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HomeMy WebLinkAbout03182 - Technical Information Report - Drainage � ��/ U� � _ _ __ . __. __.._ ...___ . __ .__ op ' s�rt�un�i ua�.rrr�t;� aErou�r : � FOR : M �t340 J(Jlt1ES SHORT PL�T � 1800 dUNE� AY�E NF. It�NTC31tI,'�'t'A�HINGTON FI LE NO. 830-002-031 PREPARED BY TOUMA ENGINEERS 6632 SOUTH 191ST PLACE, SUITE E-102 KENT, WA 98032 (425) 251-0665 December 30, 2003 ��s� p�-g� ���°���, ��__��_�� .,n,�. , � :�,.•.���� _ �;� _ .� ; , ,- -..., .�., , i\�' r�..fk �f ' .•� :�{i�, l^�C�� •�A�j. � ��r �����4�; �,'D�1 i �� �n , �3 �, ; .;^ �"=;`':; .� �s� t� e, •..;, . ..; ;;, a 94%fl � d,r,.�, :\ �Ol��:,��i,' •� �'��".YL-�`-�' (%t' i�',f.,i��E������ .., � :• ';:.���"�. �.-.,'�r Y:i tt^;:;�12••ya5=�� - 1 -�.�8� King County Department of Development and Environmental Services TECHNICAL INFORMATION REPORT (TIR} WORKSHEET Pari 1 PROJECT OWNER AND Part 2 PROJECT LOCATION AND PROJECT ENGINEER DESCRIPTION i Project Owner ��9rc �S�S,o Pr����J a17BS �`ia,�� ��� � Address Location I O v.�3�x �s�t ' - - l�ownship _ � 2.�� , Phone���_ ZZ,_ 9Zl� Range �� I Project Engineer � �' •••-••�••••••Section .5 I� /o� /vv.r�� f iov/�t� c�-i i,��o-t � Company � � Address/Phone �Zr- 2S�- b��l� � Part 3 TYPE OF PERMIT Part 4 OTHER REVIEWS AND PERMITS i APPLICATION � -� Subdivison DFW HPA Slioreline Management i �hort Subdivision COE 404 Rockery Grading DOE Dam Safety Structural Vaults Commercial FEMA Floodplain Otl�er Other COE Wetlands Part 5 SITE COMMUNITY AND DRAINAGE BASIN ' _._I Community L�e�m��iyl,�y Drainage Basin ��1� GJQ'S/ji,r�'olo� _ I ___.� Part 6 SITE CHARACTERISTICS ,c6�/.�- ± _� River Floodplain i Weilands ' Stream ' Seeps/Springs ' Criiical Stream Reach j High Groundwater�Table I Depressions/Swales Groundwater Recharge � Lake Other Steep Slopes � Z Part 7 SOILS Soil Type Slopes Erosion Potential Erosive Velcoties Additional Sheets Attached Part 8 DEVEL�PMENT LIMITATIONS REFERENCE LIMITATION/SITE CONSTRAINT Ch. 4— Downstream Analvsis Additional Sheets Attached Part 9 ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION AFTER CONSTRUCTION Sedimentation Facilities Stabilize Exposed Suriace Stabilized Construction Entrance Remove and Restore Temporary ESC Facilities Perimeter Runoff Control Clean and Rernove All Silt and Debris Clearing and Graing Restrictions Ensure Operation of Permanent Facilities Cover Practices Flag Limits of SAO and open space Construciion Sequence preservation areas Other Other 3 Part 10 SURFACE WATER SYSTEM Grass Lined Tank Infilt�ation Meihod of Analysis Channel _ ._ ___ Vault Depression Pipe Systern Compensation/Miti,yati Energy Dissapator Flow Uispersal on of Eliininated Sitp Open Channel Stora e Weiland Waiver y D►y Pond Stream Regional - ---------- Wet Pond Detention [3rief Descriplion of Sysiern Operation �`�'���'����9 _____ __�__._._ Facilily Related Site Lirnitalions Re(erenr.e Facility Limitation Part 11 STRUCTURAL ANALYSIS Part 12 EASEMENTSlTRACTS Cast in Place Vault Drainage Easement Retaining Wall ✓/�ccess Easement �P✓i.b�� I Rockery> 4' High Native Growth Protection Easernent Structural on Steep Slope Tract Other � Other — — I Part 13 SIGNATURE OF PROFESSIONAL ENGINEER I or a civil enyineer under►ny supervision my supervision have visiied tl�e site. Actual site conditions as observed were incorporated into this worksheet and the attacf�ments. -To the best o( rr�y knowledge the information provided here is accurate. C � _ , ,i s� /�'3 a�� �,� ,2�j D? /' ; Signed/Date 7 TABLE OF CONTENTS 1. PROJECT OVERVIEW 11. CONDITIONS & REQUIRMENT SUSMMARY lll. OFF-SITE ANALYSIS IV. FLOW CON"tROL ANU WATER QUALITY V. CONVEYANCE SYSTEM ANALYSIS VL SPECIAL REPORT AND STUDIES V11. BASIN AND OTHER COMMUNITY AREAS VIII. OTHER PERMITS IX. EROSION/SEDMINTATION CONTROL DESIGN X. BOND QUANiT1ES WORKSHEET _ � I. PROJECT OVERVIEW This project consists of one parcel of land approximately 0.7 I acres. The project is situated in the northeast end of the City of Renton. It is located within southeast quarter of Section 5 Township 23 North, Range 5 East W. M. The proposal is to create 4 lots, "Fill in" subdivision. Access to the proposed project will be via from Jones Avenue NE situated west of the property. There exists a house on the property, which the owners are planning to retain. The soils on the site are composed of Indianola (InC} gravelly and fine sand per the King County Soil Survey. The [ndianola series is made up of somewhat excessive drained soils that formed under conifers in sandy, recessional and stratified glacier drift. This type of soil is designated by !� King County as Type A soil and is good for infiltration systems. � The site is flat with an average slope of 2 to 4 percent. There are no steep slopes present on the site. The flow consists of sheet flow from east to west to Jones Avenue NE. There exist storm system on Jones Avenue NE consisting of underground pipe and road ditches directing the flow south to NE 12`h Street. From this point the flow is directed west along SR 900 which eventually the water flows into Lake Washington. The proposed development of the property is considered as "infill" project and it is located in a Single Family (SF) zone. The City of Renton designates the site with the SF zoning. The SF zoning allows for a minimum lot size of 4500 square feet and a maximum density of 8 units per acre. The setbacks allowed in the SF zone are as follows: front yard setbacks, 20 feet; rear yard setbacks, 20 feet, and side yards setbacks, 5 feet on all interior lots, and 15 feet on corner lots. The City of Renton Comprehensive Plan designates the site as Single-Family Residence, which is consistent with present zoning. The density for the developed portion calculates at 5.85 dwelling unit per net developed acre. There is no right of way to be deducted from the site. The proposed lots will be served from existing roads or private access easements. The street improvements including but not limited to paving, sidewalks, curb/gutter are required along the frontage of the property along Jones Avenue NE. Majority of trees will be retained except for few deciduous which fall within the building envelope of the proposed new lots. 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PRELIMINARY CONDI'I'IONS SUMMARY CORE REQUIREMEN"1'S 1-5 CORE REQUIREMENT #1: DISCHARGE AT NATURAL LOCAT[ON The allowable outflows from the site will be discharged to its natural locations. ?he level I flow control is calculated to match the developed peak discharge rate to the existing site condition peak discharge for the 2-year and 10-year. CORE REQUlREMENT #2: OFF-SITE ANALYSIS A level one downstream analysis is a portion of this report. See the analysis later in t}�is report below. CORE REQUIREMENT #3: RUNOFF CONTROL The increased peak runof�, due to any change in pervious conditions and increase of impervious areas, will be attenuated using peak rate runoff control in accordance with KCSWM , 1990 Edition. Initial calculation indicates there is no detention facility required. Please refer to attached calculation. CORE REQUIREMENT #4: CONVEYANCE SYSTEM I� Conveyance system is minimal for this proposed short plat. Storm runoff from private road and new homes will be directed into storm drain system exists on Jones Avenue NE. In order to further reduce runoffto the existing storm system, it is planned to introduce individual infiltration system for each new house. Refer to calculations for sizing single family infiltration facility. CORE REQUIREMENT #5: EROSION/SEDIMENTATION CONTROL PLAN The erosion control plan will be designed using the King Count_y storm manual. Silt fences will be used to intercept silt laden material resulting from clearing and/or construction of short plat improvements. These facilities will be adhered to rninimize any impact to downstream or offsite areas. CORE REQUIREMENT #6 - MAWTENANCE AND OPERATION N/A CORE REQUIREMENT #7 -FINANCIAL QUARANTEES AND LIABILITY I N/A I _ � CORE REQUIREMENT #8 - WATER QUALITY The impervious surfaces subject to vehicular traffic within this proposed short plat is less than 5000 square feet, thus exempted from design and installation of water quality tank or pond or similar facilities. SPECIAL REQUIREMENTS: THOSE APPLICAI3LE TO PROJECT 1. Critical Drainage Area- N/A 2. Compliance with existing Master Drainage Plan - N/A 3. Conditions Requiring Master Drainage Plan - N/A 4. Adopted Basin or Community Plans - N/A 5. Special Water Quality Controls-N/A 6. Coalescing Plate Oil/Water Separators-N/A 7. Closed Depressions - N/A 8. Use of Lakes, Wetlands, or Depressions for Detention - N/A 9. Delineation of 100 Year Flood Plain - N/A l0. Flood Protection for Type 1 and 2 Streams - N/A 1 1. Geotechnical Analysis and Report -N/A l2. Soils Analysis and Report - N/A - 8 III. OFF-S[TE ANALYSIS CORE REQUIREMENT #2: OFF-SITE ANALYSIS LEVEL ] ANALYSIS A: UPSTREAM ANALYSIS The proposed short plat does not have appreciable off-site runoff entering the site. Majority of the site is slightly higher than the road on Jones Avenue NE. The runof'f from the site sheet flow westerly toward Jones Avenue NE. B: DOWNSTREAM ANALYSiS The surface drainage from the site is directed to onsite storm system consisting of catch basins and conveyance pipe directing the flow to an existing storm system on Jones Avenue NE. The flow is directed through a 12-inch culvert south along Jones Avenue south until NE 12th Street. Thence an l 8-inch storm line directs the flow in a southwest direction to NE Sunset Blvd storm facilities. Thence via a 36-inch culvert along the north side of Sunset directs the flow west and eventually into Lake Washington near Gene Coulon Park. _ � IV. FLOW CONTROL AND WATER QUALITY The following calculations conclude that the 100-year peak flow difference between the pre-developed flow and post-developed flow is less than 0.5 cfs. In accordance with 1990 King Count Surface Water Drainage Manual detention is not required. The following calculations include: Basin areas Time of Concentration lsopulvial graphs for 2, ]0 and 100 year storms Pre-developed and Post-developed hydrographs The soil type found on this site is classified as Indianola (1nC) and is good for infiltration system. We therefore recommend installation of single family infiltration system for the three new homes to be built on Lots 2 through 4 inclusive. In discussing this matter with tt�e owner, we ascertained that the size of homes proposed on the vacant lots will average about 2000 square feet on both stories. The surface area of each house will be sized at 1000 square feet, and the roof infiltration system will be designed to accommodate a 1000-foot home. Based on Section 4.l.1-3 of 1990 KCSWDM, the size of the trench is 25 feet long per 1000 square feet of roof for the Seatac regional area (See Figure 4.5.l B below). -/4 1800 JONES SHORT PLAT ' BASIN AREA SF ACRES - CONTRIBUTING BASIN SITE AREA 30827 0.71 I�i OFF-SITE AREA 0 0.00 30827 0.71 SOIL TYPE Indianola (InC) Type "A" EXISTING CONDITIONS DEVELOPED SINGLE FAMILY LOT 28332 0.65 ACRES CN 86 EXISTING HOUSES & ROADS 2475 0.06 ACRES CN 98 PERVIOUS 0.65 CN 86 IMPERVIOUS 0.06 CN 98 DEVELOPED CONDITIONS Ex House & Driveway 2475 0.06 ACRES CN 98 New homes & Driveway 7�OU—'� 0.17 ACRES CN 98 NEW ASPHALT-SITE 5932 ' 0.14 ACRES CN 98 LANDSCAPING-SITE 14920 0.34 ACRES CN 86 TOTAL 30827 Q.37 PERVIOUS 0.34 CN 86 IMPERVIOUS 0.37 CN 98 . �� � s� � �� `"'r S.� �;�.��, _ � �� - 5��� r � 5,� AU�r�,�> Sr�� :-�� ���� �-U;; , ��.,-k � �� TIME OF CONCENTRATION - EXISTING CONDITION - FOR 2-YEAR, 24-HOUR STORM DESIGN SHEET FLOW- OFFSITE MANNING-n 0.15 OVERLAND-L 156.00 FEET PRECIPITATION-P 2.00 INCH SLOPE - S 0.05 FT/FT T = 12.06 MINUTES TIME OF CONCETRATION - DEVELOPED CONDITION SHEET FLOW- ON-SITE MANNING-n 0.15 OVERLAND-L 40.00 FEET PRECIPITATION-P 2.00 INCH SLOPE- S 0.02 FT/FT T1 = 5.95 MINUTES SHEET FLOW- ON-SITE MANNING-n 0.01 OVERLAND-L 150.00 FEET PRECIPITATION-P 2.00 INCH SLOPE- S 0.02 FT/FT T1 = 2.12 MINUTES TOTAL TIME 8.07 MINUTES � Z K I Nci (' OUN "I' 1'', WASIIINc� 'fON. StI1ZI� ACli �V /� 'f (: It 111? � Ic� N N1ANlIAI. -- -- - - _ __- —- - - - "I'Altl,l�,1.5.21t S(:� N'1?�'I'I:RN 1VASl11N(;'1'UN RUNOI�F(:URVG NUM11I{I:I2S SCS WESTERN WASHINGTON RUNOFF CURVE NUMBERS (PublisfiPti by SCS in 19£32) RunoN curve nurnbers �or selected agricultural, subur!>an arxi urb�n land use (or Type tA rainlall distribution, 2�t-hour storm dura�ion. CURVE NUMBFRS BY 1iYDROLOGIC SOIL GROUP LAND USE DESCRIPTION A B C D -- _.-- -------- - - ---- ---- -- --- --- Cultivalecl I�i�d(1) winter condilion 8fi 91 94 95 Mounlafn open areas: Iow growing brush and grasslands 74 82 89 g2 Meadow or paslure: !65� 78 85 89 Woocl or lorest I�nd: undisturbed or older second growth �2 64 is et Woocl or forest larid: young second growth or brush 55 72 81 86 Orchard: wilh cover crop 81 88 92 9`� Open spaces, lawns. �rks, golf courses, cemeteries, landscaping. good condition: grass cover on 75% or more of the area 68 80 86 90 fair condition: grass cover on 50°�6 to 7596 0l the area 77 � 85 90 92 Gravel rc�ds and parki�ig lots (y6� 85 89 91 Uirt roads and parking lots 7'2 82 87 89 Impervious surfaces, pavement, rools, e1c. �98' 98 98 98 Open water bodies: lakes, wetlands, ponds, etc. 100 100 100 100 Sinyle Family Resiclential (2) Dwelling Unit/Gross Acre � Impervious (3) 1.0 DU/GA 15 Senarate curve numbAr 1.5 DU/GA 20 sliall he snleded 2.0 DU/GA 25 lor pervious ancl 2.5 DU/GA 30 irtipervious portlon 3.0 DU/GA 34 of the site or basin 3.5 DU/GA 38 4.0 DU/GA 42 4.5 DU/GA 46 5.0 DU/GA 48 5.5 DU/GA 50 6.d DU/GA 52 6.5 DU/GA 54 7.0 DU/GA 56 Planned unil developments, °�6 impervious condominiums, apartments, must be computeci cornmercial business and industrial areas. (t) For a more delailed descrip�ion of agricultural land use curve numbers reter to Naiional Engineering Handbook, Section 4, Hydrology, Chapter 9. August 1972. (2) Assumes roof and driveway runoH is c�irected into street/storm system. (3) The remair►ing pervious areas (lawn) are considered to be in good condition for If,ese curve nun,bers. ��v 3.5.2-.l I I/92 � ' K I N (i (' l) ll N 'I' Y, W /� S II I N l� 'I' O N. S ll R I� n C I? VV A 'I' I; R I) f�, S 1 (� N h1 n N U /� 1. (2) CN valiies can he area weiyhted when they a����ly to pervious areas of sirnilar CN's (within 20 CN pointsl. I lowever, hiyh CN areas should not be comhinec� with low CN areas (unless the low CN areas are less ihan 1 5^/0 of the subl�asinl. In this case, separate hydrographs should be yenerated and sununed to form one hydrograph. _ _------- ---- -- -- ---- -------- I�IGURI?:1.5.2A IIYI)ROLO(:IC SOIL GIZOUP O�7'l1E SOILS IN KINC COUN7'Y I IYDROLOGIC NYDROLOGIC SOIL GROUP GROUP` SOIL GROUP GROUP' - _. _ _ -- — -- ----- --- - /1ldciwood C Orcas Peat D Atenls, Ncfe�worxl Mt�terial C Oridia D /lrenls, Fverett Maleiial 8 Ovall C De:�usitc C Pilchuck C i E3ellingham D Pugel D l3risrot 0 Puyallup B E3ur,kley D Ragnar B Co�stal Bear,hes Variable Renton D F�rlmont Silt Loam D Riverwash Variable Edgewick C Salal C Everell A/B `Sammamish b Indianola � Seatlle D Kits:�p C Shacar D Klaus C Si Silt C Mixr.d Alluvial Land Vari�ble Snof�omish D Neilt�n A Sultan C Newberg 8 Tukwita D Nooksack C Urban Variable FJormal Sandy Loarn D Woodiirville D HYDROLOGIC SOIL GROUP CL/1SSIFICl1TIONS /1. (Low runo(f potential). Soils t�2ving hlgh infiltration rates, even when thoroughly wetterl, and consisting cl�ielly of deep, well-to-excessively draineci sands or gravels. Tfiese soils f�avQ a iilgh rate ot water transmission. B. (Moderately low runoff potential). Soils having moderate lniil�ration rates wtien Ifioroughly wetteci, and cvnsisting cfiielly of moderately fine to moderately coarse textures. Tl�ese soils liave a moderate rate of water transmission. C. (Mocieralely high runoff potenliai). Soils having slow ir�(iltralion rates when thoroughly wetled, and consisting ctiie(ly of soils witti a layer that impedes downward movement ot water, or soils with moderately line to fine Iextures. These soils have a slow rate of water transmission. b. (High runof( potential). Soils having very slow infillration rates when thoroughly wetleci and consisling ctiiefly ot clay soils with a high swelling potential, soils witl� a permanenl high waler table, soils with a hardpan or clay layer at or near the surface, and shallow soils over nearly lmpervious niaterial. These soils have a very slow rale of water Iransmission. • From SCS, TR-55, SeCorxl Edi�ipn, June 19L�(i, Exhibit 11-1. Revision; ma�fe irorn SCS, S�il Inter�retalion Record, Forrn �15, Se��tember 19F38. ��K�) :i.5.2-2 11192 KING COUNTY, WASI� iNGTON, SURrACE WATFR D �? SIGN MANUAI. _ .- - - _. --- _ _ - - - -_.. - - - -- - -- _ _-- - TA�3LF.3 S 2C "e" AND "k" VALUrS U6ED 1N'I IMF.CA[,CUI,A'f10NS FOR HYQR(H;ItAPHS '�� � ----- ----- --- _ - ----- - -- - — --- - - - _. -------- _----- -�-- - 'n;Sheot flow F�uatlo�!.larx�bq'�Vnlues(�or IA9 k�h!nl.l(q h d Ira•rol) ��• Snppfh lU�if.eS(C�Mf,rele,as�ww`n,p�evyi,U iS�B 7� v'�.:c�ad a:.!) �.�!! Fanow�i.�f.+s a trnse�W�ur1�e(ra�e,klcie► 0 05 Cidl�valM so�whh rncyire�ver(s<. 0.?0 h/h) Q 08 GAtl�r.�i��f so�v+ilh rest.�iie eover(S> 0?0�/h) D.t7 Slwrt p,:irie�,�^,s end lawna O 1S Oe�se p�a�ses 0?4 FSe!nnlda p��•x5 Q�1 Rarpe(��awral) 0 t� V.'o-�ds w lorest whh IipM urde.h�nh 0 10 l":od1s o.lo���st with de.�se u�r7e�brush �80 - -- _. _ - ------------ ----_...-- --------- --- -- — ---- -- -- •ltarr;nfl�,.^!uos 1�sheet flow a�y,frcxn pve�lon s�d Mexlo�+�s 1975(See TR�SS. �986) 'k'Vt��Ps Vsed In T.a�+al Tlme/Time d Concererallon CA'cidttbns Sharyow Ca+centralnd Flow (AJter Ihe Inhlal'�0 h.d sl+eet Ilow,R -0.1) k� �---�---�----- �-�-'--- —- ..�----�-�-------._..... .-- I. rUIPSI WMII�PaV��QfW�I[��'�I9�ZI�IO f11�klJTM{�I1�O IO' � ? 8n�shy p���und whh ru.^e tr�ne{n -0 060) S J. fa�.v a nd:,�m�nn trn�r.cJ�ivation(n�0040) E •. I+�yl,yass(n- OOlS) B S. Short yrass,pasture nrr14.+.vns(n-COJO) tf t �, !i�,�+y�.3:e�•ou�e(n-oozs� �a 7. FavqJ arvJ urevd ereea(n-0.012) 27 Cir���net Flow Qnlemdqenl)(At Il�e���b�ni��f v�;ll�C10nrYJS A�02) k� �. f�eci�f swate wni�hy�vy p�ourd In�a(n � 0.f0) S 2. Fo��str_A d�airNge course/ravine wmi daf'�n�d cha�w�Hl I�ed(n-0.050) 10 � Rxk-finpd w�aten4ay(n=OOJS) 15 � G;assaiwaterway(n-OOJO) 17 5 Earth-Ilnod��ale�.ay(n.00?S) �p 6. CMP pipe(n.002�) ?1 7 Co�u¢te p�pe(0012) t2 0 O117C/K.71CM•3Y!Af1d N�1@� fJ�j��ln Cf�annM ilpw(Gjnttnuovs strnrm,q - C C) M� 9. fAeancir�i,slr�m whh s7*+e�+•:�Is(n- 00<O) 2p 10 Rc�l FnM sl�Pam(n-0(1J5) 2J 11. Cra;flnEv_�sfrgam(n-OOYJI 27 12. Othnl 511B�T5.R4���fR��IP c�.� . • �����:�pe 0 M7'n•• ! _ __.'._' _'- __.. __ _ .__. . .'_' __'.'_"' . _______'. __'. _...'__ ._._ _. _ _ .,__ ' ••S�o�'Fapi2r 5.TaNe 5 3.5C la eS3::.Fr<y�:annM.ps'n'�,'��es la c�.,�d�annels 3.s.2-� �r:►o KING CUUN 'fY, W ASIIINCTON, SURFACG WA7' EK I) ESIGN M ANUAL — --------__ — ---__ _ - FIGURI's 3.S.1C 2-YFAR 24-11OUR ISOPI.UVIALS , , � , � c, � � `� �� �. 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W ^ ' . �� �� �• ��� �� \ � 'l �� :�L��� � .�—. _� _ .. ... _ , � I�� ��� �� �� ' �� � �I . - � � �� � )� �_ �,���� :�- � � � i � ` / J �� _11]� „� ��( f - _ '� �. � i1�1 7 �'S � r =.�.....��7_. �F' (�I ,C y �']� f , 1 cV ry ,= -- ' 1�1 .� - �.�-� 7S� .� i � ;.z � ".. �,, '.� 't i `T' 1, i }. ,�' '---� i—.�� / � � - ��t—� "tV•• `-�` I �� ,� � .� ��� �' `t � = ' �_ •y� ,\ � � '��';� � ��.,�� ����Jr� �;� �- ,� /\ � - `� � ,�\� , l l �� �,.\ � l i,--� � ,.. , �� =� �L' � „�,f .. , . : � ,,. ,, �`-�-_`—� .�� ( �, YM�y � ' _� ry �'' ��. `- -" ` ��. , ,, _ - - ' . , - � ,.. � � 2-YEAR 24-HOUR PRECIPITATION ��., ,.3.4�""` ISOPLUVIALS OF 2-YEAR 24-HOUR �►' �' � •�«, � � a _ + 35 TOTAL PRECIPITATION IN INCHES � ry��\,�` , =.� t� ,. - -- `� /� � _ '�� ' -� 0 l 2 3 4 5 6 7 B Mlles •-J __ _ �y �y �;. ...,:,, ry �_ , ,� --,J,•;._ .,,� i; i: 300,000 3.S.1-8 � - � I/�)0 � I I . � . K 1NC; C' uUN 'I' Y, W ASIIINGTUN, SURFACE WA 'CER IIESIGN MANUA [. _ __----- _-- -- -- ____ _ _ __ _ _ __ FICURG 3.S.If. 10-YI?AR 24-IIOUR ISOPLUVIALS _ _ __ _ - -— --- _ _ _ _ ----- 2.1 �1�_�.� `,`�� _ — `, �v �� 'b� � ' t �1 �. � � .� 22 �� '� �� � � -.. < .,�� � ,ti� ; �— 23 � �� _ - -� lr� �1_ ; ' ' � , � f i .� , ' � �, � �s...� '� , �) � . � �� , C � 24 I �_. � � � � , �� �f� .. `I f , � ��� ��� 40 ?5 � ���� , �`•,, k :� _ �, � l , ��� _ .. �, � ... i 2C � ` � �� I(R�il� 1 � r � \ S� (Y C -�.�� / ',. �� �� r ) 2.7 )� ��, . 1 , l�� �„�,-., . ��, �, ?.8 , � � 't � � ,�,:_� `, �;r - 5 / 1 � 2 y \ .`� � �','t�l` I ` \` — `�-l'h._� �� , � ..�.. •� ` � : � _ . . .. ...• . � .. �. , ..., . — , , � r' 9 � � '.� � , C. t _ .,� � �i ,�-'� , +_..` � ��'j,' ,y ,� , � 3� - � Y.� �.,�„�� . . 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"� ,! � / � s,,,. �. _._ "� ' •� J F,'� �" I { 1 •S ��� }� '��- �, . .. ;+' _. - �� - -'�� — �� - . ` � `�.. �� � M;( ' .`� � � s � <: � ' � , z...}�� ",\ ��e ✓J`����� l ^{ � r ` �. � �� �i.���� �, �� i.....� �� --�� _� _ � a�. .�� � r��n� � ,�' � �� '•��� ��� ' �., � i� �_ � �, , � � . t1y '' 4 , , � y , . . �.. ., w:s / ' I .,. � � . . . ._._ _.---__...---. . _. _ . . . _ ----- � ' ^.' r .. / i r 10-YEAR 24-HOUR PRECIPITATION � t�; � �-� ` � � �.. . ,� ��,,.q5 � 3.4�" ISOPLUVIALS OF 1Q-YEAR 24-HOUR �'� ��-. - �• \�'�.� _ TOTAL PRECIPITATION IN INCHES �0�� ��• _ - _ Q - 4 ' `` ?.7 , G :�,��� - _ nJ�nj �'` � '' , O 1 2 3 4 5 6 7 B Mlles ��r "� ���� — — --��-. �� a �i -F<� �` �: ��,�.�,��, �.s.t-ir� 3;�5 - ��x► 4.n K I N �: (' O ll N 'I' Y, W A S 11 I N c: 'f O N, S U K F A C E W A 'T F: R I) E S I (i N M A N U A 1. _ _ _ — --- -- ----— ------ _ _ _ -- I�IGUItE 3.5.111 100-YI:AIi 24-HUUR ISOPLUVIALS 3 p _ L � � 1 -�, �.��, =� - Ca: � - r ._ �t . �' � __ � '�� . '�2 � F � �� .� �� . � �y.�,;-� � � ,� '� 3 i ` '`-►� ri � ti �;�;��,. �4 �- ��-:�� �' , - �-��, �� "" , � 3 3��4 3 — �� � �� ,t� „� �� ,.s� , . � r �9� ' '' K��.�" � i t ���. �� � 4.p.,� �._ �. � 1 �,, :.�' 'r ��a `� r � 4 y „ _. M —, ,,;,� _ � �, r ���� ���, 2 �� � , � . � _ � t, a �, 1 - 4. i` � � �..'. "��I _ _ �� '� ���, � = 1 ��� � , �. -�* ' �. , ;r` ; . . , _ _ , • - . _ . f _ ,, . --� � � • - � , . , . -' 43 .. � p � '' � Y � MeA�I� ( ' , ' � � O � + - � 1 44 ; --. " ' co . -�E �Y� �, � r ` �� � - - � r � f� ='n'1 1 , 1,.� � r ; �. 1 --� - - a° ,. 4S �� _, ��` ��, �0. �.�.,.,� ��� � , _ �� �,•, �._ '�J� 1 ���� , - � �� _�� ..(� A � �� � � l I ,Ji. \ 1 1' S \ : , y �6 I " • 1� �� � .y, —.`� �— � �� � u .I ._ _ �� �l ,� .� , . l ; �- .._ i �" �' � _� � � � ,; 7 a � �� � � 1 � a ` � � �. ;.� ,, � - if + � _1 4 �'��' _ ���'" , '= , � - �l r � - , .. �:- � � -• _ � �7 ' `a (l�. o � f - � � �.l YM'�� _Y j � [� �� \ � ' � ���; r\ • �! �� ` `"� � � �; � •-•—r ' r '� y� `��_ �1 � � _ � � - _ • �� ( � (\' r�- 1 L i� ' � Lr: `� -'r�� ' oa � ,1 .' [.. 11 " y� '/�. J' j „'��. }. . '� �?'��. �:.� t,s �� � l ':7.. � i _r � j`f .�y ,f� j�`• ►'l t'`�,l— � i' ,`�� � 'i1 � � i ,.,, � ' �'���. ��, �� :t s F ` ;t,. -, -. ,., � ' y_._ . I�"� � �� i� �� � � �� � �� � j I \ J �!� �- —��., ` � � � , .. 1 � � (�t 1 '� I_. .I K ��`� �. /"t C _ � C,� S .4,� t f } �i'• _ �� ':�� �N �� 1 - yH r , � \ � t � .. � � .�t. �h r) - � .F__ � _z. . �y t ,. t„_. � / `�' _,_ ".� �� `��. 7' / , er�. 1 1 �_ / �' ...I c�- `� �F � � d-� �j� „�� �� ` � .� � , _ .' � r� _ � �. ��'�: � � � '�` �`'1 �'� ('• �;,,' )�� � � ,� { � �� � .:,�: -p i � „ � / �,,,_ -� r.dk( �-....� �. •�.� ��ti � � O �: !� .44;,� T l . -i � ,.J,�. 36�, .,. _ . . - . �. � , � � � � --— - . 100-YEAR 24-HOUR PRECIPITATION t . • � , `. , 6.5 O � - �-�. E y�, - � i 3.4 ISONLUVIALS OF 100-YEAR 24-NOUR a �C� � t_ y - �, ',- � � „-,� �,,' << J 5 ' TOTAL PRECIPITATION IN INCNES �� � ;�.' � �� ' . a• � ;� _ \ r' :;. � _ a R � ,;. O 1_2 3 4 5-- 6 7 --B Mlles y .�(�. ,� 'i J"._ .-r.._?i�� � .. --- — --- 3.s.�-�3 a� �o �„` �: 3�0,��0 �. �r!(1 2 SBUH/SCS METHOD FOR COMPUTING RUNOFF HYDROGRAPH STORM OPTIONS : 1 - S . C. S . TYPE-lA 2 - 7-DAY DESIGN STORM 3 - STORM DATA FILE SPECIFY STORM OPTION: 1 S .C .S . TYPE-lA RAINFALL DISTRIBUTION ENTER: FREQ (YEAR) , DURATION(HOUR) , PRECIP (INCHES) 2 , 24, 2 . 0 - --- - - - - - -- ---------- ---------- ------------- - --------------- - ---- - - --- ******************** S . C. S . TYPE-lA DISTRIBUTION ******************** ********* 2-YEAR 24-HOUR STORM **** 2 . 00" TOTAL PRECIP. ********* - - - - - - - - - - - - -- ---- ------------------ ------------ - ----- - -- - -------- --- - ENTER: A(PERV) , CN(PERV) , A(IMPERV) , CN(IMPERV) , TC FOR BASIN NO. 1 0 . 65, 86, 0 . 06 , 98 , 12 . U6 DATA PRINT-OUT: AREA (ACRES) PERVIOUS IMPERVIOUS TC (MINUTES) A CN A CN . 7 . 6 86 . 0 . l 98 . 0 12 . 1 PEAK-Q (CFS) T-PEAK (HRS) VOL(CU-FT) . 14 7 . 83 2386 ENTER [d: ] [path] filename [ .ext] FOR STOR.AGE OF COMPUTED HYDROGRAPH: A:a3�Rg�-JONE S SPECIFY: C - CONTINUE, N - NEWSTORM, P - PRINT, S - STOP C - - -- ----- ----- --- -- --- -------------------------------- - ---- - --- ----- -- ENTER: A(PERV) , CN(PERV) , A(IMPERV) , CN(IMPERV) , TC FOR BASIN NO . 2 0 . 37 , 86, 0 . 33 , 98, 8 . 1 DATA PRINT-OUT: AREA(ACRES) PERVIOUS IMPERVIOUS TC (MINUTES) A CN A CN , 7 .4 86 . 0 . 3 98 . � 8 . 1 PEAK-Q (CFS) T-PEAK(HRS) VOL(CU-FT) . 22 7 . 83 3264 ENTER [d: ] [path] filename [ .ext] FOR STORAGE OF COMPUTED HYDROGRAPH: A;2YRD-JONES FILE ALREADY EXIST; OVERWRITE (Y or N) ? A: 2YRD-JONES ENTER [d: ) [path] filename [ .ext] FOR STORAGE OF COMPUTED HYDROGRAPH: A: 2YRD-JONES SPECIFY: C - CONTINUE, N - NEWSTORM, P - PRINT, S - STOP /3 2 SBUH/SCS METHOD FOR COMPUTING RUNOFF HYDROGRAPH STORM OPTIONS : 1 - S .C. S . TYPE-lA 2 - 7-DAY DESIGN STORM 3 - STORM DATA FILE SPECIFY STORM OPTION: 1 S .C. S . TYPE-lA RAINFALL DISTRIBUTION ENTER: FREQ (YEAR) , DURATION(HOUR) , PRECIP (INCHES) 10, 24, 2 . 9 -- - ------ -- ---- -- -- ---------------------------- - - - --- -- - -- - - - -- - - - - - - - ******************** S .C. S . TYPE-lA DISTRIBUTION ******************** ********* 10-YEAR 24-HOUR STORM **** 2 . 90" TOTAL PRECIP . ********* - --- --- -- - - - -- ----- - ------------ ---- ------------ ----- - --- - ---- ----- - - - ENTER: A(PERV) , CN(PERV) , A(IMPERV) , CN(IMPERV) , TC FOR BASIN NO. 1 0 . 65 , 86 , 0 . 06, 98�12 . 06 DATA PRINT-OUT: � AREA(ACRES) PERVIOUS IMPERVIOUS TC (MINUTES) A CN A CN . 7 . 6 86 . 0 . l 98 . 0 12 . 1 PEAK-Q (CFS) T-PEAK (HRS) VOL (CU-FT) . 28 7 . 83 4297 ENTER (d: ] [path] filename [ . ext] FOR STORAGE OF COMPUTED HYDROGRAPH: A: lOYRDX-JONES SPECIFY : C - CONTINUE, N - NEWSTORM, P - PRINT, S - STOP C - -- - - - - - - - - ----- - ---- ------------------------- - --- - ----- -- --- -- - - - - - - - ENTER: A(PERV) , CN(PERV) , A(IMPERV) , CN(IMPERV) , TC FOR BASIN NO. 2 0 . 3�, 86, 0 . 34, 88�8 . 1 DATA PRINT-OUT: AREA(ACRES) PERVIOUS IMPERVIOUS TC (MINUTES) A CN A CN . 7 .4 86 . 0 . 3 98 . 0 8 . 1 PEAK-Q (CFS) T-PEAK (HRS) VOL (CU-FT) . 38 7 . 83 5410 ENTER [d: ] [path] filename [ .ext] FOR STOR.AGE OF COMPUTED HYDROGRAPH: A: lOYRD-JONES SPECIFY: C - CONTINUE, N - NEWSTORM, P - PRINT, S - STOP /� Z /�d� �ar��s ��v�� /�l� 7 - SBUH/SCS METHOD FOR C STORM OPTIONS : 1 - S .C.S . TYPE-1A 2 - 7-DAY DESIGN STORM 3 - STORM DATA FILE SPECIFY STORM OPTION: 1 S .C.S . TYPE-lA RAINFALL DISTRIBUTION ENTER: �'REQ (��AR} , DURATION(HOUR) , PRECIP (INCHES) 100, 24, 3 . 9 --------- ---- ------ ------- ------------------ - ----------- ------- ----- -- ******************** S .C.S . TYPE-lA DISTRIBUTION ******************** ********* 100-YEAR 24-HOUR STORM **** 3 . 90" TOTAL PRECIP . ********* --- ----- - --------- -------------------------- - ----------- - ------ ------- ENTER: A(PERV) , CN(PERV) , A(IMPERV) , CN(IMPERV) , TC FOR BASIN NO. 1 . 65, 86, . 06, 98, 12 . 06 DATA PRINT-OUT: AREA(ACRES) PERVIOUS IMPERVIOUS TC (MINUTES) A CN A CN . 7 . 6 86 . 0 . 1 98 . 0 12 . 1 �) r d`l'� Cf% t a+��r� PEAK-Q (CFS) T-PEAK(HRS) VOL (CU-FT) u���D �v 2 �, S 1� �'f� .44 7 . 83 6585 -��`'i0o'Z i%.tic(4 Lv.1c(f ENTER [d: ] [path] filename [ .ext] FOR STORAGE OF COMPUTED HYDROGRAPH: B:EX100YR-ABE .' ��-- FILE ALREADY EXIST; OVERWRITE (Y or N) ? Y SPECIFY: C - CONTINUE, N - NEWSTORM, P - PRINT, S - STOP C ------------------- ------------------------------------------ --------- ENTER: A(PERV) , CN(PERV) , A(IMPERV) , CN(IMPERV) , TC FOR BASIN NO. 2 . 3�, 86, . 3�, 98, 8 . 07 DATA PRINT-OUT: AREA(ACRES) PERVIOUS IMPERVIOUS TC (MINUTES) A CN A CN . 7 .4 86 . 0 . 3 98 . 0 8 . 1 PEAK-Q (CFS1 T-PEAK(HRS) VOL(CU-FT) . 55 7 . 83 7820 ENTER [d: ] [path] filename [ .ext] FOR STORAGE OF COMPUTED HYDROGRAPH: B:ID1ll0�gRPA�E SPECIFY: C - CONTINUE, N - NEWSTORM, P - PRINT, S - STOP / S KING COUN 'I' Y, WASHINGTON, SURFACE WATER DESIGN MANUAL o A licensed septic system designer or suitably trained person working under the supervision of a licensed Professional Engineer shall make an inspection of the soit after the system is excavated, before the trenches are filled with rock to confirm that suitable soils are present. Method of Analysis/Length of Roof Downspout Infiltration Trenches I The length of trench required is based on the U.S.D.A. soil texture class, the roof area and the site location, using Table 4.5.18. The length of trench required is determined by dividing the roof area by 1000 and multiplying by the unit length I from the chart for the soil type and multiplying the result by the regional scale factor k shown in Figure 4.5.1 D. The trench length L is computed using the following equation: L = (AR/10001(I)(ky Where: AR = area of the roof tributary to the system, ft�. (Note: a typical single-family residence has a roof area of approximately 2,000 ft2.) I = the unit length of trench required per 1,000 ft� of roof area from Table 4.5.1 B, ft"' k = the regional scale factor from Figure 4.5.1 D. TABLE 4.5.1B INFILTRATION TRENCH LENGTHS FOR RESIDENTIAL ROOF DOWNSPOUT INFILTRATION SYSTEMS i i ISoil Texture Class (U.S.D.A.) Lineal Feet of Trench per 1000 Lineal Feet of Trench ft� of Roof - Sea Tac per 1000 ftz of Roof - Landsbur 1. Coa�se sands or Cobbles 15 20 2. Medium sand —� 25 30 3. Fine sand, loamy sand 60 75 4. Sand loam 100 125 5. Loam 150 190 Example: Proposed residence located at Kent East Hill Roof area (AR) = 2,000 square feet; Soil Texture Class = loamy sand; From Table 4.5.1 A, 60 ft t�ench/1000 ft' of roof, from Figure 4.5.1 D k = 1.0 L = (20001100011601{1.0) = 120 ft (Note: could be accomplished by two trenchesl. � 4.5.1-3 11/94 KING COUNTY, WASIIINGTON, SURFACE WATER DESIGN MANUAI. FIGURE 4.S.1D REGIONAL SCA[.E FACTORS __ _, ._ � � �`�-r`#�" '� i,i'!4"� �r �.�.� �- —�� r j ' �l/"�. __. � `� t � '�,, � .'- ( 3 �� � � _ - I a l •I ,��a.,_ �I' � I ��l: L }� 1 ,.. __ 1 �...� , � ;� ;.� � � .� G - ,�• � / �� ,f � - " . , ��I; E � '� � ,,.._, �� _ � ��; ��-� i` ' ,;;= a�' �l . � g �f�� � I' �s C .�(�^ � � -�-�,� ;� - 1 � , . , ` � ,� � .,' � �•` �'� � �� �. r:r , � ��- �� '` -_� �� ��, � -) ,r?� `:-� , � - �. ��� ' / �� � r T= ( ��`S� �� F; �-�� � °� j�� •' � �. ' ,r ' ,' _ -- - - � �, �_� ` -,� �.,�' �', . � i � � ,.� � ,�i � ,� � yti' � -11 '� _� ' ` _ - - ���„ �, 1 - �'� �.J 'l �_ ��'� �r� � - � � � t�" � ,�r� �a� ' ° �A�- � �°� � � �� � �,�� ,` � _ / �— �Y �Z I .'L. rl ` 1 I. MA� —�� ll � f� � r • �. [ _a • � �� � �i _ r�p 4�� _..� �T�_ I 1 . � , i I- '` �,w, ) 1 _ � � `�� — ; �n i 1 _ � ',. q1\ _ _ ,� / � '� � �- /, •_ �' ���� �-'� ,�,� J�., , j/ ���� � (� � �"�.����� �' i ��, ' t; f( ; � �,; �i �( � � �' r�_ ;s�� `, / .� " � _ \ � .�7 '"k��n. I , a� � � � ��� � ' ��a) J �a - ,F _ ( �_ �q `_-. � . -•r-. � .� � � , ��,�, 1 _ � ��� � - -�- � � < < � �.�..,,:., �, � � t�� .•,.� r,-� , `� - _ � � �j�-_ o r SEATAC * i� .�` r��_ �' � ^ ` _ � I � �,�{ 1aa 7' �°�� _ G,� ,� �'�, — � � `I , �� \ `x ;� �f �.�� �I,._ ,f;; �� �•��! l, y,`�_- c,,=... _ � �. � ' _ ` � -� � ' _ �F � ,. � ,f G� �� F �� _��" . 1 �:r. I,and+ B ;� � �',•� - «,.n.rt - _ �� `C � �;�.• b`" _ ''p �,.� /� J �',/ � - . - `� 1 I i � � a�_l� �.� �= ' —,`,` ) .' � , �; r ( �, . , ( L_ -�' ' f �_�'li � , � � � ,-�_ f__ ,� _J �� ���",, �j -�..` i;���; � ��, �� �l' �.. _ �;� _� ` _a ' 'j ,' �� t �f�.< <' - ; ` � r > \ ti � �i =� ''�' S. . ,i q� , �`�lll� � � � ,�. �. �� �.�� — �\ r% -il.�. ir ..� �� `�'.:.-� ,. --- � � � ��'��� � —_ � �� ��� � �� -� ���� ��, ��� _ �•���1 ._.. � ��y . f. 1�A � ' '��� "'.�J�� ��1 � � �-� � �. /' ��� - �1 .. � �� C ,\� ' . [y�' - . ,l !\ _ � // _C � i �-� l ..j.,._.l �(�� si J � • �` � , • � n 1-Z I � S �__� ° 'i;�`Y � ' r�� ' ��:__ r_ ���,�: ,s � � " 1 � �� > � �) l. I A•�,'•� 4-., .i • -.{" 1 � � � � ,,i ST t.l - I; `'� ? ��� �' k 1- � � �_� sT ►.o )� � -w,: . , ._l ( �-. _�- ���� �"I 1' j: , , , ��,�' . , � , � � _ . , . , -�. �; _��:..- i r• N � , � .� `\ __' r. ,� ST LO LA 0.8 `2� ��� . C:•.; -� ..�� ,.:s; LA 1.1 � � i i M0.ES Q� � �– 3 � 5 6 '� _},, �.... ^�� LA 0.9 � LA 1.0 1 I/94 � 4.5.1-7 CB TRENC , �I� � �TRENCH L Jf- L-J C B POSSlBLE ALIGNMENTS PL � N �I� w ROOF DRAlN 08SERVA TION WELL N. T.S. ROOF ,--- -------------------� I 1 I I . , lNFIL TRA TION TRENCH� 6"r� PERFORA TED PIP�SUMP OR CA TCN BASIN W/SOLID L1D (C.P.E.P. SINGLE WALL ACCEPTABLE) �ROOF DRA1N PR ��l L E �r� w SPLASH BLOCK !Y.T.S. CA TCN BASIN SUMP Wl TH OBSERVATION WELL SOLIO UD \ A SHEET COVER MA TERIAL \� ----\�\�\\��\ �� -----\--- ------ -- \ ' � M/N. M1N. � , . LEVEL . � 1' MlN. i f' i�.. � . . M/N. l:'• � '~- J F1NE MESH LEVEL SCREEN A 5. 6" PERFORA TED PlPE (C.P.E.P. SINGLE WALL � ACCEP TABLE) VARlES (SEE PLAN) 10' MNY. OBSERVATION WELL Wl1N METAL CAP & LOCK. 6" PVC PIPE �\ :: 6•M�N : � � COMPACT BACKFILL (PERFORA TED) \\ . . � . � \ WRAP 7RENCH�� 6"� PERFORATED PIPE EN77RELY W1TH WASHED ROCK 3/4"--1-1/2" FIL TER FABRIC. /�� 2' s�cT� oN � - � V. CONVEYANCE SYSTEM ANALYSIS I� The proposed storm system consists of one 12-inch pipe (double wall pipe) conveying runoff from the site. The 100-year developed runoff from the site calculated at 0.55 cfs. The 12-inch pipe proposed for this development is designed at a slope of 1.0 percent slope. The attached calculation determined that the proposed pipe at a minimum of 1.0 percent slope carries 3.86 cfs, more than 0.55 cfs anticipated for 100-year flows during post development. - /� Circular Channel Analysis & Design Solved with Manning' s Equation Open Channel - Uniform flow Worksheet Name : JONES SHORT PLAT Comment : DETERMINE CAPACITY OF 12-INCH PIPE Solve For Full Flow Capacity Given Input Data: Diameter. . . . . . . . . . 1 . 00 ft Slope . . . . . . . . . . . . . 0 . 0100 ft/ft Manning' s n. . . . . . . 0 . 012 . Discharge . . . . . . . . . 3 . 86 cfs �— T/d� �+ � �j.sSG�� 6�� Computed Results : Full Flow Capacity. . . . . 3 . 86 cfs Full Flow Depth. . . . . . . . 1 . 00 ft Velocity. . . . . . . . . . 4 . 91 fps Flow Area . . . . . . . . . 0 . 79 sf Critical Depth. . . . 0 . 84 ft Critical Slope . . . . 0 . 0097 ft/ft Percent Full . . . . . . 100 . 00 0 Full Capacity. . . . . 3 . 86 cfs QMAX @. 94D. . . . . . . . 4 . 15 cfs Froude Number . . . . . FULL Open Channel Flow Module, Version 3 . 4 (c) 1991 Haestad Methods, Inc . * 37 Brookside Rd * Waterbury, Ct 06708 /7 11 VI. SPECIAL REPORTS and STUDIES: f8 i2 , VII. BASIN and COMMUNITY PLANNfNG AREAS VIII. OTHER PERMITS /9 IX EROSION & SEDIMENTATION CONTROL The contractor shall install silt fences along the perimeter of the site as indicated on the Temporary Erosion Sedimentation Control Plan, with construction entrance 12" thick made of quarry spalls as indicated on the construction plans. Sediment Trap (if required) SA=FS*QZ/Vs SA— Sediment Trap Area FS —Factor of Safety = 2.0 QZ = 2-year flow in post-developed Vs = 0.00096 ft/sec sA = (z) *o.�9��0.00096� = 396 square feet (Required) -20 14 X. [30ND QUANTITIES WORKSHEET 2 / � 15 X1. MAMTENANCE and OPERATIONS MANUAL I � Z� � IV. FLOW CONTROL AND WATER QUALITY The following calculations conclude that the 100-year peak flow difference between the pre-developed flow and post-developed flow is less than 0.5 cfs. In accordance with 1990 King Count Surface Water Drainage Manual detention is not required. The following calculations include: Basin areas Time of Concentration Isopulvial graphs for 2, 10 and 100 year storms Pre-developed and Post-developed hydrographs The soil type found on this site is classified as Indianola(InC) and is good for infiltration system. We therefore recommend installation of single family infiltration system for the three new homes to be built on Lots Z through 4 inclusive. In discussing this matter with the owner, we ascertained that the size of h;,mes proposed on the vacant lots will average about 2000 square feet on both stories. The surface area of each house will be sized at 1000 square feet, and the roof infiltration system will be designed to accommodate a 1000-foot home. Based on Section 4.1.1-3 of 1990 KCSWDM, the size of the trench is 25 feet long per 1000 square feet of roof for the Seatac regional area (See Figure 4.5.1B below). WATER QUALITY FACILITY Required Volume = 649 c.f. ( see attached document) Available Volume = 700 c.f. ( see attached calculation) Surface area Requirement based on 1.0% of total impervious surfaces is calcufated at 14,374 s.f yields an area of 144 s.f Surface area available = 144 s.f ( see attached calculation) n I �^,� j � �%�N�� ����� � I � ` _ �� i �- �' �� - � _ __ T � �;VAILA��E SJR�ACE �?�EA �- 144 S.Y. GK �. �`JAILAB�.E .>�L;Jt,�� 2-4�" MANE-���ES �5L� X 12.;6 -- 1�8 C.'-. 2---2L�= �.�� .3+�"CP�1? 4LF X ?.i;5� = 2� C.=. �� LF C� 4•8"�!�P �JEAU �TC��A.GE A��r� c��JL'�``1 4;�i... Y� :C).;4 = �-?�3 C;.F�. A`,t�(�.��3:��. �ft.;LU?v!� _ l0�� C.f�.> 54r C.�. ........�. � ,--�''----- "`,�_ / �L.�=�� ..�__ 3.��s �t.,'-�+.� S��i�Cy{�i�:_ / �\ � �` / � + i � � '� I i 1 � �=�� S�O�AGE �,RE�, � � l :0.74 ;.�.;LIt�IEt�� F��:��T J t � � f l � i f ' i / \. / ,j� F!_ �.;0 ::;�.�I{���:P�T � .�` �� ' �� � I �------.____.__.._._-------'''� ! 48"� CI��' �'"0�7AG� PlF� CRG�S S��CTI:.Z'�J Af�ER = 3�.�Q �.F j��� DEti(:� =�TC;R���: A!?E:A = �.C:.?4 c�.F�;�:_F a SBUH/SCS METHOD FOR COMPUTING RUNOFF HYDROGRAPH STORM OPTIONS : 1 - S . C . S . TYPE-lA 2 - 7-DAY DESIGN STORM 3 - STORM DATA FILE SPECIFY STORM OPTION: 1 S . C. S . TYPE-lA RAINFALL DISTRIBUTION ENTER: FREQ (YEAR) , DURATION(HOUR) , PRECIP (INCHES) 1, 24, 0 . 67 ------------ - - - --- - - --- --- --- ----- ------------- - --------- - ----- - -- - - -- ******************** S .C.S . TYPE-lA DISTRIBUTION ******************** ********* 1-YEAR 24-HOUR STORM **** . 67" TOTAL PRECIP. ********* ---------------------------------------------------------------------- ENTER: A(PERV) , CN(PERV) , A(IMPERV) , CN(IMPERV) , TC FOR BASIN N0 . 1 0 .37, 86 , 0 . 33 , 98, 8 . 1 DATA PRINT-OUT: AREA(ACRES) PERVIOUS IMPERVIOUS TC(MINUTES) A CN A CN . 7 .4 86 .0 .3 98 . 0 8 . 1 PEAK-Q (CFS) T-PEAK(HRS) VOL (CU-FT) �j / G �/� . 04 7 . 83 649 �"—' ���lrt `lcf�lv, fp�U�e-. ENTER [d: ] [path] filename [ .ext] FOR STORAGE OF COMPUTED HYDROGRAPH: �q�P.r� �r.�a l�� — � 3 _- 2'b� _ �. �J /r� c�7�� G'/✓I�C.�� ���� � �e����D.�S���.v�� l�.�-� Grf�" I �c� � � �'ye�. a � �Z ,�� _ � �Z �'`� �•� • !�o/vm�-= �y.9��.� L��� D� �P�- � ��.� ��z = �, �,� . �f�