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HomeMy WebLinkAboutSWP272257 TEMPORARY EROSION CONTROL DRAINAGE REPORT FOR THE PLAT OF CEDAR CREST RENTON, WASHINGTON PREPARED BY: TRIAD ASSOCIATES INC. E:"' 11814 115TH AVE SE V E n KIRKLAND,WASHINGTON " 5 LJ 98034 JOB NO: 95-123 SION SEPTEMBER, 1995 p- ;�57 PREPARED BY: REVIEWED BY: MICHAEL D. MATHIA CLAY A. LOOMIS, P.E. A 19 IONZ -IG 71 1 PROJECT DESCRIPTION: The Plat of Cedar Crest is located on a133-acre site in east Renton located at the southeasterly intersection of Edmonds Ave. NE and NE 3`d St. The area to be developed comprises 96 acres with the remaining area to be kept in its' exisitng condition(Please Refer to the Level 1 Drainage Study And Preliminary Storm Drainage Calculations prepared by Barghausen Consulting Engineers, Inc. on October 12, 1995). BASIS OF DESIGN: The basis of this report is to analyze the site drainage for erosion control facility design based upon the latest, updated version of the 1990 King County Drainage Manual, Chapter 5. Copies of the applicable sections of the manual are attached for easy reference. The discharge rates are determined using the 2-year, 24-hour developed storm for each of the proposed ponds. From this the required surface area is determined. The ponds are then sized using the required parameters listed in on page 5.4.5.2-2 of the Manual. The sizing of the discharge mechanisms are also determined using the criteria listed. Because the site is essentially flat, the ponds have all had an overflow storm drain system designed to convey the post-developed flow rates shown in the Barghausen Drainage Report in the case of a total overflow of the ponds. The calculations used to determine the pond sizes and discharge rates are contained in this report. 2 1 Aiwa9 for/b x 20v0 --9-v`8 -x-- 2al�s o- ��tiD c V /0•l. 3�© Zyx32.Z �� J -- File Basin Hydrograph Storage Discharge Level pool 3 MMI VIMMMI v1i IMMMr11 IM1~Ir11 v11~1rIMI vIMI rI1 v11 iMI11 ti1�IMM1 vlI riMrll It11 v11�1MI vIMMI vIM1 VIMMI vlrlrll v11 1MrIMMrII v11MMMMr1MI vIrIM1 11 vI1 llYlrlMB �3 INPUT, MODIFY OR BROWSE DATA 1; 3 BASIN ID B10 :-CS UNIT HYDROGRAPH METHOD 3 ,DESCRIPTION TESC 10YR 3 3AREA (acres) . 32.800- RAINFALL CHOICES 17 3RAIN PRECIP ( in) . 2 .90 1 . TYPE IA 17 3TIME INTERVAL(min)•: 10 . 00 2. TYPE I 3 3TIME OF CONC (min) : 12.75 3. TYPE II 3 5RAINFALL SELECTION: 1 4. TYPE IIA 3 3ABSTRACT COEFF 0. 20 5. TYPE 3 3BASE FLOW (cfs) 0.000 6. USER 1 3 ,STORM DUR (hrs) 24. 000 7 . KC 7 DAY 3 3 8 . CUSTOM 3 3PERVIOUS PARCEL IMPERVIOUS PARCEL 03AREA: 32. 800 acres, AREA: 0.000 acres 3 XN 82 .00 CN 98 . 00 3 3 3 SUMMARY DATA s SPEAK HYDROGRAPH TIME: 8. 50 hrs 3 ,TEAK HYDROGRAPH FLOW: 8 .4759 cfs: 3 3TOTAL HYDROGRAPH VOL: 3. 4260 ac-ft. ; HOME END F1 : Find F2 :New F3:Get. F4 :T'c-Calc: F5:Delete 3 Pgup Pgdn F6:Compute F'7 : F8:Method F9 :Template F10: Exit. 3 TMrIM1�I1 IMMMMMI vIMI vI1 rIMMMI�l v11~II v1I I1 vI1 vlt�Jh1I ill vII vJI vIMI vlrlrll vIl`JI vI1 vIMI JI v1�J1�IM1~iMl~IMI vI1 vIM1 vI1 VIMM1 IMMMMr11`II v11 v11 11 1l1HlI vII�I vIMI vIMMM. File Basin Hydrograph Storage Discharge Level pool 3 MIv1I1II11M1~IMMMttillllll`Irin 3 INPUT, MODIFY OR BROWSE DATA 3 3 BASIN ID C10 SCS UNIT HYDROGRAPH METHOD 3 ,DESCRIPTION TESCP 10 YEAR 3AREA (acres) 36.000 RAINFALL CHOICES 3 3RAIN PRECIP ( in) 2. 90 1 . TYPE IA 3 3TIME INTERVAL(min) : 10.00 2. TYPE I 3 ,TIME OF CONC (min) : 19.87 3. TYPE II 3 3RAINFALL SELECTION: 1 4. TYPE IIA 3 3ABSTRACT COEFF 0 . 20 5. TYPE 3 3 3BASE FLOW (cfs) 0 .000 6. USER 1 3 STORM DUR (hrs) 24 .000 7 . KC 7 DAY 3 3 8. CUSTOM 3 3PERVIOUS PARCEL IMPERVIOUS PARCEL 3 ,AREA: 36.000 acres AREA: 0 .000 acres 3 3CN 82.00 CN 98.00 3 3 31 3 SUMMARY DATA �3 SPEAK HYDROGRAPH TIME: 8.50 hrs 3 3PEAK HYDROGRAPH FLOW: 9 .0595 cfs 3 3TOTAL HYDROGRAPH VOL: 3.7611 ac-ft 3 HOME END Fl : Find F2:New F3:Get F4 :Tc-Cale F5:Delete 3 3 1pgup Pgdn F6:Compute F7 : F8:Method F9 :Template F10:Exit 3 TM1 VII vIrIMMrIrII riF11`i1�11 till vJrll v11 vI1 v1MI rIl II rJrIMI vJMMMrJI rIrIMMI vlII1 r11 vIMI vIMI rIM1 vIMI rIMI v11 vIMMMMI vIrIMMMMI rlrll vlr1r11 VIMI wlMl rlrll vll vlrlrll vlMl�`> File Basin Hydrograph Storage Discharge Level pool 3MIIMM1�JMr11�IrlrJl'9MtI1�JrIrIMrIMrIrIr!lIMMrIrlrlMrJI�IMMMIJMMIIIIMrIrJrIMMMMMMl�JMrIMMMrIr11JMMMMMMMMIIrIMMMMMMMI�B 3 INPUT, MODIFY OR BROWSE DATA 3 BASIN ID A10 SCS UNIT HYDROGRAPH METHOD 3DESCRIPTION TESL 10YR 3AREA (acre:) 23. 600 RAINFALL CHOICES ,RAIN PRECIP ( in) 2.90 1 . TYPE IA 5TIME INTERVAL(min) : 10.00 2. TYPE I 3I'IME OF CONC (min) : 11 . 54 3. TYPE II 3RAINFALL SELECTION: 1 4. TYPE IIA 3 3ABSTRACT COEFF 0 . 20 5. TYPE 3 3 3BASE FLOW (cfs) 0.000 6. USER 1 3 3STORM DUR (hrs) 24. 000 7. KC 7 DAY 3 8. CUSTOM 3 3PERVIOUS PARCEL IMPERVIOUS PARCEL 3AREA: 23. 600 acres AREA: 0.000 acres 3 3CN 82.00 CN 98. 00 `3 4 3 SUMMARY DATA 3 SPEAK HYDROGRAPH TIME: 8. 50 hrs 3 SPEAK HYDROGRAPH FLOW: 6. 1009 cfs 3 .DOTAL HYDROGRAPH VOL: 2. 4650 ac-ft. 3 HOME END Fl:Find F2 :New F3:Get F4:Tc-Cale F5:Delete 3 3 Pgup Pgdn F6:Compute F7 : F8:Method F9 :Template F10:Exit 3 TMMMMMMMMrJrlrlrlrlrlMrJIIrIMMrIMMrIMMrIM1JMIII�JMMrIrJIIrJ�IMMMrIrIMh1�1hJrIrIrJMMrIM1I��IlIMrJM1IrIMMrIMrJrJMMI�rIMM�I_y KING COUNTY , WASHINGTON , SURFACE WATER DESIGN MANUAL i Design and Installation Specifications 1. See Figures 5.4.5.2A, 5.4.5.2B, and 5.4.5.2C for details. 2. If permanent runoff control facilities are part of the project, they should be used for sediment retention (see introduction to this section). Determining Pond Geometry 1. Obtain the discharge from the hydrologic calculations of the_peak flow for the 2-year, 24- hour developed storm�(Q The 10-year, 24-hour design storm shall be used ifthe protect size, expected timing anWduration of construction, or downstream conditions warrant a higher level of protection. If no hydrologic analysis is required, the rational method may be used(Section 4.3.3). 2. Determine the required surface area at the top of the riser pipe with the equation: SA.=2 x 02/0.00096 or 2080 square feet per cfs of inflow See Section 5.4.5.1 for.more information on the derivation of the surface area calculation. 3. The basic geometry of the pond can now be determined using the following design criteria: • Required surface area at top of-riser. • Minimum 3.5' depth from top of riser to bottom of pond. Maximum 3:1 interior side slopes and maximum 2:1 exterior slopes. The interior slopes can be increased to a maximum of 2:1 if fencing is provided at or above the maximum water surface. • One foot of freeboard between the top of the riser and the crest of the emergency spillway. • Flat-bottomed. • Minimum one foot deep spillway. • Length to width ratio between 3:1 and 6:1. Sizing of Discharge Mechanisms Principal Spillway Determine the required diameter for the principal spillway (riser pipe). The diameter shall be the minimum necessary to pass the pre-developed 10-year, 24-hour design storm (010). Use Figure 4.4.7J to determine this diameter ( h = one foot). Note that a permanent control structure may be used instead of a temporary riser. Emergency Overflow Spillway Determine the required size and design of the emergency overflow spillway for the 100-year, 24-hour developed design storm using the procedure in Section 4.4.4 (Emergency Overflow Spillway subsection). Dewatering Orifice Use the following steps to determine the size of the dewatering orifice: 1. Determine the size of the dewatering orifice(s) (minimum 1 diameter) using a modified version of the discharge equation for a vertical orifice and a basic equation for the area of a circular orifice. First, determine the required area of the orifice with the following equation: _ Af(2h)os A° 10.6x3600Tgo.5 where: Ao = orifice area (square feet) As = pond surface area (square feet) h = head of water above orifice (height of riser in feet) 5.4.5.2-2 _ 11/94 KING COUNTY , WASHINGTON , SURFACE WATER DESIGN MANUAL T = dewatering time (24 hours) 9 = acceleration of gravity (32.2 feet/second2) 2. Convert the required surface area to the required diameter of the orifice: The orifice diameter (D) in inches is: D = 24 x A� F3.14 3. The vertical, perforated tubing connected to the dewatering orifice must be at least 2 inches larger in diameter than the orifice to improve flow characteristics. The size and number of performations in the tubing should be large enough so that the tubing does not restrict flow. The flow rate should be controlled by the orifice. Additional Design Specifications Pond Divider The pond shall be divided into two roughly equal volume cells by a permeable divider that will reduce turbulence while allowing movement of water between cells. The divider shall be at least one-half the height of the riser and a minimum of 1 foot below the top of the riser. Wire- backed, 2-3.feet high, extra strength filter fabric (Section 5.4.3.1) supported by treated 4"x4"s can be used as a divider. Alternatively, staked straw bales wrapped with filter fabric may be used. If the pond is more than 6 feet deep, a different mechanism must be proposed. A riprap embankment is one acceptable method of separation for deeper ponds. Other designs that satisfy the intent of this provision are allowed as long as the divider is permeable, structurally sound, and designed to prevent erosion under or around the barrier. Depth Gauge To aid in determining sediment depth, one-foot intervals shall be prominently marked on the riser. Embankment If an embankment of more than 6 feet is proposed, the pond must comply with the criteria for Berm Embankment/Slope Stabilization in Section 4.4.4. FIGURE 5.4.5.2A SEDIMENT POND PLAN VIEW KEY DIVIDER INTO SLOPE TO PREVENT FLOW AROUND SIDES THE POND LENGTH SHALL BE 3 TO 6 TIMES THE MAXIMUM POND VOTH EMERGENCY OVERFLOW SPILLWAY a POND LENGTH (C INFLOW SILT FENCE OR EOUNALEN T DIVIDER RISER PIPE DSCHARGE TO STABILIZED CONVEYANCE. OUTLET OR LEVEL SPREADER NOTE: POND MAY BE FORMED BY BERM OR BY PARTIAL OR COMPLETE EXCAVATION 5.4.5.2-3 11/94 KING COUNTY , WASHINGTON , SURFACE WATER DESIGN MANUAL FIGURE 5.4.5.2B SEDIMENT POND CROSS-SECTION RISER PIPE CREST OF 6' MIN. WIDTH (PRINCIPAL SPILLWAY) EMERGENCY SPILLWAY OPEN AT TOP WITH .TRASH RACK PER FIG. 4.4.4E _ 1' MIN EMBANKMENT COMPACTED 957- j• _-- PERVIOUS MATERIALS SUCH AS DEWATERING DEVICE _____±_ GRAVEL OR CLEAN SAND SHALL (SEE RISER DETAIL) _ _ NOT BE USED. - - ------------- ' DEWATERING 11-11 WIRE-BACKED SILT FENCE. ORIFICE gill STAKED HAYBALES WRAPPED I I I CI I WITH FILTER FABRIC. OR. - - DISCHARGE TO STABILIZED - EQUIVALENT DIVIDER CONCRETE BASE CONVEYANCE. OUTLET OR (SEE RISER DEVIL) LEVEL SPREADER FIGURE 5.4.5.2C SEDIMENT POND RISER DETAIL POLYETHYLENE CAP PROVIDE ADEOUATE STRAPPING PERFORATED POLYETHYLENE — DRAINAGE TUBING. DIAMETER CORRUGATED O L RITER MIN. 2" LARGER THAN — DEWATERING ORIFICE. TUBING SHALL COMPLY WITH ASTM F667 AND — 3.5' MIN. AASHTO M294. _ WATERTIGHT COUPLING COUPLING DEWATERING ORIFICE. SCHEDULE C TACK WELD 40 STEEL STUB MIN. DIAMETER AS PER CALCULATIONS ��jl1111 I a"MN, r--- ALTERNATIVELY. METAL STAKES AND WIRE MAY BE USED 70 CONCRETE BASE PREVENT FLOTATION 2X RISER DIA MIN.—� Maintenance Standards 1. Sediment shall be removed from the pond when it reaches 1 foot in depth. 2. Any damage to the pond embankments or slopes shall be repaired. 5.4.5.2-1 11/94 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL o To complete the design of the temporary sediment trap: a. The "Pond Geometry Equations" section in the "Reference' portion at the back of the Manual may also be useful in designing the sediment trap. b. A 3:1 aspect ratio between the trap length and width of the trap Is desirable. Length is defined as the average distance from the inlet to the outlet of the trap. This ratio Is included in the computations for Figure 5.4.4C for the surface area at the Interface between the settling zone and sediment storage volume. C. Determine the bottom and top surface area of the sediment storage volume to be provided (see Figure 5.4.4C) while not exceeding 1.5' in depth and 3:1 side slope from the bottom of the trap. Note the trap bottom should be level. d. Determine the total trap dimensions by adding an additional 2' of depth above the surface of the sediment storage volume, while not exceeding 3:1 side slopes, for the required settling volume. (see Figure 5.4.4C) TABLE 5.4.4A HYDROLOGIC SOIL GROUP OF THE SOILS IN KING COUNTY SOIL SOiL EROD- EROD- HYDROLOGIC IBIUTY HYDROLOGIC IBILITY SOIL GROUP GROUP* FACTOR,'K' SOIL GROUP GROUP* FACTOR,W Alderwood C 0.15 Orr-as Peat D 0.00 Ariints,Alder C 0.15 Oridia D 0.49 Arents, Everett B 0.17 Ovall C 0.17 Beaus to C 0.15 Pilchuck C 0.10 �- Bellingham D 0.32 Puget D 0.28 Br&ot D 0.32 Puyallup B 0.28 Buckley D 0.32 Ragnar B 0.32 Coastal Beaches Variable 0.05 Renton D 0.43 Earimont Silt Loam D 0.37 Riverwash Variable Edgewick C 0.32 Sala) C 0.37 Everett A 0.17 Sammamish D 0.37 Indianola A 0.15 Seattle D 0.00' Kitsap C 0.32 Shacar D 0.00 r: Klaus C 0.17 SI Sat C 0.37 Mixed Alluvial Land Variable 0.10 Snohomish D' 0.32 Newton A 0.10 Sultan C 0.37 Newberg B 0.32 Tukwila D 0.00 Nooksack C 0.37 Urban Variable Norm. Sandy Loam D 0.24 Woodinville D 0.37 HYDROLOGIC SOIL GROUP CLASSIFICATIONS A. (Low runoff potential). Soils having high infiltration rates, even when thoroughly wetted,and consisting chiefly of deep,well-to-excessively drained sands or gravels. These soils have a high rate of water transmission. B. (Moderately low runoff potential). Sons having moderate infiltration rates when thoroughly wetted, and consisting chiefly of moderately fine to moderately coarse textures. These soils have a moderate rate of water transmission. C. (Moderately high runoff potential). Soils having slow Infiltration rates when thoroughly wetted, and consisting chiefly of soils with a layer that impedes downward movement of water,or soils with moderately fine to fine textures. These soils have a slow rate of water transmission. D. (High runoff potential). Soils having very slow Infiltration rates when thoroughly wetted and consisting chiefly of clay soils with a high swelling potential,sons with a permanent high water table, sous with a hardpan or clay layer at or near the surface,and shallow soils over nearly impervious material. These soils t have a very slow rate of water transmission. ' From SCS, TR-55, Second Edition,June 19M, Exhibit A-1. Revisions made from SCS, Sons Interpretation Record, Form #5, September 1988. 5.4.4.1-3 1/90 Y � tb � z I.S vniues for following slope lengths 1,fl(m) IS values for following slope lengths 1,ft(m) to (� Slope - -.-- Slope gradient 10 20 30 •10 50 60 70 80 '90 100 150 200 250 300 350 400 450 500 600 700 800 900 1000 :01 n ratio x, '', (3.0) (6.1) (9.1) (12.2) (15.2) 08.3) (21.3) (2.1.4) (27.4) (30.5) (.I6) (fit) (76) (91) (107) (122) (137) (152) (183) (213) (244) (274) (305) r 0.5 OAR3 0.07 0.07 0.08 0.08 0.09 0.09 0.09 0.09 0.10 0.10 0.11 0.11 0.12 0.12 0.13 0.13 0.13 0.14 0.14 0.14 0.15 0.15 IM:I I 0.08 0.09 0.10 0.10 0.11 0.11 0.12 0.12 0.12 0.12 0.1.1 0.1.1 0.15 0.16 0.16 0.1fi 0.17 0.17 0.18 0.18 0.19 0.19 0.20 a z 2 0.10 0.12 0.1 1 0.15 0.16 0.17 0,18 0.19 0.19 0.20 0.23 0.25 0.26 0.28 0.29 0.30 012 0.33 0.34 0.36 0.37 0.39 0.40 :1 0.14 0.18 0,20 0.22 0.23 0,25 0.26 0.27 0.29 0.29 0.32 0.35 0.38 0.40 0.42 0.43 0.45 0.46 0.49 0.51 0.54 0.55 0.57 C' 4 0.16 0.21 0.25 0.28 0.30 0.33 0.35 017 0.38 0.40 0.47 0.53 0.58 0.62 0.66 0.70 0.73 0.76 0.82 0.87 0.92 0.96 1.00 w 20:1 � - 0.17 0.24 0.29.___0.34 0.38 0.41 0.45 . 0.48 0.51---0.53 0.66 0.76 0.85 0.93 1.00 1.07 1.13 1.20 1.31 1.42 1.51 1.G0 . 1.69 6 0.21 0.30 0.37 0A3 0.49 0.52 0.56 0.60 0.64 6.G7 0.82 0.95 1.06 1.16 1.26 1.34 1.43 1.50 1.65 1.78 1.90 2.02 42.13 7 0.26 0,37 0.45 0.52 0.58 0.6.1 0.69 0.74 0.78 0.82 1.01 1.17 1.30 1.43 1.54 1.65 1.75 1.84 2.02 2.18 2.33 2.47 2.61 12'4:1 8 0.31 0.44 0.54 0.63 0.70 0.77 0.83 0.89 0.9-1 0.99 1.21 1.40 1.57 1.72 1.85 1.98 2.10 2.22 2.43 2.62 2.80 2.97 3.13 x 9 0.37 0.52 0.64 0.74 0.83 0.91 0.98 1.05 1.11 1.17 1.44 1.66 1.85 2.03 2.19 2.35 2.49 2.62 2.87 3.10 3.32 3.52 3.71 �-- 10:1 10 0.43 0.61 0.75 0.87 0.97 1.06 1.15 1.22 1.30 1.37 1.68 1.94 2.16 2.37 2.56 2.74 2.90 3.06 3.35 3.62 3.87 4.11 4.33 z 11 0.50 0.71 0.86 1.00 1.12 1.22 1.32 1.41 1.50 1.58 1.93 2.23 2.50 2.74 2.95 3.16 3.35 3.53 _a' 7 4.18 4.47 4.74 4.99 8:1 12.5 0.61 0.86 1.05 1.22 1.36 1.49 1.61 1.72 1,82_ 1.92 2.35 2.72 3.04 3.33 3.59 3.84 4.08 4.307 5.08 5.43 5.76 6.08 C) -- 0.81 1.14 1.40 1.62 1.81 1.98 2.14 2.29 2.43 2.56 3.13 3.62 4.05 4.43 4:79 b.12- "43 S72 . 6.27 6.77 7.24 7.68 8.09 O 6:1 16.7 0.96 1.36 1.67 1.92 2.15 2.36 2.54 2.72 2.88 3.04 3.72 4.30 4.81 5.27 5.69 6.08 6.45, 6.80 7.45 8.04 8.60 9.12 9.62 z N 5:1 20 1.29 1.82 2.23 2.58 2.88 3.16 3.41 3.65 3.87 4.08 5.00 5.77 6.45 7.06 7.63 8.16 8.65 9.12 9.99 10.79 11.54 12.24 12.90 tY) ja 4Y,:1 22 1.51 2.13 2.61 3.02 3.37 3.69 3.99 4.27 4.53 4.77 5.84 6.75 7.54 8.2G 8.92 9.54 10.12 10.67 11.68 12.62 13.49 14.31 15.08 a4:1 25 1.86 2.63 3.23 3.73 4.16 4.56 4.93 5.27 5.59 5.89 7.21 8.33 9.31 10.20 11.02 11.78 12.49 13.17 14.43 15.58 16.66 17.67 18.63 30 2.51 3.56 4.36 5.03 5.62 6.16 6.65 7.11 7.54 7.95 9.74 11.25 12.57 13.77 14.88 15.91 16.87 17.78 19.48 21.04 22.49 23.86 25.15 3:1 33.3 2.98 4.22 5.17 5.96 6.67 7.30 7.89 8.43 8.95 9.43 11.55 13.34 14.91 16.33 17.64 18.86 20.00 21.09 23.10 24.95 26.67 28.29 29.82 35 3.23 4.57 5.60 6.46 7.23 7.92 8.55 9.14 9.70 10.22 12.52 14.46 16.16 17.70 19.12 20.44 21.68 22.86 25.04 27.04 28.91 30.67 32.32 (� 2%:1 40 4.00 5.66 6.93 8.00 8.95 9.80 10.59 11.32 12.00 12.65 15.50 17.89 20.01 21.91 23.67 25.30 2G.84 28.29 30.99 33.48 35.79 37.96 40.01 (1� 45 4.81 6.80 8.33 9.61 10.75 11.77 12.72 13.60 14.42 15.20 18.62 21.50 24.03 26.33 28.44 30.40 32.24 33.99 37.23 40.22 42.99 45.60 48.07 C 2:1 50 k.64 7.97 9.76 11.27 12.60 13.81 14.91 15.94 16.91 17.82 21.83 25.21 28.18 30.87 33.34 35.65 37.81 39.85 43.66 47.16 50.41 53.47 56.36 55 6.48 9.16 11.22 12.96 M48 15.87 17.14 18.32 19.43 20.48 25.09 28.07 32.39 35.48 38.32 40.97 43.45 45.80 50.18 54.20 57.94 61.45 64.78 1Y.:1 57 6.82 9.64 11.80 13.63 15.24 16.69 18.03 19.28 20.45 21.55 26.40 30.48 34.08 37.33 40.32 43.10 45.72 48.19 52.79 57.02 G0.9G 64.G8 GB.Ib f,0 7.32 10.35 12.68 14.64 16.37 17.93 19.37 20.71 21.96 ;23.15 28.35 32.74 3G.60 40.10 43.31 46.30 49.11 51.77 56.71 61.25 65.48 69.45 73.21 1 K:1 06.7 8.44 11.93 14.61 16.88 18.87 20.67 22.32 23.87 25.31 26.68 32.68 37.74 42.19 46.22 49.92 53.37 56.60 59.66 65.36 70.60 75.47 80.05 84.38 � 70 8.98 12.70 15.55 17.96 20.08 21.99 2.9.75 25.39 26.93 28.39 .34.77 40.15 4489:.49117 53.11 56.78 60.23 63,48 69.54 76.12 80.30 85.17 89.78 75 9.78 13M 1 G.94 19 56 21.87 2.3.95 25.87 27.66 29.34 30.92 37.87 49 73 48.89 53.56 57.85 61.85 65.60 69.15 75.75 81.82 87.46 92.77 97.79 I%:1 80 10.55 14.93 18.28 21.11 23.60 25.85 27.93 29.85 31.66 33.38`:40.88 47.20 5237 57.81 62.44 66.75 70.80 74.63 81.7G 88.31 94.41 100.13 105.55 85 11.30 15.98 19.58 22.61 25.27 27.69 29.90 31.97s 3391 36:7443,78,5065,b6:51 ;61.91 60.87 71.48 76.82 79.92 87.55 04.67 101.09 107.23 113.03 90 12.02 17.00 20.82 24.04 26.88 29.4.1 31.80 34.60 36.06 `98 01 '16.55 53 76 60;110 0,5.84 71.11 76.02 80.63 84.99 93.11 100.57 107.51 114.03 120.20 +n 95 12.71 17.97 22.01 25.41 28.41 31.12 3.3.62 35.94 38.12 :40.18:49.21 56.82.G3:53 69.69 75.17 80.36 85.23 89.84 98.42 106.30 113.64 120.54 I27.06 z 1:1 I M 13.36 18.89 23.14 26.72 29.87 32.72 35.34 37.78 40.08. 42.24'.'51.74 59 74,66;79 73.17 79.03 84.49 89.61 94.46 103.48 111.77 119.48 126.73 133.59 'Calculated from t 65.41 X,r a+ 4•M X s.. +0.0651Jr 1 l IS- topographic fector r> + 10,000 + 00.000 /172.5J I.slope length,ft(m X 0.3048) z a-slope steepness, (' m -exponent dependent upon slope steepness (0.2 for slopes<1%,0.3 for dopes I to 3%, 0.4 for dopes 3.5 to 4.5%,and r 0.5 for dopes>5%) KING COUNTY , WASHINGTON , SURFACE WATER DESIGN MANUAL T = dewatering time (24 hours) g = acceleration of gravity (32.2 feet/second2) 2. Convert the required surface area to the required diameter of the orifice: The orifice diameter (D) in inches is: D = 24 xE� 3. The vertical, perforated tubing connected to the dewatering orifice must be at least 2 inches larger in diameter than the orifice to improve flow characteristics. The size and number of performations in the tubing should be large enough so that the tubing does not restrict flow. The flow rate should be controlled by the orifice. Additional Design Specifications Pond Divider The pond shall be divided into two roughly equal volume cells by a permeable divider that will reduce turbulence while allowing movement of water between cells. The divider shall be at least one-half the height of the riser and a minimum of 1 foot below the top of the riser. Wire- backed, 2-3 feet high, extra strength filter fabric (Section 5.4.3.1) supported by treated 4"x4"s can be used as a divider. Alternatively, staked straw bales wrapped with filter fabric may be used. If the pond is more than 6 feet deep, a different mechanism must be proposed. A riprap embankment is one acceptable method of separation for deeper ponds. Other designs that satisfy the intent of this provision are allowed as long as the divider is permeable, structurally sound, and designed to prevent erosion under or around the barrier. Depth Gauge .To aid in determining sediment depth, one-foot intervals shall be prominently marked on the riser. Embankment If an embankment of more than 6 feet is proposed, the pond must comply with the criteria for Berm Embankment/Slope Stabilization in Section 4.4.4. FIGURE 5.4.5.2A SEDIMENT POND PLAN VIEW KEY DMDER INTO SLOPE TO PREVENT FLOW AROUND SIDES THE POND LENGTH SHALL BE J TO 6 TIMES THE MAXIMUM POND WIDTH EMERGENCY OVERFLOW SPILLWAY a �Q POND LENGTH a r+FLaW a Q SILT FENCE OR EOUIVALENT pMDER RISER fPE DISCHARGE TO STAB41ZED CONVEYANCE. OUTLET OR LEVEL SPREADER NOTE: POND MAY BE FORMED BY BERM OR BY PARTIAL OR COMPLETE EXCAVATION �'U 5.4.5.2-3 11/94 • $ • °krw4 Igor Wil Nil CNI 914 � `.�� lqkl IMI a. �mom j •f , •1 • w - �i•Y�il�III� ''� ,' � \�i t Lit �. ax r l�1 , V ac JA 00 • i �B Al " I UIN) 3UKrA (- h WATER DESIGN MANUAL FIGURE 4.3.311 AVERAGE VELOCITIES FOR ESTIMATING TRAVEL TIME FOR OVERLAND FLOW* *For use with the Rational Method only; From Soil Conservation Service,Tech.Release No.55,January 1975 0 0 0 U 0 a)00 fl- CO U') 'qt CV) LO C)� C� 00000 C) 0 O CD C) 0 O O O 0000 0 0 C; cli ............. ........................il.ul.! ..... ...... ........ ...... ........................ . ........... C) .. .. ..... ...... ..... ........... .................... .............. ............ ............. ......................... 0 .............................................. ..... ........... ..... .... .................... .................. ................... .............. 0 Yj . ........... ...... 4-i- ... .................................. ..................... -'ozz ........... ................... 410 ..................... ..................... ..................... .. . ........................... ............... ........ ............................... .......................... .... .......... . ....... ........ .......... ........ ............ .................. .......................... ............f ............... L0 ................. ........... ........... ....................... N;r .. ..................... ... ... ... ................................. & .............. 'q . . . .... .... .................... -4.. ...... .............. ... ........... ... ............ .... ...... .............. .... ............................... ............... ----------- ....... ..................... C\j Qc 'fop ... .... ...... ........ ............. ... ..... ........ ............ .................. ........ ... .............. ............ ................... > ................. .4.... ................ .. .. .......... .......................... ..... ..................... ........ ............ .... .......... ....... ................................... .01. ..... .......... L0 -4.......... U') C> ... .................... ............... ........... .............. CD .................. ..................... ............. ............... ............ .......................... C) ........ .......................... ................... Cl) Cn 0 C\! C1 C) 0 0 a)00 r- (0 Ln cr) C\j LO U) IT CV) C\j C) C5 6 6 6 C;6666 6 6 0' CD\ 6 O ("/U)9dojS esinoweleM 4.3.3-6 1/90 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL 1R.' Peak Rainfall Intensity The peak rainfall intensity (IR) for the specified return frequency (R) design storm Is determined using a unit peak rainfall intensity factor OR) for a given return frequency (R) design storm using the following equation: IR = (PON) where: PR = is the total precipitation at the project site for the 24-hour duration design storm event for the given return frequency (from the Isopluvial Maps in Figures 3.5.1 C through 3.5.1 H) iR = (aR)(T,,)-(hR) ; the unit peak rainfall intensity factor Where T, = time of concentration (minutes), calculated using the method described below only (T,, minimum value is 6.3 minutes) aR and bR are coefficients (from Table 4.3.36) used to adjust the equation for the design storm return frequency (R) This "IR" equation was developed by SWM Division staff from equations originally developed by Ron Mayo, P.E.. It is based on the original Renton/Seattle Intensity/Duration/Frequency (I.D.F.) curves. Rather than requiring a family of curves for various locations in King County this equation adjusts proportionally the Renton/Seattle I.D.F. curve data by using the 24-hour duration total precipitation isopluvial maps. This adjustment is based on the assumption that the localized geo-climatic conditions that control the total volume of precipitation at a specific location also control the peak intensities proportionally. Figure 4.3.3A has been included to demonstrate that this unit peak rainfall intensity (io will generate a curve with the same characteristics as the historic 25 year I.D.F. curve. Note, T. must not be less than 6.3 minutes or greater than 100 minutes. On the historic I.D.F. curves the lower limit was set at 5 minutes, 6.3 minutes was selected based on the mathematical limits of the equation coefficients. TABLE 4.3.3E COEFFICIENTS FOR THE RATIONAL METHOD "iR° -EQUATION DESIGN STORM RETURN FREQUENCY (YEARS) aR b R 2 Year 1.58 0.58 5 Year 2.33 0 63 25_Year -_2_66 _ ---- - - —50 Year 2.75 - 0.65 100 Year 2.61 0.63 4.3.3-3 Ion t� y 5?ao st UD ST st -` v.^ M.h,11{Ln•Lry. �'eim ;P�e �•.t� •, . ,MAPLf_WOUL :.�•e //��jj�j`�V T ,e a '_./ ` ;1,04 ,\ �� �x��sr •� to; ' Lvcaliv�� Mal T�� race""�� �"� _ � c y�• /.4y�- d \�r�y, uue\ uue �y��r V re`4 � —� I `•i,uo� e.tj �� �� /web• •,/ ��. •e NAN �SAC, � �1 uae zoo' een I TAT••I• �••�:� _ _ IC I- � C. I c f •1 D 1 I •nv._�bry Y 4b uue bs Its _fil 1 1 1 1,2s ,.". \ eb ,a.. _ IICI_ .LEI Ill .�1( l Et. A%'L� - I' u ! ue — l�Ile I n' l — ,je ,.:I r`I »� � �'`,�,' - ,_�i��, ,;� Y� ,�'� — (�y/�� � ��- • ���' Isl �LJlJ la�l -;�� -..:,,, Mr,", / L r.1 � J '�' J .?\\,•,'/fie � ,d" ,p'. C \\°��x 37 roil �;�,.,,, ,�/ ,c C � � °-! l�J;•� niu �+'.:� ,�'• - ,.... LJ 4� / I,II��,� / ,hl e� _ _tee_ _.L.«•—r•"=. ^ '®\`I!\ \: :6.,:i. !1IS LSD e11 er Serjale Marlufaclu -ed Home Subdivi lion II,li , I ;I. T� f?jZA1NA6jC BAG &� "A-P