HomeMy WebLinkAbout22-R-TIR-2016-01-08-PRLM Preliminary Technical Information Report Boun Short Plat Renton, Washington Our Job No. 17625
17625.002.doc
TABLE OF CONTENTS
1.0 PROJECT OVERVIEW
Figure 1 – Technical Information Report (TIR) Worksheet
Figure 2 – Site Location
Figure 3 – Drainage Basins, Subbasins, and Site Characteristics
Figure 4 – Soils
2.0 CONDITIONS AND REQUIREMENTS SUMMARY
2.1 Analysis of the Core Requirements
2.2 Analysis of the Special Requirements
3.0 OFF-SITE ANALYSIS
4.0 FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN
A. Existing Site Hydrology
B. Developed Site Hydrology
C. Performance Standards
D. Flow Control System
E. Water Quality System
5.0 CONVEYANCE SYSTEM ANALYSIS AND DESIGN
6.0 SPECIAL REPORTS AND STUDIES
7.0 OTHER PERMITS
8.0 CONSTRUCTION STORMWATER POLLUTION PREVENTION PLAN ANALYSIS AND DESIGN
A. Erosion and Sediment Control (ESC) Plan Analysis and Design
B. Stormwater Pollution Prevention and Spill (SWPPS) Plan Design
9.0 BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT
10.0 OPERATIONS AND MAINTENANCE MANUAL
Tab 1.0
17625.002.doc
1.0 PROJECT OVERVIEW
The proposed Boun Short Plat is a single-family residential project consisting of 7 lots zoned R8.
The project is 1.32 acres in size and contains a single tax parcel (102305-9139). The site is
located at the northwest corner of N.E. 10th Street and Duvall Avenue N.E., in a portion of
Section 10, Township 23 North, Range 5 East, W.M., in the City of Renton.
The site is rectangular in shape, with a panhandle portion along the west side of the site
extending approximately 150 feet north. The site is currently undeveloped, consisting mostly of
brush and a few trees. There is also a 330-square-foot building on site that will be demolished
and removed as part of the proposed development.
The site is bound along the east property line by Duvall Avenue N.E. and by Chelan Avenue N.E.
to the west. The site is bound by single-family residences to the south and north. Access to the
site will be provided by an extension of Chelan Place N.E. north, and a proposed private alley
connecting Chelan Place N.E. and Chelan Avenue N.E.
On-site soils are mapped as Alderwood gravelly sandy loam. Please refer to the Soils Map in this
section. All drainage calculations were modeled as till soils.
The project will be constructing frontage improvements consisting of asphalt pavement, curb and
gutter, and sidewalk. All on-site roads for this project will have a 20-foot paved width.
The topography on site is generally flat, with a low area located near the southwest corner of the
site. The site generally slopes from east to west, with approximately 6 feet of topographic relief.
The project will be mass graded with cuts and fills balanced on site.
The project site consists of two (2) separate Threshold Discharge Areas (TDA), the west TDA and
the east TDA. Both TDAs trigger full drainage review as each TDA will contain more than 2,000
square feet of new plus replaced impervious surface. The project proposes to combine the two
TDAs via a surface water adjustment, which will be submitted to the City of Renton separate from
this report.
The drainage facilities are required to meet the requirements of the 2009 King County Surface
Water Design Manual (KCSWDM), and the 2010 City of Renton Amendments to the KCSWDM.
The drainage design shall meet, at a minimum, the Flow Control Duration Standard (Forested
Conditions), and Basic Water Quality Treatment. The drainage facility located in Tract A is a
combination detention/wetvault, sized for Level 2 Flow Control. The wetvault will be sized
pursuant to the 2009 KCSWDM and its amendments to ensure that the Basic Water Quality
requirements are met.
KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL
TECHNICAL INFORMATION REPORT (TIR) WORKSHEET
2009 Surface Water Design Manual 1/1/09
1 17625.003.doc
Part 1 PROJECT OWNER AND
PROJECT ENGINEER
Part 2 PROJECT LOCATION AND
DESCRIPTION
Project Owner Kent Khnor, Warring Properties
Phone (425) 453-6227
Address 845 106th Avenue N.E., Suite 200
Bellevue, WA 98044
Project Engineer Chris Jensen, P.E.
Company Barghausen Consulting Engineers , Inc.
Phone (425) 251-6222
Project Name Boun Short Plat
DDES Permit # N/A
Location Township 23 North
Range 5 East
Section 10
Site Address NWC of N.E. 10th Street &
Duvall Avenue N.E.
Part 3 TYPE OF PERMIT APPLICATION Part 4 OTHER REVIEWS AND PERMITS
Landuse Services
Subdivision / Short Subd. / UPD
Building Services
M/F / Commercial / SFR
Clearing and Grading
Right-of-Way Use
Other
DFW HPA
COE 404
DOE Dam Safety
FEMA Floodplain
COE Wetlands
Other
Shoreline
Management
Structural
Rockery/Vault/
ESA Section 7
Part 5 PLAN AND REPORT INFORMATION
Technical Information Report
Type of Drainage Review Full / Targeted /
(circle): Large Site
Date (include revision 11/17/15
dates):
Date of Final: TBD
Site Improvement Plan (Engr. Plans)
Type (circle one): Full / Modified /
Small Site
Date (include revision
dates):
Date of Final: TBD
Part 6 ADJUSTMENT APPROVALS
Type (circle one): Standard / Complex / Preapplication / Experimental / Blanket
Description: (include conditions in TIR Section 2)
Combine two threshold discharge areas
Date of Approval:
KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL
TECHNICAL INFORMATION REPORT (TIR) WORKSHEET
2009 Surface Water Design Manual 1/1/09
2 17625.003.doc
Part 7 MONITORING REQUIREMENTS
Monitoring Required: Yes / No
Start Date:
Completion Date:
Describe:
Part 8 SITE COMMUNITY AND DRAINAGE BASIN
Community Plan :
Special District Overlays:
Drainage Basin: Lower Cedar River Basin
Stormwater Requirements:
Part 9 ONSITE AND ADJACENT SENSITIVE AREAS
River/Stream
Lake
Wetlands
Closed Depression
Floodplain
Other
Steep Slope
Erosion Hazard
Landslide Hazard
Coal Mine Hazard
Seismic Hazard
Habitat Protection
Part 10 SOILS
Soil Type Slopes Erosion Potential
Alderwood Gravelly Sandy Loam 8-15% Low
High Groundwater Table (within 5 feet) Sole Source Aquifer
Other Seeps/Springs
Additional Sheets Attached
KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL
TECHNICAL INFORMATION REPORT (TIR) WORKSHEET
2009 Surface Water Design Manual 1/1/09
3 17625.003.doc
Part 11 DRAINAGE DESIGN LIMITATIONS
REFERENCE LIMITATION / SITE CONSTRAINT
Core 2 – Offsite Analysis
Sensitive/Critical Areas
SEPA
Other
Additional Sheets Attached
Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area)
Threshold Discharge Area:
(name or description) Site Threshold Discharge Area (East and West to be combined)
Core Requirements (all 8 apply)
Discharge at Natural Location Number of Natural Discharge Locations: 1
Offsite Analysis Level: 1 / 2 / 3 dated: 11/17/15
Flow Control Level: 1 / 2 / 3 or Exemption Number
(incl. facility summary sheet) Small Site BMPs
Conveyance System Spill containment located at:
Erosion and Sediment Control ESC Site Supervisor: TBD
Contact Phone:
After Hours Phone:
Maintenance and Operation Responsibility: Private / Public
If Private, Maintenance Log Required: Yes / No
Financial Guarantees and Provided: Yes / No
Liability
Water Quality Type: Basic / Sens. Lake / Enhanced Basic / Bog
(include facility summary sheet) or Exemption No.
Landscape Management Plan: Yes / No
Special Requirements (as applicable)
Area Specific Drainage Type: CDA / SDO / MDP / BP / LMP / Shared Fac. / None
Requirements Name:
Floodplain/Floodway Delineation Type: Major / Minor / Exemption / None
100-year Base Blood Elevation (or range):
Datum:
Flood Protection Facilities Describe:
Source Control Describe landuse:
(comm./industrial landuse) Describe any structural controls:
KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL
TECHNICAL INFORMATION REPORT (TIR) WORKSHEET
2009 Surface Water Design Manual 1/1/09
4 17625.003.doc
Oil Control High-use Site: Yes / No
Treatment BMP:
Maintenance Agreement: Yes / No
with whom?
Other Drainage Structures
Describe:
Part 13 EROSION AND SEDIMENT CONTROL REQUIREMENTS
MINIMUM ESC REQUIREMENTS
DURING CONSTRUCTION
Clearing Limits
Cover Measures
Perimeter Protection
Traffic Area Stabilization
Sediment Retention
Surface Water Control
Dewatering Control
Dust Control
Flow Control
MINIMUM ESC REQUIREMENTS
AFTER CONSTRUCTION
Stabilize Exposed Surfaces
Remove and Restore Temporary ESC Facilities
Clean and Remove All Silt and Debris Ensure
Operation of Permanent Facilities
Flag Limits of SAO and open space
preservation areas
Other
Part 14 STORMWATER FACILITY DESCRIPTIONS (Note: Include Facility Summary and Sketch)
Flow Control Type/Description Water Quality Type/Description
Detention
Infiltration
Regional Facility
Shared Facility
Flow Control
BMPs
Other
Vault
Biofiltration
Wetpool
Media Filtration
Oil Control
Spill Control
Flow Control BMPs
Other
KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL
TECHNICAL INFORMATION REPORT (TIR) WORKSHEET
2009 Surface Water Design Manual 1/1/09
5 17625.003.doc
Part 15 EASEMENTS/TRACTS Part 16 STRUCTURAL ANALYSIS
Drainage Easement
Covenant
Native Growth Protection Covenant
Tract
Other
Cast in Place Vault
Retaining Wall
Rockery > 4' High
Structural on Steep Slope
Other
Part 17 SIGNATURE OF PROFESSIONAL ENGINEER
I, or a civil engineer under my supervision, have visited the site. Actual site conditions as observed were
incorporated into this worksheet and the attached Technical Information Report. To the best of my
knowledge the information provided here is accurate.
Signed/Date
Tab 2.0
17625.002.doc
2.0 CONDITIONS AND REQUIREMENTS SUMMARY
2.1 Analysis of the Core Requirements
Core Requirement No. 1: Discharge at the Natural Location.
Response: Runoff from the west TDA leaves the site near the southwest corner via
sheet flow, where it is then collected by the existing storm system within Chelan Avenue
N.E. The proposed detention vault will discharge to the existing storm system within
Chelan Avenue N.E. Runoff from the east TDA leaves the site along the east property
line, where it is collected by a roadside ditch and conveyed north along Duvall Avenue
N.E. The two TDAs will be combined per a surface water adjustment.
Core Requirement No. 2: Off-Site Analysis.
Response: An off-site analysis has been performed pursuant to the 2009 KCSWDM.
See Section 3.0 for the Level 1 Off-Site Drainage Analysis.
Core Requirement No. 3: Flow Control.
Response: Flow Control Duration Standard (Forested Conditions) is required. Flow
control requirements will be met by a detention vault designed pursuant to the 2009
KCSWDM and the 2010 City of Renton Amendments to the KCSWDM. See Section 4.0
for more information.
Core Requirement No. 4: Conveyance System.
Response: The conveyance system has been designed pursuant to the 2009 KCSWDM
and the 2010 City of Renton Amendments to the KCSWDM. Conveyance calculations
and backwater analysis will be provided during final engineering.
Core Requirement No. 5: Erosion and Sediment Control.
Response: Temporary erosion control measures will be provided during final
engineering.
Core Requirement No. 6: Maintenance and Operations.
Response: All proposed storm structures will be publicly maintained by the City of
Renton; therefore, no Operation and Maintenance Manuals are required.
Core Requirement No. 7: Financial Guarantees and Liability.
Response: The project will provide a Site Improvement Bond Quantity Worksheet to
establish a bond amount for drainage facility restoration and site stabilization financial
guarantee prior to construction.
Core Requirement No. 8: Water Quality.
Response: Basic Water Quality is required for this project. This requirement is met by a
wetvault. The wetvault is in combination with the detention vault, and sizing will be
completed during final engineering.
17625.002.doc
2.2 Analysis of the Special Requirements
Special Requirement No. 1: Other Adopted Area-Specific Requirements.
Response: The proposed project is not located in a designated Critical Drainage Area.
Special Requirement No. 2: Flood Hazard Area Delineation.
Response: As indicated by the FEMA Map included in this report, the proposed site
does not lie within a floodplain or floodway of a stream, so this special requirement does
not apply.
Special Requirement No. 3: Flood Protection Facilities.
Response: The project does not rely on an existing flood protection facility or propose to
modify or construct a new flood protection facility, so this special requirement does not
apply.
Special Requirement No. 4: Source Control.
Response: The project does not require a commercial building or commercial site
development permit; therefore, this special requirement does not apply.
Special Requirement No. 5: Oil Control.
Response: This site is not classified as a High Use Site given the criteria in the 2009
KCSWDM; therefore, this special requirement does not apply.
Special Requirement No. 6: Aquifer Protection Area.
Response: The project site is not located within an Aquifer Protection Area; therefore,
this special requirement does not apply.
Tab 3.0
17625.002.doc
3.0 OFF-SITE ANALYSIS
The Level 1 Off-Site Drainage Analysis is included in this section.
LEVEL 1 OFF-SITE DRAINAGE ANALYSIS
Boun Short Plat
NWC of N.E. 10th Street and Duvall Avenue N.E.
Renton, Washington
Prepared for:
Kent Khnor
Warring Properties
845 106th Avenue N.E., Suite 200
Bellevue, WA 98044
January 6, 2016
Our Job No. 17625
CIVIL ENGINEERING, LAND PLANNING, SURVEYING
18215 72ND AVENUE SOUTH KENT, WA 98032 (425) 251-6222 (425) 251-8782 FAX
BRANCH OFFICES ¨ TUMWATER, WA ¨ LONG BEACH, CA ¨ ROSEVILLE, CA ¨ SAN DIEGO, CA
www.barghausen.com
17625.004.doc
TABLE OF CONTENTS
TASK 1 STUDY AREA DEFINITION AND MAPS
EXHIBIT A Vicinity Map
EXHIBIT B Downstream Drainage Map
EXHIBIT C Upstream Basin Map
TASK 2 RESOURCE REVIEW
EXHIBIT D FEMA Map
EXHIBIT E Sensitive Areas Folios
EXHIBIT F SCS Soils Map
EXHIBIT G Assessor’s Map
EXHIBIT H Wetland Inventory Map
EXHIBIT I Basin Reconnaissance Summary Report
TASK 3 FIELD INSPECTION
3.1 Conveyance System Nuisance Problems (Type 1)
3.2 Severe Erosion Problems (Type 2)
3.3 Severe Flooding Problems (Type 3)
EXHIBIT J Off-Site Analysis Drainage System Table
TASK 4 DRAINAGE SYSTEM DESCRIPTION AND PROBLEM DESCRIPTIONS
EXHIBIT K Drainage Complaints
TASK 5 MITIGATION OF EXISTING OR POTENTIAL PROBLEMS
17625.004.doc
TASK 1 STUDY AREA DEFINITION AND MAPS
The proposed Boun Short Plat is a single-family residential project consisting of 7 lots zoned R8. The
project is 1.32 acres in size and contains a single tax parcel (102305-9139). The site is located at the
northwest corner of N.E. 10th Street and Duvall Avenue N.E., in a portion of Section 10, Township 23
North, Range 5 East, W.M., in the City of Renton.
The site is rectangular in shape, with a panhandle portion along the west side of the site extending
approximately 150 feet north. The site is currently undeveloped, consisting mostly of brush and a few
trees. There is also a 330-square-foot building on site that will be demolished and removed as part of the
proposed development.
The site is bound along the east property line by Duvall Avenue N.E. and by Chelan Avenue N.E. to the
west. The site is bound by single-family residences to the south and north. Access to the site will be
provided by an extension of Chelan Place N.E. north, and a proposed private alley connecting Chelan
Place N.E. and Chelan Avenue N.E.
On-site soils are mapped as Alderwood gravelly sandy loam. Please refer to the Soils Map in this
section. All drainage calculations were modeled as till soils.
The project will be constructing frontage improvements consisting of asphalt pavement, curb and gutter,
and sidewalk. All on-site roads for this project will have a 20-foot paved width.
The topography on site is generally flat, with a low area located near the southwest corner of the site.
The site generally slopes from east to west, with approximately 6 feet of topographic relief. The project
will be mass graded with cuts and fills balanced on site.
The drainage facilities are required to meet the requirements of the 2009 King County Surface Water
Design Manual (KCSWDM), and the 2010 City of Renton Amendments to the KCSWDM. The drainage
design shall meet, at a minimum, the Flow Control Duration Standard (Forested Conditions), and Basic
Water Quality Treatment. The drainage facility located in Tract A is a combination detention/wetvault,
sized for Level 2 Flow Control. The wetvault will be sized pursuant to the 2009 KCSWDM and its
amendments to ensure that the Basic Water Quality requirements are met.
The site is comprised of two separate Threshold Discharge Areas (TDA): TDA 1 (west) and TDA 2 (east).
Runoff from TDA 1 generally sheet flows south and west, where it leaves the site near the southwest
corner of the site. Stormwater runoff is then collected by an existing storm system within Chelan Avenue
N.E. Runoff from TDA 2 generally sheet flows east and north, where it leaves the site along the east
property line. Stormwater runoff is collected by a roadside ditch just west of Duvall Avenue N.E. and
conveyed north.
UPSTREAM DRAINAGE ANALYSIS
The site is a localized high point, and receives negligible upstream runoff from adjacent properties.
17625.004.doc
TASK 2 RESOURCE REVIEW
· Adopted Basin Plans: The site is located within the Lower Cedar River Basin. Refer to Appendix
A for the portions of the basin that applies to this project.
· Finalized Drainage Studies: This is not applicable.
· Basin Reconnaissance Summary Report: This site is located in the Lower Cedar River Basin,
which is covered by the Lower Cedar River Basin and Nonpoint Pollution Action Plan dated July
1997 (included in Appendix A)
· Critical Drainage Area Maps: The project will not discharge to any critical areas or wetlands.
· Floodplain and Floodway FEMA Maps: Please see the enclosed FEMA Map (also in Section 1.0
of the TIR) utilized for analysis. As indicated on the map, the site is located in Zone X and is
outside of the 500-year floodplain.
· Other Off-Site Analysis Reports: A review of the Basin Reconnaissance Summary Report and a
site investigation were conducted in preparation of this Level 1 Off-Site Drainage Analysis. The
United States Department of Agriculture Soils Conservation Service Map is also provided within
Exhibit F. To our knowledge and research, there are no other reports available on file with the City
of Renton for this sub-basin and project site.
· Sensitive Areas Folios: Based on review of the King County Sensitive Areas Map Folios, the site
does not contain any On-Site Wetlands, Erosion Areas, Sensitive Areas, or Landslide Areas.
· Road Drainage Problems: This is not applicable.
· United States Department of Agriculture King County Soils Survey: Based on the Soils Map
Exhibit F) for this area, the site is underlain with Alderwood gravelly sandy loam. The soils were
modeled as till soils.
· Wetland Inventory Map: From the May Creek Wetland Inventory Report, there is no known
documentation or inventory of wetlands for the project site.
· Migrating River Studies: This is not applicable.
· City of Renton Aquifer Protection Zones: Per the City of Renton's GIS Map, the project site is
not located within an Aquifer Recharge Area.
17625.004.doc
TASK 3 FIELD INSPECTION
3.1 Conveyance System Nuisance Problems (Type 1)
Conveyance system nuisance problems, in general, are defined as any existing or predicted
flooding or erosion that does not constitute a severe flooding or erosion problem. Conveyance
system nuisance problems are defined as flooding or erosion that results in the overflow of the
constructed conveyance system for runoff events less than or equal to a 10-year event.
Examples include inundation of a shoulder or lane of a roadway. Examples include overflows
collecting in yards or pastures, shallow flows across driveways, minor flooding in crawlspaces or
unheated garages/outbuildings, and minor erosion.
There were no conveyance system nuisance problems observed during the site visit.
Furthermore, based on review of drainage complaints received from the City of Renton, there is
no evidence of past conveyance system nuisance problems occurring in the direct downstream
drainage course for both TDAs.
3.1 Conveyance System Nuisance Problems (Type 1)
Conveyance system nuisance problems are minor but chronic flooding or erosion problems that
result from the overflow of a constructed conveyance system that is substandard or has become
too small as a result of upstream development. Such problems warrant additional attention
because of their chronic nature and because they result from the failure of a conveyance system
to provide a minimum acceptable level of protection.
There were no conveyance system nuisance problems observed during the site visit. This site
will have a Level 2 Flow Control facility, which will restrict the flow of the 2-year release rate to 50
percent of the pre-developed site and will provide adequate mitigation to prevent any future
drainage complaints as a result of this proposed site development.
3.2 Severe Erosion Problems (Type 2)
Severe erosion problems are defined as downstream channels, ravines, or slopes with evidence
of or potential for erosion/incision, sufficient to pose a sedimentation hazard to downstream
conveyance systems or propose a landslide hazard by undercutting adjacent slopes. Severe
erosion problems do not include roadway or minor ditch erosion.
Based on the site visit, there was no evidence of, or potential for, erosion/incision sufficient to
pose a sedimentation hazard downstream within the limits of the study. Stormwater runoff from
the site will be collected and conveyed to a detention and water quality facility where it will then
be discharged off site. As a result, no future erosion problems should occur downstream
because of this development.
3.3 Severe Flooding Problems (Type 3)
Severe flooding problems can be caused by conveyance system overflows or the elevated water
surfaces of ponds, lakes, wetlands, or closed depressions. Severe flooding problems are defined
as follows:
· Flooding of the finished area of a habitable building for runoff events less than or equal to
the 100-year event. Examples include flooding of finished floors of homes and
commercial or industrial buildings. Flooding in electrical/heating systems and
components in the crawlspace or garage of a home. Such problems are referred to as
"severe building flooding problems."
17625.004.doc
· Flooding over all lanes of a roadway or severely impacting a sole access driveway for
runoff events less than or equal to the 100-year event. Such problems are referred to as
"severe roadway flooding problems."
Based on a review of the FEMA Map (Exhibit D) the proposed site is outside of the 500-year
floodplain, and there is no evidence of severe flooding problems encountered during our visit.
17625.004.doc
TASK 4 DRAINAGE SYSTEM DESCRIPTION AND PROBLEM DESCRIPTIONS
DOWNSTREAM DRAINAGE ANALYSIS: West TDA
In the pre-developed condition, runoff from the west TDA sheet flows to the south west corner, where it
leaves the site via sheet flow. The runoff is then collected by the existing stormwater system within
Chelan Avenue N.E. Once collected, the stormwater is conveyed approximately 185 feet via existing
storm drains west via the storm drain system within N.E. 10th Street and then discharged into an existing
regional stormwater pond (Facility ID No. 111336) approximately 500 feet west of the site. Once
detained, the stormwater is discharged back into the existing storm system in N.E. 10th Street, where it
continues to be conveyed west to the storm system within Anacortes Avenue N.E. From there, it is
conveyed north along Anacortes Avenue N.E. approximately 850 feet, bringing the total distance off site
to approximately 1,350 feet (1/4 mile) where the downstream was terminated.
In the developed condition, stormwater runoff will be collected and conveyed by the proposed on-site
conveyance system to the proposed detention vault. From there, it will be discharged into the existing
stormwater system within Chelan Avenue N.E. and maintain the downstream flowpath of the existing
conditions.
We believe that the proposed development will not significantly increase the amount of runoff entering the
existing storm system within Chelan Avenue N.E.
DOWNSTREAM DRAINAGE ANALYSIS: East TDA
In the pre-developed condition, runoff from the east TDA sheet flows east, where it leaves the site along
the east property line and is collected by an existing roadside ditch along the west side of Duvall Avenue
N.E. Once collected, stormwater runoff sheet flows north within the ditch approximately 760 feet where it
is collected by an existing stormwater system along the west side of Duvall Avenue N.E. Runoff
continues north within the existing storm system for more than 560 feet, totaling 1,320 feet (1/4 mile)
where the downstream was terminated.
In the developed condition, stormwater runoff will be collected and conveyed by the proposed on-site
conveyance system to the proposed detention vault. The stormwater will no longer be discharged to the
existing natural discharge location for the east TDA. A stormwater adjustment will be proposed to
combine the two TDAs.
We believe that the proposed development will not significantly decrease the amount of runoff entering
the existing storm system within Duvall Avenue N.E., as the existing area is undeveloped and relatively
small (35,300 sf).
Below is a list of drainage complaints within a 1-mile radius for the proposed Boun Short Plat received
from Gary Fink at the City of Renton on November 10, 2015:
1. Honey Creek Inlet: Duvall Avenue N.E. / N.E. Sunset Blvd. – Ongoing Maintenance inspection
point, clear inlet after significant storm events.
· The above complaint is a note for maintenance of an inlet, and will not be affected by the
proposed development.
2. Duvall Place N.E., South of N.E. 7th Place – Overtopping of east ditch line, sedimentation. Dec
2014.
· This complaint is located south of the site, and is not within the downstream drainage course.
17625.004.doc
3. N.E. 6th St / Duvall Ave NE – Flooding of Right of Way at NE corner of intersection. Obstruction
of drain inlet & outfall to wetland. Nov 2013.
· This complaint is located south of the site, and is not within the downstream drainage course.
4. NE 5th St / Duvall Ave NE – Ongoing Maintenance inspection point, inspect / clear wetland outfall
after significant storm events.
· This complaint is located south of the site, and is not within the downstream drainage course.
5. NE 5th Ct / Union Ave NE – Blocked grate at wetland outlet, NE corner of intersection.
Grate/Structure replaced May 2013.
· This complaint is located south of the site, and is not within the downstream drainage course.
6. 4810 NE 4th – Ongoing Maintenance inspection point. Blocked inlet results in localized right-of-
way flooding at NE 4th.
· This complaint is located south of the site, and is not within the downstream drainage course.
1
Colleen Allen
From:Gary Fink <GFink@Rentonwa.gov>
Sent:Tuesday, November 10, 2015 11:09 AM
To:Colleen Allen
Subject:Boun Short Plat / Barghausen Job #17625 Drainage Complaint History - Renton
Good Morning Colleen,
Sorry to run late on this request….let me know if you have any questions.
Gary
The following are the documented drainage issues within a one-mile radius of the Boun Short Plat site. Please note that
the information provided is sourced from recorded issues logged in City of Renton drainage complaint records and City
Maintenance records and cannot be deemed a comprehensive list of all past issues.
· Honey Creek Inlet: Duvall Ave NE / NE Sunset Blvd – Ongoing Maintenance inspection point, clear inlet after
significant storm events.
· Duvall Pl NE, South of NE 7th Pl – Overtopping of east ditch line, sedimentation. Dec 2014
· NE 6th St / Duvall Ave NE – Flooding of Right of Way at NE corner of intersection. Obstruction of drain inlet &
outfall to wetland. Nov 2013
· NE 5th St / Duvall Ave NE – Ongoing Maintenance inspection point, inspect / clear wetland outfall after
significant storm events.
· NE 5th Ct / Union Ave NE – Blocked grate at wetland outlet, NE corner of intersection. Grate/Structure replaced
May 2013
· 4810 NE 4th – Ongoing Maintenance inspection point. Blocked inlet results in localized right-of-way flooding at
NE 4th.
Refer to King County IMap drainage complaint maps for historic drainage issues prior to annexation.
Best Regards,
Gary Fink
City of Renton
Utility Systems Division - Surface Water Utility
Phone:(425) 430-7392 / Fax:(425) 430-7241
GFink@RentonWa.gov
17625.004.doc
TASK 5 MITIGATION OF EXISTING OR POTENTIAL PROBLEMS
No existing or potential problems were found during our site inspection. The proposed plan design within
the 2009 KCSWDM and the 2010 City of Renton Amendments to the KCSWDM guidelines should have
no adverse impact to future drainage conditions. Proposed flow control BMPs will be implemented and
formal flow control will be provided to ensure the runoff leaving the site meets the requirements for the
Conservation Flow Control (Level 2).
Tab 4.0
17625.002.doc
4.0 FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN
A. Existing Site Hydrology
The site is rectangular in shape, with a panhandle portion along the west side of the site
extending approximately 150 feet north. The site is currently undeveloped, consisting
mostly of brush and a few trees. There is also a 330-square-foot building on site that will
be demolished and removed as part of the proposed development.
The site is bound along the east property line by Duvall Avenue N.E. and by Chelan
Avenue N.E. to the west. The site is bound by single-family residences to the south and
north. Access to the site will be provided by an extension of Chelan Place N.E. north,
and a proposed private alley connecting Chelan Place N.E. and Chelan Avenue N.E.
There are two separate Threshold Discharge Areas (TDA) located on site. Runoff from
the West TDA leaves the site near the southwest corner, where it is collected by an
existing storm system located in Chelan Avenue N.E. Runoff from the East TDA leaves
the site near the northeast corner, where it sheet flows into an existing roadside ditch,
and continues in the ditch north along Duvall Avenue N.E. eventually discharging into
Honey Creek. The project proposes to combine the two threshold discharge areas.
B. Developed Site Hydrology
The completed project will create 7 single-family lots. The total developed area will be
1.32 acres in size. New impervious surfaces will include roadways, driveways,
sidewalks, and roof areas. The project will be providing a drainage facility.
A conveyance system consisting of catch basins and storm drain pipes will be
constructed in the roadways to collect drainage from the site and convey the runoff to the
new drainage facility.
A combination detention/wetvault will be constructed in Tract A to provide water quality
and flow control for the project. The pond will contain a control structure fitted with a riser
overflow. Stormwater from the vault will be conveyed to the existing stormwater system
within Chelan Avenue N.E.
The project proposes a single detention vault that combines the runoff from both the
West and East TDA's and discharging to the natural discharge location of the West TDA.
It is understood that a drainage adjustment will likely be necessary to divert flows as
proposed.
The vault was designed in accordance with Level 2 Flow Control methodology matching
historic peaks and durations as outlined in the 2009 KCSWDM and the 2010 City of
Renton Amendments to the KCSWDM. However, the diversion of flows from the East
TDA to the West TDA will cause a slight increase in peak flows and durations to the West
TDA even though the project is matching historic conditions from the entire site. The
drainage adjustment would be for the diversion of flows and for the increase in peaks and
durations in the West TDA. When attempting to design the mitigated flow to match
peaks and durations for the pre-developed West TDA only, it was found that a detention
vault could not reasonably be sized to match the extremely small pre-developed peaks
and durations.
17625.002.doc
C. Performance Standards
The KCRTS Runoff Time Series Program was used to size the detention facility. The
detention vault was sized for Conservation Flow Control (Level 2) based on the
requirements of the 2009 KCSWDM and the 2010 City of Renton Amendments to the
KCSWDM. Individual lot BMPs will be applied to an impervious area equal to 10 percent
of the lot size for lots less than 11,000 square feet. The BMP credit has been applied to
the impervious land cover data, which was used to size the detention vault. Please refer
to the KCRTS calculations provided in this section.
D. Flow Control System
The proposed flow control system will require a drainage adjustment as it cannot feasibly
meet the minimum requirements for flow control. The vault will be sized to meet the
historical flows of the entire site, rather than the West TDA. As mentioned above,
calculations will be provided to show that no conveyance issues will result by the
increased flow to the West TDA, and that no stormwater runoff will be taken away from
wetlands on the downstream drainage course of the East TDA.
Flow Control System details will be submitted during final engineering.
E. Water Quality System
A wetvault will be used for water quality. Sizing of the wetvault will be prepared during
final engineering.
Tab 5.0
17625.002.doc
5.0 CONVEYANCE SYSTEM ANALYSIS AND DESIGN
Conveyance system analysis will be provided in final engineering.
Tab 6.0
17625.002.doc
6.0 SPECIAL REPORTS AND STUDIES
The following special reports and studies are included:
6.1 Arborist Report prepared by Greenforest Inc. dated October 14, 2015.
Greenforest
Incorporated
C
o
n
s
u
l
t
i
n
g
A
r
b
o
r
i
s
t
4547
South
Lucile
Street,
Seattle,
WA
98118
Tel.
206-‐723-‐0656
October
14,
2015
Kent
Khnor
26721
106th
Ave
SW
Kent
WA
98030
RE:
Arborist
Report,
Boun
Short
Plat,
Parcel
No.
1023059139
You
contracted
my
services
as
a
consulting
arborist.
My
assignment
is
to:
1. Inspect
and
inventory
5
significant
trees
as
shown
on
preliminary
tree
retention
plan.
2. Confirm
significant
tree
quantity
on
site.
3. Record
tree
species,
diameter,
dripline
and
visible
defects.
4. Assess
tree
health
and
structure.
5. Prepare
a
written
report
of
findings.
I
received
a
preliminary
tree
retention
plan
from
Ivana
Halvorsen,
of
Barghausen
Consulting
Engineers,
Inc.,
locating
5
significant
trees.
I
visited
the
site
10/6/15
and
performed
a
field
inspection.
The
site
is
flat
and
covered
mostly
in
unmanaged
brambles.
I
inspected
the
5
surveyed
trees
plus
an
additional
2
trees
of
significant
size,
which
are
the
subject
of
this
report.
Six
of
the
7
trees
are
Douglas-‐fir,
and
range
in
size
from
6
to
30
inches
DBH.
The
seventh
tree
is
a
red
alder.
TREE
INSPECTION
–
Tree
Health,
Condition
and
Viability
I
marked
each
tree
with
1”
x
3.5”
aluminum
tag
indicating
tree
number.
I
visually
inspected
each
tree
from
the
ground
and
rated
both
tree
health
and
structure.
A
tree’s
structure
is
distinct
from
its
health.
This
inspection
identifies
what
is
visible
with
both.
Structure
is
the
way
the
tree
is
put
together
or
constructed,
and
identifying
obvious
defects
can
be
helpful
in
determining
if
a
tree
is
predisposed
to
failure.
Tree
health
assesses
disease,
insect
infestation
and
old
age.
No
invasive
procedures
were
performed
on
any
trees.
The
results
of
this
inspection
are
based
on
what
was
visible
at
the
time
of
the
inspection.
Kent
Khnor
RE:
Arborist
Report,
Boun
Short
Plat,
Parcel
No.
1023059139
October
14,
2015
Page
2
of
7
Greenforest
Registered
Consulting
Arborist
The
table
below
summarizes
my
inspection
results
and
provides
the
following
information
for
each
tree:
Tree
number
as
shown
on
tag
in
the
field.
Tree
Species
Common
name.
DBH
Stem
diameter
in
inches
measured
4.5
feet
from
the
ground.
Dripline
Average
branch
extension
from
the
trunk
as
radius
in
feet.
Tree
Class
Tree,
Significant:
A
tree
with
a
caliper
of
at
least
six
inches
(6"),
or
an
alder
or
cottonwood
tree
with
a
caliper
of
at
least
eight
inches
(8").
Tree,
Landmark:
A
tree
with
a
caliper
of
thirty
inches
(30")
or
greater.
Tree
Status
Indicates
if
tree
will
be
saved
or
removed.
Dangerous,
Dead
Or
Viable?
Tree,
Dangerous:
Any
tree
that
has
been
certified
as
dead,
terminally
diseased,
damaged,
or
otherwise
dangerous
to
persons
or
property
by
a
licensed
landscape
architect,
or
certified
arborist,
and
for
healthy
trees,
a
determination
by
the
arborist
whether
the
tree
is
viable
for
retention.
Visible
defects
Obvious
structural
defects
or
diseases
visible
at
time
of
inspection.
One
tree
has
been
injured
repeatedly
with
a
hatchet.
Its
trunk
is
wounded
and
it
is
the
only
tree
not
viable
for
retention.
A
couple
dozen
red
alders
are
growing
along
the
east
side
of
the
site,
though
only
1
is
of
significant
size.
Tree
No.
Species
DBH
Dripline
Tree
Class
Status:
Save
Or
Remove
Dangerous,
Dead
Or
Viable?
Visible
Defects
1
Douglas-‐fir
20”
14'
Significant
Remove
Dangerous
Hatchet
injury
on
trunk;
sequoia
pitch
moth
infestation.
2
Douglas-‐fir
16”
12’
Significant
Remove
Viable
3
Douglas-‐fir
12”
16’
Significant
Remove
Viable
4
Douglas-‐fir
30”
18’
Landmark
Remove
Viable
5
Douglas-‐fir
28”
16’
Significant
Remove
Viable
6
Douglas-‐fir
6”
6’
Significant
Remove
Viable
7
Red
alder
9”
12’
Significant
Remove
Viable
Kent
Khnor
RE:
Arborist
Report,
Boun
Short
Plat,
Parcel
No.
1023059139
October
14,
2015
Page
3
of
7
Greenforest
Registered
Consulting
Arborist
Minimum
Tree
Density
For
detached
single-‐family
development,
two
(2)
significant
trees
are
required
for
every
five
thousand
(5,000)
sq.
ft.
of
lot
area,
or
the
gross
equivalent
of
caliper
inches
provided
by
one
(1)
or
more
retained
tree.
Since
no
trees
are
retained,
supplemental
trees
are
necessary
to
meet
the
minimum
tree
density
requirement.
The
following
table
lists
the
proposed
7
lots
by
number,
size
(SF),
minimum
significant
tree
requirement,
new
trees
proposed
for
each
Lot,
retained
trees
on
each
Lot,
and
compliance
with
the
minimum
tree
density
requirement.
Fifteen
supplemental
trees
are
required
for
compliance.
Lot
Size
(SF)
Min.
Significant
Trees
Required
New
Trees1
Retained
Trees
Compliant
1
5002
2
2
0
Yes
2
5741
2
2
0
Yes
3
5890
2
2
0
Yes
4
6075
2
2
0
Yes
5
5658
2
2
0
Yes
6
5657
2
2
0
Yes
7
6453
3
3
0
Yes
The
project
landscape
architect
shall
address
location,
species,
planting
and
maintenance
specifications
for
supplemental
trees
under
separate
cover.
The
smaller
Doug-‐firs
and
alder
trees
proposed
for
removal
stand
alone
on
this
parcel
(1,
2,
3,
6,
7,).
Only
smaller
trees
and
brambles
surround
them.
There
are
no
nearby
trees
that
will
remain,
either
on
this
site
or
on
adjoining
parcels
that
could
be
impacted
by
their
removal.
The
two
trees
within
the
right-‐of-‐way
are
edge
trees
(4,
5),
and
have
been
pruned
heavily
because
of
adjacent
overhead
power
lines.
East
of
these
two
trees
is
a
stand
of
other
mature
Douglas-‐fir
on
the
adjoining
parcels.
Although
all
these
trees
are
in
a
contiguous
canopy
group,
they
have
sufficient
spacing
to
allow
good
trunk
taper
and
moderate
live
crown
ratios.
Further,
mature
trees
across
the
street
to
the
west
will
continue
to
provide
wind
buffer.
The
impact
to
adjacent
trees
will
be
negligible
to
minor
from
the
removal
of
the
two
ROW
trees.
1
When
the
required
number
of
protected
trees
cannot
be
retained,
replacement
trees,
with
at
least
a
two-‐inch
(2")
caliper
or
an
evergreen
at
least
six
feet
(6')
tall,
shall
be
planted.
Kent
Khnor
RE:
Arborist
Report,
Boun
Short
Plat,
Parcel
No.
1023059139
October
14,
2015
Page
4
of
7
Greenforest
Registered
Consulting
Arborist
Thank
you
for
your
business.
Please
let
me
know
if
you
have
any
questions.
Sincerely,
GreenForest,
Inc.
By
Favero
Greenforest,
M.
S.
ISA
Certified
Arborist
#
PN
-‐0143A
ASCA
Registered
Consulting
Arborist®
#379
ISA
Tree
Risk
Assessment
Qualified
Attachments:
1. Assumptions
and
Limiting
Conditions
2. Color
Images
of
Site
3. Site
Plan
Kent
Khnor
RE:
Arborist
Report,
Boun
Short
Plat,
Parcel
No.
1023059139
October
14,
2015
Page
5
of
7
Greenforest
Registered
Consulting
Arborist
Attachment
No.
1
-‐
Assumptions
&
Limiting
Conditions
1) A
field
examination
of
the
site
was
made
10/6/15.
My
observations
and
conclusions
are
as
of
that
date.
2) Care
has
been
taken
to
obtain
all
information
from
reliable
sources.
All
data
has
been
verified
insofar
as
possible;
however,
the
consultant/arborist
can
neither
guarantee
nor
be
responsible
for
the
accuracy
of
information
provided
by
others.
3) The
consultant/appraiser
shall
not
be
required
to
give
testimony
or
to
attend
court
by
reason
of
this
report
unless
subsequent
contractual
arrangements
are
made.
4) Loss
or
alteration
of
any
part
of
this
report
invalidates
the
entire
report.
5) Unless
required
by
law
otherwise,
possession
of
this
report
or
a
copy
thereof
does
not
imply
right
of
publication
or
use
for
any
purpose
by
any
other
than
the
person
to
whom
it
is
addressed,
without
the
prior
expressed
written
or
verbal
consent
of
the
consultant/appraiser.
6) This
report
and
any
values/opinions
expressed
herein
represent
the
opinion
of
the
consultant/appraiser,
and
the
consultant’s/appraiser’s
fee
is
in
no
way
contingent
upon
the
reporting
of
a
specified
value,
a
stipulated
result,
the
occurrence
of
a
subsequent
event,
nor
upon
any
finding
to
be
reported.
7) Construction
activities
can
impact
trees
in
unpredictable
ways.
All
retained
trees
should
be
inspected
at
the
competition
of
construction,
and
regularly
thereafter
as
part
of
ongoing
maintenance.
Kent
Khnor
RE:
Arborist
Report,
Boun
Short
Plat,
Parcel
No.
1023059139
October
14,
2015
Page
6
of
7
Greenforest
Registered
Consulting
Arborist
Attachment
No.
2
–
Color
Images
of
Site
BOUN SHORT PLAT BOUN SHORT PLATKent KhnorRE: Arborist Report, Boun Short Plat, Parcel No. 1023059139 October 14, 2015Page 7 of 7Attachment No. 3 – Site Plan
Tab 7.0
17625.002.doc
7.0 OTHER PERMITS
Postmaster / Mailbox Locations Approval
Fire Marshal / Fire Hydrant Locations Approval
Street Name Approval
King County Metro Transit Approval
Construction Stormwater General Permit (Department of Ecology)
Hydraulic Project Approval (Department of Fish and Wildlife)
Forest Practices Permit (Department of Natural Resources)
Tab 8.0
17625.002.doc
8.0 CONSTRUCTION STORMWATER POLLUTION PREVENTION PLAN ANALYSIS AND
DESIGN
A. Erosion and Sediment Control (ESC) Plan Analysis and Design
An ESC plan will be provided during final engineering.
B. Stormwater Pollution Prevention and Spill (SWPPS) Plan Design
A SWPPS plan will be provided during final engineering.
Tab 9.0
17625.002.doc
9.0 BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT
This section will be provided during final engineering.
Tab 10.0
17625.002.doc
10.0 OPERATIONS AND MAINTENANCE MANUAL
This section will be provided during final engineering.