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Keystone HarborCoastal & Hydraulic Modeling Study


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Technical Report

Keystone HarborCoastal & Hydraulic Modeling Study

Prepared for:

CH2M-Hill

This document is being released for the purpose under the authority of

Vladimir Shepsis, PhD, P.E. This document is not to be used for purposes

of permitting, final engineering design, or for construction documents.

Prepared by:

Vladimir Shepsis

Coast & Harbor Engineering


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Existing Keystone Ferry Terminal Feasibility Study December 30 2004Physical and Hydrodynamic Computer Modeling Summary Page 1

Executive Summary

IntroductionThe Hydrodynamic and Physical Modeling Study was conducted to evaluate theKeystone Harbor jetty modification alternatives. The alternatives evaluation was

conducted using 2-Dimensional computer simulations (hydrodynamic modeling) and 3-Dimensional physical (hydraulic) modeling. The use of a two-component modeling

system provides reliable and sufficient information for evaluation of the proposed

alternatives and is typical in coastal engineering practice; this approach is recommendedby US Army Corps of Engineers Coastal Engineering Manual 1100-2-1100 2003 (CEM),

Section V.

Eleven proposed alternatives were evaluated in the study, including ten Keystone Jetty

modification alternatives and the No Action Alternative (Existing Conditions). Table 1

provides a brief description of the proposed alternatives.

Please note that numbering of the alternatives below in the table is specific to the current

hydrodynamic modeling study only. Nine alternatives consist of various extensions of the

existing jetty (alignments and cross-section configurations) and one alternative,Alternative 5, consists of relocating the existing jetty approximately 300 ft to the East. In

addition, Alternative 5 includes widening the existing channel by 200 ft to the East.

Table 1 - Jetty Modification Alternatives Description

Alternative Jetty Extension AlignmentJetty Extension Material and Cross

Section

1 Existing Alignment Sloped Rock 2H:1V

1A Existing Alignment Sloped Rock 1.5H:1V

2 Existing Alignment Pile-Supported Wave Barrier

2A Existing Alignment Solid Sheetpile Wall

3 Dogleg Sloped Rock 2H:1V

3A Dogleg Sloped Rock 1.5H:1V

3B Dogleg Submerged Sloped Rock 1.5H:1V

4 Dogleg Pile-Supported Wave Barrier

4A Dogleg Solid Sheetpile Wall

5 Relocation to the East Sloped Rock 2H:1V


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Existing Keystone Ferry Terminal Feasibility Study December 30, 2004Physical and Hydrodynamic Computer Modeling Summary Page 2

The proposed alternatives were evaluated based on the comparison of the project

controlling factors before construction (known and modeled) for existing conditions withthose estimated (modeled) for each of the proposed alternatives (if they were to be

constructed). The project controlling factors that were used in the evaluation process are

as follows:

1. Cross-channel current velocities,2. Channel and harbor entrance waves,3. Sedimentation and maintenance dredging,4. Shoreline erosion and bottom scour, and5. Water quality.

1. Cross-Channel Current Velocities Controlling Factor

Cross-channel tidal current velocities were evaluated because they cause the so-

called shear effect that ferry boats are currently experiencing during theirapproach into and departure from Keystone Harbor. The Cross-Channel Current

Velocities Controlling Factor was evaluated using the calibrated and validated 2-

D Advanced Circulation Model (ADCIRC), U.S. Army Corps of Engineers.Modeling was conducted for existing conditions and for each of the proposedalternatives. Results of the modeling were analyzed and compared and show the

following:

All jetty extension alternatives (excluding Alternative 3B) wouldsignificantly reduce cross current velocities in the channel along the lengthof the extended jetty at approximately 600 ft along the channel. Reduction

of cross current velocities relatively along this stretch of the channel is

calculated at approximately 70-80% relatively to existing conditions.

Alternative 3B would provide a smaller reduction of cross currentvelocities in the channel along the extended jetty. This reduction would

not exceed 30% relatively to existing conditions.

All jetty extension alternatives would provide some reduction ( up to 20-30% ) of current velocities seaward of the extended jetty, relative to

existing current velocity conditions. However, prior to reduction, theincrease of velocities may occur immediately at the end of the extended

jetty. This immediate increase would increase the shear, specifically for

Alternatives 1, 1A, 2 and 2A.

Jetty Relocation Alternative #5 would provide >30-50% reduction of crosscurrent velocities at a distance of more than 2,000 ft of the seaward end ofthe existing jetty.

Jetty Relocation Alternative #5 would reduce the shear effect at theentrance of the harbor.

It is likely that the construction of the existing jetty in 1948 has changedthe pattern of eddies, exacerbating cross-current velocities at the entrance

to the harbor. It is likely that prior to jetty construction, the strength of thecurrents were less and/or lessened gradually toward the entrance in

relation to the natural depth. All the jetty modification alternatives would


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change (to varying extents) the tidal flow eddying patterns near the project

area. Jetty relocation alternatives would partially re-construct existingpre-1948 currents patterns at the entrance to the harbor.

From the perspective of a cross current velocities as a controlling factor,two jetty modification alternatives, Alternative 3 (or 3A) Rock Dogleg,

and Alternative 5 Jetty Relocation, are feasible. These alternatives arerecommended for further analysis.

2. Channel and Harbor Entrance Wave Controlling Factor

This factor consists of the wave parameters at the entrance to the harbor and the

potential wave effects on ferries maneuvering during their approach into and

departure from Keystone Harbor. The Channel and Harbor Entrance WaveControlling Factor was evaluated using two different 2-Dimensional computer

models, STWAVE (U.S. Army Corps of Engineers) and COASTOX (Coast &

Harbor Engineering). Modeling was conducted for existing conditions and for

each of the proposed alternatives. Results of the modeling were analyzed and

compared and show the following:

All jetty extension alternatives would reduce wave heights approachingfrom SE in the channel located along the extended jetty. All jetty

extension alternatives (if no deepening and widening channel occurs)would not alter wave conditions in the harbor relative to existing

conditions.

Relocation of the jetty (Alternative 5) would not change waves in thechannel to any significance that may effect the navigation for storms

approaching from SE and SW

Relocation of the jetty (Alternative 5) would increase wave heights inside

of the harbor relative to existing conditions for both storm conditions, SEand SW. Maximum increase of wave height during extreme 2-year return

period storm event approaching from SE, is estimated at approximately

2.0 ft. The increase of wave heights in the harbor is a result mostly ofdeepening and widening the channel that allows more wave energy to

penetrate into the harbor

All jetty extension alternatives except Alternative 3B would significantlyreduce wave energy along the shoreline during wave storms approaching

from SW.

Relocation of the jetty (Alternative 5) would reduce wave energy along

the shoreline during wave storms approaching from SW In the cases of both rock jetties and vertical wall barriers, the dogleg

alternatives seem to provide better protection in the lee side, as they are

oriented almost normal to the incident storm wave direction and create

significant shadow areas behind the structure.


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3. Sedimentation and Maintenance Dredging Controlling Factor

This factor consists of the effect of the proposed alternatives on sedimentation and

maintenance dredging requirements in the Keystone Navigation channel and

harbor. Sediment transport at Keystone Harbor was evaluated using the 2-DLAGRSED sediment transport model (Coast & Harbor Engineering). In addition,

the results from previous studies were analyzed and morphologic analysis wasperformed to validate trends in the numerical modeling results. Modeling was

conducted for existing conditions and for each of the proposed alternatives.Results of the modeling were analyzed and compared and show the following:

Since construction of the navigation project in 1948, the sedimenttransport system at the Keystone shoreline has consisted of two littoral

cells: the East Cell, East of the jetty, and the West Cell, West of thenavigation channel. These two littoral cells are separated by the jetty

and the navigation channel. The cells have a limited exchange of

sediment between them except for the artificial bypassing associated

with dredging and dredged material placement events.

The sediment transport of coarse material in the vicinity of the projecthas been predominantly from west to east. This transport contributesmost of the dredging volumes currently dredged in the channel. Prior

to the construction of the jetty in 1948, a small amount of coarse

material had contributed to the westward littoral drift. Since

construction of the jetty, only fine sediment (sand and silt) aretransported to the west around the jetty and accumulate in the channel.

For existing conditions, sand and finer material (silt, clay) erodes fromthe dredged material placement area and accumulates in the channel

and inside the harbor. Small accumulation of sand occurs in the

vicinity of the East side of the jetty. For existing conditions, erosion occurs in deep water seaward of the

harbor entrance. This result appears to be consistent with the general

bathymetry of the area. The bottom depression located seaward of thejetty was observed in all available hydrographic surveys. Though this

depression is slightly offset from the entrance in the Eastward

direction, the general trend of scour shown in the model (depth of

scour and orientation of the scour) indicates a similarity between themodeling results and typical processes observed in the field.

The nine Jetty extension alternatives (excluding Alternatives 2 and 3B)will not result in increased sedimentation and maintenance dredging

requirements in the channel and the harbor compared to existing

conditions. Furthermore, these alternatives may result in a slightreduction of sedimentation in the channel and harbor due to reduction

of westward transport of fine sediment.

The nine Jetty extension alternatives (excluding Alternatives 3B and4) will not result in loss of sand from the beach to the east of the jetty


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and will not impact on shoreline erosion to the east. Alternatives 3B

and 4 may results in slight removal of sand relatively to existingconditions due to increase of the tidal velocities at local spots of the

beach.

The Jetty relocation alternative would increase maintenance dredging

requirements during the dredging cut stabilization period,approximately 2-5 years. After that, the maintenance dredging

requirements would be similar to existing maintenance dredgingrequirements.

4. Shoreline Erosion and Bottom Scour Controlling Factor

This factor consists of the effect of the proposed alternatives on shoreline erosion

and bottom scouring to the East of the existing Keystone Navigation channel and

jetty. The Shoreline Erosion and Bottom Scour Controlling Factor was evaluatedbased on combined results from wave refraction/diffraction and sediment

transport modeling (see above Sections 2 and 3), physical modeling, and

engineering morphology analysis using historical aerial photographs. Results of

the modeling and engineering morphology analysis show the following:

Equilibrium and accreting beaches are observed to the East of theexisting jetty for approximately 2 miles along the shoreline (excludingthe area adjacent to the jetty several hundred feet). The Corps of

Engineers practice, including placement of dredged material at the

East side of the jetty has contributed to changes in the shoreline trend

from erosion patterns to relative equilibrium.

Jetty extension alternatives (excluding Alternatives 2, 3B, and 4) arenot likely to affect shoreline erosion to the East of the jetty.

Furthermore, all alternatives, excluding Alternative 3B, will reduce S-SW wave energy along the length of the shoreline adjacent to the jetty

from the East. It will result in more shoreline stability along a shortdistance adjacent to the jetty.

Jetty extension Alternatives 2, 3B, and 4 may cause a removal ofsediment from the nearshore area to the east of the jetty due to increase

bottom current velocities. It may results in altering the existing

shoreline conditions. In addition, due to complexity of refraction anddiffraction on permeable structures, these alternatives may results in

increased amounts of energy delivered to the shoreline relatively to

existing conditions.

The Jetty relocation alternative would establish the similar shorelineconditions to the East of the relocated jetty as they are currently to the

East of the existing jetty. If dredged material is placed on the beach tothe East of the jetty no shoreline erosion will occur. Furthermore, if

dredged material is placed on the shoreline during construction, a short

term advancement of the shoreline is expected.


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The Jetty relocation alternative would not effect shoreline stability tothe east from the jetty. Furthermore, relocation and placement of the

head of the jetty at a shallower depth than it is currently would resultin additional bypass of littoral drift and improvement of beach

stability to the east

5. Water Quality Controlling Factor

This factor consists of the potential effect on water quality in Keystone harbor

from the proposed alternatives relative to existing conditions. Water quality

modeling was conducted using the two-dimensional, finite element hydrodynamicmodel RMA4 (US Army Corps of Engineers) using the ADCIRC model

circulations results as input. Modeling was conducted for existing conditions and

for each of the proposed alternatives. Results of the modeling were analyzed and

compared and show the following:

Evaluations of the alternatives with regard to the water quality were

based on computed residence times at the back corner of KeystoneHarbor for each alternative. Results of computation show that most of

the nine jetty extension alternatives, excluding Alternative 3B, willslightly increase the water residence time in Keystone harbor.

However, considering the small residence times predicted (less than 30

hours for any alternative), no detectable water quality effects are

expected. Alternative 3B slightly reduces the residence time, implyinga potential increase in water circulation and exchange in the harbor.

The Jetty relocation alternative will significantly reduce the residencetime, resulting in an improvement in water quality in the harbor.

Physical ModelingA high-resolution scale physical model of the Keystone Harbor and the adjacent bottomand shoreline were constructed in a three-dimensional wave basin at Oregon State

University. Physical modeling of tidal currents, wave refraction/diffraction, and wave-induced shoreline changes were conducted to validate the numerical model that has been

subsequently used for evaluation of the proposed alternatives.

Verification was conducted by comparing the physical modeling results to numericalmodeling results. The No Action Alternative (existing conditions) was used as the basis

for verification of the numerical model. The constructed Keystone physical model was

surveyed with lasers (LIDAR) and reconstructed in the computer as a numericalmodeling grid. Computer modeling was conducted using the same boundary conditions

and input data as used for the physical model. The comparison showed that the

numerical model provides a good representation of the physical model. The mostsignificant differences between the physical and numerical modeling results are observed

at the boundary of the modeling domains, which was expected and does not affect the

modeling results in the areas of interest. The differences between the two models in the


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areas of interest, the navigation channel and the shoreline, were determined to be within

an acceptable range.

In addition to validation of the numerical model, the physical model was used to

investigate and qualitatively assess the physical processes related to jetty modification

alternatives that cannot be adequately evaluated with 2-Dimensional numerical models.For example, the physical modeling was used to investigate Alternatives 3B and 4, the

submerged rock jetty and wave barrier. The use of 2-Dimensional numerical modeling

for these alternatives is limited due to 3-Dimensional flow effects around and through thestructure.

ConclusionsAlternative 3, Dogleg with sloped rock, and Alternative 5, Jetty relocation, are considered

feasible and preferred relative to the other tested jetty modification alternatives from the

perspective of the following controlling factors: cross-channel current velocities, waves

in the channel, sedimentation and maintenance dredging requirements, shoreline erosionand water quality. Selection of the preferred alternative shall be conduced based on all

aspects of the controlling factors, including cost, environmental considerations, socialconsiderations, and others. Additional analysis for Alternative 3 needs to be conducted to

determine the effect of widening the channel on wave conditions in the harbor, channel

sedimentation, and water quality. Optimization of the Jetty relocation alternative basedon performance, economical, and environmental criteria needs to be conducted to

determine the width of the channel and length of jetty relocation.


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Table of Contents i

TABLE OF CONTENTS

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

1.1. Objectives ......................................................................................... 1

1.2. Methodology ..................................................................................... 3

2. Keystone Harbor Physical Conditions............................................................ 4

2.1. Geographic Setting and History........................................................4

2.2. Tides.................................................................................................5

2.3. Wind.................................................................................................. 7

2.4. Wave Climate ................................................................................... 9

2.5. Currents..........................................................................................11

2.6. Sediment Transport ........................................................................ 20

2.7. Shoreline and bottom slope morphology ........................................28

3. Keystone Jetty Modification Alternatives .....................................................293.1. Alternative 1.................................................................................... 30

3.2. Alternative 2.................................................................................... 30

3.3. Alternative 3.................................................................................... 30

3.4. Alternative 4.................................................................................... 31

3.5. Alternative 5.................................................................................... 32

4. Computer Simulation of Coastal Hydrodynamic Processes ........................34

4.1. Tidal Current Circulation Model ......................................................34

4.1.1. Model Description ............................................................... 34

4.1.2. Modeling Domain and Grid ................................................. 35

4.1.3. Boundary and Input Conditions........................................... 37

4.1.4. Model Verification ............................................................... 38

4.1.5. Modeling Results ................................................................ 48

4.2. Wave Transformation Modeling...................................................... 56

4.2.1. Models Description & Setup................................................56

4.2.2. COASTOX Model................................................................59

4.2.3. STWAVE Modeling and Results .........................................59

4.2.4. COASTOX Modeling and Results....................................... 614.3. Sediment Transport, Sedimentation/Scouring Modeling ................ 70


4.3.2. Model Domain Setup .......................................................... 71

4.3.3. LAGRSED Model Results...................................................76

4.4. Water Quality Modeling ..................................................................81


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Table of Contents ii


4.4.2. Model Domain Setup and Boundary Conditions ................. 82

4.4.3. Model Results ..................................................................... 83

5. Keystone Physical Modeling ........................................................................ 86

5.1. Objectives of Physical Modeling .....................................................865.2. Modeling Facilities .......................................................................... 86

5.3. Model Setup and Modeling Methodology .......................................88

5.3.1. Model Scaling ..................................................................... 88

5.4. Model Design..................................................................................90

5.4.1. Existing Conditions ............................................................. 90

5.4.2. Modeling Alternatives.......................................................... 96

5.5. Wave Generation and Measurement..............................................99

5.5.1. Wave Generation ................................................................99

5.5.2. Wave Measurement.......................................................... 100

5.6. Current Generation and Measurement .........................................102

5.6.1. Current Generation ........................................................... 102

5.6.2. Current Measurement ....................................................... 103

5.7. Shoreline Change Analysis...........................................................105

5.8. Model Testing Scheme.................................................................105

5.9. Modeling Results .......................................................................... 106

5.9.1. Cross Channel Currents Modeling Results.......................106

5.9.2. Cross Channel Currents Modeling Results.......................1075.9.3. Alternative Comparison.....................................................111

5.10. Wave Refraction/Diffraction and Shoreline Change ModelingResults.......................................................................................... 116

5.11. Physical Modeling Summary ........................................................ 127

6. Discussion, Summary, and Conclusions.................................................... 127

7. References (for computer simulation section) ...........................................132

List of Figures1.1 Cross current flow during site visit on January 30, 2004. .......................21.2 Prop from the ferry indicating a strong cross channel current................ 32.1 Keystone Harbor Geographical Location................................................52.2 Tidal elevations at Keystone Harbor....................................................... 62.3 Field Data Collection Stations A-C (2004) and Stations West and

East (2002).............................................................................................62.4 Measured Tides at Stations A-C during the Deployment Period............72.5 Location of Smith Island wind measuring station, Pt. Wilson, and

Keystone Harbor and Wind Rose (based on Smith Island data) ............9


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Table of Contents iii

2.6 Depth-Averaged Current Speed and Direction ExampleTime Series at West ............................................................................ 13

2.7 Depth-Averaged Current Speed and Direction ExampleTime Series at East Current Meter......................................................14

2.8 Distribution of Current Speeds Directed West along the Shorelineat West Station, 2002 Data...................................................................14

2.9 Distribution of Current Speeds Directed East along the Shorelineat West Station, 2002 Data...................................................................15

2.10 Distribution of Current Speeds Directed West along the Shorelineat East Station, 2002 Data....................................................................15

2.11 Distribution of Current Speeds Directed East along the Shorelineat East Station, 2002 Data....................................................................16

2.12 Current Speed Vertical Profiles at West Current Meter during Floodand Ebb Tide (dates in PST) ................................................................ 16

2.13 Current Direction Vertical Profiles at West Current Meterduring Flood and Ebb Tide (dates in PST) ..........................................17

2.14 Current Speed Vertical Profiles at East Current Meter during Floodand Ebb Tide (dates in PST) ................................................................ 17

2.15 Current Direction Vertical Profiles at East Current Meterduring Flood and Ebb Tide (dates in PST) ..........................................18

2.16 Depth-Averaged Current Speed and Direction ExampleTime Series at Station A ....................................................................... 18

2.17 Depth-Averaged Current Speed and Direction ExampleTime Series at Station B ....................................................................... 19

2-18 Depth-Averaged Current Speed and Direction ExampleTime Series at Station C....................................................................... 19

2-19 Transport patterns, bluff retreat rate and volume loss rateas developed by Keuler (1988)............................................................21

2-20 Typical composition and morphology of bluff and upperbeach which contribute sediments to Keystone Harbor ....................... 22

2.21 Wave diagram applicable to the Keystone Harbor entrance(source: Seattle District Corps of Engineers 1972)............................... 23

2.22 Littoral drift directions at Keystone developed by SeattleDistrict corps of Engineers (1972) .......................................................24

2.23 Shoreline shape and features prior to jetty construction anddredging Keystone Harbor.................................................................... 25

2.24 Dredging and disposal areas for Keystone Harbormaintenance dredging .......................................................................... 26

2.25 Dredged materials disposed east of the jetty, which feedsthe beach farther to the east.................................................................27

2.26 Transect locations for shoreline change measurements ...................... 293.1 Alternative 3, Dogleg ............................................................................ 31

3.2 Alternative 5, Jetty Relocation Alternative, Phase 1: Jetty relocatedwithout channel widening. Optimization of channel wideningshould be conducted. ........................................................................... 32

3.3 Alternative 5, Jetty Relocation Alternative, Phase 2: Jettyrelocated & channel widened. .............................................................. 33

4.1 Existing Conditions Modeling Domain.................................................. 354.2 Finite Element Modeling Grid for Entire Model Domain........................ 364.3 Modeling Domain Finite Element Grid Close-Up at Project Site........... 36


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4.4 Statistical Distribution of Tidal Ranges during SimulationPeriod and Long-Term at Admiralty Head ............................................ 38

4.5 Ebb Currents at Four Stages during the Ebb Tidal Cycleleft to bottom right .................................................................................40

4.6 Flood Currents at Four Stages during the Flood Tidal Cycle................ 414.7 Flood Currents in Physical Model of Puget Sound at University of

Washington, Seattle, WA (from Cannon et al 1978).............................424.8 Comparison of Measured and Calculated Tidal Elevations

at Station A.......................................................................................... 444.9 Comparison of Measured and Calculated Current Speeds

at Station A.......................................................................................... 444.10 Comparison of Measured and Calculated Current Speeds

at Station B.......................................................................................... 454.11 Comparison of Measured and Calculated Current Speeds

at Station C..........................................................................................454.12 Current velocity and direction for existing conditions for (a) physical

model and (b) ADCIRC simulation of the physical modeling domain. .. 474.13 Comparison of the physical modeled velocities (points) and

the ADCIRC simulated velocities (lines) along the KeystoneChannel as a function of distance from the Keystone Pier.All values are in prototype scale. .......................................................... 47

4.14 Existing Conditions Modeling Domain Close-Up at Project Site........... 494.15 Existing Conditions, Ebb Currents........................................................ 494-16 Navigation Channel Transect for Current Speed Analysis ................... 524-17 Current Speed along Navigation Channel Transect for

Existing and Alternative 1 Typical Ebb Conditions ............................... 524-18 Current Speed along Navigation Channel Transect for

Existing and Alternative 3 Ebb Conditions............................................ 534-19 Current Speed along Navigation Channel Transect for

Existing and Alternative 5 Ebb Conditions............................................ 53

4-20 Difference in Current Speed between Alternative 1 andExisting Conditions, Ebb Currents........................................................ 54



4.23 Difference in Current Speed between Alternative 1 andExisting Conditions, Flood Currents .....................................................55

4-24 STWAVE Wide-Area Domain and Wave Buoy Location...................... 584.25 STWAVE Nested Modeling Domain .....................................................584.26 Significant Wave Heights and Peak Wave Direction,

Wide-Area Domain ............................................................................... 60

4.27 Significant Wave Height and Peak Wave Direction,Nested Domain..................................................................................... 61

4.28 Method 1 of analysis, Existing Conditions SouthwestWaves, H=3.3 ft T=4 s. ......................................................................... 62

4.29 Method 1 of analysis, Existing Conditions SoutheastWaves, H=3.3 ft T=4 s.........................................................................63

4.30 Method 1 of analysis, Alternative 5, Southwest Waves,H=3.3 ft T=4 s....................................................................................... 63


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Table of Contents v

4.31 Method 1 of analysis, Alternative 5, Southeast Waves,H=3.3 ft T=4 s....................................................................................... 64

4.32 Method 1 of analysis, Alternative 3, Southwest Waves,H=3.3 ft T=4 s....................................................................................... 64

4.33 Method 1 of analysis, Existing Conditions minusAlternative 3, Southeast Waves ........................................................... 65

4.34 Method 1 of analysis, Existing Conditions minusAlternative 5, Southwest Waves ........................................................... 65

4.35 Method 1 of analysis, Existing Conditions minusAlternative 5, Southeast Waves ........................................................... 66

4.36 Method 2 analysis, Wave heights along channel centerline.Existing Conditions and Alternative 3, SE storm H=3.3 ft,T= 4,0 seconds..................................................................................... 67

4.37 Method 2 analysis, Wave heights along channel centerline.Existing Conditions and Alternative 5, SE storm H=3.3 ft,T= 4,0 seconds..................................................................................... 67

4.38 Method 3 analysis, 10 ft depth contour-line.......................................... 694.39 Method 3 analysis, Wave heights along 10 ft contour-line,

SW storm, H=3.3 ft, T=4.0 seconds .....................................................694.40 LAGRSED Model Domain for Existing Conditions................................ 734.41 Site Aerial Photo and Sediment Sizes used for Sediment Transport

Modeling ...............................................................................................744.42 LAGRSED Model Input Sediment Size Distribution Grid...................... 744.43 Sand Material Observed in the Lower Beach .......................................754.44 Sand Material Observed at the Jetty in Dredged Material

Placement Area .................................................................................... 754.45 LAGRSED Model Existing Conditions Bottom Elevation

Change after Seven-Day Simulation ....................................................774.46 East Beach near Erosion Area in LAGRSED Modeling Results........... 784.47 LAGRSED Model Alternative 1 Bottom Elevation Change

after 10-Day Simulation ........................................................................ 794.48 Existing Navigation Channel Footprint and Sedimentation

Evaluation Area .................................................................................... 804.49 RMA4 Model Existing Conditions Finite Element Domain

and Location of Concentration Measurements in Keystone Harbor..... 834.50 Existing Conditions Dye Concentrations at Four Different Simulation

Times.................................................................................................... 854.51 Concentrations as a Function of Time at Measurement

Location for Existing Conditions and Jetty Alternatives........................855.1 WRL modeling facility during construction of the model.......................875.2 1:40 Scale model setup in 3D wave basin at the OSU WRL................ 885.3 Layout for existing conditions in 3D wave basin...................................90

5.4 Photo of model of existing conditions ...................................................915.5 Photo of model topography and bathymetry during construction .........915.6 Contour of the physical model in the wave basin (based on LIDAR

data). .................................................................................................... 925.7 Bathymetry difference, between prototype and model in prototype

scale ..................................................................................................... 935.8 Modeled existing conditions .................................................................945.9 Sediment at the jetty, observation during site visit ............................... 95


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Table of Contents vi

5.10 Available to WRL Sediment Grain Size distributions VS PrototypeComponents ......................................................................................... 95

5.11 Photo of sediment placed at the south jetty (prior model runs) ............965.12 Alternative 1A jetty extension. .............................................................. 975.13 Alternative 3A jetty extension with 2 alignments. ................................. 975.14 Alternative 3B submerged jetty extension with 2 alignments................ 98

5.15 Alternative 4, Alignment 2 wave barrier................................................ 995.15 Monochrome wave data measuring grid ............................................ 1015.16 Irregular wave data measuring grid ....................................................1025.17 Photograph of the current outflow manifold........................................1035.18 Current measurement grid..................................................................1045.19 Photograph of the ADV gages mounted on the bridge ready

for measurement. ...............................................................................1055.20 (a) Modeling grid and (b) bathymetry of the ADCIRC model

of the Physical modeling domail. ........................................................ 1075.21 Comparison of the physical modeled velocities (points)

and the ADCIRC simulated velocities (lines) along the KeystoneChannel as a function of distance from the Keystone Pier. All

values are in prototype scale..............................................................1095.22 Current velocity and direction for existing conditions for (a) physical

model and (b) ADCIRC simulation of the physical modeling domain. 1105.23 Current velocity and direction for Alternative 4 for (a) physical model

and (b) ADCIRC simulation of the physical modeling domain. ...........1105.24 Existing conditions current results ......................................................1125.25 Alternative 1A current results ............................................................. 1135.26 Current velocity difference Existing Alternative 1 .........................1135.27 Current velocity difference Existing Alternative 3a ....................... 1145.28 Current velocity difference Existing Alternative 3b ....................... 1145.29 Current velocity difference Existing Alternative 4 .........................1155.30 Modeled current velocities along channel centerline for

existing and Alternative conditions .....................................................1155.31 Difference in modeled current velocities along channel centerline

for existing and Alternative conditions................................................ 1165.32 Wave Refraction/Diffraction modeling results for Existing

conditions Case 6 ...............................................................................1185.33 Wave Refraction/Diffraction modeling results for

Alternative 1A Case 6 ......................................................................... 1195.34 Wave Refraction/Diffraction modeling results for all

alternatives and cases at model grid location 15, 15.......................... 1205.35 Shoreline change analysis for Alterative 1A, Case 6

time = 0 minutes .................................................................................1205.36 Shoreline change analysis for Alterative 1A, Case 6

time = 10 minutes ...............................................................................1215.37 Shoreline change analysis for Alterative 1A, Case 6

time = 15 minutes ...............................................................................1215.38 Shoreline change analysis for Alterative 1A, Case 6

time = 20 minutes ...............................................................................122

List of Tables2.1 Pt. Wilson constructed wind climate (1984-2002), percent

occurrence (speed >= 15 kt)................................................................... 8


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2.2 Return Periods of winds from southwest at Keystone............................82.3 Deepwater wave buoy wave heights frequency of occurrences........... 102.4 Wave heights and periods for extreme storms from southeast ............102.5 Wave heights and periods for extreme storms from southwest............112.5 Dredging and Disposal Record, Keystone Harbor................................ 262.6 Shoreline retreat rate at station 1 + 00 east of the Keystone jetty........ 28

4.8 Alternative Qualitative Comparison Based ........................................... 794.12 Residence Times for Jetty Alternatives Relative to Existing

Conditions.............................................................................................845.1 Physical Model Scaling Factors............................................................ 895.2 Prototype and Model dimensions based on 1:40 Froude scaling......... 895.3 Prototype and model wave parameters.............................................. 1005.4 Model Testing Scheme....................................................................... 1065.5 Current Velocity Reduction VS Potential Distance for Deceleration... 1115.7 Case number definitions..................................................................... 1175.9 Existing conditions shoreline change qualitative summary................. 1235.10 Alternative 1a shoreline change qualitative summary .................. 1235.11 Alternative 3a shoreline change qualitative summary ........................124

5.12 Alternative 3b shoreline change qualitative summary ........................1255.13 Alternative 4 shoreline change qualitative summary ..........................126


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Coastal & Hydraulic Modeling Study Page 1Keystone Harbor December 30, 2004

Keystone Harbor Coast & Hydraulic Study

1. Introduction

1.1. Objectives

Coast & Harbor Engineering (CHE) was contracted by CH2M HILL to

conduct a coastal and hydraulic modeling study to investigate feasibility ofmodification to the existing entrance of Keystone Harbor in order to improve

navigation conditions and safety of operation for existing and future ferrytraffic.

It has been documented by previous studies (for example see CH2M HILL,

2002 Report) that cross currents at the entrance to the harbor are a threat tonavigation for Washington State Ferry (WSF) vessels. The tidal currents at

the seaward end of the jetty generate a strong cross channel flow with

velocities (based on non instrumented observations) 4-6 knots (6-9 ft per

second). Figure1.1 shows the type of cross current flow observed onJanuary 31, 2004. Ferries entering the harbor are exposed to strong

hydrodynamic forces on the stern (due to crosscurrent flow) while the bow is

in still water, sheltered by the jetty. Force imposed to the vessel creates amoment that turns the bow clockwise toward the jetty, and vice versa. Ferries

exiting the harbor are exposed to a force on the bow while the stern is in the

sheltering area. Figure 1.2 shows the trace of the ferry leaving the harbor.The arrow shows the direction of ferry sweeping inside of the channel.

To counteract the current force, the captain must maintain the propeller thrustof the rudder to steer. However, the space for vessel maneuvering is limited,

especially if the vessel maintains a speed to control steering. For example, in

a typical approach to the dock, the vessel starts deceleration approximately

miles (1,320) ft from the wing walls. However, the available distance fordeceleration at Keystone Harbor is only 700 ft, which is approximately half of

the normally required distance.

The feasibility study has been initiated by WSF to develop and evaluate the

alternatives for improving navigation conditions at the entrance to the harbor.

These alternatives include a wide range of engineering components, consisting

of jetty modifications, dredging, change the configuration of the entrance


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channel, relocation of the ferry terminal, etc. The CHE study evaluated the

alternatives that include jetty modifications component only (description ofthe alternatives is presented in Section 3). The description of the alternatives

is presented in Section 3 of this report. It should be noted that the numbering

of alternatives presented herein is specific to this report only. It was done to

distinguish the specific objectives of this particular study - the feasibility ofjetty modifications, alone without any other components.

The proposed alternatives were evaluated based on comparison of the project

controlling factors before construction (known and modeled) for existing

conditions with those estimated (modeled) for each of the proposedalternatives (if they were to be constructed). The evaluation of the

alternatives was conducted based on the following controlling factors:

Cross current velocities,

Wave conditions in the channel and in the harbor,

Channel sedimentation and maintenance dredging requirements,

Shoreline erosion Shoreline erosion and bottom scour, and

Water quality.

This Technical Report describes each of the listed factors and issues

separately in subsequent sections and summarizes them in a comparative

analysis.

Figure 1.1 Cross current flow during site visit on January 30, 2004.


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Figure 1.2 Propeller from the ferry indicating a strong cross channel current

1.2. Methodology

Methodology of the study was developed to provide reliable and sufficient

information for evaluation of the proposed harbor entrance modification

alternatives. The methodology has been developed to include two major

components: Two-Dimensional (2-D) computer modeling, and 3-D physicalmodeling. The two-component approach is typical in coastal engineering

practice and is recommended in the US Army Corps of Engineers CoastalEngineering Manual 1100-2-1100 2003 (CEM), Section V, for coastal

projects that include harbor entrances and coastal inlets.

The physical processes constituting development and evolution of coastalinlets and harbors are extremely complex and diverse. There is no one single

engineering method that is able to reliably describe performance of harbor

entrance structures and their potential effects on coastal processes such astidal flow, sediment transport, shoreline and sea bottom morphology. Two

methods selected for the study complement each other and improve reliability

of the results. A detailed description of computer and physical modeling isdiscussed in appropriate sections of the report (See Sections 4 and 6).

In addition, each of the models, physical and computer, has certain limitationsand abilities to simulate the same physical processes and effect from the

alternative structures. For example: 2-D numerical modeling is limited in

simulating vertical stratification of the flow and effects from submerged or


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vertically variable structures, while physical model does not have this type of

limitation. The other example is limitation of physical modeling to simulatesediment transport that includes fine particles including small gravel and sand.

In summary the two-component methodology has provided reliable results for

engineering analysis and evaluation of alternatives.

2. Keystone Harbor Physical Conditions

Keystone harbor physical conditions that are discussed herein include geographical

location, bathymetry and topography, tide elevations, wind, waves, sediment andsediment transport characteristics, geomorphology of coastline. It should be noted that

project physical characteristics are obtained from the data compilation and reviewprogram. The additional information on Keystone physical conditions that was developed

in computer and physical modeling is presented in appropriate sections of the report.

2.1. Geographic Setting and HistoryKeystone Harbor, Washington, is located on the west side of Whidbey Island,a distance of 4 nautical miles across Admiralty Inlet from the city of Port

Townsend on the Olympic Peninsula (See Figure 2.1).

Keystone Harbor is an artificial harbor constructed by the Corps of Engineersin 1948 Appendix A presents the copy of Congress Authorization to the

Navigation project that states: The Purpose of the breakwater or jetty is

primarily to prevent shoaling in the entrance channel by encroachment ofgravel that is being moved along the beach from east by prevailing littoral

currents. Evidently, at this time (prior 1948) no concern regarding crosscurrent velocity effect on navigation conditions (rather than channel shoaling)

had existed. It was also believed that sediment transport predominately is fromwest to east. The practical experience and the current study, discussed below

in the report, show that the perceptions regarding cross current velocitynavigation hazard and sediment transport, used for original design were not

correct.

Keystone Harbor is bordering the southwestern edge of Lake Crockett. Anarrow beach of gravel separates the lake from the harbor. There is no

navigation access to the lake.

The Keystone Harbor Federal Project includes a mooring basin, a navigation

channel 1,000 feet long by 200 feet wide, a rock breakwater, and a boat

launch ramp. WSDOT operates a ferry from a dock at the head of themooring basin. The originally authorized depth of the channel was 18 ft mean

lower low water (MLLW). In 1992 the channel depth was re-authorized to 25

ft MLLW. However, the dredging depth usually includes advanced


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maintenance dredging that result in total depth after dredging at approximately

2.0 ft deeper than the authorized depth. Maintenance dredging in the channelis required every 4 to 6 years. Dredged material is routinely placed on the

beach east of the breakwater as beach nourishment replacing littoral drift

material that is cut off from the transport zone by the project. More detail

maintenance dredging history in the entrance channel is presented below inSection 2.6, Sediment Transport.

Figure 2.1 Keystone Harbor Geographical Location

2.2. Tides

Tides at Keystone Harbor and in Puget Sound in general consist of semi-

diurnal, mixed tides. The characteristics of tide elevations are presented in

Figure 2.2.

Tide measurements at the project area were conducted as a part of current data

collection program. Tides were measured at three current measuring stations(A, B, and C) within Admiralty Inlet from February 24 to March 15, 2004 and

at two stations (West and East) during 2002 period. Figure 2.3 shows location

of the measuring stations.

The analysis of measurements shows that tide elevations are nearly identical

at these three stations. Small increase of tidal ranges from Station A toStation B and further to Station C indicates on the tide wave propagates into

Puget Sound. Figure 2.4 shows the measured tidal elevations at all three

stations. The figure shows the tidal wave propagation toward the sound


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through the stations. The measured tide data were used further for validation

of tidal flow circulation computer model (See Section 4.2).

Figure 2.2 Tidal elevations at Keystone Harbor

Figure 2.3 Field Data Collection Stations A-C (2004) and Stations West and East(2002)


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-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2/28/04 0:00 3/1/04 0:00 3/3/04 0:00 3/5/04 0:00 3/7/04 0:00 3/9/04 0:00

Date and Time (UTC)

TidalElevation(m,

MSL)

Station AStation BStation C

Figure 2.4 Measured Tides at Stations A-C during the Deployment Period

2.3. Wind

The wind climate for the project area is influenced mainly by winds in

Admiralty Strait and in the Strait of Juan de Fuca. Winds are significant to the

project through wave and current generation, sediment transport, and vessel

handling. Wind data suitable for the project area was compiled and analyzedat two stations, Smith Island and Point Wilson. Smith Island wind data are

available from NOAA for the period 1984 through the present. The windspeed-direction-frequency of occurrence pattern at Smith Island is shown in

Figure 2.5.

Wind data recorded at Smith Island, while of excellent quality and indicative

of the general pattern of winds in this part of Puget Sound, were required

adjustment before application to Keystone Harbor. The distance from

Keystone to Smith Island is 14 miles. A short-term wind record at PointWilson (near the town of Port Townsend, 5 miles distant) was compared

statistically with that of Smith Island (CH2M HILL 2002) to deriveoccurrence frequencies applicable to the project site. The Point Wilson windexposure was judged to better represent conditions at Keystone from

directions other than southwest. A systematic difference noted in the two

records during overlapping time periods was the basis of the adjustmentapplied to the Smith Island data to derive project-specific wind statistics.

Details of the analysis and derivation of the adjustment factors are presented

in the feasibility study (CH2M HILL 2002). The original data of Point

Tides at Station C (red

are slightly higher)


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Wilson was affected by sheltering by the topography in the direction sector

between 180 and 280 degrees (south to west sector), so a correlation withSmith Island winds could not be determined specifically for those directions.

The factor of 0.92 derived for other directions was applied to Smith Island

winds to represent winds from the southwest over the wave generating area

for Keystone Harbor.

Wind speed, direction, and frequency of occurrence synthesized for analysisof wave-related processes at Keystone is listed in Table 2.1. Table 2.1

quantifies the percent time that speeds are equaled or exceeded in the period

of record. Speeds corresponding to probabilities of occurrence smaller thanthose listed in the table were analyzed by applying the data to a log Pearson

Type III extremal distribution. The calculated exceedance probabilities and

corresponding return periods and wind speeds from the southwesterly

quadrant are listed in Table 2.2.

Table 2.1 Pt. Wilson constructed wind climate (1984-2002), percent occurrence (speed >= 15 kt)WIND DIRECTION (oT)

Spd (kt) 10 20 30 40 50 60 70 150 160 170 180 280 290 300 310 320 330 340

15-19 0.0021 0.0021 0.0005 0.0004 0.0004 0.0003 0.0003 0.0016 0.0136 0.0204 0.0170 0.0012 0.0085 0.0092 0.0105 0.0144 0.0013 0.0021

20-24 0.0011 0.0011 0.0003 0.0002 0.0000 0.0000 0.0000 0.0008 0.0069 0.0103 0.0086 0.0006 0.0043 0.0046 0.0053 0.0073 0.0007 0.0011

25-29 0.0006 0.0006 0.0002 0.0001 0.0000 0.0000 0% 0.0004 0.0036 0.0053 0.0045 0.0003 0.0022 0.0024 0.0027 0.0038 0.0003 0.0006

30-34 0.0003 0.0003 0.0001 0% 0% 0% 0% 0.0002 0.0017 0.0026 0.0021 0.0002 0.0011 0.0012 0.0013 0.0018 0.0002 0.0003

35-39 0.0001 0.0001 0.0000 0% 0% 0% 0% 0.0001 0.0007 0.0010 0.0008 0.0001 0.0004 0.0005 0.0005 0.0007 0.0001 0.0001

40-44 0.0000 0.0000 0.0000 0% 0% 0% 0% 0.0000 0.0002 0.0003 0.0002 0.0000 0.0001 0.0001 0.0001 0.0002 0.0000 0.0000

45-49 0.0000 0.0000 0% 0% 0% 0% 0% 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

50-54 0% 0% 0% 0% 0% 0% 0% 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

TOT >=15 kt 0.418% 0.418% 0.116% 0.0630% 0.0402% 0.0367% 0.0367% 0.312% 2.660% 3.990% 3.325% 0.238% 1.664% 1.794% 2.051% 2.820% 0.256% 0.418%

NO. C

0


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Figure 2.5 Location of Smith Island wind measuring station, Pt. Wilson, andKeystone Harbor and Wind Rose (based on Smith Island data)

2.4. Wave ClimateThe wave climate at Keystone Harbor and the adjacent areas is complicated

and consists of at least three major wave systems: Pacific Ocean waves, wind

storms from the Strait of Juan de Fuca, and local Admiralty Bay wind-waves.

Pacific Ocean Waves System:Pacific Ocean deepwater water wave

information was compiled from the La Perouse Bank Wave Buoy #C46206

(Canadian Marine Environmental Service), located at approximately 70 milesoffshore (126.00 W and 48.83 N). The buoy location is depicted on Figure

4.24 at the seaward end of the wave modeling domain used for wave

transformation numerical modeling (See Section 4). The buoy data consists

of wave parameters, wave height and wave period, for 16-year period, 1984 to2003 (with small gaps) at one hour frequency of observation. Frequency of

occurrence of wave heights based on the buoy data is presented in Table 2.3.


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Table 2.3 Deepwater wave buoy wave heights frequency of occurrences

Wave Statistics for Complete Data Set - Canadian Station c46206 - Number of Occurrances

Period (seconds)

Wave Height (m) 0-3 3-6 6-9 9-12 12-15 15-18 18-21 21-24 24-27 27-30 >30 %

>10 2 2 0.0%

9-10 1 1 6 0.0%

8-9 2 8 11 0.0%

7-8 14 40 25 0.1%

6-7 3 125 253 94 0.5%5-6 35 595 900 399 1.9%

4-5 345 1896 2238 860 5.2%

3-4 7 1701 5089 4865 1415 12.8%

2-3 306 5185 11863 7992 2036 3 26.9%

1-2 1 1809 12990 16672 6973 3097 2 40.8%

0-1 85 437 3675 2538 2466 2842 18 11.8%

% 0.1% 2.5% 23.5% 38.1% 25.3% 10.6% 0.0% 0.0% 0.0% 0.0% 0.0%

Strait of Juan de Fuca Wave System:Wind waves in the Strait of Juan de

Fuca is a significant constituent to the wave system at the project area. Due to

long fetch, wind waves in the straight can be developed to a significant heightand long period. Analysis of these waves was conducted using numerical

modeling and wind data compiled from the La Perouse Bank Wave Buoy

#C46206 (See Section 4).

Local Wind Wave System:The local wind waves are generated by frequent

winds acting in 1500-260

osegment. The analysis of wind data performed

during the Feasibility Study (CH2MHill 2002) was limited to wave origins,

approaching from Southeast, between 150 and 180 degrees (True North). An

extended wind-wave analysis was conducted based on additional wind data(See Section 2.3) and numerical modeling (See Section 4).

Two major locally generated wind wave systems approaching from Southeast

and Southwest directions were selected for evaluation of the alternatives

further. Extreme wave parameters for the southeast and southwest wind

generated waves were calculated and are listed in Tables 2.4 and 2.5.

Table 2.4 Wave heights and periods for extreme storms from southeast

Return Period(yrs)

Wave Height(ft)

Wave Period(Sec)

5 3.09 3.59

10 3.29 3.69

20 3.47 3.7850 3.71 3.89

100 3.86 3.96


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Table 2.5 Wave heights and periods for extreme storms from southwest

Return Period(yrs)

Wave Height(ft)

Wave Period(Sec)

5 2.71 3.41

10 2.93 3.54

20 3.13 3.63

50 3.41 3.77

100 3.61 3.87

2.5. Currents

Keystone Harbor, located near the entrance to Puget Sound, is in an area of

strong influence of tidal currents. These currents move in and out of

Admiralty Inlet, past numerous geographic features along Whidbey Island andthe Olympic Peninsula near Port Townsend. Several prominent geographic

features impact tidal flows in the area. Point Wilson on the OlympicPeninsula causes significant eddying and flow variability in the tidal currentson both ebb and flood tide. Cross-channel variability at Admiralty Inlet has

required multiple measurement locations across the channel to resolve the

variations of the along-channel flow through the sections (Cannon et al 2001).

Past studies have also noted the high variability in the circulation in theeastern Strait of Juan de Fuca, including complex patterns of eddies, fronts,

and shore-directed current components, which tend to increase with eastward

distance into the system towards Admiralty Inlet (Holbrook et al 1980).

In order to determine the project site specific conditions, the field

measurement programs had been conducted in 2002 and 2004.

Currents from 2002Data Collection Program:

2002 data collection program consisted of deployment two stations, West andEast, equipped with Acoustic Doppler Current Profiler (ADCP) meters

(CH2MHill 2003). Location of the stations is shown in Figure 2.3. The

current meter stations were deployed along the shoreline at water depths 36.2feet and 34.3 ft MLLW for West and East stations respectively. The sensor

head of each ADCP was approximately 9.8 feet above the seabed. Each

instrument recorded the average speed and direction of the current over a 10-

minute averaging period for each 1-meter thick water layer from the sea

surface to the layer 1 meter above the top of the ADCP. Stations collecteddata for 18 days, from June 28 to July 15, 2002.

Current data from both East and West stations showed prevailing flow in a

southwesterly ebb direction the majority of time regardless of whether the

current is ebbing (flowing northward out of Admiralty Inlet) or flooding(flowing southward into Admiralty Inlet). Figures 2.6 and 2.7 show the time

series of current velocities and directions measured at West and East Stations


28/49


respectively. The figures show that most of the time velocities are directed

toward 240 -260 degrees (to the west). Change in the flow to the oppositedirection corresponds to reduction of current velocities. Figures 2.8 through

2.11 show the results of comparison the eastward and westward directed

current for West and East stations. The figures show strong statistical

predominance of current velocities on both stations to the west.

Based on review and analysis of field data it appears that the stations,specifically west station, were located in a persistent counterclockwise

rotating gyre that has only brief periods when the current reverses and flows

in an easterly direction at much less speed than the persistent ebb flow. TheEast station, however, has longer periods in which the persistent ebb flow

reverses to become a flood current, sometimes nearly as strong as the

persistent ebb flow.

Current data from both East and West stations also showed that the velocityspeeds and directions are reasonably homogeneous over the water column.Figures 2.12 and 2.13 are the snapshots of stratification current velocities and

directions at West station at different measuring events. Figures 2.14 and 2.15

are the snapshots of stratification current velocities and directions at East

station at different measuring events. Evaluation of stratification of currentvelocities suggests that the flows along the shoreline can be adequately

represented by a depth-average numerical model. Data from 2002 measuring

program also are used below for calibration and validation of tidal flowcirculation computer model.

Currents from 2004 Data Collection Program

2004 data collection program consisted of deployment three stations, each of

them equipped with ADCP current meter. Location of the stations is shownabove

1in Figure 2.3 and also specified below.

Station Location

Station A -122.6935 W; 48.1606 N; Depth =38.5 ft MLLW

Station B -122.7124 W; 48.1222 N, Depth = 18.1 ft MLLW

Station C-122.6056 W; 48.1200 N Depth = 18.0 ft MLLW

The current data were colleted at these stations during the period fromFebruary 24 to March 15, 2004, total of 10 days. The locations of these

stations were selected predominately for calibration and validation ofnumerical model (See Section 5). The data from the stations also were used to

describe the general pattern of flow and validate conclusions from 2002 data

collection program.

1Current meters were deployed at the same tripods as a pressure (tide elevation) gauges.


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The current data from all three stations reiterated observation from the

previous study regarding homogeneous current speeds and directions over the

water column and applicability of depth-averaged numerical models fordescribing the flow fields in Admiralty Inlet. However in distinction to

previous West and East stations, the current data from A, B, and C stationsshowed a distinguishing difference in flow directions during flood and ebbcycles. Figures 2.16, 2.17, and 2.18 show depth averaged current velocities

and directions at Stations A, B, and C for a four-day period, beginning fromFebruary 28, 2004. Different directions of ebb and flood currents may be

observed at all stations. It appears that eddies forming a predominant

westward flow (observed based on 2002 datasets) are more frequently

observed features at the area adjacent to the Keystone jetty. It is possible thatconstruction of the jetty in 1948 has contributed to phenomena of eddies

formation at the entrance to the harbor. It is notable that current directions at

Station C indicate fluctuations that are nearly continuous through the tidal

cycles. It is possible that Station C, located along the shoreline, at the samedepth as West and East stations, but at the boundary of transition zone of the

eddy controlled flow. Data from 2002 measuring program also are usedbelow for calibration and validation of tidal flow circulation computer model.

0

200

400

600

800

1000

1200

7/1/02 0:00 7/2/02 0:00 7/3/02 0:00 7/4/02 0:00 7/5/02 0:00

Date and Time (UTC)

CurrentSpeed(mm/s)

0

60

120

180

240

300

360

Direction(degreesTrueNorth)

Speed

Direction

Figure 2.6 Depth-Averaged Current Speed and Direction Example Time Series

at West


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0.0

0.2

0.4

0.6

0.8

1.0

1.2

7/1/02 0:00 7/2/02 0:00 7/3/02 0:00 7/4/02 0:00 7/5/02 0:00

Date and Time (UTC)

CurrentSpeed(m/s)

0

60

120

180

240

300

360


Speed

Direction

Figure 2.7 Depth-Averaged Current Speed and Direction Example Time Series

at East Current Meter

0 0.2 0.4 0.6 0.8 1 1.20

2

4

6

8

10

12

14

16

18

20

22

Velocity magnitude (m/s)

Percentage%

Figure 2.8 Distribution of Current Speeds Directed West along the Shoreline

at West Station, 2002 Data


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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90

5

10

15

20

25

30

35

40

45

50


Percentage%

Figure 2.9 Distribution of Current Speeds Directed East along the Shoreline

at West Station, 2002 Data

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

5

10

15

20

25


Percentage%

Figure 2.10 Distribution of Current Speeds Directed West along the Shoreline at

East Station, 2002 Data


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0 0.2 0.4 0.6 0.8 1 1.20

5

10

15

20

25

30

35

40

45


Percentage%

Figure 2.11 Distribution of Current Speeds Directed East along the Shoreline at East

Station, 2002 Data

0.0

2.0

4.0

6.0

8.0

10.0

12.0

0 200 400 600 800 1000 1200 1400

Current Speed (mm/s)

HeightAboveBottom(

m)

7/11/02 16:307/11/02 21:007/12/02 2:007/12/02 7:107/12/02 9:407/12/02 13:007/12/02 17:00

Figure 2.12 Current Speed Vertical Profiles at West Current Meter during Flood and

Ebb Tide (dates in PST)


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0.0

2.0

4.0

6.0

8.0

10.0

12.0

0 45 90 135 180 225 270 315 360

Direction (degrees True North)

HeightAboveBottom(

m)

7/11/02 16:30

7/12/02 2:00

7/12/02 7:10

7/12/02 9:40

7/12/02 13:00

7/12/02 17:00

Figure 2.13 Current Direction Vertical Profiles at West Current Meter during Flood

and Ebb Tide (dates in PST)

0.0

2.0

4.0

6.0

8.0

10.0

12.0

0 100 200 300 400 500 600 700

Current Speed (mm/s)

TotalDepth(m)

6/30/02 19:30

7/1/02 0:20

7/1/02 7:00

7/1/02 10:10

7/1/02 11:20

7/1/02 16:50

Figure 2.14 Current Speed Vertical Profiles at East Current Meter during Flood



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0.0

2.0

4.0

6.0

8.0

10.0

12.0

0 45 90 135 180 225 270 315 360

Direction (degrees True North)

HeightAboveBottom(

m)

6/30/02 19:30

7/1/02 0:20

7/1/02 7:00

7/1/02 10:10

7/1/02 11:20

7/1/02 16:50

Figure 2.15 Current Direction Vertical Profiles at East Current Meter during Flood


0

500

1000

1500

2000

2500

3000

2/28/04 0:00 2/29/04 0:00 3/1/04 0:00 3/2/04 0:00 3/3/04 0:00

Date and Time (UTC)

Depth-AveragedCurrentSpeed(mm

/s)

0

60

120

180

240

300

360

Direction(degrees,

TrueNorth)

Speed

Direction

Figure 2.16 Depth-Averaged Current Speed and Direction Example Time Series at

Station A


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0

500

1000

1500

2000

2500

3000

2/28/04 0:00 2/29/04 0:00 3/1/04 0:00 3/2/04 0:00 3/3/04 0:00

Date and Time (UTC)

Depth-AveragedCurrentSpeed(mm/s)

0

60

120

180

240

300

360


Speed

Direction

Figure 2.17 Depth-Averaged Current Speed and Direction Example Time Series at

Station B

0

500

1000

1500

2000

2500

3000

2/28/04 0:00 2/29/04 0:00 3/1/04 0:00 3/2/04 0:00 3/3/04 0:00

Date and Time (UTC)

Depth-AveragedCurrentSpeed(mm/s)

0

60

120

180

240

300

360

Direction(degreesTrueN

orth)

Speed

Direction

Figure 2-18 Depth-Averaged Current Speed and Direction Example Time Series at

Station C


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2.6. Sediment Transport

Since the time of constructing the navigation project in 1948 the sediment

transport system at the Keystone shoreline has consisted of two littoral cells:

East Cell, eastward from the jetty and West Cell, westward from thenavigation channel. These two littoral cells are separated by the jetty and

navigation channel. The cells have a limited exchange of sediment between

them except for the artificial bypassing associated with the dredging eventswhen sediment from the West cell is placed in the East cell. It should be

noted that no direct measurements of sediment transport in the project area are

known to have been made and evaluation of sediment transport is based onreview and analysis of morphological indicators, aerial photographs, harbor

dredging activities, publications and previous studies at the area.

High bluffs of glacial outwash, containing materials in the size range of sand

to boulders, are located northwest and southeast from the project area. Figure

2.19 illustrates the topography and emphasizes the bluff features near the site.Active erosion of the bluffs by wave undercutting of the toe, followed by

episodic collapse of the bluff face is the mechanism for supplying sediment to

the littoral system of this shoreline reach. Waves and currents then transportmaterial into the harbor.

Previous studies (for example Keuler, 1988) provided estimates of bluffretreat rate on the east side of Admiralty Bay of approximately 0.21 meters

(0.7 ft) per year. Based on the average bluff height and retreat rate, the

estimated volume contribution from sediment eroded off the bluff to the

littoral system was 3 cu m (~4 cy) per linear meter of shoreline per year or12,000 cu m (more than 15,000 cu yd) for the entire southward part of the

Keystone shoreline per year..

The previous study (Keuler, 1988) also calculated the bluff retreat rate at a

location north of Admiralty Head to be 15 cm per year. The estimated bluffvolume loss was 4 cu m per meter of shoreline per year

2. Typical bluff

material at Admiralty Head is shown in Figure 2.20. Sediments are sorted

according to size, or more specifically hydrodynamic characteristics, and the

fine material is expected to be carried offshore to a less turbulentenvironment.

The dominant direction of transport has been inferred from wave approach

angle relative to the shoreline and morphological indicators, evident fromaerial photographs, maps and site assessments. The main pathway of

2It should be noted that the location at which this estimate applies (Pt. Partridge) may not be a good basis

for estimating the sediment supply rate at Admiralty Head, but Pt. Partridge is the nearest location to

Admiralty Head for which data exist for estimating a bluff retreat rate..


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sediment toward Keystone Harbor, as indicated in Figure 2.19. (Keuler

1988), is eastward from Admiralty Head. The Seattle District Corps ofEngineers studied the harbor shoaling (Seattle District 1972) and diagrammed

the wave climate as shown in Figure 2.21. The wave diagram was the basis of

a transport study that resulted in a transport pathway diagram (Figure 2.22),

and indicates net transport is eastward from the harbor entrance. Farthereastward and southward along this same shoreline the transport direction is

northward and westward. Between these two reaches is a zone of

convergence.

Figure 2-19 Transport patterns, bluff retreat rate and volume loss rate as developed

by Keuler (1988)


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Figure 2-20 Typical composition and morphology of bluff and upper beach whichcontribute sediments to Keystone Harbor


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Figure 2.21 Wave diagram applicable to the Keystone Harbor entrance(source: Seattle District Corps of Engineers 1972)


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Figure 2.22 Littoral drift directions at Keystone developed by Seattle District corpsof Engineers (1972)

The Seattle District estimated that from 1960 to 1972, the rate of placement of

dredged material on the east side of the jetty was approximately equal to therate at which waves transport the material away from the disposal site. It is

significant to note in the Seattle District report that material dredged in 1949

and 1955 was disposed in deep water east of Keystone. During that time the

beach east of the jetty eroded rapidly, requiring repairs to the shore end of theeast side of the breakwater. Since that time sediment continuity and an

approximately equilibrium shoreline shape and position have been maintainedby mechanically placed sediments dredged from Keystone Harbor.

Figure 2.23 shows the shoreline shape before the harbor was created and

indicates the equilibrium configuration. Note the small accumulation of beach

material on the west (updrift) side of the dock, indicating eastward nettransport.

The jetty and dredged channel after construction in 1948 became a complete

barrier to longshore transport of coarse material. The jetty extends across the

shoreline and the toe is located at about -50 feet of the water depth. The depthat the jetty toe is below the depth of closure, meaning that waves do not move

sediment at that depth. The depth of closure for 50-year storm conditions

(Hallermeier 1983) was estimated at less than 10 ft. MLLW. Therefore, theharbor traps most of littoral sediment moving eastward around Admiralty

Head, as well the jetty and channel trap the most amount of sediment moving

westward around the jetty tip in suspension. Sedimentation of the channel and


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harbor from the westward littoral drift consists mostly of sand and fine

particle3.

Figure 2.23 Shoreline shape and features prior to jetty construction and dredgingKeystone Harbor

Sediment transport continuity past the harbor entrance has been maintainedartificially by dredging accumulated sediment from the harbor and placing it

at the shoreline on the east side of the jetty for a distance of about 700 feet.

Maintenance dredging occurs approximately every 6 years since initialdredging in 1948. A complete list of dredge dates, volumes and disposal sites

is listed in Table 2.5. The location of typical dredging areas and disposal site

used by the Corps of Engineers during Keystone Harbor maintenancedredging operations are shown in Figure 2.24.

3This interpretation was taken into consideration for computer modeling of sediment transport (See Section

4.3)


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Figure 2.24 Dredging and disposal areas for Keystone Harbor maintenancedredging

Table 2.5 Dredging and Disposal Record, Keystone Harbor

Type Year Amount Dredged Disposal Site

Original Dredge 1948 CY

Maintenance 1954 23,900 Approx. 500 ft offshore

Maintenance 1960 27,000 Beach east of the basin (east of Jetty)




Maintenance 1980 26,000 Within the State's underwater park


Maintenance 1993 33,000

Beach east of the basin (east of Jetty)25,000 cu yd at beach, rest at Open

Water Disposal Site near PortTownsend



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The dredging record suggests an average of approximately 1,100 cu yd of

sediment enters the channel annually. Most of this sediment is dredged from

the western part of the channel and consists of sandy and gravelly materialsimilar to that found on the dredged material disposal site east of the jetty.

Figure 2.25 shows the material sizes in the disposed dredged material. Somesmall amount of material is dredged at the eastern part of the channel andinside the harbor. This material is represented by sand and finer particles. It

is likely that the source of this material is the westward sediment transport

delivered by tidal flow in suspension from the littoral zone east of the jetty.

Figure 2.25 Dredged materials disposed east of the jetty, which feeds the beachfarther to the east

Analysis of dredging data and activities and findings from previous studies

suggests that the sediment transport of coarse material in the vicinity of the

project has been predominantly from west to east. In support of this statementcalculations of ratio between east-west and west-east sediment transport

potentials using wave power methods (CEM, 2003) were conduced. Wavedata, described above and available bathymetry survey data were used as input

parameters. The results of calculations show that west-east component of thelittoral drift at the entrance to the harbor is approximately in order larger than

that of east-west direction.

Prior to construction of the jetty in 1948, a small amount of coarse material

had contributed to the westward (east to west) littoral drift. Since construction


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of the jetty, only fine sediment (sand and silt) are transported to the west

around the jetty and accumulates in the channel. If construction of the jetty in1948 was to reduce maintenance dredging, it appears that location of the jetty

on the east side of the channel had not been the optimal solution.

2.7. Shoreline and bottom slope morphology

The shoreline and bottom slope of Keystone coastline are subjected to various

hydrodynamic and geological forces and are in constant change. Historical

shoreline change at the area east of the jetty was analyzed with measurementsof the positions of high tide line and top of the bank. These measurements

were obtained from previous studies (Seattle District COE, 1972). Theprevious measurements were taken along the transects spaced 100 feet apart.

The area of measurements extended 600 ft eastward from the jetty. Shoreline

retreat rates calculated for the area approximately 600 ft east from the jetty(transect 1 + 00) are summarized in Table 2.6. The tabulated retreat rates

represent the shoreline of the disposal area which is intended to be a feedsource for maintaining sediment continuity along the beach east of the jetty.Material was deposited at this shoreline in 1954, 1960, 1966, and 1971. The

seaward slope of the disposed material is steeper than the equilibrium slope,

and rapid initial adjustment of this artificial shoreline results in higher

retreat rates.

Table 2.6 Shoreline retreat rate at station 1 + 00 east of the Keystone jetty

Shoreline average retreat rate (ft/yr)

Range of years MHHW shoreline Top of Bank

1957 - 1960 7 8

1960 - 1966 27 30

1966 - 1970 18 25.5

1971 - 1974 31.5 27

As part of this study the shoreline change analysis was extended eastward for

more than a mile distant from the harbor. Figure 2.26 shows the location ofthe transects for measurements of shoreline retreat

app9_section13

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