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Home My WebLink AboutCT 01-03; CALAVERA HILLS VILLAGE E-1; TEMPORARY DESILTING BASIN REPORT; 2003-11-20CALAVERA HILLS PHASE II TEMPORARY DESILTING BASIN REPORT JOB NO. 98-1020 PREPARED: NOVEMBER 20, 2003 C60223 EXP ('1* QFC /-d KEITH HANSEN RCE 60223 EXP. 06/30/04 O'DAY CONSULTANTS, INC. 2710 LOKER AVENUE WEST, SUITE 100 CARLSBAD, CALIFORNIA 92008-6603 TEL: (760) 931-7700 FAX: (760) 931-8680 ///za/eli DATE L 7 INTRODUCTION During the construction phase of Calavera Hills Phase II, desilting basins are used I throughout the site to minimize the amount of sediment that could leave the site in the event of rain. Enclosed are the calculations to determine the necessary sizes of the desilting basins in order to function in accordance with California Regional Water I Quality Control Board and local standards. On November 18, 2003 O'Day Consultants conducted a field survey to verify that the desilting basins were constructed, at a minimum, to the sizes calculated. I I I. I I I I I DESILTING BASIN SIZING As = 1.2 Q/Vs (OPTION 3 REGIONAL WATER QUALITY CONTROL BOARD FACT SHEET) DESIGN PARTICLE SIZE = 0.01 MM 01 Vs = 0.00024 FT/SEC USING A 10 YR, 6 HOUR STORM EVENT Q1OAVG=CIAVGA C = 0.45 (LARGE PARCEL> 2 AC) 'AVG = P6/6 = 1.7 1N/6 HR = 0.28 IN/HR Q = (.45)(.28)A = 0.13A SURFACE AREA NEEDED = As = 1.2Q/Vs = 650 SF/AC VOLUME = RUNOFF FROM 1" 24 HOUR STORM PER CITY OF CARLSBAD FOR BARREN LAND WITH SOIL TYPE D CN =93 DIRECT RUNOFF FROM A 1" STORM = 0.45 IN = 0.375 FT VOLUME = (0.375)(43,560 SF/AC) = 1634 CF/AC 1634 CF WITH 650 SF GIVES A BASIN HEIGHT = 2.5' FOR BASINS DEEPER THAN 2.5' 650 SF/AC WILL DETERMINE BASIN SIZE Option 2: Sediment basin(s), as measured from the bottom of the basin to the principal outlet, shall have at least a capacity equivalent to 3,600 cubic feet of storage per acre draining into the sediment basin. The length of the basin shall be more than twice the width of the basin. The length is. determined by measuring the distance between the inlet and the outlet; and the depth must not be less than three feet nor greater than five feet for safety reasons and for maximum efficiency. I Option 3: Sediment basin(s) shall be designed using the standard equation: As=1.2QJVs Where: As is the minimum surface area for trapping soil particles of a certain size; Vs is the settling velocity of the design particle size chosen; and Q=C x I x A where Q is the discharge rate measured in cubic feet per second; C is the runoff coefficient; I is the precipitation intensity for the 10-year, 67hour rain event and A is the area draining into the sediment basin in acres The design particle size shall be the smallest soil grain size determined by wet sieve analysis, or the fine silt sized (0.01nun) particle, and the Vs used shall be 100 percent of the calculated settling velocity. The length is determined by measuring the distance between the inlet and the outlet; the length shall be more than twice the dimension as the width; the depth shall not be less than three feet nor greater than five feet for safety reasons and for maximum efficiency. (two feet of storage, two feet of capacity). The basin(s) shall be located on the site where it can be maintained on a year-round basis and shall be maintained on a schedule to retain the two feet of capacity; I OR Option 4: The use of an equivalent surface area design or equation, provided that the I design efficiency is as protective or more protective of water quality than Option 3. . I A sediment basin shall have a means for dewatering within 7-calendar days following a storm event. Sediment basins may be fenced if safety (Worker or public) is a concern. I The outflow from a sediment basin that discharges into a natural drainage shall be provided with outlet protection to prevent erosion and scour of the embankment and channel. I 1 .. 15 I I I Li I F~ I COUNTY OF SAN DIEGO 10-YELR 6-11OUft PRECIPIThTgO DEPARTMENT OF SANITATION FLOOD CONTROL 16 ISPLUVLS OF 10-VE& 6-3Ut PRECIPITATION I1 tEflTIIS OF Ail I NCH '-I 3 330 4! U.S. DEPAR1 NATIONAL OCEANIC AN SPECIAL STUDIES ORANCfl OFFICL 3C 118 45' 30' 15' 1170 45' 30' 15' 116 RUNOFF CURVE NUMBERS FOR HYDROLOGIC SOIL-COVER COMPLEXES (C N) TABLE I-A-i AMC la = O.2S Cover Hydrologic Soil Groups Treatment Hydrologic Land Use or Practice 3 Condition 4 A B C D Water Surfaces (during floods) 97 98 99 99 Urban Commercial - industrial 89 90 91 '92 High density residential 75 82 88 90 Medium density residential 13 80. 86 88 Low density residential 70 .. 78 84 87 Barren ' 78' 86 91 Fal' low Straight row 76 85 90 92 Vineyards (See accompanying land-use' description) disked 76 85 90 92 annual grass or Poor 65 78 85 89 legume cover Fair 50 69 79 84 Good 38 , 61 .74 80 74" 84 90 92 72.82 87 89 Straight row Poor 72 81 88 91 Good ' , 67 78 85 89 Contoured Poor 70 79 81+ 88 Good 65 75 82 86 Poor 71 82 88 91 Fair 55 72 81 86 I-A-5 I I I I I I 'I I I I I I I I I I I I I Roads5 (hard surface) (dirt) Row crops Narrowleaf chaparral (LAGEK(WEJ TRIBUTARY AREA = 6.41 AC DESIGN AREA = 6.41 (650) = 4,167 SF BASIN IS 55' WIDE x 85' LONG x 4' DEEP SURFACE AREA = 4,675 SF BASIN IS ADEQUATELY SIZED VILLAGE K (CENTRAL) TRIBUTARY AREA = 2.86 AC DESIGN AREA = 2.86 (650) = 1,859 SF DESIGN VOLUME = 2.86 (1634) = 4,673 CF MCMILL1N TO RAISE OUTLET PIPE 1.5', ADD 2 COURSES OF SAND BAGS, AND EXTEND OUTLET TO DOWNSTREAM OUTLET TO TAMARACK ON 11-20-03. ONCE COMPLETE: BASIN AREA = 55'x 75'=4,125 SF AVG DEPTH = 1.25' VOLUME = 5,156 CF BASIN IS ADEQUATELY SIZED 7VILLAGE K (EAST TRIBUTARY AREA = 6.03 AC DESIGN AREA = 6.03 (650) = 3,920 SF PAVING IS IMMINENT SHOULD THERE BE A THREAT OF RAIN BEFORE PAVING OCCURS, A 40' WIDE x 100' LONG x 3' DEEP BASIN SHALL BE BUILT USING SAND BAGS IN THE CUL-DE-SAC [TILLAGE U TRIBUTARY AREA = 12.26 AC DESIGN AREA = 12.26 (650) = 7,969 SF I BASIN IS 50' WIDE x 165' LONG x 6' DEEP SURFACE AREA = 8,250 SF I BASIN IS ADEQUATELY SIZED I I I I I I I I I I I I I I I I VILLAGE X TRIBUTARY AREA = 7.66 + 22.98 = 30.64 AC DESIGN AREA = 30.64 (650) = 19,916 SF BASIN IS 200' WIDE x 150' LONG x 3' DEEP (AVG) SURFACE AREA = 30,000 SF I :BASIN IS ADEQUATELY SIZED iLAGEW(N) I TRIBUTARY AREA = 7.84 AC DESIGN AREA = 7.84 (650) = 5,096 SF BASIN IS 35' WIDE x 150' LONG x 5' DEEP I SURFACE AREA = 5,250 SF BASIN IS ADEQUATELY SIZED I I TRIBUTARY AREA (WORST CASE) COLLEGE BLVD = 5,000'x 120'= 13.77 AC I VILLAGE U = 12.26 AC VILLAGE Y = 7.66 AC VILLAGE X = 22.98 AC VILLAGE W (SOUTH) =15.24 AC I TRIANGLE = 8.16 AC TOTAL = 80.07 AC DESIGN AREA = 80.07 (650) = 52,046 SF I DESIGN VOLUME = 80.07 (1634) = 130,834 CF BASIN IS 140' x 500' x 2' DEEP (AVG) SURFACE AREA = 70,000 SF I VOLUME = 140,000 CF BASIN IS ADEQUATELY SIZED I I I I I I