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Home My WebLink AboutPD 07-02; KAWANO RESIDENCE; HYDROLOGY CALCULATIONS FOR KAWANO RESIDENCE; 2007-03-06II W. HYDROLOGY CALCULATIONS S For KAWANO RESIDENCE 44 'j 7g- APN: 205-220-54-00 CITY OF CARLSBAD, CALIFORNIA Prepared For Gary & Allison Kawano 3690 Highland Drive Carlsbad, CA 92008 PE 1544 PREPARED BY: PASCO ENGINEERING, INC. 535 N. HIGHWAY 101, SUITE A SOLANA BEACH, CA 92075 (858)259-8212 DATE: 01-09-06 REVISED: 3-6-07 T C nprfAf) w ~ITER, RCE 68964 S DATE I U • N:\Hydrology & Hydraulicst1544 HYDRO REPORT.doc S PE # 1544 8:44 AM 3/7/2007 S_J S P0-o.1 Hydrology Study for Kawano Residence PE 1544 TABLE OF CONTENTS SECTION DISCUSSION...............................................................................A CONCLUSION..............................................................................B PRE-CONSTRUCTION 100 YEAR HYDROLOGY CALCULATIONS :........0 POST-CONSTRUCTION 100 YEAR HYDROLOGY CALCULATIONS .......D APPENDIX..................................................................................E Sub-basin 3 Volume Calculation Sub-basin 3 Velocity Calculation Sub-basin 4 Volume Calculation Isopluvials Intensity Duration Curve SCS Soil Classification Delineated Drainage Map N:Hydrology & Hydraulics1544 HYDRO REPORT.doc PE # 1544 8:44 AM 3/7/2007 Hydrology Study for Kawano Residence PE 1544 A. INTRODUCTION The purpose of this report is to analyze the storm water runoff produced from the 100 year storm event of the developed site on Highland Drive. The subject property is physically located at 3690 Highland Drive, Carlsbad California. The property is geographically located at N 33009'00" W 117019'00". Pre-Developed Conditions The existing condition of the project site consists of an existing house at 3690 Highland Drive. A detached driveway off Highland Drive allows for access to the residence. The site is surrounded by single family residences to the north and east. The western boundary is Highland Drive and along the south is Magnolia Avenue. The site is characterized .by a ridge running in the north south direction. Rainfall collected on the eastern portion of the site flows towards the eastern boundary of the site. Runoff in the eastern portion of the property then sheet flows over the eastern property line. Rainfall collected in the western portion of the site generally sheet flows in a westerly direction where runoff ultimately sheet flows over Highland Drive away from the project site. The highpoint of the site occurs near the existing residence at an elevation of 175.0'. The low point occurs along Highland Drive near the north west portion of the site at an elevation of 168.6'. The total volume generated by the site in its existing condition is 0.75 cfs. The calculations for this volume can be seen in the section C of this report. Post- Development Conditions The proposed development consists of the construction of a detached garage with guest residence above. Runoff from the site will flow in the same general manner as in the pre- development condition of the site. Runoff collected in the western portion of the site will continue to flow to the west and runoff collected in the eastern -portion of the site will continue to flow to the east. For the post-development analysis the site was divided into five drainage sub-basins. Runoff generated in sub-basins 1, 2, and 5 do not increase impervious surface and as a result do not contribute to the increase in runoff. Sub-basin 3 collects runoff from a portion of the roof and rain that falls in the rear of the proposed structure. Runoff collected in this sub-basin travels over grass BMP from the rear of the structure to. the front of the structure and discharges along Highland Drive. The total flow for this area N:\Hydrology & Hydraulics\1544 HYDRO REPORT.doc PE # 1544 8:44 AM 3/7/2007 Hydrology Study for Kawano Residence PE 1544 was determined to be 0.24 cfs with a maximum velocity of 3.22 fs. The calculations for this volume and velocity can be seen in the appendix, sheet 1 and 2, respectfully. Sub-basin 4 collects runoff from a portion of the roof and from the proposed driveway. This runoff is then directed to flow towards and over grass BMP strips located at the ends of the proposed driveway. The volume for this sub-basin was found to be 0.25 cfs. The calculations for this volume can be seen in the appendix, sheet 6. The total volume generated by the site in its post-construction condition is 0.78 cfs. The calculations for this volume can be seen in section D of this report Drainage patterns in the eastern portion of the site will not be affected by the proposed structure and therefore not analyzed as part of this hydrology report. A detailed map illustrating the delineated drainage basins has been included in this report. Methodology and Results Introduction The hydrologic model used to perform the hydrologic analysis presented in this report utilizes the Ration Method (RM) equation, Q=CIA. The RM formula estimates the peak rate of runoff based on the variables of area, runoff coefficient, and rainfall intensity. The rainfall intensity (I) is equal to: I = 7.44 x P6 x Where: I = Intensity (in/hr) P6 = 6-hour precipitation (inches) D = duration (minutes - use Tc) Using the Time of Concentration (Tc), which is the time required for a given element of water that originates at the most remote point of the basin being analyzed to reach the point at which the runoff from the basin is being analyzed. The RM equation determines the storm water runoff rate (Q) for a given basin in terms of flow (typically in cubic feet per second (cfs) but sometimes as gallons per minute (gpm)). The RM equation is as follows: Q=CIA Where: Q= flow (in cfs) C = runoff coefficient, ratio of rainfall that produces storm water runoff (runoff vs. infiltration/evaporation/absorption/etc) I = average rainfall intensity for a duration equal to the Tc for the area, in inches per hour. A = drainage area contributing to the basin in acres. N:\Hydrology & Hydraulicstl 544 HYDRO REPORT.doc PE # 1544 8:44 AM 3/7/2007 Hydrology Study for Kawano Residence PE 1544 The RM equation assumes that the storm event being analyzed delivers precipitation to the entire basin uniformly, and therefore the peak discharge rate will occur when a raindrop that falls at the most remote portion of the basin arrives at the point of analysis. The RM also assumes that the fraction of rainfall that becomes runoff or the runoff coefficient C is not affected by the storm intensity, I, or the precipitation zone number. The hydrologic soil group classification for the site is "D". The methodology used herein to determine Qioo is the modified rational method. The computer modeling program utilized to perform the hydrologic analysis of the proposed project site is produced by Advanced Engineering Software (AES2003). The pre and post-development runoff coefficients, used to analyze the both conditions, were determined by using weighted "C" average. C= 0.90 x (% impervious) + Cp x (1-%impervious) Where: Cp = pervious surface runoff coefficient (varies depending on soil type from 0.2 to 0.35 - since analysis assumes type d soils Cp =0.35) For the proposed development the runoff coefficient utilized for the hydrologic analysis of sub-basin 3 is 0.60, based on 45% impervious surface. For sub-basin 4 the runoff coefficient was determined to be 0.86 based on 94% impervious surface. B. CONCLUSION Based on the information and calculations contained in this report it is the professional opinion of Pasco Engineering, Inc. that the proposed method of capturing and conveying the runoff on the corresponding Grading Plan will function to adequately convey Qioo to the appropriate points of discharge. In addition, the proposed drainage will not have an adverse affect on adjacent properties or downstream drainage facilities. N:HydroIogy & Hydraulics\1 544 HYDRO REPORT.doc PE # 1544 8:44 AM 3/7/2007 Hydrology Study for Kawano Residence PE 1544 C. PRE- CONSTRUCTION 100 YEAR HYDROLOGY CALCULATIONS N:HydroIogy & Hydraulics\1544 HYDRO REPORT.doc PE# 1544 8:44 AM 3/7/2007 Pre-construction Runoff Volume Calculation This calculation represents the total volume of runoff from the entire western portion of the project site (sub-basins 1-4). -Assumptions: P6=2.6 Duration, Time of Concentration (D,Tc)= 5 minutes -Area = 9,760 sf or 0.22 ac Impervious surface = 2,630 sf Pervious Surface = 7,130 sf -Runoff Coefficient, C C, Impervious = 0.90 C, Pervious = 0.35 C = (2,630)(0.90)+(7.130)(0.35) = 0.498 9,760 -Intensity, I I = 7.44xP6xD"-0.645 I = 7.44x2.6x5"-0.645 = 6.85 Q=CIA Q = 0.498x6.85x0.22 = 0.75 cfs Hydrology Study for Kawano Residence PE 1544 D. POST-CONSTRUCTION 100 YEAR HYDROLOGY CALCULATIONS N:\Hydrology & llydraulics\1544 HYDRO REPORT.doc PE # 1544 8:44 AM 3/7/2007 Post-construction Runoff Volume Calculation This calculation represents the total volume of runoff from the entire western portion of the project site (sub-basins 1-4). -Assumptions: P6=2.6 Duration, Time of Concentration (D,Tc)= 5 minutes -Area = 9,760 sf or 0.22 ac Impervious surface =2,935 sf Pervious Surface = 6,825 sf -Runoff Coefficient, C C, Impervious = 0.90 C, Pervious = 0.35 C = (2.935)(0.90+(6.825)(0.35) = 0.515 9,760 -Intensity. I I = 7.44xP6xD"-0.645 I = 7.44x2.6x5^-0.645 = 6.85 Q=CIA Q = 0.515x6.85x0.22 0.78 cfs Hydrology Study for Kawano Residence PE 1544 E. APPENDIX N:\Hydrology & Hydraulics\1544 HYDRO REPORT.doc PE # 1544 8:44 AM 3/7/2007 Q = 0.60x6.85x0.059 Sub-basin 3 Runoff Volume Calculation -Assumptions: P6=2.6 Duration, Time of Concentration (D,Tc)= 5 minutes -Area = 2,593 sf or 0.059 ac Impervious surface = 1,175 sf Pervious Surface = 1,418 sf -Runoff Coefficient, C C, Impervious = 0.90 C, Pervious = 0.35 C =(1,175)(0.90)+(1.418)(0.35) = 0.60 2,593 -Intensity, I I = 7.44xP6xDA0.645 I = 7.44x2.6x5"-0.645 = 6.85 Q=CIA Kawano Velocity Worksheet for Triangular Channel Project Description Project File n:\haested\academicfmw\1544.fm2 Worksheet Kawano Flow Element Triangular Channel Method Manning's Formula Solve For Discharge Input Data Mannings Coefficient 0.013 Channel Slope 0.043000 ft/ft Depth 0.10 ft Left Side Slope 50.000000 H : V Right Side Slope 100.000000 H: V Results Discharge 2.41 cfs Flow Area 0.75 ft2 Wetted Perimeter 15.00 ft Top Width 15.00 ft Critical Depth 0.15 ft Critical Slope 0.005906 ft/ft Velocity 3.22 ft/s Velocity Head 0.16 ft Specific Energy 0.26 ft Froude Number 2.54 Flow is supercritical. 02/14/07 Academic Edition FlowMaster v5.17 03:44:24 PM Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 (203) 755-1686 Page 1 of 1 Sub-basin 4 Runoff Volume Calculation -Assumptions: P6=2.6 Duration, Time of Concentration (D,Tc)= 5 minutes -Area = 1,900 sf or 0.043 ac Impervious surface = 1,780 sf Pervious Surface = 120 sf -Runoff Coefficient, C C, Impervious = 0.90 C, Pervious = 0.35 C = (1,780)(0.90)+(120)(0.35) = 0.86 1,900 -Intensity, I I = 7.44xP6xD"-0.645 I = 7.44x2.6x5"-0.645 = 6.85 Q=CIA Q = 0.86x6.85x0.043 = 0.25 cfs San Diego County Hydrology Manual Section: 3 Date: June 2003 Page: 6 of 26 Table 3-1 RUNOFF COEFFICIENTS FOR URBAN AREAS Land Use I Runoff Coefficient "C" Soil Type NRCS Elements Elements 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 bU/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 (1-IDR) 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 0.71 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 1.) 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 rernain 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