HomeMy WebLinkAboutRS_Drainage Review Exemption_APPROVED
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May Creek Trestle Drainage Review Exemption Request
To: Jonathan Chavez, PE, City of Renton
From: Charles Dewey, PE
Copies: Bob Doherty, PE
File
Date: July 23, 2020
Subject: May Creek Trestle Maintenance Project
Project No.: 33248.A
The May Creek Trestle project is a maintenance project in the City of Renton to repair an existing rail trestle
bridge to the proposed use as a pedestrian bridge along the Eastside Rail Corridor Regional Trail. The May Creek
trestle consists of 4 timber trestle spans with a total length of approximately 60 feet. The trestle was built in 1960.
Timber piles, caps and stringers have been treated with preservatives by Osmose, most recently indicated in
1997. Previous cursory bridge inspection information was available and reviewed as part of the BNSF East
Corridor Bridge Safety Inspection Report, dated April 15, 2011.
In addition to pedestrian use, maintenance vehicle traffic was evaluated using the standard H-10 truck in
accordance with the AASHTO LRFD Guide Specifications for the Design of Pedestrian Bridges. Proposed trail
use of the bridge is considered interim, with an expected life of 10-15 years. Therefore, repair of existing bridge
members is limited to those necessary for safe use in that time frame. Long term rehabilitation and evaluation of
full bridge replacement options were not considered.
Based on evaluation of the trestle, repairs are recommended in order to utilize the bridge for the multi-use trail.
Our site inspections revealed defects and deterioration in timber and steel members. This typically consists of
internal decay in timber stringers, piles and cap beams and rusting of steel cap beams. Repair recommendations
account for 1) severity of deterioration, 2) desired lifespan of the repaired structure, and 3) load rating of bridge
members. In addition to repairing and rehabilitating existing components of the bridge, existing timber railroad ties
and existing steel railroad tracks will be removed, and new decking and railing will be installed.
The proposed plan for the May Creek Trestle creates 2,510 SF of land disturbing activity. Of the 2,510 SF total
area there is 1,700 SF of New + Replaced Impervious Area, as indicated on Figure 1, Project Impacted Areas.
The 2017 City of Renton Surface Water Design Manual defines maintenance as:
“Maintenance means those usual activities taken to prevent a decline, lapse, or cessation in the use of
currently serviceable structures, facilities, BMPs, equipment, or systems if there is no expansion of any of
these, and there are no significant hydrologic impacts. Maintenance includes the repair or replacement of
non-functional facilities and BMPs, and the replacement of existing structures (e.g., catch basins,
manholes, culverts) with different types of structures, if the repair or replacement is required to meet
current engineering standards or is required by one or more environmental permits and the functioning
characteristics of the original facility or structure are not changed. For the purposes of applying this
definition to the thresholds and requirements of this manual, CED will determine whether the functioning
characteristics of the original facility, structure, or BMP will remain sufficiently unchanged to consider
replacement as maintenance.”
APPROVED
01/06/2021 msippo
DEVELOPMENT ENGINEERING DIVISION
Page 2
May Creek Trestle Drainage Review Exemption Request July 23, 2020
k:\project\33200\33248a\projectdocs\reports\exemption from drainage review.docx
Therefore, an exemption is requested from the drainage review of the project based on the definition of
maintenance projects per the 2017 City of Renton Surface Water Design Manual.
PROJECT SITE AREASSFACNEW IMPERVIOUS AREA2900.0067REPLACED IMPERVIOUS AREA1,4100.0324VEGETATION8100.0186TOTAL LAND DISTURBING ACTIVITY AREA2,5100.0577IMPACTED AREASPROJECT IMPACTED AREASxDepartment of Natural Resources andParks - Parks and Recreation DivisionCapital Planning and Development201 S. Jackson St, Suite 700Seattle, Washington 98104Tel (206) 296-4232 | Fax (206) 263-6217FILE RE9ISIONCHECKEDDRAWNDATEPROJ 7/6/2020RDRD248AERC MAY CREEK TRESTLEREHA%ILITATIONRENTON, WAKING COUNTY, WA, CONTRACT NO. E00645E19OF 1011241 Willows Road NE, Suite 200Redmond, WA 98052425.822.4446www.otak.comSTA
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H
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HITECTNO. 1199 EXP. 07/08
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FIGURE 1