21c_Hydraulics_Report.pdf

U.S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

WESTERN FEDERAL LANDS HIGHWAY DIVISION

610 East Fifth Street Vancouver Washington, 98661

RIVER S BRIDGE TS&L HYDRAULICS REPORT

To: Mike Traffalis, WFLHD Project Manager From: Megan Frye, WFLHD Hydraulics Engineer Date: November 13, 2015 Project: Design for River S Bridge Replacement, WA RRP RIDG 100(2)

Background

The Western Federal Lands Highway Division (WFLHD), in cooperation with the U.S Fish and Wildlife Service - Ridgefield Wildlife Refuge, is proposing construction of a new bridge crossing over Lake River to the Ridgefield Wildlife Refuge River S Unit. The project begins at the intersection of South Hillhurst Road and South Refuge Road and continues approximately

0.5 miles to the intersection at the River S Unit Entry Station.

The intent of the project is to provide safe and efficient access to the River S Unit by replacing the existing bridge. The existing access is a narrow steep, gravel road with an at-grade railroad crossing followed by a one-lane bridge. The access road and one-lane bridge is too narrow for the types and volume of traffic accessing the River S Unit. Information collected by the Ridgefield National Wildlife Refuge indicates vehicle traffic and visitation is increasing and they expect that trend to continue. The at-grade railroad crossing directly adjacent to the narrow, winding entrance road and one-lane bridge creates an inefficient, unsafe traffic situation.

The proposed structure is a two-lane, grade separated bridge. Widening the bridge to two lanes will provide more efficient access to the River S Unit and raising the bridge above the railroad crossing will eliminate disturbance in traffic created by the at-grade railroad crossing.

The purpose of this memorandum is to document the recommendations for the proposed bridge crossing at Lake River. The results of site morphological, hydrologic, hydraulic, and scour analyses and recommendations for bridge orientation, low chord elevation, foundation depths, and scour protection are presented.

Conclusions and Recommendations

Bridge Low Chord

Lake River is classified as navigable water by the US Coast Guard. The clearance restriction for the proposed structure matches the existing bridge low chord elevation of 37.2 feet (NGVD 1947) which equates to 40.5 (NAVD 88).

Design guidance for WFLHD recommends a minimum of 3.5 to 5 feet of clearance above the 50-year water surface elevation where the potential for woody debris exists. Based on previous bridge inspections, a moderate amount of floating and submerged debris in the channel should be expected. The 50-year water surface elevation, 26 feet (NAVD 88), was identified in the current Flood Insurance Study for Clark County developed by the Federal Emergency Management Agency (Flood Insurance Study Number 53011CV001A, September 5, 2012) which can be found in Appendix E. The low chord elevation of 40.5 feet (NAVD 88) needed for the grade separated bridge option over the existing railroad crossing exceeds the minimum clearance requirements driven by the water surface elevation.

The hydraulic capacity of the proposed bridge assumes a multi-span, 529-foot bridge with a 250-foot waterway width.

Scour

Although analysis shows riprap in not required some riprap or erosion matting is recommended at the west abutment to mitigate the potential erosion both during high flow. If deemed necessary, set the riprap/erosion mat crest at 29.5 feet (2.5 feet above the 100-year water surface elevation). Place the riprap/erosion mat toe at two feet below the existing ground elevation at the west abutment. Grade the finished surface of the riprap slopes at 1.75(h):1(v). If riprap is selected, use Class 3 riprap, placed in a minimum 2.5-foot thick layer and on a geotextile fabric.

See Appendix C for suggested riprap details. See Appendix D for riprap size calculations.

Stream Impacts

The proposed structure should have no impact on the stream function. Comparing the number of obstructions in the channel with the existing structure (19 bents) and the proposed structure (2 drilled shafts), the proposed structure should have less restriction on the stream flow conveyance, sediment transport, or woody debris transport.

Floodplain and Flood-rise Impacts

There is private property along the east bank of Lake River at the proposed bridge location. The proposed structure should not have an appreciable impact on the flooding risk upstream or downstream given the reduced number of obstructions in the channel upon construction of the proposed structure and removal of the existing structure.

Construction

The proposed bridge construction may require some form of temporary work structure. The temporary work structure should not limit navigability along Lake River. The minimum low chord should be 40.5 feet. The contractor will be required to submit drawings for all temporary structures including design calculations and supporting data.

Pile driving activities are anticipated to be restricted to July through October. All other construction activities can take place at any time. Debris tarps will be required to prevent construction debris from entering the channel. The existing timber structure will be removed as a part of the proposed project. The timber pile bents will either be removed completely or cut flush with the channel bottom.

The location and geometry of the proposed bridge is shown on the Preliminary Layout Sheet in Appendix C.

Site Conditions

Lake River is an overflow channel of the Columbia River. The channel gradient both upstream and downstream of the proposed bridge is around 0.001 feet/feet. The streambed material is predominately sandy silt. Around the proposed crossing, the channel is confined on the east with a relatively steep, 1(h):1(v), well-vegetated bank and confined on the west by a man-made dike.

At the crossing, the dike sits approximately 450 feet from the west bank with a wide, grassy floodplain between the dike and the bank. Downstream of the crossing, the dike sits approximately 100 feet from the west bank with a grassy floodplain between the two. See Appendix A for aerial photos of the site.

The existing water quality and proposed actions for monitoring water quality during construction can be found the Water Quality Report (Megan Frye, WFLHD 2014) found in Appendix E.

The OHWM line was documented and surveyed by the Federal Highway Administration on June 2012 as 11.70 feet (NAVD 88). The ordinary high water mark (OHWM) as defined by the shoreline management act (SMA) is a biological vegetation mark. According to RCW 90.58.030, the definition of ordinary high water mark is the “ ordinary high water mark on all lakes, streams, and tidal water is that mark that will be found by examining the bed and banks and ascertaining where the presence and action of waters are so common and usual, and so long continued in all ordinary years, as to mark upon the soil a character distinct from that of the abutting upland, in respect to vegetation as that condition exists on June 1, 1971, as it may naturally change thereafter, or as it may change thereafter in accordance with permits issued by a local government or the department: Provided, that in any area where the ordinary high water mark cannot be found, the ordinary high water mark adjoining salt water shall be the line of mean higher high tide and the ordinary high water mark adjoining fresh water shall be the line of mean high water”.

For determination of State Lands Boundary, the US Fish and Wildlife Service, through a contract with Minister-Glaeser Surveying, Inc. in 2000, performed a survey to update a Washington Department of Natural Resources permit. To determine the mean high water (MHW, river side property boundary) at Columbia River mile 90 (equivalent river mile to the River S access bridge), Minister-Glaeser documented and recorded with Clark County Washington (Book 25, page 50) the State Lands Boundary. Note three of this recorded document states, ““ Ordinary High Water Line: The ordinary high water line, (OHWL) for the Columbia River Mile 89-92 was computed from the United States Army Corps of Engineers, (USACE) publication “ Flood Profiles, CL-03-116, April 1973 Revision.” The OHWL at the Columbia River Mile 90 is 13.6 Columbia River Datum (CRD).”” The FHWA River S Access Bridge project is being developed in NAVD 1988 therefore, Aquatics Land Lease documents will be prepared showing the State Lands Boundary at elevation 13.6 feet (CRD), 14.58 feet (NGVD 1947), and 17.86 feet (NAVD 88).

The existing bridge is a one-lane, timber structure 332 feet in length. The original bridge was constructed with 19 spans. A 56-foot, main span was added in 1980 to provide an increased horizontal opening. This was carried out under a Vancouver Lake dredge contractor through a permit action with the US Fish and Wildlife Service. The low chord elevation is 40.5 feet (NAVD 88). The Bridge Inspection and Appraisal Report developed by the Ridgefield National Wildlife Refuge, both in August 2008 and August 2010, list no sign of scour at the existing bridge. Both reports identify a 4-foot high vertical bank and active sloughing along the west shoreline requiring minor repairs to the bank protection.

Hydrology

Lake River originates approximately 7 miles upstream of the proposed bridge at Vancouver Lake. It is fed by major tributaries Flume Creek, Whipple Creek, Salmon Creek, and Burnt Bridge Creek. Lake River is a tributary to the Columbia River. The confluence is approximately two miles downstream of the proposed bridge. Lake River, like the Columbia River, is tidally influenced. At the confluence with Lake River and the Columbia River, the mean tide range is approximately 2 feet based on NOAA Water Level predictions.

According to the Geotechnical Condition Assessment developed by FHWA, the geology in the area consists of cataclysmic-flood deposits, conglomerate, and alluvium. The cataclysmic-flood deposits are described as unconsolidated clay, silt, and fine to medium sand. The conglomerate is described as semi-consolidated pebble and cobble gravel containing minor lenses of cemented sand. The alluvium is described as unconsolidated sediments underlying modern floodplains of the Columbia River and Lake River.

Peak discharges for Lake River were estimated using the Columbia River Flood Profiles, Flood Insurance Study (Clark County, Washington and Incorporated Areas - Flood Insurance Study Number 53011CV001A). The drainage area is shown in Figures 1 and 2 of Appendix A. Peak discharge estimates are presented in Appendix B.

Water Surface Elevations and Flow Velocities

Water surface elevations were estimated using the FEMA, Flood Insurance Study for Clark County, Washington and the average velocities were estimated by applying the estimated peak flow water surface elevations and channel characteristics in the FHWA, Hydraulic Toolbox Channel Analysis (Hydraulics Toolbox Version 4.1). Results are summarized in Appendix D.

Floodplain and Flood-rise Limitations

Executive Order 11988, Floodplain Management, established federal policies for protecting floodplains and floodways. The intention of the associated regulations is to avoid, to the extent practical, adverse impacts to floodplains; minimize the impact of floods to human safety, health, and welfare; and avoid supporting land use development that is incompatible with the natural and beneficial floodplain values. When avoidance is not possible, the policies require appropriate consideration of methods to minimize adverse impacts.

The bridge is located within an area of special flood hazard designated by a Federal Emergency Management Agency (FEMA) flood insurance rate map (FIRM) or detailed mapping study (FIS). A volume equivalent to the volume of fill placed within the 100-year floodplain will be added within the floodplain so the total volume within the 100-year floodplain remains the same.

Based on the site conditions, the proposed bridge is not expected to result in a rise in the 100-year water surface elevation. FHWA policy allow up to one-foot rise in the 100-year water surface elevations.

Scour

A HEC-18 based scour analysis was performed. Geotechnical boring logs indicate sandy silt layer extending down approximately 8 feet. Silty gravel with sand and sandy silty with traces of gravel is found below the sandy silt layer extending down 25 feet. Draft bore logs from the geotechnical investigation can be found in Appendix E.

The primary mode of scour expected at the proposed bridge is pier scour for the 100-year and 500-year flood events at 3.61 feet and 3.74 feet respectively. Although no scour at the abutments was determined in the calculations, the flow conditions at the 100-year and 500-year flood are difficult to represent accurately in the calculations without a more comprehensive two-dimensional flow analysis as the flow will be divided in both the channel and on the west floodplain. Given the relatively flat gradient and slow velocities, the expected conditions at the west abutment can be approximated without an in depth modeling effort. Scour analysis and results are summarized in Appendix D.

attachments: Appendix A – F