The URL can be used to link to this page

Home My WebLink AboutPLAT OF EAGLE RIDGE <S, � 4205 148th Ave.N.E.Suite 200 CORE Bellevue,Washington 98007 425.885.7877 Fox 425.885.7963 DESIGN PLAT OF EAGLE RIDGE RENTON, WASHINGTON for PACIFIC HUTS AND CASTLES, INC. STORM DRAINAGE CALCULATIONS AS\ w Project No.: 99102 �� =r Prepared by: Brennan P. Taylor, P.E. y Approved by: David E. Cayton, P.E. o Date: October 2000 �aMAL��... 1=�12-O 1 11 00 ENGINEERING • PLANNING SURVEYING PLAT OF EAGLE RIDGE RENTON,WASHINGTON STORM DRAINAGE CALCULATIONS TABLE OF CONTENTS Section I. Introduction II. Offsite Analysis A. Upstream Drainage B. On-Site Drainage C. Downstream Drainage III. Flow Control and Water Quality Analysis and Design A. Hydraulic Analysis B. Detention Routing Calculations C. Water Quality Calculations IV. Conveyance System Analysis and Design V. Erosion Control Calculations I. Introduction The Eagle Ridge project is located in the southeast quadrant of the intersection of SE 128'h Street (NE 40'St.) and 148"Avenue SE in Renton, Washington. This parcel is approximately 4.2 acres and was recently annexed to the City of Renton in the Maplewood Annexation. An existing asphalt contractor occupies the adjacent property east of the site. The south adjacent parcel includes the proposed Plat of Maplewood. See Figure 1 for vicinity map. The majority of the site is currently young alder saplings, Douglas fir, western hemlock and other trees. The site generally slopes to the southwest at approximately 5%. No wetlands exist on-site. The proposed improvements include the construction of 17 single family dwellings with related grading, utility, and road construction. Onsite generated storm water runoff will be directed to a combination wetpond/detention pond in the southwest corner of the site. g w 1 9f 40111 09S y 1� I y 3 Ar lilll M I I I / • " 3S AY NIMI'Jh IU6/ OMZ91 ' l ———� I jc 3S Al Gi x1091— W v- ---.— VI L— -- 1—.�— �rQ -- 3 —1 » I a R E Linr x•M �3L �, i- e� «un Q? I N I I I i 3S AV N19S1 4" Zvit�, a _ ..' SITEC n� i t W G a AV ¢ a �+ :i"t.i.�1 may Aau.:.l.}.L'SYY;:}:iii:^.i::"si1 ►'35 I I zc » NJmI n 1 Is UAV 35 AY N10S1 °J 1 r i IC ;If v not wlAw mat u not LnrxlA" 1 7 I 1� nr xurt ( I 3f AV x1Ml I •<1 e� » G ;i✓ p I IA I mod' 3s AY Nlisl I I G I YI I v Atip pal. i I I - I I 3S AV C 1441r ^ if Ai OIOI L AY q ' l j M G G 6 ix -- --•- >: i a r it AY G"W 1 9 l 34 V L 1l V/ r l M ' toUAW XMI :•.. `c - I Gt I Ls�.x1/u .r i• r ..c. e . Krn r ,41YEY1� . 3N I I 1YI Y Ala w �:i�i! z I w SL 1 a� i 3fb > f•M:Y f,- [i ri Q "It ILG 4S �'� .L'�AV - C►' x Y r a < _—.__r( �3-. I t is Ar ('s. s ► t � rA 3S Nl t Lf n ux��''i> ,.: .y Wpk •� �! 1 W7166 iv I V ` Arwra MA. I E • h� �" Y� �>xMo iTi r AV n 311 AY NiiW]Yv N A Y •3° "„W' VICINITY MAP I A� I 3 I ot. EAGLE RIDGE a►. It CORE DESIGN NO. 99102 Y>,r G�pN �; it nY . H. Offsite Analysis A. UPSTREAM DRAINAGE There are no upstream tributary areas draining onto the site. Runoff from SE 128" Street right-of-way drains to the south roadway ditch and flows west, off-site. This roadside ditch is drained to the southwest into a separate drainage basin via drainage ditches and culverts. Runoff from the adjacent asphalt company flows south onto the Maplewood property. See Figure 2 for Existing Drainage Basin Map. B. ON-SITE DRAINAGE Stormwater runoff on-site generally flows in a southwesterly direction over forested terrain to the 148t'Avenue SE right-of-way. 148'Ave SE is currently under construction as part of the Maplewood Property project. There are no existing channels on-site all existing flows are sheet flow to the southwest. C. DOWNSTREAM DRAINAGE Runoff from the project drains onto the Maplewood Property site. The Maplewood Property project will improve 148 h Ave NE on the west side of the site and install a storm drainage conveyance system which accept runoff from the Eagle Ridge project. A 12" pipe form the new 148'Ave SE conveyance system will be stubbed to the southwest corner of the site (Inlet 71A of the Maplewood Property project). As mentioned earlier, the Maplewood Property is currently under construction. The storm water runoff from the site is conveyed approximately 3500 feet through the newly constructed storm drainage system of the Maplewood Property. The Maplewood storm system discharges to a pair of 24 culverts located immediately south of the intersection of 148`h Ave SE and SE 136"' St. The twin 24" culverts convey storm water to a grassy swale which runs southeast and then south for approximately 700 II. Offsite Analysis (cont.) C. DOWNSTREAM DRAINAGE (cont.) feet until it reaches a 30" CMP Pipe on the north side of the Plat of Briar Hills. This 30" CMP pipe directs the flows through the Plat of Briar Hills at varying slopes of 0.6 to 3.8% (see Figure 3 for Downstream Drainage Map). There is one "off-line"detention pond approximately 4900 feet downstream which is thoroughly grassed and shows no sign of recent inundation. The 30"inch CMP ultimately drains to another"off-line" detention pond approximately 5800 feet downstream near the south end of Briar Hills. This detention pond shows evidence of recently detained flows filling up the bottom 2 feet of the pond (the pond has seven feet of available storage). This pond releases to a rip-rapped discharge at the top of a natural drainage ravine. The ravine eventually discharges to the Cedar River approximately one and a half miles downstream of the subject property. The downstream flow path has no apparent signs of flooding or extensive erosion. loop 0 a.- I-,15 NN cn 350 k4.rivi:i:.iii:wtCj•�'•• � . �a a {; Cw .a.. •� t =i •� e�.�9 oa�r1 s a DOWNSTREAM DRAINAGE MAP !� •- � - —� �, j EAGLE RIDGE 00 N CORE DESIGN NO. 99102 W III. Flow Control and Water Quality Analysis and Design A. Hydraulic Analysis The drainage analysis was modeled using the King County Runoff Time Series software. The onsite soils are Alderwood, hydrologic group C and KCRTS group Till. See soils map included in Section 3 Offsite Analysis of this report. The site is located in the Sea- Tac rainfall region with a location scale factor of 1.0. Existing Conditions The site is 4.21 Acres in size. The existing ground cover is till-forest. The following information was used for generating time series and flow frequencies. EXISTING CONDITIONS Total Area=4.21 acres 99102ex GROUND COVER AREA acre Till-Forest 4.21 Onsite existing conditions flow frequency analysis: PEAK FLOW RETURN CFS PERIOD 0.340 100 year 0.315 50 year 0.265 25 year 0.204 10 year 0.196 5 year 0.172 3 year 0.117 2 year 0.072 1.3 year 0.007 1.1 year /S.E. 128TH ST 4 1AC &Jg_4j�+ iT) 4 * 4@0.52 LIJ •P •� ' i �0 0.7 OD .462 7`1 20' ACCESS --iO' ACCESS UTILITY EASEMENT Ap UTILITY EASEMENT` JF vs, 3 10 M 1.2 j SHOP I/CGNC F� Li 2 1.8 00 2 21- 14 Lr 14 19 W 429.81 0- C? 16 17 i + STORM ORAINAGE OPEN SIA \\"� 3 0, • N 88': ON-SITE 0 I'd BASIN MAP e _.0P eD • ;IZZI 0 1p, & • EAGLE RIDGE jlj At,c-& P�� ov f. CORE DESIGN NO. 99102 Flow Frequency Analysis Time Series File:99102ex.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency Analysis------- Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) Period 0 .265 2 2/09/01 18:00 0.340 1 100.00 0.990 0.072 7 1/06/02 3 :00 0.265 2 25.00 0.960 0.196 4 2/28/03 3 :00 0.204 3 10.00 0.900 0.007 8 3/24/04 20:00 0.196 4 5 .00 0.800 0.117 6 1/05/05 8:00 0.172 5 3 .00 0.667 0.204 3 1/18/06 21:00 0.117 6 2.00 0.500 0.172 5 11/24/06 4 :00 0.072 7 1.30 0.231 0.340 1 1/09/08 9:00 0.007 8 1.10 0.091 Computed Peaks 0.315 50.00 0.980 SHEET NO. 11 KING COUNTY AREA, WASI (RENTON QUADRANG J Anu_ ISSAQUAH 12 Mi. 10' 1 680000 FEET 11220 7130"�^ AgD i ghlanSeh : : .. AgC r. ``••.` .� •',1 ,9 423• AgC •i. 5 r;• .1 .. Age •_• .1 I • An o u% ■ Trailer ii: -n.EvB I ♦�■ ■• i . ' ark:- .ii = ii° .B 'iiBM 4WXr� 11 �-----T— •ii I• 5%6 • �Greenwood[;e , ••� ,•,•, I 180 000 ABC FEET iC - �. u An nvEt. 'SPIT aaa;l 11 raffia \ p ' a 121: aa\ n J n •15•- - - -- Ev C �lI AkF xa' ��°,r P •, •r Is I l�r alir Py AkF a'`.• I . el • I BM ti •8 ' '•,ti• ``I• �i : Eve If AkF Py CO/f Cor, I •'il EvB I 1i - -\•f gC n• / r� •AkF J x• Rh ° Py:i Ma AkF Z AgD` �• _ Py _ -\•��A`a,=AkF - _ _. J r 'o N o .• Ma > as ` Py 21 h P�• Eliot y a° 4` i`ii' I I __ , �I •o' Py Rh J �� sa A C I z x glop �b •t1� I ur 0-\N a g \-``` ••AkF i u°zU AkF � Ng � F Park P .,pVE �F`p .�a I ■ � y 169 EvC ABC I e 7 ii I M ( B` AgD AkF 2 ,• A e J I KING COUNTY AgC AgD _ SOILS MAP 1 BMp �v 42e IFc I EAGLE RIDGE AmC I 0' Age` . I 1 27 Pme I „r 492 CORE DESIGN No. 99102 1 I ' I r I I 3.2.2 KCRTS/RUNOFF FILES METHOD--GENERATING TIME SERIES TABLE 3.2-2.B EQUIVALENCEBETWEEN SCS SOIL TYPES AND KCRTS SOIL TYPES SCS Soil Type SCS KCRTS Soil Notes Hydrologic Group Soil Group Iderwood A B A C A D C Till Arents,Alderwood Material (AmB, AmC) C Till Arents, Everett Material (An) B Outwash 1 Beausite (BeC, BeD, BeF) C Till 2 Bellingham (Bh) D Till 3 Briscot (Br) D Till 3 Buckley (Bu) D Till 4 Earlmont(Ea) D Till 3 Edgewick (Ed) C Till 3 Everett(EvB, EvC, EvD, EwC) A/B Outwash 1 Indianola (InC, InA, InD) A Outwash 1 Kitsap (KpB, KpC, KpD) C Till Klaus (KsC) C Outwash 1 Neilton (NeC) A Outwash 1 Newberg (Ng) B Till 3 Nooksack (Nk) C Till 3 Norma (No) D Till 3 Orcas (Or) D Wetland Oridia (Os) D Till 3 Ovall (OvC, OvD, OvF) C Till 2 Pilchuck (Pc) C Till 3 Puget (Pu) D Till 3 Puyallup (Py) B Till 3 Ragnar(RaC, RaD, RaC, RaE) B Outwash 1 Renton (Re) D Till 3 Sala] (Sa) C Till 3 Sammamish (Sh) D Till 3 Seattle (Sk) D Wetland Shalcar(Sm) D Till 3 Si (Sn) C Till 3 Snohomish (So, Sr) D Till 3 Sultan (Su) C Till 3 Tukwila (Tu) D Till 3 Woodinville (Wo) D Till 3 Notes. 1. Where outwash soils are saturated or underlain at shallow depth (<5 feet) by glacial till, they should be treated as till soils. 2. These are bedrock soils, but calibration of HSPF by King County DNR shows bedrock soils to have similar hydrologic response to till soils. 3. These are alluvial soils,some of which are underlain by glacial till or have a seasonally high water table. In the absence of detailed study,these soils should be treated as till soils. 4. Buckley soils are formed on the low-permeability Osceola mudflow. Hydrologic response is assumed to be similar to that of till soils. 1998 Surface Water Design Manual 9/1/98 3-25 S,; CTION 3.2 RUNOFF COMPUTATION AND ANALYSIS METHODS KCRTS Land Cover Types KCRTS supports four land cover types:forest,pasture, grass, and impervious. 77hese cover types shall be applied as specified in Table 3.2.2.0(below). TABLE 3.2.2.0 KCRTS COVER GROUPS AND AREAS OF APPLICATION KCRTS APPLICATION Cover Group Predevelo ment P Post-Development Forest All forest/shrub cover, irrespective of All permanent(e.g., protected by age. covenant or SAC)designation) onsite forest/shrub cover, irrespective of age, planted at densities sufficient to ensure 80%+canopy cover within 5 years. Pasture All grassland, pasture land, lawns, and Unprotected forest in rural residential cultivated or cleared areas, except for development may be considered half lawns in redevelopment areas with pasture, half grass. predevelopment densities in excess of 4 DU/GA.. Grass Lawns in redevelopment areas with All post-development grassland7andpredevelopment densities in excess of landscaping and all onsite foresnd 4 DU/GA.. not protected by covenant or SASA designation (except in rural areas as noted above). Wetland All delineated wetland areas (except All delineated wetland areas(except cultivated/drained farmland). cultivated/drained farmland). Impervious(') All impervious surfaces, including All impervious surfaces, including heavily compacted gravel and dirt compacted gravel and dirt roads, parking roads, parking areas, etc., and open areas, etc., and open water bodies, water bodies (ponds and lakes). including onsite detention and water 7 quality ponds. c>> Impervious acreage used in KCRTS computations should be the effective impervious area (EIA). This is the gross impervious area multiplied by the effective impervious fraction (see Table 3.2.2.E, p. 3-28). Non-effective impervious areas are considered the same as the surrounding pervious land cover. The following four factors were considered in specifying the above land cover types to be used in hydrologic analysis with KCRTS: • Cover types are applied to anticipate ultimate land use conditions. For example, probable clearing of woodland after development is nominally complete suggests that the post-development land use be, specified as grassland(either pasture or grass)unless the forest cover is protected by covenant. • In areas of redevelopment,there are often significant changes between the predevelopment and post- development efficiencies of the drainage system. For example,in conversion of low density residential areas to higher density land use, impervious areas prior to redevelopment may not be efficiently connected to a drainage system(e.g., downspouts draining to splash blocks, ditched instead of piped roadway systems). These problems are addressed by defining an"effective impervious fraction"for existing impervious areas and by generally requiring predevelopment grasslands to be modeled as pasture land. 9/1/98 3-26 1998 Surface Water Design Manual .5ECTION 3.2 RUNOFF COMPUTATION AND ANALYSIS METHODS FIGURE 3.2.2.A RAINFALL REGIONS AND REGIONAL SCALE FACTORS ST 1.0/ ST 1.1 ST 1.0 LA 0.8 LA 0.9 LA 1.0 LA 1.2 ' ��- rt'I,r•r. SNOXONISX COUNTY KINO COUNTY Awj X j FS 7'jiFi -'A r .. ELLE.VUE` xx. IIRRJ .,re I 6 V!1it t i+ rmmmN — r r _ NTO I o. wn f S TAC'� Ir' �•� 1 /// aRasmX LANDSBURG � r uNT:: f MOURN �� Y+•••+"• lLACk ST 1.1 `R" r YAC '=1KlNO COUNTY' 1 PIERCE COUNTY � ( ST 1.0 Regions and LA 1.oi Rainfall Re g LA 0.8 Regional Scale Factors LA 0.9 u Incorporated Area LA 1.0 LA 1.2 —c:z River/Lake Major Road 9/l/98 3-22 1998 Surface Water Design Manual Developed Conditions The developed site will consist of 17 single family residences with associated roadway and utilities The impervious area was calculated using the criteria in the 1998 King County Surface Water Design Manual page 3-27 which states that 4000sf of impervious per lot should be assumed. All other impervious surfaces were measured by a planimeter. D. Impervious Area Delineation Onsite road and sidewalk 28,960 sf Impervious area of lots 4000sf*17 lots 68,000 sf Total impervious area 96,960 2.22 acres The input used for the KCRTS analysis is summarized in the table below: DEVELOPED CONDITIONS Total Area=4.21 acres 99102dev GROUND COVER AREA acre Till-Grass (Landscaping) 1.99 Impervious 2.22 Onsite developed conditions flow frequency analysis: PEAK FLOW RETURN CFS PERIOD 1.47 100 year 1.27 50 year 0.865 25 year 0.857 10 year 0.758 5 year 0.716 3 year 0.716 2 year 0.590 1.3 year F-- 0.565 1.1 year Flow Frequency Analysis Time Series File:99102dev.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency Analysis------- FlowRate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) Period 0.716 5 2/09/01 2 :00 1.47 1 100 .00 0.990 0.565 8 1/05/02 16:00 0.865 2 25 .00 0.960 0. 865 2 2/27/03 7:00 0 .857 3 10 .00 0 .900 0.590 7 8/26/04 2 :00 0.758 4 5.00 0 .800 0.716 6 10/28/04 16:00 0.716 5 3 . 00 0.667 0.758 4 1118106 16:00 0.716 6 2 . 00 0.500 0.857 3 10/26/06 0:00 0.590 7 1.30 0.231 1.47 1 1/09/08 6:00 0.565 8 1.10 0.091 Computed Peaks 1.27 50.00 0.980 B. Detention Routing Calculations The detention/water quality facility will be a combination water quality and detention pond. Per the hearing examiner's conditions, the facility will be designed according to the Sept. 1998 KCSWDM instead of the 1990 KCSWDM that is normally required in the City of Renton. Since the level of protection was not specified by the hearing examiner, the detention portion of the pond will be sized according to a Level 1 Analysis (Conveyance Protection)using the KCRTS software. The Level 1 Analysis results in a 276% increase in detention volume from the 1990 KCSWM methods used in the preliminary storm drainage calculations. Sizing the pond by the 1998 KCSWDM and KCRTS Computer Software Reference Manual, the 2 and 10 year flows are matched. Since the KCRTS software is not very user friendly when custom stage storage relationships are used, the actual stage storage relationship was approximated with a trapezoidal pond having a similar stage storage relationship. The attached table shows the relationship of the Actual pond to the KCRTS trapezoidal pond. The flows to match for the 2 year and 10 year flow are 0.293 cfs and 0.505 cfs respectively. The following table summarizes the routing results. ROUTING RESULTS 2 year storm 10 year storm Qp allowable release cfs 99102 re 0.12 0.20 Qp into pond cfs 99102dev 0.716 0.857 Qp released from the design pond 0.0.12 0.20 cfs 99102out Pond live storage required CF 17,445 27,016 The control structure has 2 orifices to meet the detention criteria to match the 2 and 10- year storm events. The first orifice has a diameter of 1.64 inches. The second orifice is at a stage of 2.70 feet with a diameter of 1.54 inches. The primary overflow for the pond is the riser pipe within the control structure. The KCRTS program calculates the overflow over the riser when routing the hydrographs through the detention facility. This is evidenced by the fact that the riser stage is 3.7 feet and the maximum stage of the detention pond 3.86 feet. This translates to a maximum water surface of 442.86. The secondary overflow for the pond will be via a jailhouse weir. The overflow elevation for the 100-year developed flow will be calculated assuming there is a blockage in the control structure. The jailhouse weir can be analyzed using the standard weir equation: Q=9.739DH312 where Q =flow (1.47 cfs) D =riser diameter(4 feet) H=head above weir (ft) The head required to drive this flow is 0.11 feet. The CB structure is placed at the overflow elevation of 442.86. The secondary overflow elevation is therefore 442.86 + 0.11 =442.97. In addition to the secondary emergency overflow, the City requires an emergency overflow spillway. The primary overflow elevation is EL 442.86 (shown as design water surface on the plans). The secondary overflow flow elevation is EL 442.97 (shown as overflow elevation on the plans) which will also be the top of the rip-rap of the emergency overflow spillway. The required spillway length is calculated below. L=(QIOW(3.21H3/2)) - (2.4H) Qioo= 1.47 cfs (tributary to pond) Assume H=0.2'(minimum value) L= (1.47/(3.21(0.2)3/2)) - (2.4(0.2)) =4.64' The minimum length of overflow spillways is 6 feet. The emergency overflow elevation of the spillway is EL 442.97 + 0.2' =EL 443.17 POND VOLUME CALCULATIONS (LIVE STORAGE) CORE#99102 BUTTAR PROPERTY ELEVATION- INCREMENTALl TOTAL VOLUME VOLUME VOL SF CF CF GCF) 439.0 5080 0 O 5,776 440.0 6472 5,776 l" a 15,232 - ,n. ; 442.0 8760 21,008 20 58Q- 9 400 . 443.0 10040 30,408 Is 444.0 11420,; R 41,138 �t to S blrt5lJ ToTt1E l(7�l�' -r#4E Kcf--T-S iG.TvA L Poof) LS 5Ll i6e L� �L t 6 rr Ly eorsts ""tArl®/ . Retention/Detention Facility Type of Facility: Detention Pond Side Slope: 3 .60 H:1V Pond Bottom Length: 85.09 ft Pond Bottom Width: 60.34 ft Pond Bottom Area: 5134. sq. ft Top Area at 1 ft. FB: 11201. sq. ft 0.257 acres Effective Storage Depth: 3 .70 ft Stage 0 Elevation: 439.00 ft Storage Volume: 27040. cu. ft 0.621 ac-ft Riser Head: 3 .70 ft Riser Diameter: 18.00 inches Number of orifices: 2 Full Head Pipe Orifice # Height Diameter Discharge Diameter (ft) (in) (CFS) (in) 1 0.00 1.64 0.140 2 2.70 1.54 0.064 4.0 Top Notch Weir: None Outflow Rating Curve: None Stage Elevation Storage Discharge Percolation Surf Area (ft) (ft) (cu. ft) (ac-ft) (cfs) (cfs) (sq. ft) 0.00 439.00 0. 0.000 0.000 0.00 5134. 0.02 439.02 103 . 0.002 0.010 0.00 5155. 0.03 439.03 155. 0.004 0.013 0.00 5166. 0.05 439.05 258. 0.006 0.016 0.00 5187. 0.07 439.07 362. 0.008 0.019 0.00 5208. 0.09 439.09 466. 0.011 0.021 0.00 5229. 0.10 439.10 519. 0.012 0.023 0.00 5240. 0.12 439.12 624. 0.014 0.025 0.00 5261. 0.14 439.14 729. 0.017 0.027 0.00 5282. 0.15 439.15 782. 0.018 0.029 0.00 5293. 0.25 439.25 1317. 0.030 0.037 0.00 5399. 0.35 439.35 1862 . 0.043 0.043 0.00 5507. 0.45 439.45 2418. 0.056 0.049 0.00 5616. 0.55 439.55 2985. 0.069 0.054 0.00 5726. 0.65 439.65 3563 . 0.082 0.059 0. 00 5837. 0.75 439.75 4153 . 0.095 0.063 0.00 5949. 0.85 439.85 4753 . 0.109 0.067 0.00 6062 . 0.95 439.95 5365. 0.123 0.071 0.00 6176. 1.05 440.05 5988. 0.137 0.075 0.00 6291. 1.15 440.15 6623 . 0.152 0.078 0.00 6407. 1.25 440.25 7270. 0.167 0.081 0.00 6524. 1.35 440.35 7928. 0.182 0.085 0.00 6643 . 1.45 440.45 8598. 0.197 0.088 0.00 6762. 1.55 440.55 9281. 0 .213 0.091 0.00 6882 . 1.65 440.65 9975. 0.229 0.094 0.00 7003. 1.75 440.75 10681. 0.245 0.096 0.00 7126. 1.85 440.85 11400. 0.262 0.099 0.00 7249. 1.95 440.95 12131. 0.278 0.102 0.00 7373. 2.05 441.05 12875. 0.296 0.104 0.00 7499. 2.15 441.15 13631. 0.313 0.107 0.00 7625. 2 .25 441.25 14400. 0.331 0.109 0.00 7753 . 2.35 441.35 15182. 0.349 0.112 0.00 7881. 2.45 441.45 15976. 0.367 0.114 0.00 8011. 2 .55 441.55 16784. 0.385 0.116 0.00 8142. 2 .65 441.65 17605. 0.404 0.119 0.00 8273 . 2 .70 441.70 18020. 0.414 0.120 0.00 8340. 2 .72 441.72 18187. 0.418 0.120 0.00 8366. 2 .73 441.73 18271. 0.419 0.122 0 .00 8379. 2 .75 441.75 18438. 0.423 0.125 0.00 8406. 2 .76 441.76 18523 . 0.425 0.129 0.00 8419. 2 .78 441.78 18691. 0.429 0.133 0.00 8446. 2 .80 441.80 18860. 0.433 0.139 0.00 8473 . 2 .81 441.81 18945. 0.435 0.144 0.00 8486. 2 .83 441.83 19115. 0.439 0.145 0.00 8513. 2 .84 441.84 19200. 0.441 0. 147 0.00 8526. 2.94 441.94 20060. 0.461 0.157 0.00 8661. 3.04 442 .04 20933 . 0.481 0.165 0.00 8797. 3.14 442 .14 21819. 0.501 0.172 0.00 8933. 3 .24 442 .24 22719. 0.522 0.178 0 .00 9071. 3 .34 442 .34 23633 . 0.543 0.185 0.00 9210. 3 .44 442.44 24561. 0.564 0.190 0.00 9350. 3 .54 442 .54 25503 . 0.585 0.196 0.00 9491. 3 .64 442.64 26460. 0.607 0.201 0.00 9633 . 3.70 442 .70 27040. 0.621 0.204 0.00 9718. 3 .80 442 .80 28019. 0.643 0.671 0.00 9862 . 3 .90 442 .90 29013 . 0.666 1.520 0.00 10007. 4.00 443.00 30021. 0.689 2 .620 0.00 10152. 4.10 443 .10 31043 . 0.713 3 .920 0.00 10299. 4.20 443 .20 32080. 0.736 5.390 0.00 10447. 4 .30 443 .30 33133. 0.761 6.820 0.00 10596. 4.40 443 .40 34200. 0.785 7.360 0.00 10745. 4.50 443 .50 35282 . 0.810 7.850 0.00 10896. 4.60 443 .60 36379. 0.835 8.320 0.00 11048. 4.70 443 .70 37491. 0.861 8.760 0.00 11201. 4.80 443 .80 38619. 0.887 9.180 0.00 11355. 4.90 443.90 39762 . 0.913 9.580 0.00 11510. 5.00 444.00 40921. 0.939 9.960 0.00 11666. 5.10 444 .10 42096. 0.966 10.330 0.00 11823 . 5.20 444.20 43286. 0.994 10.690 0.00 11981. 5.30 444.30 44492 . 1.021 11.030 0.00 12140. 5.40 444.40 45714. 1.049 11.370 0.00 12300. 5.50 444.50 46952. 1.078 11.690 0.00 12462 . 5.60 444 .60 48206. 1.107 12.010 0.00 12624. 5.70 444 .70 49477. 1.136 12 .320 0.00 12787. Hyd Inflow Outflow Peak Storage Target Calc Stage Elev (Cu-Ft) (Ac-Ft) 1 1.47 ******* 1.18 3 .86 442 .86 28616. 0.657 2 0.72 ******* 0.54 3 .77 442.77 27734. 0.637 3 0.72 0.20 0.20 3 .70 442.70 27016. 0.620 4 0.76 ******* 0. 19 3 .46 442 .46 24768 . 0.569 5 0.86 ******* 0. 19 3 .40 442.40 24195. 0.555 6 0.45 0.12 0.12 2 .63 441.63 17445. 0.400 7 0.56 ******* 0.10 1.87 440.87 11553 . 0.265 8 0.59 ******* 0.08 1.30 440.30 7589. 0.174 ---------------------------------- Route Time Series through Facility Inflow Time Series File:99102dev.tsf Outflow Time Series File:rdout Inflow/Outflow Analysis Peak Inflow Discharge: 1.47 CFS at 6:00 on Jan 9 in Year 8 Peak Outflow Discharge: 1.18 CFS at 9:00 on Jan 9 in Year 8 Peak Reservoir Stage: 3 .86 Ft Peak Reservoir Elev: 442 .86 Ft Peak Reservoir Storage: 28616. Cu-Ft 0.657 Ac-Ft Flow Frequency Analysis Time Series File:rdout.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency Analysis------- FlowRate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) (ft) Period 0.535 2 2/09/01 15:00 1.18 3 .86 1 100.00 0.990 0.100 7 12/28/01 17:00 0.535 3 .77 2 25.00 0.960 0.188 5 2/28/03 7:00 0.204 3 .70 3 10.00 0.900 0.083 8 8/26/04 6:00 0.191 3.46 4 5.00 0.800 0.118 6 1/05/05 16:00 0.188 3 .40 5 3 .00 0.667 0.191 4 1/18/06 23 :00 0.118 2 .63 6 2 .00 0.500 0.204 3 11/24/06 8 :00 0.100 1.87 7 1.30 0.231 1.18 1 1109108 9:00 0.083 1.30 8 1.10 0.091 Computed Peaks 0.965 3 .83 50.00 0.980 C. Water Quality Volume Calculations Based on the location of the site, "Basic Water Quality Treatment' is required for sizing the wetpond. The required volume of dead storage will be designed per KCSWDM Section 6.4.1.1. The following variables were used in the calculation: Volume Factor(f) = 3 Rainfall =0.039 feet or 0.47 inches Where A;= area of impervious surface=2.22 Acres =96703.2 sf Atg= area of till soil covered with grass= 1.99 Acres = 86684.4 sf. Vr=[0.9A;+ 0.25Atg] x(R/12) Vr=[(0.9)(96703.2) + (0.25)(86684.4)]0.039 =4239.5 CF Vb =f*Vr=3(4239.5) = 12,718 CF The volume provided is 13,270 cubic feet. See the volume calculation sheet on the next page. 4 POND VOLUME CALCULATIONS (DEAD STORAGE) CORE# 99102 BUTTAR PROPERTY ELEVATION AREA INCREMENTAL TOTAL CELL1&2) VOLUME VOLUME SF CF CF 434.0 516 0 13,270 439.0 4792 13,270 IV. Conveyance Calculations The proposed conveyance system performance was analyzed using the rational method. The system was modelled using the 25 year and 100 year design storm events. The subbasins used to calculate the runoff contributing to each structure are shown on the attached map. Runoff coefficient values for each subbasin were selected based on the developed characteristics of each individual area, impervious pavement (C=0.90) or lot areas (C=0.60). The attached Storm Conveyance System Design spreadsheets compute tributary flows using the rational method as discussed previously and present a summary of pipe capacity flows. The tributary flows were inserted into the attached Backwater Calculations spreadsheets to calculated the headwater elevation at each structure. The last column in the spreadsheets (untitled)reflects the difference between each structure rim elevation and the calculated headwater elevation at that structure. Per attached spreadsheets, all pipe segments have sufficient capacity to convey and contain the 25 year and 100 year storm events, per Core Requirements#4, 1998 KCSWDM. NW 1/4, NW 1/4, SEC. 14, 1 W t'• L3 N., Muc. a c., rr.m. 30' I 0' 30' I 0' l Z I I 45SO t nW 4�STA.50M nFF 4.F Wo+m xmrr UQN. v I , 12T 4�O I 1 11� / 49 g r, I.l.1 R GONIROL ON.NO. 1852 \ I \ \ \\ REn D SSRKwss Yt%i1UN.N V V �1 r 1 $1RfF/J�o RAW Or BEARMG4'N 2 I I jf// 1(.S'�FrC.[.71 /� /• -T- — eaz2,7�v " ,to -III 1Vi// In (N88121'23W - K.0 1 S. l_ " r N.E. 47H ST.I ° l i i l - _ /a ) 21 191'V MEAS m' I - (262247�- MFJ1S) 11 �j 262387-MFAS 16 P60VA&��FePafA q�,�Mpy 0 - c(2622.�3 - K.CA AM aa+MCW 70 COMM �Y SO 70 eE ��70 �7E u `; a � _ 7r INTAK 7JA r Q � A Wr ` e` cr ----—__-- -- uoN No 18S -=- --- - --i I -------� - � Ex. G ' xup`. ----- aazir7o I I I -°/ , I 6F AAJA7/tD AWiix ,a 1? 1g I �-, i i I. f i 7�, I I 4 t l I ` t RiOMEW) J I , I $ CaWRACM 70 CLINDM E o J 1 : J1 � CB7 11 J I wzCB 8 I y I I - 0.87 ac. ` ^ 1 .06 ac. N Z �$ ��,n r I _ 2z5'ol9a I u i oz�u , arf-t.2 � e \. 91 c`m J • I Q _ r1U5C R9811 l --- -- - -�z� � CB �J __ ----' a Icw.mnc r SCALE: 1" = 40' 1 a; r � 4 ice 7` 0.08 ac. so I J 4 ssco L-, d- L'( -; - - (STA Of rnN uUs INLET 4A >j -- s---- - 1 0.46 ac. a � 2 0.08 ac. l• ---- �, �\ CB 10 I C l I ; 7 ,��- �� -- 1.i7LF1' 0.48 ac. - SR OIAO mx4 7w a '6 m S7a 1(o1a W CB4 \ 44 \ I 0.08 ac. ---- ---� -=- 1 11 , — ' ,'h OUTFACE 1 1 ff2'$r.w// ZAAff I"�1 \ I J o I'I : l 16 �. CB 5 T 01 .E ourFActl 0.12 ac. 7Y 154'r 111111 I, 1 11 2 �':� _ I p �2' �•' I I \ \I ,11; W/ 7iYP o ao LSL I_ I 1 1 1 I u-, 9FXTAC C4..71 -_�yJ L_ _ -Ste' RaW W 12'�432(1° if 1 .� 12 �p �. -N88 "W- 111`1 ��y�YI'Wi1yCg1�. a0271Q�1 1°° \ti IK7- -ro¢a4t?--_-I e4-w;og -i---__-- *'_-_7,5✓-_:„-_�__-.�-:, r'- I t 11 1 p�!�.t � f (� � e•� +1r4` 7)WIfir Q; Sll6 I W/Ott]B'tOl/ilfA7f ,I II ;1: 1%1,1) \ �.p SW&.TAM CAM NB 1 1 I I`� 2'44428E ; \ �FQS� j t \`\ l �~• �f 1 \.1,1hi1 $'l+atca44? 71P£4 SR 4, , , \ I P�. U �1 it, \ I,') :)�I '7A -••.:.a oiazr I{) 1 I I ; 1 �\ tl p�1 p��,. ;! `\ l V 1t� 4 w sac 1m14425 I11 I� i .FII '��.t� ;I 1�s. \'��I 12'E Q7.55 li 1 . I• ,1 1 1\ CONVEYANCE SYSTEM 4 1 I 1``t BASIN MAP 74 EAGLE RIDGE CORE DESIGN NO. 99102 l -- Z �`liii.a.�' �xx:.��'i�;..TT�i77��i..EE',(��':..i(�'� �i`��.aa�i�.�ji'`{.��i i[�.s�i..�: iii '.'i '..! i:''�1:�.,Tiii`iE'iEE'E'i`i`i ;.... ....... l.l.•1•.1'� (3v ::f3.i. .��Il\:::: ::..... LOCATION: KING COUNTY 24-HR RAINFALL: 3.46 INCHES JOB NAME: EAGLE RIDGE JOB NUMBER: 99102 PREPARED BY: DEC DESIGN STORM: 25 YEAR • . ........ . . TRi$1tTARY:::E:i.i:iipd;:;i`;::ii.isFiPIE;.:....::i:P.IAE.:::.:iiiYtPE:::i:;�!G`4i7•�-:::::'f11AVE#,.....:.:.:. i8 i.' i�a!ss5 :.:.:::.:::.:.:.:.:.:.:.:..:.:.:.:.:.:.:.:.:.:.:.:.::.:.:::.:.:.:.:.:.:.:.:..:.:.:.:.:.:.:..:.:.:.:.:.:.:.:.:.::.:.:.:.:.:.:.......:.:.....:.:.::.:............................:.:.:....................... .ii�:�1!E SE��IN��N7!'ii:iiiiiiii°��•�°'i i ii:::':OirkFtC��N��::�:: "�° �i�i' ::.:�:;o:"E?:.:?;`:':' i.:.:`':':''.''.':i :::::,: :;::: ::: ,:::i:5:::: °`°�'i ::::i:fii:i:iii`;i ........ .;:SLOPE: .FR. M..: .;. .......:.:C c3t3:SY.ii:;:`•.:::: ...:•..... .;.;.:E4.C)... E`(R11NUT�Sjpi.iii�+1/BR)i`E: E iiiiYC33•S)....i;°i.;:.;:a::::::;....tIiYCBESkE (PERCENT).i:fiFEEF} ;:(ETdEC). :fMgvtf77CS)i (CFS}i (BTI&CC:} (pEHCENTI i 10 9 0.48 0.60 0.29 0.29 10.00 2.06 0.59 0.012 12 7.0 39 6.57 1 0.10 10.21 13.00 5.8% 9 6 0.08 0.90 0.07 0.36 10.10 2.05 0.74 0.012 12 2.0 28 4.62 0.10 5.46 6.95 13.5% 8 7 1.06 0.60 0.64 0.64 10.00 2.06 1.31 0.012 12 0.5 55 3.44 0.27 2.73 3.47 48.0% 7 6 0.87 0.60 0.52 1.161 10.27 2.03 2.35 0.012 12 5.4 88 9.59 0.15 8.971 11.42 26.2% 6 5 0.46 0.60 0.28 1.79 10.42 2.01 3.60 0.012 12 0.5 52 3.47 0.25 2.73 3.47 131.9% 5 5A 0.12 0.90 0.11 1.90 10.67 1.98 3.76 0.012 12 9.0 58 13.05 0.07 11.58 14.74 32.5 4A 4 0.08 0.90 0.07 0.07 10.00 2.06 0.15 0.012 12 2.0 28 2.64 0.18 5.46 6.95 2.7% 4 4B 0.081 0.90 0.07 0.14 10.18 2.04 0.29 0.012 1 12 1 2.0 72 3.51 0.34 5.46 6.95 5.4% 11/10/00 CORE DESIGN,INC. PAGE 1 J...............�lu�;. .,..fJ.,... l l ............ LOCATION: KING COUNTY 24-HRRAINFALL: 3.95 INCHES JOB NAME: EAGLE RIDGE JOB NUMBER: 99102 PREPARED BY: DEC DESIGN STORM: 100 YEAR s c}F i'::IinliuFaGc': . j�K;!iY�.?1,...,.?t►,...,.,.,.��J...............:...............................................................................T....... Y...•.............•..........R)�E,...,..,.,.p!hl.,.,...Nt E. .�C trnf.......'f .v£v......•... �. .. ........ .. e............x.............. ...............#'l'.... Gi1:B�tMIY.:.:.: tE'.? iiiAilLAiiiiii5i ll ......' g.. I. N ii o CI N3.ii iiiiiii'AR�iI::;:;5 ;. 'i' `.':'''ii' .i iiiiiii°�"''.Gi;i;i °' :; ```i``'```?ii:i'i`'`'`:`'``?caNC.....iNtr Ns11i.....F..P....�..G......�'..•:::.:.:.:.:.:.:.:.:.:.::::.:G...:......:.:..:.::.:.:.:.:.:::::::.:u:.:Q:.::.:.:.:.:.;.:.;.;....:.:.:.:.:.:.:.:.:..:......�.nW.;.;..:M?4?gNtNC�S;..binnfETE#;;:SLOY�:::::4�NG7N::�'�QC!tk..;.:.;l7ME:.:.:..;. EF�fii,LJ:::w. .:.::;�4 nGT FROM::::::::T41::::::::::::1:AC3L1cS}::::::::::::::.:.:...:.:.:.:.:..:.:.:.:E.....:.:.:.::.:(A:.: ):.::.1 !NIfT65):..:.:(FN/SRj...........t3'S::::::::::::::;��q�,;::::::::: t�iC9E ERCENT: •..... ............................ ....... ........ ...........,.,.,,.,.,.. ,3..... X?.........5}'. (Y.,......,) :.L:FEET}., ..(F.TSkC) ..4!11M37i';5):.:':(CFS):.'; Y1!'TI&ff;} 10 9 0.48 0.60 0.29 0.29 10.00 2.42 0.70 0.012 12 7.0 39 7.02 0.09 10.21 13.00 6.8% 9 6 0.08 0.90 0.07 0.36 10.09 2.40 0.87 0.012 12 2.0 28 4.83 0.10 5.46 6.95 15.8% 8 7 1.06 0.60 0.64 0.64 10.00 2.42 1.54 0.012 12 0.5 55 3.58 0.26 2.73 3.47 56.3% 7 6 0.871 0.60 0.52 1.161 10.26 2.38 2.75 0.012 12 5.4 88 9.94 0.15 8.971 11.42 30.7% 6 5 0.46 0.60 0.28 1.79 10.40 2.36 4.23 0,012 12 0.5 52 3.47 0.25 2.73 3.47 155.0% 5 5A 0.12 0.90 0.11 1.90 10.65 2.32 4.42 0.012 12 9.0 58 13.71 0.07 11.58 14.74 38.1% 4A 4 0.08 0.90 0.07 0.07 10.00 2.42 0.17 0.012 12 2.0 28 2.99 0.16 5.46 6.951 3.2% 4 4B 0.08 0.9 0071 0.141 10.16 2.39 0.34 0.012 12 2.0 72 3.75 0.32 5.461 6.95 6.3% 11/10/00 CORE DESIGN, INC. PAGE 1 ............... ....... JOB NAME: EAGLE RIDGE PREPARED BY: DE CAYTON JOB NUMBER: 99102 DESIGN STORM: 25YEAR ENTRANCE ENTRANCE HEAD OUTLET INLET N JAPPROACH BEND JUNCTION PIPE PIPE NIANNING'S�.LOUTL�'T INLET PIP FLOW VELOC41AIL-ATEJ FRICTION HGL IIEAD 'AD CONTROL C-N��ERTOL VELOCITY HE. HEAD lEADWATER FV 'A EL, FROM� TO FLOW LENGTH DIA. n T14LE All PIPE VELOCITY H: AT.. LOSS ELEVATION LOSS LOSS ELIVATIO�ELEVATIOJ HEAD LOSS LOSS ELEVATION CB ca (CFS) (FEET) (IN) VALUE (FEET) (S (F] (FEET) (FEE FEE EE EE FEET) (FEET) (FEET) (FEET) (FEV-n RIM EL 4B 4 0,29 72 12 0.012 438.03 439047 0.79 0,37 0.00 442.77 0.00 442.77 0000 000 442.78 439.47 0.00 0,00 0.00 442.78 443.03 0.25 442 7' 4 4A 0.1 28 12 0.012 439.47 440.03 0.79 019 0.00 442.78 0.00 442.78 0.00 0,00 442.79 440.03 0.00 0.00 000 442.78 443.03 0.25 5A 5 3,76 58 12 0,012 438.00 443.22 0.79 4.79 0.36 442,77 0.54 444,22 0.18 0.18 444.58 444.67 0.33 0.11 0.00 444.45 447.02 157 5 6 3.60 52 12 0.012 443.22 443.48 0.79 4.58 0.33 444.45 0.45 444.90 0.16 0.16 445.22 444.93 0.14 0.00 0,49 445.58 447.41 1.83 6 7 2,35 88 12 0.012 443.48 448.23 079 2,99 0.14 445.58 0.32 449,23 0.07 0.07 449.37 9 - 44938 0.04 0.19 0.0o 449.53 451.70 2.17 7 8 1,31 55 12 0.012 448.23 448.50 0.79 L67 0.04 449.53 0.06 449.59 0.02 0.02 449.64 449.20 0.00 0.00 0.00 l44964 452.00 2.36 6 1 9 0.74 28 12 0.012 443.48 1 444.04 1 079 0.94 0.01 445.58 0.01 445.59 1 0.01 0.01 445,60 1 444.04 0.01 0,02 0.00 44561 447.41 1.802 9 1 10 0.59 39 12 0.012 444.04 1 446.77 1 0.79 0.75 0.01 445.61 0.01 447.77 1 0.00 0,00 447.78 1 446.77 0.00 0.00 0,00 447.78 450.27 149 11/10/00 DODDS ENGINEERS,INC. PAGE 1 ............. ............. JOB NAME: EAGLE RIDGE PREPARED BY: DE CAYTON JOB NUMBER: 99102 DESIGN STORM; 100 YEAR ENTRANCEIENTRANCE OUTLET INLET APPROACH REND JUNCTION CONTROL TLET U H EXIT 0 1 �IEADWA.ER PIPE PIPE MANNING'S�,OUTLET INLET PIPE FLOW VELOCI AILWATE FRICTION I GL HEAD HEAD CONTROL CONTROL VELOCITY HEAD HEAD 0 LOSS [LO S FROM TO FLOW!LENGTH: DIA. n LEVATION ELEVATION AREA VELOCITY ELEVATIOD ELEVATION LOSS SS ELEVATIOJELEVATIO HEAD LOSS LOSS ELEVATION VALUE (FEET) (FEET) (SO FT) (FT/qvcl M (FEET) r S F IRDIEI CB CB (CFS) (FEET) (IN) I �:E, EFTI (FEET) r) 4B 4 0.34 72 1 12 0.012 438,03 439.47 0.79 0.43 0.00 442.86 0.01 442.87 0.00 0.00 442,87 439A7-- 0.00 0.00 0,00 442.87 443.03 0.16 4 4A 0,17 28 1 12 0.012 4397 440.03 0.79 022 0.00 442.87 0.00 442.87 0,00 OM 442.97 440.03 0.00 OM 0.00 442.97 443.03 0.16 5A 5 4,42 58 12 0.012 438.00 443.22 0.79 563 0.49 442.86 0,75 444.22 0.25 015 444.71 444.67 0.45 0.15 OM 444.41 447.02 2.61 5 6 4,23 52 12 0.012 44122 443.48 0.79 539 0.45 444,41 0,62 445,03 0.23 0.23 445.48 444.93 0.19 0+00 0068 445+96 447.41 1.45 6 7 2.75 88 12 0,012 44148 44823 0,79 150 0,19-- 4596 0.44 449.23 0.10 0.10 449.42 44938 0,06 0.27 0.00 449.63 451.70 2.07 7 8 1.54 55 12 0,012 448.23 448.50 0+79 L96 0.06 449,63 0.09 449,71 0.03 0.03 449077 44920 0,00 0.00 0.00 449.77 452,00 123 17 29 12 0.012 443,48 444,04 0.79 0 1 0.02 1 445,96 1 0.01 1 445M 0,01 0.01 446.00 444.04 1 0.01 0.03 1 0.00 1 446.01 44T41 IAO IP9 IF,o�111,70 39 12 0.012 444�04 446.77 0.79 0,89 0.01 1 446.01 1 0.01 1 447.77 0,01 _0.01 44T78 446.77 1 0.00 0.00 1 0.00 1 447.78 450.27 2.49 11/10/00 DODDS ENGINEERS,INC. PAGE 1 SECTION 3.2 RUNOFF COMPUTATION AND ANALYSIS METHODS FIGURE 3.2.1.0 25-YEAR 24-HOUR ISOPLUVIALS 2L� g�_- SN XO�ISN COUNTY KING COUNTY 2� REF r�'� �� ✓- 2,y m ► dIV h' 2z-sr'as`.# - 5.0 t ko Ysfi s S 3 ,M4 �� I r y ' M ' !Pv • ij�Cb wa CID! 06 11.* PIERCE COUNTY WESTERN i7 KING COUNTY s.5 N � $,0 25-Year 24-Hour 4.5 h 1 Precipitation in Inches CO """� �� ` ��`' 9/1/98 1998 Surface Water Design Manual 3-16 3.2.1 RATIONAL METHOD FIGURE 3.2.1.1) 100-YEAR 24-HOUR ISOPLUVIALS _"M- — --- --- -- �� yr — ——— -- — COUNTY N COUNTY tna ✓ � A ff � JW UZ �a ,�- � •a sae: '..,i ✓ `...,ti .t E � 4. t,}}.x. .. ; _ :S / 1 •.ails, ..+^''�� s . a e 4 s `ta •a f.6x8 A e � .� ``� a r�t��Yh 1-1 C[COUNTY , t WESTERN KING COUNTY o�o �,, s.s H 5.5 100-Year 24-Hour Precipitation in Inches 0 2 MBes h� h� 1998 Surface Water Design Manual 9/1/98 3-17 A � V. Erosion Control Calculations The intent of this erosion and sedimentation control plan is to minimize erosion and the transport of construction related sediments off-site. This design will utilize interceptor swales and ditches to route all runoff originating from disturbed areas of the site to the permanent drainage facility, modified with the necessary erosion control measures. The sedimentation control facilities were designed using the methodology as presented in Chapter 5 of the KCSWDM. This plan will also include constructing temporary filter fabric fencing along the south and east property lines and the placing of mulch, straw, chips or hydroseeding on all disturbed areas which will be exposed during the wet season as required, see plan sheet C2.31, note 7. Sediment Pond Calculations • Tributary area=4.2 acres • Design flow, Q2=0.94 cfs (see attached basin summary) • SA=2 x Q2/0.00096 = 1,958 sf(required at top of riser) • Side slopes=3:1 • Depth of dead storage= 5.0' • Depth of live storage=4.5' • Surface area at top of riser= 9,900 sf • Riser: Design flow, Q10 = 1.77 cfs (see attached basin summary) 18" diameter riser with 1 foot of head� 8.5 cfs (see attached Fig. 4.4.7J) • Emergency Overflow Spillway: Design flow, Q100=2.71 cfs (see attached basin summary) Overflow to be provided by the permanent structure, max. flow>>2.00cfs • Dewatering Orifice: Orifice area=As(2h)0-5/(10.6)(3600)Tgos _ (9,900)(2)(4.5)0-5/(10.6)(3600)(24)(32.2)0s = 0.0081 sf Orifice diameter=24(orifice area/7r)o.s =24(0.0081/Tc)o.s = 1.22 inch. USE 1 inch min. 1 y 11/14/00 6 : 51 : 16 am Dodds Engineers, Incorporated page 1 EAGLE RIDGE CORE JOB # : 99102 --------------------------------------------------------------------- --------------------------------------------------------------------- BASIN SUMMARY BASIN ID : SPOND002 NAME: SEDIMENT CONTROL POND, 2 YR SBUH METHODOLOGY TOTAL AREA. . . . . . . : 4 . 20 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE . . . . : TYPElA PERV IMP PRECIPITATION. . . . : 2 . 00 inches AREA. . : 4 . 20 Acres 0 . 00 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 89 . 00 0 . 00 TC. . . . . 5 . 00 min 0 . 00 min ABSTRACTION COEFF: 0 .20 PEAK RATE : 0 . 94 cfs VOL: 0 . 36 Ac-ft TIME : 480 min BASIN ID: SPOND010 NAME : SEDIMENT CONTROL POND, 10 YR SBUH METHODOLOGY TOTAL AREA. . . . . . . : 4 . 20 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE. . . . : TYPElA PERV IMP PRECIPITATION. . . . : 2 . 94 inches AREA. . : 4 . 20 Acres 0 . 00 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 89 . 00 0 . 00 TC. . . . . 5 . 00 min 0 . 00 min ABSTRACTION COEFF: 0 . 20 PEAK RATE : 1 . 77 cfs VOL: 0 . 65 Ac-ft TIME: 480 min BASIN ID: SPOND100 NAME: SEDIMENT CONTROL POND, 100 YR SBUH METHODOLOGY TOTAL AREA. . . . . . . : 4 .20 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE. . . . : TYPEIA PERV IMP PRECIPITATION. . . . : 3 . 95 inches AREA. . : 4 . 20 Acres 0 . 00 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 89 . 00 0 . 00 TC. . . . . 5 . 00 min 0 . 00 min ABSTRACTION COEFF: 0 . 20 PEAK RATE: 2 . 71 cfs VOL: 0 . 97 Ac-ft TIME : 480 min ` 4111110KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL FIGURE 4.4.7J RISER INFLOW CURVES Weir Flow Orifice Flow 100 . 36 33 30 27 24 a 21 d � U 18 7 U a 15 a 12 10 or ElE 1 0.1 1.0 10.0 HEAD IN FEET (measured from crest of riser) SOURCE: USDA-SCS QWIER = 9.739 DH= aORIFICE =3.782 D2H1rz 0 in cfs, D and H in feet 4.4.7-10 1/90