Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015"

CITY OF RENTON SEAPLANE BASE MAINTENANCE DREDGING, CHALLENGES BEYOND THE SCOPE OF MAINTENANCE DREDGING

J. G. Dawson1, R. S. Phillips2

ABSTRACT The City of Renton’s (City) Will Rogers-Wiley Memorial Seaplane Base is located at the southern end of Lake in Renton, Washington, adjacent to the Cedar River delta. Maintenance dredging was required at the end of 2013 in order to mitigate for Cedar River flooding that occurred in 2009, which caused large amounts of sediment to be deposited near the existing seaplane base facilities. Built-up sediment near the temporary mooring facilities and access ramp had a significant effect on seaplane pilot safety, due to limited depths during taxi, take-off and landing operations. Coast & Harbor Engineering was hired to assist with regulatory permitting, final design and assist with construction management during dredging operations.

Several issues related to permitting, the development of feasible design criteria, and restriction son construction operations, made dredging at the seaplane base challenging. The first issue of the project was that a portion of the dredge prism was within Washington State submerged lands, which meant the Federal Emergency Management Administration (FEMA) was partially responsible for providing financial assistance to the City of Renton for dredging activities as part of mitigating the effects of the 2009 flood event. Second, a portion of the dredge prism was within privately owned submerged lands requiring the City to obtain easements to dredge these areas. Third, King Country Metro sewer lines and private communication lines restricted the dredge prism to strict offsets, limited room for construction equipment and required atypical dredge cuts. Fourth, the unique location of the seaplane base relative to the Cedar River outlet and delta formation made water quality monitoring for the protection of migrating salmon difficult during dredging construction. Lastly, the seaplane base is located at the end of the City’s main for the Renton Municipal requiring the Federal Aviation Administration (FAA) to regulate all construction related activity conducted within the vertical elevation prism (determined by the FAA). From a construction logistics and scheduling perspective, these restrictions made the potential for aviation-related construction delays critical to the Contractor meeting their developed schedule.

The unique location, property boundaries, physical restrictions and State and Federal regulations made maintenance dredging at the City of Renton’s Will Rogers-Wiley Memorial Seaplane Base challenging within several aspects of permitting, design and construction. Dredging started in December 2013 and was successfully completed in February 2014. Dredging operations restored the seaplane base to pre-2009 Cedar River flood conditions and allowed pilots to enjoy a safer and more operable facility.

Keywords: Dredging, flooding, seaplane, aviation, water quality, federal

INTRODUCTION The City of Renton’s (City) Will Rogers Wiley Post Memorial Seaplane Base is located at the southern end of in Renton, Washington. The seaplane base is situated along the shoreline, directly north of the City’s municipal airport (Clayton Scott Field) utilized by both private and commercial airplane traffic, most notably the Boeing Commercial Company, which uses the municipal runway for the initial flights of aircraft. The seaplane base is used primarily by private aircraft (e.g. seaplanes and/or float planes), allowing tenants to utilize a launch ramp, maneuvering basin and temporary moorage along two (2) floating concrete docks, one orientated in the east-west directions and one orientated in the north-south directions.

1 Coastal Engineer, Coast & Harbor Engineering, a Division of Hatch Mott MacDonald, 110 James Street STE 101, Edmonds, Washington, 98020, USA, T: 425-778-5763, Fax: 425-778-6883, Email: [email protected]. 2 Principal Coastal Engineer, Coast & Harbor Engineering, a Division of Hatch Mott MacDonald, 110 James Street STE 101, Edmonds, Washington, 98020, USA, T: 425-778-6042, Fax: 425-778-6883, Email: [email protected].

286 Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015"

Directly east of the City’s seaplane base (approximately 100 meters) is the outllet of the Cedar River, one of the larger tributaries into Lake Washington. As a result of geomorphic processes, a delta and a several dynamic channels have formed at the outlet of the Cedar River into Lake Washington. Figure 1 shows a plan view of the southern end of Lake Washington, the project site, and the approximate extent of the Cedar River delta in the vicinity of the project site.

Figure 1. Plan view of the project site located at the southern end of Lakee Washington in Renton, WA.

Following a Cedar River flooding eventn in January 2009, large volumes of sediments were carried down the river and deposited within the delta and surrounding areas. Due to the orientation of the delta channels at the time of the 2009 flooding, sediment carried by the Cedar River into Lake Washington was directed at the City’s seaplane base launch ramp, floating concrete docks and maneuvering basin. Deposited sedimennt from the flooding events within the area of the City’s seaplane base severely limited depths required for safe launching, navigation and take- off/landing activities for the seaplane users. This prompted the City to initiate the permitting process, final design and ultimately maintenance dredging construction was conducted tto mitigate for the impacts of the 2009 flooding event. Upon completion of dredging in February 2014, approximately 12,230 m³ (16,000 CY) of material was removed from the City’s seaplane base dredging area.

Upon initiating the permitting phase, the City and their consultant, Coast & Harbor Engineering (CHE), a Division of Hatch Mott MacDonald, ran into several permitting, design and constructionn phase related issues that required project-specific strategies and methods to be implemented in order to successfully complete the City’s maintenance dredging project.

This paper will present and discuss project-specific issues and complexities due to the unique location, submerged land boundaries, physical restrictions and State and Federal regulations during the permitting, design, and construction phases of the City of Renton’s seaplane base maintenaannce dredging project. Some of the specific issues discussed within this paper include; (1) submerged lands ownership; (2) correspondence with the Federal

287 Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015"

Emergency Management Administration (FEMA) as a result of the 2009 flood events; (3) consideration of utility and communication line locations within the design dredging prism; (4) Federal Aviation Administration (FAA) construction safety and phasing; and lastly (5) water quality considderations for the protection of migrating salmon species during construction. The following sub sections describe the project specific challenges and the successful mitigating actions in detail.

PROJECT CHALLENGES The projectc -specific challenges the City of Renton faced throughout the permitting, design and construction phases of the Will Rogers Wiley Post Memorial Seaplane Base Maintenance Dredging project extended beyond the common issues associated with most maintenance dredging projects. These project specific issues and challenges encountered by the project team and the contractor throughout the duration of the City’s maintenance dredging project are discussed further within the following sub-sections.

Submerged Lands Ownership The initial challenges during the permitting and early design process were directly associated with the horizontal limits of the dredging area and the types of submerged lands ownnerships that existed within it. Figure 2 shows a plan view of the approximate dredge area limits and surrounding area within Lake Washington. The colored areas in the figure represent the different types of submerged land ownership that existed within the horizontal dredge limits. The red area indicates public Department of Natural Resources (DNR) submerged land, the green area represents submerged land leased from DNR by the City, the blue area represents City owned submerged land and the purple/magenta area represents privately owned submerged land. Yellow lines within the figure represent utility (sewer) or communication lines that either run through or adjacent to the dredge prrism.

Figure 2. Plan view of the project site located at the southern end of Lake Washington in Renton, WA showing the various typpes of properties (public/private) and utility/communication lines addjacent to or within the dredging area.

During the permitting and design phases of City’s maintenance dredging project, offset distances from existing the utilities and communication lines were established and the appropriate submerged lands easements/permissions were

288 Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015" obtained and incorporated into the final design documents. Several other issues directly related to submerged lands ownership within the City’s project area ultimately lead to other challenges associated with permitting, design and maintenance dredging construction and are further discussed in detail within the following sub-sections.

FEMA Correspondence Following the January 2009 flooding events, the City of Renton applied for finnancial assistance from the Federal Emergency Management Administration (FEMA). FEMA would provide financial assistance that would pay for a portion of the maintenance dredging area. Specifically, the financial assistance would cover a percentage of the public lands (e.g. DNR and City of Renton submerged lands shown in Figure 1) to mitigate for the sedimentation within the seaplane base caused by the Cedar River flooding evennt in 2009. Figure 3 shows a plan view of the delineated dredging areas that were either determined eligible or not eligible for Federal financial assistance. The red area represents the private property submerged lands (easeement area) that was not eligible for financial assistance. The green area represents the FEMA qualified submerrged lands that were eligible for FEMA financial assistance.

Figure 3. Plan view of the project site located at the southern end of Lake Washington in Renton, WA showingn the FEMA qualified submerged lands and the private property easement area (not qualified).

The associated challenge with delineating dredging areas eligible for FEMA financial assistance required the City and CHE to break up the dredging area based upon the aforementioned submerged land ownership areas, determine accurate post-construction dredging volumes and coordinate with FEMA following construction. In the end, approximately 70% of the dredged volume was eligible for FEMA ffinancial assistance. Close coordination with the dredging contractor, accurate calculation of dredging volumes and post-construction coordination with FEMA ultimately lead to the City receiving significant financial assistance for the mainnttenance dredging work to mitigate for the effects of the 2009 Cedar River flooding event.

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Communication and Utility Lines within or Adjacent to the Dredge Area The horizontal coordinates and vertical elevations of two submerged utility/communication lines during the permitting phase of the City’s dredging project were critical to developing final design documents and providing the contractor with accurate information to safely complete dredging construction at the City’s seaplane base. The approximate locations and orientations of the two lines relative to the dredging area are shown in Figure 2 above. During the permitting and design phases of the project, several challenges arose regarding the accuracy of As-Built documents, historical design plans, and information pertaining to the horizontal location(s) or vertical elevation(s), and their respective datums.

The AT&T communication line running in the North-South direction, west of the project area was identified within historical design drawings and project information provided by the City. The location and alignment of the communication line was within approximately 5 meters of the top of slope of the design prism. During design, within the technical specifications and dredging plan notes, no barge anchoring or spudding zones were established within the approximate easement of this communication line to deter the Contractor from anchoring or deploying spuds along the alignment of the known line. Additional information gathered from more recent horizontal location surveys of this communication line were provided to City near the end of final design and incorporated within the final design plans and technical specifications to further aid the Contractor in avoiding the areas along the alignment of the communication line during dredging construction. As a precautionary step, the newly provided survey information allowed the Contractor to locate the horizontal position of the communication line and use temporary marking buoys throughout the duration of construction.

The second obstacle extending through the dredge prism was a reinforced concrete sewer line owned by King County Metro, which extended in the east-west direction across the length of the northern edge of the dredging prism. Locating the sewer line required close coordination with the City, specifically during design and dredging construction. The main challenge faced by the City and their consultant had to do with the out of date information provided to the County, as the original as-built drawings, notes and pertinent information dated back to 1962 and referenced a vertical datum that was no longer being used in Washington State.

During the design phase, vertical dredging tolerances and construction notes were added in the vicinity of the metro sewer line to restrict the contractor from conducting over-dredging, barge anchoring or spudding in the established metro sewer line easement. Additionally, special grading was incorporated within the dredging design in order to accommodate for the vertical elevation change of the sewer line in the northwest corner of the dredging prism.

Prior to the beginning of construction, previously produced technical condition reports of the sewer line were acquired by the City, and in coordination with the contractor, the project team was able to locate the approximate top elevation of the utility line relative to the project vertical datum and confirm that no modifications to the dredging design or additional vertical tolerances were necessary. During construction, the contractor was notified to closely monitor material dredged in the vicinity of the metro sewer line and report any discrepancies in material type to the City and/or the consultant and cease dredging immediately if materials inconsistent with those expected within the dredge prism were encountered. Following construction, dredging was fully executed according to the project plans and technical specifications without disrupting the existing utility or communication lines adjacent to or within the design dredging prism.

FAA Construction Safety and Phasing Aviation safety during construction operations adjacent to is regulated by the Federal Aviation Administration (FAA) and the airport operator. Due to the close proximity of the seaplane base dredging project to Runway 16-34 at the Renton Municipal Airport, and per the FAA’s Advisory Circle 150/5370-2F, the City was responsible for the development and submittal of two key pre-construction documents: (1) a Notice to Airmen (NOTAM); (2) a Construction Safety and Phasing Plan (CSPP). The NOTAM is a formal notice issued by the FAA to inform pilots using airport facilities of potential hazards and/or construction occurring at a specific airport. The second document required by the FAA is the CSPP, which establishes construction requirements, of which are mostly unrelated to dredging construction. The CSPP requirements directly related to dredging construction included dredging equipment height requirements adjacent to the City’s runway, dredging construction phasing and communication relative to airport operations, and hazard marking and lighting for contractor owned equipment.

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In response to the construction requirements outlined within the CSPP developed by the City, the contractor developed a Safety Plan Compliance Document (SPCD) to ensure compliance with the City’s CSPP during construction operations. All of the aforementioned documents were essential in developing a safe construction plan compliant with FAA regulations.

During the design and construction phases of the City’s dredging project, severral construction engineering tactics were considered in order to develop a plan for handling the requireements established within the CSPP. The biggest challenge facing the contractor for this project was the construction equipment height restrictions relative to the CSPP elevation contour prism developeed by the City. An example plan and sections of the CSPP contour elevation prism in the vicinity of the dredging prism is shown in Figures 4 and 5. The prism indicates thee maximum elevation contractor equipment may extend beyond the established elevatiion of Runway 16-34 at the Renton Municipal Airport. If contractor owned equipment extended beyond the vertical limits of this prism, they were required to schedule construction operations around critical airport activities.

Figure 4. Plan view of the project site located at the southern end of Lake Washington in Renton, WA showing the elevation prism for Runway 16-34 at the Renton Municipal Airport.

291 Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015"

Figure 5. Section view of the projeect site located at the southern end of Lake Washington in Renton, WA showing the elevation prism for Runway 16-34 at the Renton Municipal Airport.

The contractor’s Derek Barge was equipped with a large crane which had an apprroximate maximum boom elevation of 33.5 meters (110 feet) above the water line. The limiting elevation of the CSPP contour prism in the dredging area was approximately 0.5 meters (about 2 feet) above the water line. Contractor conformance with the established limiting of elevation of the CSPP prism was obviously not feasible. Therefore, to mitigate for the CSPP equipment height restrictions, a communication plan was established betweeen the City, the FAA, and the Contractor which required the contractor to relocate and/or lower crane booms to be in compliance with the established CSPP elevation prism whenever the Airport or FAA required. Fortunately, during the duration of dredging construction (approximately 6 weeks) at the City’s seaplane base, the contracttor was only reequired to move equipment a few times due to flight operations.

Water Quality Monitoringn State and Federal agencies were interested and actively involved in ensuring water quality requirements for in-water construction activities within and around the City’s seaplane base dredging area were strictly adhered to. This was due in large part to the vicinity of the dredging project to the Cedar River outlet into Lake Washington, which is a well-known migration route for many species of Salmon.

Prior to construction, the City and their consulting team met with the Washington State Department of Ecology (DOE), the agency responsible for enforcing water quality standards in Washington State, to determine an appropriate background measurement point for comparing water quality measurements (i.e turbidity, measured in Nephelomete ric Turbidity Units, NTUs) during dredging operationss, as per Washington Administrative Code 173- 201A-200 for freshwaters of the State, turbidity was not to exceed 5 NTU’s over background conditions when the background turbidity is 50 NTU or less; or a 10 percent increase inn turbidity when the background turbidity is more than 50 NTU.. For this project, a turbidity “point of compliance” was located radially approximately 45 meters (150 feet) from the point of disturbance within the dredging area (i.e. 45 meters from the clamshell bucket entering the water). The background condition point for comparison with the “point of compliance” measurement was located at

292 Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015" the northern end of one of the Cedar River delta channels. Prior to the start of construction, the background measurement location, shown in Figure 6 below, was determined during the City’s on-site meeting with the DOE, as the highest turbidity reading within the area. During constructiion, this would allow the Contractor the most flexibility when conducting measurements at the “point of compmpliance” in comparison to the turbidity of the background measurement location.

Figure 6. Plan view of the project site located at the southern end of Lake Washington in Renton, WA showing the Cedar River delta channel formations, the approximate backgrround measurement location, an example “Point of Compliance” measurement location and the approximate dreddge area.

Prior to the start of construction, the prroximity of the project site to the outlet of the Cedar River, a major spawning route for Salmon, piqued the interest of State and Federal agenciees responsible for reviewing and enforcing water quality criteria. During the construction-phase, review of weekly water quality monitoring reports submitted to the Agencies by the Contractor indicated no exceedances of the established monitoring criteria. Upon completion of the dredging, any potential delays to project schedules were avoided as a direct result of the City’s pre-construction correspondence efforts with the State and Federal agencies responsibble for enforciing water quality compliance.

CONCLUSIONS The unique project site, property booundaries, physical restrictions and State and Federal regulations made maintenance dredging at the City of Renton’s Will Rogers-Wiley Memorial Seaplane Base made several aspects of the permitting, design and construction phases challenging. The issues and challenges discussed within this paper and the mitigative measures to reduce their impacts to the City’s dredging projeect are summarized and outlined in the Table 1 below.

293 Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015"

Table 1. Project specific challenges and mitigative actions applied.

Project Challenge Mitigative Actions Applied

 Accumulated property boundary information Submerged Lands via City and County GIS data sources Ownerships  Applied for private property construction easements  Accumulated property boundary information via City and County data sources  Initiated correspondence with the FEMA FEMA Correspondence during permitting, design, and construction  Quantified dredge volumes for financial assistance based upon delineated property (submerged land) boundaries  Reviewed as-built drawings and previously produced condition/location assessments Communication/Utility  Modified dredging design elevations and Line Design slopes based upon communication/utility Considerations line easements and vertical clearances  Located communication/utility lines in field prior to construction.  Owner/Engineer completed and submitted a Construction Safety Phasing and Phasing FAA Phasing and Plan (CSPP) prior to the start of construction Safety Correspondence  Contractor completed and submitted a Safety Plan Compliance Document (SPCD)  Issued a Notice to Airmen (NOTAM)  Early correspondence by Owner/Engineer Water Quality with pertinent state or federal agencies to Monitoring develop water quality monitoring plan and monitoring criteria

Dredging started in December 2013 and was successfully completed in February 2014. Dredging operations restored the seaplane base to pre-2009 Cedar River flood conditions and allowed pilots to enjoy a safer and more operable seaplane base facility. . REFERENCES

O’Donnell, M. (2011). “Operational Safety on Airports During Construction.” Advisory Circular, AC No. 150/5370- 2F, Federal Aviation Administration.

CITATION Dawson, J.G. and Phillips, R.S. “City or Renton seaplane base maintenance dredging, challenges beyond the scope of maintenance dredging,” Proceedings of the Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015", Houston, Texas, USA, June 22-25, 2015.

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