HomeMy WebLinkAboutRS_S_Singh_Short_Plat_Review_OTAK_Memo_181031.pdfTechnical Memorandum
To: Clark Close, Senior Planner
City of Renton
From: Kevin O’Brien, Senior Ecologist
Stephanie Modjeski, Wetland Scientist
Copies:
Date:
Subject:
Project No.:
October 31, 2018
S. Singh Short Plat Critical Areas Review
32847.F
Introduction
The City of Renton (City) has requested Otak, Inc. (Otak) to conduct a review of associated critical areas reports
for the proposed 6-lot hillside subdivision called the S. Singh Short Plat. Two critical areas reports have been
submitted with the land use application: a Critical Areas Report prepared by Habitat Technologies (dated April 22,
2017) and a Wetland and Stream Reconnaissance Report prepared by Altmann Oliver Associates, LLC (dated
May 16, 2018). A previous land use application called the Defoor Short Plat included a record of professional
studies identifying critical areas on the subject property. The City has requested Otak to conduct a review to
resolve inconsistencies between the two new reports and previous records on file regarding the critical areas on
site.
The subject property, Parcel #0007200196, is located on Renton Avenue S between S 9th Street and S 10th Street
in the City of Renton, King County, Washington. Otak conducted a field survey of the subject property and a
review of previously prepared critical areas information to evaluate the classifications of streams, drainage
features, and wetlands on site. Otak also evaluated the S. Singh Short Plat plan and its compliance with the City
of Renton Municipal Code (RMC) Chapter 4-3-050 (Critical Areas Regulations).
Documents Reviewed
•Wetland and Stream Reconnaissance Report, prepared by Altmann Oliver As sociates, LLC (dated March
16, 2018),
•Preliminary Short Plat Plans for Singh Short Plat, prepared by CORE Design Engineering (CORE) (June
20, 2017),
•Critical Areas Report, prepared by Habitat Technologies (dated April 22, 2017),
•Defoor Short Plat Hearing Examiner Decision (dated October 17, 2006),
•Defoor Short Plat Layout #2, prepared by PACE (dated June 2006),
•Defoor Property; Geomorphic Assessment, prepared by Talasaea Consultants, Inc. (Talasaea) and
GeoEngineers (dated May 1, 2006),
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S. Singh Short Plat Critical Areas Review October 5, 2018
•Hydrogeological Consultation; Stream B Corridor, prepared by Icicle Creek Engineers (ICE) (dated March
24, 2006),
•Reconsideration Request of Administrative Determination of Un-mapped Stream/Wetland Classification
for Defoor Properties (Parcel Nos. 000720196, 0007200194, and 2023059085), prepared by The City of
Renton (dated December 7, 2005)
•Defoor Properties (Parcel Nos. 000720196, 0007200194, and 2023059085) Request for Reconsideration
and Appeal, prepared by Talasaea (dated November 17, 2005),
•Administrative Determination of Un-Mapped Stream/Wetland Classification for Defoor Properties (Parcel
Nos. 000720196, 0007200194, and 2023059085), prepared by The City of Renton (dated November 3,
2005),
•Defoor Wetland and Stream Basin Restoration Plan, Existing Conditions, and Overview Plan, prepared by
Talasaea (dated June 28, 2005),
•Defoor Property Downstream Drainage Map, prepared by CORE (dated June 2005).
The following resources were also reviewed on September 27, 2018 as part of the background research on the
property prior to the site investigation:
•City of Renton (COR) Maps (http://rp.rentonwa.gov/Html5Public/Index.html?viewer=CORMaps),
•City of Renton Document Center (https://rp.rentonwa.gov/WebLink/Welcome.aspx),
•Google Earth Pro,
•King County iMap (http://gismaps.kingcounty.gov/iMap/),
•United States Department of Agriculture-National Resource Conservation Service (USDA-NRCS) Web
Soil Survey (https://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm ),
•U.S. Fish and Wildlife –National Wetland Inventory (NWI)
(https://www.fws.gov/wetlands/data/mapper.HTML),
•Washington State Department of Natural Resources (DNR)- Washington LIDAR Portal
(http://lidarportal.dnr.wa.gov/#47.45403:-122.21724:17),
•Washington Department of Fish and Wildlife (WDFW) Priority Habitat and Species maps
•WDFW Salmonscape maps
•Existing Conditions Map for Defoor Short Plat, by PACE Engineering, dated August 2008, available at
https://rp.rentonwa.gov/weblink/3/doc/325902/Page1.aspx ,
•USGS Quadrangle Maps from 1897 to 1991, available at https://ngmdb.usgs.gov/topoview/,
•Historic Aerial and Topography Maps, available at https://www.historicaerials.com/viewer,
•Washington Geological Information Portal-DNR Coal Mine Maps, available at
https://geologyportal.dnr.wa.gov/#coal.
Summary of Existing Critical Areas Information
In November 2005 the City of Renton (City) prepared a response to a request by Talasaea Consultants, Inc.
(Talasaea) for the classification of four unmapped streams and one unmapped wetland on the subject property.
The City determined that Wetland B shall be classified as Category III with a 25-foot standard buffer width,
Streams A and C and Drainage 1 shall be classified as Class 4 streams with a 35-foot standard buffer width, and
Stream B shall be classified as a Class 3 stream with a 75-foot standard buffer width.
S. Singh Short Plat Critical Areas Review
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October 31, 2018
In a response letter by the City to Talasaea (December 2005), the City stated that Streams B, C, and Drainage 1
are not Class 5 streams. Class 5 streams are artificially constructed channels and are non-regulated. The City
determined that the features created by point discharge erosion do not constitute artificially constructed channels,
and therefore, the drainage features do not meet the criteria for Class 5 streams.
A hydrogeological study was conducted in March 2006 by Icicle Creek Engineers (ICE) to determine the
classification for Stream B on the subject property. It was determined that Stream B is not a naturally occurring
stream and is the result of unmanaged stormwater discharge from the culvert from which the stream originates.
A geomorphic assessment was prepared in May 2006 by Talasaea and GeoEngineers. It was determined that
Stream A is a naturally occurring stream, and Stream B is not a naturally formed stream.
A critical areas report was prepared by Habitat Technologies in Apri l 2017. No wetlands were identified on site.
Three surface water drainages (Streams A, B, and C from previous reports) were identified as emanating from
three culverts on Renton Avenue and were determined to be artificial intentionally created, non-regulated
features.
A review of the 2017 Habitat Technologies Critical Areas report was prepared by Altmann Oliver Associates, LLC
(AOA) in May 2018. The report concurred with Habitat Technologies in that all three drainage features are
stormwater conveyance features, and non-regulated streams.
Findings
Otak biologists completed a site visit and critical areas review of the property on October 1, 2018. The property
was walked, and soil pits dug at various points.
Three drainages were identified on the subject property in the locations of Stream A, B, and C as identified in
previous reports (Figure 1). Each drainage emanates from a 12- to 16-inch plastic culvert beneath Renton Avenue
S and discharges onto concrete riprap splash pads on the hillslope. None of these drainages are mapped by
WDFW , DNR, or King County.
1. We concur with Habitat Technologies and Altmann Oliver Associates that Stream s A, B, and C are not
regulated features per RMC 4-3-050.G.7b.
Stream A (Drainage A) appears to be a ravine which conveys stormwater from the culvert beneath Renton
Avenue South. No water was observed in the drainage at the time of the field survey. The drainage is located in a
natural ravine dominated by upland vegetation such as big leaf maple (Acer macrophyllum), snowberry
(Symphoricarpos albus), and Himalayan blackberry (Rubus armeniacus). The drainage channel has little
definition near the culvert discharge source and becomes deeply incised near the center of the property with no
sorted substrate. The drainage does not connect to any other surface waterbody. No evidence of Drainage A
crossing the power line corridor to the south was found, contrasting with City of Renton map. Drainage A shows
evidence of localized scour and rilling.as a result of the stormwater input combined with the steep slopes
associated with that portion of the property. Water from Drainage A may contribute to the hydrology of the stream
and/or wetland on the property to the west of the
The topography in the mapped location of “Stream C” forms a shallow swale that slopes towards “Stream A”. No
stream or defined channel was observed. Stream C is a drainage (Drainage C) path that sheet flows to Drainage
A, emanating from a piped outfall beneath Renton Avenue S.
S. Singh Short Plat Critical Areas Review
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October 31, 2018
Per RMC 4-3-050.G.7b, Streams A and C on the subject property are non-regulated drainages. Both streams
appear to receive no hydrological input other than that provided by the upgradient stormwater catchbasins and
conveyance.
Stream B forms two distinct braids (B1 and B2). B1 is located on the northernmost portion of the property and B2
is located immediately south. B1 has substrate of fines and gravels and flows through a defined shallow channel.
B1 had flowing water at the time of the field visit, indicating some groundwater contribution to flow as the other
stormwater drainages were dry. B2 appears to be an artificial drainage. B2 is deeply incised and is the result of
erosional scour on the hillslope. B2 had less surface water flowing in the channel than B1. Stream B flows west
and converges with an unnamed tributary to Thunder Hills Creek on Parcel #2023059163, immediately west
adjacent to the subject property. Similar to the situation with Streams A and C, Stream B (Drainage B) appears to
derive most of its hydrology from stormwater at its outfall on Renton Avenue South, with a likely groundwater
component originating within the stormwater system upgradient. The observed flow at the time of the site visit
may be due to groundwater infiltrating into the stormwater pipes in the system or stormwater from the previous
day’s small rain events, derived from the larger stormwater conveyance system associated with Drainag e B
compared to Drainage A and C. City of Renton mapping indicated that the outfalls to Streams A, B, and C were
only linked the upgradient stormwater pipes and catchbasins, and groundwater expressing into stormwater pipes
would not have been present historically prior to installation of the stormwater system. Water from Stream B,
however, does flow down the steeply wooded slope and eventually contributes flow to a mapped stream (Thunder
Hills Creek) through an untyped tributary on the property to the west of the S. Singh Short Plat property. The
untyped tributary is mapped by DNR and the City of Renton.
2.No wetlands were observed on the subject property. Vegetation in the forested habitat on the property
consisted primarily of upland species. Soils were examined and consisted of sandy loams and were not hydric,
and no direct or indirect signs of hydrology were noted, with the exception of the flow in Drainage B and evidence
of erosion in Drainage A. The previously mapped wetland associated with Drainage B was not observed during
the site visit. The off-site wetland to the west was observed, and a stream associated with the wetland crossed
the power line corridor west of and beyond the S. Singh Short Plat Property.
Conclusion: Drainages A, B, and C appear to be driven by storm water input where the outfalls were deliberately
located to convey stormwater down the forested slope. Deliberate placement of the stormwater outfalls and the
downgradient flow paths may be considered as created in that hydrology would not have been present without
stormwater input. Hydrological input in the Drainages on the subject property appears to be stormwater-driven,
with a possible groundwater component derived from potential stormwater pipe breaks or failures. As such,
Drainages A, B, and C appear to meet the RMC criteria to be considered non-regulated by the City on the subject
property, although the stream and wetland on the property to the west would likely be regulated. Wetland habitat
was not observed on the subject property.
S. Singh Short Plat Critical Areas Review
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October 31, 2018
Photos
Photo 1: Ravine with Drainage A, view downstream (west).
S. Singh Short Plat Critical Areas Review
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October 31, 2018
Photo 2: Ravine with Drainage A, view upstream (east).
Photo 3: Drainage B2, deeply incised.
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October 31, 2018
Photo 4: Drainage B
Photo 5: Culvert beneath Renton Avenue S, discharges water to Drainage B.
S. Singh Short Plat Critical Areas Review
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October 31, 2018
Photo 6: Drainage C, looking west and north
2,257
188
City of Renton Parcel 000720-0196
This map is a user generated static output from an Internet mapping site and
is for reference only. Data layers that appear on this map may or may not be
accurate, current, or otherwise reliable.
None
5/16/2018
Legend
1280 64
THIS MAP IS NOT TO BE USED FOR NAVIGATION
Feet
Notes
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WGS_1984_Web_Mercator_Auxiliary_Sphere
Information Technology - GIS
RentonMapSupport@Rentonwa.gov
City and County Boundary
Addresses
Parcels
Water Service Areas
Wastewater Service Areas
Discharge Point
Water Quality
Stormwater Main
Culvert
Virtual Drainline
Private Network Structures
Inlet
Manhole
Utility Vault
Unknown Structure
Private Control Structure
Private Discharge Point
Private Water Quality
Private Detention Facilities
Pond
Tank
Vault
Wetland
Private Pipe
Private Culvert
Private Open Drains
Figure 1
Drainage B
Drainage A
Drainage C