HomeMy WebLinkAbout03125 - Technical Information Report - Drainage ��ai��e�-T�To�tl�yv�s� I�.c. - � .
'�i�rv�}%ors�.�I�rir}et`s •�n�i1Y���s� .� � - ���� ���1 Z�
� � . , . . ` - : � ' `:���:� :�� :� .. ' . . �. �
� . � . . . . .. - , . .
S7'Q�M'DK�AI�AiCE REPO�ZT :�� � �
� . . . , ' : _�: - � � �
m _ . . ,. . : . .
� . : � � � � . . ; . . : : � :.� � ����� ���
. � � . . . ._ - ,.: .. hSA� p � [GQ7 � . �_
� a�= : �: . .. � :� : _ . . .
. � �. : . �a��._, . . .� . _ . .
NtC1�1lLSON�SHk3.R`f.RL�9,�':: , `;. . � . . ��.
, . �.. 2300 N����8�K.:S�' _. - ,. . . ' . . . ., � . � �
� . �RENT�N; ilVa 980�6� �_� �. . � � � : , .. _ . � .
. �OEt . � � � . . � � � .
�. � � . � . �,5,rc�:�E� : �.
; . . _ � . , . ., . � . _ � :�.��f w�s��'�'��
�� Q' '� ��
c�:-
. � �.� •;, �'' '. � . -
. . � - _ -
. : B�a��ii�r�oL���r� � ' i ' �� � . � :
� . 23�Q N�:�sT'��:ST �st�s . .
RE�tTQ��I, WA 98b�6 " �� ; � '�Fctsr�c� � � -
��, t
- _ � � 3
.. ��bNAL ��,��' �.(�O
,_ . �
.. . . � l.:.r,'_"���
. � . . � . . � : . � . � � �
. " ; . - . . . . I
o: �`, ' .
� il�ctga�t T, ,2�O.Q3 ���ii�� �: ^ � � . . . . .
_ _ � . . .
. . �� 1�.�� ;'�:_ _ . :
- . c.� �.:�oB n�o: �oo��-��o . . . . . � � .
_ . , . �r-e�a��.e.ct by-Ldrry S �rueger;� E. .: - , . : .
� ' . . _._..._s�_"_ . � . . . � . . _ . .. . -�.L .."L. . __ . . .. ..._"_'._""____.'__ _ __._-'
. PlioriE �S3:s52.43�0 T. . - 3'ola FT,�e� 3Q�.2S�:41$9 � : Fa�: �5�.35'?:�955
. � �4�'� _Centra�Ave Sxiite 10� �-Ifent;��i�`1� 9�03�. :
- Visit Cr.a���x�I��rthwest oii tlie,web�ai. ��t� f�v�v�:GI'c'�111�I'11�V.CQII� ' .
. . _ . . . . . . . .. . � . t� � .. . � . � .. �.. . . . - r..• : . .� � ' � �. � ' .. � • . .
,.:. : .. � . . , . . .. ':. .. . .. . ... . . . . .
. : .:. f� �•'
� . _ . . " -. : .. �3/,2.5" �
TABLE OF CONTENTS
i. PROJECT OVERVIEW
II. CONDITIONS AND REQUIREMENTS SUMMARY
!!I. OFFSITE ANALYSIS
IV. FLOW CONTROLNVATER QUALITY FACILITY ANALYSIS AND
DESIGN
V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN
VI. SPECIAL REPORTS AND STUDIES
VII. OTHER PERMITS
Vill. EROSIONISEDIMENTATION �ONTROL DESIGN
IX. BOND QUANTITIES, FACILITY SUMMARIES AND DECIARATION OF
COVENANT
X. OPERATIONS AND MAINTENANCE MANUAL �
APPENDlX A: RETENTION CALCULATIONS
APPENDIX B: CONVEYANCE CALCULATIONS
I. PROJECT OVERVIEW
Existing Conditions:
This project is located at 2300 NE 28"' Street. It lies along the north side of NE
28`�' Street. The site is approximately 0.82 acres. The site consists of mostly
grass with some trees. There is an existing home, asphalt driveway, and two
sheds on the property. The existing topography slopes from the southeast
toward the northwest. However due to the great permeability of the soils, the
runoff tends to merely infiltrate into the surrounding soils. Soil tests show that
the soil has about 8°-12° of tight loam sitting above at least 6' of clean medium
sand.
Proposed Condi#ions:
The project proposes to subdivide the site into four residential lots. Access to
the Iots will be provided via a combination of a private street off of NE 28�' Street
and a shared driveway located along the east property line. New roof runoff for
Lot 1 will be conveyed to a downspout infiltration trench. New roof runoff for
Lots 3 and 4, the private street and shared driveway will be conveyed to
infiltration trenches. Frontage improvements will also be routed to an infiltration �
trench located on Lot 1. �
II. CONDITIONS AND REQUIREMENTS SUMMARY �
The core requirements of the King County Surface Water Design Manual
(KCSWDM) will be provided as follows: '
Core Requirement#1, Discharge at #he Natural Location: �I
The natura! discharge location for this site is into the surrounding soils. I
Roof runoff will be conveyed to infiltration trenches. The private street I
and shared driveway will be conveyed to infiltration trenches. Frontage i
improvements will also be routed to an infiltration trench located on Lot 1. �I
Core Requirement#2, Offsite Analysis: I
An offsite analysis was not required by the City of Renton because this �
project proposes to infiltrate all new impervious surfaces on site. i
Therefore, the downstream limits of this project will not be affected.
Core Requirement#3, Flow Control:
Flow control will be provided via infiltration.
Core Requirement#4, Conveyance System:
The conveyance system wiil consist of two catch basins, storm pipes and
a thickened edge. Conveyance calculations of the pipe are provided in
Appendix B.
Core Requirement #5, ErosioNSedimentation Control:
An erosion and sedimentation control plan has been designed. Some of
the tesc measures to be implemented are a construction entrance, silt
fence, and seeding.
Core Requirement #6, Maintenance and Operations:
A maintenance and operations manual will be provided prior to permit
issuance.
Core Requirement#7, Financial Guarantees and Liability:
The owner will provide this information prior to permit issuance.
Core Requirement#8, Water Quality:
This project is exempt from water quality per Exemption #1.
III. OFFSITE ANALYSIS
An offsite analysis has not been provided because this project proposes to
infiltrate all new impervious surfaces on site. Therefore, the downstream !�m���
of this project will not be affected. See attached soil infiltration test:
IV. FLOW CONTROlJWATER QUALlN FACILITY ANALYSIS 8� DESIGN
All new on-site impervious surfaces will be routed to ir�filtration trenches.
Frontage improvements will be routed to an infiltration trench located on Lot 1.
Retention calculations are provided in Appendix A.
Water quality facilities are not required per Exemption 1, since less than 5000 sf
of new pgis will be added.
Proposed pgis— Existing pgis to be removed = New pgis added
[8324 sf (new road &frontage improvements)j— [3720 (existing asphalt
driveway}) = 4604 sf< 5000 sf
V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN
The conveya�ce system will consist of two catch basins, storm pipes and a
thickened edge. Conveyance calculations of the pipe are provided in Appendix
B.
VI. SPECIAL REPORTS AND STUDIES
No special reports or studies are known to exist for this project.
Vtl. OTHER PERMITS
Na other permits are known to be required at this time.
VIII. EROStONISEDIMENTATION CONTROL DESIGN
An erosion and sedimentation control plan has been designed. Some of the tesc
measures to be implemented are a construction entrance, silt fence, and
seeding.
Per Appendix D.4.3 of the KCSWDM, silt fence can be used as the sole form of
treatment when the flowpath is 200 feet with a slope of 16.7% or less. This site
has a slope of about 4% with a flow path of about 120' within the areas to be
disturbed, thus satisfying the criteria
IX. BOND QUANTITIES, FACILITY SUMMARIES AND DECLARATION OF
COVENANT
This information will be provided prior to permit issuance if requested.
X. MAINTENANCE AND OPERATtONS MANUAL
A maintenance and operations will be provided prior to permit issuance.
APPENDIX A
RETENTION CALCULATIONS
RETENTION CALCULATIONS:
Two infiltration trenches are proposed for this project to control runoff from the�posed road.
The two trenches receive runoff froi�o basins as follows: �b� ���
Trench 1: Frontage improvem�t�and road s 0 �1.1�(Basin 1)
...—�..Trench 2: Road north of 0+81:14 and 2 lots qf impervious (Basm 2) �,iZ t /t�� %�, 1 g /��
Since the proposed trenches don't have an ove w path, they must infiltrate the 100 year flow
and an additionaV 0.5 factor of safety must be applied 10 the infiltralion rate. 100 year flow rates
are provided in the following pages.
�aes�9n= �measu�ed X F���a X Fa�y X Fq�� F�y=4D/W+0.05
_ (4)(3.3)/4+ 0.05= 3.35 (use 1)
�r��rea= 1 i�/min, Ftestin9= 0.3, Fgeometry= �.O, F�„�;�= U.8
1�;��=1 X .3X1.OX0.8= 0.24in/minX0.5 = 0.12iNmin
Absorption rate = 0.12 in/min = .01 ft/min = .000167 ft/s
�--
Required Trench Area =l a�yF I�/absorption ra
Trench 1: 0.027�0�00�16�7 ��161.6 sf (provide 41' x 4'wide trench = 165 sfl �
Trench 2: 0.118 cfs/.000 61 7 ft/s=706.6 provide 118' x 6'wide trench =708 s
Presettling Basin Calcs:
Trench 1: Treatment volume = 0.75 X Vr
Vr=(0.9)(2590) X 0.47/12 = 91.3
.75XVr = 68.5cf
� �, 7
� Use Type 2-54° with 4.31' below invert:
3.1415927 X (4.52/4) X 4.31' = 68.5 ef �,
Trench 2: Treatment volume = 0.75 X Vr ► � � �
Vr=(0.9)(10884) X 0.47112 = 383.7
.75XVr = 287.7cf
Use Type 2-72" with 10.2' below invert:
3.1415927X (6214) X10.2' = 288.3cf