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Home My WebLink AboutSDP 16-13; CARLSBAD VETERANS HOUSING; DRAINAGE REPORT; 2020-06-05DRAINAGE REPORT OAK VETERANS HOUSING (SDP 16-13, GR 2020-0008, Drawing No. 523-5A) June 5, 2020 c3 No. 46548 C) Exp. 6/30/21 Cp *'( Wayne \7. Chang, MS, PEZ048 choullummam Civil Engineering o Hydrology a Hydraulics a Sedimentaon P.O. Box 9496 Rancho Santa Fe, CA 92067 (858) 692-0760 TABLE OF CONTENTS Introduction........................................................................................................................................ 1 Hydrologicand Hydraulic Analyses .................................................................................................. 2 Conclusion..................... APPENDICES A. 100-Year Rational Method Analyses and Supporting Data INTRODUCTION The Oak Veterans Housing project is located at 965 and 967 Oak Avenue in the city of Carlsbad (see the Vicinity Map). The project proposes 24 veterans' housing units on a 0.434 acre site. The project will contain a three-story building with a ground level parking structure, hardscape, and landscaping. The site is currently developed with two single-family residences, which will be demolished prior to development. A site development plan (SDP) was approved during entitlements. The project is currently in the final engineering phase and the grading plans are being prepared by Kettler Leweck Engineering. CITY Of? 00ANS1D Vicinity Map This report contains the final engineering hydrologic and hydraulic analyses. The analyses include pre- (existing condition) and post-project (proposed condition) 100-year hydrologic analyses as well as hydraulic analyses of the proposed private storm drain system. HYDROLOGIC AND HYDRAULIC ANALYSES Hydrologic analyses were performed to determine the 100-year flow rates under pre- and post- project conditions. The County of San Diego's 2003 Hydrology Manual rational method procedure was used for the 100-year hydrologic analyses since the overall drainage areas are less than an acre. The rational method input parameters are summarized below and the supporting data is included in Appendix A: Precipitation: The 100-year, 6- and 24-hour precipitation values are 2.60 and 4.50 inches, respectively. Drainage areas: The on-site drainage basins were delineated from the base topography prepared for the project and grading plans by Kettler Leweck Engineering as well as roof drainage information provided by the architect. The existing and proposed condition overall on-site drainage basins were set equal to allow a comparison of results. There is an off-site area to the east that is tributary to the project. Separate drainage facilities system will be constructed to convey runoff from the off-site area to Oak Avenue to prevent commingling with the on-site runoff. The off-site area is 0.26 acres as shown on the attached Proposed Condition Rational Method Work Map. Runoff from the off-site area will be captured by a proposed trench drain along the site's easterly property line. The trench drain will convey the runoff to a curb outlet onto Oak Avenue. Hydrologic soil groups: The hydrologic soil groups were determined from the Natural Resources Conservation Service's (NIRCS) Web Soil Survey. The soil group in the study area is entirely type B. Runoff coefficients: The runoff coefficients were based on the existing and proposed condition impervious percentages outlined in the County Hydrology Manual. Under existing conditions, the overall on-site drainage area is 23 percent impervious, so the low density residential (2.9 DU/A or 25 percent) category was assumed. Under proposed conditions, the overall on-site drainage area is 75 percent impervious, so the high density residential (43.0 DU/A or 80 percent) category was assumed. Both land use categories have slightly higher percent impervious than actual conditions, but the proposed has a greater delta, so the comparison of results will be slightly conservative. For the off-site drainage area, the low density residential (2.9 DU/A or 25 percent) category was assumed based on the current conditions. Flow lengths and elevations: The flow lengths and elevations were obtained from the base topography and engineering plans. Table 1 summarizes the 100-year rational method results. The table indicates that the project will cause a 1.6 cfs increase in the 100-year flow rate. The actual increase will be less if the effects of the six proposed biofiltration basins is considered. Therefore, the project will have minimal impacts on storm runoff. Condition C I, in/hr A, ac Qioo, cfs Existing (Node 12) 0.41 3.80 0.44 0.7 Proposed (Node 36) 0.77 6.66 0.44 2.3 Off-site (Proposed Node 44) 0.41 5.59 0.27 0.6 Table 1. Rational Method Analyses The on-site storm drain system is private. Normal depth hydraulic analyses for sizing of the private storm drain pipes are provided by the "pipeflow" routines in the proposed condition CivilDesign Rational Method output. This is the typical procedure for private storm drain pipes. The private storm drains are being designed based on the normal depth results. CONCLUSION Hydrologic and hydraulic analyses have been performed for final engineering of the Oak Veterans Housing project. The analyses were based on grading plans by Kettler Leweck Engineering as well as the architects input on roof drainage. The site is small at less than 0.5 acres, so the resulting flow increase will be small and further mitigated by the six biofiltration basins. 3 F-11 APPENDIX A 00-YEAR RATIONAL METHOD ANALYSES AND SUPPORTING DATA LEGEND: k t "v TERDRAINAGE BASIN BOUNDARY TE 5 0.44 _C DRAINAGE BASIN AREA FLOW PATH NUMBER 1-7 F10 RATIONAL METHOD NODE BUILDING ib 40 BUILDING 1" = 20' I / I H _ 0 20 II 1101 LLJ i z I N / I LU Il A CONCRETE DWYi ° 0ry .44 AC co W to IN ) Fl-fl _ HED H / -- / / / CONCRETE BUILDING EXISTING CONDITION RATIONAL ME- LEGEND: = DRAINAGE BASIN BOUNDARY OVERLAND FLOW PATH PROPOSED DRAINAGE FACILITY 0.26 AC DRAINAGE BASIN AREA 110 I RATIONAL METHOD NODE NUMBER (9 1 = 20'PROPOSED TRENCH J f'\ DRAIN TO STREET 0 2O, H Di 111TEIRS Tv rz LU 'N Qo PROPOSED CONDITION RATIONAL METHOD WORK MAP _______________________________IIIIIII ______ 1111110 I ' I'IIIIIIIIIIIIIIII Intensity (in/hr) i. -• = 6-Hour Pre JllIIl;IIIIIII b! 11-141-11-1,161, 1,151,111 ON 111,911w!111111. 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K'•.\ ,21 0 - \j I 245' P24=4.5" AnUSD DPW IMFIERLAL M e X l C 3230 S 32'30' 3 0 3Mlles San Diego County Hydrology Manual Section: 3 Date: June 2003 Page: 6of26 Table 3-1 RUNOFF COEFFICIENTS FOR URBAN AREAS Land Use Runoff Coefficient "C" Soil Type NRCS Elements County Elements % IMER. A '13' C D Undisturbed Natural Terrain (Natural) Permanent Open Space 0* 0.20 0.25 0.30 0.35 Low Density Residential (LDR) Residential, 1.0 DU/A or less 10 0.27 0.32 0.36 0.41 Low Density Residential (LDR) Residential, 2.0 DU/A or less 20 0.34 0.38 0.42 0.46 Low Density Residential (LDR) Residential, 2.9 DU/A or less 25 0.38 0.41 0.45 0.49 Medium Density Residential (MDR) Residential, 4.3 DU/A or less 30 0.41 0.45 0.48 0.52 Medium Density Residential (MDR) Residential, 7.3 DU/A or less 40 0.48 0.51 0.54 0.57 Medium Density Residential (MDR) Residential, 10.9 DU/A or less 45 0.52 0.54 0.57 0.60 Medium Density Residential (MDR) Residential, 14.5 DU/A or less 50 0.55 0.58 0.60 0.63 High Density Residential (HDR) Residential, 24.0 DU/A or less 65 0.66 0.67 0.69 0.71 High Density Residential (HDR) Residential, 43.0 DU/A or less 80 0.76 0.77 0.78 0.79 Commercial/Industrial (N. Corn) Neighborhood Commercial 80 0.76 0.77 0.78 0.79 Commercial/Industrial (G. Corn) General Commercial 85 0.80 0.80 0.81 0.82 Commercial/Industrial (O.P. Corn) Office Professional/Commercial 90 0.83 0.84 0.84 0.85 Commercial/Industrial (Limited I.) Limited Industrial 90 0.83 0.84 0.84 0.85 Commercial/Industrial (General I.) General Industrial 95 0.87 0.87 0.87 0.87 *The values associated with 0% impervious may be used for direct calculation of the runoff coefficient as described in Section 3.1.2 (representing the pervious runoff coefficient, Cp, for the soil type), or for areas that will remain undisturbed in perpetuity. Justification must be given that the area will remain natural forever (e.g., the area is located in Cleveland National Forest). DU/A = dwelling units per acre NRCS = National Resources Conservation Service 3-6 C 33 94-SN LA S S 468210 468250 6 Hydrologic Soil Group—San Diego County Area, California 468050 - 468130 33°944N ,-- I \ V NA \\ ,3 \\ \\ - _ , -: K s - $k Ilk 40 -\ 'S 21, 001, 33937W 4681 Map Scab: 1:1,720 Wpdnd on A landscape (lix 8.5') sheet Meters o N o 25 so ioo 150 Feet J 0 50 100 200 300 Map prnjection: Web Mercator Corner coordinates: WGSE4 Edge tics: UTM Zone uN WGS84 USDA Natural Resources Web Soil Survey MM Conservation Service National Cooperative Soil Survey 4681L ObL 3 5/4/2016 Page 1 0f4 Hydrologic Soil Group—San Diego County Area, California MAP LEGEND MAP INFORMATION Area of Interest (AOl) C The soil surveys that comprise your AOl were mapped at 1:24,000. Area of Interest (AOl) • C/D Warning: Soil Map may not be valid at this scale. Soils Soil Rating Polygons D Enlargement of maps beyond the scale of mapping can cause 22 A D Not rated or not available misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting AID Water Features soils that could have been shown at a more detailed scale. ..-. Streams and Canals Transportation Please rely on the bar scale on each map sheet for map BID 4-g4 Rails measurements. [ C Interstate Highways Source of Map: Natural Resources Conservation Service C/D Web Soil Survey URL: http:llwebsoilsurvey.nrcs.usda.gov US Routes Coordinate System: Web Mercator (EPSG:3857) D OW-1 Major Roads Maps from the Web Soil Survey are based on the Web Mercator Not rated or not available ___ Local Roads projection, which preserves direction and shape but distorts __ distance and area. A projection that preserves area, such as the Soil Rating Lines Background Albers equal-area conic projection, should be used if more accurate A Aerial Photography calculations of distance or area are required. AID This product is generated from the USDA-NRCS certified data as of B the version date(s) listed below. B/D Soil Survey Area: San Diego County Area, California Survey Area Data: Version 9, Sep 17, 2015 C Soil map units are labeled (as space allows) for map scales 1:50,000 C/D or larger. j. D Date(s) aerial images were photographed: Nov 3, 2014—Nov 22, . Not rated or not available 2014 Soil Rating Points The orthophoto or other base map on which the soil lines were A compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting • AID of map unit boundaries may be evident. • B • B/D USDA Natural Resources Web Soil Survey 5/4/2016 21111111111111 Conservation Service National Cooperative Soil Survey Page 2 of 4 Hydrologic Soil Group—San Diego County Area, California Hydrologic Soil Group Hydrologic Soil Group— Summary by Map Unit - San Diego County Area, California (CA638) Map unit symbol Map unit name Rating Acres in AOl Percent of AOl MIC) Manna loamy coarse sand, 2 to percent slopes B - 11.1 100.0% Totals for Area of Interest 11.1 100.0% Description Hydrologic soil groups are based on estimates of runoff potential. Soils are -assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long-duration storms. The soils in the United States are assigned to four groups (A, B, C, and D) and three dual classes (AID, BID, and C/D). The groups are defined as follows: Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly wet. These consist mainly of deep, well drained to excessively drained sands or gravelly sands. These soils have a high rate of water transmission. Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture. These soils have a moderate rate of water transmission. Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission. Group D. Soils having a very slow infiltration rate (high runoff potential) when thoroughly wet. These consist chiefly of clays that have a high shrink-swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission. If a soil is assigned to a dual hydrologic group (AID, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are in group 0 are assigned to dual classes. Rating Options Aggregation Method: Dominant Condition Component Percent Cutoff: None Specified USDA Natural Resources Web Soil Survey 5/4/2016 Conservation Service National Cooperative Soil Survey Page 3 of 4 San Diego County Rational Hydrology Program CIVILCADD/CIVILDESIGN Engineering Software, (c)1991-2009 Version 7.8 Rational method hydrology program based on San Diego County Flood Control Division 2003 hydrology manual Rational Hydrology Study Date: 03/15/20 ------------------------------------------------------------------------ Oak Veterans Housing Final Engineering Existing Conditions 100-Year Storm Event ********* Hydrology Study Control Information ********** Program License Serial Number 4028 ------------------------------------------------------------------------ Rational hydrology study storm event year is 100.0 English (in-lb) input data Units used Map data precipitation entered: 6 hour, precipitation(inches) = 2.600 24 hour precipitation(inches) = 4.500 P6/P24 = 57.8% San Diego hydrology manual 'C' values used ++++++++++++++++++++++++++++++++++++++++++++++..+++++++-I-++++++++++++++ Process from Point/Station 10.000 to Point/Station 12.000 INITIAL AREA EVALUATION Decimal fraction soil group A = 0.000 Decimal fraction soil, group B = 1.000 Decimal fraction soil group C = 0.000 Decimal fraction soil group D = 0.000 [LOW DENSITY RESIDENTIAL (2.9 DU/A or Less Impervious value, Ai = 0.250 Sub-Area C Value = 0.410 Initial subarea total flow distance = 269.000(Ft.) Highest elevation = 71.100(Ft.) Lowest elevation = 68.000(Ft.) Elevation difference = 3.100(Ft.) Slope = 1.152 1 INITIAL AREA TIME OF CONCENTRATION CALCULATIONS: The maximum overland flow distance is 70.00 (Ft) for the top area slope value of 1.15 %, in a development type of 2.9 DU/A or Less In Accordance With Figure 3-3 1 Initial Area Time of Concentration = 9.91 minutes TC = [1.8*(1.1_C)*distance(Ft. )".5)/(% slopeA(1/3)] TC= [1.8*(1.1_0.4100)*( 70.000".5)/( 1.152'(1/3)1= 9.91 The initial area total distance of 269.00 (Ft.) entered leaves a remaining distance of 199.00 (Ft.) Using Figure 3-4, the travel time for this distance is 2.56 minutes for a distance of 199.00 (Ft.) and a slope of 1.15 % with an elevation difference of 2.29(Ft.) from the end of the top area Tt = [11.9*length(Mi)A3)/(elevation change(Ft.))Y'.385 *60(min/hr) = 2.565 Minutes Tt=[(l1.9*0.03773)/(, 2.29)]A.385= 2.56 Total initial area Ti = 9.91 minutes from Figure 3-3 formula plus 2.56 minutes from the Figure 3-4 formula = 12.48 minutes Rainfall intensity (I) = 3.798(In/Hr) for a 100.0 year storm Effective runoff coefficient used for area (Q=KCIA) is C = 0.410 Subarea runoff = 0.685(CFS) Total initial stream area = 0.440(Ac.) End of computations, total study area = 0.440 (Ac.) 2 San Diego County Rational Hydrology Program CIVILCADD/CIVILDESIGN Engineering Software, (C) 1991-2009 Version 7.8 Rational method hydrology program based on San Diego County Flood Control Division 2003 hydrology manual Rational Hydrology Study Date: 06/05/20 ------------------------------------------------------------------------ Oak Veterans Housing Final Engineering Proposed Conditions 100-Tear Storm Event Hydrology Study Control Information ********** ---------------------------------------------------------------------- Program License Serial Number 4028 ------------------------------------------------------------------------ Rational hydrology study storm event year is 100.0 English (in-lb) input data Units used Map data precipitation entered: 6 hour, precipitation(inches) = 2.600 24 hour precipitation(inches) = 4.500 P6/P24 = 57.8% San Diego hydrology manual 'C' values used Process from Point/Station 10.000 to Point/Station 12.000 INITIAL AREA EVALUATION **** Decimal fraction soil group A = 0.000 - Decimal fraction soil group B = 1.000 Decimal fraction soil group C = 0.000 Decimal fraction soil group D = 0.000 [HIGH DENSITY RESIDENTIAL (43.0 DU/A or Less Impervious value, Al = 0.800 Sub-Area C Value = 0.770 Initial subarea total flow distance = 86.000(Ft.) Highest elevation = 71.100(Ft.) Lowest elevation = 67.300(Ft.) Elevation difference = 3.800(Ft.) Slope = 4.419 % Top of Initial Area Slope adjusted by User to 4.767 % INITIAL AREA TIME OF CONCENTRATION CALCULATIONS: The maximum overland flow distance is 95.00 (Ft) for the top area slope value of 4.77 %, in a development type of 43.0 DU/A or Less 1 In Accordance With Figure 3-3 Initial Area Time of Concentration = 3.44 minutes TC = [1.8*(1.1_C)*distance(Ft.)A.5)/(% slopeA(1/3)I TC = [1.8*(1.1_0.7700)*( 95.000".5)/( 4.767"(1/3)1= 3.44 Calculated TC of 3.440 minutes is less than 5 minutes, resetting TC to 5.0 minutes for rainfall intensity calculations Rainfall intensity (I) = 6.850(In/Hr) for a 100.0 year storm Effective runoff coefficient used for area (Q=KCIA) is C = 0.770 Subarea runoff = 0.422(CFS) Total initial stream area = 0.080(Ac.) Process from Point/Station 12.000 to Point/Station 14.000 PIPEFLOW TRAVEL TIME (Program estimated size) **** Upstream point/station elevation = 63.620(Ft.) Downstream point/station elevation = 62.810(Ft.) Pipe length = 86.10(Ft.) Slope = 0.0094 Manning's N = 0.013 No. of pipes = 1 Required pipe flow = 0.422(CFS) Nearest computed pipe diameter = 6.00(In.) Calculated individual pipe flow = 0.422(CFS) Normal flow depth in pipe = 3.97(In.) Flow top width inside pipe = 5.68 (In.) Critical Depth = 3.97(In.) Pipe flow velocity = 3.06(Ft/s) Travel time through pipe = 0.47 mm. Time of concentration (TC) = 3.91 mm. Process from Point/Station 14.000 to Point/Station 14.000 SUBAREA FLOW ADDITION Calculated TC of 3.909 minutes is less than 5 minutes, resetting TC to 5.0 minutes for rainfall intensity calculations Rainfall intensity (I) = 6.850(In/Hr) for a 100.0 year storm Decimal fraction soil group A = 0.000 Decimal fraction soil group B = 1.000 Decimal fraction soil group C = 0.000 Decimal fraction soil group D = 0.000 [HIGH DENSITY RESIDENTIAL (43.0 DU/A or Less Impervious value, Ai = 0.800 Sub-Area C Value = 0.770 Time of concentration = 3.91 mm. Rainfall intensity = 6.50(In/Hr) for a 100.0 year storm Effective runoff coefficient used for total area (Q=KCIA) is C = 0.770 CA = 0.146 Subarea runoff = 0.580(CFS) for 0.110(Ac.) Total runoff = 1.002(CFS) Total area = 0.190(Ac.) 61 ++++-1-+++++++++++++++++++++++++++++++++++++++-1-+++++++++++++++++++++++++ Process from Point/Station 14.000 to Point/Station 16.000 PIPEFLOW TRAVEL TIME (Program estimated size) **** Upstream point/station elevation = 62.810(Ft.) Downstream point/station elevation = 61.750(Ft.) Pipe length = 109.13(Ft.) Slope = 0.0097 Manning's N = 0.013 No. of pipes = 1 Required pipe flow = 1.002(CFS) Nearest computed pipe diameter = 9.00(In.) Calculated individual pipe flow = 1.002(CFS) Normal flow depth in pipe = 5.10(In.) Flow top width inside pipe = 8.92(m.) Critical Depth = 5.51(In.) Pipe flow velocity = 3.88(Ft/s) Travel time through pipe = 0.47 mm. Time of concentration (TC) = 4.38 mm. Process from Point/Station 18.000 to Point/Station 16.000 SUBAREA FLOW ADDITION Calculated TC of 4.377 minutes is less than 5 minutes, resetting TC to 5.0 minutes for rainfall intensity calculations Rainfall intensity (I) = 6.850(In/Hr) for a 100.0 year storm Decimal fraction soil group A = 0.000 Decimal fraction soil group B = 1.000 Decimal fraction soil group C= 0.000 Decimal fraction soil group D = 0.000 [HIGH DENSITY RESIDENTIAL (43.0 DU/A or Less Impervious value, Ai = 0.800 Sub-Area C Value = 0.770 Time of concentration = 4.38 mm. Rainfall intensity = 6.850(In/Hr) for a 100.0 year storm Effective runoff coefficient used for total area (Q=KCIA) is C = 0.770 CA = 0.185 Subarea runoff = 0.264(CFS) for 0.050(Ac.) Total runoff = 1.266(CFS) Total area = 0.240(Ac.) Process from Point/Station 16.000 to Point/Station 16.000 SUBAREA FLOW ADDITION **** Calculated TC of 4.377 minutes is less than 5 minutes, resetting TC to 5.0 minutes for rainfall intensity calculations Rainfall intensity (I) = 6.850(In/Hr) for a 100.0 year storm Decimal fraction soil group A = 0.000 Decimal fraction soil group B = 1.000 Decimal fraction soil group C = 0.000 3 Decimal fraction soil group D = 0.000 [HIGH DENSITY RESIDENTIAL (43.0 DU/A or Less Impervious value, Ai = 0.800 Sub-Area C Value = 0.770 Time of concentration = 4.38 mm. Rainfall intensity = 6.850(In/Hr) for a 100.0 year storm Effective runoff coefficient used for total area (Q=KCIA) is C = 0.770 CA = 0.231 Subarea runoff = 0.316(CFS) for 0. 060 (Ac . Total runoff = 1.582(CFS) Total area = 0.300 (Ac.) Process from Point/Station 16.000 to Point/Station 20.000 PIPEFLOW TRAVEL TIME (Program estimated size) **** Upstream point/station elevation = 61.740(Ft.) Downstream point/station elevation = 61.450(Ft.) Pipe length = 29.62(Ft.) Slope = 0.0098 Manning!s N = 0.013 No. of pipes = 1 Required pipe flow = 1.582(CFS) Nearest computed pipe diameter = 9.00(In.) Calculated individual pipe flow = 1.582(CFS) Normal flow depth in pipe = 7.13(In.) Flow top width inside pipe = 7.31(In.) Critical Depth = 6.95(In.) Pipe flow velocity = 4.22(Ft/s) Travel time through pipe = 0.12 mm. Time of concentration (TC) = 4.49 mm. Process from Point/Station 16.000 to Point/Station 20.000 CONFLUENCE OF MINOR STREAMS Along Main Stream number: 1 in normal stream number 1 Stream flow area = 0.300(Ac.) Runoff from this stream = 1.582(CFS) Time of concentration = 4.49 mm. Rainfall intensity = 6.850(In/Hr) +++++++++++++++++++++++++++-l-+++++++++++++++++++++++++++++++++++++++++I Process from Point/Station 30.000 to Point/Station 32.000 INITIAL AREA EVALUATION **** Decimal fraction soil group A = 0.000 Decimal fraction soil group B = 1.000 Decimal fraction soil group C = 0.000 Decimal fraction soil group D = 0.000 [HIGH DENSITY RESIDENTIAL (43.0 DU/A or Less 4 Impervious value, Ai = 0.800 Sub-Area C Value = 0.770 Initial subarea total flow distance = 42.000(Ft.) Highest elevation = 71.100(Ft.) Lowest elevation = 70.600(Ft.) Elevation difference = 0.500(Ft.) Slope = 1.190 % Top of Initial Area Slope adjusted by User to 1.905 % INITIAL AREA TIME OF CONCENTRATION CALCULATIONS: The maximum overland flow distance is 75.00 (Ft) for the top area slope value of 1.91 %, in a development type of 43.0 DU/A or Less In Accordance With Figure 3-3 Initial Area Time of Concentration = 4.15 minutes TC = [1.8* (1 1-C) *distance (Ft.) A .5)/(% slope" (1/3)1 TC = [1.8*(1.1_0.7700)*( 75.000".5)/( 1.905"(1/3)1= 4.15 Calculated TC of 4.15Q minutes is less than 5 minutes, resetting TC to 5.0 minutes for rainfall intensity calculations Rainfall intensity (I) = 6.850(In/Hr) for a 100.0 year storm Effective runoff coefficient used for area (Q=KCIA) is C = 0.770 Subarea runoff = 0.211(CFS) Total initial stream area = 0.040(Ac.) Process from Point/Station 32.000 to Point/Station 34.000 PIPEFLOW TRAVEL TIME (Program estimated size) Upstream point/station elevation = 65.700(Ft.) Downstream point/station elevation = 64.700(Ft.) Pipe length = 93.67(Ft.) Slope = 0.0107 Manning!s N = 0.013 No. of pipes = 1 Required pipe flow = 0.211(CFS) Nearest computed pipe diameter = 6.00(In.) Calculated individual pipe flow = 0.211(CFS) Normal flow depth in pipe = 2.50(In.) Flow top width inside pipe = 5.92 (In.) Critical Depth = 2.76(In.) Pipe flow velocity = 2.72(Ft/s) Travel time through pipe = 0.57 mm. Time of concentration (TC) = 4.72 mm. Process from Point/Station 34.000 to Point/Station 34.000 SUBAREA FLOW ADDITION **** Calculated TC of 4.724 minutes is less than 5 minutes, resetting TC to 5.0 minutes for rainfall intensity calculations Rainfall intensity (I) = 6.850(In,/Hr) for a 100.0 year storm Decimal fraction soil group A = 0.000 Decimal fraction soil group B = 1.000 Decimal fraction soil group C = 0.000 Decimal fraction soil group D = 0.000 5 [HIGH DENSITY RESIDENTIAL (43.0 DU/A or Less Impervious value, Ai = 0.800 Sub-Area C Value = 0.770 Time of concentration = 4.72 mm. Rainfall intensity = 6.850(In/Hr) for a 100.0 year storm Effective runoff coefficient used for total area (Q=KCIA) is C = 0.770 CA = 0.108 Subarea runoff = 0.527(CFS) for 0.100(Ac.) Total runoff = 0.738(CFS) Total area = 0.140(Ac.) Process from Point/Station 34.000 to Point/Station 20.000 ''' PIPEFLOW TRAVEL TIME (Program estimated size) **** Upstream point/station elevation = 64.700(Ft.) Downstream point/station elevation = 64.080(Ft.) Pipe length = 63.95(Ft.) Slope = 0.0097 Manning!s N = 0.013 No. of pipes = 1 Required pipe flow = 0.738(CFS) Nearest computed pipe diameter = 9.00(In.) Calculated individual pipe flow = 0.738(CFS) Normal flow depth in pipe = 4.25(In.) Flow top width inside pipe = 8.99(In.) Critical Depth = 4.70(In.) Pipe flow velocity = 3.60(Ft/s) Travel time through pipe = 0.30 min. Time of concentration (TC) = 5.02 mm. Process from Point/Station 34.000 to Point/Station 20.000 ' CONFLUENCE OF MINOR STREAMS Along Main Stream number: 1 in normal stream number 2 Stream flow area = 0.140(Ac.) Runoff from this stream = 0.738(CFS) Time of concentration = 5.02 mm. Rainfall intensity = 6.832(In/Hr) Summary of stream data: Stream Flow rate TC Rainfall Intensity No. (CFS) (mm) (In/Hr) 1 1.582 4.49 6.850 2 0.738 5.02 6.832 Qmax(1) = 1.000 * 1.000 * 1.582) + 1.000 * 0.895 * 0.738) + = 2.243 Qmax(2) = 0.997 * 1.000 * 1.582) + 6 1.000 * 1.000 * 0.738) + = 2.317 Total of 2 streams to confluence: Flow rates before confluence point: 1.582 0.738 Maximum flow rates at confluence using above data: 2.243 2.317 Area of streams before confluence: 0.300 0.140 Results of confluence: Total flow rate = 2.317(CFS) Time of concentration = 5.021 mm. Effective stream area after confluence = 0.440 (Ac.) Process from Point/Station 20.000 to Point/Station 36.000 PIPEFLOW TRAVEL TIME (Program estimated size) **** Upstream point/station elevation = 64.080(Ft.) Downstream point/station elevation = 60.640(Ft.) Pipe length = 20.27(Ft.) Slope = 0.1697 Manning's N = 0.013 No. of pipes = 1 Required pipe flow = 2.317(CFS) Nearest computed pipe diameter = 9.00(In.) Calculated individual pipe flow = 2.317(CFS) Normal flow depth in pipe = 3.62(In.) Flow top width inside pipe = 8.82(In.) Critical Depth = 8.13(In.) Pipe flow velocity = 13.95 (Ft/s) Travel time through pipe = 0.02 mm. Time of concentration (TC) = 5.04 mm. Process from Point/Station 40.000 to Point/Station 42.000 INITIAL AREA EVALUATION **** Decimal fraction soil group A = 0.000 Decimal fraction soil group B = 1.000 Decimal fraction soil group C = 0.000 Decimal fraction soil group D = 0.000 [LOW DENSITY RESIDENTIAL (2.9 DU/A or Less Impervious value, Ai = 0.250 Sub-Area C Value = 0.410 Initial subarea total flow distance = 25.000(Ft.) Highest elevation = 89.000(Ft.) Lowest elevation = 73.000(Ft.) Elevation difference = 16.000(Ft.) Slope = 64.000 % INITIAL AREA TIME OF CONCENTRATION CALCULATIONS: The maximum overland flow distance is 100.00 (Ft) for the top area slope value of 64.00 %, in a development type of 7 2.9 DU/A or Less In Accordance With Figure 3-3 Initial Area Time of Concentration = 3.11 minutes TC = [1.8*(1.1_C)*distance(Ft.)*.5)/(% slope"(1/3)] TC = [1.8*(1.1_0.4100)*( 100.000'.5)/( 64.000A(1/3)]= 3.11 Calculated TC of 3.105 minutes is less than 5 minutes, resetting TC to 5.0 minutes for rainfall intensity calculations Rainfall intensity (I) = 6.850(In/Hr) for a 100.0 year storm Effective runoff coefficient used for area (Q=KCIA) is C = 0.410 Subarea runoff = 0.028(CFS) Total initial stream area = 0.010(Ac.) ++++++.+++++++++-I-++++-I-++.++++++++++++++++++++++++++++++.++.+++.+++++++ Process from Point/Station 42.000 to Point/Station 44.000 IMPROVED CHANNEL TRAVEL TIME Upstream point elevation = 73.000(Ft.) Downstream point elevation = 71.000(Ft.) Channel length thru subarea = 176.000(Ft.) Channel base width = 3.000(Ft.) Slope or 'Z' of left channel bank = 10.000 Slope or 'Z' of right channel bank = 10.000 Estimated mean flow rate at midpoint of channel = 0.360(CFS) Manning's 'N' = 0.040 Maximum depth of channel = 1.000(Ft.) Flow(q) thru subarea = 0.360(CFS) Depth of flow = 0.112(Ft.), Average velocity = 0.782(Ft/s) Channel flow top width = 5.235(Ft.) Flow Velocity = 0.78(Ft/s) Travel time = 3.75 mm. Time of concentration = 6.86 mm. Critical depth = 0.070(Ft.) Adding area flow to channel Rainfall intensity (I) = 5.588(In/Hr) for a 100.0 year storm Decimal fraction soil group A = 0.000 Decimal fraction soil group B = 1.000 Decimal fraction soil group C = 0.000 Decimal fraction soil group D = 0.000 [LOW DENSITY RESIDENTIAL I (2.9 DU/A or Less Impervious value, Al = 0.250 Sub-Area C Value = 0.410 Rainfall intensity = 5.588(In/Hr) for a 100.0 year storm Effective runoff coefficient used for total area (Q=KCIA) is C = 0.410 CA = 0.111 Subarea runoff = 0.590(CFS) for 0.260(Ac.) Total runoff = 0.619(CFS) Total area = 0.270(Ac.) Depth of flow = 0.150(Ft.), Average velocity = 0.920(Ft/s) Critical depth = 0.098 (Ft.) End of computations, total study area = 0.710 (Ac.) 8