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HomeMy WebLinkAboutCT 05-21; GREYHAWK BUSINESS PARK; PRELIMINARY HYDROLOGY STUDY; 2009-11-11i;t2c1 zc,c? / Date / PRELIMINARY HYDROLOGY STUDY I I I I I I I I I I I I I I I I I I I STATE STREET CONDOS Job No. 051117-05 Prepared: March 11, 2009 Prepared by: O'DAY CONSULTANTS, INC. 2710 Loker Avenue West, Suite 100 Carlsbad, California 92010-6609 Tel: (760) 931-7700 Fax: (760)931-8680 RCE 32014 Georg 'D Exp. 12/31/10 PRELIMINARY HYDROLOGY STUDY STATE STREET CONDOS TABLE OF CONTENTS ITEM PAGE COVER SHEET.................................................................................i TABLE OF CONTENTS..........................................................................ii 1.0 INTRODUCTION......................................................................1 1.1 PURPOSE OF STUDY......................................................1 1.2 VICINITY MAP..............................................................1 1.3 SCOPE........................................................................1 1.4 HYDROLOGIC ANALYSIS ................................................ 1 2.0 HYDROLOGY............................................................................2 2.1 RATIONAL METHOD DESCRIPTION..................................2 2.2 SOIL HYDROLOGIC GROUP DETERMINATION...................2 2.3 HYDROLOGY CALCULATION KNOWN VARIABLES............3 I 3.0 EXISTING CONDITIONS ANALYSIS.............................................3 3.1 EXISTING TIME OF CONCENTRATION..............................3 3.2 RAINFALL INTENSITY....................................................3 I 3.3 EXISTING CONDITIONS DISCHARGE.................................4 4.0 PROPOSED CONDITION ANALYSIS.............................................4 I 4.1 PROPOSED TIME OF CONCENTRATION ............................. 4 4.2 RAINFALL INTENSITY....................................................5 4.3 PROPOSED CONDITIONS DISCHARGE...............................5 P I L I I I I I - ii - 05-1117-5 I I I I I I I I I I I I I I I I I I I I I I I I I I PRELIMINARY HYDROLOGY STUDY STATE STREET CONDOS TABLE OF CONTENTS ITEM PAGE 5.0 CONCLUSION..........................................................................6 6.0 ATTACHMENTS ....................................................................... 7 ATTACHMENTS VICINITY MAP (LARGE SCALE) SAN DIEGO COUNTY HYDROLOGY MANUAL EXCERPTS (2005) FIGURE 3-1: INTENSITY-DURATION DESIGN CHART 100-YEAR RAINFALL ISOPLUVIAL -6 HOUR 100-YEAR RAINFALL ISOPLU VIAL -24 HOUR 0 TABLE 3-1: RUNOFF COEFFICIENTS FOR URBAN AREAS TABLE 3-2: MAXIMUM OVERLAND FLOW LENGTH & INITIAL TIME OF CONCENTRATION FIGURE 3-3: RATIONAL FORMULA - OVERLAND TIME OF FLOW NOMOGRAPH SOIL HYDROLOGIC MAP CITY OF CARLSBAD DESIGN STANDARDS - CHAPTER 5 PRELIMINARY HYDROLOGY STUDY EXHIBIT -iii - 05-1117-5 I I I I I I I I I I I I I I I I I I I PRELIMINARY HYDROLOGY STUDY STATE STREET CONDOS 1.0 INTRODUCTION 1.1 PURPOSE OF STUDY This drainage study was prepared to determine runoff quantities for State Street Condos before and after development. 1.2 VICINITY MAP The State Street Condos are located as follows: PACIFIC OCEAN CITY OF SAN lIARCOS CITY OF ENCINITAS - VICINITY MI? NO S4LE 1.3 SCOPE This study will analyze the 100-Year Design Storm Event Discharge for the State Street Condos site. 1.4 HYDROLOGIC ANALYSIS The existing condition of the site for the purposes of this report consists of several cottages, walkways and landscaping. The existing hydrology was analyzed in this study using runoff coefficients consistent with a medium-density residential development over Type 'B' soils (C-0.51) for the site. The existing Qioo is 0.59 cfs. 1 - 05-1117-5 PRELIMINARY HYDROLOGY STUDY STATE STREET CONDOS The proposed developed condition for State Street Condos as shown on the Tentative Map consists of two multi-unit buildings being constructed on the north and south ends of the site with a drive aisle in the middle. A total of 9 residential units are being proposed. A majority of the runoff will flow via sheet flow and through roof drains into landscape areas and then continue to sheet flow to the gutter. The Tc of the developed State Street Condos (per the Tentative Map design) was assumed to be five minutes, due to the small area of the project (Ch. 5, Section 2.0 - City of Carlsbad Engineering Standards, page 2 of 5). To be consistent with a high-density residential development over Type 'B' soils, a runoff coefficient of 0.67 was used. The Qioo for the proposed conditions is 0.78 cfs. 2.0 HYDROLOGY This hydrologic analysis was performed according to the 2003 San Diego County Hydrology Manual. The Rational Method was used to determine flows. The Rational Method estimates the peak rate of runoff at any location in a watershed as a function of the drainage area (A), runoff coefficient (C), and rainfall intensity (I) for a duration equal to the time of concentration (Tc), which is the time required for water to flow from the most remote point of the basin to the location being analyzed. 2.1 RATIONAL METHOD DESCRIPTION The rational method, as described in the San Diego County Hydrology Manual (2003), was used to estimate surface runoff flows. The basic equation: Q = CIA C = runoff coefficient (varies with surface) I = intensity (varies with time of concentration) A = area in acres In addition, the soil hydrologic group for the project site will also need to be determined first. 2.2 SOIL HYDROLOGIC GROUP DETERMINATION Per the Soil Hydrologic Groups Map in the San Diego County Hydrology Manual (2003), the soil group for the State Street Condos is Group W. A copy of the Soil Hydrologic Groups Map is provided in Section 2: Attachments for reference. I I I I -2- 05-1117-5 I I Li Li I I I I ii L I I I I PRELIMINARY HYDROLOGY STUDY STATE STREET CONDOS 2.3 HYDROLOGY CALCULATION KNOWN VARIABLES The following are the known variables for the hydrology calculations A = area (acres) = 0.28 acres CEXiSt = Existing runoff coefficient = 0.51 (Table 3-1) Cp 0 = Proposed runoff coefficient = 0.67 (Table 3-1) D = length of run = 150 (use 75 based on Table 3-2) P6 = 100 Year Storm Event 6 Hour Value = 2.5 in/hr S = slope = 2.0% 3.0 EXISTING CONDITION ANALYSIS By the rational method, as described in the San Diego County Hydrology Manual (2003), the surface runoff for the 100-Year Design Storm Event for the existing conditions is as follows: 3.1 EXISTING TIME OF CONCENTRATION Time of concentration is calculated as follows: Tc = T + TT Where: T =1.8(1.1_C)D½ S 1/3 Therefore: T = [1.8 (1.1- C) D /21 /S 1/3 = [1.8 (1.1 -.67) (75) ½ / (2.0) 1/3 = [(1.8) (.43) (8.66)] / 1.2599 = 6.703 /1.2599 = 5.32 minutes And: Tj =5 minutes (per City of Carlsbad Standards for small areas) Therefore: Tc = T+T =5.32+5.0 = 10.32 minutes 3.2 RAINFALL INTENSITY Rainfall intensity is calculated as follows: 1100 = 7.44 (P6) (Tc °645 ) Therefore: 1100 = 7.44 (P6) (Tc 0.645) = 7.44 (2.5) (10.32 _0.645) = 7.44 (2.5) (0.22 19) = 4.13 in/hr 3- 05-1117-5 I I I I I I I I I I I I I I I I I I I PRELIMINARY HYDROLOGY STUDY STATE STREET CONDOS 3.3 EXISTING CONDITIONS DISCHARGE Discharge is calculated as follows: Qioo = C Iloo x A Therefore: Qioo =CxI100 xA = (0.51) x (4.13) x (0.28) =0.5898cfs =0.59cfs This discharge is at Confluence Point A. Confluence Point A is at the intersection of the western alley and State Street, in the center of the cross gutter. 4.0 PROPOSED CONDITION ANALYSIS By the rational method, as described in the San Diego County Hydrology Manual (2003), the surface runoff for the 100-Year Design Storm Event for the proposed conditions is as follows: 4.1 PROPOSED TIME OF CONCENTRATION Time of concentration is calculated as follows: Tc = T + TT Where: T = 1.8(1.1 —C)D" s 1/3 Therefore: T = [1.8 (1.1— C) D ½ 1/3 = [1.8 (1.1— .67) (75) ½j / (2.0)1/3 = [(1.8) (.43) (8.66)] / 1.2599 = 6.703 /1.2599 = 5.32 minutes And: Ti = 5 minutes (per City of Carlsbad Standards for small areas) Therefore: Tc = T+T = 5.32 + 5.0 = 10.32 minutes -4- 05-1117-5 I I I I I I I I U I I I I I I I I I I PRELIMINARY HYDROLOGY STUDY STATE STREET CONDOS 4.2 RAINFALL INTENSITY Rainfall intensity is calculated as follows: '100 = 7.44 (P6) (Tc _0645) Therefore: 1100 =7.44 (P6) (Tc 0.645) = 7.44 (2.5) (10.32 -0.645 ) = 7.44 (2.5) (0.2219) =4.13 in/hr 4.3 PROPOSED CONDITIONS DISCHARGE Discharge is calculated as follows: Qioo = C x Iioo x A Therefore: Qioo =CxI100 xA = (0.67) x (4.13) x (0.28) = 0.7748 cfs = 0.78 cfs This discharge is at Confluence Point A. Confluence Point A is at the intersection of the western alley and State Street, in the center of the cross gutter. -5- 05-1117-5 I I I I I I I I I I I I I I I I I I I PRELIMINARY HYDROLOGY STUDY STATE STREET CONDOS 5.0 CONCLUSION The results of the analysis of State Street Condos Qioo at Confluence Point A is presented below: Q100 Analysis at Confluence Point A Confluence Qioo Qioo Qioo Point Existing Proposed Difference cfs cfs cfs A 0.59 0.78 +0.19 The increase in Qioo of 0.19 cfs is due to the increase in the residential density of the proposed State Street Condos. The increase in residential density will increase the impervious surface area of the State Street Condos site. -6- 05-1117-5 I PRELIMINARY HYDROLOGY STUDY STATE STREET CONDOS 6.0 ATTACHMENTS I The following attachments are provided at the end of this report for the Preliminary Hydrology for the State Street Condos: .I • Vicinity Map (Large Scale) San Diego County Hydrology Manual Excerpts (2003) Figure 3-1: Intensity-Duration Design Chart I c 100-Year Rainfall Isopluvial - 6 Hour 100-Year Rainfall Isopluvial —24 Hour Table 3-1: Runoff Coefficients for Urban Areas I c Table 3-2: Maximum Overland Flow Length & Initial Time of Concentration Figure 3-3: Rational Formula - Overland Time of Flow Nomograph Soil Hydrologic Map I . City of Carlsbad Design Standards - Chapter 5 Preliminary Hydrology Study Exhibit I I I I I I I I Lii I I 1 -7- 05-1117-5 I I I 1 CITY OF OCEANSIDE I I i CITY OF VISTA OF I I I I I I I I I I I CITY OF ENCINITAS VICINITY MAP NO SCALE CITY OF SAN MARCOS - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - San Diego County Hydrology Manual Section: 3 Date: June 2003 Page: 6 of 26 Table 3-1 RUNOFF COEFFICIENTS FOR URBAN AREAS Land Use Runoff Coefficient "C" Soil Type % IMPER. A B C D NRCS Elements County Elements 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 (OP. 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 I I I I I I I I I I I I I I I I 'I I I San Diego County Hydrology Manual Section: 3 Date: June 2003 Page: 12of26 Note that the Initial Time of Concentration should be reflective of the general land-use at the upstream end of a drainage basin. A single lot with an area of two or less acres does not have a significant effect where the drainage basin area is 20 to 600 acres. Table 3-2 provides limits of the length (Maximum Length (LM)) of sheet flow to be used in hydrology studies. Initial T1 values based on average C values for the Land Use Element are also included. These values can be used in planning and design applications as described below. Exceptions may be approved by the "Regulating Agency" when submitted with a detailed study. Table 3-2 MAXIMUM OVERLAND FLOW LENGTH (LM) & INITIAL TIME OF CONCENTRATION (T' Element* DU/ Acre .5% 1% 2% 3% 5% 10% LM T1 LM Ti LM Ti LM Ti LM Ti LM Ti Natural 50 13.2 70 12.5 85 10.9 100 10.3 100 8.7 100 6.9 LDR 1 50 12.2 70 11.5 85 10.0 100 9.5 100 8.0 100 6.4 LDR 2 50 11.3 1 70 10.5 85 9.2 100 8.8 100 7.4 100 5.8 LDR 2.9 50 10.7 70 10.0 85 8.8 95 8.1 100 7.0 100 5.6 MDR 4.3 50 10.2 70 9.6 80 8.1 95 7.8 100 6.7 100 5.3 MDR 7.3 50 9.2 65 8.4 80 7.4 95 7.0 100 6.0 100 4.8 MDR 10.9 50 8.7 65 7.9 80 6.9 90 6.4 100 5.7 100 4.5 MDR 14.5 50 8.2 65 7.4 80 6.5 90 6.0 100 5.4 100 4.3 HDR 24 50 6.7 65 6.1 75 5.1 90 4.9 95 4.3 100 3.5 HDR 43 50 5.3 65 4.7 75 4.0 85 3.8 95 3.4 100 2.7 N. Corn 50 5.3 60 4.5 75 4.0 85 3.8 95 3.4 100 2.7 G. Corn 50 4.7 60 4.1 75 3.6 85 3.4 90 2.9 100 2.4 O.P./Com 50 4.2 60 3.7 70 3.1 80 2.9 90 2.6 100 2.2 Limited I. 50 4.2 60 3.7 70 3.1 80 2.9 90 2.6 100 2.2 General 1. 50 3.7 1 60 1 3.2 1 70 1 2.7 80 2.6 90 2.3 1 100 1.9 *See Table 3-1 for more detailed description 3-12 - - - - - - - - - - - - - - - - - - - 100 30 U) W I-- U.1 LL z 20 w C) z - z W (I) w 0 -J LL U) cx 0 10 -J 0 Ix U.1 w EXAMPLE: Given: Watercourse Distance (0) = 70 Feet Slope(s)=1.3% 1.8(1.1-C)V Runoff Coefficient (C) = 0.41 3V__ T= - Overland Flow Time (1); 9.5 Minutes SOURCE: Airport Drainage, Federal Aviation Administration, 1965 FIGURE Rational Formula - Overland Time of Flow Nomograph [ 2.50% slope IF 2.0 -0 VOO4, 000 - 33-30' County of San Diego Hydrology Manual r - - I c 1 Soil Hydrologic Groups 33*16- • gen ç Led OCEAN SoilGroups Group A - Group B -' 1 Group C Group D CPeT Undetermined Data Unavailable DEL vk STA GIS GIS IWPERIAL - - __ ______ * E 32O -- ___ _______ __ 32 3 0 3 Miles __ ____ _________ I I I CHAPTER 5- DRAINAGE AND STORM DRAIN STANDARDS 1. GENERAL I A All drainage design and requirements shall be in accordance with the latest City of Carlsbad Standard Urban Storm Water Mitigation Plan (SUSMP), Jurisdictional Urban Runoff Management Plan (JURMP), Master Drainage and Storm Water I Quality Management Plan and the requirements of the City Engineer and be based on full development of upstream tributary basins. B. Public drainage facilities shall be designed to carry the ten-year six-hour storm I underground and the 100-year six-hour storm between the top of curbs. All culverts shall be designed to accommodate a 100-year six-hour storm with a one I foot freeboard at entry conditions such as inlets and head walls. C. The use of underground storm drain systems, in addition to standard curb and gutter shall be required: When flooding or street overflow during 100-year six-hour storm cannot be maintained between the top of curbs. When 100-year six-hour storm flow from future upstream development (as proposed in the existing General Plan) will cause damage to structures and I improvements. 3) When existing adequate drainage facilities are available for use (adjacent to proposed development). I 4) When more than one travel lane of arterial and collector streets would be obstructed by 10-year 6-hour storm water flow. Special consideration will be I required for super-elevated streets. D. The use of underground storm drain systems may be required: I 1) When the water level in streets at the design storm is within 1' of top of curb. When velocity of water in streets exceeds 11 FPS. 1 When the water travels on surface street improvements for more than 1,000'. I The type of drainage facility shall be selected on the basis of physical and cultural adaptability to the proposed land use. Open channels may be considered in lieu of underground systems when the peak flow exceeds the capacity of a 48" diameter RCP. Fencing of open channels may be required as determined by the City I Engineer. Permanent drainage facilities and right-of-way, including access, shall be provided from development to point of approved disposal. I Page 1 of 5 I I I I G Storm Drains constructed at a depth of 15' or greater measured from finish grade to the top of pipe or structure shall be considered deep storm drains and should be avoided if at all possible. When required, special design consideration will be required to the satisfaction of the City Engineer. Factors considered in the design I will include: 1) Oversized specially designed access holes/air shafts I 2) Line encasements Oversizing lines Increased easement requirements for maintenance access Water-tight joints I 6) Additional thickness of storm drain The project designer should meet with the planchecker prior to initiation of design to I review design parameters. Concentrated drainage from lots or areas greater than 0.5 acres shall not be I discharged to City streets unless specifically approved by the City Engineer. Diversion of drainage from natural or existing basins is discouraged. I J. Drainage design shall comply with the City's Jurisdictional Urban Runoff Management Plan (JURMP) and requirements of the National Pollutant Discharge Elimination System (NPDES) permit. I 2. HYDROLOGY Off site, use a copy of the latest edition City 400-scale topographic mapping. Show I A existing culverts, cross-gutters and drainage courses based on field review. Indicate the direction of flow; clearly delineate each drainage basin showing the I area and discharge and the point of concentration. B. On site, use the grading plan. If grading is not proposed, then use a 100-scale plan or greater enlargement. Show all proposed and existing drainage facilities and drainage courses. Indicate the direction of flow. Clearly delineate each drainage I basin showing the area and discharge and the point of concentration. I C. Use the charts in the San Diego County Hydrology Manual for finding the "Ta" and "I". For small areas, a five minute "Ta" may be utilized with prior approval of the City Engineer. I D. Use the existing or ultimate development, whichever gives the highest "C" factor. E. Use the rational formula Q = CIA for watersheds less than 0.5 square mile unless alternate method is approved by the City Engineer. For watersheds in excess of I an 0.5 square mile, the method of analysis shall be approved by the City Engineer prior to submitting calculations. I I Page 2 of 5 I H I I 3. A Street - provide: Depth of gutter flow calculation. Inlet calculations. Show gutter flow Q, inlet Q, and bypass Q on a plan of the street. B. Storm Drain Pipes and Open Channels - provide: Hydraulic loss calculations for: entrance, friction, junction, access holes, bends, angles, reduction and enlargement. Analyze existing conditions upstream and downstream from proposed system, to be determined by the City Engineer on a case-by-case basis. Calculate critical depth and normal depth for open channel flow conditions. Design for non-silting velocity of 2 FPS in a two-year frequency storm unless otherwise approved by the City Engineer. All pipes and outlets shall show HGL, velocity and Q value(s) for design storm. Confluence angles shall be maintained between 450 and 900 from the main upstream flow. Flows shall not oppose main line flows. 4. INLETS A Curb inlets at a sump condition should be designated for two CFS per lineal foot of opening when headwater may rise to the top of curb. B. Curb inlets on a continuous grade should be designed based on the following equation: Q0.7L(a+y)312 Where: y = depth of flow in approach gutter in feet a = depth of depression of flow line at inlet in feet L = length of clear opening in feet (maximum 30 feet) Q = flow in CFS, use 100-year design storm minimum Grated inlets should be avoided. When necessary, the design should be based on the Bureau of Public Roads Nomographs (now known as the Federal Highway Administration). All grated inlets shall be bicycle proof. All catch basins shall have an access hole in the top unless access through the grate section satisfactory to the City Engineer is provided. Page 3 of 5 I I I cross Catch basins/curb inlets shall be located so as to eliminate, whenever possible, gutters. Catch basins/curb inlets shall not be located within 5' of any curb return or driveway. Minimum connector pipe for public drainage systems shall be 18". G Flow through inlets may be used when pipe size is 24" or less and open channel I flow characteristics exist. 5. STORM DRAINS I A Minimum pipe slope shall be .005 (.5%) unless otherwise approved by the City Engineer. I B. Minimum storm drain, within public right-of-way, size shall be 18" diameter. Provide cleanouts at 300' maximum spacing, at angle points and at breaks in grade greater than 1%. For pipes 48" in diameter and larger, a maximum I spacing of 500' may be used. When the storm drain clean-out Type A dimension of "V" less "Z" is greater than I 18", a storm drain clean-out Type B shall be used. The material for storm drains shall be reinforced concrete pipe designed in I conformance with San Diego County Flood Control District's design criteria, as modified by Carlsbad Standard Specifications. Corrugated steel pipe shall not be used. I Plastic/rubber collars shall be prohibited. Horizontal curve design shall conform to manufacturer recommended I specifications. Vertical curves require prior approval from the City Engineer. The pipe invert elevations, slope, pipe profile line and hydraulic grade line for design flows shall be delineated on the mylar of the improvement plans. Any I utilities crossing the storm drain shall also be delineated. I D The strength classification of any pipe shall be shown on the plans. Minimum -load for RCP shall be 1350 in all City streets or future rights-of-way. Minimum D-load for depths less than 2', if allowed, shall be 2000 or greater. I G For all drainage designs not covered in these Standards, the current San Diego County Hydrology and Design and Procedure Manuals shall be used. H. For storm drain discharging into unprotected or natural channel, proper energy dissipation measures shall be installed to prevent damage to the channel or erosion. In cases of limited access or outlet velocities greater than 18 fps, a concrete energy dissipater per SDRS D-41 will be required. I Page 4 of 5 I I I. The use of detention basins to even out storm peaks and reduce piping is I permitted with substantiating engineering calculation and proper maintenance agreements. Detention basins shall be fenced. 1 J. Desiltation measures for silt caused by development shall be provided and cleaned regularly during the rainy season (October 1 to April 30) and after major rainfall as required by the City Engineer or his designated representative. I Adequate storage capacity as determined by the City Engineer shall be maintained at all times. I K. Protection of downstream or adjacent properties from incremental flows (caused by change from an undeveloped to a developed site) shall be provided. Such flows shall not be concentrated and directed across unprotected adjacent I properties unless an easement and storm drains or channels to contain flows are provided. Unprotected downstream channels shall have erosion and grade control I L. structures installed to prevent degradation, erosion, alteration or downcutting of the channel banks. M. Storm drain pipes designed for flow meeting or exceeding 20 feet per second will require additional cover over invert reinforcing steel as approved by the City Engineer. I N. Storm drain pipe under pressure flow for the design storm, i.e., HGL above the soffit of the Ope, shall meet the requirements of ASTM C76, C361, C443 for water-tight joints in the sections of pipe calculated to be under pressure and an I additional safety length beyond the pressure flow point. Such safety length shall be determined to the satisfaction of the City Engineer taking into consideration such factors as pipe diameter, Q, and velocity. I 0. An all weather access road from a paved public right-of-way shall be constructed to all drainage and utility improvements. The following design parameters are required: Maximum grade 14%, 15 MPH speed, gated entry, minimum paved I width 12 feet, 38' minimum radius, paving shall be a minimum of 4" AC over 4" Class II AB, turnaround required if over 300'. Work areas should be provided as I project approved by the plan checker. Access roads should be shown on the tentative approval to ensure adequate environmental review. P. Engineers are encouraged to gravity drain all lots to the street without use of a I yard drain system. On projects with new street improvements proposed, a curb outlet per SDRSD 0-27 shall be provided for single-family residential lots to allow yard drains to connect to the streets gutter. I I I Page 5 of 5 I C I PRELIMINA R Y DRA INA GE . STUDY SHEET 1 OF 1 0' 20' 10' 40' (#%AS r. 4$ -nAv LEGEND NODE D/REC11ON OF FLOW 6W. 9N rP B , () RA SIN BOUNDARY - ' ~ V~l Ile _1L - 611 STATE STREET 'EXISTIiVG, 1101 A VO/ I . ~k/d V010 /, ~~N V,~p ~0~ - - P - - 1_ - - _JL STA TE STREET (EXISTING) -. 1.11. ..........I.. ..... .. .I if I T7.I7TTI ------------- - STING CONDITIONS PROPOSED CONDITIONS EXISTING SITE DRAINAGE ' PATTERN CONFLUENCE C _BASIN ED 0.51 _I 413 _ACRES_ 0.28. 0.59 PROPOSED. SITE DRAINAGE PATTERN C, ___'ACRES Q100 CONFLUENCE __BASIN PB 0.67 _I 4.13 0.28 0.78 CONFLUENCE POINT DISCHARGE COMPARISON CONFLUENCE POINT EXIST AREA acres PROP AREA acres DIFF. AREA acres EXIST Qioo cfs PROP Qioo cfs DIFF Qioo cfs A 0.28 0.28 —0.00 0.59_ 0.78 +0.19 TOTAL 0.28 0.28 —0.00 0.59_ 0.78 +0.19 0 DESIGNED BY: J.P.Q. DATE: MARCH2009 DRAWN BY.-____J-S- SCALE: -AS SHOWN PROJECT MGR.:_G.O. JOB NO.: 051117 CONSULT NTS 2710 Laker Ave West ' . Civil Engineering ENGINEER OF WORK Suite 100 Planning Carlsbad, California 92010 Processing 760-931-7700 Surveying Fox: 760-931-8680 DATE: Oday@Odayconsultants.com GEORGE O'IMY RCE:32014 ©2009 O'Day Consultants, Inc. ._-.L "--....-....--- I G:\051117\0517DS01.dwg Mar 16, 2009 11:33am Xrefs: 0517MAP; 0517topo; Revised Floor Plan; 0517S11E H H -