ACOE Breakwater Study Proposal

Water Circulation Modeling

and

Water Quality Monitoring/Modeling

For

Hilo Bay, Hawaii

FINAL

Scope of Work

Prepared for: Milton T. Yoshimoto, CEPOH-PP-C

Honolulu District, US Army Corps of Engineers

Prepared by: Thomas D. Smith, CEPOH-EC-T

Honolulu District, US Army Corps of Engineers
Mitchell E. Brown, CEERD-HV-B
U.S. Army Engineer Research and Development Center
Coastal and Hydraulics Laboratory
Dr. Tracy Wiegner
University of Hawaii at Hilo

General Background: In response to a request from the County of Hawaii to the U.S.
Army Corps of Engineers, Honolulu District (POH), this scope of work was prepared
with assistance from the U.S. Army Engineer Research and Development Center
(ERDC), Coastal and Hydraulics Laboratory (CHL), to address numerical modeling of
circulation, wave transformation, and water quality improvement in Hilo Bay. In a letter
of request from the County of Hawaii to POH (dated 14 October 2004) Mayor Harry Kim
indicated that Hilo Bay appears degraded to an undefined degree such that it does not
provide a suitable environment for recreation and aesthetic enjoyment of the area. The
initial focus of the numerical modeling will be to apply the appropriate models to assess
various project alternatives to promote greater water circulation in Hilo Bay in order to
improve water quality. Model results and predictions for up to five alternative plans will
be fully documented in a technical report to facilitate selection of an appropriate course
of action. Two of the alternatives to be considered are described in the attached
January 2005, ?Report on Water Quality Improvement to Hilo Bay, Hilo, Hawaii? that
was provided in response to Mayor Kim?s letter referenced above.

The criteria for assessing alternative plans in this study are determined by examining

changes in wave, current circulation, water quality, and residence time, as well as by
determining areas subject to stagnant or weak circulation or focused wave energy
resulting from proposed construction. The initial modeling efforts will concentrate on

quantifying change in circulation and wave patterns with and without the alternatives in
place for a range of forcing conditions. Multiple storms and non-storm conditions will be
simulated.

The Coastal Inlets Research Program (CIRP) has developed the Inlet Modeling

System (IMS) for simulating and predicting physical processes at and in the vicinity of
coastal inlets and for coastal regions. The IMS is distributed within the Surfacewater
Modeling System (SMS) interface developed by Brigham Young University (BYU).
Hydrodynamic and Morphologic Steering Modules allow models to share information
such that the combined processes of waves, currents, sediment transport, and
morphology change can be simulated.

The proposed water circulation modeling will consists of three phases that

encompass six technical tasks: 1) field data collection and assessment to include
compilation of existing data, 2) development of circulation, wave, and water quality
model grids, 3) development of forcing conditions for the models, 4) model validation, 5)
model simulations, and 6) analysis and report preparation. The final product from these
tasks is a set of calibrated hydrodynamic and wave models for the project site.

The models to be applied are as follows:

1) Circulation Model ? ADCIRC: The ADCIRC hydrodynamic model simulates the

circulation and water levels associated with both tides and storms. A two-
dimensional depth-integrated (2DDI) version of ADCIRC will be applied. ADCIRC
has been extensively applied in the Atlantic and Pacific Oceans (and world wide) to
simulate circulation and associated storm surge and currents. (A finite element grid
has been developed for the Hawaiian Islands by CIRP, and another project for the
island of Oahu is currently underway.)

The ADCIRC hydrodynamic modeling will require the following components:

Develop model grid to include recent bathymetry and shoreline data.

Calibrate and verify the circulation model to known wind conditions also including

tidal constituent contributions for the project domain for 2- to 4-week simulation
validation period. This will determine if the atmospheric input and tides are
sufficient to drive the model or if additional assessment is needed.

Assist in the development/selection of alternative forcing conditions.

Model multiple storms and one non-storm period for each alternative.

Display circulation patterns via particle tracking.

2) CH3D Hydrodynamic and Water Quality Transport Modeling: The overall water

quality of Hilo Bay is directly impacted by the inputs to the Bay via rivers, overland
flow and point source discharges and the rate at which these inputs are diluted and
flushed from the system. Increasing the circulation within Hilo Bay will decrease
flushing time, which should result in improved water quality. In order to assess the
degree of increased circulation and flushing for the structural alternatives being
considered, a number of modeling conditions are required. These modeling

conditions will be performed using a combination of ADCIRC (Luettich et al. 1992)
and CH3D (Chapman et al. 1996), in which ADCIRC water surface elevation and
currents are used to derive boundary conditions for the near-field CH3D circulation
and flushing simulations. CH3D is not part of the previously mentioned IMS suite of
models, but is supported by the SMS interface.

The CH3D hydrodynamic modeling component will require the following tasks:

Grid development to include recent bathymetry and shoreline data including

structural alternatives within the grid.

Development of fresh water inputs.

2DDI tidal calibration for the existing condition.

2DDI circulation and flushing alternative simulations using the existing and

structural alternative grids.

3) Wave Transformation Modeling ? STWAVE: STWAVE is a spectral wave model,

which is capable of representing wave-current interaction, wave-wave interaction,
wave-structure interaction and breaking (Smith et al. 1999). The ADCIRC and
STWAVE models will be coupled to allow the interchange of radiation stresses from
STWAVE to ADCIRC, and, wind-, and wave-generated currents from ADCIRC to
STWAVE.

Application of STWAVE will require the following steps:

Development of computational grid to simulate wave propagation.

Verification of calculated waves by comparison to measurements.

Water Circulation Study Phases

An approach toward development of a hydrodynamic modeling system for this

project is pursued in a phased process. Activities include identifying, assembling and
assessing available data, field data collection, grid development, current and water level
calibration/verification, and nearshore wave transformation. Phase 1 will be conducted
first. Phases 2 and 3 can be conducted in parallel, after Phase 1 is completed.

Phase 1: Phase 1 involves the assembly of geographic, bathymetric, hydrodynamic
(waves and circulation), fresh water inflow and meteorological data necessary to
develop and calibrate the modeling system. An assessment of the quality of available
data will aid in the specification of necessary additional field measurements. Field data
collection is to include deployment of three wave/current gages and acquisition of water
current profiles within Hilo Bay by use of a remotely controlled roving sensor. Tracer
and drogue studies will also be conducted as necessary to quantify surface currents
throughout the bay. The gages will be deployed for a minimum of one month. The PDT
will develop and calibrate the ADCIRC model for wind and tide forcing. Development of
the numerical model grid will focus on coarse resolution in the deep ocean water,
increased resolution around the island of Hawaii and highly detailed resolution in the
nearshore regions of the project site. Any recent bathymetric data will be evaluated and
incorporated into the model grid. Additional topographic and/or hydrographic survey

data acquisition is not part of this scope of work. The ADCIRC model will be validated
via comparison to hourly water level measurements for Hilo Bay from a NOAA gauge
available for a 14-year period from 1991 to the present day in addition to the site
specific field data to be collected. Also a 4-year record exists for the same location,
which contains 6-minute water level information from 2001 to the present day. ADCIRC
simulations for Phase 1 can be submitted to the ERDC?s High Performance Computing
Center for faster turnaround.

Estimated Cost: $ 115,000

Phase 2: A nested CH3D grid will be developed using shoreline and bathymetric data
discussed in Phase 1 and including river inflow boundary locations and data. An
example of a medium resolution nested CH3D grid for Hilo Bay is shown below, which
includes the existing breakwater structure. The grid displays the SMS feature arcs,
which define grid patches. A patch or group of patches can be modified to add or
remove resolution, and change geographic features. However, a restriction of structured
grid models such as CH3D requires that any row or column maintain the same number
of segments throughout. The grid-patch generation method allows one to easily modify
shorelines or structural features within the grid.

Depth-averaged tidal calibration of the baseline grid will be performed utilizing

boundary water surface elevations derived from the ADCIRC simulations. The flushing
efficiency resulting from the project design alternatives will be investigated for the
selected storms and non-storm conditions. This relative flushing efficiency will be
determined by comparing an initial and spatially constant tracer concentration,
throughout Hilo Bay, with the resulting concentration at selected sites and times. It is
envisioned that the worst-case scenario for flushing, thus the most appropriate for
evaluating the relative flushing efficiency of the structural alternatives, will occur during
non-storm, low/no river inflow periods that occur in summer and early fall.

Estimated Cost: $ 40,000

Phase 3: A range of atmospheric and tidal forcing conditions will be established to
simulate multiple storm and long-term non-storm conditions for all project alternatives.
An STWAVE grid will be developed and calibrated for the study area. ADCIRC and
STWAVE will be coupled for all events. Wind and pressure fields generated by a
combination of National Center for Environmental Prediction (NCEP) and National
Center for Atmospheric Research (NCAR) winds and pressures adjusted for local
observations will be used as additional forcing conditions for the hydrodynamic model.
The coupled ADCIRC/STWAVE model of all alternatives and events must presently be
simulated on fast desktop computer workstations, which decreases the turnaround time
for each simulation relative to simulations on the HPCC machines.

Estimated Cost: $ 40,000

Water Quality Monitoring

Overview: Hilo Bay waters have been known to exceed state water quality standards
since the late 1970s and were formally included on the US Environmental Protection
Agency?s (USEPA) 303(d) list of impaired waterbodies in 1998 (Koch et al. 2004).
Parameters exceeding standards include turbidity, nutrients, and fecal bacterial
indicators. The listing of Hilo Bay for nutrients and sediment has been determined
solely by means of visual assessment and not by direct measurements of these
parameters. To understand how Hilo Bay functions as an ecosystem, water quality and
circulation data are needed for the Bay, as well as water quality and discharge data for
the river draining into the Bay. UHH proposes to collect the baseline data on sediment
and nutrient inputs to the Bay, and to assess the response of the Bay to these inputs
under base and storm flow conditions. This information along with USACE circulation
data will allow Hawai`i County to identify the best and most cost-effective remediation
actions to improve Hilo Bay water quality.

Background: Reports are scarce and only one peer-reviewed paper exists for Hilo Bay
(Silvius et al. 2005). Most water quality data for Hilo Bay are from consultant reports for
Environmental Assessments (EA) and Environmental Impact Statements (EIS) from
USACE evaluations, and Hawai`i Department of Health (HDOH) and the United States
Geological Survey (USGS) monitoring (Silvius et al. 2005). However, these studies
were not designed to evaluate how Hilo Bay operates under different conditions (i.e.
baseflow vs. storms).

State of knowledge on Hilo Bay ? Hilo Bay is considered a salt wedge estuary that is

stratified with a freshwater surface layer existing up to a mile offshore (Dudley &
Hallacher 1991). This stratification is most pronounced during wet season when
surface runoff to Hilo Bay is high. The dense saline layer moves offshore at depth with
the tide and the upper freshwater layer is pushed shorewards by easterly and
northeasterly trade winds. There is minimal mixing between freshwaters and saltwater
layers inside the breakwater because wave energy is low. Low wave energy also
allows sediments carried by the rivers to settle out into the lower salty layer, where they
may be transported back into the Bay with the incoming tide. Tidal velocities are
probably too low to re-suspend bottom sediments, but suspended sediments will move
in and out of Hilo Bay with the tide.

The Hilo Bay watershed has one of the highest precipitation rates on the Hawaiian

Islands, ranging from 3 meters on the coast to 6 meters at the upper elevations annually
(Juvik & Juvik 1998). Hence, it is no surprise that the amount of freshwater entering
Hilo Bay is far greater than any other Hawaiian estuary. Surface waters are primarily
discharged into Hilo Bay from the Wailoa and Wailuku Rivers. Wailoa River is a
groundwater-fed flood-control channel that discharges into Waiakea Pond prior to
entering Hilo Bay. Waiakea Pond is the single largest source of groundwater into Hilo
Bay (M & E Pacific 1980). It is estimated that and 1.8 million cubic meters of
groundwater enters the Bay in this area (M & E Pacific 1980). The Wailuku River is the
largest perennial river in the state and the largest source of surface water to Hilo Bay.

Wailoa

Wailuku

(�M

)

Figure 2. Comparison of average (�SD) nitrate concentrations in the Wailoa and
Wailuku Rivers, Hilo, HI over October 19, October 26, November 2, and November 9.
Data were collected by the MARE 350 class during Fall 2005 semester.

The average flow of water from the Wailuku River into Hilo Bay is 1 million cubic meters
(range: 40 thousand -7 billion cubic meters; M & E Pacific 1980). Surprisingly, little is
known about the inputs of sediments and nutrients from these rivers. Currently, HDOH,
in collaboration with USGS, are quantifying storm inputs of sediments and nutrients
from Waiakea and Alenio gulches (both feed into Wailoa River) to Hilo Bay as a part of
HDOH total daily maximum load (TMDL) program. Inputs of sediments and nutrients
from the Wailuku River are currently being measured by UHH (Dr. Tracy Wiegner,
Marine Science) and US Department of Agriculture Forest Service (Dr. Richard
MacKenzie). Response of Hilo Bay to these inputs is unknown.

Much of the concern surrounding Hilo Bay?s water quality stems from the fact that

Hilo Bay?s waters are not clear. High-relief drainage and intense rainfall in Hilo Bay?s
watershed may contribute to naturally high sediment loads observed in the rivers during
storms. It is suspected that the Wailuku River delivers the majority of sediments to Hilo
Bay during storms and is the reason behind the poor water clarity in the Bay.
Preliminary data from UHH has found that turbidity is 10 times higher in Wailuku River
than Wailoa River during recent storms in October and November 2005 (Figure 1).
Currently, it is not known how long the Bay?s waters stay turbid following a storm and
whether these sediment inputs impact the ecosystem.

Another possible factor

contributing to the low water
clarity in Hilo Bay are algal
blooms. Algal blooms result
when nutrients are prevalent
and their presence gives
coastal waters a greenish tint.
As previously mentioned, the
USEPA 303(d) impaired listing
for Hilo Bay for excessive
nutrients was based solely on
visual assessment. From these
assessments, it was assumed

that Hilo Bay had high nutrient concentrations because the water had ?a greenish tint?,
resulting from suspected algal blooms (Silvius et al. 2005). Actual nutrient and
chlorophyll a (chl a) data for Hilo Bay are scarce. Preliminary data from UHH indicates
that nutrient concentrations are five
times greater in the Wailoa than the
Wailuku River (Figure 2), suggesting
that Wailoa may be the primary surface
water source of nutrients to Hilo Bay
(MARE 350 unpublished data). The
effect of these nutrient inputs to Hilo Bay
has not been assessed to date.

The temporal scale over which the

few turbidity and nutrient samples were

Oct 26

Nov 2

Nov 9

Date

Tur

i
d
it
y
(N

)

fall

(cm)

Wailoa
Wailuku

Figure 1. Comparison of average (�SD) turbidity values in the Wailoa and Wailuku Rivers in
Hilo, HI over different rainfall amounts. Rainfall data was obtained from
http://www.prh.noaa.gov/hnl/pages/hiclimate.php. Rainfall amounts were calculated using data
from two days prior to sampling. Turbidity data were collected during MARE 350 class during
Fall 2005 semester.

collected is inadequate to characterize the range of conditions experienced in Hilo Bay.
It is assumed that inputs of sediments and nutrients to Hilo Bay are high during storms;
however, these events have not been historically targeted. Current research efforts by
UHH, HDOH, and USGS are beginning to quantify storm inputs of sediments and
nutrients into Hilo Bay from the Wailuku River, Alenio Gulch, and Waiakea Gulch.
Information on how Hilo Bay responds to storms over temporal and spatial scales is not
known. Storm inputs of nutrients are thought to stimulate algal blooms; however, no
direct measurements have verified this. Additionally, the importance of these algal
blooms as a food source to higher trophic levels, like commercially and recreationally
important fish, is unknown.

Overall, the Hilo Bay Restoration Plan recommends (Silvius et al. 2005):

Identifying sources of sediments and nutrients to Hilo Bay from surface waters

under base and storm flow conditions

Collection of baseline chemical and ecological data to substantiate visual

assessment of nutrients (making direct measurements of nutrient and chl a
concentrations)

Examining the response of algae in Hilo Bay to base and storm flow conditions

?Scientific coordination to ensure that samples are continuously and constantly

gathered, without interruptions or changes in protocols, and with much better
spatial coverage than provided by? previous studies.

The study proposed below by UHH will begin to collect critical baseline data for Hilo

Bay that is: 1) essential for understanding how the Bay functions under baseflow and
storm conditions, 2) recommended by the Hilo Bay Restoration Plan, 3) needed to
develop a successful and cost effective restoration plan, and 4) required to evaluate
whether modification of the breakwater by USACE will improve Hilo Bay water quality.

Monitoring: Experimental Design: This study will specifically examine how storms
affect water quality (sediments, nutrients, chl a) in Hilo Bay by comparing conditions in
the Bay before and following a storm event over a one-year period. A similar design
has been successfully used by Ringuet & Mackenzie (2005) to evaluate the effects of
storms on water quality and algae in Southern Kaneohe Bay, Oahu.

Site Description: For this project,
eight stations will be sampled for
sediments, nutrients, and chl a (Figure
3). Two stations will be located in the
freshwater portion of the Wailoa and
Wailuku Rivers. These stations will be
used to determine the amount of
sediments and nutrients entering the
Bay from surface waters. Four
stations will be located inside of Hilo
Bay. Two Hilo Bay stations will be
located along a transect following the

Wailuku River

Wailoa River

(

Control 1

Control 2

Proposed Sites

Control Sites

Estimated
Trajectory

(

Figure 3. Proposed sampling stations in Hilo Bay.

Wailoa River plume (Figure 3). The other two Hilo Bay stations will be located along a
transect following the Wailuku River plume (Figure 3). This transect will be on a slight
angle to the northwest of the river?s mouth because previous studies have shown that
the Wailuku River plume is deflected northwest in Hilo Bay (Dudley & Hallacher 1991).
Two control sites will be located outside of the Hilo Bay breakwater (Figure 3). Plumes
from either river should not affect these control sites. Most of the proposed stations
have been previous sampled by UHH through research and class projects (data shown
in Figures 1 and 2).

Sampling Strategy: Water samples from the river and bay stations will be collected
under base and storm flow conditions during the wet and dry season over a one-year
period. Each station will be sampled for suspended sediments, nutrients, and chl a for
five days during each season, under both base and storm flow conditions. This time
frame was selected based on previous findings from Kaneohe Bay, where algae
bloomed after three to five days following a storm (Ringuet & Mackenzie 2005).
Because the focus of this study is to evaluate water quality in Hilo Bay before and after
a storm, water samples will be collected from surface waters where river sediments and
algae are most likely concentrated due to the Bay?s stratification. For this study, storm
conditions will be defined as when Hilo receives more than 5 cm of rain in 24 hours.
This rainfall amount is based on current research Dr. Wiegner, who has found that 5 cm
of rain corresponds to a rise in the Wailuku River by 1 m, which is the average stage
height for a storm event based on historical USGS data. Rainfall data for Hilo Bay will
be obtained from a NOAA website (http://www.prh.noaa.gov/hln/pages/hiclimate.php).
Following a storm, all stations will be sampled for five consecutive days. Baseflow
conditions will be defined as when Hilo receives less than 5 cm of rain over a period of
five days prior to collection (Ringuet & Mackenzie 2005)

To estimate sediment and nutrient inputs to Hilo Bay from the Wailoa and Wailuku

Rivers, water samples will be collected at the two river stations during base and storm
flow conditions. For the Wailoa station, a depth integrated sampler will be used to
collect all samples. Stage height and discharge for the Wailoa River will be measured
using a staff gage and velocity meter, respectively. For the Wailuku River, a depth-
integrated sampler will be used to collect water under base flow conditions and an
automated storm sampler will be used to collect water during storms. A storm sampler
has been installed on the Wailuku River near the USGS gage for current UHH research.
Discharge for the Wailuku River will be calculated using stage height measured at the
USGS gaging station and stage height-discharge relationship previously established by
this agency. Concentration and discharge data will be used to calculate sediment and
nutrient fluxes from the Wailoa and Wailuku Rivers to Hilo Bay under base and storm
flow conditions.

Measurements: Parameters regulated by HDOH for estuarine water quality will be
targeted for this study (HDOH 2004). Nutrients [total nitrogen (TN), ammonium (NH4+),
nitrate (NO3-), total phosphorus (TP), phosphate (PO43-), dissolved silicon (H4SiO4)],
pH, turbidity, total suspended sediments (TSS), and chl a will be measured during the
wet and dry season under base and storm flow conditions. Additionally, dissolved

organic carbon (DOC) and particulate carbon (PC) will be measured at the request of
USACE for their eutrophication model. NH4+ (USGS I-2525), NO3- (USEPA 353.4), TP
(USGS I-4650-03), PO43- (USEPA 365.5), and H4SiO4 (USEPA 366) will be measured
using standard autoanalyzer methods. TN and DOC will be measured on a Shimadzu
TOC-V CSH, TNM-1 following the recommendations by Sharp et al 2002. Turbidity will
be measured on a Hach 2100P Turbidimeter. TSS will be measured using standard
methods (APHA et al. 1995). PC will be analyzed on a CHN analyzer (Costech
Analytical Technologies). Chl a will be measured using USEPA method 445.0. To
characterize the conditions at each station when sampling, physiochemical parameters
(salinity, conductivity, temperature, dissolved oxygen concentration, dissolved oxygen
percent saturation, light penetration) will be measured using a YSI multi-parameter
meter and a Li-Cor light meter, respectively. At the request of USACE, depth profiles
for these physiochemical parameters will be measured at the six Hilo Bay stations.
Meteorological data (rainfall, winds, waves, and tides) will also be obtained for the
sampling dates.

Monitoring Outcomes: Essential baseline water quality data for Hilo Bay will be
collected to complement circulation data being collected and numerical water quality
models to be run USACE. This information will allow for a greater understanding of how
Hilo Bay functions. With this understanding, appropriate restoration actions can be
developed and implemented to improve Hilo Bay water quality.

Estimated Cost: $66,000

Water Quality Modeling

Background: Design alternatives for the Hilo Bay breakwater will result in differing
wave and circulation patterns. Depending on the point and non-point loadings to the
bay, the alteration of the baseline flushing of the bay can result in varying degrees of
water quality improvement. Water quality modeling techniques can be used to predict
the concentration and persistence of various water quality parameters, such as
dissolved oxygen.

Numerical models are widely used to study water quality issues. Among the water

quality issues models have been used for include assessment the effectiveness of
proposed remediation measures, determination of the impacts of different pollutant
sources, distribution of substances in the water column and sediments, and impacts of
changes in circulation upon water quality conditions. Models are used to look at the fate
and transport of constituents such as nutrients, contaminants, salinity, temperature,
algae, dissolved oxygen, and coliforms. More advanced models are capable of
simulating living resources such as Submerged Aquatic Vegetation (SAV), zooplankton,
and benthic invertebrates such as clams.

Levels of Water Quality Modeling: The level of water quality modeling required is
dependent upon the problem being addressed. In some cases, the problem is a single
constituent in the water column that can be modeled alone. Examples would be

temperature, salinity, or coliforms. These constituents are assumed to not be
influenced by other parameters in the water column. In other cases a suite of
constituents are required to address a water quality issue due to the interdependence of
the constituents. An example of this would be dissolved oxygen which is impacted by
processes such as algal production/respiration, nutrients, reaeration, and oxygen
demanding substances in the water column and sediments.

All water quality modeling requires data. A time series of information is required for

all boundaries (open water and tributary). In addition, flow and concentration (or load)
information is required for all point source dischargers along with estimates for loadings
originating in watershed that have direct contribution to the receiving water body.
Finally, if the issue of concern, such as eutrophication or contaminants, involves
sediments, then information on the chemical makeup of the sediments is required. All
of this information can be obtained from a sampling program conducted in conjunction
with the modeling study.

In many instances dissolved oxygen is the constituent of interest. It is often used as an
indicator of the health of the system. Low dissolved oxygen levels result from a
combination of poor circulation, oxygen demand in the water column exceeding
reaeration, and excessive oxygen demand in the sediments. Low dissolved oxygen
levels can have negative impacts upon living resources either by retarding their growth
or by killing the creatures

Water quality modeling techniques can be used to determine the dissolved oxygen

impact resulting from a change in circulation due to breakwater removal or relocation.
Various levels of modeling effort are available to address these issues and are
summarized below. Prior to selecting one approach over another it must be determined
to what standard will the results be held by reviewing agencies and others.

1. Eutrophication ? Involves the modeling of dissolved oxygen, algae, nutrients,

and carbon. Realistic loads (observed or estimated) are required for all
major discharges in the system. In addition, information on constituent
concentrations are required for development of boundary conditions and for
calibration. Sediment processes could either be specified or simulated with a
sediment diagenesis model. This is the most involved approach in time and
money and would provide the most defendable results provided there is an
adequate data base for model development.

2. DO/BOD/SOD - Similar to number 1 except that all oxygen demand is

specified as a Biochemical Oxygen Demand (BOD). Sediment Oxygen
Demand (SOD) is specified as a constant rate and together with BOD are the
only sinks for DO. Information is required on DO and BOD levels throughout
the system for cursory model calibration. Information (observed or estimated)
is required for all significant discharges. While less involved than level 1, this
approach still requires some calibration. The results from this study are less

defensible as algae are left out and the impact of algal photosynthesis and
respiration are omitted.

3. Residence Time - Not a measure of dissolved oxygen but a measure of the

impact that circulation changes have on the time that water stays in a certain
area. Assuming that oxygen demands are the same throughout the system,
an increase in residence time would indicate a decrease in flushing and a
decrease in DO. This is a very simplified approach relying heavily on
inferences.

All of the above levels of model should indicate similar results as long as the water

quality conditions are dominated by circulation. All three levels will require roughly the
same level of effort for generating the hydrodynamics required to drive the water quality
model.

Though not listed above, an additional option is not to model dissolved oxygen or

water quality. Instead, evaluate hydrodynamic results and infer from them whether the
conditions in the vicinity of the breakwater have changed. In this approach there is a
pre-supposition that the conditions will not greatly change and that there are no strong
gradients or plumes in the system. This approach is the simplest and cheapest but also
the least defensible and should only be chosen if it is clear that the reviewing authority
would accept such an approach.

Coliforms are also another water quality constituent of concern as their presence in

elevated levels is taken as an indication of bacterial contamination and potentially
pathogens. As such, excessive coliform levels result in restrictions for swimming,
fishing, and shell fishing. Coliforms originate in the guts of warm blooded creatures.
They typically enter water bodies as a result of runoff from the watershed or from
wastewater treatment plants.

Coliforms can be modeled rather simplistically. There is no reproduction or

generation in the water body. Once the coliforms are introduced into the water column
they are removed at a specified rate. The rate can be independent of other constituents
or a function of environmental constituents such as salinity.

Chemical contaminants in the form of metals, PCBs, and pesticides in the water

column and sediments can degrade the water column and restrict the use. Typical
sources of these contaminants are watershed loadings or sediment fluxes. As these
contaminants are found in sediments they provide a persistent source to the water
column and living resources. Modifications to circulation resulting from a breakwater
removal or modification could lower the level in the water column if flushing is
increased. However, the issue of the contaminated sediments would not be addressed
by this measure and could require remediation or capping to limit the sediment source
of contaminants.

Estimated Cost: $109,000

Study Management

1) Project Management: CEPOH-PP-C shall assign a Project Manager (PM) to direct

study efforts, maintain project milestone schedule and manage study funding. The
PM shall establish a Project Delivery Team (PDT) comprised of POH, ERCD and
non-Federal members as applicable. The PM will develop a Project Management
Plan to serve as a guide for conduct of study tasks. A network of study activities will
be established by the PM in the US Army Corps of Engineers? P2 scheduling
software.

2) Technical Management: CEPOH-EC-T shall assign a Technical Manager (TM) to

manage numerical model and field data collection efforts as well as provide regular
updates of work progress to the PM. The TM shall coordinate accomplishment of
the work tasks described in this scope of work with the Project Delivery Team (PDT)
and attend PDT meetings upon request from the PM. CEPOH-EC-T shall participate
in the in-progress meetings with the PDT, as required, and in general, keep the PM
informed on the progress of work. Assume ten such meetings with the PDT, are
necessary.

Estimated Cost: $ 75,000

Deliverables

Water Circulation Modeling: The water circulation modeling will be completed over a
12 month period following notice to proceed. Amount for preparation of the draft final
report includes labor costs for compilation and writing in addition to editing, publishing
and printing costs. Amount for CHL travel outlined in the table below includes $15K per
person for up to two weeks in duration for site visit/field data collection. These costs
include travel, labor and per diem for two ERDC staff members.

1. Monthly progress reports on the water circulation modeling will be provided.

2. Field data will be collected for a minimum of one month as described above. Field
notes and raw data sets will be provided along with a detailed report of data acquisition,
quality control and quality assurance.

3. Water circulation model will be calibrated to field data.

4. Water circulation will be quantified for existing conditions and five additional
alternative plans.

5. The calibrated model for the project site and final Technical Report will be delivered
following completion of Phase 3.

Water Quality Monitoring (work-in-kind): The following deliverables will be provided
by UHH to the Honolulu District of the USACE:

1. Nutrient sample data in formats compatible with input to the proposed USACE water
quality numerical models.

2. Draft and final report documenting nutrient sample collection, meteorological data for
the sample collection periods (to include at a minimum rainfall, winds, waves and tides),
description of sample concentration trends for each collection period, and
summary/conclusion of sampling results.

3. Final deliverables will be provided to Honolulu District personnel within 12 months
from the date of the notice to proceed.

Water Quality Modeling: The following water quality modeling deliverables will be
provided:

1. Monthly progress reports on the water quality modeling will be provided.

2. Water quality modeling will be conducted for the parameters monitored by UHH as
described in detail above.

3. Water quality models will be calibrated to the UHH monitoring data for existing
conditions at Hilo Bay.

4. Water quality modeling will be conducted for five alternatives plans as investigated in
the water circulation studies.

5. The calibrated model for the project site and final Technical Report will be delivered
to the Honolulu District for distribution and future use.

Study Costs

Cost

($K)

Water Circulation Modeling

Phase 1

115

Phase 2

Phase 3

Report 25

Travel (CHL)

Sub-total 250

Water Quality Monitoring
(work-in-kind)

Water Quality Modeling

109

Technical Management

Project Management

Total 500K

References:

APHA, AWWA, and WEF. 1995. Total solids dried at 103-105 C. In: Eaton, A.D., L.S.,
Clesceri, and A.E. Greenberg (eds.), Standard Methods for the Examination of Water
and Water Water, 19th edition. American Public Health Association, Washington, D.C.

Chapman, R. S., Johnson, B. H., and S. R. Vemulakonda. (1996). ?Users Guide for the
Sigma Stretched Version of CH3D-WES; A Three-Dimensional Numerical
Hydrodynamic, Salinity and Temperature Model,? Technical Report HL-96-21, U.S.
Army Engineer Waterways Experiment Station, Vicksburg, MS.

Dudley, W.C. Jr and L. E. Hallacher. 1991. Distribution and dispersion of sewerage
pollution in Hilo Bay and contiguous waters. Final report. County of Hawai`i
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HDOH. 2000. Hawai`i?s implementation plan for polluted runoff control.

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Hawai`i Island Journal. 2004. What?s wrong with Hilo Bay? Juvik, J, and S. Juvik.
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Smith, J. M., Resio, D. T., and Zundel, A. K. (1999). ?STWAVE: Steady-State Spectral
Wave Model. Report 1, User?s Manual for STWAVE Version 2.0,? Instructional Report
CHL-99-1, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS.