The URL can be used to link to this page

Home My WebLink About03143 - Technical Information Report - Drainage ' �� Core Design,Inc. CORE 14711 N.E 29fh Place Suite #101 8ellevue,Washington 98007 �DESIGN 425.885.7877 Fax 425.885.7963 � �3��3 . m � FINAL STORM DRAINAGE REPORT FOR BR.ANDAL VILLAGE SHORT PLAT RENTON, W�SHINGTON p'S�a �i Q�' � � � Q � h � ,c�'�F��g��'� SSI��G Prepared by: Scott R. Borgeson, P.E. Revie��ed by: Edgar T. Jones, P.E. Date: �lovember, 2003 IXPIRES 4/20/aS c �. ;;r - � .-_ . i� ��03 RECEIVED Core No.: Q3067 NOV 1 ; 200? �� nLDWG D�v;�, E�ti��;!NEER!,NG P�ANNINv � SL�'RVEYING �3/4�� BRANDAL VILLAGE SHORT PLAT TABLE OF CONTENTS � I. Pro�ect Overview II. Existing Conditions Summary III. Off-Site Analysis A. Upstream Tributary Area B. Downstream Analysis IV. Developed Conditions Summary A. Hydrologic Analysis B. Detention Routing Calculations C. Water Quality Volume Calculation D. Emergency Overflow Riser E. Conveyance Calculations V. Temporary Sediment Trap VI. Special Reports and Studies (Not included in this report, but listed for informational purposes only.) A. Geotechnical Engineering Study— Proposed Brandal Village — 628 Union Avenue Northeast — Renton, Washington By: Earth Consultants, Inc. Dated: July 25, 2003 B. Wetland Investigation Report By: Alder Northwest CORE DESIG\, INC BR�NDAL VILLaGE SHORT PL:�T PaQe ? I. PROJECT OVERVIE�'�' The Brandal Village Short Plat is a proposed seven lot single-family residential development located in the City of Renton at 628 Union Avenue N.E. It lies within Section 10, Township 23N, Range SE in King County. See the Vicinity Map below. The project site measures approximately 2.68 acres. The natural site �adient slopes down to the east towards a wetland area that is both on-site and on adjacent properties. The site is currently undeveloped and is covered with pasture grass and sparse �oupings of trees. The proposed development activity is located on the upper, westem portion of the site «-ith the lower, eastern site area to remain largely in its natural condition. Stormwater runoff from the project site will be managed in accordance with the requirements of the 1998 King County Surface Water Design Manual (KCSWDM). A detention vault is proposed in arder to satisfy the Level II Flow Control and Basic Water Qualiry standards. i I j � �� I 4 3 I 5 � S a��0• L NE`�N� pH R�. l��Nj��SSa� 00 I i �9C0 Z �' w �, h 2W Z _� > � _� Q Z i �m z � � g 9 � �ITE ? 10 Q ,� �� R E N I C �� i al i,.i I � - � �IN D ' �E 4TH STREE- n i �. BM °T. 3M PT. ��5 � �BSL 2�a3 � NE� ', GREfNW00D I i ' CEMElERY i , i ' » ,6s ,s ,s N '4 I I � MqpC � i I E � Yq�� i , 'CEDAR � RD � I� ✓l� MAPLEWOOD : �� GOLf CCURSE I � V"ICINITY MAP \ot to Scale CORE DESIGN. I'_�C BR.�NDAL VILL.�GE SHOR'1' PL.aT Paee 3 II. EXISTING CONDITIONS SUNIIVIARY The existing site covers approximately 2.68 acres, however the proposed development activity is concentrated in the upper, western portion of the site, where approximately 0.87 acres will be disturbed. The remainder of the site will remain as wetland and buffer, with the disturbed buffer areas being restored to their existing condition. Since the stormwater runoff characteristics of the restored buffer areas will be equivalent to their existmg conditions and since these areas are not tnbutary to the proposed stormwater detention facilities, they will not be included in the stormwater modeling. The existing ground cover of the portion of the site that is to be developed is a combination of till- pasture and till-forest. 'The drainage analysis for the Brandal Village Short Plat was modeled using the King County Runoff Time Series software. The soils are KCRTS group Till. The site is located in the Sea-Tac rainfall region with a location scale factor of 1.0. The following information was used for generating time series and flow frequencies. T'he KCRTS Flow Frequency Analysis program output for the exisring conditions is included below. EXISTING CONDITIONS Total Area= 0.87 acres (03467ex) GROUND COVER :�REA (acre) Till-Forest 0.40 Till-Pasture 0.47 I KCRTS Output for Existing Conditions r^�ow Frequency Analysis � Time Series File:03067ex.tsf � Project Location:Sea-Tac ---Annual Peak Flow Rates-- -----�low Frequency Analysis- --- -- Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prcp (CFS) (C�S) Period 0 . 058 2 2/09/O1 18:00 0. 085 1 100.00 0 .99G 0 . 019 7 1/05/02 16:00 0 . 058 2 25.00 0 . 960 0.049 3 2/28/03 3 :00 0.049 3 10.00 0 .900 0.004 8 3/24/04 19:00 0 .047 4 5 .00 0 .800 0 .028 6 1/OS/05 8 :00 0 . 044 5 3 .00 0 . 66? 0 . 047 4 1/18/06 20:00 0 .028 6 2 .00 0 .500 0.044 5 11/24/06 4 :00 0 .019 7 1.30 0 .231 0 . 085 1 1/09%08 6: 00 0 . 004 8 1.10 0 . 091 Computed Peaxs 0 . 0''6 50 . 00 0 . 980 CORE DESIGI�. I\C. BI2�\D.aL �'ILL�GE SHOR'I' PL.aT Pa,e-� III. OFF-SITE aN�LYSIS A. UPSTRE��I TRIBLTT:�RY ARE� Stormwater from Union Ave Iv'.E., along the project's western boundary, is collected in the roadway tight line conveyance system and is therefore not tributary to the project site. The project site receives stormwater runoff from the developed areas to the north and to the west of the site. The area to the north consists of moderately dense, primarily single- family development, the majority of which is part of The Orchards neighborhood. A detention pond that was constructed for The Orchards is located approximately 350 feet upstream of the project site. Stormwater from all of the parcels lying north of the pond and south of N.E. 8`h Street appears to be routed through the detention facility. The pond discharDes in a southwesterly direction to the adjacent wetland area. The wetland flows in a southwesterly direction and crosses onto the project site through an 18"-diameter culvert, after receiving additional stormwater runoff from the condominium and single- family developments along it's eastern and western borders. The plat of The Vineyards is tributary to this wetland both upstream of the project site and along the site's eastern boundary. B. DO��TSTREA�I ��1ALYSIS The wetland flows across the project site and exits through another 18"-diameter culvert under a �avel driveway at the site's southern boundary. From here, the wetland flows across another portion of The Vineyards project before entering a tight line conveyance system in Union Avenue N.E., as described in more detailed in the excerpt from the Technical Information Report for The Vineyards, which was prepared by American Engineering Corporation, included at the end of this section. Please also refer to the Kroll Map at the end of this section for a visual depiction of the upstream and downstream tributary areas. CORE DE�IGN. 1NC BR�'D�L VILL�GE SHORT PL.�'T PaQe � . � . , l� , ;�Q. ,�� , c� '\� ' �� / �� G�J N. DEV"ELOPED CONDITIONS SU11�IM�RY �-�'��'��`� � �' ;�� :�. HYDROLOGIC ANALYSIS The developed site will include seven single-family lots with a u-shaped private access - drive. The detention and water quality vault will be located in an easement at the south �� end of the project site. The impervious area per lot was calculated based on the `�J� maximum allowable footprint with the setback restrictions of this zone. For each lot, 1,955 s.f. of building coverage, 400 s.f. of driveway area and 150 s.f. of concrete patio area was assumed to comprise the impervious area. The roof areas of four of the lots will be dispersed to the existing wetland through the use of downspout dispersion trenches designed in accordance with the specifications shown in the KCSWDM, including Figure C.2.F. This will help to maintain the health of the wetland system by more closely matching the natural conditions. On page 1-27 of the KCSWDM, exemptions from Core Requirement #3 — Flow Control are identified. Specifically, item 2-B specifies that, "If the project is a single family residential project, flow control BMPs must be applied within the threshold discharge area as specified in Small Site Drainage Requirernents (detached Appendix C)." Chapter C.2 - Flow Control B�1Ps includes the following language that dictates that dispersion be utilized: "Dispersion or infiltration BMPs are required for small site proposals applyina for single family residential building permits or short plats, except in the following case: If the existing lot is smaller than 22,000 square feet, or if the short plat creates lots less than 22,000 square feet, then infiltration is required if suitable soils are present. If soils will not support infiltration, then other flow control BMPs must be considered. If site constraints make dispersion and infiltration unfeasible, then the site may be connected to the storm drainage system with p�rforated tightline connection (see Section C.2.5, p.C-23)." Uue to the till soils present on this site, which are inherently poor draining, infiltration would not be feasible. Dispersion is an available alternative, however, since adequate space exists to allow dispersion without adverse downstream impacts, since approximately 1.8 acres of the site will remain in it's natural condition or be restored to the same. The proj ect owner has chosen to preserve the on-site wetland and buffers in a separate tract. However, if this area was protected in an easement across the back of the lots, the average lot size of the four lots for which dispersion is proposed would be approximately 25,000 square feet. Section �.2.2 — BMPs for Reducing Facility Size states, "The flow control BMPs presented in this section may be used tc reduce the size of required flow control facilities implemented as described below." This refers the reader to the follo�ving criteria #2, "If roof runoff is dispersed according to the requirements of Section �.12 (p. 5-9) on single family lots ;reater than �r equal to 22,000 square feet, and the vegetated flowpath of the roof runoff is �0 feet or longer, the roof area may be modeled as grassed surface rather than impervious surface when sizing the required flow control facility." (:ORE DESIG�i, I�iC BR:1rD:�L VILL:�GE SHORT YL:�T Page 5 :�s discussed above, this project effectively provides approximately 25,OOU square feet of lot area for the four lots that will utilize roof downspout dispersion in the preserved native �owth protection area. Also, a minimum 50 foot vegetated flow path between the dispersion trenches and the delineated wetland edge has been provided. Therefore, the criteria under Section �.2.2 have been satisfied and for this reason, the roof area of four of the lots (0.18 acres) were modeled as Till Grass in sizing the proposed detention vault. The driveways and patios for these four lots will still be tributary to the detention vault and were still included in impervious area quantity listed in the table below. Please refer to the Developed Conditions exhibit at the end of this section for a visual representation of the proposed improvements and the detained and dispersed catchment areas. The drainage analysis for the developed conditions were modeled using the King County Runoff Time Series software. The soils are KCRTS �oup Till and the site is located in the Sea-Tac rainfall region with a location scale factor of 1.0. The following information was used for jenerating time series and flow frequencies. The KCRTS Flow Frequency Analysis program output for the developed conditions is included below. DEVELOPED CONDITIONS Total Area= 0.87 acres (03067dv) GROUND COVER ARE�(acre) Till-Grass (Landsca ina) 0.43 (includes 0.18 acres of dispersed roof area) Impervious (Buildings & aving) 0.44 KCRTS Output for Developed Conditions F�ow Frequency Analysis Time Series File:03067dv.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flcw Frequency Anaiysis------- Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS} Period 0. 145 5 2/09/O1 2:00 0.299 1 100 .00 0. 990 0.114 8 1/05/02 16:00 0. 175 2 25 .00 0 .960 0. 175 2 2/27/03 7:00 0 .171 3 10.00 0.900 0. 117 7 8/26/04 2:�0 0. 153 4 5 .00 0.800 0. 143 6 10/28/04 16:00 0. 145 5 3 . 00 0 .60'? 0. 153 4 1/18/06 16:00 0 .1�3 6 2 . 00 0.500 0. 171 3 10/26/06 0:00 0. 117 7 1.30 0 .2�1 0 .299 1 1/09/08 6:00 0 . 114 8 _. �0 0 .091 Com.tiuted Peaks 0 . 25"' �C . 00 0 . 98C CORE DESIGN, I�lC BRaYDAL V�ILL�aGE SHORT PL�"I' Pa�e � B. DETENTI0I�T ROUTING CAI.CtiLATIONS � The City of Renton has specified that the detention facility shall have Level 2 Flow Control. The detention/water quality facility will be a combination water quality and detention vault. The vault has been designed according to the 1998 KCSWDM. The , �Y,,� Retention/Detention Facility printout from KCRTS is included below. Per the_Duration�'�' Comparison Analysis, the first cutoff has a % change less than zero, the maximum positive excursion is less than 10%, and more than one-half of the % change's are less than zero, therefore, Level 2 requirements are fulfilled. The required internal plan view dimensions of the vault are 20' by �0' and the required live storage volume is 8,062 c.f. The vault has been designed to have internal plan view dimensions of 20' by �2'and will provide 8,320 c.f. of detention from the live/dead starage interface elevation of 394.80 to the maximum �vater surface elevation of 402.80. KCRTS Output for Detention Facilitv Sizing RetentionjDetention Facilit;✓ Type of Facility: Detention Vault Facility Length: 50. 00 f� Facility Width: 20. 00 f� Facility ?�rea: 1000. sq. �t Effective Storage Depth: 8. 00 ft Stage 0 Elevation: 394 . 80 ft Storage Volume: 8000. cu. f� Riser Head: 7. 90 ft Riser Diameter: 12 . 00 inches Number of oriiices: 2 Full Head Pipe Orifice # Height Diameter Discharge Diamet�.r (ft) (in) (CFS) (in} 1 0 .00 0.50 0. 019 2 5.20 0 .88 0. 034 4 . 0 Top Notch Weir: None Outflow Rating Cunre: None Stage Elevation Storage Discharge Percolation (ft) (ft) (cu. ft) (ac-ft) (cfs) (cfs} 0.00 394. 80 100. 0.002 0.000 0.00 0.01 394 .81 110 . 0 .003 0.001 0 .00 0.02 394 . 82 120 . 0. 003 0.001 0 . 00 0 . 03 394 . 83 130 . 0 . 003 0 .001 0 . 00 0. 04 394.84 140. 0 .003 0 .001 0 . 00 0. 05 394.85 150 . 0.003 0. 001 0 . 00 0.18 394 .98 280 . 0.006 0 .003 0 . 00 0.31 395 .11 410 . 0 .009 0 . 004 0 .00 0.45 395.25 550 . 0 .013 0 . 005 0 . 00 0.58 395 .38 680 . 0 .016 0 .005 0 . 00 0.72 395 .52 820 . 0 .019 0 . 006 0 . 00 0 . 85 395 .65 950 . 0.022 0 . 006 0 . 00 0. 98 395 .78 '_080. 0.025 0 . 007 0 . 00 1. 12 395. 92 1220 . 0.028 0.007 0 . �0 1.25 396. 05 1350. 0 . 031 0 .008 0 . 00 1.39 396 . i9 1490 . 0 .034 0 .008 0 . 00 CORE DESIGI�. II�C. BRA�TDAL VILLAGE SHORT PLaT Page S 1.52 396.32 1620. 0. 037 0. 008 0.00 1.65 396.45 1750. 0. 040 0 . 009 0.00 1.79 396 .59 1890. 0 .043 0.009 0.00 1.92 396 .72 2020. 0 .046 0.009 0.00 2 .06 396. 86 2160. 0 .050 0.010 0.00 2 . 19 396.99 2290 . 0.053 0.010 0 .00 2 .32 397. 12 2420 . 0.056 0. 010 0 .00 2 .46 397.26 2560 . 0.059 0. 011 0.00 2 .59 397.39 2690. 0.062 0 . 011 0 .00 2 .72 397.52 2820. 0.065 0 . 011 0. 00 2 . 86 397.66 2960. 0.068 0 .011 0.00 2 .99 397.79 3090 . 0.071 0 .012 0.00 3 .13 397.93 3230 . 0. 074 0 .012 O.OQ 3 .26 398.06 3360 . 0 .077 0.012 0.00 3 .39 398 .19 3490 . 0 .080 0.012 0.00 3 .53 398.33 3630 . 0.083 0.013 0 .00 3 .66 398.46 3760 . 0.086 0.013 0 .00 3 .80 398.60 3900 . 0. 090 0. 013 0 .00 3 . 93 398 .73 4030 . 0.093 0. 013 0 . 00 � .06 398. 86 4160 . 0.096 0.014 0.00 � .20 399.00 4300. 0.099 0.014 0.00 = .33 399.13 4430 . 0. 102 0 .014 0.00 � .47 399.27 4570 . 0. 105 0.014 0.00 � . 60 399.40 4700. 0. 108 0.015 0.00 � . 73 399.53 4830. 0.111 0. 015 0 .00 4 . 87 399.67 4970. 0.114 0. 015 0 .00 5 .00 399. 80 5100 . 0.117 0. 015 0 .0� � .14 399. 94 5240 . 0.120 0.015 0 .00 � .20 400.40 5300 . 0. 122 0.015 0. 00 � .21 400.01 5310 . 0. 122 0.016 0. 00 5 .22 400.02 5320. 0. 122 0.016 0.00 5 .23 400.03 5330. 0. 122 0 .017 0.00 5 .24 400 .04 5340 . 0. 123 0 .018 0.00 5 .25 400 . 05 5350 . 0 . 123 0.020 0.00 5 .26 400. 06 5360. 0. 123 0. 021 0.00 5 .27 400. 07 5370. 0.123 0. 021 0 .00 � .41 �00.21 5510 . 0. 126 0.025 0 .00 � .54 400.34 5640 . 0. 129 0. 028 0 .00 � .57 400.47 5770 . 0. 132 0. 030 0.00 5 . 81 400.61 5910 . 0. 136 0.033 0.00 5 .94 400.74 6040 . 0. 139 0 .034 0.00 6. 08 400.88 6180 . 0. 142 0 .036 0. 00 6 .21 401. 01 6310. 0. 145 0 .038 0. 00 5 . 34 401. 14 6440. 0. 148 0.039 0 .00 6 .48 401.28 6580. 0.151 0.041 0 .00 6 . 61 401.41 6710 . 0. 154 0.042 0.00 6 .75 40i.55 6850 . 0.157 0. 043 0.00 0 . 88 401. 68 6980 . 0. 160 0. 045 0 .00 ? .O1 401.81 7110 . 0. 163 0. 046 0 .00 ?.15 401.95 725a . 0.166 0.047 0.00 �.28 402 .08 7380 . 0. 169 0.048 0.00 ?.42 402 .22 7520 . 0. 173 0.049 0 .00 7.55 402.35 7650 . 0. 176 0. 050 0 .00 7.68 402 .48 7780 . 0. 179 0 .052 0 . 00 7 . 82 402 .62 7920 . 0. 182 0 .053 0 . 00 ? . 90 402 .70 8000 . 0.184 0.053 0.00 3 .00 402 .80 5100. 0. 186 0.362 0.00 � .10 402 . 90 8200. 0. 188 0 .926 0 .00 8 .20 403 . 00 8300 . 0. 191 1.660 0 .00 8 .30 403 . '0 �400 . 0 . 193 2 .450 0 . 00 8 .10 4�3 . 20 8500 . C . 195 2 . �3C � . CO CCJRE DESIGN. I�C. BR�\D,aL VILL,aGE SHORT PL�T Paee 9 3 .�0 403 . 30 36Q0 . U . _97 2 . 990 0 . 00 8 .60 403 .40 8700 . 0.200 3 .220 0 . 00 8.70 403 .50 8800 . 0.202 3 .440 0.00 8.80 403 . 60 8900 . 0.204 3 .650 0.00 8.90 403 . 70 9000. 0.207 3 .840 0.00 9.00 403 . 80 9100. 0.209 4 .030 0.00 9.10 403 . 90 9200. 0 .211 4 .200 0.00 9.20 404 .00 9300. 0.213 4 .370 0. 00 9.30 404 . 10 9400. 0.216 4 .540 0.00 9.40 404 .20 9500. 0.218 4 .700 0.00 9.50 404 . 30 9600 . 0.220 � .850 0.00 9.60 404 .40 9700. 0.223 5 .000 0 .00 9.70 404 .50 9800. 0.225 5 .140 0 . 00 Hyd Inflow Outflow Peak Storage Target �alc Stage Elev (Cu-Ft) iac-Fti 17��r 1 0.30 ******* ��0.25 7. 96 402 .76 8062 . 0. 185 25y✓ 2 0. 14 0.06 0.06 7. 90 402 .70 8003 . 0. 184 �,� �� 3 0. 17 ******* � 0.05` 6. 89 401.69 6992 . 0.161 S�r 4 0. 18 ******* i0.04 6.45 401.25 6550 . 0. 150 35 5 0.15 ******* 0.03 5 .98 400.78 6082. 0.1?0 Z.o 6 0. 14 ******* 0.01 � 4. 81 399.61 4912 . 0.113 ' �,3 7 0.11 ******* 0.011 3 . 98 398.78 4075. 0 .094 i.� 8 0. 12 ******* 0.01 ', 2 . 67 397 .4? 2?72 . 0 . 664 � Route Time Series through Facility Inflow Time Series File:03067dv. tsf Out�low Time Series rile:o�o6�or Inflow/Qutflow Analys��s Peak Inflow Discharge: 0 .299 CFS a� 5 : u0 vn �an 9 in `lear d Peak Outflow Discharge: 0.245 CFS a� 9:�0 on Jan 9 ir. Year � Peak Reservoir Stage: 7.96 Ft Peak Reservoir Elev: 402.76 Ft Peak Reservoir Storage: 8062 . Cu-Ft . 0.185 Ac-Ft Flow Frequency Ana-ysis Time Series File:03067ot.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates-- -----rlow Frequency Analysis------ Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) (ft) Period 0. 060 2 2/09/O1 20:00 0.245 7.96 1 100 .00 0.990 0.013 7 12/29/O1 10:00 0.060 7.90 2 25.00 0 . 960 0 .041 4 3/06/03 22 :00 0.045 6.89 3 10.00 0 . 900 0.011 8 8/26/04 7:00 0.041 6.45 4 5. 00 0 . 800 0 .015 6 1/06/OS 15:00 0.035 5.98 5 3 . 00 0 . 66? 0.035 5 1/18/06 23:00 0 .015 4 .81 6 2 .00 0 . 500 0.045 3 11/24/06 8:00 0. 013 3 . 98 7 1.30 0 .231 0.245 1 1/09/08 9:00 0. 011 2 .67 8 1 . 10 0 . 09'� ��mputed ?eaks O . i83 ? . 9a �0 . ��0 0 . ?80 CORE DE�IG\. II�C BRa,�1D�L. ��'1LL�GE SHORT PLaT Pa,e i�i F1ow ruraticn from Time Ser'_es �i�e: 0306?ot. ts� Cutoff Count Frequency CDF Exceedence_Probabili�y CFS � � % 0 . 001 35161 57 .340 57.340 42 . 660 0 .427E+00 0 . 003 7569 12 .343 69. 684 30. 316 0 .303E+00 Q . 004 4336 7.071 76.755 23 .245 0 .232E+00 Q . 006 4534 7.394 84 . 149 15. 851 0. 159E+00 � . 008 3643 5.941 90.090 9. 910 0. 991E-01 0 . ��09 2607 4.251 94 .341 5. 659 0.566E-01 0 . 011 1037 1.691 96.032 3 . 968 0.397E-01 0 . 013 1114 1.817 97.849 2. 151 0 .215E-01 C . 014 719 1.173 99. 022 0. 978 0 .978E-02 0 . 016 372 0 .607 99. 628 0 . 372 0.372E-02 J . 018 9 0.015 99.643 0.357 0.357E-02 0 . 019 4 0.007 99.649 0.351 0.351E-02 0 . �21 3 0 .005 99.654 0.346 0.346E-02 0 . 023 18 0 .029 99.684 0.316 0.316E-02 0 . 024 20 0 .033 99.716 0.284 0 .284E-02 0 . 026 10 0.016 99.733 0.267 0 .267E-02 G . 028 13 0.021 99.754 0.246 0.246E-02 0 . 029 13 0 .021 99.775 0 .225 0.225E-02 0 . 031 11 0.018 99.793 0 .207 0.207E-02 0 . 033 13 0.021 99. 814 0. 186 0.186E-02 0 . 034 28 0 .046 99. 860 0. 140 0.140E-02 0 . 036 15 0.024 99. 884 0. 116 0.116E-02 0 . 038 5 0.008 99.892 0. 108 0.108E-02 0. 039 12 0.020 99.912 0. 088 O.SS1E-03 I � .041 8 0 .013 99. 925 0 . 075 0.750E-03 0 . 043 13 0 .021 99. 946 0 . 054 0 .538E-03 0 . 044 10 0.016 99. 962 0 . 038 0.375r�-03 0 . 046 6 0.010 99. 972 0. 028 0.277E-03 0 . 048 3 0.005 99.977 0. 023 0.228E-03 G . 049 4 0.007 99.984 0. 016 0.163E-03 � . 051 3 0.005 99.989 0. 011 0.114E-03 0 . 053 3 0 .005 99. 993 0. 007 0.652E-04 0 . 054 3 0 .005 99. 998 0. 002 0. 163E-04 0 . 056 0 0.000 99.998 0. 002 0. 163E-04 0 . 058 0 0 .000 99. 998 0 . 002 O .lo'3E-04 0 . 059 0 O .00C 99. 998 � . 002 0 . 153E-04 Duration Compariscn �-�aylsis Base File: 03067ex.tsf New File: 03067ot.tsf Cutorf Units : Discharge in CFS r'Ih� �ti' � --- --rraction of Time----- --------Check of Tolerance------- 5�� Cutoff Base New %Change Probability Base New �sCh � �� 0 . 015 � 0 .79E-02 0.87E-02 9.3 0 .79E-02 Q.015 0. 015 AO<�. 0 . 018 ; 0.57E-02 0.35E-02 -37 .6 � 0 .57E-02 0. 018 0.015 -18. 1 � . 022 0 .44E-02 0.33E-02 -25 .9 � 0 .44E-02 0.022 0.015 -30.8 � . 025 �� 0 .34E-02 0.27E-02 -19. 8 � 0 .34E-02 0.025 0.021 -15.6 0 . 029 I 0 .26E-02 0 .23E-02 -11.1 � 0.26E-02 0 .029 0. 026 -8.4 0 . 032 � 0. 19E-02 0 .19E-02 1 .7 � 0 .19E-02 0 .032 0. 032 0.7 0 . 035 I 0. 13E-a2 0. 12E-02 -9. 8 � 0 .13E-02 0.035 0. 035 -2 .3 0 . 039 � 0. 96E-03 0.95E-03 -1.7 I 0 .96E-03 0.039 0. 038 -0. 8 � . 042 � 0 .60E-03 0.60E-03 0 . 0 j 0. 60E-03 0.042 0. 042 0.3 0 . 046 � 0 .34r�-03 0.31E-03 -9.5 j 0. 34E-03 0.0?6 0. 045 -1.2 :, . 049 ! 0. 18E-03 0.20E-03 9.1 � 0. 18E-03 0 .049 0.049 0.4 � . 052 ; 0 . 13E-03 0. 82E-04 -37 .5 I 0 . 13E-03 0 . 052 0. 051 -2 . 8 O . O�n' I 0 .�9E-04 0 . 16=-04 -50 . ? I 0 .49E-0� �� . 056 0 . 053 -5 . 1 CORE DESIGi�. INC. BR-�\D:�L�ZLLAGE SHORT PL�T Page I1 'v = Maximum positi e excursion 0.003 cfs ( 6. 0�) occuring at 0 .057 cfs on the Base Data:03067ex.tsf and at 0. 060 cfs on the New Data:03067ot.tsf Maximum negative excursion = 0 .009 cfs (-36 . O�a occuring at 0 .024 cfs on the Base Data:03067ex.tsf and at 0 . 015 cfs on the New Data: 03067ot.tsf KCRTS Output Duration Analvsis Plot � 8 x co 0 o _ �ic�_-_— ,_,. �-`;4 '.�::Ub1'T�7L'f ♦ R `'�`� u� } 0 0 �..� I ��. � _.,�� 0 o �,'� .-. � LL ` U '�� M � � O � o �`�R U .M1,� N � �: � N � O O /� �� UO - _ ._�z``` O O `--�,� � _ O � �...-.��. O ' :> �"�Q� � � , : i�T'T-i� 10 -' 10-0 10 -� �10 -z ,� �i ��o Probabiliry Exceedence --- ;�Sta't�'�;/l��.:Q�..:�.�"` �_:t�Irboz-MinomlEOut..r�-"KCRT5�Quta�t0301.��.:.��-aPaused-KCRTS ��.�..�PSiued��-Helplfies..��,Paused-Duratio..- �.� ?l7.VA-. CORE DE�IG�. INC BRa\D:�L V"II.LaGE SHORT PL�T Pave 12 SEC. 10 TWP. 23N. RGE. 5E. W.M. ___' �i ' � �-�^ �� . . - = - , ,- i i � ro•avr..sa • • _ . :��' - E9r>m -�-�-- hi , i �'_ - � I , 3 � LOIS� ��-'�� ' � , j � + CYWSAl(/CT A%IFAL[Al[i/ � �_ , `._s _ ��.,�7� _ � �/ � I . � I `7FIAETAK.WT. CI.3I.»i � j ',. � .� r•� .� /� 9YlCt3! � •.i.� � I` �PPRAF�(X/IFALL -�� -: .. �'m . liB 271Ff 1 � � �� I �� SfFQEI.IY��IT C4a-]Jc � � Z �� aa►.�anwlnrl su.3+ra �otr - ' — — -- — 1 : i — ' � • � �oM navv awe ow� CB` �� r� – j0(/1FA� A i ' I ' � u�xsa�+ rmv+cu.� stxm uv., � . ��, i - �o'Pl?..SD l , _ � . �� JCAf SCF AFTK..;. £5Y'T/D 6"lE!Q2 A7 '. ��0• � � i., � � 9lTClA /+ . 12�lE39950 a��397.0� a_ � I a� ��+ �` [iB 11A[! LOIS 1-7 . . : - - ( �. �+ ``�; � .�� ':,,E,,,,,,p„�,,,�, ,:'\ �` ►� z`•` m� SD DEIFN,�ION/IYATER QUAUTY Y,4ULT 1� �P�. __ a I . t � �j�� '- :� �� ' '� Z� Q�.T��T C�..� . I 1 , \�� -t-�- - ..QFF�E'R.wa rrf�ClnCw�flA�v. . `..� I I PVI. .m ESY7 s ' 2�°¢ sos.90 � flA -__-.. - a -�. ��. �_� \�� -�� _ -"- ._ !0'PV!SO fSA/� \ I _ ID LO7S!-7 I - - � -J I , _ � � � � �- -1�te73-T-d J � —- ._+ . -j ��. 0'PVL 9J ' ,...�v � — _ —_ — — _- _'r faLl— .— -- _ �(.rv . I � �_ � [.�/7� _ — _ � \$f lZ I ,- � �w � 4 a � j �:, � a P ; , — — �� I ., y� , � 4� �� . � � _ . , _'. `t... - _ �_ - -I _ __._ _ _ - �- - i" I I. _ _ p T —� _ � � � CB na�r ' � -�I \ A f+6q&0 LT -: I `i�- � �r . �. 9' IEM7.1 __c ' 'ti ..�5._ Y O �� ..._ (� � / - �� `. . _ _ �6"� ....�6-�,IIXtJ . I,YF6'PIC... � ��. �I , . 120N�/C(XA9p7A7E - I) ��JQf 6 PK-- �--.:�f�GJ.S� 6'IE IAUS . - 6'E KIR�f . 6�E AOIR5 . . I T ��'� � I �-� -� ....I 6•�� `'-- �. �.6 f 10d3 , . _ �".,. . .. ' � /E lARQ7 t �� I /1'dE.NSlSO 16�A9'Y�1EL1l/lY� -, c �- 6'E�01.3 �� I j'� { - � . AG7�ESS '�- �-.d. �. �'��. "�.. - ��'f'6'PIC . .i � _ _ `I! I j � -� ' �lU E0T5-.1�-7 SfE � �� _ � . `�`:. ',- '` O i I � IP i�' - ' - . "' __ AB'/'�17F�AGY.ESS, . . . V� I I i � . �.�. � _ RI0.�D SECDOY.. ---�- _ ' � `., r g• , I' u�"-.� ! TX _ `- .. '' - __ - = � -� �` � . - " � � �JO � j� I„�, i i � _. � ' `o -- �n d- r^, ■ �v ._ � � r � . � _ �z i� I � ' 16�PRlY,17F IlTd/IY�. . . � "� ' �� I -��-'-- r� ! � AGYF55£�lSSf]/IQVVT � � � � s �� _1! � - � f] --�`u i -- ID LO75{-7�StE - --- _- -- � --3 . --:.. �n'.� - _ '�-.. 3 b. � �� "- .Y/T. GI37 FOP -_ �� _ . . !6"PIBY,IIF.UA'AY! � : �i , -IS'OPAANC Q� I y psv��ss , ' ��, ^�', _� �- Ac�ss Et�vT.,, �: �Q � s r �n+o.stsnav. m�o�s,-�.st� `_ z�,,,s-i � ,1 i.azu��o�i�x' � t._ a�� _ Y w '1 i ^ �� . � - ��; a- - , ''*� -67/T.C337 fAP� _ I. I �� _ '� -.I � ` ' nc��ia . , -" �� J �,. '�� ^_ ,� � � ��- '� '�� _ " � ''-� � Rt]A7fEEMT.D!B'1HUY � !0'PCLi�CUR!7Y? �.no�x � . � 1 0. a�'- ��'-'.l_�--�___---_---- -__ ____ Z< 1 i ' iVSTAfL CYWC-. �'.. ...-.... .._ _ c a . = 1 � o %7/01££M$'T.,27�9/d`A.WN -------------- - x r ' �� I� � 'S.. . SFE`Yk7AC 94T.C3.Tl• 'r t p�Sff�. �r� . � s�; _..� , �p � �t.IRNK l?4VSIAlL-CQ�IC :-�' - I ,� i i .";. � .. �• .4/TCl3t, � *;n I - __' � � .�l.`7qliK gF� � �� ---��- - --- -- ------- -'�------- ----- -- --�- ---� - -� ---- - c�- .- ��- -/ t _ . I_ ' � . _ ' . . �,. _9/T GtJ7"� — —�- • _ -_ � K �t.. 1 _ - —�_�' __ - _ ;� �e � 3lYQ'P�.`3. "'- �£ .ewa.R.s �". __ . �.. ' __ __ ___-- _I � � - _ � . . .. -. ,1 . ..� " __ � _ _ . . — _ - — _—�fr—� t " - s"- . ._- . . -. �� ... , ' _.��e .� -, .. ��' ." ' ..i. wil.� - _ - _ — f 1 - --' — � � a . : ____ m �.�.� . y. � T— � � . ,._ p' — ~�� ---- - - p�r- *' _�+ �-- '� -"'----�- ;y �� i o I ---w---— - ---. �t o�.� � r.' � I - - -��r �-.- -. -, - . ._, nsI ----- .�_r •-��--�• "� c-- -��--•�ir��, -i , -- ---�-��. .- ---•--. - � -'' -.. -•-... . i . , . i q 9 � --^ • --,--� �- .. a • 9�� UN/ONAVE N.� `, :. � „ -> ,3,,.85^ -- . "� I I I.. _ _ 3$'-°6 n __ � _ �'.. _. _ . - -- s NOOK5'1 E"W _ - -— _,�.�.. � � �623.69 _---�--�r= - ; � _- ._— -- '.�. a --"�--�---�- ' i — � -- - � i ^ -1 � , ' � , � �i R00�AREA OF LOTS 2 & ,3 DEI�OPED COND/AONS ROOF AREA OF LOTS° 2 � ,3 TO BE DISPERSED r0 i�FT1AN0 DETA,'NED AREA B,�SIN TO BE DISPERSED TO W�TLAND � 7-CT}!�E 29M/kw�::501 �� 8dlww�Wa�p�m 98007 �25:885.7977 Fvi I45.88.5.796? ��o�srctv El3Glh'EERfYG • PLArYN!NG � SUAVc'YING C�E\%LL. ��'E�� Ol�!�' T,-O�'VS BR�?iV% AL !/,�L L,Q G�'= SN. OR T P�.';=a T �CALE. � f) � (�( 1� �/G�' T,� ��VAl�D �l��%�LOf"'�IV%CI�,� T `� I�0�� 0;H ;✓C/,IUC �E ec��uF �v;: �aol�s ,J ,;� � �.-,T t PJD V. 2CO3 � �H== O� �- --- ----- -- - — , � --��-- � Dt�SIGNEu rTJ c � a _ - _ . !�— -l�L� -- -- T��.�`�v- .�;�J�:�B t� ' C�r�.�tv'r_; �;�' -- --I s?90s�� C. WATER QUALITY VOLUME C:�LCULATION The City of Renton requires that the Basic Water Quality Vlenu be used to design the water quality facility for this project. The required volume was calculated per KCSWDM Section 6.4.1.1. The lowest 4 feet of the proposed detention vault will be utilized to fulfill this requirement, including 1' average of sediment storage depth. The water quality vault was sized only for the areas that will be tributary to it, specifically the impervious lot coverage, alley paving and �ass/landscaped areas in the developed portion of the site. The following variables were used in the calculation: Volume Factor(� =3.0 Rainfall =0.47 inches Area= developed basin Where A; = area of impervious surface (s fl A�= area of till soil covered with grass (s fl A�= area of till soil covered with forest (s fl Ao= area of outwash soil covered with grass or forest (s fl Vb = f x [0.9A; - 0.25Atg +O.IA�+ O.OlAa] x (R'12) Vb = 3.0 x [(0.9)(19,200) + (0.25)(10,900)] x (0.47 r' 12) = 2,351 CF The proposed detention vault has been calculated with internal plan view dimensions of 20' by 52'. Providing the required 3' of dead storage for water quality over the entire plan view area will provide approximately 3,120 c.f. of dead storage, exclusive of sediment storage, which exceeds the minimum required. Additionally, an average of 1 I foot of sediment storage will also be provided over the entire vault bottom. �� D. EiVIERGENCY OVERFLOW RISER The 12"-diameter orifice structure will also serve as the emergency overflow route. The structure diameter was checked for adequacy per the KCSWDM Figure �.3.4.H, Riser Inflow Curves, and the accompanying equations to verify its adequacy for conveying the developed conditions 100-year design storm event of 0.299 cfs, as calculated with KCRTS using one hour time steps. Qw,e�r= 9.739 D H'�z, Qw-e;r= 0.299 cfs, D = 12 inches = 1 foot (acting as a weirj .�. H = [QWe1C-' 9.739 D]�� _ [0.299 % (9.739*1)]�� = 0.10 feet Therefore, the overflow riser structure can convey the 100-year desi�n storm event with 0.10 feet of head above the top of the ri�er. CORE DESIGi��. INC. BRa�DaL VILL.aGE SHORT PLaT Page i= E. CONVEYANCE CAI.CULATIONS The King County Backwater program (KCBW) was used to perform an analysis of the adequacy of the proposed conveyance system to convey the 25-year and 100-year storm , events in compliance with the criteria established in the 1998 KCSWDM. There are two basins that collect stormwater runoff. Each has one catch basin and a single pipe run. Each of these two pipe runs were modeled using KCBW. For simplicity, the peak flows calculated for the entire site in the developed condition were routed through both of the conveyance systems, even though each will only receive a fraction of this flow. The � program output shows the results of routing the 25-year and 100-year peak flows through each of the pipe runs. The maximum headwater reached was 402.77 in both pipe runs, which is 0.61 feet below the proposed rim elevations, which satisfies the criteria specified by King County. The actual KCBW program output is included below. KCBW Output I BACKWATER COMPUTER PROGRAM FOR PIPES Pipe data from file:03067-1.bwp Surcharge condition at intermediate junctions Tailwater Elevation:402.76 feet Discharge Range:0.18 to 0 .3 Step of 0.12 [cfs] Overflow Elevation:403 .38 feet I Weir:NONE �, Upstream Velocity:0.4 feet/sec ' PIPE NO. 1: 38 LF - 12"CP @ 11. 825 Oti'I'LET: 395 . 01 IlILET: 399 .�0 INTYP: 5 4�CFS) HW(FT) HW ELEV. * N-FAC DC DN 'I�i� DO DE HWO HWI ******,r***********x*****,r******************+*********************************** 0.18 3 .27 402 .77 * 0.012 0.18 0.09 7.75 7 . 75 3 .27 3 .27 0. _'' 0.30 3 .26 402 .76 * 0.012 0 .23 0 . 11 7 .75 7 . 75 3 .26 3 .26 0.25 BACKTdATER COMPUTER PROGRAM FOR PIPES Pipe data from file:03067-2 .bwp Surcharge condition at intermediate junctions Tailwater Elevation:402 .76 feet Discharge Range:0.18 to 0 .3 Step cf U . �2 [cfs] Overflow Elevation:403 .38 feet Weir:NONE Upstream �7elocity:0.4 feet/sec PIPE NO. 1 : 78 LF - 12"CP � 5 .76� OUTLET: 395 . 01 INLET: 399.5Q INT`�P: 5 Q(CFS) HW(FT) HW ^nLEV. * N-FAC DC DN TW DO DE HWO HWI **************************************�r***********************�r***************� 0 . 18 3 .27 402 .77 * 0 . 012 0.18 0.10 7.75 7. 75 3 .27 3 .27 0.2C 0 . 30 3 . 2'? 402 ."%� * 0 . 012 0 .23 G . 13 � . 75 7 . �5 3 .26 3 .27 0 .28 CORE DESIGN, INC. BR�VDAL VILL:�GE SHORT PL.aT Page l�4 V. TEMPORARY SEDIMENT TRAP A sediment trap will be used for temporary erosion and sedimentation control during construction, in accordance with the requirements of the KCSWDM that the contributing drainage area be 3 acres or less. The temporary sed'unent trap needs to have a mnumum surface area based on the following equarion(per KCSWDM, 1998 edirion,pages D-26 to D-27): SA=FS(Q�/Vs) FS (Factor of Safety} =2 (to account for non-ideal settling) Qz (Dev 2-yr flow)= 0.143 cfs VS=0.00096ftJs (settling velocity for medium silt) SA =298 sf As designed, the sediment trap will have a minimum surface area of 500 square feet at elevation 395.0, a bottom elevation of 391.� and a top of berm elevation of 396.0. These dimensions satisfy the surface area requirement calculated above and the minimum settling depth requirement of 3.5'. Temporarv Emrgencv Overflow Spillway The emergency overflow spillway was designed per the requirements of Section 5.3.1.2 ,, of the 1998 KCSWDM using the following equation: L = �Qioo/ (3.21 H��z�� —2.4 H L = [0.299 cfs i (3.21*0.2'�)] —(2.4*0.2} = 0.56 feet The KCSWDM specifies that the minimum overflow spillway width shall be 6 feet, so the overflow spillway for the sediment trap was designed at the minimum width since the calculated width was less than the minimum. The spillway was designed with an overflow elevation of 395.0 and will discharge to the existing on-site conveyance swale. CORE DESIGN, INC BRaNDAL VILL�GE SHORT PLAT Page 15 I��