2002 Monitoring Program Report - Pacific County, Washington files/benson beach.pdf · 2002...

2002 Monitoring Program Report Benson Beach Demonstration Project Phase 1

PACIFIC INTERNATIONAL ENGINEERING PLLC

2002 Monitoring Program Report Benson Beach Demonstration Project Phase 1 Prepared by: Vladimir Shepsis, Ph.D., P.E. Coastal Engineer

February 2003

PACIFIC INTERNATIONAL ENGINEERING PLLC

POST OFFICE BOX 1599 • 123 SECOND AVENUE SOUTH • EDMONDS, WASHINGTON • 98020

Table of Contents

2002 Monitoring Program Report i Benson Beach Demonstration Project Phase I

Table of Contents

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

2. Phase 1 Demonstration Project Design and Implementation .... 7 2.1 Objectives ....................................................................... 7 2.2 Design and Planning ....................................................... 8 2.3 Implementation and Operational Data ........................... 11 2.4 Major Conclusions From This Section ........................... 14

3. Hydrodynamic Processes Monitoring Data ............................. 15 3.1 Waves........................................................................... 15

3.1.1 North Jetty Re-handling Site Wave Station........ 15 3.1.2 Station 2. Columbia River Bar Wave Buoy......... 22 3.1.3 Station 3. Site E................................................. 25

3.2 Currents ........................................................................ 29 3.3 Major Conclusions From This Section: .......................... 34

4. Monitoring Benson Beach Morphology and Sediments........... 35 4.1 Topography................................................................... 35 4.2 Nearshore Bathymetry .................................................. 41 4.3 Aerial Photography........................................................ 42 4.4 Sediments ..................................................................... 48

5. Conclusions and Recommendations....................................... 51

6. References ............................................................................. 53

Appendices

A Scope of Work

B Figures B1 through B6

List of Figures

1 Vicinity Map............................................................................... 2 2 Mouth of Columbia River Disposal Sites ................................... 3 3a Cumulative MCR Dredged Material Disposal Volumes by

Sites for the Period Between 1970-2002................................... 3 3b Cumulative MCR Dredged Material Disposal Volumes by

Active Sites E and F for the Period Between 1989-2002........... 4 4 Aerial Photograph, Long Beach Peninsula from North Jetty

to Willapa Bay Entrance............................................................ 5 5 Schedule of Data Collection...................................................... 9

Table of Contents

ii 2002 Monitoring Program Report Benson Beach Demonstration Project Phase I

6a July 16, 2002, First Load, Pump-off In Progress ......................11 6b July 16, 2002, First Load, Sediment Discharge at the

Benson Beach Demonstration Project .....................................12 7 Benson Beach Demonstration Project, Hopper Dredge

Sugar Island Pump-out Versus Pump-in Time .........................13 8 Benson Beach Demonstration Project, Hopper Dredge

Dredging and Disposal Total Cycle Time .................................14 9a Buoy Marks Location of Wave and Current Meter Station 1.....16 9b Wave and Current Meter Station 1 Prior to Deployment ..........16 10 Water Surface Time Series......................................................17 11 Station 1, Wave Time Series (Significant Wave Height,

Period, Direction, Water Depth) Versus Station 3 Wave Data for the Period Between July 11, 2002 Through September 19, 2002 ................................................................18

12 Station 1, Wave Time Serious (Significant Wave Height, Period, Direction, Water Depth) Versus Station 3 Wave Data for the Period Between September 19 Through December 2, 2002 ...........................................................................19

13 Station 1, Wave Parameters Timed Series for the Period Between July 16-17, 2002 .......................................................20

14a Station 1, Wave Rose, for the Period Between July 11, 2002 through September 19, 2002 ...................................................21

15 Station 1 Wave Statistics Comparison, 2002-2000 ..................22 16 Station 2, Columbia River Bar Buoy Compiled 1996-2002,

Month of July, Wave Rose, Aerial Photograph of North Jetty Dated July 29, 2002.................................................................24

17 Station 2, Columbia River Bar Buoy Compiled 1995-2002 Summer Time Wave Rose, Aerial Photograph of North Jetty Dated July 29, 2002.................................................................25

18a Wave Buoy at Site E (1 of 2) ...................................................27 18b Wave Buoy at Site E, Prior to Deployment (2 of 2) ..................27 19 Station 3, Wave Parameters Time Series for the Period

Between December 7-17, 2002 ...............................................28 20 Station 1, Example of Processed Current Velocities and

Directions Measured by SonTec ADP......................................30 21 Station 1, Example of Processed Current Velocities and

Directions Measured by ADV...................................................31 22 Station 1, Current Data Rose Plot – Depth Average

Currents, for the Period Between July 11, 2002 Through August 31, 2002 ......................................................................32

23 Station 1, Depth Average Current Velocities and Directions Statistics ...........................................................................33

24 Topographic Survey Transects ................................................36 25 Beach Profile Volume Change Relative to Before Sediment

Placement ...........................................................................37 26 CLAMMER Conducting a Beach Topographic Survey .............38

Table of Contents

2002 Monitoring Program Report iii Benson Beach Demonstration Project Phase I

27 Example of Topographic Survey Image, July 13, 2002 ........... 39 28 Benson Beach Surface Elevations Change for the Period

Between July 20, 2002 and July 13, 2002............................... 40 29 Benson Beach Nearshore Bathymetry July 15, 2002 .............. 43 30 Benson Beach Nearshore Bathymetry August 6, 2002 ........... 44 31 Benson Beach Nearshore Bathymetry Change Between

August 6, 2002 and July 15, 2002........................................... 45 32 Aerial Photograph July 9, 2002; Sediment Placement Area .... 46 33 Aerial Photograph July 21, 2002 ............................................. 47 34 Aerial Photographs of Benson Beach on July 7, 2001 and

July 21, 2002 .......................................................................... 47 35 Results of Sediment Sampling Analysis Mid Sampling Area,

Transect BB 28 Between July 15-24, 2002 ............................. 49

List of Tables

1 Benson Beach Perceptions and Hypotheses ............................ 7 2 Summary - Bids for 2002 Dredging at MCR, Columbia River

and Coos Bay ......................................................................... 10 3 Benson Beach Transect Unit Volume Changes (cy/per

linear ft)................................................................................... 35 4 Volume Changes Inside of Dashed Line (Figures 27-32) ........ 39

G:\PI & JV Project Files\0132.D-Coastal Erosion Prj\312 Benson Beach\4-Tech Docs\2002\Report\2-19-03VS-HH-jvFINALReport.doc

Acknowledgments

2002 Monitoring Program Report v Benson Beach Demonstration Project Phase I

Acknowledgments

The Monitoring Program and this Report was conducted and prepared by a team of engineers and scientists from Pacific International Engineering PLLC (headed by Vladimir Shepsis, Ph.D., P.E., Principal and Coastal Engineer) in conjunction with the Department of Ecology. The team wishes to express its gratitude to the following persons and entities assisting in the preparation of this Report:

Coastal Communities of Southwest Washington

Washington State Department of Ecology: George Kaminsky

U.S. Army Corps of Engineers, Portland District: Doris McKillip, Hans “Rod” Moritz, Karen Garmire, and Sheryl Carrubba

U.S. Geological Survey: Peter Ruggiero

Cover photograph courtesy of the Portland District, US Army Corps of Engineers.

Introduction

2002 Monitoring Program Report 1 Benson Beach Demonstration Project Phase I

1. Introduction

The purpose of this report is to present a summary of the data and technical information collected during the Monitoring Program of the Phase 1 Benson Beach Demonstration Project. The data collection program was developed and conducted by Pacific International Engineering PLLC (PI Engineering) and the Washington State Department of Ecology (DOE) under the contract with the Southwest Washington Coastal Communities. The report also includes the project-related data collected by USGS and NOAA under different programs.

The Benson Beach Demonstration Project (Demonstration Project) is located at the south end of the Long Beach Peninsula and immediately north of the North Jetty of the Columbia River Navigation Project (see Figure 1). The background and purpose for the Demonstration Project and the Monitoring Program at Benson Beach is as follows:

• The Corps of Engineers has conducted regular maintenance dredging operations in order to provide safe and reliable commercial navigation through the Mouth of the Columbia River (MCR). Typically, four to five million cubic yards of sediment per year are dredged in the MCR and disposed of at various open water disposal sites located offshore at various depths, typically from 40 to 300 ft deep. The locations of current and historic disposal sites are shown on Figure 2. Three ocean disposal sites, Site E, Site F, and the North Jetty Site, have been used in recent years. During the 2003 dredging season, a new “deepwater site” has been proposed in addition to the resumption of placement at Site A. Volumes of the sediment placed on each of the disposal sites have been varied depending on physical conditions at the sites, as well as economical and permitting issues.

• The information regarding volumes of MCR sediment placed at various disposal sites during the last 32 years (since 1970) is compiled and presented in Figure 3a. Figure 3a shows cumulative volumes of disposal at Sites A, B, E and F. The total volume of MCR sediment disposed at Sites A and B for 26 years is approximately 68 million cy. The schedule of sediment disposal at the different sites for the last 13 years was extracted from the total MCR database and is presented in Figure 3b. Figure 3b presents the cumulative volume of sediment placed at Site F since 1989, and is approximately 14 million cy.

Introduction

2 2002 Monitoring Program Report Benson Beach Demonstration Project Phase I

Figure 1 Vicinity Map

Introduction


Figure 2 Mouth of Columbia River Disposal Sites

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Figure 3a Cumulative MCR Dredged Material Disposal Volumes by Sites for the Period Between 1970-2002

Introduction


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Figure 3b Cumulative MCR Dredged Material Disposal

Volumes by Active Sites E and F for the Period Between 1989-2002

• Previous studies demonstrated that the approximately 100 miles of

coastline of the State of Washington and coastline of the northern part of the State of Oregon originated from and have been created and maintained by the sediment coming from the Columbia River. Figure 4 shows the coastline of the Long Beach Peninsula (approximately 19 miles) that has been dependent on sediment delivered by the Columbia River.

• Washington Coastal Erosion Study (Gelfenbaum, et al. [1999], Peterson, et al. [1991]) determined that the rate of delivery of sand sediments to the coast from the Columbia River has diminished over the past century and currently may not exceed two million cy per year. Therefore, the amount of material being delivered into the littoral system and available to build and sustain Washington and Oregon beaches has been significantly reduced. The sediment dredged at the MCR project constitutes the littoral system budget. It is critical for the coastal zone that this sediment is available for the longshore sediment transport and that it is disposed of in the vicinity of the littoral drift system. By definition of various scientists and engineers, the seaward boundary of the littoral system (depth of closure) at the MCR is in the range between 50 and 100 ft. It can be noted that most of the historical and current disposal site depths are deeper than the above 50-100 ft depth criteria.

The MCR is an extremely dynamic area, subject to wind waves, swell, and strong currents on a daily basis. Dredging of the MCR Navigation Channel has been feasible only by using hopper dredges (bottom-dredge) for open water disposal. The use of a

Introduction


cutterhead pipeline dredge, which is the traditional technique for placement of sediment to the nearshore zone and beach nourishment, is limited at this area. The assumption that placement of dredged material from the MCR project onto Benson Beach nearshore area is not feasible has been developed and transformed into a strong perception.

Figure 4 Aerial Photograph, Long Beach Peninsula from North Jetty to Willapa Bay Entrance (photograph courtesy of DOE)

Introduction


The Demonstration Project has been developed to determine the feasibility of an alternative to place sediment dredged from the MCR in the surf zone at Benson Beach. The purpose of analyzing the data collected during the Demonstration Project is to evaluate the hypothesis of the “technical feasibility” of nearshore placement of the dredged sediment from MCR at Benson Beach. The data and information collected during Phase I also will be used to optimize the technology of direct or re-handled sediment placement at Benson Beach, and/or to identify an alternative disposal site and technologies if indeed Benson Beach is not a feasible and/or comprehensive solution.

The Demonstration Project is an adaptive management project, consisting of several phases that can be and have been adjusted to the data obtained from the preceding phase, conditions of MCR dredging project, funds available, and permit restrictions. Currently, the Demonstration Project has been scheduled with four phases:

• Phase 1: Placement of a small volume (43,000 cy) of MCR sediment using direct pump-off facilities of the hopper dredge

• Phase 2: Placement of a large volume (~260,000 cy) of MCR sediment using direct pump-off from the hopper dredge

• Phase 3: Placement of a large volume (~500,000 cy) of MCR sediment using a re-handling sump and dredging technology.

• Phase 4: Placement of a regular volume (to be determined by previous phases) of MCR maintenance dredging using a re-handling sump and dredging technology.

Phase 1, placement of a small volume (43,000 cy) of MCR sediment using direct pump-off facilities of the hopper dredge, was implemented in July 2002. The Monitoring Program included field data collection and analysis began on July 2002, and lasted through January 2003. A progress report on the Monitoring Program was prepared and issued by PI Engineering and DOE on July 29, 2002 with assistance from USGS. The current report provides the final results of the Monitoring Program for the year 2002 and recommendations for the next phase of the Benson Beach Demonstration Project in 2003.

Phase 1 Demonstration Project Design and Implementation


2. Phase 1 Demonstration Project Design and Implementation

2.1 Objectives

The main objective of Phase 1 of the Demonstration Project was to acquire actual operational data for use in the determination of the technical feasibility of direct placement of MCR dredged sediment at the Benson Beach surf zone.

The operational and financial feasibility of the Demonstration Project using Benson Beach as an alternative dredged disposal site will be determined through testing and validation of the existing perceptions and hypotheses regarding wave and current conditions at the re-handling site, dredge production rates on placement sediment, and dispersivity of the sediment at the shoreline. The major perceptions that have precluded previous Benson Beach direct sediment placement are summarized in Table 1. Table 1 also includes hypotheses that support the feasibility of using Benson Beach as a site for placement of MCR dredged material.

Table 1. Benson Beach Perceptions and Hypotheses

Perception Hypothesis

Wave conditions at the North Jetty do not allow re-handle of dredged material.

North Jetty at the specified location provides a shadow zone, protecting re-handling operations from west and northwest waves.

Current velocities at the North Jetty most of the time are not permissible for re-handling operations.

Current velocities at the proposed re-handling site are in the permissible range for re-handling operations.

Benson Beach disposal is of very limited capacity.

Placement of dredged material in the surf zone increases the dispersion of placed sediment and allows significant disposal capacity.

Dredge production rate for re-handling of dredged material at the North Jetty site is very low and is not practical.

Benson Beach re-handle production rate is comparable to Hopper Dredge production rate with the deepwater disposal site.

The general and detailed Scopes of Work for the Monitoring Program are presented in Appendix A. The Scopes of Work were coordinated with the Portland District Corps of Engineers, Coastal Communities, Washington Parks and DOE. The implementation of the Monitoring Program was a combined effort between PI Engineering, DOE, Portland District Corps of Engineers, and the USGS.

Placement of dredged material at Benson Beach began on July 16 and was completed on July 19, 2002. The total volume of dredged material was 43,730 cy. The Monitoring Program data collection began on July



5, 2002 and continued through December 2002. The Monitoring Program included wave and current measurements, bathymetric and topographic surveys, sediment sampling, aerial and ground photography and compiling dredge operational data. The schedule of data collection is summarized in Figure 5.

The following sections of the report discuss the data collection methodology, data description, results of the analysis, and recommendations for the next phases of the Demonstration Project.

2.2 Design and Planning

Project planning and implementation involved extensive coordination between the Portland District Corps of Engineers as well as state and local interests, including the Lower Columbia River Channel Coalition (LCRCC, Port of Portland, Port of Longview, Port of Long Beach, and Port of Kalama), and the Coastal Communities of Southwest Washington. Funds for the Benson Beach Demonstration Project consisted of three parts; the Portland District Corps of Engineers contributed $200,000.00; the Coastal Communities of Southwest Washington $275,000.00; and the LCRCC $550,000.00. The Coastal Communities of Southwest Washington group also arranged all required permits for the placement of sediment on Benson Beach.

The Demonstration Project was conducted as part of the Corps’ 2002 contract for dredging at MCR, Columbia River and the entrance to Coos Bay, Oregon as part of an alternate bid schedule. In effect, the Demonstration Project was an additive bid item. The Corps solicited bids for two separate schedules of bid items, one with and one without sediment placement on Benson Beach. The bids received are summarized in Table 2.



Figure 5 Schedule of Data Collection



Table 2. Summary: Bids for 2002 Dredging at MCR, Columbia River and Coos Bay

Govt. Estimate NATCO Manson Bean Stuyvesant

Unit Price Total

Unit Price Total

Unit Price Total

Unit Price Total

Total for Schedule A Items 1-8 $5,201,594 $4,485,349 $4,755,500 $5,099,575

Schedule B

Items 1-8 $5,201,594 $4,485,349 $4,755,500 $5,099,575

Benson Beach Mobilization Item 9 $59,844 $555,464 $475,000 $250,000

Additional Cost for Benson Beach Sediment Placement

Item 10A- First 25,000 cubic yards $1.97 $49,250 $5.02 $125,500 $7.00 $175,000 $2.04 $51,000

Item 10B- Over 25,000 cubic yards $1.83 $137,250 $5.02 $376,500 $6.00 $450,000 $2.04 $153,000

Sub-total Benson Beach Items 9-10 $246,344 $1,057,464 $1,100,000 $454,000

Total for Schedule B $5,447,938 $5,542,813 $5,855,500 $5,553,575



Contractor NATCO was the lowest bidder for both schedules and was selected by the Corps to conduct the work. Sugar Island, the hopper dredge privately owned by NATCO, was used for sand placement on Benson Beach. Sugar Island is a 281 foot long split hull hopper dredge with direct pump-out capability. The loaded draft is 19 ft. The hopper capacity is 2,800 cy and it is capable of dredging to depths of 70 ft.

2.3 Implementation and Operational Data

Placement of dredged sediment on Benson Beach was done July 16-19, 2002. A total of 43,727 cy of fine sand was pumped ashore from Sugar Island through a flexible 27” diameter pipeline. The total length of the pipeline was approximately 200 ft and it was routed over the North Jetty to the placement area. Figure 6a shows the dredge during pump-out operation and Figure 6b shows sediment discharge at Benson Beach. The first load was placed on July 16 at approximately 9:30 AM. The dredge pumped sand onto Benson Beach only during daytime. At night, the hopper dredge placed sediment at open water disposal Site E.

Figure 6a July 16, 2002, First Load, Pump-off In Progress



Figure 6b July 16, 2002, First Load, Sediment Discharge at the

Benson Beach Demonstration Project

The Benson Beach placement area was specified to be north of the North Jetty at a distance no less than 200 ft. Discharge was planned to be within the surf zone, between Mean Higher High Water (MHHW) and Mean Lower Low Water (MLLW) levels. The intent was to investigate the dispersivity of sediments subjected to wave and current impacts in the surf zone. However, during placement operations, the contractor used land equipment to grade beach elevations. These operations distorted the observations of natural dispersivity of placement of the beach sediment.

The hopper dredge operational data, including production rates, dredging time, pumping time, open water disposal time (when occurring during the Demonstration Project), hopper loads, loaded draft and light drafts were collected by the Corps of Engineers during the Demonstration Project. Figure 7 shows the time of pump-out and pump-in cycles during the Demonstration Project. It should be noted that the pump-out cycle is longer than pump-in cycle an average of 25-35 minutes. This ratio would probably vary slightly for different types of dredges, but would not be significantly different from the range shown in Figure 7.

Figure 8 compares the combined dredging and disposal cycle time between pump-off operations to Benson Beach and open water disposal. Figure 8 confirms that the total cycle time for the Benson Beach disposal is longer than that of bottom dump disposal at Site E.



The average cycle time for Benson Beach placement was approximately 170 minutes. For Site E disposal, the average cycle time was approximately 100 minutes. The additional time required for the Benson Beach dredging and disposal cycle versus Site E dredging and disposal cycle on average is determined to be approximately 70 minutes. It should be noted that the average volume of sediment in the hopper dredge was nearly the same for Benson Beach and Site E placement during this time; 2,331 cy for Benson Beach and 2,377 cy for Site E.

It should be noted that the excessive cycle time for the Demonstration Project depends on the basis of comparison. No disposal operation by the Sugar Island hopper dredge occurred at Site F during the period of the Demonstration Project. Therefore, no direct comparison of dredging and disposal cycles for Benson Beach and Site F disposal can be done. However, considering the distance between Site E and Site F, approximately 3 miles, and assuming a hopper dredge speed of approximately 10 knots, it is estimated that the additional time required for Site F dredging and disposal cycle versus Site E cycle is approximately 35-40 minutes. When comparing this number with the Benson Beach disposal cycle time, one may conclude that the total cycle time to Site F is comparable to that for Benson Beach.

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Figure 7 Benson Beach Demonstration Project, Hopper Dredge Sugar Island Pump-out Versus Pump-in Time



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Figure 8 Benson Beach Demonstration Project, Hopper Dredge

Dredging and Disposal Total Cycle Time

2.4 Major Conclusions From This Section

• The pump-off dredged material from hopper dredge directly to the Benson Beach is technically feasible.

• In the range of the observed weather conditions, it was safe for hopper dredge to conduct pump-out operations in close proximity to the North Jetty.

• The dredging and disposal cycle time for the Benson Beach placement is longer than that for Site E by approximately 70 minutes.

• The dredging and disposal cycle time for Benson Beach placement is comparable to the dredging and disposal cycle time for Site F. It is likely that any disposal site located 2 or more miles seaward from Site F would require the same or longer time than Benson Beach sediment placement.

• The pump–off cycle time, including hook-up operations, were longer than the pump-in cycle time by approximately 20-25 minutes.

Hydrodynamic Processes Monitoring Data


3. Hydrodynamic Processes Monitoring Data

3.1 Waves

Wave data were collected to validate the hypothesis regarding the North Jetty shading effects at the proposed re-handling area. In addition, wave data were collected to develop a database for further computer simulations (computer model validation, calibration, and input parameters) of the dispersivity of the sediment placed in the surf zone at Benson Beach.

Wave data have been collected during the Demonstration Project at three stations:

• Station 1 North Jetty re-handling site • Station 2 Offshore at the Mouth of Columbia River bar (NOAA

waver-rider buoy) • Station 3 Site E

3.1.1 North Jetty Re-handling Site Wave Station

Station 1 was located at the proposed re-handling area, approximately 400 ft to the south from the North Jetty (see Figure 8) at the depth of approximately 30 ft MLLW. The coordinates of Station 1 are as follows: 46.274491°N, 124.06322°W (NAD83 datum). Station 1 was deployed on July 11, 2002 and recorded data through December 2, 2002. The stations was recovered, serviced and re-deployed on September 19, 2002. The station was equipped with a SonTek hydra directional wave gage that measured pressure and water velocity bursts at 4 Hz for approximately 17 minutes at one-hour intervals. Figures 9a and 9b show the equipment before and after deployment.



Figure 9a Buoy Marks Location of Wave and Current Meter

Station 1

Figure 9b Wave and Current Meter Station 1 Prior to

Deployment

An example of one burst of data recorded by the station is presented in Figure 10.



Water Surface Time SeriesBurst 151 07/16/2002 0:00

Peak Flood Condition

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Figure 10 Water Surface Time Series

The data was processed and analyzed using standard analytical procedure (Earle, et al. 1995). Figures 11 and 12 shows a time series of significant wave height, peak period, wave direction and sensor depth measured throughout the two deployments from July 11 through September 19 and from September 19 through December 2, respectively.

Figure 13 plots the wave data for the period from July 16 through 19, 2002 when the hopper placed dredged sediment at Benson Beach.

The maximum recorded significant wave height measured at the station during the period from July 11 through December 2, 2002 is 13.8 ft with an associated period of 15.9 seconds occurring on November 8, 2002. Statistical analysis of collected wave data was conducted and the results are depicted on Figure 14. Figure 14 shows the wave rose of wave height distributions for the period July 11 through September 19, 2002. It can be noted that most of the wave direction recorded at Station 1 are from the southwest direction and are confined in the sector of 210° to 240°. Wave direction coincides relatively accurately with the alignment of the jetty. The waves that were originated generally from the west and northwest directions (see below Columbia River Buoy Data) were diffracted by the jetties and the MCR entrance channel to the southwest direction.



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Figure 11 Station 1, Wave Time Series (Significant Wave Height, Period, Direction,

Water Depth) Versus Station 3 Wave Data for the Period Between July 11, 2002 Through September 19, 2002



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Figure 12 Station 1, Wave Time Serious (Significant Wave Height, Period, Direction,

Water Depth) Versus Station 3 Wave Data for the Period Between September 19 Through December 2, 2002



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Figure 13 Station 1, Wave Parameters Timed Series for the Period Between

July 16-17, 2002



Figure 14a Station 1, Wave Rose, for the Period Between July 11, 2002 through

September 19, 2002

In addition to the wave rose, statistical analysis determined the wave heights distribution with regard to selected wave height ranges (bins) (see Figure 15). Data from Figure 15 shows that significant wave heights larger than 3.0 ft occurred 7 percent of the time during the period July 11 through September 18.



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July 11-September 18, 2002

Figure 15 Station 1 Wave Statistics Comparison, 2002-2000

Station 1 wave statistical analysis results were compared to the data from the previous measurements. It should be noted that the wave data collection was conducted at the same location as Station 1, approximately 400 ft south of the North Jetty, during the period between August through October 2000. Detailed results of these measurements are presented in the PI Engineering Report entitled “Benson Beach Demonstration Project” (2001). The data from previous measurements were extracted and plotted on the above Figure 15. The occurrence of wave heights larger than 3.0 ft for the 2000 measurements is approximately 11 percent of the time. This occurrence exceeds the occurrence for 2002 measurements (July11 through September 18, 2002). However, both data sets show that the occurrence is relatively infrequent (10 percent of the time).

There are no standards that regulate re-handling operations based on wave height conditions. Upon discussion with various dredging contractors, it is suggested that 3.0 ft wave height is a criteria that may preclude pump-out or re-handling operations. The data shows that this criteria may occur at the North Jetty re-handling site approximately 10 percent of the time during dredging operations. Considering this as a low percentage of occurrence, one may suggest that the hypothesis regarding North Jetty shading effect on re-handling operations is valid.

3.1.2 Station 2. Columbia River Bar Wave Buoy

Wave Station 2 is operated by NOAA and is located approximately 18 nautical miles from the tip of the North Jetty in a water depth of 420 ft. The instrument records wave height, period, and direction. The data



from the buoy were compiled and statistically processed and analyzed. Figure 11 above shows a time series of wave height, period and direction superimposed with the data from the wave gage deployed by PI Engineering inside the North Jetty (Station 1).

There is a qualitative correlation between wave height data measured at the NOAA Buoy and at Station 1. The pattern of wave height changes at Station 1 follows the pattern of wave height changes at the NOAA buoy. Most of the time, an increase or reduction of wave height at Station 1 corresponds to the increase or reduction of wave height at the NOAA buoy, though the wave heights at Station 1 are always smaller than those measured at the NOAA buoy. The distinguishing feature between the data from these two stations is that wave heights at Station 1, inside the North Jetty are clearly modulated by the tidal current. Wave heights are higher during a flood tide when incoming waves are traveling with the current, unlike incoming waves traveling against the current on an ebb tide. Also, wave directions clearly change as they travel onshore over the Columbia River entrance channel. Wave data at the NOAA buoy are indifferent to a tidal stage and tidal flow fluctuation.

The highest recorded offshore significant wave height during any deployment was 28.5 ft and occurred on November 8, 2002. The corresponding maximum significant wave height that day inside the North Jetty was 13.8 ft.

Statistical analysis of the data was conducted to determine wave heights and directions distribution during the period of dredging and dredged material disposal. For this purpose, the data from Columbia Wave Buoy were extracted for summer period from 1995 to 2002 data-set. The results are presented in Figures 16 and 17. Figure 16 is a wave rose for the month of July (compiled period 1996-2001) and Figure 17 shows the wave rose for April to September (compiled period 1995-2002).



Figure 16 Station 2, Columbia River Bar Buoy Compiled 1996-2002, Month of July, Wave Rose, Aerial Photograph of North Jetty Dated July 29, 2002



Figure 17 Station 2, Columbia River Bar Buoy Compiled 1995-2002 Summer Time

Wave Rose, Aerial Photograph of North Jetty Dated July 29, 2002

The wave roses show that during the summer periods, the likely time of MCR dredging and disposal, wave directions are predominately from north through northwest. These waves, when arriving at the entrance, are shaded by the North Jetty and will not directly impact the proposed area of dredged material re-handling.

3.1.3 Station 3. Site E

Wave measuring at Station 3 has been conducted to develop the database for the analysis and computer simulation of a dispersivity of the Benson Beach placement area. In addition, the data from Station 3



would be used for developing the alternative MCR disposal sites, if Benson Beach is found to be not feasible. Station 3 was deployed at Ocean Dredged Material Disposal Site E, near the Coast Guard “G7” navigation buoy on December 6, 2002. The location of the wave station was identified with the following coordinates: N46°15.0583’, W124°06.5107. The depth at the deployment site during deployment was approximately -44 ft MLLW.

Wave measurements at Site E were collected with a TRIAXYS™ wave buoy moored on a 68-meter-long mooring with an anchor weighing approximately 750 kg (1700 lbs). The TRIAXYS™ wave buoy is comprised of a 36-inch-diameter sphere with internal batteries, solar panels and a sensor and telemetry module, and one VHF transmitter system with antenna. The mooring includes a buna-N rubber cord compliant section approximately 15 m in length to decouple the mooring from the buoy and allow unrestricted buoy motions in the wave field.

The buoy was set up to record a 24-minute burst of wave data once each hour, beginning at the top of the hour. After the sampling period, the buoy processed the measured data on-board and then transmitted the processed data to a shore-based receiver, via a VHF radio. The shore receiver radio and computer were installed in the USCG Lifeboat Station, Cape Disappointment Communications Center. The computer was connected to a modem and telephone line, allowing remote access to the data.

Figures 18a and 18b show the buoy during its deployment near Site E. Figure 19 shows the wave data, significant and maximum heights, period, and direction measured during the deployment. In addition, wave data, simultaneously measured at the NOAA Columbia River water buoy (Station 2) are also plotted on the same Figure 19. It can be noted that some similarity in a general trend of wave heights changes at these two stations. However, actual values of wave heights at specific date and/or storm event at these two stations do not correlate. Wave heights at Station 3 are sometimes smaller (likely a typical wave attenuation effect) or larger (likely a typical wave shoaling effect) than the wave heights at deepwater Station 2. Unusually large waves occurred from December 13-17, with a peak significant wave height of 30 ft recorded at the Columbia River Bar Buoy on December 16, 2002.

After approximately 10 days of operation, the cable connecting the wave buoy with the anchor broke, and the buoy drifted away from Station 2. The buoy was found and the data were recovered. Currently, the wave data from the buoy are being processed. Analysis



of the recovered data may develop valuable information for the decision making process regarding the need for an additional Station 3 data collection effort.

Figure 18a Wave Buoy at Site E (1 of 2)

Figure 18b Wave Buoy at Site E, Prior to Deployment (2 of 2)



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Figure 19 Station 3, Wave Parameters Time Series for the Period Between December 7-17, 2002



3.2 Currents

Current data were collected to validate the hypothesis regarding limited effect from tidal currents on the re-handling operation at the proposed re-handling site. Current data were collected simultaneously with and on the same tripod as the wave data at Station 1. The current data were collected using Acoustic Doppler Profiler (ADP) and Acoustic Doppler Velocimeter (ADV) instruments.

The ADP is a 500 kHz SonTek instrument with the instrument transducers located 0.68 m above the bottom (there is a 0.4 m blanking distance between the transducers and the first depth profile). The recorded velocity is an average velocity over three points in a horizontal plane at each elevation. The three points correspond to the intersection of the horizontal plane with the three divergent beam geometry of the SonTek ADP. Also, each velocity measurement is a temporal average over a 3-minute sampling period. A velocity time series was obtained through the water column, at points spaced at 0.5 m intervals from the instrument on the seafloor to the water surface. Current speed and direction were measured at each point every 10 minutes.

Current data at Station 1 were collected from July 12 through October 10, 2002. The data were processed and analyzed. Figure 20 is an example of current velocities and directions measured at Station 1 using ADP Current Meter. Current speeds and directions at this figure are represented as vectors. The length of vector is proportional to the speed. The direction of the vector from its origin on the X-axis is the direction of current flow. Note that a line pointing toward the northeast means the water particles are flowing towards the northeast. A flood current (incoming tide) has the lines pointing to the northeast.

The ADV instrument measures current velocity at a single point near the bottom. The ADV was part of a SonTek Hydra system and includes a pressure sensor. The ADV sampling point was located 1.15 m above the bottom, and pointed upward. The ADV measures the water particle velocity in three dimensions, with a cylindrical sampling volume approximately 1 cm in diameter. The instrument was operated in burst mode. Data was recorded at a 4 Hz rate (4 samples per second) for 17.1 minutes, every hour.



Figure 20 Station 1, Example of Processed Current Velocities

and Directions Measured by SonTek ADP

Current data at Station 1 using ADV gage were obtained for the period from July 12 through October 10, 2002. Data were processed and analyzed. Figure 21 is an example of current velocities and directions measured with ADV gage and represented in vector-format.



Figure 21 Station 1, Example of Processed Current Velocities

and Directions Measured by ADV

The current data obtained upon data collection and processing includes a significant size of database, consisting of current velocities and directions throughout the water columns (approximately 11 points spaced with 0.5 meters) every 10 minutes during the period of approximately 5 months. The maximum recorded depth averaged current velocity during the 2002 Monitoring Program was 2.2 ft/second at azimuth 073° on October 2, 2002.

Statistical analysis of the current data was conducted and the results of analysis are presented in Figures 22 and 23. Figure 22 is a current velocity rose overlaid on the aerial photograph of the North Jetty. The current rose is based on data from the first deployment, July 11 to



August 31, 2002. The current roses show current speed distributions by direction. Note that the current directions plotted on the rose coincide with the true direction of the coordinate system. For example, flood current would have a direction towards the east-northeast. In addition to the directional roses, Figure 23 was plotted to show current speed distributions with regard to selected ranges (bins).

Figure 22 Station 1, Current Data Rose Plot – Depth Average Currents, for the

Period Between July 11, 2002 Through August 31, 2002



Station 1, Depth Average Currents Velocities and Direction Statistics

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Figure 23 Station 1, Depth Average Current Velocities and Directions Statistics

Current velocity data collected at Station 2 during the Demonstration Project was compared to the data from the previous measurement (see Figure 23). A previous measurement was conducted at the same location, south of the North Jetty, during the period between August 22 to October 5, 2000. A comparison of these two data sets (2000 and 2002 measurements) shows that in general the occurrence of current velocities at higher speeds (>1.5 ft per seconds) measured in 2002 exceeds that of measured in 2000. However, none of these occurrences exceed 6-8 percent of the time.

It can be noted that currents at Station 1 are predominantly of two-directional character, i.e., east-northeast during flood tide and west-southwest during ebb tide. Northeast currents occur more frequently than southeast currents, as shown in the current rose plot in Figure 22. During the Demonstration Project, the contractor experienced some difficulties with positioning of the hopper dredge during ebb tide. At these times (ebb tide) a tugboat was used to secure the position of the hopper dredge. Because of the recognized tidal flow effects, the hopper dredge pump-out operations were conducted only at flood tide. No tugboat was required for securing the position of the hopper dredge during flood tide conditions.

It should be noted that there are no standards that regulate re-handling operations based on current velocities at the re-handling area. Upon discussion with various dredging contractors, it is suggested that 1.5-ft/second current speed of northeast direction is a criteria that may preclude pump-out or re-handling operations. The data shows that



currents exceeding 1.5 ft/second may occur at the North Jetty re-handling site approximately 5-10 percent of the time during dredging operations.

3.3 Major Conclusions From This Section:

The hypothesis regarding North Jetty wave shading effect on the proposed Benson Beach re-handling site has been validated with field data and analysis. Two years of site-specific wave measurements and seven years of Columbia River Bar Buoy directional wave data show that wave heights inside the North Jetty are relatively small and allow re-handling operations at the proposed North Jetty re-handling site most of the time during normally scheduled dredging operations.

• The hypothesis regarding the ability to operate (from the perspective of tidal flow impacts) the re-handling operations at the proposed Benson Beach re-handling site has been validated with the field data analysis. Two-year current measurement data show that current velocities at the proposed re-handling site would permit re-handling operations for most of the time. During tide flood and slack conditions, there is most likely no need for a securing tugboat. During ebb tide, re-handling operation most of the time would be feasible, but the need for a securing tugboat may exist.

Monitoring Benson Beach Morphology and Sediments


4. Monitoring Benson Beach Morphology and Sediments

4.1 Topography

Topographic survey data were collected to identify the fate of placed sediment and the effect of this sediment on the existing upper beach-land formations. Two types of topographic data have been collected during the Demonstration Project: Cross-shore beach profiles (measured with GPS mounted-backpacks) and surface mapping, using the CLAMMER surveying vehicle. The beach profile surveys were conducted along 32 cross-shore transects typically, spaced at 25-meter (~ 80 ft) intervals from the North Jetty to approximately 800 meters (~2500 ft) north of the North Jetty. The profile lines are oriented in an east-west direction and are aligned with the transects previously collected by the Southwest Washington Coastal Erosion Study. The data from the profile surveying were processed and analyzed. Three typical transects, Line Nos. 362040, 363020, and 363930 were selected for more detailed analysis. These transects are located at distances 650 ft, 1,650 ft, and 2,550 ft south from the North Jetty respectively. Line No. 362040 is aligned at the placement area. The transects with complete survey data were plotted and are presented in Figure 24.

The data from cross-sectional topographic surveys confirmed that the sediment was placed on the beach mostly between elevations from +6 to –2 ft, MLLW (surf zone) as was specified by the design. After placement and during the period of monitoring, some changes had occurred along the cross-sections. Assuming that erosion and accretion at adjacent areas show sediment movement, one may suggest that material has moved in different directions. Some of the material moved onshore forming a temporary dune, some of material moved seaward filling the trough between first nearshore bar and shoreline1.

Table 3 Benson Beach Transect Unit Volume Changes (cy/per linear ft)

Distance to North

Jetty 7/13-7/20 7/20-7/24 7/24-7/29 7/29-8/2 8/2-8/8 8/8-8/21 8/21-9/20 9/20-10/24 +650 ft 59 80 89 84 91 87 112 109 +1,650 ft -9 6 11 2 7 18 49 60 +2,550 ft 0 -6 23 26 11 19 32 25

1 It should be noted that a natural trend of migration the placed sediment was disturbed by the Contractor, and by moving sand from the land base equipment. The cross-sectional topographic survey data may not be representative for the period of actual placement and should consider more information starting August 8, following the Contractor’s equipment leaving the project site.



Benson Beach - Profile - Line 362040 - 650 feet from North Jetty

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Figure 24 Topographic Survey Transects



Areas of cross-sectional changes at each of three transects were calculated and presented in Table 3 and graphically in Figure 25.

Beach Profile Volume Change Relative to Before Sediment Placement

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Figure 25 Beach Profile Volume Change Relative to Before Sediment Placement

Data in the table shows the changes of the cross-sectional area relative to the original (pre-construction) section. Plus indicates accretion, minus indicates erosion. In general, the data in the table show increases of unit volumes of sediment at the cross-sections. The first abrupt increase of unit volumes on one transect (closest to the disposal) coincides with the placement of dredged sediment. A continued increase of unit volumes on all transects indicates an influence from the natural processes, most likely forming on a typical summer beach configuration. At the end of measurements, approximately three months after the placement of dredged material, the total volume increase is approximately two times relative to the initial placed volume. Data from profiling surveys shows the immediate local effect from placement of 43,000 cy was offset with natural accreting processes corresponding to the formation of the summer beach cross-section typical for the Demonstration Project. The data also shows that the sediment placed or migrated onshore of the upper part of the beach above +6 ft MLLW most likely had been conserved at a longer time and was subjected to less dispersion than other portions of the Demonstration Project.

In addition to cross-section surveys, surface mapping surveys were conducted along the beach using the CLAMMER vehicle (see Figure 26). The surveys extended from the vicinity of the North Jetty to North Head. This type of survey creates an accurate 3-dimensional



interpretation of beach surface of the surveyed area. Figure 27 is an example of this surface plotted for Benson Beach prior to the placement of sediment on July 13, 2002.

Figure 26 CLAMMER Conducting a Beach Topographic

Survey (Photograph courtesy of DOE)

The surface data were processed to identify the differences in the surface elevation and volumes between successive surveys. Subtracting a successive beach surface data set from preceding beach surface data set, the three-dimensional interpretation of the change at beach elevations is determined. A total of 7 beach surface surveys were conducted. Differences between the original (pre-construction) beach surface and surfaces from each following survey were identified and plotted on Figure 28 and Figures 29 through 33 (see Appendix A. Color on figures indicates the depth of erosion or accretion with regard to the legend depicted on figures. A dashed line is plotted on the figures to focus the attention at the same area. In addition, volume of changes in the vicinity of the area confined with the dash line were calculated and presented in Table 4.



Figure 27 Example of Topographic Survey Image, July 13, 2002

Table 4 Volume Changes Inside of Dashed Line (Figures 27-32)

Period between surveys Volume of changes, cy

7/13-7/20 32,000

7/20-7/24 37,000

7/24-7/29 36,000

7/29-8/02 37,000

8/02-8/08 36,000

88/08-8/21 35,000

8/21-9/20 48,000

9/20-10/24 37,000

Figure 28 shows the change in bottom elevation that may relate to the placement of sediment on the beach during July. Volume of material changes in the confined are is illustrated by a dash line area measuring approximately 32,000 cy. It is noticeable that the volume of sediment change inside the dash line after placement of sediment has not changed significantly (see Table 4).



Figure 28 Benson Beach Surface Elevations Change for the

Period Between July 20, 2002 and July 13, 2002

The following questions may be asked:

• Was the accreted area built and maintained during the Monitoring Program with sediment placed during the Phase 1 Demonstration Project?

• Was the accretion inside the dashed area the result of placed sediment, or was it a coincidence with the natural processes forming a summer beach?

Unfortunately, the available data are not sufficient to provide the answers to these questions with any level of confidence. One practical suggestion from the observed effect of stability sediment inside of the dashed area is that placement of sediment in the area below +6 ft MLLW most likely would increase the dispersion of the placed material during the summer months, i.e., July through September.

In the meantime, significant erosion occurred to the north and seaward from the placed area even during the placement of sediment (see



Figure 28). Volume of erosion at these areas most likely significantly exceeds that measured at the dashed area. Figure 28 shows further dynamic changes of the beach surface. Also, even more significant changes at the accreted and eroded parts of the beach are observed to the north and seaward from the dashed area.

The next set of figures, presented in Appendix B (Figures B-1 through B-6) demonstrates all sorts of changes, including accretion and erosion at the entire area of the Demonstration Project. Due to the limits of the survey, it is not feasible to identify the actual volume of changes at the upper part (above –2 ft MLLW) of the Demonstration Project. However, preliminary estimates indicate that these changes are in the order and larger than the volume of placed sediment during the Phase 1 Demonstration Project. Analysis variability and scales of changes that occurred at Benson Beach areas for several months after construction leads to the conclusion that these changes are influenced by the natural “summer” beach formation processes. The relatively small volume of placed sand (43,000 cy) might create the local effect at the upper part of the south end of Benson Beach. However, at the scale of the entire beach area (even upper beach) and considering “winter” beach formation processes, this effect is small and is likely within the level of “noise” in the natural system. To distinguish the effect of the placed sand on the upper Benson Beach area, the amount of sand required would likely be several times larger (probably 5 to10 times) than that placed during the Phase 1 Demonstration Project.

4.2 Nearshore Bathymetry

Nearshore bathymetry data were collected to identify potential changes at the bottom slope of the Demonstration Project that may result from the placement of 43,000 cy of dredged sediment during the 2002 Demonstration Project. Nearshore bathymetry measurements were funded by the Corps of Engineers and were collected by the USGS/DOE team on July 15 and August 6, 2002. Approximately 22 nearshore bathymetry transects were collected between the North Jetty and the North Head. Within approximately 800 m north of the North Jetty, transects were spaced at 100 meters (~300 ft) intervals. North of this point, the transect spacing was approximately 200 meters (~600 ft). The transects are oriented in an east-west direction, to align with previous nearshore bathymetry and topography surveys collected by the Southwest Washington Coastal Erosion Study. Near the North Jetty, the surveys extend approximately 2 km (1.2 miles) offshore to approximately 8 m (25 ft) water depth on Peacock Spit, and further to the north, the transects extend to approximately 12 m (38 ft) water depth.



Figures 29 and 30 show in plain view the contours developed from the data of July 15 and August 6, 2002 nearshore survey. In addition, the nearshore bathymetry data is used to develop “ difference plots” . A three-dimensional surface is defined for each survey, and the linear distance between the surfaces of separate surveys are calculated and plotted. Figure 31 is the difference plot showing the changes in bottom surface elevations (erosion / accretion) that occurred during approximately the one-month period between July 15 and August 6, 2002. The total budget of changes shows that erosion prevailed above accretion and total volume of erosion is approximately 527,000 cy. The fate of eroded material from the bottom slope has not been determined. It may be deposited further onshore as part of the accumulation of material noted in the beach topographic surveys (discussed below) or removed by the longshore sediment transport. The analysis of the bathymetric survey data indicates that the scale of the natural processes is at least an order of magnitude larger than the scale of the Demonstration Project sediment placement of 43,000 cy. Under these circumstances, the effect of the dredged material on bottom slope is at a level of noise that cannot be accurately detected. In order to be able to identify this effect, it is assumed that the volume of placement should be 5 to 10 times larger than that of the Phase 1 Demonstration Project.

4.3 Aerial Photography

Aerial photography of the Demonstration Project and the North Jetty areas were conducted to identify possible changes in shoreline and landforms of the upper beach as a result of placement of the dredged material in the surf zone. Aerial photography has been conducted before and after sediment placement on Benson Beach. A flight-line of eight photographs extending along the shoreline from the North Jetty to past North Head was flown on January 28, July 9, July 21, August 12 and September 11, 2002. The next aerial photographs are scheduled on March 30, 2003. The photos are taken at a vertical angle and are scheduled to coincide with low tide.

As part of the Monitoring Program, the DOE prepared and installed on July 12, 2002, a total of 14 ground control points (photo control targets) between the North Jetty and the North Head for the purpose of enabling the capability of ortho-rectifying the aerial photographs. Eleven of the targets were made of material (4 or 5 from white target tape, and 6 or 7 from black tar paper) and 3 of the targets were made using spray paint. In addition to new control points, DOE has identified 7 existing targets (existing objects that appeared as prominent features in previous aerial photography). The precise



positions of the aerial photo control targets were surveyed with GPS on Monday July 15 and Thursday, July 18.

Figure 29 Benson Beach Nearshore Bathymetry July 15, 2002



Figure 30 Benson Beach Nearshore Bathymetry August 6, 2002



Figure 31 Benson Beach Nearshore Bathymetry Change

Between August 6, 2002 and July 15, 2002

The analysis of aerial photograph data included rectification, visual review, measurements of the areas of interest, and superimposing successive photographs. Aerial photographs of the area prior to placement on July 9, 2002, and at the end of the Monitoring Program on September 11, 2002, are illustrated in Figures 32 and 33.

The analysis of the aerial photographs shows changes of the shoreline position and land features at the surf zone of Benson Beach during the period of monitoring. An accurate description of the changes is distorted by different tidal elevations during each flying event. However, in general it can be noted that the shoreline has advanced and the accreted feature appeared at the seaward boundary of the disposal area. To evaluate whether these changes are related to the placement of 43,000 cy of sediment, the aerial photographs from previous years were compiled and analyzed. Figures 34a and 34b show the aerial photograph of the same area taken July 7, 2001 in comparison with the July 21, 2002 photograph. The accreted feature at approximately the same location is shown on both photographs. It is



likely that the formation of this feature is a result of natural processes and the highly dynamic environment at the Demonstration Project.

Figure 32 Aerial Photograph July 9, 2002; Sediment

Placement Area

Review of all collected photographs leads to the assumption that the scale of natural processes controlling sediment transport, deposition, and erosion is significantly larger that the scale of the 2002 Demonstration Project. The changes of the shoreline and landforms resulting from placement of 43,000 cy of sediment are at the level of noise in the system and cannot be observed and distinguished from the natural sediment dynamics.



Figure 33 Aerial Photograph July 21, 2002

Figure 34 Aerial Photographs of Benson Beach

on July 7, 2001 and July 21, 2002

34a 34b



4.4 Sediments

Surface sediment samples were collected in an attempt to determine the trend of migration of the placed dredged sediment along the Demonstration Project. The basis for this effort was an assumption that differences between dredged sediment and native sediment grain size distributions would allow tracing dredged sediment and determine the path of its migration.

Sediment samples were taken at seven cross-shore beach survey transect lines in the vicinity of the dredged material placement site. The samples were taken at four locations along the transect: swash zone, mid-beach, toe, and the dune. Each sediment sample was taken at approximately the same location surveyed with GPS. A total of 56 sediment samples were collected on July 15, July 20, July 24 and August 8, 2002.

Sieve analyses were performed on each sediment sample by the DOE to estimate the grain size distribution. Statistical analysis of the grain size distribution included calculating the percent passing, median grain size and standard deviation. The results of the analysis were used to generate plots of the grain size as a function of distance from the North Jetty for each sampling date. Figure 35 is an example of this type of analysis. In addition, the analysis was done to determine time variation of the grain size distribution at each sampling point.

The results of the analysis show that the median grain size at all locations is statistically constant. Trends both in time and along the beach are within the calculated error bars and therefore a statistically significant trend cannot be concluded. The contractor’s bulldozer routinely re-distributed sediment during placement, and it is likely that this activity eliminated any trends in the sediment size distribution. This leads to the conclusion that the simplistic approach using grain size analysis may not be sufficient to determine the fate of dredged sediment at the Demonstration Project.

Summary on Morphology and Sediment Monitoring:

• Analysis of variability and scales of changes that occurred at Benson Beach areas for several months after construction leads to the conclusion that these changes have resulted largely from natural processes with some input from the dredged material placed on the beach. The changes due to sand material placement likely occurred at the south end of the upper part of the beach. The changes at other parts of Benson Beach due to the dredged material placement were not detected and probably were at the level of



noise in the natural system. To distinguish the effect of the placed sand on the upper Benson Beach area, the amount of sand should likely be several times larger (probably 5 to10 times) that that placed during the Phase 1 Demonstration Project

Mid BB 28

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Figure 35 Results of Sediment Sampling Analysis Mid Sampling Area,

Transect BB 28 Between July 15-24, 2002

• The area of direct sediment placement during the Phase 1 Demonstration Project has a tendency to conserve a volume of sediment above +6 ft MLLW. To increase the dispersivity of disposal site at Benson Beach, it appears that the placement should be seaward from +6 ft MLLW.

• The total budget of changes at the bottom slope since the Phase 1 Demonstration Project shows the net erosion at approximately 527,000 cy. The fate of eroded material from the bottom slope has not been determined. The bathymetric survey data show that the scale of the natural processes is on an order of magnitude larger than the scale of the Phase 1 Demonstration Project.

• The effect of dredged material placed on the lower part of the beach profile during the Demonstration Project was not detectable



on the scale of natural processes. In order to be able to identify this effect, it is assumed that the volume of placement should be 5 - 10 times larger than that of the Phase 1 Demonstration Project.

• Review of aerial photograph data and nearshore bathymetry leads to the preliminary conclusion that the scale of natural processes controlling sediment transport, deposition, and erosion at the Demonstration Project is significantly larger than the scale of the 2002 Demonstration Project. The changes of the shoreline and landforms resulting from placement of 43,000 cy of sediment are at the level of noise in the system and cannot be observed and distinguished from the natural sediment dynamics.

• Due to small amount of sediment placed at the Demonstration Project during Phase 1, the collected morphological and sediment data are not sufficient to provide an accurate estimate for the dispersivity of the placed material. To enable an accurate evaluation of dispersivity at the Demonstration Project, it is recommended that the minimum volume of placement be in the range 150,000-250,000 cy of sand.

Conclusions and Recommendations


5. Conclusions and Recommendations

Placement of material dredged from the Mouth of the Columbia River (MCR) project onto Benson Beach at Fort Canby State Park adjacent to the North Jetty under Phase 1 (2002) of the Demonstration Project was successfully completed between July 16 and July 19, 2002. Approximately 43,000 cy of sediment dredged from the MCR were placed in the surf zone between elevations +6 ft MLLW and –2 ft MLLW.

Analysis of the results support the following specific conclusions:

• Pump-off of the dredged sediment from a hopper dredge directly into the surf zone at the Benson Beach site is technically feasible.

• A dredge may operate and pump-off safely in close proximity to the North Jetty under the conditions experienced during the Demonstration Project. Sea conditions, wave parameters, and currents were within the range predicted in previous studies. The experience from actual operations suggests that safe operations could take place in most conditions that have been predicted to occur during the normal dredging window.

• The dredging and disposal cycle time required for direct placement of dredged material at the Benson Beach surf zone is approximately 70 minutes longer than for Site E. The dredging and disposal cycle for direct placement at Benson Beach is comparable to the dredging and disposal cycle time for deepwater Site F using similar equipment. It is likely that disposal at any site located more than two miles seaward of Site F would require a longer cycle time than disposal at Benson Beach.

• The natural summer process whereby large quantities of sand migrate in and out of the surf and nearshore zones produced a background condition that precluded an accurate determination of the fate of the relatively small quantity of material placed during Phase 1 of the project.

The results of the Phase 1 Demonstration Project support a decision to proceed to the Phase 2 evaluation of the placement of dredged sediment into the surf zone at Benson Beach.

Some specific recommendations for Phase 2 include the following:

Conclusions and Recommendations


• In order to evaluate sediment dispersal and capacity accurately at Benson Beach, a minimum volume of placement for a second phase of the Demonstration Project should be at least in the range 150,000-250,000 cy of sand.

• In order to maximize the dispersivity of the disposal site at Benson Beach, placement of sediment should be seaward from the elevation of +6 ft MLLW. The mechanical spreading of pumped sand on the beach should be limited to that necessary for maintaining the opening at the discharge end of the pipeline.

• Improvements to the efficiency of re-handling dredged sediment to Benson Beach through means such as the use of a sump and cutterhead dredge (or other adequate equipment) located in the lee of the North Jetty should be developed. This could result in a lower cost for the Benson Beach disposal option

References


6. References

Ballard, R.L. (1964). “ Distribution of Beach Sediment near the Columbia River” , University of Washington, Department of Oceanography, Technical Report No. 98.

Earle, M.D., McGhee, D. and Tubman, M. (1995). “ Field Wave Gaging Program Wave Data Analysis Standard” , Instruction Report CERC-95-1, US Army Corps of Engineers, Waterways Experiment Station.

Gelfenbaum, G., Sherwood, C.R., Peterson, C.D., Kaminsky, G.M., Buijsman, M., Twichell, D.C., Ruggiero, P., Gibbs, A.E. and Reed, C. (1999). “ The Columbia River Littoral Cell: A Sediment Budget Overview” , Proceedings of the Coastal Sediments ’99 Conference, American Society of Civil Engineers, pp. 1660-1675.

Lockett, J.B. (1967). “ Sediment transport and diffusion: Columbia estuary and entrance” , Journal of the Waterways and Harbors Division, Proceedings of the American Society of Civil Engineers, Vol. 93, pp. 167-175, No. WW4.

Moritz, H.R., Kraus, N.C., Hands, E.B. and Slocum, D.B. (1999). “ Correlating Oceanographic Processes with Seabed Change, Mouth of the Columbia River, USA, Proceedings of the Coastal Sediments ’99 Conference, American Society of Civil Engineers, pp. 1643-1659.

National Oceanographic and Atmospheric Administration, National Data Buoy Center, Columbia River Bar Buoy, No. 46029, web site: http://cdip.ucsd.edu/cgi-bin/sta_index?name=Columbia_River_Bar&id=NDBC_46029&src=http://www.ndbc.noaa.gov/station_page.phtml?$station=46029.

Pacific International Engineering (2001). “ Benson Beach Demonstration Project” December 13, 2001

Peterson, C. D., M. E. Darienzo, D. J. Pettit, P. L. Jackson, and C. L. Rosenfeld (1991). “ Littoral-cell development in the convergent Cascadia margin of the Pacific Northwest” , USA, SEPM Special Publication No. 46, From Shoreline to Abyss, p. 17-34.

Phipps, J.B. and Smith, J.M. (1978). “ Coastal Accretion and Erosion in Southwest Washington” , Washington Department of Ecology Report No. 78-12.

Sherwood, C.R. and Creager, J.S. (1990). “ Sedimentary Geology of the Columbia River Estuary” , In: Progress in Oceanography, Vol. 25, pp. 15-79.

Smith, J.D. and Hopkins T.S. (1972). “ Sediment transport on the continental shelf off Washington and Oregon in light of recent lowest measurements. In: Shelf sediment transport: processes and patterns, D.J.P. Swift, D.B. Duane and O.H. Pilkey, editors, Dowden, Hutchinson and Ross, Stroudsburg, Pennsylvania, 143-180 pp.

References


Sternberg, R.W. (1986). “ Transport and Accumulation of river-derived sediment on the Washington continental shelf, USA” , Journal of the Geological Society of London, Vol. 143, pp. 945-956.

Sternberg, R.W. and McManus, D.A. (1972). “ Implications of sediment dispersal from long-term, bottom current measurements on the continental shelf of Washington. In: Shelf sediment transport: processes and patterns, D.J.P. Swift, D.B. Duane and O.H. Pilkey, editors, Dowden, Hutchinson and Ross, Stroudsburg, Pennsylvania, 181-194.

US Army Corps of Engineers, “ Topographic Surveying” (1994). EM-1110-1-1005, Washington, D.C.

US Army Corps of Engineers, Portland District (1999). “ Integrated Feasibility Report for Channel Improvements and Environmental Impact Statement” , Appendix H, Volume 1, Exhibit B, pp. 76.

US Geological Survey and Washington State Department of Ecology (2001). “ Southwest Washington Coastal Erosion Study” , http://www.ecy.wa.gov/programs/sea/swce/.

Appendix A

SCOPE OF WORK

2002 Monitoring Program Report A-1 Appendix A

SCOPE OF WORK (General)

Year 1 Benson Beach Test Project Monitoring Program

The Year 1 Benson Beach Test Project Monitoring Program is designed to evaluate the success of the Year 1 project and is focused on two issues: 1. Identify the safe conditions needed for re-handling operations at the North Jetty and

determine the wave, current, and other constraints on these operations. This monitoring is designed to validate Assumptions 1 and 2, described above.

2. Estimate the dispersion of dredged material placed on Benson Beach. This monitoring is designed to validate Assumption 3.

The proposed Monitoring Program includes wave and current measurements, topographic beach surveys and aerial photography. Wave Data

Wave data at the North Jetty will be collected from a station deployed on the seafloor in the vicinity of the hopper dredge mooring barge. The depth of installation of the station will be -26 to -30 ft mllw. Water surface elevation will be measured by the wave gage in bursts at 4 Hz for approximately 17 minutes at one-hour intervals during the length of each deployment. Data collection will last approximately three months and will include the time when the mooring barge is in use and sediment is being placed on Benson Beach. Measurements may last one month after the completion of sediment placement, if a need for further measurements is determined. The instrument will be serviced approximately once per month. The wave gage will help define the period of time when wave conditions preclude pump-out operations at Benson Beach. Also, the measured wave energy may be correlated with the dispersion of sediment placed at Benson Beach. Current Data

Current data at the North Jetty will be collected by ADCP, a doppler current meter on the station deployed at the bottom in the vicinity of the hopper moorage barge. The depth of installation of the station will be -26 to -30 ft mllw. Current velocities and directions will be measured at one-hour intervals during the length of each deployment. Data collection will last approximately three months and include the time when the mooring barge is in use and sediment is being placed on Benson Beach. Measurements may last one month after the completion of sediment placement if need of the measurements is determined. The instrument will be serviced approximately once per month. The current meters will help determine the period of time that current velocities preclude re-handling dredged material to the Benson Beach.

A-2 2002 Monitoring Program Report Appendix A

Topographic Surveys

Beach profile topographic surveys will be conducted on a regular bi-weekly schedule while sediment is being placed on Benson Beach, and for a one-month period after completion of the re-handling work. Surveys will be conducted along established cross-sections. Cross-sections will be taken at 20 transects extending from the North Jetty past North Head. Each transect will extend from a point at least 300 ft past mean higher high water to as low on the beach profile as practical. Surveys will be timed so as to measure elevations as low on the beach face as possible. Topographic surveys will be conducted in accordance with the accuracy standards specified in the Corps of Engineers manual “ Topographic Surveying” , Corps, 1994 (EM-1110-1-1005). The topographic data will use the mllw datum. The survey schedule and plan may be adjusted during placement operations as a result of changing field conditions or to better meet the objectives of the Monitoring Program. Aerial Photography

Aerial photography will be conducted approximately each month while sediment is being placed on Benson Beach. The photography will be parallel to the shoreline and extend from the North Jetty past North Head. The photos will be at a vertical angle and will be scheduled to coincide with low tide.


SCOPE OF WORK (Detailed)

Benson Beach Detailed Monitoring Program

Wave Data

Wave data at the North Jetty will be collected from a station deployed on the seafloor in the vicinity of the hopper dredge mooring barge. The depth of installation of the station will be -26 to -30 ft mllw. Coordinates of deployment are as follows: Latitude Longitude NAD 83, Easting 7300846.81; Northing 970721.65. Waves will be measured by the wave gage in bursts at 4 Hz for approximately 17 minutes at one-hour intervals during the length of each deployment. The wave gage will be in service for three months. Deployment will occur July 9-10, weather permitting. The instrument will be serviced approximately once per month. Redeployment is scheduled for the end of October 2002. Wave data will be processed using standard procedures, and data will be presented in progress and final reports. Current Data

Current data will be collected from a station deployed on the seafloor in the vicinity of the hopper dredge mooring barge. Current data will be collected by Acoustic Doppler Current Profiler (ADCP). Current velocities and directions will be measured at one-hour intervals. Data collection will last approximately three months. Deployment will occur July 9-10, weather permitting. The instrument will be serviced approximately once per month. Redeployment is scheduled for the end of October 2002. Current data will be processed using standard procedures, and data will be presented in progress and final reports. Topographic Surveys

Schedule: 1. Pre-disposal, 2. During disposal (assuming 4 days duration of disposal), 3. Post-disposal, 4. 3-4 days (0.5 week) post disposal, 5. 6-8 days (1 week) post-disposal, 6. 10-12 days (1.5 week) post-disposal, 7. 14-16 days (2.5 week) post-disposal, 8. 1 month post-disposal, 9. 2 months post-disposal, and 10. 3 months post-disposal

A-4 2002 Monitoring Program Report Appendix A

Area of survey: Beach Profiles: From jetty to 600 ft north of disposal site; from dunes/inland vegetation to low water. CLAMMER topography: From Jetty to North Head; from low water to upper beach near toe of dune or vegetation. Density of survey: Beach Profiles: 150 ft spacing between profiles from jetty to 600 ft north of disposal site (approx 20 profiles). CLAMMER topography: approximately every 75 ft in across-shore distance. Results of the survey will be processed timely and be available in hard-copy and electronic formats. The survey schedule and plan may be adjusted during placement operations as a result of changing field conditions. Ground Photography

Ground photography will be conducted at fixed locations on the North Jetty. Ground photography will be conducted several times per day during placement operation. Upon completing placement of the sediment, photography will coincide with topographic surveying. Aerial Photography

Aerial photography related to the Benson Beach project will be conducted two times, before and after sediment placement on Benson Beach. The photography will be parallel to the shoreline and extend from the North Jetty past North Head. The photos will be taken at a vertical angle and will be scheduled to coincide with low tide. It should be noted that bimonthly aerial photographing has been conducted for the project area since 2000 and will continue through 2002-2003 period. The data from this photographing effort will be compiled and used for the analysis and the report. Sediment Sampling Schedule:

1. Pre-disposal, 2. Post-disposal, 3. 3-4 days (0.5 week) post disposal, 4. 14-16 days (2.5 week) post-disposal, 5. 1 months post-disposal, and 6. 3 months post-disposal

Area of sampling: Along five beach profiles - 150 ft and 300 ft north from the disposal; at the centerline of the disposal; 150 ft and 300 ft south from the disposal.


Reporting

Data obtained from the monitoring program will be processed, analyzed and presented in progress and final reports. A preliminary progress report is due September 1, 2002. A final draft report will be issued December 20, 2002. Meetings and Coordination

Meetings and coordination with the Corps of Engineers and the contractor will occur during the data collection program. Three meetings with all interested parties will include presentations on the results of the monitoring program, and will be scheduled after completion of the project, progress report, and final report.

Appendix B

FIGURES B1 THROUGH B6

2002 Monitoring Program Report B-1 Appendix B

Figure B-1 Benson Beach Topography Difference Plot

July 24 – July 13, 2002

B-2 2002 Monitoring Program Report Appendix B


July 29 – July 13, 2002



August 2 – July 13, 2002



August 8- July 13, 2002



August 21 – July 13, 2002


Figure B-6 Benson Beach Topography Difference Plot September 20 – July 13, 2002

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