HomeMy WebLinkAboutRS_KC Solar Lights Flood Hazard Data Memo_v1
Parks and Recreation Division
Department of Natural Resources and Parks
King Street Center
201 South Jackson Street, Suite 700
Seattle, WA 98104-3855
206-477-4527 TTY Relay: 711
Date: 17 June 2025
TO: Ashley Wragge, Assistant Planner, City of Renton, Planning Division
FM: Jon Polka, P.E., King County Parks and Recreation Division (PARKS)
Collin Bond, E.I.T., King County PARKS
RE: Flood Hazard Data for Solar Equity Project
The purpose of the memo is to address flood hazard data (per RMC 4-3-050G.4 and 4-8-120) for
the proposed installation of two off-grid, solar powered area lights.
PROJECT BACKGROUND
The King County Solar Equity Project proposes to install two off-grid solar powered area lights.
One light is to be placed in Boulevard Lane Park and the other is to be placed along the Lake to
Sound Trail. The project will provide sustainable solar panels and energy efficient lighting. This
project will enhance the usability, comfort, and safety in trail areas.
IMPROVEMENT DESCRIPTION
The light pole footing will be precast offsite to avoid a concrete spill and to speed up
construction. The footing will be 2-feet in diameter and 8-feet long, but the footing will be set to
6 to 8 inches above ground surface to protect the pole from mowing and other trail maintenance
activities. Soil spoils will be removed and disposed of outside of the floodplain.
FLOODPLAIN IMPACTS
BOULEVARD LANE PARK
There is one proposed solar lighting improvement for Boulevard Lane Park. The proposed
area lighting (AL3-1) will be installed at approximately 378.0’ (NAVD 88) per the 2025
King County Digital Ground Model. This ground elevation is higher than the base flood
Flood Hazard Data for Solar Equity Project
June 2025
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elevation of 372.2’ per FEMA Cross Section BK near the project location. Therefore, the
light pole is above and outside of the Special Flood Hazard Area based on its elevation. See
Figure 1 for more information.
LAKE TO SOUND TRAIL (GREEN RIVER & BLACK RIVER CONVERGENCE) –
APPROX.
There is one proposed solar lighting improvement for the Lake to Sound Trail near the Black
River. The proposed area lighting (TL1-1) will be installed at approximately 17.2’ per the
2025 King County Digital Ground Model. This is located within a Zone AE floodplain of the
Green-Duwamish River where the base flood elevation is approximately 23’ per the FEMA
FIRMette (see Figure 2).
RMC 4-3-050G.4.e.vi prohibits development in Zone AE special flood hazard areas, unless it
is demonstrated that the water surface elevations of the base flood will not increase more
than one foot at any point within the community. This single light pole is a small, isolated
obstruction and part of a minor project that will not result in a one-foot increase in water
surface elevation consistent with the following FEMA guidance:
“There are other minor projects that probably will not increase flood stages. For example,
small, isolated obstructions such as a mailbox, a pitcher’s mound, or a single telephone
pole can be permitted without requiring no-rise certification.”
- FEMA Guidance for Flood Risk Analysis and Mapping: 11.1.1. Exemption for Minor
Projects
If required, compensatory storage can be provided on site to counteract the volume lost from
the installation of the light pole. Per RMC 4-3-050G.4.g a compensatory storage calculation
was performed to account for the storage volume lost from the addition of the light pole (3.2
ft3). The location and elevation of the proposed improvement is shown in Figure 3.
Compensatory storage calculations are provided in Figure 4.
Jon D. Polka, P.E.
King County Department of
Natural Resources and Parks
Date: June 17, 2025
cc: Tom Early, Capital Project Manager, King County Parks
Flood Hazard Data for Solar Equity Project
June 2025
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SUPPORTING FIGURES
Figure 1. Boulevard Lane Park Improvements
Note: 1’ & 5’ contours from site survey and King County 2023 Digital Ground Model
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Figure 2. FEMA FIRMette (Lake to Sound Trail location)
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Figure 3. Lake To Sound Trail Improvements
Note: 2’ & 10’ contours from site survey and King County 2023 Digital Ground Model
Flood Hazard Data for Solar Equity Project
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Figure 4. Lake To Sound Trail Compensatory Storage Calculation