The URL can be used to link to this page

Home My WebLink AboutCUP 02-23; PRELIMINARY HYDROLOGY REPORT; 2002-09-09PRELIMINARY HYDROLOGY REPORT FOR LARWIN PARK Carlsbad, California September 9, 2002 Prepared by: GVP Consultants 3764 Cavern Place Carlsbad, California 92008-6585 760.720.0500 LU o.41 Zo 204 11m cc - MJI 'V, ~C(Vrr"' RECEIVED SEP r72002 CITY OF CARLSBAD PLANNING DEPT. Preliminary Hydrology Report LARWIN PARK CONTENTS Page Purpose References Conclusions Hydrology Calculations 2 Appendices Appendix A Hydrology Map - Existing Conditions Appendix B Hydrology Map - Proposed Conditions Preliminary Hydrology Report LARWIN PARK Purpose The purpose of this report is to perform a preliminary analysis of the impact of the proposed Larwin Park improvements on drainage patterns: Planned improvements are separated into the "northerly site" development of an existing graded pad off Vancouver Street, and the "southerly site" construction of additional parking for the dog park and future trail. Since the parking lot will be constructed of permeable materials. (D.G.) and involves no modification of drainage areas, this report concentrates on the northerly site. The existing graded pad at the northerly site drains southerly to the natural canyon. Flows from the pad into the canyon have resulted in erosion at the edge of the graded pad. To control erosion of canyon and avoid impacts of constructing a storm drain to the bottom of the canyon, the proposed design diverts 1.6 acres of the graded area and drains it into the existing storm drain in Vancouver Street. Approximately 0.8 acres of the proposed park area continues to drain westerly into the natural open space. Drainage will be sheet flow to avoid erosion. References 200-scale GIS topographic mapping San Diego County Hydrology Manual (Draft), Sept. 2001 Drawing 189-5 Improvement Plans for CT 74-4 Drawing 189-5A Grading Plans for CT 74-4 Preliminary Grading and Utility Plan, sheet '6 of 11 of Conditional Use Permit Site Plan Package Conclusions Preliminary calculations indicate that the development of the northerly site and the resultant diversion of 1.6 acres into the existing storm drain will increase the 100-yr. runoff by 2.7 c.f.s. (6%). The existing storm drain appears to have sufficient capacity for the minor increase in flow, and drains into an existing detention basin which will serve to further mitigate the effects of the increase. The construction of the small parking area off Vancouver Street will require relocation of the existing curb inlet. Since the inlet is at the low point in the street, a trench grate in the gutter is proposed in conjunction with a new curb inlet to the north of the new driveway. Detailed hydrology calculations will be done with final design of the project which will include calculations for sizing of proposed onsite small-diameter storm drain, grated inlets, and the inlets on Vancouver Street. GVP CONSULTANTS JOB LAQuJit P)4& 3764 Cavern Place SHEET NO. _2.OF (10 CARLSBAD, CA 92008-6585 Ph (760) 720-0500 Fax (760) 720-2282 CALCULATED BY__________________ DATE________________ gvanpeski@homecom CHECKED BY______________________ DATE_________________ SCALE a-.---- -_--.------- .(....CAl-C....UIA 1..U.........fr ........... ......... ........................................ ........................................................ . ............................................................................................................................ O 4 oF t-1.4+.jL.z4t Cb D ipZn L4L 5 ' O Q, 5Z •ri 4) ft)¼!b QCF - x'i I&I f ,'\ 4.6 ........................................ .. ... -o R' ?? st 5.47 is') 45 nJhv1 cab— CIA 4L $Z =1i: *reV )t-'PP CFFi Cue t"F o 16. . 25 lie rZuP.cpp CII.- - (o1(41S)('zL) th GVP CONSULTANTS 3764 Cavern Place CARLSBAD, CA 92008-6585 Ph (760) 720-0500 Fax (760) 720-2282 gvanpeski@home.com JOB SHEET NO._______________________ OF_______(10 ____________ CALCULATED BY_________________________ DATE CHECKED BY DATE Table 3-1 RUNOFF COEFFICIENTS FOR URBAN AREAS Land Use I Runoff Coefficient "C" Soil Type NRCS Elements County Elements % IMPER. A B C D Undisturbed Natural Terrain Permanent Open Space 0* 0.20 0.25 0.30 Low Residential, 1.0 DU/A or less 10 0.27 0.32 0.36 0.41 Low Residential, 2.0 DU/A or less 20 0.34 0.38 0.42 0.46 Low Residential, 2.9 DU/A or less 25 0.38 0.41 0.45 0.49 Medium Density Residential Residential, 4.3 DU/A or less 30 0.41 0.45. 0.48 Medium Density Residential Residential, 7.3 DU/A or less 40 0.48 0.51 0.54 0.57 Medium Density Residential Residential, 10.9 DU/A or less 45 0.52 0.54 0.57 0.60 Medium Density Residential Residential, 14.5 DU/A or less 50 0.55 0.58 0.60 0.63 High Density Residential Residential, 24.0 DU/A or less 65 0.66 0.67 0.69 0.71 High Density Residential Residential, 43.0 DU/A or less 80 0.76 0.77 0.78 0.79 Commercial/Industrial Neighborhood Commercial 80 0.76 0.77 0.78 0.79 Commercial/Industrial General Commercial 85 0.80 0.80 0.81 0.82 Commercial/Industrial Office Professional/Commercial 90 0.83 0.84 0.84 0.85 Commercial/Industrial Limited Industrial 90 0.83 0.84 0.84 0.85. Commercial/Industrial General Industrial 95 0.95-67 0.9587 0.958 0.9587 *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 11 0 1 1'fl. ' OF Orange "4-11 o. County of San Diego Hydrology Manual De Rainfall Isopluvials 100 Year Rainfall Event -6 Hours Isopluvial (inches) a Leucdia Endnftas 3 Cardiffbythesea Solaná Beath Del Mar La Pacific Beath Mission Beadi Oman Beac Point Loma Iuuy_nywpIilIigtls1ai1y.anI Map Notes Stateplane Projeion, Zone6, NAD83 Creation Date: June 22, 2001 NOT TO BE USED FOR DESIGN CALCULATIONS MILES amed 36" RCP outfall to detention basin Worksheet for Circular Channel Project Description Project File c:\program fileshaestad\academic\fmw\data\larwin p.fm2 Worksheet 36" RCP to detention basin Flow Element Circular Channel Method Manning's Formula Solve For Discharge Input Data Mannings Coefficient 0.013 Channel Slope 0.005000 ft/ft Depth 3.00 ft Diameter - 36.00 in Results Discharge 47.16 cfs Flow Area 7.07 ft2 Wetted Perimeter 9.42 ft Top Width 0.73e-7 ft Critical Depth 2.24 ft Percent Full 100.00 Critical Slope 0.006095 ft/ft Velocity 6.67 ft/s Velocity Head 0.69 ft Specific Energy 3.69 ft Froude Number 0.12e-3 Maximum Discharge 50.73 cfs Full Flow Capacity 47.16 cfs Full Flow Slope 0.005000 ft/ft Flow is subcritical. 09/09/02 Academic Edition FlowMaster v5.17 01:15:27 PM Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 (203) 755-1666 Page 1 of 1 A VIA VERA Lj ..' 'fl - N. \ q ' - - -V, %/L- N N OWN - j.III'JIIIJI I __180:'.SI( /t / - - - -- LJLLIIIIILJ '_-•. - - - .. - .5 - WATE' PP- 07, "Ns"I'll, N, )2W HY j) 2.C) LXJc PIA, DR EKt'57I)G CO_tiT1O-)S LW PAZK 70 r •0 ,../( r/11:/::/, T / / N eb VIA VERA A -77 IK JLt1P \\ A.\V I WATE \ \\\ \\ 260 G[7:j\