#Data set: Suspended Sediments and Bed Load Sediments

#Location: Kahe Point, Oahu, Hawaii

The Kahe Generating Station is located in a valley between Kahe Point 
and Nanakuli on the Wai`anae coast of the island of O`ahu, approximately 
18 miles west of Honolulu.  The station currently consists of six 
oil-fired, steam electric generation units.

#Time Span: 1976 - 1997 

#Project:

KAHE GENERATING STATION
NPDES MONITORING PROGRAM

The Hawaiian Electric Company Inc. (HECO),
under requirements of National Pollutant Discharge Elimination
System (NPDES) Permit HI0000019, Section C.5

#Abstract: 

HECO annually conducts and reports results of a biological monitoring
program for waters receiving effluent from the Kahe Generating Station,
O'ahu, Hawai'i.

#Data Originator:
 
Environmental Department
Hawaiian Electric Company
P. O. Box 2750
Honolulu, Hawaii  96840

#Historical Overview

The Kahe Generating Station commenced operation in 1963. Since then, 
over 50 reports characterizing the marine environment have been prepared 
for or by HECO. Early consultant reports by Marine Advisors (1964), 
B. K. Dynamics (1971), and URS Research Co. (1973) described the general 
baseline conditions of the Kahe nearshore marine environment. The results 
of these and other studies were summarized in an Environmental Impact 
Assessment prepared by Stearns-Roger, Inc. (1973) for the expansion of 
the Kahe Station to six generating units.

After 1973, HECO's Environmental Department conducted extensive NPDES 
marine monitoring studies to determine the conditions of the Kahe 
nearshore environment during the station's expansion to six generating 
units and the relocation of the Kahe shoreline outfall to its present 
offshore site (Coles and McCain, 1973; Coles and Fukuda, 1975, 1983,
1984; Environmental Department, 1976; McCain, 1977; Coles, 1979, 1980; 
Coles et al., 1981, 1982, 1985, 1986; Fukuda and Oda, 1987; Environmental 
Department, 1988, 1989, 1990, 1991, 1992, 1993 1994 and 1995). Several of 
these reports also document the impacts of major storms on the Kahe 
nearshore environment that occurred in 1980, 1982 and 1992, and the 
subsequent recovery of the storm-damaged areas that are influenced by 
power station operation. These NPDES monitoring reports were submitted 
to the DOH upon completion and are herewith incorporated by reference.

#Methodologies and Discussion

Introduction

The volume of sand and silt entrained and circulated by operation of the 
Kahe Generating Station is an environmental parameter of considerable 
geological and biological importance. Wave-suspended sediments are 
carried in cooling water through the station's condensers and discharged 
from the station's outfall. Sediment entrainment represents a potential 
loss of sand from the littoral system which consequently affects the supply 
of sand available to maintain beach configurations in the area. Biologically, 
deposition of entrained sand off the outfall and the distribution of silt 
suspended in the thermal plume represent potential stressors for benthic 
(bottom-dwelling) organisms, which may have no mechanisms for ridding 
themselves of sediments, or must expend energy to do so. Burial of hard reef 
surfaces by sand and silt diminishes the surface area available for 
recruitment of sessile benthic organisms and eliminates habitat of motile 
benthos and demersal fishes.

HECO has monitored sediment entrainment and throughput related to the 
station's circulating cooling water system since 1977. The startup of 
Kahe Unit 6 resulted in a noticeable increase of annual sediment entrainment 
rates. However, Hurricane Iwa reduced sand levels along the entire Kahe 
reef front in late 1982, and sediment entrainment values have been steadily 
declining since. This is because less sand has been available near the 
intake to be entrained. The following study presents the eighteenth year 
of sediment entrainment monitoring with six Kahe units in operation.

Methods

Two categories of sediment were measured to estimate the total amount of 
sand presently being entrained by the Kahe Generation Station: 1) suspended 
and 2) bed load sediments.

Suspended Sediments

Sediment throughput samples were taken at Units 1-4 and 5-6 discharge 
points within the Kahe outfall transition basin. Samples were collected 
by placing a 0.25-m diameter plankton net directly in the discharge. The 
110 *m mesh plankton net was held approximately 10 m behind the discharge 
ports for at least three minutes at a depth of 0.5 m.  Flow rates determined 
with a General Oceanics digital flow meter were then used to calculate 
the total volumes of water sampled. Samples were collected four times in 1996, 
including two periods of medium to high surf. Pertinent data relating to 
weather and sea conditions were recorded.  Measured amounts of suspended 
sediment were converted to units of ml/m3 by dividing by the total volume 
of seawater sampled. These were then extrapolated to daily throughput 
estimates by multiplying by the volume of cooling water circulated under 
operation of all six generating units (3.257 x 106 m3/day).

Sand throughput calculations were based on wave characteristics determined 
for a typical year at Kahe by Marine Advisors (1964). Since wave action 
directly influences the amount of sand and sediment suspended in the water 
column, percent frequencies of occurrence of summer and winter surf conditions 
were estimated for wave direction and height. Daily sand throughput estimates 
obtained during the current sampling period were categorized under similar 
sea and swell conditions, and correlated to Marine Advisers (1964) seasonal 
frequency-of-occurrence values for respective wave characteristics to determine 
a one-year sand throughput estimate. Where sand throughput data under certain 
wave characteristics were unavailable, average throughput data based on 
historical information were used in the calculations.

Bed Load Sediments

Much of the sediment entrained by the Kahe Generating Station accumulates 
as bed load at the shoreline intake basin and within the two intake forebays 
where water motion is insufficient to keep larger particles suspended. Bed 
load from the forebays is periodically pumped directly into the circulating 
water system downstream of the condensers and is carried by effluent to the 
station's outfall. Generally, HECO operations personnel conduct pumping and 
record dates, durations and pumping rates to enable calculation of the total 
volume of sediment pumped from the forebays. However, contractors are hired 
occasionally to pump or dredge sand from the forebays, intake or discharge 
basin, during which sand removal volumes are based on contractors' estimates. 
Whenever sediment was dredged, the volume removed was estimated by the number 
of truck loads required to transport the sediment to its deposition site.

#References:

B-K Dynamics, Inc. 1971. Marine environmental impact analysis, 
Kahe Power Plant. Report to Hawaiian Electric co., Inc. 350 p.

Brock, R. E. 1992. Status of coral communities fronting the Kahe 
Generating Facility, Kahe Point, Oahu following Hurricane Iniki. 
Report to the Environmental Department, Hawaiian, Electric Co. Inc. 12 p.

Coles, S. L. 1979. Annual report. Kahe Generating Station. NPDES 
monitoring program, vol. 1, text. Honolulu. 263 p.

______ 1980. Annual report. Kahe Generating Station. NPDES monitoring 
program, vol. 1, text. Honolulu. 277 p.

______ and D. T. Fukuda. 1975. Reef coral and algal communities of the 
Kahe nearshore region of Oahu, Hawaii. Environmental Department, Hawaiian 
Electric Co., Inc., 89 p.

______ D. T. Fukuda, and C. R. Lewis. 1981. Annual report. Kahe Generating 
Station. NPDES monitoring program, vol. 1, text. Honolulu, 237 p.

______ D. T. Fukuda, and C. R. Lewis. 1982. Annual report. Kahe Generating 
Station. NPDES monitoring program, vol. 1, text, 221 p.

______ and D. T. Fukuda. 1983. Annual report. Kahe Generating Station. 
NPDES monitoring program, vol. 1, Text, 173 p.

______ and D. T. Fukuda. 1984. Annual report. Kahe Generating Station, 
NPDES monitoring program, vol. 1, text, 225 p.

______ D. T. Fukuda, and K. S. Oda. 1985 Annual report. Kahe Generating 
Station, NPDES monitoring program, vol. 1, text, 172 p.

______ K. S. Oda, and J. M. Peck. 1986 Annual report. Kahe Generating 
Station, NPDES monitoring program, 109 p.

______ and J. C. McCain. 1973. Effects of the Kahe Generating Station on 
the nearshore environment. A report of the 1973 monitoring program. Hawaiian 
Electric Co., Inc., Honolulu, 199 p.

Environmental Dept. 1976 Interim report, Kahe Generating Station monitoring 
Program. Hawaiian Electric Co., Inc., Honolulu, 311 p.

______ 1988. Annual report. Kahe Generating Station, NPDES monitoring 
program. 66 p.
______ 1989. Annual report. Kahe Generating Station, NPDES monitoring 
program. 69 p.

______ 1990. Annual report. Kahe Generating Station, NPDES monitoring 
program. 62 p.

______ 1991. Annual report. Kahe Generating Station, NPDES monitoring 
program. 60 p.

______ 1992. Annual report. Kahe Generating Station, NPDES monitoring 
program. 57 p.

______ 1993. Annual report. Kahe Generating Station, NPDES monitoring 
program for 1992, 33 p.

______ 1994. Annual report. Kahe Generating Station, NPDES monitoring 
program for 1993, 32 p.

______ 1995. Annual report. Kahe Generating Station, NPDES monitoring 
program for 1994, 32 p.

______ 1996. Annual report. Kahe Generating Station, NPDES monitoring 
program for 1995, 32 p.

Fukuda, D. T. and K. S. Oda. 1987. Annual report. Kahe Generating Station, 
NPDES monitoring program, 69 p.

Marine Advisers, Inc. 1964. Analysis of littoral processes, Kahe, Oahu. 
Report to the Hawaiian Electric Co., 62 p.

McCain, J. C. 1977. Final report. Kahe generating station, NPDES monitoring 
program, vol. 1, text. Hawaiian Electric Company, Inc., Honolulu, 427 p.

Stearns Roger Inc. 1973. Environmental assessment, Kahe Generating Station 
Units Five and Six. Report to the Hawaiian Electric Co., Inc., 350 p.

URS Research Co. 1973. Marine environment impact assessment report for 
Hawaiian Electric Co., Inc., Kahe Point Facility, Oahu, Hawaii. URS no. 
7220-3, 280 p.

#Files:

kahe96.doc   1996 Report (MSWORD Ver 6.0) 

All of the following files are ASCII text.  These files
were derived from kahe96.doc.

table2.txt   Sand throughput estimates 
table3.txt   Sand/silt entrainment based on frequency of wave occurrence
table4.txt   Removal of sand bed load from Kahe cooling water system
table5.txt   Total volumes of sand (m3) entrained by Kahe Power Station 
             estimated by dredging removal and suspended throughput
