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Home My WebLink AboutPD 312; Donahoe Residence - Althea Lane; Hydrology Report; 1989-06-23SDE 3644 JUNE 23, 1989 0176 .MIS ENGINEERING DEPT. LIBRARY City of Carlsbad 2075 LaS Palmas Drive Carisbad, CA 92009-4859 HYDROLOGY & HYDRAULIC CALCULATIONS FOR THE DONAHOE RESIDENCES LmGP- UkJG DESCRIPTION: PARCELS 3 & 4 OF P.M. 12016 CITY OF CARLSBAD PERMIT NO. DRAWING NO. 299-8 & 299-9 ENGINEER OF WORK 4, &&& >,BjgkLJtd R.C.8. #284'1;19 SDE 3644 PAGE 2 PARCELS 3 & 4, P.M. 12016 HYDROLOGY STUDY DRAWING NO. 299-8 & 9 I. ASSUMPTIONS BASED UPON A SITE INVESTIGATION, IT IS MY DETERMINATION THAT AN OVERALL HYDROLOGY STUDY WOULD BE THE MOST EFFICIENT WAY MANUAL" WAS EMPLOYED, BASED ON THE FOLLOWING CRITERIA: TO ANALYZE THESE PROPERTIES. THE COUNTY "DESIGN & PROCEDURE -SOIL TYPE - GROUP D (WORST CASE) -LAND USE - SINGLE FAMILY RESIDENTIAL c=o .55 11. DESCRIPTION OF LAND & HISTORY THE MAJORITY OF THE DRAINAGE BASIN CONSISTS OF GENTLY ROLL- ING TERRAIN WITH A MIXTURE OF BOTH OLDER AND NEWER HOMES. THE VEGETATION SEEMS TO BE CONSISTENT WITH SOUTHERN CALIFOR- NIA, ie, SCRUBS, GRASS LAWNS, MIXTURE OF IMPERIOUS SURFACES TREES ETC. 111. EXPLANATIONS OF CALCULATIONS THE DRAINAGE BASIN IN QUESTION WAS DIVIDED INTO SUB- WATERSHEDS. THESE WATERSHEDS WERE DETERMINED WITH CON- SIDERATION GIVEN TO THE TOPOGRAPHY OF THE AREA AND THE ARIES FOR THE WATERSHEDS NOT LYING ON EXISTING STREETS CROSS THE TOPOGRAPHICAL LINES AT RIGHT ANGLES. THE DRAINAGE BASIN HAS BEEN DIVIDED INTO FIVE MAIN SECTIONS LATE THE APPROPRIATE TC, TIME OF CONCENTRATION AND Q FLOW FOR THE AREA. PRESENSE OF STREETS AND "GUTTER'' FLOW. (NOTE THAT BOUND- A-E. SECTION A HAS BEEN SUBDIVIDED INTO SIX AREAS TO CALCU- ALL CALCULATIONS TO FIND TC AND Q FOR AREAS A1 - A6 -E WERE DONE IN FOLLOWING MANNER. THE RESULTS ARE PRESENTED IN TABULAR FORM. SDE 3644 PAGE 3 JUNE 23, 1989 EXAMPLE: AREA AC AREA (A2) = 2.4 Ac DELTA H = MAX HEIGHT - MIN HEIGHT = 320' - 245' = 75' OVERLAND LENGTH = DISTANCE FROM MAX HEIGHT TO MIN HEIGHT L = 650' % SLOPE = DELTA H/L (100%) = 75'/650' (100%) = 11.5% USE URBAN DRAINAGE CHART WITH % SLOPE ABOVE AND OVERLAND LENGTH TO FIND OVERLAND TRAVEL TIME USE INTENSITY-DURATION DESIGN CHART WITH DURATION, T TO FIND IN- TENSITY. I = 3.4 IN/HR USE RATIONAL METHOD Q = CIA WHERE C = 0.55 QlOO = 0.55 X 3.4 X 2.4 = 4.5 cfs CHECK FOR GUTTER FLOW AND GUTTER FLOW APPLIES FOR THIS AREA. SDE 3644 PAGE 4 JUNE 23, 1989 GUTTER FLOW: DELTA H = MAX STREET HEIGHT - MIN STREET HEIGHT = USE ELEVATION @ INLET FOR MIN STREET HEIGHT = 40' = 245'- 205' GUTTER LENGTH = 1100' % STREET SLOPE = DELTA H/L (100%) = 40/1100 (100%) = 3.6% USE QlOO = 4.5 cfs (FROM OVERLAND PART), THE GUTTER AND ROADWAY FIND THE VELOCITY OF Q. DISCHARGE - VELOCITY CHART INCLUDED AND THE % STREET SLOPE TO v = 4.4 fps TIME = DISTANCE/VELOCITY = 1100'/4.4 fps = (244 SEC) / 60 = 4 MIN. Tc = Toverland + Tgutter = 15 MIN. + 4 MIN. = 19 MIN. IC = 2.9 IN/HR QlOO = CIA = 0.55 X 2.9 X 2.4 QlOO = 3.8 cfs ,- ... .. " L oc N c n n- 0 4 m uo 9 (umu "C 6-but Precipitation (inches) '. .. 0lnoY)oyI 0 uf 0 Y) ! L.UD USE Undeveluped Residenrial: Rum 1 RUSOFF COEFFICIENTS (RATIONAL XETHOD) Coefficient, C Soil Group (1) Single Family .JO .a; .50 .33 ” !lulti-Units .45 .50 .60 . TO ?lobile Homes (2) .45 . 50 . 55 .65 80% Impervious Commercial (2) Industrial (2) 90% Impervious SOTES: . 70 .i5 .a0 ,> - . a3 . so .35 . 90 . P5 (1) Obtain soil group from maps on file with the Departnent of Sanitarid:I and Flood Control. (2) Where actual conditions deviate significantly from the tabulated C, may be revised by multiplying 80% or 90% by the ratio of acvJa? imperviousness values of 30% or 908, the values given for coefficiez: imperviousness to the tabulated imperviousness. However, in no cssc commercial property on D soil group. shnll the final coefficient be less than 0.50. For example: Cor.s:der Actual imperviousness . = 50% Tabulated imperviovsness = SO? Revised C = X 0.85 0.55 -€6 I. . ." ... ....... *"". ... . _. . .. , .-._ .. .. . -. . ,- . . . .. . . . .. .. .. .. . .. SDE 3644 JUNE 23, 1989 PAGE 5 HYDRAULIC CALCULATIONS PARCEL 3, P.M. 12016 DRAWING NO. 299-8 I. ASSUMPTIONS THE FLOW ONTO THIS PROPERTY IS VIA AN EXISTING 18" CMP CUL- VERT SYSTEM AND URBAN OVERLAND FLOW. THE FIRST CALCULATIONS WILL BE TO CHECK THE CAPACITY OF THE EXISTING GRATED INLETS ON PARK DRIVE. ~ ~ 11. CALCULATIONS INLET A: = CAPACITY OF "G-1" INLET (BUREA OF PUBLIC ROADS) P = 2(A + B) = 2(3 + 1i25) = 8.5 FT. QlOO @ A = 44.5 cfs % SLOPE = 3.8% (SLOPE OF PARK DRIVE (COLORED GREY)) FROM "GUTTER AND ROADWAY DISCHARGE CHART" DEPTH = .4 FEET FROM THE "CAPACITY OF GRATE INLET IN SUMP" Qcap = (.75) (8.5) = 6.4 cfs SDE 3644 PAGE 6 JUNE 23, 1989 INLET B P = 8.5 FEET- AS ABOVE Qb = 5.7 cfs % SLOPE = 3.870 ( FROM GUTTER AND ROADWAY DISCHARGE CHART ) DEPTH = .32 FT FROM "CAPACITY OF GRATE INLET IN SUMP CHART" Qcap = (.52) (8.5) = 4.4 cfs = Qcap = 4.4 cfs OUTFLOW OF EXISTING 18" CMP Q TOTAL = QcapA i QcapB + Qc = 6.4 + 4.4 + 6.4 = 17.2 THE QlOO OF 17.2 Cf6 ENTERS THE PROPOSED CONCRETE LINED BROW DITCH AS SHOWN ON PLAN. SEE COMPUTER ANALYSIS FOR KIN SLOPE OF BROW DITCH. USE QTOTAL = 17.2 cfs. SDE 3644 PAGE 7 JUNE 23, 1989 DIAMETER (INCHES) ... .30 MANNINGS N ....... .016 SLOPE (FT/FT) ........ 0.0100 Q (cfs) ........... 17.20 DEPTH (FT) ........... 1.26 DEPTH/DIAMETER .... 0.50 VELOCITY (fps) ....... 6.84 VELOCITY HEAD..... 0.73 AREA (Sq, Ft.) ....... 2.51 CRITICAL DEPTH....... 1.40 CRITICAL SLOPE.... 0.0073 CRITICAL VELOCITY.... 6.07 FROUDE NUMBER..... 1.20 USE SoMIN = 1.0% AREA E QlOO = 1.8cfs THIS FLOW IS FROM ALTHEA LN AND ENTERS PROPOSED CURB OUTLET PER IMPROVEMENT PLAN DWG. NO. 292-4 -CAPACITY OF TYPE "A" (D-25) CURB OUTLET A = 0.75 S.F. R = 0.75/6.5 = 0.115 N = 0.014 S = .017 Qcap = 1.486 X 0.75 X 0.115 X .017= 2.43 CFS 0.014 Q cap > QlOO O.K. SEE FOLLOWING SHEET FOR VELOCITP ANALYSIS. PAGE 8 SDE 3644 JUNE 23, 1989 DIAMETER (INCHES) ... 30 MANNINGS N ....... .016 SLOPE (FT/FT) ........ 0.0200 Q (cfs) ........... 18.00 DEPTH (FT) ........... 1.07. DEPTH/DIAMETER.... 0.43 VELOCITY (fps) ....... 8.95 VELOCITY HEAD..... 1.24 AREA (Sq> Ft.) ....... 2.01 CRITICAL DEPTH....... 1.44 CRITICAL SLOPE.... 0.0074 CRITICAL VELOCITY.... 6.17 FROUDE NUMBER.... 1.75 AREA D QlOO = AREA A + AREA B + AREA C + AREA D ? T - CAP THROUGH PIPE = 6.4 cfs + 4.4cfs + 6.4 cfs + 0.8 cfs = 18.0 cfs THIS IS THE TOTAL FLOW FROM ALL THE BROW DITCHES TO THE FINAL ENERGY DISSIPATOR. USE NO. 2 BACKING PER CITY OF CARLSBAD STANDARDS. SDE 3644 PAGE 9 JUNE 23, 1989 HYDRAULIC CALCULATIONS PARCEL 4 P.M. 12016 DRAWING NO. 299-9 AREA E DIAMETER (INCHES) ... 24 MANNINGS N ....... .016 SLOPE (FT/FT) ........ 0.0200 Q (cfs) ........... 1.80 DEPTH (FT) ........... 0.36 DEPTH/DIAMETER... . 0.18 VELOCITY (fp6) ....... 4.75 VELOCITY HEAD..... 0.35 AREA (Sq> Ft.) ....... 0.38 CRITICAL DEPTH....... 0.46 CRITICAL SLOPE.... 0.0068 CRITICAL VELOCITY.... 3.25 FROUDE NUMBER..... 1.68 SDE 3644 PAGE 10 JUNE 23, 1989 CHECK VELOCITY AND Q @ PROPOSED CURB OUTLET @ SOUTHWEST CORNER OF PROPERTY. DIAMETER (INCHES) ... 24 MANNINGS N ....... .016 SLOPE (FT/FT) ........ 0.0150 Q (cfs) ........... 1.8 DEPTH (FT) ........... 0.30 DEPTH/DIAMETER.... 0.19 VELOCITY (fps) ....... 4.29 VELOCITY HEAD..... 0.29 AREA (Sq> Ft.) ....... .42 CRITICAL DEPTH....... .46 CRITICAL SLOPE.... 0.0068 CRITICAL VELOCITY.... 3.25 FROUDE NUMBER..... 1.46 - BASED ON CURB OUTLET CALC FOR D.P. #3 Qcap = 2.43 > QlOO = 2 (0.9) = 1.8 CFS