HomeMy WebLinkAboutRS_CRTTWoldeBFEStudy23_1011Project No. 220211
Page 1 of 1
Priority 1: Critical issue requiring discussion
Priority 2: Factual or substantive error or issue that should be corrected prior to publication
Priority 3: Editorial suggestion to improve readability or other idea
Comment Response Tracking Table
Base Flood Elevation Study – 13710 SW May Valley Road, Renton, WA
Document Type:
Calculation Drawing Specification Study-Report Other:
Document Name & Description:
Base Flood Elevation Study
SUBMITTAL: ITR COPY City Review COPY
DATE: July 28, 2022 COMMENTS DUE DATE: RETURN COMMENTS TO:
REVIEWER NAME: City of Renton TITLE: DEPARTMENT:
No. Page # Line # Priority
(1, 2 or 3) Comment Commentor Response
1 5 Memo Comment:
Recreating "existing conditions" is key to this analysis. I assume you generated contours using 2016 LiDAR and
showed them on Attachment 2-2. Were these 1-ft contours? LiDAR tends to lose accuracy in forested/vegetated areas.
Were there any irregularities in the generated contours?
Email Comment:
Development of “existing conditions” model on page 5. This is key to the entire analysis of the impact of the patio
construction. Aspect should give some detail about how they used LiDAR. Did they generate 1-ft contours? Were there
any adjustments or refinements made to that data due to vegetation potentially impacting the accuracy of LiDAR?
City of
Renton
1-ft contours were generated from the 2016 LiDAR data and these are what are shown on Attachment 2-2. We agree that LiDAR
tends to lose accuracy in forested/vegetated areas; however, upon examination of the LiDAR surface and resulting 1-ft contours no
irregularities were identified. The 2016 LiDAR Technical Data Report (metadata that accompanied the LiDAR data from WADNR)
discusses the processing methodologies performed that removed laser returns for vegetation and human-made structures to arrive at
the ground surface model.
2 6 Based on observations, LiDAR, and the recent survey data, the May Creek meander along the
Wolde property is gradually migrating southward by eroding into the tall steep southern bank. As
the lateral migration progresses, it continues to move the stream thalweg and left bank of the creek
away from the patio area. Aspect believes this is a natural process rather than any response to patio
construction.
Memo Comment:
How so? Please explain. When was the patio constructed? How long prior to patio construction has channel migration
been happening? Have you used historical LiDAR data to confirm this claim if enough definition.
Email Comment:
On page 6, Aspect argues that channel migration is natural and unrelated to the patio construction. Given the very minor
encroachment of the patio into the floodplain, this is probably true, but they should expand upon it. What year was the
patio constructed and how long do they think this has been happening?
City of
Renton
The patio was constructed sometime between 2017 and 2021. We reviewed available WA DNR LiDAR hill shades from 2003,
2005, and 2016 and while these hill shades do not use a consistent light direction, we believe they show that a slow lateral migration
has been occurring along the left bank.
3 16/17 Memo Comment:
Include in this report screen shots of cross sections 362 to 445 under pre and post project conditions and 100-year water
surface elevations.
Email Comment:
On pages 16/17, a comment was added about adding the HEC-RAS cross sections to this report for the cross section
along the Wolde property.
City of
Renton Attachment 2-6 will be added that includes both pre and post project HEC-RAS cross sections with 100-year water surface
elevations.
4 Model Email Comment:
It is also requested that Aspect provide the HEX-RAS model altogether as well.
City of
Renton
The model will be provided as a digital attachment.