and the entirety of Hanamā‘ulu, Nāwiliwili, and Pūʻali 

Streams. Stream reaches in dike-impounded-groundwater and 

thickly saturated settings generally are referred to as “gaining 

reaches” because groundwater contributes to streamflow.

Freshwater-lens settings are high-permeability aquifers that 

occur in dike-free lava flows where fresh groundwater forms a 

lens-shaped body that buoyantly overlies denser saltwater from 

the ocean. The lens has a low-altitude water table and groundwater 

flows toward the coast where it naturally discharges to springs, 

streams, wetlands, and submarine seeps. A freshwater-lens setting 

is postulated to occur in the southern part of Koloa and Hanapēpē 

aquifer systems, which underlays most of Waikomo Stream 

and the lower reaches of Lāwaʻi Stream, Wahiawa Stream, and 

Hanapēpē River. Stream reaches in the freshwater-lens setting 

generally are referred to as “losing reaches” because streamflow 

discharges to the groundwater body. According to Izuka and others 

(2018), the boundary between dike-impounded-groundwater and 

freshwater-lens settings in southern Kauaʻi is uncertain owing to 

insufficient water-level data. 

Surface-Water Use

Historically, plains in the low-lying lands in the study 

area were used mainly for sugarcane cultivation. Established 

in 1835, Koloa Plantation was the first sugar plantation in 

Hawaiʻi (Wilcox, 1996). Situated in the Māhā‘ulepū area and 

Waikomo Stream basin (fig. 5), the plantation depended on 

water from neighboring lands owing to the lack of surfacewater and groundwater resources in the area. The diversion, 

conveyance, and storage systems owned and managed 

by Koloa Plantation include the 2.3-million gallon Waita 

Reservoir, the second largest reservoir in Hawai‘i. Koloa 

Plantation was acquired by Grove Farm in 1948. Grove Farm 

originally owned lands and operated diversion systems in 

the Hulē‘ia Stream basin. After ending its sugar business 

in 1974, Grove Farm leased lands to Līhuʻe Plantation and 

McBryde Sugar Company for continued sugar production. 

Līhuʻe Plantation, established in 1849, was the second-oldest 

sugar plantation in Hawaiʻi. The plantation originally owned 

lands and operated diversion systems in the Wailua River 

and Hanamā‘ulu Stream basins. The diversion systems span 
Description of the Study Area 7

men20-4010_fig04

Wailua

Waikomo

Hanamā‘ulu

Nāwiliwili

Hulē‘ia

Hanapēpē

Wahiawa

Aepo Lāwa‘i Kalāheo

Māhā‘ulepū

0 4 2 KILOMETERS

0 4 2 MILES

Base modified from U.S. Geological Survey digitaldata. Universal Transverse Mercator projection,zone 4, North American Datum 1983.

EXPLANATION

Aquifer system

Anahola (partly shown)WailuaHanamā‘uluKoloaHanapēpēMakaweli (partly shown)

Hydrogeologic setting—From Izuka and 

others (2018)

Dike-impounded groundwaterThickly saturatedFreshwater lens

Hydrologic-unit boundary—From State of 

Hawai‘i (2017a)

StreamStreamflow-measurement location

Stream-gaging station and number—Station 

in operation during base period from 1961 to 2019aStation monitored regulated flowbStation monitored natural flow from January 

to December 2017 and these records were used for record augmentation

Stream-gaging station and number—Station 

established for this study and monitors natural low-flow conditions only

Partial-record measurement site and map 

identifier—See table 5 for map identifier description

16068000

16052400

P18

22°00'

159°32'

22°04'

21°56'

159°28' 159°24'

159°20'

P1

16052400

16057900

P2

P3

P5

P6

P7

P8

P9

P11 P12

P13

P14

P15

P16

P17 P18

P1P2P3P4P5P6P7P8P9P10P11P12P13P14P15P16P17P18

Right Branch ‘

Ōpaeka‘a

North Fork WailuaNorth Fork WaikokoSouth Fork Waikoko‘Ili‘ili‘ulaNorth Fork Hanamā‘uluSouth Fork Hanamā‘uluHanamā‘ulu Tributary

NāwiliwiliPū‘ali

PāohiaKamo‘oloaKu‘iaKu‘ia Tributary‘Ōma‘oPō‘ele‘ele

WahiawaLeft Branch Wahiawa

Partial-record site identifierand stream name

160490001605240016057900160600001606800016071500

Hanapēpē

Lāwa‘i

WaiahiSouth Fork WailuaEast Branch North Fork WailuaLeft Branch ‘

Ōpaeka‘a

Stream-gaging station number and and stream name

16071500

16068000

16049000b

P4

P10

Pū‘ali

16060000a

North

Fork Wailua River

So u t h Fork

Wa i ul aRiver

Hanamā‘ulu Stream

Hulē‘ia S t re am

Nāwiliwili Str eam

Pū‘ali

Stream

Lāwa‘i S tream

Wah ai wa Stream

Han ēpa ēp vi R re

Waikomo Stream

159°20' 159°30' 159°40'

22°10'

22°00'

21°50'

Study

area

PACIFIC OCEAN

KAUA‘I

Figure 4. Hydrogeologic settings in the study area, southeast Kaua‘i, Hawai‘i.
8

Low-Flow Characteristics of Streams from Wailua to Hanapēpē, Kaua‘i, Hawai‘

51 mi of ditches with 18 stream intakes and transported an 

average 100–140 million gallons of water per day. Within 

the Līhuʻe Plantation lands, the East Kauaʻi Water Company 

used water from North Fork Wailua River. Līhuʻe Plantation 

ended sugar production in November 2000 (Sommer, 2000). 

McBryde Sugar Company originally owned lands and 

operated diversion systems in the Lāwa‘i Stream, Kalāheo 

Gulch, Wahiawa Stream, and (lower) Hanapēpē River basins. 

With limited access to surface-water resources, the company 

focused on developing groundwater resources and water 

storage. Groundwater pumps were powered by the company’s 

two hydropower facilities, one located on the northern slopes 

of Kaua‘i and the second in Kalāheo Gulch basin. McBryde 

Sugar Company built Alexander Reservoir (capacity of more 

than 800 million gallons) to capture water sources at the head 

of Wahiawa Stream basin (fig. 5). McBryde Sugar Company 

ended sugar production in 1994. 

As a result of sugar plantation closures, water use shifted 

from irrigation of sugarcane to irrigation of diversified crops 

and hydropower development. During the study period, many 

of the surface-water diversions originally operated by the 

plantations continued to be used (fig. 5). The upper reaches 

of Wailua River, Hanamā‘ulu Stream, and Hulē‘ia River 

were diverted by several interconnected ditches that supply 

irrigation water for seed production, commercial forestry, 

pasture management, and diversified crops. Water diverted 

from Waiahi Stream, a tributary of South Fork Wailua River, 

supported two hydropower facilities in the valley. Nāwiliwili 

Stream provided irrigation water for taro cultivation and 

diversified crops within the valley. Lāwa‘i and Wahiawa 

Streams supplied irrigation water for coffee cultivated near 

the south shore and landscape irrigation. The upper tributaries 

of Hanapēpē River provided irrigation water mainly for seed 

production and pasture management in the western coastal 

areas (State of Hawai‘i, 2016, p. 50). Hanapēpē River was also 

diverted in the lower reach to irrigate taro farms in the valley 

and coffee fields in lower Kalāheo Gulch basin. Information 

on surface-water diversions is gathered from County of Kaua‘i 

and State of Hawai‘i reports, accounts from current landowners 

within the study area, and visual observations during field 

investigations by USGS personnel. The conditions related to 

the diversion and uses of surface water in the study area apply 

to the study period and may not represent future conditions 

because landownership and the uses of water may change.

Historical Surface-Water Availability

Streamflow data that describe the natural (unregulated) 

low-flow conditions of the study-area streams are limited. Natural 

flow is streamflow that is not affected by factors including 

surface-water diversions, irrigation return flows, or groundwater 

withdrawals. Two inactive continuous-record stream-gaging 

stations––station 16053000 on Kamoʻoloa Stream and 16054000 

on Kuʻia Stream (fig. 1)––monitored natural flow from November 

1939 to June 1941. The median discharge is the flow that has been 

equaled or exceeded 50 percent of the time during a specified 

period. Median discharges for the period of record at the stations 

are 4.0 cubic feet per second (ft3/s) on Kamoʻoloa Stream and 

1.7 ft3/s on Kuia Stream (table 1). With less than 2 years of 

available data, the duration discharges may not be representative 

of long-term conditions.

Data that describe historical diverted conditions may not 

apply to the present day; however, they provide information that 

is useful for understanding the diversion practices that occurred 

during the study period. In addition, ditch-flow data at surfacewater diversion intakes and associated flow-duration discharges 

can provide some information on streamflow availability because 

many diversion intakes were constructed to capture a majority of 

the streamflow during low-flow conditions. Multiple surface-water 

diversions have existed on the same stream to capture streamflow 

gained between the diversions. 

A number of ditch-flow gaging stations operated at or 

near surface-water diversions within the study area prior to 

2001 (table 1, fig. 5). A majority of ditch-flow gaging stations 

were located in the Wailua River and Hulēʻia Stream basins. 

On North Fork Wailua River, station 16100000 monitored flow 

diverted from a stream on the island’s northern slopes that was 

discharged to a tributary of North Fork Wailua River. Station 

16061000 monitored flow diverted from the river to ʻIliʻiliʻula 

North Wailua Ditch and downstream station 16062000 

monitored flow diverted to Stable Storm Ditch. On South 

Fork Wailua River, station 16061200 monitored total diverted 

flow from North Fork Wailua River and Waikoko Stream in 

the ʻIliʻiliʻula North Wailua Ditch. The difference in ditchflow records at stations 16061000 and 16061200 represents 

diverted flow from Waikoko Stream assuming no gain or 

loss of ditch flow between the stations. Station 16057000 

monitored flow diverted from Waiahi Stream, a tributary of 

South Fork Wailua River, to Upper Līhuʻe Ditch. Downstream 

station 16058000 monitored flow diverted from South Fork 

Wailua River to Hanamā‘ulu Ditch. In Hulēʻia Stream basin, 

station 16056800 monitored flow diverted from two tributaries 

of South Fork Wailua River and two tributaries of Hulēʻia 

Stream to the Waiahi-Kuʻia Aqueduct. Stations 16053400 and 

16053600 monitored flow diverted from two tributaries of 

Hulēʻia Stream to upper and lower Haʻikū Ditch, respectively. 

Station 16054200 monitored flow diverted from tributaries of 

Hulēʻia Stream to Kōloa Ditch and eventually conveyed to the 

Māhā‘ulepū area. 
Description of the Study Area 9

men20-4010_fig05

Nort h

Fork Wailua River

So u t h Fork

Wa i ul aRiver

Hanamā‘ulu Stream

Hu ēl ‘ia S tream

Nāwiliwili Str eam

Pū‘ali

Stream

Lāwa‘i S tream

Wah ai w a t S er ma

na H

pa pē Rē evi r

Waikomo Stream

Wailua

Waikomo

Hanamā‘ulu

Nāwiliwili

Hulē‘ia

Hanapēpē

Wahiawa

Aepo

Lāwa‘i Kalāheo Māhā‘ulepū

16100000

16061000

16061200

16062000

16070000

16058000

16057000

16053400

16053600

16056800

16054200

16039000

16064000

Pū‘ali

0 4 2 KILOMETERS

0 4 2 MILES Base modified from U.S. Geological Survey digital

data. Universal Transverse Mercator projection,zone 4, North American Datum 1983.

Hydrologic-unit boundary—From 

State of Hawai‘i (2017a)

StreamMajor surface-water diversion 

system—Does not reflect operational status of the diversion system

Major surface-water diversion 

intake on study-area stream

—

In operation during study period from 2015 to 2019

Major surface-water diversion 

intake on study-area stream

—

Unknown operational status

Ditch-flow gaging station at 

surface-water diversion intake and station number—Inactive during study period from 2016to 2019

EXPLANATION

16070000

22°00'

159°32'

22°04'

21°56'

159°28'

159°24'

159°20'

Stable Storm Ditch 

‘Ili‘ili‘ula North Wailua Ditch 

North Intake Ditch 

Waiahi ‘Ili‘ili‘ula Ditch 

Waiahi-Ku‘ia Aqueduct 

Upper Līhu‘e Ditch 

Hanamā‘ulu Ditch 

'A'ahoaka Ditch 

Waiahi Upper Powerhouse

Kōloa Ditch

Lāwa‘i

Waiahi Lower Powerhouse

 Intake Ditch

Waita Reservoir

Alexander Reservoir

Farmers Ditch

Pump 3 Ditch

Upper Ha‘ikū Ditch

Lower Ha‘ikū Ditch

159°20' 159°30' 159°40'

22°10'

22°00'

21°50'

Study

area

PACIFIC OCEAN

KAUA‘I

Figure 5. Map showing locations of major surface-water diversion systems and associated intakes, and U.S. Geological Survey ditch-flow gaging stations in the study area, southeast Kaua‘i, Hawai‘i.
10

Low-Flow Characteristics of Streams from Wailua to Hanapēpē, Kaua‘i, Hawai‘i Table 1. Low-flow duration discharges at inactive continuous-record streamflow and ditch-flow gaging stations in the study area, southeast Kaua‘i, Hawai‘i. USGS station number USGS station name, Kauai, HI Altitude, in feet Period of record Number of complete water years Complete water years used in computation Discharge, in ft3/s, for selected percentages of time (from 50 to 95 percent) the indicated discharge was equaled or exceeded 50 55 60 65 70 75 80 85 90 95 Historical continuous-record stream-gaging stations 16053000 Kamooloa Stream nr Koloa 1,050 1939–41 0 Period of record 4.0 3.8 3.5 3.2 3.0 2.8 2.5 2.1 1.9 1.6 16054000 Kuia Stream nr Koloa 1,050 1939–41 0 Period of record 1.7 1.6 1.6 1.5 1.5 1.4 1.4 1.4 1.3 1.2 Historical continuous-record ditch-flow gaging stations 16039000 Hiloa Ditch nr Eleele 700 1911–15 3 1913–15 37 34 33 31 31 28 28 25 23 19 16053400 Upper Haiku Ditch nr Puhi 470 1963–71 6 1965–70 6.7 4.6 3.1 2.3 1.6 0.78 0.32 0.15 0.080 0.030 16053600 Lower Haiku Ditch nr Puhi 400 1963–71 6 1965–70 3.3 2.7 2.4 2.2 1.9 1.7 1.5 1.2 1.1 0.79 16054200 Koloa Ditch nr Koloa 620 1964–71 6 1965–70 15 13 12 11 10 9.0 8.0 6.8 5.2 4.3 16056800 Waiahi-Kuia Aqueduct nr Puhi 730 1964–71 6 1965–70 2.0 1.6 1.1 0.59 0.25 0.090 0 0 0 0 16057000 Lihue Ditch nr Lihue 550 1910–19 4 1910–13 9.6 8.8 8.4 8.1 7.2 5.4 3.8 0 0 0 16058000 Hanamaulu Ditch nr Lihue 420 1910–19 7 1910–14, 1917–18 32 31 29 28 25 19 15 11 8.7 5.6 16061000 North Wailu

Ditch nr Lihue

1,100 1932–85 53 1933–85 19 19 18 18 17 17 16 15 14 9.1

16061200 N. Wailua Ditch 

blw Waikoko Str nr Lihue

1,070 1965–2002 37 1966–2002 22 21 21 20 20 19 18 17 16 9.6

16062000 Stable Storm 

Ditch nr Lihue

710 1937–2002 65 1938–2002 0.28 0.20 0.14 0.11 0.050 0.020 0 0 0 0

16064000 Kanaha Ditch nr 

Lihue

540 1912–55 36 1914, 1917–22, 

1927–55

2.4 1.5 1.1 0.85 0.67 0.48 0.40 0.32 0.25 0.080

16070000 Aahoaka Ditch nr 

Kapaa

400 1966–72 5 1967–71 0 0 0 0 0 0 0 0 0 0

16100000 Hanalei Tunnel 

Outlet nr Lihue

1,210 1932–85 53 1933–85 28 26 25 23 20 17 13 7.0 3.1 0.60

[USGS, U.S. Geological Survey; HI, Hawaii; nr, near; N, North; blw, below; Str, Stream; ft3/s, cubic feet per second. Database limitations preclude the use of Hawaiian diacritical marks in USGS station names. Altitude values interpolated from USGS 1:24,000-scale digital hypsography data. A water year is a 12-month period that extends from October 1 to September 30 of the following year and is named according to the year during which the period ends]
Methods

Methods

The following sections provide an overview of datacollection sites established, flow-duration statistics and how 

they are computed, and the record-augmentation techniques 

used in this study.

Data-Collection Sites

Three types of streamflow-measurement sites are described 

in this report: (1) a continuous-record stream-gaging station, 

which provides a continuous record of discharge at a location 

in the stream; (2) a partial-record station, which commonly has 

10 or more systematic streamflow measurements at a location 

in the stream; and (3) a miscellaneous site, which typically has 

less than 10 streamflow measurements that may not have been 

collected in a systematic manner as with a partial-record station. 

In this study, a long-term continuous-record stream-gaging 

station (long-term station) has 10 or more complete water years 

of natural-flow record, and a short-term continuous-record 

station (short-term station) has less than 10 complete water 

years of natural-flow record. A low-flow partial-record site 

has a series of streamflow measurements that have been made 

under low-flow conditions. An example of a miscellaneous 

site is a seepage-run measurement site where only one or two 

measurements have been made for the purposes of determining 

seepage gains and loses along a stream reach.

The following sections describe short-term continuousrecord stream-gaging stations, partial-record sites, and seepage-run 

discharge-measurement sites established for this study.

Short-Term Stations

Two short-term continuous-record stream-gaging stations 

that monitored natural low flow were established to serve 

as potential index stations (table 2). Station 16057900 was 

located on Waiahi Stream upstream from the Waiahi upper 

powerhouse. Station 16052400 was located on right branch 

Lāwaʻi Stream upstream from the Lāwaʻi Intake Ditch and a 

diversion intake for a nursery in the area (fig. 1). During the 

study period, two long-term stations were operated within the 

northernmost boundary of the study area in the Wailua River 

basin (fig. 1). The short-term stations were established for this 

study because of a lack of long-term stations in the southern 

part of the study area. Information from these short-term 

stations was needed to estimate streamflow characteristics at 

partial-record sites in the southern part of the study area where 

discharges may not correlate well with discharges at existing 

long-term stations in the northern part of the study area.

Each short-term station recorded instantaneous stage 

values in 15-minute intervals with no real-time capability. A 

stage-discharge relation (rating curve) was developed from 

paired discharge and stage measurements at the short-term 

stations for the range of flow-duration discharges––between 

Q95 and Q50––that are of interest in this study. Using this 

relation, discharge at the station is determined from a stage 

measurement. 

The Waiahi short-term station has been in operation 

since November 2015. The Lāwaʻi short-term station was in 

operation from February 2016 to March 2017, and May 2017 

to March 2018. In March 2017, the station equipment was 

damaged by a high-flow event and it was repaired in May 

2017. Subsequently in March 2018, the station was destroyed 

by a high-flow event that altered the stream channel near the 

station. Reinstallation of the station was deemed unfeasible 

owing to the instability of the stream channel at the time.

Station 16049000 on Hanapēpē River is an active 

continuous-record stream-gaging station that monitors flow 

regulated by upstream surface-water diversions on right and 

left branch Kōʻula Rivers. During calendar year 2017, these 

upstream diversions were not in operation (Howard Greene, 

Gay & Robinson, oral commun., 2018). Continuous record 

during this period that the station monitored natural flow 

was used in record augmentation to estimate flow-duration 

discharges at the station. For simplicity, station 16049000 is 

referred as a short-term station in this report because the station 

has less than 10 complete water years of natural-flow record.

Partial-Record Sites

Partial-record sites were established on 3 main streams and 

15 tributary streams in the study area (fig. 1). To characterize 

natural low-flow availability of these streams, partial-record sites 

were established upstream from all surface-water diversions. 

Discharges measured at the partial-record sites may include 

discharge from upstream development tunnels because flow from 

a development tunnel is considered water that would otherwise 

have naturally discharged into the stream.

For record augmentation, about 10 discharge measurements 

are generally made at a partial-record site during periods of low 

flow (Rantz and others, 1982). The discharge measurements 

should be made under a variety of low-flow conditions and during 

independent recessions. A streamflow recession is defined as 

the period when flow returns to low-flow conditions following a 

period of direct runoff. Hydrographs from nearby active long-term 

stations were checked to determine when recessions occurred in 

the study-area streams. For this study, discharge measurements 

were made at each of the partial-record sites between February 

2016 and January 2020, and bracketed the range of flow-duration 

discharges––between Q95 and Q50––as indicated by nearby active 

continuous-record stream-gaging stations that monitored natural 

flow. This approach was used to increase the accuracy of the entire 

range of estimated flow-duration discharges at the partial-record 

sites. Discharge measurements were made with acoustic Doppler 

velocimeters (ADV), processed, reviewed, approved, archived, 

and available in the USGS National Water Information System 

database at https://waterdata.usgs.gov/hi/nwis/nwis.

Most discharge measurements at the partial-record sites 

were made during stable-flow conditions, as documented by 

recording the height of water surface—commonly referred to 

as gage height or stage—during the time when the discharge 
12

Low-Flow Characteristics of Streams from Wailua to Hanapēpē, Kaua‘i, Hawai‘i Table 2. Low-flow duration discharges at active long-term continuous-record stream-gaging stations and short-term continuous-record low-flow gaging stations established in the study area, southeast Kaua‘i, Hawai‘i. USGS station number USGS station name, Kauai, HI Altitude, in feet Drainage area, in square miles Period of record Num- ber of complete water years Complete water years used in computation Length of record, in years Discharge, in ft3/s, for selected percentages of time (from 50 to 95 percent) the indicated discharge was equaled or exceeded Total flow Base flow 50 55 60 65 70 75 80 85 90 95 50 70 Long-term continuous-record stream-gaging stations 16010000 Kawaikoi Stream nr Waimea 3,420 3.8 1909–16, 1919–P 102 1912, 1914, 1920–2019 102 12 11 9.6 8.5 7.4 6.7 5.8 5.0 4.2 3.4 6.7 4.9 1943–2019 77 12 11 9.3 8.3 7.4 6.5 5.7 4.9 4.2 3.3 6.6 4.9 1961–2019 59 12 10 9.3 8.2 7.4 6.5 5.8 5.0 4.2 3.3 6.6 4.8 1984–2013 30 11 9.5 8.4 7.5 6.7 6.0 5.2 4.6 4.0 3.1 6.1 4.5 16019000 Waialae Str at alt 3,820 ft nr Waimeaa 3,820 2.1 1920–32, 1952–P 76b 1921–31, 1953–2019 78 6.4 5.7 5.0 4.5 4.0 3.6 3.3 2.9 2.6 2.2 3.4 2.8 1953–2019 67 6.4 5.7 5.1 4.5 4.0 3.6 3.3 2.9 2.6 2.2 3.5 2.8 1961–2019 59 6.4 5.8 5.1 4.5 4.0 3.6 3.3 2.9 2.6 2.2 3.5 2.8 1984–2013 30 6.0 5.2 4.7 4.2 3.7 3.4 3.0 2.8 2.5 2.2 3.2 2.7 16068000c EB of NF Wailua River nr Lihue 500 6.2 1912–P 104 1913–14, 1916–17, 1920–2019 103 30 28 26 24 23 21 19 18 16 14 22 18 1943–2019 77 29 27 25 23 22 20 18 17 15 13 21 

1961–2019 59 28 26 25 23 21 20 18 16 15 13 21 171984–2013 30 27 25 24 22 21 19 18 16 15 13 20 172017–19 3 31 30 28 26 24 22 20 19 17 15 22 19

16071500c Left Branch 

Opaekaa Str nr Kapaa

460 0.75 1960–P 59 1961–2019 59 1.5 1.4 1.2 1.1 1.0 0.90 0.80 0.70 0.60 0.50 1.2 0.80

1984–2013 30 1.3 1.2 1.1 1.0 0.90 0.80 0.70 0.70 0.60 0.50 1.1 0.802017–19 3 1.5 1.4 1.3 1.2 1.1 1.0 1.0 0.90 0.80 0.60 1.2 0.90

16097500 Halaulani Str at 

alt 400 ft nr Kilauea

390 1.2 1957–P 61 1959–2019 61 7.2 6.8 6.4 6.1 5.7 5.4 5.1 4.8 4.5 4.0 5.8 5.0

1961–2019 59 7.2 6.8 6.4 6.1 5.7 5.4 5.1 4.8 4.5 4.0 5.8 5.01984–2013 30 6.8 6.4 6.1 5.8 5.5 5.2 4.9 4.6 4.3 3.9 5.6 4.9

[USGS, U.S. Geological Survey; HI, Hawaii; nr, near; Str, Stream; alt, altitude; ft, feet; EB, East Branch; NF, North Fork; Riv, River; blw, below; RB, Right Branch; US, upstream; P, present (2019); ft3/s, cubic feet per second; --, not applicable. Database limitations preclude the use of Hawaiian diacritical marks in USGS station names. Altitude values interpolated from USGS 1:24,000-scale digital hypsography data. A water year is a 12-month period that extends from October 1 to September 30 of the following year and is named according to the year during which the period ends]
Methods

Table 2.—Continued

USGS 

station 

number

USGS station 

name, 

Kauai, HI

Altitude,

in feet

Drainage 

area, in 

square 

miles

Period of 

record

Number of 

complete 

water years

Complete water 

years used in 

computation

Length 

of 

record, 

in years

Discharge, in ft3/s, for selected percentages of time (from 50 to 95 percent)

the indicated discharge was equaled or exceeded

Total flow Base flow

50 55 60 65 70 75 80 85 90 95 50 70

16108000 Wainiha River 

nr Hanalei

960 10.4 1952–P 64 1953–55, 

1959–2019

64 77 71 67 63 59 56 53 50 47 43 55 49

1961–2019 59 77 71 67 63 59 56 53 50 47 43 55 491984–2013 30 76 70 66 63 60 56 53 50 47 43 55 49

Short-term continuous-record stream-gaging stations

16049000 Hanapepe 

Riv blw Manuahi Str nr Eleele

222 18.5 1917–20, 

1927–Pd

95 1961–2019f -- 69 67 63 56 50 48 46 45 43 42 -- --

16052400 RB Lawai 

Stream 

300 ft US of fork

600 2.2 2016–18 3e 1961–2019f -- 3.0 2.4 2.2 1.7 1.3 1.2 0.87 0.63 0.53 0.35 -- --

16057900 Waiahi Str 

US Upper Powerhouse

815 4.1 2015–P 3e Period of record -- 26 24 22 21 19 18 17 16 15 13 -- --

2017–19 -- 25 24 22 21 19 18 17 16 15 14 -- --

aSelected flow-duration discharges computed from discharge record at station 16019000 with daily mean discharges estimated for October 13, 2016, June 22, 2019, and June 23, 2019. Daily mean discharge 

is typically computed from continuous record of unit values collected at 15-minute intervals. Partial record of unit values was used to estimate daily means on the aforementioned days.

bNumber of complete water years does not include water year 2017 with missing daily mean discharge for October 13, 2016 and water year 2019 with missing daily mean discharge for June 22 and 23, 2019.cContinuous streamgaging station located within the study area.dStation monitored natural flow from January to December 2017 and these records were used in this study for record augmentation.eNumber of complete water years for low-flow record. fSelected flow-duration discharges extended with discharge record at 16068000.
14

Low-Flow Characteristics of Streams from Wailua to Hanapēpē, Kaua‘i, Hawai‘

measurements were being made. Discharge measurements that 

were made when the stage was highly variable, that is, when 

stream stage changed by more than ±0.02 ft, were not used to 

estimate streamflow characteristics.

Seepage-Run Discharge-Measurement Sites

The spatial distribution of streamflow gains and losses 

along stream reaches in study-area streams was characterized 

by seepage-run measurements. A seepage run consists of 

several streamflow measurements collected on the same day 

at specific sites along a stream under stable-flow conditions to 

determine the magnitude of streamflow gains and losses, and 

to identify flowing and dry stream reaches. Stream reaches can 

either gain water (groundwater discharge into stream) or lose 

water (stream discharge into a groundwater body), depending 

on the altitude of the water table relative to the streambed. 

Seepage-run measurements combined with low-flow durationdischarge estimates can provide water-availability information 

for downstream reaches and help determine whether the 

stream flows continuously from the mountains to the ocean 

(commonly referred to in Hawai‘i as mauka to makai flows).

Seepage runs were conducted in eight of the nine study 

basins (Pūʻali Stream basin was excluded) as part of this study 

and targeted flow conditions different from those of previous 

seepage runs. For example, if a previous seepage run was 

conducted under conditions when an index station was flowing 

at about a Q60 discharge, the seepage run conducted as part of 

this study would target lower-flow conditions as indicated by 

the same index station. This was done to characterize seepage 

gains and losses over a range of flow conditions.

Flow-Duration Statistics

Natural low-flow characteristics of the study-area streams 

are described using flow-duration discharges. Flow-duration 

curves display the complete range of flows in a stream and have 

been extensively used for hydrologic planning and design (Vogel 

and Fennessey, 1995), especially in the field of water-resource 

management. A flow-duration curve is a cumulative-frequency 

distribution that shows the percentage of time that specified 

discharges at a location in a stream are equaled or exceeded during 

a specified period; hence, the curve shows the relation between 

magnitude and frequency of streamflow. 

Daily mean discharges are typically used to construct 

the flow-duration curves because they allow for more detailed 

examination of the duration characteristics of a stream (Smakhtin, 

2001, p. 154) compared to flow-duration curves constructed from 

weekly, monthly, or annual streamflow data. A flow-duration 

curve is constructed by first ranking the daily mean discharges for 

a given period of record in descending order, then computing the 

exceedance probability of each discharge, and finally plotting the 

discharges against their exceedance probabilities (Ries and Friesz, 

2000, p. 8). The exceedance probabilities are computed with the 

Weibull formula (Loaiciga, 1989, p. 82):

P k

n k n k    1

, , 1 2, , 3 ..., (1)

where Pk is the exceedance probability of a daily mean 

discharge with rank k;

k is the rank of a daily mean discharge; and

n is the total number of daily mean discharges 

for the given period of record.

The 50-percent flow-duration discharge, commonly 

referred to as median (Q50) discharge, is one of the most 

representative and frequently computed flow-duration 

statistics. The Q50 discharge is the flow that has been equaled 

or exceeded 50 percent of the time during a specified period. 

Flow-duration discharges that describe low-flow conditions 

are generally considered to be those equal to or less than the 

Q50 discharge, and they are represented by the lower end of the 

flow-duration curve. The natural low-flow characteristics of 

this study are represented by flow-duration discharges between 

the Q95 and Q50 discharges in 5-percent increments—Q95, Q90, 

Q85, Q80, Q75, Q70, Q65, Q60, Q55, and Q50.

Record Augmentation

Record augmentation is used to determine selected low-flow 

duration discharges for short-term and partial-record stations 

for a base period that is representative of long-term hydrologic 

conditions in the study area. It is an index-streamgage approach in 

which streamflow information from a continuously gaged basin is 

applied to a basin with limited streamflow data (Eng and others, 

2011). This method involves correlating concurrent streamflow 

data points between the measurement site of interest (shortterm stations and partial-record sites) and a nearby long-term 

station (index station) to develop a statistical relation. About 10 

concurrent streamflow data points are generally needed to apply 

record augmentation (USGS Office of Surface Water, Technical 

Memorandum no. 86.02, December 16, 1985). The model built 

from the correlation between the data points is used to compute 

flow-duration discharges at the measurement site of interest from 

corresponding flow-duration discharges at the index station for the 

base period. The base period is a common period during which all 

index stations used in the analysis are in operation with complete 

water years of streamflow data for computing various flowduration discharges.

The Maintenance of Variance Extension Type 1 (MOVE.1) 

record-augmentation technique described by Hirsch (1982) and 

the graphical-correlation technique described by Searcy (1959, 

p. 14) are used to extend streamflow records for this study. Both 

record-augmentation techniques assume that the relation between 

concurrent records at the index stations and measurement site of 

interest is the same during the selected base period (Ries, 1993, 

p. 21). Selecting the appropriate record-augmentation technique 

for estimating streamflow characteristics depends on the relation 

between data points at the measurement site of interest and the 

concurrent data points at the index station. The initial procedures 

used prior to the application of record-augmentation techniques 

are as follows:
Methods

1. Compute the 95-, 90-, 85-, 80-, 75-, 70-, 65-, 60-, 55-, and 

50-percent flow-duration discharges for the base period at 

selected index stations (table 2).

2. Plot the base-10 logarithms of data points at the 

measurement sites (short-term stations and partial-record 

sites) and concurrent data points at each selected index 

station to determine which index station provides the 

best statistical relation by comparing the correlation 

coefficients. Index stations with correlation coefficients 

greater than 0.80 are examined.

3. Assess for curvature in the plots developed in step 2. 

When little or no curvature is detected in a relation on a 

logarithmic plot, the MOVE.1 technique is used to estimate 

flow-duration discharges. When curvature is evident in the 

relation, the graphical-correlation technique is used.

MOVE.1 Technique

The statistical relation developed with the MOVE.1 

technique is based on the line of organic correlation regression 

method. Hirsch and Gilroy (1984) and Helsel and Hirsch (2002) 

showed that the line of organic correlation method was most 

appropriate for record augmentation of hydrologic data compared 

with ordinary least squares and least normal squares regression 

methods. The general procedure for the MOVE.1 technique 

begins with the transformation of concurrent data points at the 

index station and measurement site to base-10 logarithms, and 

then computation of the means and standard deviations of the 

transformed values. The low-flow duration discharges for the base 

period at the index station are also computed and transformed to 

base-10 logarithms. Estimates of low-flow duration discharges at 

the measurement site are determined using the MOVE.1 formula 

(eq. 2) and then converted to the original (nontransformed) units of 

measurement in ft3/s.

Y m

s

s i y X m y

x

  ( ) i x  (2)

where Yi is the base-10 logarithm of the estimated 

low-flow duration discharge at the partialrecord site;

 Xi is the base-10 logarithm of the computed 

low-flow duration discharge at the index 

station;

my is the mean of the base-10 logarithms of the 

discharge measurements at the partialrecord site;

mx is the mean of the base-10 logarithms of the 

concurrent daily mean discharges at the 

index station;

sy is the standard deviation of the base-10 

logarithms of the discharge measurements 

at the partial-record site; and

sx is the standard deviation of the base-10 

logarithms of the concurrent daily mean 

discharges at the index station.

Granato (2009) developed the Streamflow Record Extension 

Facilitator program to automate the MOVE.1 technique; this 

program is used in this study to facilitate record augmentation. 

The MOVE.1 results are evaluated by analyzing several regression 

statistics computed by the program. Those statistics include the 

correlation coefficient (r), residual error for each data point (ei), 

the leverage of each data point (hi), the mean square error (MSE), 

the root mean square error (RMSE), and a modified Nash-Sutcliff 

coefficient of efficiency (E). The correlation coefficient (Vogel and 

Stedinger, 1985; Helsel and Hirsch, 2002) measures the strength 

of the linear relation between concurrent discharges at the index 

station and measurement site. The residual error is the uncertainty 

in the estimated flow-duration discharges at the measurement 

sites. The leverage of a data point reflects the influence it has on 

the statistical relation. A high leverage likely indicates an outlier 

in the discharges at the measurement sites and the statistical 

relation would be skewed towards this data point. The RMSE 

(or standard deviation) is the square root of the variance, and 

it aggregates the differences (or residuals) between individual 

estimated and measured discharges at the measurement sites into a 

single predictive measure. The modified Nash-Sutcliff coefficient 

of efficiency (Legates and McCabe, 1999), with values ranging 

from negative infinity to 1, determines the accuracy to which the 

statistical relation predicts low-flow duration discharges at the 

measurement sites from the low-flow duration discharges at the 

index station. A coefficient of efficiency of zero indicates that 

the mean of discharges at the measurement site is as accurate 

for predicting flow-duration discharges as the regression model. 

A negative coefficient of efficiency occurs when the mean of 

discharges at the measurement site is a better predictor than the 

regression model. For this study, acceptable values of correlation 

coefficients (r) and modified Nash-Sutcliff coefficients of 

efficiency (E) are those equal to or greater than 0.80 and 0.50, 

respectively. The equations used to compute these regression 

statistics can be found in Granato (2009).

Graphical-Correlation Technique

In the graphical-correlation record-augmentation technique, 

a curve of relation is plotted through the data points at the 

measurement site and concurrent data points at the index station. 

The data points are plotted on an arithmetic scale when drawing 

the curve of relation to reduce curvature in the extreme low flows 

and to avoid long downward extrapolations of the data (Ries, 

1993, p. 21). The selected low-flow duration discharges at the 

measurement site are determined by reading the discharges of the 

measurement site from the best fit curve of relation that correspond 

to the low-flow duration discharges at the index station.

Index Stations and Selection of Base Period

An index station is a continuous-record stream-gaging station 

that measures natural flow and has a sufficient length of record for 

estimating streamflow characteristics representative of long-term 

conditions. It is usually located along the same stream as the site of 

interest at which flow-duration discharge estimates are needed or 
16

Low-Flow Characteristics of Streams from Wailua to Hanapēpē, Kaua‘i, Hawai‘

in a nearby stream basin that is hydrologically similar to that of the 

site of interest. Searcy (1959, p. 14) defines hydrologic similarity 

between two drainage basins as having the same probability of 

rainfall, not necessarily the occurrence of concurrent rainfall. 

Proximity is a common criterion for selecting index stations, 

although remote index stations as far away as 50 miles have 

been used to estimate streamflow characteristics (Searcy, 1959, 

p. 14). In a study by Cheng (2014) that characterized low-flow 

availability for streams in west Maui, data at one partial-record site 

correlated with an index station on Moloka‘i about 20 mi away.

Six active long-term continuous-record stream-gaging 

stations on Kauaʻi that monitored natural flow were considered 

potential index stations as a result of the limited number 

of long-term stations in the study area (table 2). Stations 

16068000 on east branch of North Fork Wailua River and 

16071500 on left branch ʻŌpaekaʻa Stream are the only longterm stations in the study area, and both stations are located in 

the North Fork Wailua River basin (fig. 1). 

Selection of a base period for adjusting streamflow 

records is critical to obtaining comparable low-flow estimates 

among the measurement sites. Flow-duration discharges may 

vary when computed from different time periods because the 

distribution of streamflow is not constant with time (Ries, 

1993, p. 18). When flow-duration discharges are estimated 

from multiple index stations with different time periods and 

(or) record lengths, the time-sampling errors are generally 

larger than those computed with similar record periods. 

Therefore, streamflow records at index stations are commonly 

limited to a common base period to minimize time-sampling 

errors and to ensure that differences in flow characteristics 

are associated with spatial differences in climate and drainage 

basin characteristics (Searcy, 1959, p. 12).

The base period should also be of sufficient length 

that is representative of long-term streamflow conditions. 

Fontaine (1995) used data from five long-term stations on the 

island of O‘ahu, each with more than 60 years of record, and 

demonstrated that estimates of streamflow characteristics are 

improved with increased record length (see fig. 2 and table 9 

in Fontaine, 1995). A minimum of 10 years of record generally 

is used to estimate streamflow characteristics such as the 

long-term median discharge. If the length of record is deemed 

inadequate for representing long-term streamflow conditions, 

record-augmentation techniques are commonly used to adjust 

the short-term record to a longer period (Ries, 1993, p. 18). 

The 59-year period 1961–2019 is selected as the base period 

for this study because (1) this period is representative of recent 

hydrologic conditions, (2) this period is of sufficient length to 

represent long-term hydrologic conditions, and (3) the greatest 

number of long-term stations are operated within this 59-year 

period.

At the six active long-term stations that monitored 

natural flow, selected annual statistics––Q90, Q70, and Q50

discharges and mean flow––computed for each water year 

from daily mean values of total flow (U.S. Geological Survey, 

2020b) and base flow were evaluated for trends in the base 

period. Trend analyses at the stations were conducted using 

methods described in Bassiouni and Oki (2013). The baseflow component of total flow was estimated from daily mean 

values of streamflow using a base-flow separation method 

described in Wahl and Wahl (1995). This method previously 

has been used for streams on Moloka‘i, Kaua‘i, Maui, and 

Oahu to estimate base flow (Oki, 1997; Izuka and Gingerich, 

1998; Gingerich, 1999; Fontaine, 2003; Engott and others, 

2017; Johnson and others, 2018; Izuka and others, 2018; 

Oki and others, 2020) and provides a reasonable estimate of 

base flow for perennial streams in Hawai‘i. The base-flow 

separation method defines local minimums within consecutive, 

nonoverlapping N-day periods and requires two parameters: 

f, the turning-point test factor, and N, the number of days in 

a test window. In this study, the f and N values used for the 

stations were 0.9 and 5 days, respectively, as determined 

using the method described in Wahl and Wahl (1995). Annual 

statistics from each station were normalized by dividing each 

annual statistic by the corresponding statistic calculated over 

the entire base period. For example, the record of annual 

mean flows during the base period for a station is normalized 

by dividing each annual mean flow by the overall mean 

flow during the base period. Trends were tested using the 

nonparametric Mann-Kendall test (Hirsch and Slack, 1984) 

at a significance level of 5 percent. Kendall’s tau coefficient, 

which ranges from -1 to +1, measures the strength of the 

correlation between flow and time. A tau value of -1 indicates 

that all flows decrease with increasing time; a tau value of +1 

indicates that all flows increase with increasing time. Sen’s 

slope was used to assess the magnitude of the overall change 

associated with each significant trend at the 5-percent level of 

significance. Sen’s slope is most accurate for evenly spaced 

data, which was generally the case for data at the active longterm stations in this study.

Trends in annual total-flow and base-flow statistics at 

all the stations were downward except for the trend in Q90

discharges at station 16068000 (table 3). At all six stations, 

trends in mean base flow were statistically significant at 

the 5-percent level of significance. Statistically significant 

downward trends of the annual total-flow and base-flow 

statistics were detected using data from stations 16019000 

and 16108000. For station 16068000, the only statistically 

significant downward trend for the flow characteristics 

tested is associated with mean base flow. Downward trends 

in streamflow are consistent with an earlier assessment 

(Bassiouni and Oki, 2013) that indicated decreases in rainfall. 

Long-term downward trends in base flows of streams may 

indicate a reduction in water availability for offstream and 

instream uses. Whether the downward trends in total flow and 

base flow of streams will continue in the future is unknown 

owing to uncertainties associated with potential climate 

change and watershed response to the changes. Therefore, 

low-flow duration discharges estimated at measurement 

sites established as part of this study need to be re-evaluated 

periodically to ensure that they are representative of flow 

conditions during which interim instream-flow standards are 

being established.
Methods

Table 3. Results of the Mann-Kendall test for trends in annual flows from 1961 to 2019 at six active long-term stations monitoring natural flow, 

Kaua‘i, Hawai‘i.

Annual statistic

Total streamflow Base flow

Tau Sen’s slope P-value Tau Sen’s slope P-value

USGS station 16010000

Q90 -0.122 -0.003 0.174 -0.144 -0.004 0.108

Q70 -0.151 -0.004 0.093 -0.158 -0.004 0.079

Q50 -0.198 -0.005 0.027 -0.183 -0.004 0.041

Mean -0.181 -0.004 0.044 -0.266 -0.005 0.003

USGS station 16019000

Q90 -0.208 -0.004 0.020 -0.176 -0.003 0.050

Q70 -0.170 -0.004 0.058 -0.164 -0.002 0.068

Q50 -0.210 -0.004 0.019 -0.226 -0.003 0.012

Mean -0.219 -0.005 0.014 -0.283 -0.004 0.002

USGS station 16068000a

Q90 -0.018 0.000 0.849 0.007 0.000 0.943

Q70 -0.070 -0.001 0.440 -0.009 0.000 0.922

Q50 -0.127 -0.002 0.157 -0.098 -0.002 0.275

Mean -0.105 -0.003 0.244 -0.178 -0.003 0.047

USGS station 16071500a

Q90 -0.101 -0.004 0.261 -0.061 -0.003 0.496

Q70 -0.205 -0.008 0.022 -0.164 -0.007 0.068

Q50 -0.224 -0.008 0.012 -0.219 -0.007 0.014

Mean -0.172 -0.006 0.055 -0.254 -0.007 0.005

USGS station 16097500

Q90 -0.089 -0.001 0.323 -0.106 -0.001 0.236

Q70 -0.118 -0.002 0.189 -0.101 -0.002 0.263

Q50 -0.171 -0.003 0.057 -0.160 -0.002 0.074

Mean -0.110 -0.002 0.219 -0.195 -0.003 0.030

USGS station 16108000

Q90 -0.189 -0.002 0.035 -0.145 -0.002 0.106

Q70 -0.207 -0.003 0.021 -0.197 -0.002 0.028

Q50 -0.210 -0.003 0.019 -0.197 -0.002 0.028

Mean -0.265 -0.004 0.003 -0.244 -0.003 0.007

[Bold red type indicates statistically significant negative trend (5-percent level) using the standard Mann-Kendall test; Sen’s slope, in cubic feet per second per 

year; p-value, 2-sided significance level attained by the data; USGS, U.S. Geological Survey; Qxx, discharge in cubic feet per second for selected xx percentages 

of time (90, 70, 50 percent) the indicated discharge was equaled or exceeded]

aContinuous stream-gaging station located within the study area.

Analysis of Low Flows at Different Types of 

Measurement Sites

The data points used to develop the statistical models 

between the measurement site of interest and the index station 

for computing low-flow duration discharges differ for different 

types of measurement sites, which include short-term stations 

and partial-record sites for this study. These measurement sites 

are defined in the “Data-Collection Sites” section.

Short-Term Stations

A short-term continuous-record stream-gaging station 

has less than 10 complete water years of natural-flow record. 

The procedures for estimating low-flow duration discharges at 

short-term stations are documented in Cheng (2016, p. 13–14) 

and summarized as follows.

1. Extract daily mean discharges during stable streamflow 

recessions from the short-term station. A streamflow 

recession is the period when flows return to low-flow 

conditions following a period of direct runoff. Stable 

recession daily mean discharges are selected from 

streamflow recessions that continue for 4 or more 

consecutive days. The second to last day of each 

streamflow recession was selected to be used in record 

augmentation. The second to last day (instead of the last 

day) of each streamflow recession was used because it 
18

Low-Flow Characteristics of Streams from Wailua to Hanapēpē, Kaua‘i, Hawai‘

yielded more concurrent data at the index and short-term 

stations that can be used in record augmentation.

2. Extract stable recession daily mean discharges from the 

index stations using criteria in step 1, and select the stable 

recession daily mean discharges that are less than the baseperiod Q40 discharge (rather than the Q50 discharge). This 

allows for the statistical relation to be defined for the full 

range of low-flow statistics to be estimated, particularly for 

cases in which stable recession daily mean discharges at Q50

conditions are not available at the index station but stable 

recession daily mean discharges at higher flow conditions 

are available.

3. Determine pairs of concurrent stable recession daily

means between the short-term and index stations. 

Concurrent stable recession daily mean discharges from 

the short-term and index stations must be from at least 10 

independent recessions.

4. Using the data determined in the previous step, apply steps

2 and 3 of the initial procedures used prior to the application 

of record-augmentation techniques as described in the 

“Record Augmentation” section.

5. Develop a model, using the appropriate record-augmentation 

technique (MOVE.1 or graphical) determined in step 4, 

between concurrent stable recession daily means at the 

short-term and index stations.

6. Using the model developed in the step 5, compute

flow-duration discharges at the short-term station from 

corresponding flow-duration discharges at the index station 

for the base period.

Partial-Record Sites

A partial-record site commonly has 10 or more systematic 

(consistent) streamflow measurements at a location in the 

stream. The procedures for estimating low-flow duration 

discharges at partial-record sites are documented in Cheng 

(2016, p. 14–15) and are summarized as follows. 

1. Determine daily mean discharges at the index stations that 

are concurrent with the streamflow measurements at the 

partial-record site, and select the daily mean discharges at 

the index stations that are less than the Q40 discharge. This 

allows for the statistical relation to be defined for the full 

range of low-flow statistics to be estimated, particularly for 

cases in which daily mean discharges at Q50 conditions are 

not available at the index station but daily mean discharges 

at higher flow conditions are available.

2. Using the data determined in step 1, apply steps 2 and 3

of the initial procedures used prior to the application of 

record-augmentation techniques as described in the “Record 

Augmentation” section.

3. Develop a model, using the appropriate record-augmentation 

technique (MOVE.1 or graphical) determined in step 2, 

between streamflow measurements at the partial-record site 

and concurrent daily mean discharges at the index station.

4. Using the model developed in the step 3, compute

flow-duration discharges at the partial-record site from 

corresponding flow-duration discharges at the index station 

for the base period.

Results and Discussion

Estimates of natural low-flow duration discharges of shortterm stations and partial-record sites, and results of seepage 

runs are discussed in the following sections. Data supporting the 

interpretations and results of this study are available within the 

report tables and from the USGS National Water Information 

System (U.S. Geological Survey, 2020a,b). Map identifier (Map 

ID) is used instead of the USGS station number for references 

to partial-record and seepage-run discharge-measurement 

sites. The index stations used, record-augmentation techniques 

applied, and selected regression statistics computed for the 

low-flow duration-discharge estimates at short-term stations and 

partial-record sites in the study-area streams are summarized 

in table 4. Estimated flow-duration discharges at partial-record 

sites in the study-area streams are summarized in table 5 

and figure 6. Flow-duration discharges at short-term stations 

16052400 on Lāwaʻi Stream and 16049000 on Hanapēpē River 

(table 2) were estimated using daily means at the stations and 

those at the partial-record sites were estimated using discrete 

discharge measurements collected at the sites. 

Natural Low-Flow Duration Discharges

Short-Term Stations

Short-term stations on Waiahi (16057900) and right branch 

Lāwaʻi Streams (16052400) were established to serve as optional 

index stations if the discharges at the partial-record sites did 

not correlate well with discharges at other index stations. Both 

stations monitored natural low-flow conditions––between Q95

and Q50––that are of interest in this study. The Waiahi short-term 

station had three complete water years of continuous low-flow 

data (2017–19); water year 2016 was incomplete because the 

station was installed in November 2015. Low-flow duration 

discharges computed for water years 2017–19 range from 14 to 

25 ft3/s (table 1). The Lāwaʻi short-term station did not have any 

complete water years of record because it was damaged twice by 

high-flow events; therefore, low-flow duration discharges for the 

period of record were not computed.

At continuous-record stream-gaging stations, an 

instantaneous discharge record (at 15-min interval) is derived 
Results and Discussion

Table 4. Summary of record-augmentation methods, regression equations, and selected regression statistics for partial-record sites in the study-area streams, southeast Kaua‘i, Hawai‘i.[ID, identifier; USGS, U.S. Geological Survey; HI, Hawaii; Riv, River; blw, below; Str, Stream; nr, near; RB, Right Branch; ft, feet; US, upstream; mi, mile; LB, Left Branch; NF, North Fork; N, North; Dt, Ditch; SF, South Fork; trib, tributary; Res, Reservoir; S, South; Rd., Road; DS, downstream; W, West; SW, southwest; Hwy, Highway; EB, East Branch; alt, altitude; MOVE.1, Maintenance of Variance Extension Type 1; Xi, base-10 logarithm of the computed low-flow duration discharge at the index station; Yi, base-10 logarithm of the estimated low-flow duration discharge at the partial record site; --, not applicable; SREF, 

Streamflow Record Extension Facilitator program; r, correlation coefficient; RMSE, root mean square error; E, modified Nash-Sutcliff coefficient of efficiency. Database limitations preclude the use of Hawaiian 

diacritical marks in USGS station names]

Map IDa USGS station number USGS station name, Kauai, HI Index station with USGS station number and station name, Kauai, HI Record- augmentation technique MOVE.1 regression equation Regression statistics generated from SREF Number of measurements (n) used in record augmentation r RMSE E

Short-term continuous-record stream-gaging stations

16049000 16049000 Hanapepe Riv blw Manuahi Str nr 

Eleele

16068000 EB of NF Wailua River 

nr Lihue

Graphical -- -- -- -- --

16052400 16052400 RB Lawai Stream 300 ft US of fork 16068000 EB of NF Wailua River 

nr Lihue

MOVE.1 Yi = 0.01 + 2.76 

(Xi − 1.28)

0.91 0.131 0.56 10

16057900 16057900 Waiahi Str US Upper Powerhouse No correlation -- -- -- -- -- --

Partial-record sites

P1 220423159235501 RB Opaekaa Stream 0.3 mi US of LB 16071500 Left Branch Opaekaa Str 

nr Kapaa

Graphical -- -- -- -- 10

P2 220346159280601 NF Wailua River US Blue Hole intake 16019000 Waialae Str at alt 3,820 ft 

nr Waimea

MOVE.1 Yi = 1.35 + 0.42 

(Xi − 0.64)

0.94 0.033 0.62 8

P3 + P4 220326159275401 + 

220325159275401

NF Waikoko Str US Iliiliula N Wailua 

Dt + SF Waikoko Str US Iliiliula N Wailua Dt

16057900 Waiahi Str US Upper 

Powerhouse

MOVE.1 Yi = 0.65 + 1.87 

(Xi − 1.28)

0.89 0.108 0.58 10

P5 220224159282301 Iliiliula Str trib 4 US N Wailua Ditch 16097500 Halaulani Str at alt 400 ft 

nr Kilauea

MOVE.1 Yi = 1.04 + 0.68 

(Xi − 0.87)

0.92 0.040 0.64 11

P6 + P7 220054159244001 + 

220037159242901

Hanamaulu Str 1 mi US N Kapaia 

Res + 

Hanamaulu Str 0.6 mi US S Kapaia Res

16068000 EB of NF Wailua River 

nr Lihue

MOVE.1 Yi = 0.11 + 0.63 

(Xi − 1.31)

0.88 0.057 0.51 9

P6 220054159244001 Hanamaulu Str 1 mi US N Kapaia Res 16068000 EB of NF Wailua River 

nr Lihue

Graphical -- -- -- -- 10

P7 220037159242901 Hanamaulu Str 0.6 mi US S Kapaia 

Res

No correlation -- -- -- -- -- --

P8 215923159235601 Hanamaulu tributary US of return 

flow

No correlation -- -- -- -- -- --

P9 215833159232601 Nawiliwili Stream at Rapoza Rd. No correlation -- -- -- -- -- --P10 215737159230301 Puali Stream 0.6 mi DS Aakukui Rd No correlation -- -- -- -- -- --P11 215853159281801 Paohia Str US Koloa Ditch 16052400 RB Lawai Stream 300ft 

US of fork

MOVE.1 Yi = 0.43 + 0.58 

(Xi − 0.01) 0.89 0.084 0.57 11

P12 215851159273901 Kamooloa Str US Papuaa Res intake 16052400 RB Lawai Stream 300ft 

US of fork

MOVE.1 Yi = 0.82 + 0.45 

(Xi − 0.02) 0.93 0.056 0.60 11
20

Low-Flow Characteristics of Streams from Wailua to Hanapēpē, Kaua‘i, Hawai‘i Table 4.—Continued Map IDa USGS station number USGS station name, Kauai, HI Index station with USGS station number and station name, Kauai, HI Record- augmentation technique MOVE.1 regression equation Regression statistics generated from SREF Number of measurements (n) used in record augmentation r RM

E

P13 215822159282601 Kuia Str 0.7 mi W of Papuaa Res 16071500 Left Branch Opaekaa Str 

nr Kapaa

Graphical -- -- -- -- 10

P14 215751159283901 Kuia Str trib 1 mi SW of Papuaa Res 16052400 RB Lawai Stream 300 ft 

US of fork

MOVE.1

Yi = -0.60 + 2.44 

(Xi − 0.02)

0.90 0.379 0.55 12

P15 215608159285801 Omao Stream at Kaumualii Hwy No correlation -- -- -- -- -- --P16 215538159292301 Poeleele Stream at Kaumualii Hwy No correlation -- -- -- -- -- --P17 215751159311801 Wahiawa Stream US Alexander Res 16097500 Halaulani Str at alt 400 ft 

nr Kilauea

MOVE.1

Yi = 0.50 + 1.55 

(Xi − 0.81)

0.90 0.099 0.59 8

P18 215754159311601 LB Wahiawa Str 400 ft US Alexander 

Res

No correlation -- -- -- -- -- --

aRefer to figure 1 for station location.

from the rating curve developed for the station and used to 

compute a record of daily means. An instantaneous discharge is 

not computed if the corresponding instantaneous stage is outside 

the range of stage values applicable to the rating curve developed 

for the station. Low-flow duration discharges for water years 

2017–19 at the Waiahi short-term station were computed assuming 

the daily mean flow for days with incomplete instantaneous 

discharge record to be higher than the median flow. To determine 

the validity of this assumption, low-flow duration discharges 

computed using the assumption were compared to low-flow 

duration discharges computed by including days during which the 

daily means were computed from partial instantaneous discharge 

record. The Waiahi short-term station had 195 days out of 1,095 

days (17 percent) with missing instantaneous discharge values 

for water years 2017–19. For 187 of these days, the daily means 

were not computed owing to high instantaneous stages falling 

outside of the range of stage values applicable to the rating curve. 

Since the daily means for these days computed from partial 

instantaneous record were higher than the median flow, these 

daily means would not affect the computed low-flow duration 

discharges. For the remaining 8 days with missing daily means, 

the daily means were not computed owing to low instantaneous 

stages falling outside of the range of stage values applicable to 

the rating curve. The daily means for these days computed from 

partial instantaneous record were lower than the median flow and 

would affect the computation of low-flow duration discharges at 

the station. Low-flow duration discharges computed by including 

daily means for days with partial instantaneous discharge record 

and those computed using the assumption showed differences of 

0.2 ft3/s for the Q50 and Q60 discharges; 0.1 ft3/s for the Q55, Q70, 

and Q75 discharges; 0.05 ft3/s for the Q65 and Q85 discharges; 0.04 

ft3/s for the Q90 discharge; and no difference for the Q80 and Q95

discharges. Therefore, computing low-flow duration discharges 

at the Waiahi station using only days with complete instantaneous 

discharge record is reasonable.

The representativeness of low-flow duration discharges 

at the Waiahi short-term station of long-term flow conditions 

was evaluated by comparing low-flow duration discharges 

computed for the short-term period (water years 2017–19) 

with those computed for the base period (1961–2019) at 

the two active long-term stations in the study area––station 

16068000 on east branch of North Fork Wailua River and 

station 16071500 on left branch ʻŌpaekaʻa Stream. A majority 

of the differences between low-flow duration discharges 

computed for water years 2017–19, which correspond to 

complete water years of data available at the Waiahi shortterm station, and those computed for the base period were 

2 percent or less at both long-term stations. Data at Waiahi 

station showed the highest correlation with data at index 

station 16068000, with a correlation coefficient (r) of 0.73. 

However, this r value does not meet acceptable values of r for 

record augmentation set forth in this study (r values ≥0.80); 

therefore, low-flow duration discharges at the Waiahi shortterm station were not extended to the base period. Using the 

duration discharges at station 16068000 for the period 2017–

19 and the base period (table 2), as well as the annual mean 
Results and Discussion

Table 5. Estimated flow-duration discharges at partial-record sites in the study-area streams, southeast Kaua‘i, Hawai‘i, for base period 1961–2019.[ID, identifier; USGS, U.S. Geological Survey; HI, Hawaii; RB, Right Branch; mi, mile; US, upstream; LB, Left Branch; NF, North Fork; Str, Stream; N, North; Dt, Ditch; SF, South Fork; trib, tributary; Res, Reservoir; S, South; Rd., Road; DS, downstream; W, West; SW, Southwest; Hwy, Highway; ft, feet; Riv, River; blw, below; nr, near; ft3/s, cubic feet per second; --, not applicable. Database limitations preclude the use 

of Hawaiian diacritical marks in USGS station names. Altitude values interpolated from USGS 1:24,000-scale digital hypsography data]

Map 

IDa USGS station number USGS station name, Kauai, HI

Drainage 

area, in 

square 

miles

Discharge, in ft3/s, for selected percentages of time (from 50 to 95 percent)

the indicated discharge was equaled or exceeded

50 55 60 65 70 75 80 85 90 95

Wailua River basin

P1 220423159235501 RB Opaekaa Stream 0.3 mi US of LB 0.4 1.1 1.0 0.98 0.93 0.86 0.80 0.70 0.60 0.52 0.48

P2 220346159280601 NF Wailua River US Blue Hole intake 1.8 26 25 24 23 22 21 20 19 18 17

P3 + P4 220326159275401 + 

220325159275401

NF Waikoko Str US Iliiliula N Wailua 

Dt + SF Waikoko Str US Iliiliula N Wailua Dt

1.1 7.4 6.8 5.8 5.3 4.9 4.0 3.6 3.2 2.8 2.5

P5 220224159282301 Iliiliula Str trib 4 US N Wailua Ditch 1.6 11 10 10 9.7 9.2 8.9 8.6 8.2 7.9 7.3

Hanamā‘ulu Stream basin

P6 + P7 220054159244001 + 

220037159242901

Hanamaulu Str 1 mi US N Kapaia 

Res + Hanamaulu Str 0.6 mi US S Kapaia Res

1.1 1.6 1.5 1.4 1.4 1.3 1.3 1.2 1.1 1.0 0.96

P6 220054159244001 Hanamaulu Str 1 mi US N Kapaia Res 0.8 1.2 1.2 1.2 1.1 1.1 1.0 1.0 0.83 0.81 0.74P7 220037159242901 Hanamaulu Str 0.6 mi US S Kapaia 

Res

0.3 <0.44b <0.44b <0.44b <0.44b <0.44b <0.44b <0.44b <0.44b <0.44b <0.44b

P8 215923159235601 Hanamaulu tributary US of return 

flow

0.2 <0.40b <0.40b <0.40b <0.40b <0.40b <0.40b <0.40b <0.40b <0.40b <0.40b

Nāwiliwili Stream basin

P9 215833159232601 Nawiliwili Stream at Rapoza Rd. 1.4 -- -- -- -- -- -- -- -- -- --

Pū‘ali Stream basin

P10 215737159230301 Puali Stream 0.6 mi DS Aakukui Rd 0.8 -- -- -- -- -- -- -- -- -- --

Hulē‘ia Stream basin

P11 215853159281801 Paohia Str US Koloa Ditch 0.9 5.0 4.4 4.2 3.6 3.1 2.9 2.5 2.0 1.8 1.5

P12 215851159273901 Kamooloa Str US Papuaa Res intake 2.3 11 9.7 9.2 8.3 7.4 7.0 6.1 5.3 4.9 4.1

P13 215822159282601 Kuia Str 0.7 mi W of Papuaa Res 1.0 5.7 5.4 4.7 4.4 4.2 4.0 3.7 3.5 3.4 3.3

P14 215751159283901 Kuia Str trib 1 mi SW of Papuaa Res 0.6 3.2 2.0 1.5 0.84 0.46 0.33 0.16 0.073 0.047 0.018

Waikomo Stream basin

P15 215608159285801 Omao Stream at Kaumualii Hwy 0.4 <0.19b <0.19b <0.19b <0.19b <0.19b <0.19b <0.19b <0.19b <0.19b <0.19b

P16 215538159292301 Poeleele Stream at Kaumualii Hwy 0.6 <0.22b <0.22b <0.22b <0.22b <0.22b <0.22b <0.22b <0.22b <0.22b <0.22b

Wahiawa Stream basin

P17 215751159311801 Wahiawa Stream US Alexander Res 1.8 3.7 3.4 3.1 2.9 2.6 2.4 2.2 2.0 1.8 1.5

P18 215754159311601 LB Wahiawa Str 400 ft US Alexander 

Res

0.3 -- -- -- -- -- -- -- -- -- --

aRefer to figure 1 for station location.bHighest discharge measured during the study period.
22

Low-Flow Characteristics of Streams from Wailua to Hanapēpē, Kaua‘i, Hawai‘

rainfall at Waiʻaleʻale rain gage (fig. 3), it was determined that 

the period 2017–19 was generally wetter than the base period. 

Therefore, low-flow duration discharges computed for water 

years 2017–19 at the Waiahi short-term station may also be 

higher than those for the base period. 

Low-flow duration discharges at the Lāwaʻi short-term 

station were extended to the base period using index station 

16068000 on east branch of North Fork Wailua River in the 

MOVE.1 technique (table 4). Two outliers were removed 

from the regression relation. Low-flow duration discharges 

computed for the base period range from 0.35 to 3 ft3/s 

(table 2) and these were used to estimate low-flow duration 

discharges at relevant partial-record sites.

Station 16049000 on Hanapēpē River monitored natural 

flow during calendar year 2017, when upstream surface-water 

diversions on right and left branch Kōʻula Rivers were not in 

operation (Howard Greene, Gay & Robinson, oral commun., 

2018). Flow-duration statistics at the station were estimated using 

the procedures to estimate low-flow duration discharges at shortterm stations. Index station 16068000 on east branch of North 

Fork Wailua River was used in the graphical-correlation technique 

to extend the Hanapēpē River calendar year 2017 record to the 

base period (fig. 7A). One outlier was removed from the graphical 

fit. Low-flow duration discharges computed for the base period 

range from 42 to 69 ft3/s (table 2).

Partial-Record Sites

The MOVE.1 technique was used to estimate low-flow 

duration discharges for a majority of the partial-record sites 

in the study area, including North Fork Wailua River, the 

confluence of north and south Waikoko Streams, ‘Ili‘ili‘ula 

Stream, the confluence of north and south fork Hanamāʻulu 

Streams, Pāohia Stream, Kamo‘oloa Stream, a branch of Ku‘ia 

Stream, and Wahiawa Stream. Discharges at the confluence of 

north and south fork Waikoko Streams and at the confluence 

of north and south fork Hanamāʻulu Streams were the sum 

of discharges measured at each stream fork, respectively. 

Selected natural low-flow duration-discharge estimates at the 

partial-record sites are listed in table 5. Measured discharges at 

the partial-record sites and concurrent daily mean discharges 

at selected index station are summarized in tables 6–13. 

A measured discharge at a partial-record site was not 

used in record augmentation if (1) the discharge was measured 

when the hydrograph from the selected index station indicated 

highly variable flows, (2) the discharge was measured on 

the same streamflow recession as another measurement, 

(3) the discharge has high measurement error and a second 

measurement (check measurement) may have been made 

subsequent to the first measurement at a different nearby 

measurement section in an effort to reduce measurement error, 

or (4) the concurrent daily mean discharge at the index station 

is of provisional status at the time this report was prepared. 

The MOVE.1 relations between measured discharges at the 

partial-record sites and concurrent daily mean discharges at 

the index stations have correlation coefficients (r) that range 

from 0.88 to 0.94 and modified Nash-Sutcliff coefficients 

of efficiency (E) that range from 0.51 to 0.64. Note that the 

closer the coefficient of efficiency is to 1, the more accurate 

the statistical model is. Low-flow duration discharges 

for three sites––North Fork Wailua River, confluence of 

north and south fork Hanamāʻulu Streams, and Wahiawa 

Stream––were estimated with less than 10 measurements. 

Measured discharges at the partial-record sites used for record 

augmentation generally capture a wide distribution of flows 

between the Q95 and Q50 duration discharges that are of interest 

in this study. Therefore, the low-flow duration-discharge 

estimates are considered to be representative of the entire 

range of low-flow conditions in these streams.

Low-flow duration discharges for partial-record sites 

on right branch ʻŌpaekaʻa Stream, north fork Hanamāʻulu 

Stream, and a branch of Kuʻia Stream were estimated using 

the graphical-correlation technique (table 4). A curvilinear 

trend provides the best fit to the plot of measured discharges at 

the partial-record sites and concurrent daily mean discharges 

at the selected index station (fig. 7). Low-flow duration 

discharges were estimated with 10 measurements at each 

partial-record site and the measured discharges used for 

record augmentation generally capture a wide distribution of 

flows between the Q95 and Q50 duration discharges that are 

of interest in this study (tables 9, 14, and 15). Therefore, the 

low-flow duration-discharge estimates are considered to be 

representative of the entire range of low-flow conditions in 

these streams.

Measured discharges at partial-record sites on south 

fork Hanamāʻulu Stream (table 9), tributary of Hanamāʻulu 

Stream (table 9), Nāwiliwili Stream (table 16), Pū‘ali Stream 

(table 17), left branch Wahiawa Stream (table 13), ʻŌmaʻo 

Stream (table 18), and Pōʻeleʻele Stream (table 18) do not 

correlate with data at any index stations. On the day with 

the highest discharge at each of these partial-record sites, 

the corresponding concurrent daily mean discharge at each 

index station was greater than the median discharge at that 

index station. Thus, low-flow duration discharges at south 

fork Hanamāʻulu Stream, tributary of Hanamāʻulu Stream, 

ʻŌmaʻo Stream, and Pōʻeleʻele Stream are likely below the 

highest discharges measured during the study period of 0.44, 

0.40, 0.19, and 0.22 ft3/s, respectively. Data collected at the 

Nāwiliwili Stream partial-record site may have been affected 

by random diverted-flow releases from the upper Līhuʻe Ditch 

(fig. 5). Accessible reaches of Pū‘ali Stream were limited 

owing to streambank vegetation and streambed material, and 

the only discharge-measurement section available based on 

reconnaissance survey was downstream from a pond in a golf 

course. Twelve discharge measurements were collected during 

the study period; however, the discharges do not correlate with 

data at any index stations because the measured discharges 

may have been affected by draining of the pond. Discharge 

measurements collected at left branch Wahiawa Stream do not 

correlate with data at any index stations nor do they correlate 

with data at the partial-record site located on main channel of 

Wahiawa Stream.
Results and Discussion

23men20-4010_fig

Wailua

Waikomo

Hanamā‘ulu

Nāwiliwili

Pū‘ali

Hulē‘ia

Hanapēpē

Wahiawa

Aepo Lāwa‘i Kalāheo Māhā‘ulepū

0 42 KILOMETERS

0 4 2 MILES Base modified from U.S. Geological Survey digital data. Universal Transverse Mercator projection,

zone 4, North American Datum 1983.

EXPLANATION

Altitude above mean sea level, in feet

5,243>0

Hydrologic-unit boundary—From State of 

Hawai‘i (2017a)

StreamStreamflow-measurement location—Each 

measurement location is labeled with station number or map identifier. Numbers in parentheses indicate natural discharge, in cubic feet per second, equaled or exceeded 90, 70, and 50 percent of the time during 1961–2019.aValues represent the total discharge at the 

confluence of sites P3 and P4 bValues applicable to 2017–19

cValues represent the total discharge at the 

confluence of sites P6 and P7 dLess than (<) highest discharge measured during 

study period 2016–20 eLow-flow duration discharges could not be estimated

Stream-gaging station—In operation during base 

period from 1961 to 2019

Stream-gaging station—Station established for 

this study and monitors natural low-flow conditions only 

Partial-record measurement site—See table 5 for map 

identifier description

159°20' 159°30' 159°40'

22°10'

22°00'

21°50'

Study

area

PACIFIC OCEAN

KAUA‘I

P1 (0.52, 0.86, 1.1)

16052400 (0.53, 1.3, 3.0)

16057900 (15, 19, 25)b

P2 (18, 22, 26)

P5 (7.9, 9.2, 11)

P6 (0.81, 1.1, 1.2)

P7 (< 0.44)d

P8 (< 0.40)d

P9e

P11 (1.8, 3.1, 5.0)

P12 (4.9, 7.4, 11)

P13 (3.4, 4.2, 5.7)

P14 (0.047, 0.46, 3.2)

P15 (< 0.19)d

P16 (< 0.22)d

P17 (1.8, 2.6, 3.7) P18e

16071500 (0.60, 1.0, 1.5)

16068000 (15, 21, 28)

16049000 (43, 50, 69)

P10e

P6+P7 (1.0, 1.3, 1.6)c

P3

P4

P3+P4 (2.8, 4.9, 7.4)c

P1P2P3P4P5P6P7P8P9

Right Branch ‘Ōpaeka‘aNorth Fork WailuaNorth Fork WaikokoSouth Fork Waikoko‘Ili‘ili‘ulaNorth Fork Hanamā‘uluSouth Fork Hanamā‘uluHanamā‘ulu TributaryNāwiliwili

Partial-record site identifier and stream name

1604900016052400160579001606800016071500

HanapēpēLāwa‘iWaiahiEast Branch North Fork WailuaLeft Branch ‘Ōpaeka‘a

Stream-gaging-station numberand stream name P10

P11P12P13P14P15P16P17P18

Pū‘aliPāohiaKamo‘oloaKu‘iaKu‘ia Tributary‘Ōma‘oPō‘ele‘eleWahiawaLeft Branch Wahiawa

22°00'

159°32'

22°04'

21°56'

159°28'

159°24'

159°20'

 North

Fork Wailua River

So u t h Fork

Wa i ul aRiver

Hanamā‘ulu Stream

Hulē‘ia S t re am

Nāwiliwili Str eam

Pū‘ali

Stream

Lāwa‘i S tream

Wah ai wa Stream

 Han ēpa ēp vi R r e

Waikomo Stream

Figure 6. Map showing discharge, in cubic feet per second, that is equaled or exceeded 90, 70, and 50 percent of the time during 1961–2019 at active stream-gaging stations and partial-record 

sites in the study area, southeast Kaua‘i, Hawai‘i.
24

Low-Flow Characteristics of Streams from Wailua to Hanapēpē, Kaua‘i, Hawai‘

men20-4010_fig07

0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

Q50

Q70

Q90

Discharge, in cubic feet per second,

left branch ‘Ōpaeka‘a Stream at gaging station 16071500

Discharge, in cubic feet per second,

Ku‘ia Stream at partial-record site 215822159282601

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0 4 8 12 16 20 24 28 32 36

Q50

Q70

Q90

Discharge, in cubic feet per second,

Hanamā‘ulu Stream at partial-record site 220054159244001

Discharge, in cubic feet per second,

east branch of North Fork Wailua Stream at gaging station 16068000

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

0 0.4 0.8 1.2 1.6 2.0 2.4 2.8

Discharge, in cubic feet per second,

right branch ‘Ōpaeka‘a Stream at partial-record site 220423159235501

Discharge, in cubic feet per second,

left branch ‘Ōpaeka‘a Stream at gaging station 16071500

Q50

Q70

Q90

Q50

Q70

Q90

Discharge, in cubic feet per second,

Hanapēpē River at gaging station 16049000

Discharge, in cubic feet per second,

east branch of North Fork Wailua Stream at gaging station 16068000

0 4 8 12 16 20 24 28 32

0

10

20

30

40

50

60

A 70 B

C D

Figure 7. Plots showing the graphical relation between measured discharges at short-term continuous-record and partial-record sites 

and concurrent daily mean discharges at index stations, southeast Kaua‘i, Hawai‘i. A, Concurrent daily mean discharges at stream-gaging 

station 16049000 on Hanapēpē River and concurrent daily mean discharges at stream-gaging station 16068000 on east branch of North 

Fork Wailua River. B, Partial-record site 220423159235501 on right branch ‘Ōpaeka‘a Stream and concurrent daily mean discharges at 

stream-gaging station 16071500 on left branch ‘Ōpaeka‘a Stream. C, Partial-record site 220054159244001 on north fork Hanamā‘ulu 

Stream and concurrent daily mean discharges at stream-gaging station 16068000 on east branch of North Fork Wailua River. D, Partialrecord site 215822159282601 on Ku‘ia Stream and concurrent daily mean discharges at stream-gaging station 16071500 on left branch 

‘Ōpaeka‘a Stream. 
Results and Discussion

Table 6. Measured discharges at partial-record site 220346159280601 on North Fork Wailua River and concurrent daily mean discharges at stream-gaging 

station 16019000 on Wai‘alae Stream, southeast Kaua‘i, Hawai‘i.

[ft3/s, cubic feet per second; ID, identifier. Measured discharge that is underlined is excluded from record augmentation because the hydrograph from the index station 

indicated highly variable flows during the time the measurement was made]

Date Daily mean discharge in ft3/s

 on Wai‘alae Stream

Measured discharge in ft3/s on North Fork Wailua River 

(Map ID P2 in fig. 1, tables 4–5)

02/22/2016 8.20 20.2

04/25/2016 9.34 34.0

06/08/2016 6.36 23.6

09/27/2016 3.85 22.3

01/19/2017 2.90 18.7

02/22/2017 5.52 11.3

05/04/2017 3.01 19.7

08/03/2017 2.20 18.1

11/20/2017 7.21 17.4

02/12/2018 4.56 21.2

02/22/2019 7.01 26.4

[ft3/s, cubic feet per second; ID, identifier]

Table 7. Measured discharges at partial-record sites 220326159275401 on north fork Waikoko Stream and 220325159275401 on south fork 

Waikoko Stream and concurrent daily mean discharges at stream-gaging station 16057900 on Waiahi Stream, southeast Kaua‘i, Hawai‘i.

Date

Daily mean discharge in 

ft3/s

 on Waiahi Stream

Measured discharge in ft3/s

 on north fork Waikoko Stream

(Map ID P3 in fig. 1, tables 4–5)

Measured discharge in ft3/s

 on south fork Waikoko Stream

(Map ID P4 in fig. 1, tables 4–5)

Measured discharge in ft3/s

 on north and south fork 

Waikoko Streams combined

02/22/2016 11.8 2.45 0.42 2.87

04/25/2016 30.0 7.98 2.38 10.4

06/08/2016 20.7 4.06 1.40 5.46

09/27/2016 23.7 4.47 1.28 5.75

01/19/2017 15.2 1.82 0.57 2.39

05/04/2017 19.4 2.02 1.30 3.32

08/03/2017 17.8 2.75 0.81 3.56

09/28/2017 14.9 1.92 0.57 2.49

02/12/2018 22.1 4.92 1.58 6.50

02/22/2019 20.9 5.15 1.87 7.02

[ft3/s, cubic feet per second; ID, identifier. Measured discharge that is underlined is excluded from record augmentation because the hydrograph from the index 

station indicated highly variable flows during the time the measurement was made]

Table 8. Measured discharges at partial-record site 220224159282301 on ‘Ili‘ili‘ula Stream and concurrent daily mean 

discharges at stream-gaging station 16097500 on Hālaulani Stream, southeast Kaua‘i, Hawai‘i.

Date Daily mean discharge in ft3/s

 on Hālaulani Stream

Measured discharge in ft3/s on ‘Ili‘ili‘ula Stream

(Map ID P5 in fig. 1, tables 4–5)

03/11/1983 5.30 9.80

02/24/2016 6.37 9.01

05/16/2016 6.18 9.16

06/07/2016 11.1 13.2

04/14/2017 8.25 21.0

01/17/2018 4.09 7.50

03/07/2018 9.51 12.8

05/01/2018 10.4 13.8

05/09/2018 9.56 12.4

08/08/2018 9.06 13.8

05/13/2019 6.09 9.27

12/09/2019 7.41 13.0
26

Low-Flow Characteristics of Streams from Wailua to Hanapēpē, Kaua‘i, Hawai‘

Table 9. Measured discharges at partial-record sites 220054159244001 on north fork Hanamā‘ulu Stream, 220037159242901 on south fork 

Hanamā‘ulu Stream, and 215923159235601 on tributary of Hanamā‘ulu Stream, and concurrent daily mean discharges at stream-gaging station 

16068000 on east branch of North Fork Wailua River, southeast Kaua‘i, Hawai‘i.

[ft3/s, cubic feet per second; ID, identifier; --, no data. Measured discharge that is underlined is excluded from record augmentation because the hydrograph from 

the index station indicated highly variable flows during the time the mseasurement was made]

Date

Daily mean discharge 

in ft3/s

 on east branch of North 

Fork Wailua River

Measured discharge in ft3/s

 on north fork Hanamā‘ulu 

Stream

(Map ID P6 in fig. 1, tables 4–5) 

Measured discharge in ft3/s

 on south fork Hanamā‘ulu 

Stream

(Map ID P7 in fig. 1, tables 4–5) 

Measured discharge in ft3/s

 on north and south fork 

Hanamā‘ulu Streams 

combined

Measured discharge in ft3/s

 on tributary of Hanamā‘ulu 

Stream

(Map ID P8 in fig. 1, tables 4–5) 

02/25/2016 11.8 0.80 0.25 1.05 --

04/27/2016 33.6 1.33 0.41 1.74 0.40

05/16/2016 17.8 1.10 0.44 1.54a --

05/20/2016 30.4 -- -- -- 0.06

06/06/2016 29.1 -- -- -- 0.06

06/07/2016 34.3 0.91 -- -- --

06/13/2016 26.5 -- 0.29 -- --

11/07/2016 17.4 1.05 0.23 1.28 0.05

12/16/2016 28.3 1.21 0.20 1.41 0.05

01/05/2017 43.1 1.43 0.10 1.53 0.07

07/20/2017 19.9 1.32 -- -- --

09/22/2017 14.3 0.62 0.18 0.80 0.17

10/19/2017 32.9 1.25 0.34 1.59 --

10/30/2017 21.8 0.99 0.40 1.39 --

12/08/2017 29.2 -- 0.35 -- --

12/12/2017 23.8 1.13 0.39 1.52 --

01/17/2018 13.1 0.79 0.24 1.03 --

aMeasured discharge is excluded from record augmentation because it is an outlier.

Table 10. Measured discharges at partial-record site 215853159281801 

on Pāohia Stream and concurrent daily mean discharges at stream-gaging 

station 16052400 Lāwa‘i Stream, southeast Kaua‘i, Hawai‘i.

[ft3/s, cubic feet per second; ID, identifier; --, no data. Measured discharge that 

is underlined is excluded from record augmentation because the hydrograph 

from the index station indicated highly variable flows during the time the 

measurement was made]

Date

Daily mean discharge 

in ft3/s

 on Lāwa‘i Stream

Measured discharge in ft3/s

 on Pāohia Stream

(Map ID P11 in fig. 1, tables 4–5)

06/10/2016 1.39 2.97

11/18/2016 0.79 1.70

04/06/2017 -- 1.75

06/01/2017 1.11 3.22

08/10/2017 0.25 1.71

09/07/2017 0.47 1.56

12/07/2017 1.60 2.90

12/21/2017 0.59 1.88

05/02/2018 2.99a 5.33

08/07/2018 1.44a 3.95

08/21/2018 1.43a 3.46

11/20/2018 1.61a 3.28

aMeasured discharge. Continuous streamgaging station 160524000 on 

Lāwa‘i Stream was damaged in March 2018.

Table 11. Measured discharges at partial-record site 215851159273901 on 

Kamo‘oloa Stream and concurrent daily mean discharges at stream-gaging 

station 16052400 Lāwa‘i Stream, southeast Kaua‘i, Hawai‘i.

[ft3/s, cubic feet per second; ID, identifier; --, no data. Measured discharge that 

is underlined is excluded from record augmentation because the hydrograph 

from the index station indicated highly variable flows during the time the 

measurement was made]

Date

Daily mean discharge 

in ft3/s

 on Lāwa‘i Stream

Measured discharge in ft3/s

 on Kamo‘oloa Stream 

(Map ID P12 in fig. 1, tables 4–5)

11/29/2016 3.18 11.1

12/16/2016 1.33 6.96

03/16/2017 -- 7.82

06/01/2017 1.11 7.28

08/10/2017 0.25 4.20

09/07/2017 0.47 4.30

10/30/2017 1.07 7.15

11/21/2017 1.46 8.24

12/12/2017 1.18 6.17

12/21/2017 0.59 4.44

12/22/2017 0.59 4.34b

02/08/2018 -- 15.5

03/12/2018 2.19 7.99

08/21/2018 1.43a 9.20

aMeasured discharge. Continuous streamgaging station 160524000 on 

Lāwa‘i Stream was damaged in March 2018.

bMeasured discharge is excluded from record augmentation because it is on 

the same recession as the discharge measured on 12/21/2017.
Results and Discussion

Table 12. Measured discharges at partial-record site 215751159283901 on 

Ku‘ia Stream and concurrent daily mean discharges at stream-gaging station 

16052400 Lāwa‘i Stream, southeast Kaua‘i, Hawai‘i.

[ft3/s, cubic feet per second; ID, identifier; --, no data. Measured discharge that 

is underlined is excluded from record augmentation because the hydrograph 

from the index station indicated highly variable flows during the time the 

measurement was made]

Date

Daily mean discharge 

in ft3/s

 on Lāwa‘i Stream

Measured discharge in ft3/s

 on Ku‘ia Stream

(Map ID P14 in fig. 1, tables 4–5)

05/18/2016 0.63 0.18

06/10/2016 1.39 0.50

11/18/2016 0.79 0.21

12/29/2016 3.16 2.24

03/16/2017 -- 0.96

04/06/2017 -- 0.23

06/01/2017 1.11 0.49

08/10/2017 0.25 0.008

09/07/2017 0.47 0.006

11/21/2017 1.46 0.44b

12/21/2017 0.59 0.21

05/02/2018 2.99a 1.12

08/07/2018 1.44a 0.82

08/21/2018 1.43a 0.54

11/20/2018 1.61a 0.62

aMeasured discharge. Continuous streamgaging station 160524000 on 

Lāwa‘i Stream was damaged in March 2018.

bMeasured discharge is excluded from record augmentation because of high 

measurement error.

Table 13. Measured discharges at partial-record sites 215751159311801 on Wahiawa Stream and 215754159311601 on 

left branch Wahiawa Stream, and concurrent daily mean discharges at stream-gaging station 16097500 on Hālaulani Stream, 

southeast Kaua‘i, Hawai‘i.

[ft3/s, cubic feet per second; ID, identifier; --, no data. Measured discharge that is underlined is excluded from record augmentation 

because the hydrograph from the index station indicated highly variable flows during the time the measurement was made]

Date

Daily mean discharge 

in ft3/s

 on Hālaulani Stream

Measured discharge in ft3/s

 on Wahiawa Stream 

(Map ID P17 in fig. 1, tables 4–5)

Measured discharge in ft3/s

 on left branch Wahiawa Stream 

(Map ID P18 in fig. 1, tables 4–5)

03/14/2017 5.77 2.28 3.07

06/06/2017 8.49 4.46 0.23

02/08/2018 11.4 6.92 0.69

06/20/2018 7.54 3.42 0.31

08/21/2019 4.55 2.37 0.11

10/23/2019 6.62 4.85 0.34

11/07/2019 5.04 1.91 0.20

11/12/2019 4.97 1.85 0.11

12/02/2019 16.2 9.07 0.54

01/22/2020 --a 3.76b 0.64

aApproved data not available as of 6/23/2020.

bMeasured discharge is excluded from record augmentation because concurrent daily mean discharge on Hālaulani Stream is 

of provisional status.

Table 14. Measured discharges at partial-record site 220423159235501 

on right branch ‘Ōpaeka‘a Stream and concurrent daily mean discharges at 

stream-gaging station 16071500 on left branch ‘Ōpaeka‘a Stream, southeast 

Kaua‘i, Hawai‘i.

[ft3/s, cubic feet per second; ID, identifier. Measured discharge that is 

underlined is excluded from record augmentation due to insufficent data at 

the index station that could be used ascertain stable-flow conditions]

Date

Daily mean discharge 

in ft3/s

 on left branch 

‘Ōpaeka‘a Stream

Measured discharge in ft3/s

 on right branch ‘Ōpaeka‘a 

Stream

(Map ID P1 in fig. 1, tables 4–5)

06/13/2016 1.06 0.89

10/27/2016 0.93 0.94

12/09/2016 1.10 1.24

02/02/2017 0.80 0.76

08/24/2017 0.54 0.44

10/19/2017 1.00 0.93

12/08/2017 1.38 1.07

12/22/2017 1.11 0.94

01/18/2018 0.88 0.70

08/13/2018 2.50 1.30

08/22/2018 1.69 1.11
28

Low-Flow Characteristics of Streams from Wailua to Hanapēpē, Kaua‘i, Hawai‘

Table 15. Measured discharges at partial-record site 215822159282601 on 

Ku‘ia Stream and concurrent daily mean discharges at stream-gaging station 

16071500 on left branch ‘Ōpaeka‘a Stream, southeast Kaua‘i, Hawai‘i.

[ft3/s, cubic feet per second; ID, identifier]

Date

Daily mean discharge in 

ft3/s

 on left branch ‘Ōpaeka‘a 

Stream

Measured discharge in ft3/s

 on Ku‘ia Stream

(Map ID P13 in fig. 1, tables 4–5)

06/10/2016 1.04 4.38

11/18/2016 0.58 3.76

12/29/2016 1.47 6.20

03/16/2017 1.53 5.23

04/06/2017 1.07 3.92

06/01/2017 0.86 3.87

08/10/2017 0.58 3.30

09/07/2017 0.41 3.13

10/30/2017 0.96 4.02

12/07/2017 1.45 5.87

Table 16. Measured discharges at partial-record site 215833159232601 on 

Nāwiliwili Stream, southeast Kaua‘i, Hawai‘i.

[ft3/s, cubic feet per second; ID, identifier]

Date

Measured discharge in ft3/s

 on Nāwiliwili Stream

(Map ID P9 in fig. 1, tables 4–5)

10/09/1996 0.51

10/05/2017 0.50

10/11/2017 1.77

10/19/2017 0.68

11/21/2017 0.93

12/07/2017 0.62

01/17/2018 0.51

03/07/2018 0.74

08/07/2018 1.62

08/13/2018 1.82

05/13/2019 3.64

06/07/2019 2.57

09/12/2019 1.54

Table 17. Measured discharges at partial-record site 215737159230301 on 

Pū‘ali Stream, southeast Kaua‘i, Hawai‘i.

[ft3/s, cubic feet per second; ID, identifier]

Date

Measured discharge in ft3/s

 on Pū‘ali Stream

(Map ID P10 in fig. 1, tables 4–5)

02/26/2016 1.88

04/29/2016 3.05

05/17/2016 1.82

06/09/2016 2.01

09/28/2016 0.82

10/27/2016 1.00

11/16/2016 1.33

03/16/2017 2.24

04/26/2017 1.85

06/06/2017 6.39

10/11/2017 2.18

11/21/2017 2.65

Table 18. Measured discharges at partial-record sites 215608159285801 on 

‘Ōma‘o Stream and 215538159292301 on Pō‘ele‘ele Stream, southeast Kaua‘i, 

Hawai‘i.

[ft3/s, cubic feet per second; ID, identifier; --, no data]

Date

Measured discharge in ft3/s

 on ‘Ōma‘o Stream 

(Map ID P15 in fig. 1, tables 4–5)

Measured discharge in ft3/s

 on Pō‘ele‘ele Stream 

(Map ID P16 in fig. 1, tables 4–5)

09/15/1939 0.39 --

09/15/1939 0.23 --

09/18/1939 0.38 --

09/18/1939 0.25 --

12/04/1939 0.49 --

12/04/1939 0.30 --

12/08/1939 0.51 --

12/08/1939 0.30 --

01/17/1940 0.31 --

01/17/1940 0.51 --

01/26/1940 0.28 --

01/26/1940 0.46 --

02/26/1940 0.35 --

02/26/1940 0.22 --

03/15/1940 0.37 --

03/15/1940 0.23 --

02/23/2016 0.11 0.04

04/26/2016 0.08 0.19

05/17/2016 0.13 0.08

06/09/2016 0.18 0.06

09/28/2016 0.19 0.22

11/16/2016 0.19 0.22

01/18/2018 0.00 0.06

Streamflow Gains and Losses

As part of this study, a seepage run was conducted on all 

study-area streams except Hanamāʻulu Stream because discharge 

measurements from three previous seepage runs are available, 

and Pūʻali Stream because many reaches of the stream were 

inaccessible. Results of available seepage runs on study-area 

streams are discussed in upstream to downstream order. Seepage 

gains and losses along a reach were computed as the difference 

between the upstream and downstream discharges, accounting 

for major tributary inflows and diversions of water within the 

reach. To determine whether a stream supports mauka to makai 

flow under natural-flow conditions, seepage rates (expressed 

as the streamflow gain or loss in ft3/s per mile of stream reach 

[(ft3/s)/mi]) computed using discharges on measured reaches 

were extrapolated to nearby reaches on the same stream where 

measurements were not available. 

North Fork of Wailua River

Discharge measurements from two seepage runs are 

available to characterize seepage gains and losses on selected 

reaches of North Fork Wailua River. The February 22, 2017, 

seepage run (fig. 8) was conducted under conditions when 

index station 16068000 on east branch North Fork Wailua River 
Results and Discussion

men20-4010_fig08

200

400

600

800

1000

1400

1800

2200

4600

2600

3000

5000 4200

400

400

400

600

800

1800

2200

1800

1400

P1

22°05'

22°00’

159°20'

159°25'

159°30'

P2 (11.3)

A4 (2.07)

A5 (6.58)

A7 (-0)

A8 (29.2)

A9 (0.75)A11 (20.3)

A15 (61.5)

A16 (0.89)

A17 (+0.10)

A19 (2.76)

A20 (65.0)

WailuaReservoir

Wai ul a Di ct h ‘Ili‘ili‘u al N r o ht

S table StormDitch

A‘a h oka‘a

Ditch

+3.8 (9.2) +3.6 (11.2)

-0.06 (-0.2)

Wailua Di ct h

North Fork

Wailua River

0

21 KILOMETERS

2 1 MILES

0

Base modified from U.S. Geological Survey digitaldata. Universal Transverse Mercator projection,zone 4, North American Datum 1983.

Map IDP1P2A4A5A7A8A9A11A15A16A17A19A20

Station number22042315923550122034615928060122035915926430122040215926420116062000160630002203521592602011606800022032415924380122032415924360122034615923590122025815922210116071000

Station name, Kauai, HIRB Opaekaa Stream 0.3 mi US of LBNF Wailua River US Blue Hole intakeUpper L trib of NF Wailua RiverL trib NF Wailua R nr Stable Storm DtStable Storm Ditch nr LihueNF Wailua River nr alt 650 ftNF Wailua tributary nr station 16063000EB of NF Wailua River nr LihueNF Wailua R .5 mi US Aahoaka DitchNF Wailua trib .45 mi US Aahoaka DitchSpillway A Wailua Res at Kuamoo RdNF Wailua tributary US of stn 16071000 NF Wailua River nr Kapaa

Station number and name associated with map identifier (ID)[RB, Right Branch; mi, mile; US, upstream; LB, Left Branch; NF, North Fork; L, left; trib, tributary; R, River; nr, near; Dt, Ditch; alt, altitude; ft, feet; EB, East Branch; Res, Reservoir; Rd, Road; stn, station. Database limitations preclude the use of Hawaiian diacritical marks in USGS station names]

Line of equal altitude relative to mean sea level, 

in feet—Contour interval varies

Hydrologic-unit boundary—From State of Hawai'i (2017a)Diversion systemMeasured seepage run stream reach—Net seepage 

gain (+) or loss (-) in cubic feet per second (ft3/s) per 

mile and total seepage gain or loss, in ft3/s (shown in 

parentheses), for stream reach between two main stream channel sites. Dashed where seepage rates include unmeasured inflows within stream reach

Stream reach not surveyed during the seepage runPartial-record site—Labeled with map IDSeepage-run discharge-measurement site—Labeled 

with map ID and discharge in ft3/s. Site with map ID 

starting with “P” is also a partial-record site

Main stream channelTributary to main streamDitch— (-) diversion of flow or (+) return flowSite from another seepage run

EXPLANATION

A8 (29.2)

A4 (2.07)

A17 (+0.10)

+3.8 (9.2)

200

P1

North Fork Wailua River—February 22, 2017, seepage-run results

159°20' 159°40'

22°10'

22°00' Map area

KAUA‘I

Figure 8. Map of measurement sites and results for the February 2017 seepage run on North Fork Wailua River, Kaua‘i, Hawai‘i.
30

Low-Flow Characteristics of Streams from Wailua to Hanapēpē, Kaua‘i, Hawai‘

was flowing at about a Q75 discharge (daily mean of 19.8 ft3/s, 

table 2), and the discharge measured at the partial-record site 

(P2, map identifier in the figure corresponds to the location of 

the first major stream in discussion) was flowing below a Q95

discharge (daily mean of 11.3 ft3/s, table 5). The September 

21, 1982, seepage run (fig. 9) was conducted under conditions 

when index station 16068000 was flowing above the medianflow discharge (daily mean of 37.0 ft3/s, table 2), and discharge 

measured at partial-record site P2, which was 24.3 ft3/s 

computed as the sum of discharges measured at sites A2 and A3, 

was flowing at a Q60 discharge (table 5). No dry reaches in the 

main stream channel were observed during the seepage runs. 

The 2017 seepage run (fig. 8) consists of 12 measurement 

sites located between altitudes of about 30 and 1,110 ft, with flows 

in the main stream channel ranging from 11.3 to 65.0 ft3/s. The 

seepage run was conducted under natural-flow conditions; Stable 

Storm Ditch was abandoned and all flow diverted by the ‘Ili‘ili‘ula 

North Wailua Ditch intake was returned to the river immediately 

downstream of the intake beginning the day prior to the seepage 

run at 15:00 hours and continuing through the seepage run. 

The Wailua Ditch intake was not active during the seepage run; 

however, a small amount of flow from the reservoir was returned 

to the river by way of spillway A at Kuamoʻo Road (A17). 

The river generally gained flow in the reach downstream from 

‘Ili‘ili‘ula North Wailua Ditch intake (P2) to site A15. This gain is 

presumed to originate mainly from groundwater discharge from a 

thickly saturated hydrogeologic setting. In the reach between site 

A15 and about 2 mi upstream from the river mouth (A20), the 

measured loss of 0.2 ft3/s does not include flow from a tributary 

near the A‘ahoaka‘a Ditch intake; thus, the actual seepage loss is 

greater than computed.

The 1982 seepage run (fig. 9) consists of 17 measurement 

sites located between altitudes of about 30 and 1,110 ft, with flows 

in the main stream channel ranging from 23.5 to 82.1 ft3/s. Flows 

were measured within the same stream reach as the 2017 seepage 

run. The 1982 seepage run was conducted following a long period 

of high rainfall, which contributed to higher base flows in the river. 

Diversions affecting streamflow during the seepage run include the 

‘Ili‘ili‘ula North Wailua Ditch intake and the streamflow-diversion 

intake to Wailua Reservoir. Discharge measurements indicate 

generally a gaining reach between ‘Ili‘ili‘ula North Wailua Ditch 

intake (A2) and about 2 miles upstream from the river mouth 

(A20) with the most substantial gains in the lower reach between 

sites A15 and A20.

Under flow conditions of the seepage run, North Fork Wailua 

River flows continuously from the ‘Ili‘ili‘ula North Wailua Ditch 

level to site A20 under natural-flow conditions. Under divertedflow conditions when ‘Ili‘ili‘ula North Wailua Ditch intake 

diverts all the low flow in the stream, the stream may run dry in 

the reach between the intake and the river’s confluence with the 

first major tributary (A4). Most of North Fork Wailua River is 

within the thickly saturated hydrogeologic setting (fig. 4), where 

the groundwater level is above stream altitude and groundwater 

typically discharges into the stream. Extrapolation of seepage rates 

on North Fork Wailua River to the downstream unmeasured reach 

to determine flow continuity from site A20 to the confluence with 

South Fork Wailua River is not appropriate because the seepage 

rates include unmeasured inflows from tributaries. 

South Fork of Wailua River

South Fork Wailua River begins at the confluence of major 

tributaries ‘Ili‘ili‘ula and Waiahi Streams. Tributary Waikoko 

Stream joins with Stable Storm Ditch and discharges to 

‘Ili‘ili‘ula Stream. Discharge measurements from four seepage 

runs are available to characterize seepage gains and losses on 

selected reaches of the major tributaries and South Fork Wailua 

River. As part of this study, seepage runs were conducted for 

Waikoko Stream on September 28, 2017, ‘Ili‘ili‘ula Stream on 

December 9, 2019, and Waiahi Stream and South Fork Wailua 

River on January 21, 2020 (fig. 10, map areas B and C). The 

seepage runs were conducted during conditions when long-term 

station 16068000 was steadily flowing below a Q95 discharge 

(daily mean of 12.1 ft3/s, table 2) for the 2017 Waikoko Stream 

seepage run, and above a median discharge for the 2019 

‘Ili‘ili‘ula Stream (daily mean of 40.4 ft3/s, table 2), 2020 

Waiahi Stream and South Fork Wailua River seepage runs (daily 

mean of 41.1 ft3/s, table 2). The March 11, 1983, seepage run 

(fig. 11, map areas B and C) was conducted during conditions 

when long-term station 16068000 was flowing at about a Q95

discharge (daily mean of 13.0 ft3/s, table 2).

The 2017, 2019, and 2020 seepage runs (fig. 10, map areas 

B and C) were conducted under diverted-flow conditions; intakes 

at ‘Ili‘ili‘ula North Wailua Ditch, South Intake Ditch, WaiahiKuia Aqueduct, transmission ditch between ‘Ili‘ili‘ula and Waiahi 

Streams, and Hanamāʻulu Ditch were in operation during the 

seepage runs. Stable Storm Ditch conveyed water from North Fork 

Wailua River to Waikoko Stream, which discharges into ‘Ili‘ili‘ula 

Stream upstream from its confluence with Waiahi Stream. Intakes 

at the North Intake Ditch and upper Līhu‘e Ditch on ‘Ili‘ili‘ula 

Stream were inactive during the seepage runs. Not all flow 

contributions from major tributaries to the river were considered in 

the calculation of seepage gains and losses owing to inaccessibility 

of the stream sites. The 2017 seepage run on Waikoko Stream 

(fig. 10, map area B) consists of five measurement sites located 

between altitudes of about 640 and 1,110 ft, with flows in the 

main stream channel ranging from 0.35 to 1.64 ft3/s. Discharge 

measurements collected during the seepage run show a net gain 

in the 2.2-mi reach between the ‘Ili‘ili‘ula North Wailua Ditch 

dam (B3) to upstream from its confluence with Stable Storm 

Ditch (B4). The 2019 seepage run on ‘Ili‘ili‘ula Stream (fig. 10, 

map area B) consists of 12 measurement sites located between 

altitudes of about 440 and 1,110 ft, with flows in the main stream 

channel ranging from 0.21 to 13.0 ft3/s. Results of the seepage 

run show a net gain in the 1.2-mi reach from the Waiahi ‘Ili‘ili‘ula 

Ditch dam (C2) to the North Intake Ditch dam (C9). The net gain 

in the 3-mi reach between the North Intake Ditch dam (C9) and 

the confluence of ‘Ili‘ili‘ula and Waiahi Streams (C12) includes 

unmeasured inflow from tributaries. The 2020 seepage run on 

Waiahi Stream (fig. 10, map area C) consists of 13 measurement 

sites located between altitudes of about 440 and 820 ft, with flows 

in the main stream channel ranging from 13.1 to 74.2 ft3/s. The 
Results and Discussion

men20-40110_fig09

200

400

600

800

1000

1400

1800

2200

4600

2600

3000

5000 4200

400

400

400

600

800

1800

2200

1800

1400

P1

22°05'

22°00’

159°25'

159°30'

A2 (-23.5)A3 (0.77)

A8 (31.4)

A4 (4.34)A5 (19.4)A6 (25.2)A7 (-0.02)

A10 (0.12)A11 (36.9)A12 (-15.4)A13 (9.21)A14 (43.8)

A15 (51.3)

A16 (1.95)

A17 (+7.97)

A18 (+0.23)

A20 (82.1)

WailuaReservoir +0.4 (0.7) 0 (0.0)

+10.3 (6.2)

+9.4 (7.5) +6.2 (20.6)

P2

Wai ul a Di ct h ‘Ili‘ili‘u al N r o ht

Stable Storm Ditch

A‘ahok a‘a Ditch

Wailua Di ct h

North Fork

Wailua River

0

21 KILOMETERS

2 1 MILES

0

Base modified from U.S. Geological Survey digitaldata. Universal Transverse Mercator projection,zone 4, North American Datum 1983.

Map IDP1P2A2A3A4A5A6A7A8A10A11A12A13A14A15A16A17A18A20

Station number2204231592355012203461592806011606100022034615928020122035915926430122040215926420122035815926390116062000160630002203481592557011606800022035615924470122035615924480122035415924480122032415924380122032415924360122034615923590122034215923440116071000

Station name, Kauai, HIRB Opaekaa Stream 0.3 mi US of LBNF Wailua River US Blue Hole intakeNorth Wailua Ditch nr LihueNF Wailua R DS Iliiliula N Wailua DtUpper L trib of NF Wailua RiverL trib NF Wailua R nr Stable Storm DtNF Wailua River US Stable Storm DtStable Storm Ditch nr LihueNF Wailua River nr alt 650 ftNF Wailua trib .9 mi DS Stable Storm DtEB of NF Wailua River nr LihueDiversion fr NF Wailua R to Wailua ResNF Wailua split W of Wailua Res intakeNF Wailua R DS Wailua Res intakeNF Wailua R .5 mi US Aahoaka DitchNF Wailua trib .45 mi US Aahoaka DitchSpillway A Wailua Res at Kuamoo RdSpillway B Wailua Res .2mi DS Kuamoo RdNF Wailua River nr Kapaa

Station number and name associated with map identifier (ID)[RB, Right Branch; mi, mile; US, upstream; LB, Left Branch; NF, North Fork; nr, near; R, River; DS, downstream; N, North; Dt, Ditch; L, Left; trib, tributary; alt, altitude; ft, feet; EB, East Branch; fr, from; Res, Reservoir; W, West; Rd, Road. Database limitations preclude the use of Hawaiian diacritical marks in USGS station names]

Line of equal altitude relative to mean sea level, 

in feet—Contour interval varies

Hydrologic-unit boundary—From State of Hawai'i (2017a)Diversion systemMeasured seepage run stream reach—Net seepage 

gain (+) or loss (-) in cubic feet per second (ft3/s) per 

mile and total seepage gain or loss, in ft3/s (shown in 

parentheses), for stream reach between two main stream channel sites. Dashed where seepage rates include unmeasured inflows within stream reach

Stream reach not surveyed during the seepage runPartial-record site—Labeled with map IDSeepage-run discharge-measurement site—Labeled 

with map ID and discharge in ft3/s. Site with map ID 

starting with “P” is also a partial-record site

Main stream channelTributary to main streamDitch—(-) diversion of flow or (+) return flowSite from another seepage run

EXPLANATION

A2 (23.5)

A4 (4.34)

A7 (-0.02)

+0.4 (0.7)

200

P1

159°20' 159°40'

22°10'

22°00'

Map area

KAUA‘I

North Fork Wailua River—September 21, 1982, seepage-run results

Figure 9. Map of measurement sites and results for the September 1982 seepage run on North Fork Wailua River, Kaua‘i, Hawai‘i.
32

Low-Flow Characteristics of Streams from Wailua to Hanapēpē, Kaua‘i, Hawai‘

men20-4010_fig10a

200

400

600

800

1000

1400

1800

2200

4600

2600

3000

5000 4200

400

400

400

600

800

1800

2200

1800

1400

1000

800

22°05'

22°00’

159°20'

159°25'

159°30'

+11 (51)

E1 (54.9)

E3 (+24.7)

E5 (131a

)

Wai ul a Di ct h

‘Ili‘ili u‘ al N r o ht

Stable Storm Ditch

A‘ahok a‘a Ditch

Wailua Di ct h

0

21 KILOMETERS

2 1 MILES

0

Base modified from U.S. Geological Survey digitaldata. Universal Transverse Mercator projection,zone 4, North American Datum 1983.

Sou ht Fork

Wai ul

a

River

Map IDE1E3E5

Station number22015715925470122013615924460116060000

Station name, Kauai, HISF Wailua River DS Iliiliula Str confHanamaulu Ditch return to SF WailuaSF Wailua River nr Lihue

Station number and name associated with map identifier (ID)[SF, South Fork; DS, downstream; Str, Stream; conf, confluence; nr, near. Database limitations preclude the use of Hawaiian diacritical marks in USGS station names]

Line of equal altitude relative to mean 

sea level, in feet—Contour interval varies

Hydrologic-unit boundary—From State 

of Hawai'i (2017a)

Diversion systemMeasured seepage run stream reach

—

Net seepage gain (+) or loss (-) in cubic feet per second (ft3/s) per mile 

and total seepage gain or loss, in ft3/s 

(shown in parentheses), for stream reach between two main stream channel sites. Dashed where seepage rates include unmeasured inflows within stream reach

Stream reach not surveyed during the 

seepage run

Seepage-run discharge-measurement 

site—Labeled with map ID and discharge in ft3/s aDaily mean discharge at continuous 

streamgage

Main stream channelDitch—(-) diversion of flow or (+) return 

flow

Site from another seepage run

EXPLANATION

E1 (54.9)

E3 (+24.7)

+11 (51)

200

159°20' 159°40'

22°10'

22°00'

Map area

KAUA‘I

South Fork Wailua River—January 21, 2020, seepage-run results

Map area in C

Map area in B

A

Figure 10. Map of measurement sites and results for the September 2017, December 2019, and January 2020 seepage runs on South Fork Wailua River, Kaua‘i, Hawai‘i.
Results and Discussion

men20-4010_fig10b

Stable Storm Ditch

1000

800

600

1000

1400

800

1800 2200

C6 (0)

C8 (-0)

+1.4 (1.74)

+6.4 (19.1)

P5 (13.0)

C2 (0.21)

C5 (0.53)

C3 (0.20)

C4 (+0.10)

C7 (1.49)

C9 (4.27)

C10 (21.0)

C11 (-38.8)

C12 (5.61)

P3 (1.92)

P4 (0.57)

B5 (0.41)

B3 (0.35)

B4 (1.64)

+0.6 (1.29)

Waiahi ‘Ili‘ili‘ula

Ditch

North Intake Ditch

‘Ili‘ili u‘ al Nor ht Wai ul a Di ct h

0

0.5 0.25 KILOMETER

0.5 0.25 MILE

0

Base modified from U.S. Geological Survey digitaldata. Universal Transverse Mercator projection,zone 4, North American Datum 1983.

Map IDP3P4B3B4B5P5C2C3

Station number220326159275401220325159275401220325159275201220309159262101220308159262201220224159282301220221159282201220221159282101

Station name, Kauai, HINF Waikoko Str US Iliiliula N Wailua DtSF Waikoko Str US Iliiliula N Wailua DtWaikoko Str blw diversion damWaikoko Str .3mi US Stable StormTrib to Waikoko .3mi US Stable StormIliiliula Str trib 4 US N Wailua DitchIliiliula Str DS Waiahi Iliiliula DitchL trib Iliiliula DS Waiahi Iliiliula Dt

Station number and name associated with map identifier (ID)[NF, North Fork; Str, Stream; US, upstream; N, North; Dt, Ditch; SF, South Fork; blw, below; mi, mile; trib, tributary; L, Left; LB, Left Branch; DS, downstream; conf, confluence; div, diversion. Database limitations preclude the use of Hawaiian diacritical marks in USGS station names]

Map IDC4C5C6C7C8C9C10C11C12

Station number220220159281901220224159281001220207159280101220228159273601220229159273201220229159273101220205159255801220156159255201220157159255101

Station name, Kauai, HIWaiahi Iliiliula Dt spillway, IliiliulaLB trib Iliiliula DS N Wailua DtWaiaka Str DS Waiahi Iliiliula DitchTrib to Iliiliula US N Intake DitchNorth Intake Ditch on Iliiliula StreamIliiliula Stream DS N Intake DitchWaikoko Str at Iliiliula Str confIliiliula Stream div to Waiahi StreamIliiliula Str DS div to Waiahi Str

Line of equal altitude relative to mean 

sea level, in feet—Contour interval varies

Diversion systemMeasured seepage run stream reach

—

Net seepage gain (+) or loss (-) in cubic feet per second (ft3/s) per mile 

and total seepage gain or loss, in ft3/s 

(shown in parentheses), for stream reach between two main stream channel sites. Dashed where seepage rates include unmeasured inflows within stream reach

Stream reach not surveyed during the 

seepage run

Seepage-run discharge-measurement 

site—Labeled with map ID and discharge in ft3/s. Site with map ID 

starting with “P” is a partial-record site

Main stream channelTributary to main streamDitch—(-) diversion of flow or (+) return 

EXPLANATION

flow

C2 (0.21)

C4 (+0.10)

C3 (0.20)

+1.4 (1.74)

2

200

2°05'

22°00’

159°20'

159°25'

159°30'

Wailua River area

B

Waikoko and ‘Ili‘ili‘ula Streams—September 28, 2017, 

and December 9, 2019, seepage-run results

B

Waikoko

Stream

‘Ili‘ili‘ula Stream

Figure 10.—Continued
34

Low-Flow Characteristics of Streams from Wailua to Hanapēpē, Kaua‘i, Hawai‘

men20-4010_fig10c

+9.0 (32.3)

+24.3 (7.3)

D12 (0.71)

D20 (74.2)

 

Ku hi- ia a W

qA ai deu t cu

 Nort h nI kat

e D itch

 Upper Lihue Ditch

South In

at ke Ditch

D3a (25.2) D4 (+0.91)

D6 (+15.9)

D7 (-36.2)

D8 (13.1)

D9 (-8.04)

D10 (+0.10)

D14 (+0.26)

D15 (38.4)

D16 (64.0)

D18 (2.78)

+3.5 (7.4)

1000

800

600

1000

1400

a W ai i h ‘I il i‘ li u‘ la

hcti D

Wa ai hi S rt e ma

0

0.5 0.25 KILOMETER

0.5 0.25 MILE

0

Base modified from U.S. Geological Survey digitaldata. Universal Transverse Mercator projection,zone 4, North American Datum 1983.

Map IDD3D4D6D7D8D9D10

Station number16057900220122159275301220108159275201220110159275201220108159275202220107159274801220114159274901

Station name, Kauai, HIWaiahi Str US Upper PowerhouseWaiahi Upper PH throwawayWaiahi Upper Powerhouse tailraceSouth Intake Ditch on Waiahi StrWaiahi Str DS South Intake DitchWaiahi-Kuia Aqueduct Intake on Waiahi StrInflow DS Upper PH

Station number and name associated with map identifier (ID)[Str, Stream; US, upstream; PH, Powerhouse; DS, downstream; L, Left; trib, tributary; Dt, Ditch; nr, near. Database limitations preclude the use of Hawaiian diacritical marks in USGS station names]

Map IDD12D14D15D16D18D20

Station number220113159273001220103159264001220103159264101220106159263801220108159263901220151159255101

Station name, Kauai, HIL trib Waiahi DS South Intake DitchWaiahi Lower PH throwawayWaiahi Str DS Lower PH throwawayWaiahi Str US Upper Lihue Dt damL trib Waiahi Str nr lower powerhouseWaiahi Str US Hanamaulu Ditch

Line of equal altitude relative to mean sea 

level, in feet—Contour interval varies

Diversion systemMeasured seepage run stream reach

—

Net seepage gain (+) or loss (-) in cubic feet per second (ft3/s) per mile and total 

seepage gain or loss, in ft3/s (shown in 

parentheses), for stream reach between two main stream channel sites. Dashed where seepage rates include unmeasured inflows within stream reach

Stream reach not surveyed during the 

seepage run

Seepage-run discharge-measurement 

site—Labeled with map ID and discharge in ft3/s aStreamgaging station with flow-duration 

estimates in table 2

Main stream channelTributary to main streamDitch—(-) diversion of flow or (+) return flowSite from another seepage run

EXPLANATION

D3 (25.2)

D12 (0.71)

D6 (+15.9)

+3.5 (7.4)

22°05'

200

22°00’

159°20'

159°25'

159°30'

Wailua River area

C

Waiahi Stream—January 21, 2020, seepage-run results

C

Figure 10.—Continued
Results and Discussion

men20-4010_fig11a

200

400

600

800

1000

1400

1800

2200

4600

2600

3000

5000 4200

400

400

400

600

800

1800

2200

1800

1400

1000

800

22°05'

22°00’

159°20'

159°25'

159°30'

+0.9 (1.78)

E1 (0.17) E4 (6.18) E5 (7.64)

E2 (4.40)

E6 (0.72) E8 (1.53)

E7 (1.77)

+2.6 (4.23)

+1.1 (1.46)

Wai ul a Di ct h

‘Ili‘ili u‘ al N r o ht

Stable Storm Ditch

A

a‘ hoka‘a Ditch

Wai ul

a Di ct h

0

2 1 KILOMETERS

2 1 MILES

0Base modified from U.S. Geological Survey digitaldata. Universal Transverse Mercator projection,zone 4, North American Datum 1983.

Sou ht Fork

Wai ul

a

River

Map IDE1E2E4E5E6E7E8

Station number2201571592547011605850022021915923390116060000220210159224701220143159225701220151159215901

Station name, Kauai, HISF Wailua River DS Iliiliula Str confSF Wailua River nr Rock Quarry nr LihueSF Wailua .3 mi S of Hanamaulu airstripSF Wailua River nr LihueR trib SF Wailua River US Wailua FallsR trib SF Wailua River at Maalo RdR trib SF Wailua River US Fern Grotto

Station number and name associated with map identifier (ID)[SF, South Fork; DS, downstream; Str, Stream; conf, confluence; nr, near; mi, mile; S, South; R, Right; trib, tributary; US, upstream; Rd, Road. Database limitations preclude the use of Hawaiian diacritical marks in USGS station names]

Line of equal altitude relative to mean 

sea level, in feet—Contour interval varies

Hydrologic-unit boundary—From State 

of Hawai'i (2017a)

Diversion systemMeasured seepage run stream reach

—

Net seepage gain (+) or loss (-) in cubic feet per second (ft3/s) per mile 

and total seepage gain or loss, in ft3/s 

(shown in parentheses), for stream reach between two main stream channel sites. Dashed where seepage rates include unmeasured inflows within stream reach

Stream reach not surveyed during the 

seepage run

Seepage-run discharge-measurement 

site—Labeled with map ID and discharge in ft3/s

Main stream channelTributary to main steamSite from another seepage run

EXPLANATION

E1 (0.17)

E3 (0.72)

+2.6 (4.23)

200

159°20' 159°40'

22°10'

22°00'

Map area

KAUA‘I

South Fork Wailua River—March 11, 1983, seepage-run results

Map area in B

Map area in C

A

Figure 11. Map of measurement sites and results for the March 1983 seepage runs on South Fork Wailua River, Kaua‘i, Hawai‘i. 
36

Low-Flow Characteristics of Streams from Wailua to Hanapēpē, Kaua‘i, Hawai‘

men20-4010_fig11b

Stable Storm Ditch

+1.5 (6.4)

P5 (9.80)

1000

800

600

1000

1400

C2 (0.42)

C3 (0.20)

C4 (+0.10)

B6 (+29.1)

C11 (-36.4)

C12 (0.15)

800

B7 (0.30)

1800 2200

P3

P4

‘Ili‘ili u‘ l a Nor ht

a W ilua D ti hc

Waiahi ‘Ili‘ili‘ula

Ditch

North Intake Ditch

B

0

0.5 0.25 KILOMETER

0.5 0.25 MILE

0

Base modified from U.S. Geological Survey digitaldata. Universal Transverse Mercator projection,zone 4, North American Datum 1983.

Map IDP3P4P5C2C3

Station number220326159275401220325159275401220224159282301220221159282201220221159282101

Station name, Kauai, HINF Waikoko Str US Iliiliula N Wailua DtSF Waikoko Str US Iliiliula N Wailua DtIliiliula Str trib 4 US N Wailua DitchIliiliula Str DS Waiahi Iliiliula DitchL trib Iliiliula DS Waiahi Iliiliula Dt

Station number and name associated with map identifier (ID)[NF, North Fork; Str, Stream; US, upstream; N, North; Dt, Ditch; SF, South Fork; trib, tributary; DS, downstream; L, Left; conf, confluence; div, diversion. Database limitations preclude the use of Hawaiian diacritical marks in USGS station names]

Map IDC4B6B7C11C12

Station number220220159281901220320159261801220311159261001220156159255201220157159255101

Station name, Kauai, HIWaiahi Iliiliula Dt spillway, IliiliulaStable Storm Dt .27 mi US Waikoko StrWaikoko Str nr Stable Storm DitchIliiliula Stream div to Waiahi StreamIliiliula Str DS div to Waiahi Str

Line of equal altitude relative to mean 

sea level, in feet—Contour interval varies

Diversion systemMeasured seepage run stream reach

—

Net seepage gain (+) or loss (-) in cubic feet per second (ft3/s) per mile 

and total seepage gain or loss, in ft3/s 

(shown in parentheses), for stream reach between two main stream channel sites. Dashed where seepage rates include unmeasured inflows within stream reach

Stream reach not surveyed during the 

seepage run

Partial-record site—Labeled with 

map ID

Seepage-run discharge-measurement 

site—Labeled with map ID and discharge in ft3/s. Site with map ID 

starting with “P” is a partial-record site

Main stream channelTributary to main streamDitch—(-) diversion of flow or (+) return 

EXPLANATION

flow

C2 (0.42)

C4 (+0.10)

C3 (0.20)

+1.5 (6.4)

200

P3

22°05'

22°00’

159°20'

159°25'

159°30'

Wailua River area

B

‘Ili‘ili‘ula Stream—March 11, 1983, seepage-run results

‘Ili‘ili‘ula Stream

Figure 11.—Continued
Results and Discussion

men20-4010_fig11C

+9.3 (2.8)

+0.5 (0.2)

uK-i hai a W

qA ai deu t cu

Nor ht

nI at

ek D hcti

Upper Lihue

Ditch

South In at ke Di ct h

D3a (16.5) D1 (5.96)

D5 (+26.2)

D7 (-42.6)

D13 (3.78) D9 (-0.25)

D11 (0) D14 (+4.62) D19 (-39.2)

D17 (3.67)

D18 (0.91)

+1.1 (3.78)

1000

800

600

1000

1400

D2 (13.7)

D20 (8.9b

)

+2.0 (4.3)

C11 (-36.4)

D21 (-45.3)

a W ai i h I‘ li‘ili u‘ al hcti D

Wa ai hi S rt e ma

C

0

0.5 0.25 KILOMETER

0.5 0.25 MILE

0

Base modified from U.S. Geological Survey digitaldata. Universal Transverse Mercator projection,zone 4, North American Datum 1983.

Map IDC11D1D2D3D5D7D9

Station number22015615925520122011915928060122012015928050116057900220205159280101220110159275201220107159274801

Station name, Kauai, HIIliiliula Stream div to Waiahi StreamIole Str nr upper powerhouseWaiahi Str DS conf w Iole StrWaiahi Str US Upper Powerhouse

Waiahi Iliiliula Ditch DS Waiaka StrSouth Intake Ditch on Waiahi StrWaiahi-Kuia Aqueduct Intake on Waiahi Str

Station number and name associated with map identifier (ID)[div, diversion; Str, Stream; nr, near; DS, downstream; conf, confluence; w, with; US, upstream; PH, powerhouse; Dt, Ditch; L, Left; trib, tributary; mi, mile; fr, from; SF, South Fork; R, River. Database limitations preclude the use of Hawaiian diacritical marks in USGS station names]

Map IDD11D13D14D17D18D19D20D21

Station number220107159274701220101159264301220103159264001220107159263801220108159263901220109159261901220151159255101220156159254701

Station name, Kauai, HIWaiahi Str DS Waiahi Kuia AqueductWaiahi Str nr lower powerhouseWaiahi Lower PH throwawayWaiahi Str DS Upper Lihue Dt damL trib Waiahi Str nr lower powerhouseUpper Lihue Dt .37 mi DS fr intakeWaiahi Str US Hanamaulu DitchHanamaulu Ditch nr SF Wailua R intake

Line of equal altitude relative to mean sea 

level, in feet—Contour interval varies

Diversion systemMeasured seepage run stream reach

—

Net seepage gain (+) or loss (-) in cubic feet per second (ft3/s) per mile and total 

seepage gain or loss, in ft3/s (shown in 

parentheses), for stream reach between two main stream channel sites. Dashed where seepage rates include unmeasured inflows within stream reach

Stream reach not surveyed during the 

seepage run

Seepage-run discharge-measurement 

site—Labeled with map ID and discharge in ft3/s aStreamgaging station 16057900 with 

flow-duration discharge estimates in table 2

bDischarge computed by subtracting 

discharge at C11 from discharge at D21

Main stream channelTributary to main streamDitch—(-) diversion of flow or (+) return flowSite from another seepage run

EXPLANATION

D3 (16.5)

D12 (5.96)

D6 (-42.6)

+9.3 (2.8)

2

200

2°05'

22°00’

159°20'

159°25'

159°30'

Wailua River area

C

Waiahi Stream

—March 11, 1983, seepage-run results

Figure 11.—Continued
38

Low-Flow Characteristics of Streams from Wailua to Hanapēpē, Kaua‘i, Hawai‘

2020 seepage run on South Fork Wailua River (fig. 10) consists 

of three measurement sites located between altitudes of about 240 

and 430 ft, with flows in the main stream channel ranging from 

54.9 to 131 ft3/s. The 2020 seepage-run measurements indicate a 

net gain in the 0.3-mi reach of Waiahi Stream between continuousrecord low-flow station 16057900 near the upper powerhouse 

(D3) and South Intake Ditch dam (D8) and in the 2.1-mi reach 

between upper Līhuʻe Ditch dam (D16) and Hanamāʻulu Ditch 

intake (D20). The net gains in the 3.6-mi reach of Waiahi Stream 

between South Intake Ditch dam (D8) and upper Līhuʻe Ditch 

dam (D16), and in the measured reach on South Fork Wailua 

River from the confluence of ‘Ili‘ili‘ula and Waiahi Streams 

(E1) to continuous station 16060000 (E5) include unmeasured 

inflows from tributaries. Seepage gains are presumed to originate 

mainly from groundwater discharge from the thickly saturated 

hydrogeologic setting.

The 1983 seepage run on South Fork Wailua River and 

its tributaries (fig. 11, map areas B and C) consists of 30 

measurement sites, located between altitudes of about 230 

and 1,110 ft, with flows in the stream channel ranging from 

0.15 ft3/s on ‘Ili‘ili‘ula Stream to 16.5 ft3/s on Waiahi Stream. 

Results of the 1983 seepage run are comparable to those 

of the 2019 and 2020 seepage runs, with lower magnitudes 

of seepage gains in the selected reaches. Flow at Waikoko 

Stream upstream from its confluence with ‘Ili‘ili‘ula Stream 

(fig. 11, map area B) is the sum of discharges measured at 

the confluence of Waikoko Stream and Stable Storm Ditch 

(B6 and B7) and assumes no seepage gains and (or) losses 

in the downstream reach. Flow at Waiahi Stream upstream 

from Hanamāʻulu Ditch intake (D20; fig. 11, map area C) was 

estimated from discharges measured at the transmission ditch 

(C11) and Hanamāʻulu Ditch (D21). 

Seepage-run measurements indicate that under the flow 

conditions of the seepage runs, South Fork Wailua River flows 

continuously from the ‘Ili‘ili‘ula North Wailua Ditch level to 

continuous-record stream-gaging station 16060000 (E5) under 

natural-flow conditions. During the base period (1961–2019), 

the stream did not run dry at station 16060000, with the lowest 

discharge at 7.6 ft3/s. Extrapolation of seepage rates on South Fork 

Wailua River to the downstream unmeasured reach to determine 

flow continuity to the ocean is not appropriate because the seepage 

rates include unmeasured inflows from a number of tributaries.

Hanamā‘ulu Stream

Previous seepage runs on Hanamāʻulu Stream were 

conducted on October 9, 1996 (fig. 12), September 13,1973, a

September 20, 1973 (fig. 13). The September 13, 1973, seepage 

run did not consider flow contribution from the tributary at site 

F8; thus, a subsequent seepage run was conducted a week later 

that included flow from the tributary. The 1996 seepage run was 

conducted under conditions when index station 16068000 was 

flowing at about a Q65 discharge (daily mean of 23.0 ft3/s, table 2). 

The first 1973 seepage run was conducted under conditions when 

index station 16068000 was flowing at about a Q92 discharge 

(daily mean of 14.0 ft3/s, table 2), and the second 1973 seepage 

run was conducted when index station 16068000 was flowing at 

about a Q62 discharge (daily mean of 24.0 ft3/s, table 2).

The 1996 seepage run (fig. 12) consists of four measurement 

sites located between altitudes of about 110 and 360 ft, with flows 

in the main stream channel ranging from 10.9 to 23.7 ft3/s. The 

1973 seepage run (fig. 13) consists of six measurement sites, 

located between altitudes of about 90 and 200 ft, with flows in the 

main stream channel ranging from 5.73 to 19.6 ft3/s. The 1996 

seepage-run measurements indicate a generally gaining reach 

from sites F3 to F7 and the 1973 seepage-run measurements 

indicate a generally gaining reach from sites F4 to F9. Flow 

contributions from major tributaries to the measured reach were 

considered in the calculation of seepage gains and losses. The 

measured gains were most likely from groundwater discharge 

from the thickly saturated hydrogeologic setting. Both seepage 

runs were conducted under diverted-flow conditions. The 

headwaters of Hanamāʻulu Stream flow into Kapaia Reservoir, 

which regulates downstream flow in the main stream channel. 

Several tributaries, which may be affected by return flows from 

the upper and lower Līhu‘e Ditches, flow into the 3.3-mi stream 

reach downstream from the reservoir. Seepage-run discharge 

measurements are not available within this reach because 

many areas may have been inaccessible owing to surrounding 

vegetation of the stream channel. 

Results of these previous seepage runs indicate seepagegain rates in the measured reaches. Extrapolation of seepage 

rates to the downstream unmeasured reach for determining 

flow continuity from mauka to makai would assume that the 

downstream unmeasured stream reach is also gaining. With 

this assumption, and under flow conditions of the seepage runs, 

including flow regulation by Kapaia Reservoir, Hanamāʻulu 

Stream flows continuously from site F3 to the ocean.

Nāwiliwili Stream

Discharge measurements from two seepage runs are 

available to characterize seepage gains and losses in selected 

reaches of Nāwiliwili Stream. The September 12, 2019, 

seepage run (fig. 14) was conducted during conditions when 

nearby long-term station 16068000 was flowing at about a Q80

discharge (daily mean of 18.6 ft3/s, table 2). The October 9, 

1996, seepage run (fig. 15) was conducted during conditions 

when nearby station 16068000 was flowing at about a Q65

discharge (daily mean of 23.0 ft3/s, table 2). 

The 2019 seepage run (fig. 14) consists of eight measurement sites located between altitudes of about 90 and 230 ft, 

with flows in the main stream channel ranging from 1.54 to 

5.86 ft3/s. The seepage run was conducted under natural-flow 

conditions; all the flow diverted at a stream-diversion intake 

near an altitude of about 195 ft (G2) was returned to the 

stream at sites G6 and G7. Discharge measurements indicate 

a net gain in the 0.5-mi reach between the uppermost site (P9) 

and downstream from the diversion intake at site G3, and a 

net loss in the 1.8-mi reach downstream from the intake (G3) 

to about 1.7 mi upstream from the stream mouth (G9). Flow 

contribution from a tributary just upstream of site G8 was not 
Results and Discussion

men20-4010_fig12

100

200

300

400

500

600

700

800

900

1000

P7

P8

P6

159°21'

159°23'

159°25'

22°01'

21°59'

F1 (0.85)

F2 (0.24)

F3 (10.9)

F7 (23.7)

KapaiaReservoir

wo L r e hī L e‘ u D ti hc

Kapaia Ditch

+6.4 (12.8)

Upper Līhu‘e Ditch

0

10.5 KILOMETER

1 0.5 MILE

Map IDF1F2F3F7P6P7P8

0Base modified from U.S. Geological Survey digitaldata. Universal Transverse Mercator projection,zone 4, North American Datum 1983.

Station number220024159234101220008159230401215932159225201215930159215901220054159244001220037159242901215923159235601

Station name, Kauai, HIR trib 1 Hanamaulu.9mi DS Upper Lihue DtR trib 2 Hanamaulu .7mi DS Lo Lihue DtHanamaulu Str .23mi US Kapaia DitchHanamaulu Str 600ft US Kuhio HwyHanamaulu Str 1 mi US N Kapaia ResHanamaulu Str 0.6 mi US S Kapaia ResHanamaulu tributary US of return flow

Station number and name associated with map identifier (ID)[R, Right; trib, tributary; mi, mile; DS, downstream; Dt, Ditch; Lo, Lower; Str, Stream; US, upstream; ft, feet; Hwy, Highway; N, North; Res, Reservoir; S, South. Database limitations preclude the use of Hawaiian diacritical marks in USGS station names]

Line of equal altitude relative to mean 

sea level—Contour interval 100 feet

Hydrologic-unit boundary—From State 

of Hawai'i (2017a)

Diversion systemMeasured seepage run stream reach

—

Net seepage gain (+) or loss (-) in cubic feet per second (ft3/s) per mile 

and total seepage gain or loss, in ft3/s 

(shown in parentheses), for stream reach between two main stream channel sites

Stream reach not surveyed during the 

seepage run

Partial-record site—Labeled with 

map ID

Seepage-run discharge-measurement 

site—Labeled with map ID and discharge in ft3/s

Main stream channelTributary to main streamSite from another seepage run

EXPLANATION

+6.4 (12.8)

F3 (10.9)

F1 (0.85)

200

P6

159°20' 159°40'

22°10'

22°00'

Map area

KAUA‘I

Hanamā‘ulu Stream—October 9, 1996, seepage-run results

Hanamā‘ulu Stream

Figure 12. Map of measurement sites and results for the October 1996 seepage run on Hanamā‘ulu Stream, Kaua‘i, Hawai‘i.
40

Low-Flow Characteristics of Streams from Wailua to Hanapēpē, Kaua‘i, Hawai‘

men20-4010_fig13

100

200

300

400

500

600

700

800

900

1000

P7

P8

P6

159°21'

159°23'

159°25'

22°01'

21°59'

F4 (5.73a

)

F5 (5.93a

)

F6 (6.95a

)

F7 (7.30a

,

8.29b

)

F8 (10.9b

)

F9 (15.2a, 19.6b

)

+0.7 (0.20)

+1.1 (1.02)

+1.8 (0.35)

+2.0 (0.4)

KapaiaReservoir

wo L er ī L hu e‘ D ti hc

Kapaia Ditch

Upper Līhu‘e Ditch

0

10.5 KILOMETER

1 0.5 MILE

Map IDF4F5F6F7F8F9P6P7P8

0Base modified from U.S. Geological Survey digitaldata. Universal Transverse Mercator projection,zone 4, North American Datum 1983.

Station number215932159223501215932159222401215918159220001215930159215901215933159215501215929159215201220054159244001220037159242901215923159235601

Station name, Kauai, HIHanamaulu Str .14mi blw Kapaia DitchHanamaulu Str .4mi DS Kapaia DitchHanamaulu Str nr Wilcox HospitalHanamaulu Str 600ft US Kuhio HwyLeft trib US Hanamaulu nr Lau Kona PkHanamaulu Str nr Lau Kona ParkHanamaulu Str 1 mi US N Kapaia ResHanamaulu Str 0.6 mi US S Kapaia ResHanamaulu tributary US of return flow

Station number and name associated with map identifier (ID)[Str, Stream; mi, mile; blw, below; DS, downstream; nr, near; ft, feet; US, upstream; Hwy, Highway; trib, tributary; Pk, Park; N, North; Res, Reservoir; S, South. Database limitations preclude the use of Hawaiian diacritical marks in USGS station names]

Line of equal altitude relative to mean sea 

level—Contour interval 100 feet

Hydrologic-unit boundary—From State of Hawai'i 

(2017a)

Diversion systemMeasured seepage run stream reach

—

Net seepage gain (+) or loss (-) in cubic feet per second (ft3/s) per mile and total seepage gain or 

loss, in ft3/s (shown in parentheses), for stream 

reach between two main stream channel sites

Stream reach not surveyed during the seepage runPartial-record site—Labeled with 

map ID

Seepage-run discharge-measurement site

—

Labeled with map ID and discharge in ft3/s aDischarge measured on September 13, 1973

bDischarge measured on September 20, 1973

Main stream channelTributary to main streamSite from another seepage run

EXPLANATION

F4 (5.73)

F8 (10.9)

+2.0 (0.4)

200

P6

159°20' 159°40'

22°10'

22°00'

Map area

KAUA‘I

Hanamā‘ulu Stream—September 13 and 20, 1973, seepage-run results

Hanamā‘ulu

Stream

Figure 13. Map of measurement sites and results for the September 1973 seepage runs on Hanamā‘ulu Stream, Kaua‘i, Hawai‘i.
Results and Discussion

men20-4010_fig14

100

200

300

400

500 600

700

800

900

159°22'

159°24'

21°59'

21°58'

P9 (1.54)

G2 (-2.64)

G3 (3.06)

G4 (0)

G7 (+0.55)

G6 (+2.27)

G9 (5.01)

G8 (5.86)

+8.3 (4.16) 0 (-0.02)

-1.1 (-0.85)

Nāwiliwili Stream—September 12, 2019, seepage-run results

Nāwil wi ili Stream

0

1 0.5 KILOMETER

1 0.5 MILE

0

Base modified from U.S. Geological Survey digitaldata. Universal Transverse Mercator projection,zone 4, North American Datum 1983.

Map IDP9G2G3G4G6G7G8G9

Station number21583315923260121583115923020121583215923020121583315923000121583315922520121583415922500116055500215807159215801

Station name, Kauai, HINawiliwili Stream at Rapoza Rd.Taro intake at Nawiliwili StreamNawiliwili Stream DS taro intakeNawiliwili trib 270 ft DS taro intkTaro ditch return to Nawiliwili StrTaro side ditch return Nawiliwili StrNawiliwili Str at Heleko Road at LihueNawiliwili Str 1.7 mi US mouth

Station number and name associated with map identifier (ID)[Rd., Road; DS, downstream; trib, tributary; ft, feet; intk, intake; Str, Stream; mi, miles; US, upstream. Database limitations preclude the use of Hawaiian diacritical marks in USGS station names]

Line of equal altitude relative to mean sea 

level—Contour interval 200 feet

Hydrologic-unit boundary—From State of 

Hawai'i (2017a)

Diversion systemMeasured seepage run stream reach—

Net seepage gain (+) or loss (-) in cubic feet per second (ft3/s) per mile and total 

seepage gain or loss, in ft3/s (shown in 

parentheses), for stream reach between two main stream channel sites. Dashed where seepage rates rates include unmeasured inflows within stream reach

Stream reach not surveyed during the 

seepage run

Seepage-run discharge-measurement 

site—Labeled with map ID and discharge in ft3/s. Site with map ID starting with “P” 

is a partial-record site

Main stream channelTributary to main stream

Ditch—(-) diversion of flow or (+) return flowSite from another seepage run

EXPLANATION

G8 (5.86)

G4 (0)

G2 (-2.64)

+8.3 (4.16)

200

159°20' 159°40'

22°10'

22°00'

Map area

KAUA‘I

Figure 14. Map of measurement sites and results for the September 2019 seepage run on Nāwiliwili Stream, Kaua‘i, Hawai‘i.
42

Low-Flow Characteristics of Streams from Wailua to Hanapēpē, Kaua‘i, Hawai‘

men20-4010_fig15

100

200

300

400

500

600

700

800

900

159°22'

159°24'

21°59'

21°58'

P9 (0.51)

G2 (-1.91)

G3 (1.22)

G8 (4.41)

+5.2 (2.62) +2.8 (2.75)

G5 (1.66)

Nāwiliwili Stream—October 9, 1996, seepage-run results

Nāwil wi ili Stream

0

1 0.5 KILOMETER

1 0.5 MILE

0

Base modified from U.S. Geological Survey digitaldata. Universal Transverse Mercator projection,zone 4, North American Datum 1983.

Map IDP9G2G3G5G8

Station number21583315923260121583115923020121583215923020121583415923000116055500

Station name, Kauai, HINawiliwili Stream at Rapoza Rd.Taro intake at Nawiliwili StreamNawiliwili Stream DS taro intakeNawiliwili Str DS of confluenceNawiliwili Str at Heleko Road at Lihue

Station number and name associated with map identifier (ID)[Rd., Road; DS, downstream; Str, Stream. Database limitations preclude the use of Hawaiian diacritical marks in USGS station names]

Line of equal altitude relative to mean sea 

level—Contour interval 200 feet

Hydrologic-unit boundary—From State of 

Hawai'i (2017a)

Diversion systemMeasured seepage run stream reach

—

Net seepage gain (+) or loss (-) in cubic feet per second (ft3/s) per mile and total 

seepage gain or loss, in ft3/s (shown in 

parentheses), for stream reach between two main stream channel sites. Dashed where seepage rates rates include unmeasured inflows within stream reach

Stream reach not surveyed during the 

seepage run

Seepage-run discharge-measurement 

site—Labeled with map ID and discharge in ft3/s. Site with map ID starting with “P” 

is a partial-record site

Main stream channel

Ditch—(-) diversion of flow or (+) return flowSite from another seepage run

EXPLANATION

G8 (4.41)

G2 (-1.91)

+5.2 (2.62)

200

159°20' 159°40'

22°10'

22°00'

Map area

KAUA‘I

Figure 15. Map of measurement sites and results for the October 1996 seepage run on Nāwiliwili Stream, Kaua‘i, Hawai‘i.
Results and Discussion

considered in the calculation of seepage loss; therefore, the 

indicated seepage loss may be underestimated. The measured 

gain in the upper reach was most likely from groundwater 

discharge from the thickly saturated hydrogeologic setting. 

Downstream from site G9, the stream was either inaccessible 

or unmeasurable owing to the surrounding vegetation of the 

stream channel. Flow was observed in the stream about 0.9 mi 

upstream from the stream mouth during the seepage run. 

The 1996 seepage run (fig. 15) consists of five measurement 

sites located between altitudes of about 140 and 230 ft, with 

flows in the main stream channel ranging from 0.51 to 4.41ft3/s

The seepage run was conducted under diverted conditions and 

the magnitude of measured gains in the upper stream reach 

between sites P9 and G5 is substantially lower than that from the 

2019 seepage run. Seepage gains were measured in the lower 

stream reach between sites G5 and G8 during the 1996 seepage 

run, although potential unmeasured tributary flow may have 

contributed to the apparent gain in this reach. No substantial net 

gain or loss was measured in the same stream reach during the 

2019 seepage run.

To determine flow continuity from mauka to makai on 

Nāwiliwili Stream, the seepage rate of –1.1 (ft3/s)/mi in the stream 

reach between sites G8 and G9 for the 2019 seepage run was 

extrapolated to the 1.9-mi stream reach downstream from the 

measured reach for the seepage run, with a computed seepage loss 

of 2.09 ft3/s within this reach. This loss would be less than the flow 

of 5.01 ft3/s measured at site G9; therefore, with this assumption 

and under flow conditions of the seepage-run measurements, 

Nāwiliwili Stream flows continuously from an altitude of about 

230 ft (P9) to the ocean under natural-flow conditions.

Hulē‘ia Stream

Discharge measurements from two seepage runs are 

available to characterize seepage gains and losses in selected 

reaches on Hulēʻia Stream. The November 14, 2019, seepage 

run (fig. 16) was conducted during conditions when long-term 

station 16068000 was flowing at about a Q65 discharge (daily 

mean of 22.5 ft3/s, table 2). The October 8, 1996, seepage 

run (fig. 17) was conducted during conditions when station 

16068000 was flowing at about a Q62 discharge (daily mean of 

24.0 ft3/s, table 2). Both seepage runs were conducted under 

diverted-flow conditions; flows in the upper tributaries were 

diverted by several interconnected ditches. No dry reaches in 

the main stream channel were observed during the seepage runs. 

The 2019 seepage run (fig. 16) consists of six measurement 

sites located between altitudes of about 240 and 480 ft, with flows 

in the main stream channel ranging from 17.3 to 24.6 ft3/s. The 

1996 seepage run (fig. 17) consists of nine measurement sites 

located between altitudes of about 30 and 550 ft, with flows in 

the main stream channel ranging from 1.33 to 10.6 ft3/s. Results 

of both seepage runs indicate a generally gaining stream in the 

measured reaches. Discharge measurements collected during 

the 2019 seepage run indicate a gain of 6.3 ft3/s in the 2.7-mi 

measured reach between sites H6 and H9; however, three minor 

tributaries––collectively 0.65 mi2 or less than 2 percent of the 

Hulēʻia drainage area––were not measured during the seepage 

run. Discharge measurements collected during the 1996 seepage 

run indicate a generally gaining stream between sites H2 and 

H12, although potential unmeasured tributary flows may have 

contributed to the apparent gain in some reaches. Measured gains 

were most likely from groundwater discharge from the thickly 

saturated hydrogeologic setting.

Extrapolation of seepage rates to the downstream 

unmeasured reach for determining flow continuity from mauka 

to makai would assume that the downstream unmeasured 

stream reach is also gaining. With this assumption, and under 

the flow conditions of the seepage runs, Hulēʻia Stream flows 

continuously from site H2 to the ocean under natural-flow 

conditions.

Waikomo Stream

A seepage run was conducted on January 22, 2020, on 

Waikomo Stream as part of this study (fig. 18) with no available 

discharge measurements from previous seepage runs. The 

seepage run was conducted during conditions when long-term 

station 16068000 was flowing at above the median discharge 

(daily mean of 37.4 ft3/s, table 2). The seepage run consists 

of five measurement sites located between altitudes of about 

40 and 210 ft, with flows in the main stream channel ranging 

from 15.5 to 18.8 ft3/s. During the seepage run, flow in the 

upper tributaries was diverted by several ditches and flow from 

Waita Reservoir (fig. 5) was discharged to Waikomo stream 

downstream from site I1. A golf course located near site I3 

diverted streamflow (measured at site I4) to maintain water level 

in a pond within the golf course. According to a representative 

of the golf course, all of the diverted flow was returned to the 

stream about 800 ft downstream from the diversion intake. 

Unfortunately, the return flow could not be quantified owing 

to lack of a usable discharge-measurement section; the return 

flow was discharged vertically upward through a pipe partly 

covered with boulders in the stream to mimic a small waterfall 

on the left streambank. Discharge measurements indicate a net 

loss in the 1-mi reach upstream from the golf course diversion. 

The measured loss most likely discharged to the underlying 

freshwater-lens hydrogeologic setting.

To determine flow continuity from mauka to makai on 

Waikomo Stream, the seepage rate of –0.1 (ft3/s)/mi in the stream 

reach between sites I3 and I5 was extrapolated to the 0.2-mi 

stream reach downstream from the measured seepage-run reach, 

with a computed seepage loss of 0.02 ft3/s within this reach. The 

lower unmeasured reach of Waikomo Stream is within the same 

hydrogeologic setting as the measured reach––a freshwater-lens 

setting (fig. 4) where the groundwater level is below stream 

altitude and the stream typically discharges to the groundwater 

body––which suggests that the lower unmeasured reach is most 

likely a losing reach. With this assumption, and under the flow 

conditions of the seepage run, which includes a substantial amount 

of flow contribution from Waita Reservoir, Waikomo Stream flows 

continuously from site I2 to the ocean. A seepage run conducted 

under lower flow conditions is needed to determine whether 
44

Low-Flow Characteristics of Streams from Wailua to Hanapēpē, Kaua‘i, Hawai‘

men20-4010_fig16

100

200

300

400

600 800

1000

1400

1800

2200

2600

400

600

600

800

1000

2200

P11

P12

P13

P14

159°22'

159°26'

159°30'

22°00’

21°58'

21°56'

H9 (0.96)

H4 (0.43)

H7 (0.01) H6 (17.3)

H5 (0)

H11 (24.6)

+2.3 (6.3)

Hulē‘ia Stream

0

2 1 KILOMETERS

2 1 MILES

0

Base modified from U.S. Geological Survey digitaldata. Universal Transverse Mercator projection,zone 4, North American Datum 1983.

Map IDH4H5H6H7H9H11P11P12P13P14

Station number21574915927190121574415926290121574215926310121574215926070121570415925280116055000215853159281801215851159273901215822159282601215751159283901

Station name, Kauai, HIWeoweopilau Str at Kahili RdTrib to Huleia Str nr Halfway BridgeHuleia Stream near Halfway BridgeHalenanahu Str .4mi US Huleia conflPuakukui Str 620ft US Huleia StrHuleia Str nr LihuePaohia Str US Koloa DitchKamooloa Str US Papuaa Res intakeKuia Str 0.7 mi W of Papuaa ResKuia Str trib 1 mi SW of Papuaa Res

Station number and name associated with map identifier (ID)[Str, Stream; Rd, Road; trib, Tributary; nr, near; mi, mile; US, upstream; confl, confluence; ft, feet; Res, Reservoir; W, west; SW, southwest. Database limitations preclude the use of Hawaiian diacritical marks in USGS station names]

Line of equal altitude relative to mean sea 

level, in feet—Contour interval varies

Hydrologic-unit boundary—From State of 

Hawai'i (2017a)

Diversion systemMeasured seepage run stream reach

—

Net seepage gain (+) or loss (-) in cubic feet per second (ft3/s) per mile and total 

seepage gain or loss, in ft3/s (shown in 

parentheses), for stream reach between two main stream channel sites. Dashed where seepage rates include unmeasured inflows within stream reach

Stream reach not surveyed during the 

seepage run

Partial-record site—Labeled with map IDSeepage-run discharge-measurement 

site—Labeled with map ID and discharge in ft3/s

Main stream channelTributary to main streamSite from another seepage run

EXPLANATION

H6 (17.3)

H5 (0)

+2.3 (6.3)

200

P11

159°20' 159°40'

22°10'

22°00'

Map area

KAUA‘I

Hulē‘ia Stream—November 14, 2019, seepage-run results

Figure 16. Map of measurement sites and results for the November 2019 seepage run on Hulē‘ia Stream, Kaua‘i, Hawai‘i.
Results and Discussion

men20-4010_fig17

100

200

300

400

600 800

1000

1400 1800 2200

2600

400 600

600

800

1000

2200

P11

P12

P13

P14

159°22'

159°26'

159°30'

22°00’

21°58'

21°56'

H10 (0.25)

H8 (4.95)

H2 (1.33)

H1 (0.57)

H3 (3.08)

H7 (0.07)

H6 (4.24)

H11 (6.34)

H12 (10.6)

+0.4 (0.64) +2.0 (4.3)

+1.1 (1.14)

+1.9 (1.75) +0.8 (1.16)

Hulē‘ia Stream

0

2 1 KILOMETERS

2 1 MILES

0

Base modified from U.S. Geological Survey digitaldata. Universal Transverse Mercator projection,zone 4, North American Datum 1983.

Map IDH1H2H3H6H7H8H10H11H12P11P12P13P14

Station number21574015928130121573815928050121575315927260121574215926310121574215926070121571815925330121570215925340116055000215635159235101215853159281801215851159273901215822159282601215751159283901

Station name, Kauai, HILeft trib Huleia .35mi DS Koloa DitchHuleia Str below confl with Kuia StrHuleia Stream at Kahili RoadHuleia Stream near Halfway BridgeHalenanahu Str .4mi US Huleia conflHuleia Stream blw Aakukui RoadPuakukui Str .25mi US conf w Huleia StrHuleia Str nr LihueHuleia Stream at Haiku RoadPaohia Str US Koloa DitchKamooloa Str US Papuaa Res intakeKuia Str 0.7 mi W of Papuaa ResKuia Str trib 1 mi SW of Papuaa Res

Station number and name associated with map identifier (ID)[trib, tributary; mi, mile; DS, downstream; Str, Stream; confl, confluence; US, upstream; blw, below; conf, confluence; w, with; nr, near; Res, Reservoir; W, west; SW, southwest. Database limitations preclude the use of Hawaiian diacritical marks in USGS station names]

Line of equal altitude relative to mean sea 

level, in feet—Contour interval varies

Hydrologic-unit boundary—From State of 

Hawai'i (2017a)

Diversion systemMeasured seepage run stream reach—

Net seepage gain (+) or loss (-) in cubic feet per second (ft3/s) per mile and total 

seepage gain or loss, in ft3/s (shown in 

parentheses), for stream reach between two main stream channel sites. Dashed where seepage rates include unmeasured inflows within stream reach

Stream reach not surveyed during the 

seepage run

Partial-record site—Labeled with 

map ID

Seepage-run discharge-measurement 

site—Labeled with map ID and discharge in ft3/s

Main stream channelTributary to main streamSite from another seepage run

EXPLANATION

H2 (1.33)

H1 (0.57)

+1.9 (1.75)

200

P11

Hulē‘ia Stream—October 8, 1996, seepage-run results 159°20' 159°40'

22°10'

22°00'

Map area

KAUA‘I

Figure 17. Map of measurement sites and results for the October 1996 seepage run on Hulē‘ia Stream, Kaua‘i, Hawai‘i.
46

Low-Flow Characteristics of Streams from Wailua to Hanapēpē, Kaua‘i, Hawai‘

men20-4010_fig18

0

0.5 KILOMETER 1

0.5 1 MILE

0

Base modified from U.S. Geological Survey digital

data. Universal Transverse Mercator projection,

zone 4, North American Datum 1983.

100

200

300

400

500

600

700

800

900

1000

1400

P15

P16

I1 (+5.76)

I2 (18.8)

I3 (15.6)

I5 (15.5)

-3.2 (-3.2)

-0.1 (-0.1a

)

I4 (-2.06)

Waikomo Stream

159°27'

159°28'

159°29'

159°30'

21°57

21°56'

21°55'

21°54'

21°53'

Map ID

I1

I2

I3

I4

I5

P15

P16

Station number

215421159280101

215414159280201

215335159275501

215258159280301

215336159275501

215608159285801

215538159292301

Station name, Kauai, HI

Waita Res spillway at Maluhia Rd

Waikomo Stream at Koloa Rd

Waikomo Stream 1mi US mouth

Golf course div on Waikomo Str

Waikomo Stream at Poipu Rd

Omao Stream at Kaumualii Hwy

Poeleele Stream at Kaumualii Hwy

Station number and name associated with map identifier (ID)

[Res, Reservoir; Rd, Road; mi, mile; US, upstream; div, diversion; Str, Stream; 

Hwy, Highway. Database limitations preclude the use of Hawaiian diacritical 

marks in USGS station names]

Line of equal altitude relative to mean 

sea level, in feet—Contour interval 

varies

Hydrologic-unit boundary—From State 

of Hawai'i (2017a)

Diversion system

Measured seepage run stream reach—

Net seepage gain (+) or loss (-) in 

cubic feet per second (ft3

/s) per mile 

and total seepage gain or loss, in ft3

/s 

(shown in parentheses), for stream 

reach between two main stream 

channel sites

a

Diverted water at site I4 was 

assumed to be returned upstream of 

site I5.

Stream reach not surveyed during the 

seepage run

Partial-record site—Labeled with 

map ID

Seepage-run discharge-measurement 

site—Labeled with map ID and 

discharge in ft3

/s

Main stream channel

Ditch—(-) diversion of flow or (+) return 

flow

EXPLANATION

I2 (18.8)

I1 (+5.76)

-3.2 (-3.2)

200

P15

159°40' 159°20'

22°10'

22°00'

Map area

KAUA‘I

Waikomo Stream—January 22, 2020, seepage-run results

Figure 18. Map of measurement sites and results for the January 2020 seepage run on Waikomo Stream, Kaua‘i, Hawai‘i
Results and Discussion

Waikomo Stream flows continuously when flow contributions 

from Waita Reservoir are reduced.

Lāwa‘i Stream

Discharge measurements from two seepage runs are available 

to characterize seepage gains and losses in selected reaches of 

Lāwaʻi Stream. The September 19, 2019, seepage run (fig. 19) 

was conducted during conditions when discharge measured at 

short-term station 16052400 (J1) was flowing at 0.52 ft3/s, which 

is about a Q90 discharge (station 16052400 in table 2). Discharges 

measured at sites J4 and J14 during the seepage runs indicate that 

results from 2019 are representative of lower flow conditions 

than those from the October 7, 1996, seepage run (fig. 20). Both 

seepage runs were conducted under diverted-flow conditions; flow 

in Lāwaʻi Stream was diverted by the Lāwaʻi Intake Ditch near an 

altitude of about 590 ft. 

The 2019 seepage run consists of 12 measurement sites 

located between altitudes of about 40 to 600 ft, with flows in 

the main stream channel ranging from 0.08 to 0.52 ft3/s. Results 

from the seepage run indicate a generally gaining stream in the 

3.7-mi reach downstream from Lāwaʻi Intake Ditch (J3). Flow 

contribution from major tributaries to the stream was considered 

in the calculation of seepage gains and losses for the 2019 seepage 

run. The 1996 seepage run consists of four measurement sites 

located between altitudes of about 40 to 590 ft, with flows in 

the main stream channel ranging from 0.67 to 1.15 ft3/s. Flow 

contribution from spring input at site J12 was not considered 

during the 1996 seepage run; thus, the actual seepage gain is less 

than computed.

To determine flow continuity from mauka to makai on 

Lāwaʻi Stream, the seepage rate of 0.03 (ft3/s)/mi in the stream 

reach between sites J13 and J14 for the 2019 seepage run was 

extrapolated to the 0.9-mi stream reach downstream from the 

measured reach for the seepage run as both reaches are in a similar 

hydrogeologic setting. Seepage-run discharge measurements 

indicate that under flow conditions of the seepage-run discharge 

measurements, Lāwaʻi Stream flows continuously from site J1 

(station 16052400) to the ocean under natural-flow conditions.

Wahiawa Stream

Two seepage runs were conducted on Wahiawa Stream 

as part of this study (fig. 21) with no available discharge 

measurements from previous seepage runs. The November 12, 

2019, seepage run was conducted during conditions when 

discharge measured at the partial-record site (P17) was 

flowing at 1.85 ft3/s, which is about a Q90 discharge (table 5). 

The seepage run consists of seven measurement sites located 

between altitudes of about 220 and 1,720 ft, with flows in the 

main stream channel ranging from 0.06 to 2.39 ft3/s. During 

the seepage run, streamflow was unstable while collecting 

measurements at sites K6 and K7; thus, repeat discharge 

measurements were collected at these sites on January 24, 

2020, to determine gains and losses in the lower 1.3-mi reach.

The headwaters of Wahiawa Stream discharge into Alexander 

Reservoir and discharge at site K4 represented leakage from 

the reservoir into the stream. The 2020 seepage run was 

conducted during conditions when flow was released from 

the reservoir into the stream upstream from site K6. Stage 

measurements recorded during the time the two discharge 

measurements were collected indicate stable-flow conditions. 

Results from the 2019 and 2020 seepage runs indicate net 

gains in the 0.3-mi reach upstream from the reservoir and the 5.1-mi 

reach downstream from the reservoir. The reach downstream of site 

K6 to the coast is in a uniform hydrogeological setting (Izuka and 

others, 2018), and the seepage rate between sites K6 and K7 was 

used to characterize the seepage rate downstream of site K7 to the 

coast. Seepage-run discharge measurements indicate that under the 

flow conditions of the seepage run, including flow regulation by 

Alexander Reservoir, Wahiawa Stream flows continuously from site 

K4 to the ocean.

Hanapēpē River

Discharge measurements from two seepage runs are available 

to characterize seepage gains and losses on selected reaches of 

Hanapēpē River. The September 21, 2017, seepage run (fig. 22) 

was conducted under conditions when discharge measured at site 

L4 was 48.0 ft3/s, which is about a Q75 discharge (station 16049000 

in table 2). The October 10, 1996, seepage run (fig. 23) was 

conducted under conditions when discharge measured at site L4 

was 17.7 ft3/s, which is below a Q95 discharge (station 16049000 

in table 2). Both seepage runs were conducted under divertedflow conditions; flow in the upper tributaries was diverted by the 

Kōʻula Ditch stream-diversion intakes during the 1996 seepage run 

and flow in the lower reaches was diverted by the Farmers Ditch 

stream-diversion intake during both seepage runs. 

The 2017 seepage run (fig. 22) consists of eight 

measurement sites located between altitudes of about 10 

to550ft, with flows in the main stream channel ranging f

20.8 to 48.0 ft3/s. Measured discharges from the seepage run 

indicate a generally gaining stream in the upper 3.3-mi reach 

between the confluence of left and right branch Kōʻula Rivers 

(L1 and L2) and continuous station 16049000 (L4), with several 

tributaries possibly contributing to some of the measured gain 

within this reach. This upper stream reach is situated within a 

dike-impounded-groundwater setting where the stream generally 

gains flow from groundwater discharge. The lower 3.5-mi reach 

between continuous station 16049000 (L4) and about 1.7m

upstream from the stream mouth (L11) generally lost flow. 

Measured losses in the lower reach are within the measurementerror bounds (see Limitations of Approach section). The 1996 

seepage run (fig. 23) consists of seven measurement sites 

located between altitudes of about 20 to 220 ft, with flows in the 

main stream channel ranging from 1.39 to 19.9 ft3/s. Measured 

discharges from the seepage run indicate a net gain in the lower 

2.3-mi reach between continuous station 16049000 (L4) and 

L5 and in the 1-mi reach between sites L8 and L12, and a net 

loss in the 0.5-mi reach between sites L5 and L8, which may be 

attributed to an unmeasured diversion within this reach. 
48

Low-Flow Characteristics of Streams from Wailua to Hanapēpē, Kaua‘i, Hawai‘

men20-4010_fig19

0

0.5 KILOMETER 1

0.5 1 MILE

0

Base modified from U.S. Geological Survey digital

data. Universal Transverse Mercator projection,

zone 4, North American Datum 1983.

100

200

300

400

500

600

700

800

900

1000

1200 1400

1600

1800

2000

700

900

800

700

J1a (0.52) J2 (0.14)

J3 (-0.67) J4 (0.08)

J5 (0.12)

J8 (0.16)

J9 (0.16) J10 (0)

J12 (0.03) J11 (0.18)

J13 (0.20)

J14 (0.23)

+0.06 (0.04)

+0.04 (0.04)

0 (0.00)

+0.03 (0.03)

+0.33 (0.02)

-0.11 (-0.01)

+0.64 (0.09)

Lāwa‘i Intake Ditch

21°58'

21°56'

21°54'

159°30'

159°31'

Map ID

J1

J2

J3

J4

J5

J8

J9

J10

J11

J12

J13

J14

Station number

16052400

215614159303101

215610159302901

215609159302901

215544159302901

215508159301701

215436159303101

215436159303201

215434159303401

215433159303701

215431159303601

16052500

Station name, Kauai, HI

RB Lawai Stream 300ft US of fork

Lawai trib US Lawai Ditch

Lawai Ditch intake on Lawai Str

Lawai Str DS Lawai Ditch intake

Lawai Str .2mi US Kaumualii Hwy

Lawai Str .7 mi DS Kaumualii Hwy

Lawai Str .1 mi US spring input trib

Lawai trib .8 mi DS Waha Rd

Lawai Str US spring input

Trib with spring input to Lawai Str

Lawai Str near NTBG

Lawai Str nr Koloa

Station number and name associated with map identifier (ID)

[RB, Right Branch; ft, feet; US, upstream; trib, tributary; Str, Stream; DS, downstream; mi, 

mile; Hwy, Highway; Rd, Road; NTBG, National Tropical Botanical Garden; nr, near. Database 

limitations preclude the use of Hawaiian diacritical marks in USGS station names]

Line of equal altitude relative to mean sea 

level, in feet—Contour interval varies

Hydrologic-unit boundary—From State of 

Hawai'i (2017a)

Diversion system

Measured seepage run stream reach—

Net seepage gain (+) or loss (-) in cubic feet 

per second (ft3

/s) per mile and total seepage 

gain or loss, in ft3

/s (shown in parentheses), 

for stream reach between two main stream 

channel sites

Stream reach not surveyed during the 

seepage run

Seepage-run discharge-measurement site—

Labeled with map ID and discharge in ft3

/s a

Streamgaging station 16052400 with 

flow-duration discharge estimates in table 2

Main stream channel

Tributary to main stream

Ditch—(-) diversion of flow or (+) return flow

Site from another seepage run

EXPLANATION

J1 (0.52)

J2 (0.14)

J3 (-0.67)

+0.06 (0.04)

200

159°40' 159°20'

22°10'

22°00'

Map area

KAUA‘I

Lāwa‘i Stream—September 19, 2019, seepage-run results

Lāwa‘i Stream

Figure 19. Map of measurement sites and results for the September 2019 seepage run on Lāwa‘i Stream, Kaua‘i, Hawai‘i.
Results and Discussion

men20-4010_fig20

0

0.5 KILOMETER 1

0.5 1 MILE

0

Base modified from U.S. Geological Survey digital

data. Universal Transverse Mercator projection,

zone 4, North American Datum 1983.

100

200

300

400

500

600

700

800

900

1000

1200 1400

1600

1800

2000

700

900

800

700

J4 (0.68)

J14 (1.15)

-0.01 (-0.01)

+0.1 (0.26)

J6 (0.67)

J7 (0.22)

J1a

Lāwa‘i Intake Ditch

21°58'

21°56'

21°54'

159°30'

159°31'

Map ID

J1

J4

J6

J7

J14

Station number

16052400

215609159302901

215535159303101

215514159304901

16052500

Station name, Kauai, HI

RB Lawai Stream 300ft US of fork

Lawai Str DS Lawai Ditch intake

Lawai Str at Kaumualii Hwy

Lawai trib on Lauoho Rd

Lawai Str nr Koloa

Station number and name associated with map identifier (ID)

[RB, Right Branch; ft, feet; US, upstream; Str, Stream; DS, downstream; Hwy, 

Highway, trib, tributary; Rd, Road; nr, near. Database limitations preclude the use of 

Hawaiian diacritical marks in USGS station names]

Line of equal altitude relative to mean sea 

level, in feet—Contour interval varies

Hydrologic-unit boundary—From State of 

Hawai'i (2017a)

Diversion system

Measured seepage run stream reach—

Net seepage gain (+) or loss (-) in cubic feet 

per second (ft3

/s) per mile and total seepage 

gain or loss, in ft3

/s (shown in parentheses), 

for stream reach between two main stream 

channel sites. Dashed where seepage rates 

include unmeasured inflows within stream 

reach

Stream reach not surveyed during the 

seepage run

Seepage-run discharge-measurement site—

Labeled with map ID and discharge in ft3

/s a

Streamgaging station 16052400 with 

flow-duration discharge estimates in table 2

Main stream channel

Tributary to main stream

Site from another seepage run

EXPLANATION

J4 (0.68)

J7 (0.22)

+0.1 (0.26)

200

159°40' 159°20'

22°10'

22°00'

Map area

KAUA‘I

Lāwa‘i Stream—October 7, 1996, seepage-run results

Lāwa‘i Stream

Figure 20. Map of measurement sites and results for the October 1996 seepage run on Lāwa‘i Stream, Kaua‘i, Hawai‘i.
50

Low-Flow Characteristics of Streams from Wailua to Hanapēpē, Kaua‘i, Hawai‘

men20-4010_fig21

100

200

300

400

500

600

700

800

900

1000

1200

1400

1600 1800

2000

2200

2400

2600

2800

K5 (0.07b)

K4 (0.06b

)

P18 (0.11b

)

P17 (1.85b

)

K3 (2.39b

)

K6 (0.28b

, 7.91c)

K7 (1.52b

, 8.38c)

+1.4 (0.43)

+0.04 (0.15)

+0.4 (0.47a

)

Alexander Reservoir

Wahiawa

Stream

21°58'

21°56'

21°54'

159°30'

159°32'

159°34'

Map ID

P17

P18

K3

K4

K5

K6

K7

Station number

215751159311801

215754159311601

215745159311901

215723159314801

215723159314901

215518159325601

215438159334401

Station name, Kauai, HI

Wahiawa Stream US Alexander Res

LB Wahiawa Str 400 ft US Alexander Res

Wahiawa Str .13mi DS conf w LB

Wahiawa Str .38 mi DS Alexander Res

Wahiawa tributary DS Alexander Res

Wahiawa Str at Kaumualii Hwy

Wahiawa Str .8mi US Halewili Rd

Station number and name associated with map identifier (ID)

[US, upstream; Res, Reservoir; LB, Left Branch; Str, Stream; ft, feet; mi, mile; 

DS, downstream; conf, confluence; w, with; Hwy, Highway; Rd, Road. Database 

limitations preclude the use of Hawaiian diacritical marks in USGS station 

names]

0

1 2 KILOMETERS

1 2 MILES

0

Base modified from U.S. Geological Survey digital

data. Universal Transverse Mercator projection,

zone 4, North American Datum 1983.

159°40' 159°20'

22°10'

22°00'

Map area

KAUA‘I

Wahiawa Stream—November 12, 2019, and January 24, 2020, seepage-run results

Line of equal altitude relative to mean sea 

level, in feet—Contour interval varies

Hydrologic-unit boundary—From State of 

Hawai'i (2017a)

Diversion system

Measured seepage run stream reach—

Net seepage gain (+) or loss (-) in cubic feet 

per second (ft3

/s) per mile and total seepage 

gain or loss, in ft3

/s (shown in parentheses), 

for stream reach between two main stream 

channel sites

a

January 24, 2020, discharges used in 

calculation

Stream reach not surveyed during the 

seepage run

Seepage-run discharge-measurement site—

Labeled with map ID and discharge in ft3

/s. 

Site with map ID starting with “P” is a 

partial-record site

b

Discharge measured on November 12, 2019

c

Discharge measured on January 24, 2020

Main stream channel

Tributary to main stream

EXPLANATION

K4 (0.06)

K5 (0.07)

+1.4 (0.43)

200

Figure 21. Map of measurement sites and results for the November 2019 and January 2020 seepage run on Wahiawa Stream, Kaua‘i, Hawai‘i.
Results and Discussion

men20-4010_fig22

0

21 KILOMETERS

1 2 MILES

0

Base modified from U.S. Geological Survey digital

data. Universal Transverse Mercator projection,

zone 4, North American Datum 1983.

200

400

600

800

1000

1400

1800

2200

2600

3000

3400

3800

4200

1800

1400

1000

L1 (24.7)

L2 (13.6)

L3 (0.05)

L10 (-25.8)

L7 (+0.04)

L6 (-0.19)

L4a

 (48.0)

L11 (20.8)

Kō‘ula Ditch

Farmers Ditch

+2.9 (9.6)

-0.3 (-1.2)

Hanapēpē River

22°20'

22°00'

21°58'

21°56'

21°54'

159°30'

159°32'

159°34'

Map ID

L1

L2

L3

L4

L6

L7

L10

L11

Station number

215921159314101

215916159313701

16048000

16049000

215523159333701

215519159335101

215515159335901

215501159342801

Station name, Kauai, HI

RB Koula River US Koula Ditch

LB Koula River DS Manawaiopuna Falls

Manuahi Str at Koula nr Eleele

Hanapepe Riv blw Manuahi Str nr Eleele

Palama intake from Hanapepe River

Palama Ditch return 1 to Hanapepe Rv

Ditch before split to Farmers and Pump 3

Hanapepe River nr Kapa Reservoir

Station number and name associated with map identifier (ID)

[RB, Right Branch; US, upstream; LB, Left Branch; DS, downstream; Riv, River; blw, 

below; Str, stream; nr, near; Rv, River. Database limitations preclude the use of 

Hawaiian diacritical marks in USGS station names]

Line of equal altitude relative to mean sea 

leve, in feet—Contour interval varies

Hydrologic-unit boundary—From State of 

Hawai'i (2017a)

Diversion system

Measured seepage run stream reach—

Net seepage gain (+) or loss (-) in cubic 

feet per second (ft3

/s) per mile and total 

seepage gain or loss, in ft3

/s (shown in 

parentheses), for stream reach between 

two main stream channel sites. Dashed 

where seepage rates include 

unmeasured inflows within stream reach

Stream reach not surveyed during the 

seepage run

Seepage-run discharge-measurement 

site—Labeled with map ID and 

discharge in ft3

/s a

Natural flow-duration discharge 

estimates in table 2

Main stream channel

Tributary to main stream

Ditch—(-) diversion of flow 

or (+) return flow

Site from another seepage run

EXPLANATION

L4 (48.0)

L2 (13.6)

L6 (-0.19)

+2.9 (9.6)

200

159°40' 159°20'

22°10'

22°00' Map area

KAUA‘I

Hanapēpē River—September 21, 2017, seepage-run results

Figure 22. Map of measurement sites and results for the September 2017 seepage run on Hanapēpē River, Kaua‘i, Hawai‘i.
52

Low-Flow Characteristics of Streams from Wailua to Hanapēpē, Kaua‘i, Hawai‘

men20-4010_fig23

0

1 KILOMETERS 2

1 2 MILES

0

Base modified from U.S. Geological Survey digital

data. Universal Transverse Mercator projection,

zone 4, North American Datum 1983.

200

400

600

800

1000

1400

1800

2200

2600

3000

3400

3800

4200

1800

1400

1000

L4a (17.7)

L5 (19.9)

L8 (1.39)

L9 (-16.4)

L13 (0.16)

L14 (0.13) L12 (1.64)

+1.0 (2.2)

-4.2 (-2.1)

+0.2 (0.25)

Kō‘ula Ditch

Farmers Ditch

Hanapēpē River

22°20'

22°00'

21°58'

21°56'

21°54'

159°30'

159°32'

159°34'

Map ID

L4

L5

L8

L9

L12

L13

L14

Station number

16049000

215532159333201

215519159335501

215518159335501

215459159344601

215502159345801

215456159350001

Station name, Kauai, HI

Hanapepe Riv blw Manuahi Str nr Eleele

Hanapepe Riv US Palama intake

Hanapepe Riv DS Farmers Ditch intake

Farmers Ditch from Hanapepe Riv

Hanapepe Riv 250 ft DS Pump 1 Ditch

Kapahili Gl at Farmers Ditch

Kapahili Gl US Hanapepe Riv conf

Station number and name associated with map identifier (ID)

[Riv, River; blw, below; Str, Stream; nr, near; US, upstream; DS, downstream; ft, feet; 

Gl, Gulch; conf, confluence. Database limitations preclude the use of Hawaiian 

diacritical marks in USGS station names]

Line of equal altitude relative to mean sea 

level, in feet—Contour interval varies

Hydrologic-unit boundary—From State of 

Hawai'i (2017a)

Diversion system

Measured seepage run stream reach—

Net seepage gain (+) or loss (-) in cubic 

feet per second (ft3

/s) per mile and total 

seepage gain or loss, in ft3

/s (shown in 

parentheses), for stream reach between 

two main stream channel sites. Dashed 

where seepage rates include 

unmeasured inflows within stream reach

Stream reach not surveyed during the 

seepage run

Seepage-run discharge-measurement 

site—Labeled with map ID and 

discharge in ft3

/s a

Natural flow-duration discharge 

estimates in table 2

Main stream channel

Tributary to main stream

Ditch, (-) diversion of flow 

or (+) return flow

Site from another seepage run

EXPLANATION

L4 (17.7)

L13 (0.16)

L9 (-16.4)

+1.0 (2.2)

200

159°40' 159°20'

22°10'

22°00' Map area

KAUA‘I

Hanapēpē River—October 10, 1996, seepage-run results

Figure 23. Map of measurement sites and results for the October 1996 seepage run on Hanapēpē River, Kaua‘i, Hawai‘i.
Limitations of Approach 53

To determine flow continuity from mauka to makai 

on Hanapēpē River, the seepage rate of 0.2 (ft3/s)/mi in the 

stream reach between sites L8 and L12 for the 1996 seepage 

run was extrapolated to the 1.3-mi stream reach downstream 

from the measured reach for the seepage run, with a computed 

gain of 0.26 ft3/s within this reach. The 1996 seepage rate 

between sites L8 and L12 was used to determine flow 

continuity because it considered all inflows and outflows 

within the measured reach. The reach downstream of site L12 

to the coast is in a uniform hydrogeological setting (Izuka 

and others, 2018), and the seepage rate between sites L8 and 

L12 was used to characterize the seepage rate downstream of 

site L12 to the coast. Seepage-run discharge measurements 

indicate that under the flow conditions of the seepage run, 

Hanapēpē River flows continuously from the Kōʻula Ditch 

level to the ocean under natural-flow conditions. Under 

diverted-flow conditions, when the Kōʻula Ditch intakes divert 

all low flows in the river, the river may run dry downstream 

from the intakes. The length of this potentially dry reach is 

assumed to be relatively short because available records (water 

years 1918–20, 1928–2019) at continuous station 16049000 

(L4) indicate the river was not dry during the time the gage 

was in operation and the lowest flow recorded was 5.3 ft3/s.

Limitations of Approach

Low-flow duration discharges at partial-record sites in 

the study area were estimated with MOVE.1 and graphical 

record-augmentation techniques. For this study, the accuracy of 

the estimates was largely dependent on (1) the strength of the 

correlation between concurrent discharges at the index stations 

and partial-record sites; (2) the number of discharge measurements 

at the partial-record sites that were available for use in record 

augmentation and the range of flow conditions represented by 

the measurements; (3) the accuracy of the individual discharge 

measurements; and (4) the appropriateness of the models used to 

represent low-flow discharges.

Based on the regression diagnostics, the MOVE.1 regression 

models provide accurate low-flow duration-discharge estimates. 

For this study, acceptable values of correlation coefficients (r) 

and modified Nash-Sutcliff coefficients of efficiency (E) are those 

greater than or equal to 0.80 and 0.50, respectively. Coefficients 

of efficiency (E) that indicate the predictive ability of the models 

range from 0.51 to 0.64 and the correlation coefficients (r) range 

from 0.88 to 0.94. For right branch ʻŌpaekaʻa Stream, north fork 

Hanamāʻulu Stream, a branch of Kuʻia Stream, and Hanapēpē 

River, the graphical fits were plotted through as many of the data 

points as possible to accurately represent the correlation between 

concurrent discharges at the index station and partial-record sites. 

The arithmetic plots generally exhibit minimal spread around the 

graphical fits without outliers. 

The MOVE.1 regression models used to estimate low-flow 

duration discharges are generally developed based on 10 or 

more concurrent data points at the index stations and partialrecord sites. Models that are developed based on eight or nine 

concurrent data points––sites P2, P6+P7, and P17 (table 4)––

yielded satisfactory low-flow duration-discharge estimates with r

values greater than or equal to 0.89 and E values greater than or 

equal to 0.55. The graphical models were developed based on 10 

or more concurrent data points at the index stations and partialrecord sites. Most of the discharge measurements used for record 

augmentation at the partial-record sites generally are between 

Q95 to Q40 flow conditions as indicated at the associated index 

stations. Discharge measurements at Q40 flow conditions allow 

for the statistical relations to be defined for the full range of 

low-flow statistics to be estimated. Therefore, the flow-duration 

estimates are considered to be representative of the low-flow 

conditions at the partial-record sites. 

Factors that could contribute to discharge-measurement 

errors include, but are not limited to, the condition of the 

measuring instrument and instrument error, characteristics 

of the measurement cross section, spacing and number of 

observation verticals in a cross section, changing stage during 

the measurement, flow depth and velocity, and environment 

(Rantz and others, 1982, p. 179–180). One of four ratings—

excellent, good, fair, or poor—is assigned to the measurement 

to account for some of the aforementioned factors that could 

potentially affect the accuracy of the measurement, and thus 

provide some measure of quality for the discharge measurement. 

For discharges measured with an ADV, the rating is based on 

the Interpolated Variance Estimator (IVE) computed by the 

measuring equipment. The IVE is an estimator of uncertainty 

based on a statistical analysis of depth and velocity data 

collected during the discharge measurement (Cohn and others, 

2013). Discharge measurements with an IVE value of 2 percent 

or less are generally rated excellent, between 2 and 5 percent 

are rated good, between 5 and 8 percent are rated fair, and 8 

percent or more are rated poor. Errors that result from changing 

flow conditions are not considered by the IVE. Out of more 

than 120 discharge measurements used in record augmentation 

for this study, more than half of the measurements were rated 

good, about a quarter were rated fair, about 16 percent were 

rated excellent, and the remaining were rated poor. Ten of the 

measurements were made during changing stage conditions of 

less than ±0.02 ft; six of these measurements were rated good, 

two rated excellent, one rated fair, and one rated poor. 

Low-flow duration discharges at index stations and partialrecord sites are applicable to the base period over which they 

have been computed. For this study, 59 years of streamflow 

data (water years 1961–2019) were available at the index 

stations. Whether low-flow duration discharges at the index 

stations provide estimates of streamflow characteristics at the 

partial-record sites that are representative of future long-term 

flow conditions is less certain. Low-flow duration discharges 

computed from the base-period record are generally lower than 

those computed from the longer-term record (table 2). At the six 

active long-term continuous-record stream-gaging stations that 

monitored natural flow, trends in annual total-flow and baseflow statistics––Q90, Q70, and Q50 discharges and mean flow––

generally were downward. Trends in mean base flow were 

statistically significant at the 5-percent level of significance 
54

Low-Flow Characteristics of Streams from Wailua to Hanapēpē, Kaua‘i, Hawai‘

for all stations. Whether the downward trends in total flow and 

base flow of streams continue in the future is unknown, owing 

to uncertainties associated with potential climate change and 

watershed response to the changes. Extrapolation of low-flow 

duration discharges to future conditions assumes that the 

hydrologic conditions that occurred during the base period will 

continue in the future.

Seepage gains and losses along selected study-area stream 

reaches were computed as the difference between the upstream 

and downstream discharges, excluding major tributary inflows and 

diversions of water within the reach when measured. Considering 

the potential errors in discharge measurements and that some 

tributary inflows could not be measured owing to inaccessibility, 

the estimated seepage gains and losses may not accurately reflect 

the true gains and losses within a reach. Measured tributary 

inflows and diversions of water introduce additional errors in the 

seepage estimates, and this is especially apparent in the Waiahi 

and ‘Ili‘ili‘ula Streams seepage runs. Direct measurement of 

diverted flow and (or) inflow is preferred when estimating seepage 

gains and losses along a reach. However, that may not always be 

possible owing to lack of a representative discharge-measurement 

section. Where a direct measurement of diverted flow and (or) 

inflow could not be made because of a lack of usable measurement 

section, discharges were measured upstream and downstream of 

the diverted flow and (or) inflow and the difference is the flow of 

interest. Errors associated with each additional measurement made 

during a seepage run to quantify inflows and outflows collectively 

decrease the accuracy of the seepage estimates.

Suggestions for Future Work

Measured discharges at many partial-record sites correlated 

with discharges at the Lāwa‘i short-term station (16052400) 

established for this study. Reactivating the continuous station 

on this stream for the long term would increase the level of 

confidence of the estimated low-flow duration discharges at 

relevant partial-record sites. Continued operation of the Waiahi 

station (16057900) for the long term would increase the accuracy 

of low-flow duration discharges computed for the station and 

those at relevant partial-record sites. Accuracy of low-flow 

duration discharge estimates at the partial-record sites could 

also benefit from additional measurements, especially for North 

Fork Wailua River and Hanamā‘ulu and Wahiawa Streams. 

Discharge measurements are needed at a different measurement 

section on Nāwiliwili Stream that is not affected by random 

ditch-flow releases for estimating natural low-flow characteristics. 

Accessible reaches of Pū‘ali Stream were limited during the study 

period owing to streambank vegetation and streambed material. 

If a usable measurement section on Pū‘ali Stream becomes 

accessible in the future, additional discharge measurements would 

improve the estimates of natural low-flow characteristics at the 

measurement site. Additional natural-flow data at the Hanapēpē 

River continuous-record stream-gaging station that span multiple 

water years would increase accuracy and confidence in the 

estimated low-flow duration discharges at the station.

Seepage runs that were made under diverted-flow 

conditions could be improved by temporarily ceasing diversions 

and conducting the seepage runs during natural-flow conditions. 

However, a temporary halt in the operation of surface-water 

diversions on a stream for the duration of a seepage run is 

logistically challenging to the diverters and poses hardship on 

the surface-water users; therefore, this approach is oftentimes 

impractical. A seepage run conducted under diverted-flow 

conditions requires discharge measurements made to quantify 

diverted flow, which increases uncertainty in computed 

seepage estimates. A seepage run conducted under natural-flow 

conditions minimizes that uncertainty by eliminating the need 

to quantify diverted flows, thereby producing more accurate 

seepage estimates. Changes in diversion practices may occur 

as the State continues to implement interim instream-flow 

standards and temporarily stopping diversion of water for the 

purpose of conducting a seepage run may become more feasible 

in the future. Additional discharge measurements in the lower 

reaches during seepage runs conducted under natural-flow 

conditions could also help to improve the understanding of flow 

continuity to the coast.

Summary and Conclusions

The State of Hawai‘i Commission on Water Resource 

Management establishes instream-flow standards to describe 

flows necessary to protect the public interest in the stream 

with consideration of current and future water uses. Surfacewater resources in an area must be quantified to effectively 

manage water resources for competing uses. The purpose of 

this study was to characterize natural (unregulated) streamflow 

availability under low-flow conditions for selected streams in 

southeast Kaua‘i, Hawai‘i, which include North Fork Wailua 

and South Fork Wailua Rivers; Hanamā‘ulu, Nāwiliwili, 

Pūʻali, Hulēʻia, Waikomo, Lāwaʻi, and Wahiawa Streams; 

and Hanapēpē River. The results of this study can be used by 

water managers to develop technically sound instream-flow 

standards for the study-area streams. 

Low-flow characteristics under natural streamflow conditions 

of the study-area streams were determined by analyzing historical 

and current streamflow data from continuous-record streamgaging stations and miscellaneous sites, and additional data 

collected at partial-record sites. Two short-term continuous-record 

stream-gaging stations that monitored low flows on Waiahi 

and right branch Lāwaʻi Streams were established to serve as 

additional index station options for partial-record sites in the study 

area. A continuous-record stream-gaging station on Hanapēpē 

River monitored natural flow during calendar year 2017 and 

the streamflow record during that period was used to estimate 

low-flow characteristics at the station. Eighteen partial-record 

sites––3 on main streams and 15 on tributary streams––were 

established, mainly upstream from all existing surface-water 

diversions, where discharge measurements were made between 

February 2016 and January 2020. Along with the two short-term 

stations established for this study, all six active continuous-record 
References Cited

stations that monitored natural flow on Kauaʻi––Kawaikōī 

Stream, Wai‘alae Stream, east branch of North Fork Wailua River, 

left branch ‘Ōpaeka‘a Stream, Hālaulani Stream, and Wainiha 

Stream––were considered as potential index stations for estimating 

Q95 (95-percent) to Q50 (median or 50-percent) flow-duration 

discharges using the MOVE.1 and graphical-correlation recordaugmentation techniques.

At the Waiahi short-term continuous-record streamgaging station, the estimated natural Q95 to Q50 discharges 

range from 14 to 25 ft3/s. At the Lāwaʻi short-term 

continuous-record stream-gaging station, the estimated natural 

Q95 to Q50 discharges range from 0.35 to 3.0 ft3/s. At station 

16049000 on Hanapēpē River, low-flow duration discharges 

for the base period range from 42 to 69 ft3/s.

Within the Wailua River basin, the estimated natural Q95

to Q50 discharges at the established partial-record sites range 

from 0.48 to 1.1 ft3/s for right branch ʻŌpaekaʻa Stream, 17 

to 26 ft3/s for North Fork Wailua River, 2.5 to 7.4 ft3/s for the 

confluence of north and south Fork Waikoko Streams, and 

7.3 to 11 ft3/s for ‘Ili‘ili‘ula Stream. Within the Hanamāʻulu 

Stream basin, the estimated natural Q95 to Q50 discharges at the 

established partial-record sites range from 0.96 to 1.6 ft3/s for 

the confluence of north and south fork Hanamāʻulu Streams 

and 0.74 to 1.2 ft3/s for north fork Hanamāʻulu Stream. Within 

the Hulē‘ia Stream basin, the estimated natural Q95 to Q50

discharges at the established partial-record sites range from 1.5 

to 5.0 ft3/s for Pāohia Stream, 4.1 to 11 ft3/s for Kamo‘oloa 

Stream, 3.3 to 5.7 ft3/s for the north tributary Ku‘ia Stream, and 

0.018 to 3.2 ft3/s for the south tributary of Ku‘ia Stream. The 

estimated natural Q95 to Q50 discharges at the established partialrecord site on Wahiawa Stream range from 1.5 to 3.7 ft3/s. 

Upper-bound estimates of low-flow duration discharges 

at partial-record sites on south fork Hanamāʻulu, Hanamāʻulu 

tributary, ʻŌmaʻo, and Pōʻeleʻele Streams were estimated based 

on the highest discharges measured during the study period 

that correspond to the concurrent daily mean discharge at each 

index station that were greater than the median discharge at 

that index station, which were 0.44, 0.40, 0.19, and 0.22 ft3/s, 

respectively. Measured discharges on Nāwiliwili, Pū‘ali, and left 

branch Wahiawa Stream do not correlate with discharges at any 

active long-term continuous-record stream-gaging stations that 

monitored natural flow and therefore flow-duration discharges 

estimates are not available.

The discharge estimates are representative of the 59-year 

base period—water years 1961 to 2019—over which they have 

been computed. Based on the MOVE.1 regression statistics and 

the range of discharges measured at the partial-record sites (which 

included the entire low-flow range of interest), the flow-duration 

discharge estimates at the partial-record sites are considered 

to be accurate and representative of base-period conditions. 

Additional discharge measurements will help to increase the level 

of confidence of the flow-duration discharge estimates at all the 

partial-record sites. Whether low-flow duration discharges at the 

index stations provide estimates of streamflow characteristics 

at the partial-record sites that are representative of future longterm flow conditions is less certain. At the six active long-term 

continuous-record stream-gaging stations that monitored natural 

flow, trends in annual total-flow and base-flow statistics––

Q90, Q70, and Q50 discharges and mean flow––generally were 

downward. Whether the downward trends in total flow and base 

flow of streams will continue in the future is unknown as a result 

of uncertainties associated with potential climate change and 

watershed response to the changes.

Seepage-run discharge measurements together with low-flow 

duration discharge estimates at the partial-record sites can provide 

information on natural streamflow availability in the lower stream 

reaches and indicate whether the streams support mountain-toocean (mauka to makai) flow, which is important for assessing 

the biological potential of a stream to support native stream fauna. 

Seepage-run results from previous studies and from this study were 

analyzed to characterize streamflow gains and losses on selected 

reaches of streams in the study basins. Gaining and losing reaches 

were determined by computing the difference between the upstream 

and downstream discharges, excluding any tributary inflows and 

diversions of water within the reach when measured. Available 

seepage-run measurements show that the study-area streams are 

generally gaining streams in the measured reaches, except for 

Waikomo Stream and the lower reaches of North Fork Wailua River 

and Nāwiliwili Stream. Measured seepage-gain rates that considered 

all inflows and outflows within the measured reaches ranged 

between 0.03 and 24.3 ft3/s per mile of stream reach. Seepage gains 

are presumed to originate mainly from groundwater discharge from 

a thickly saturated hydrogeologic setting for streams in the Wailua 

River, Hanamā‘ulu Stream, Nāwiliwili Stream, and Hulēʻia Stream 

basins, and from a dike-impounded-groundwater hydrogeologic 

setting for streams in the Waikomo Stream, Lāwa‘i Stream, 

Wahiawa Stream, and Hanapēpē River basins. Under the flow 

conditions of the seepage runs, a majority of the study-area streams 

flow continuously from mauka to makai. Where a stream discharges 

into a reservoir––Hanamā‘ulu and Wahiawa Streams––a dry reach 

may occur immediately downstream from the reservoir to the point 

of seepage gain in the stream.

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Manuscript approved November 6, 2020

Edited by Katherine Jacques

Illustration support by JoJo Mangano

Layout by Cory Hurd
ISSN 2328-0328 (online)

https://doi.org/10.3133/sir20205128

Cheng—Low-Flow Characteristics of Streams from Wailua to Hanapēpē, Kaua‘i, Hawai‘i—Scientific Investigations Report 2020–5128