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HomeMy WebLinkAboutCT 2018-0001; WALNUT BEACH HOMES; PRELIMINARY HYDROLOGY STUDY; 2018-06-01- ... ... ... ,.. ... ... ... ,.. .. ... -... .. ... ... ... ... .. ... .. ... .. ... ... ... ""'' ... PRELIMINARY HYDROLOGY STUDY FOR TENTATIVE MAP/ SITE DEVELOPMENT PERMIT 362 WALNUT A VENUE CT 2018-0001 / CDP 2018-0003 / PUD 2018-0001 CITY OF CARLSBAD, CA PREPARED FOR: RINCON REAL ESTATE GROUP 3005 S. EL CAMINO REAL SAN CLEMENTE, CA 92672 PREPARED BY: PASCO LARET SUITER & AS SOCIA TES, INC. 535 N. HIGHWAY IOI, SUITE A SOLANA BEACH, CA 92075 PH: (858) 259-8212 Prepared: January 2018 Revised: March 2018 Revised: May 2018 Final: June 20 I 8 ... II, .. ,,. II, ... ... II, ... .. ... .. ---II, -.. ... ... .. .., -... ... .. .. II, .. -.. .. ... Executive Summary Introduction Existing Conditions Proposed Project Conclusions References Methodology Introduction TABLE OF CONTENTS County of San Diego Criteria City of Carlsbad Standards Runoff Coefficient Determination Hydrology & Hydraulic Model Output Pre-Developed Hydro logic Model Output (I 00-Year Event) Post-Developed Hydrologic Model Output (JOO-Year Event) Detention Analysis (I 00-Year Event) Appendix Appendix A: Hydrology Support Material PLSA 2808-01 SECTION 1.0 1.1 1.2 1.3 1.4 1.5 2.0 2.1 2.2 2.3 2.4 3.0 3.1 3.2 3.3 4.0 ... .. -... - ... --.. .. -.. ... .. ... - 1111 ... ... .. .. .. .. ... .. .. ... .. ... .. .. 1111 .. 1111 .. .. PLSA 2808-01 1.0 EXECUTIVE SUMMARY 1.1 Introduction This Preliminary Hydrology Study for the proposed development at 362 Walnut Avenue has been prepared to analyze the hydro logic and hydraulic characteristics of the existing and proposed project site. This report intends to present both the methodology and the calculations used for determining the runoff from the project site in both the pre-developed ( existing) conditions and the post-developed (proposed) conditions produced by the 100- year, 6-hour storm . 1.2 Existing Conditions The subject property is located between Tamarack Avenue and Carlsbad Village Drive, and is geographically settled between the Coastal Rail Trail and railroad tracks to the east, and Lincoln Street, a public street, to the west. The site is bordered by Walnut Avenue to the south, and existing single-and-multi-family residential developments to the north, east, and west. The existing site consists of two single-family residences, with a driveway, hardscape, and landscape improvements typical of this type of development. The property is located within the Carlsbad watershed, and, more specifically, the Agua Hedionda Hydrologic Area. The existing site is comprised of approximately 0.574 acres. Based on a study of the existing topography, the site generally drains from east to west, towards the southwest comer of the property. There does not appear to be any existing storm drain infrastructure located onsite to convey drainage, and runoff sheet flows through the site to the western property line. To the north of the property, an existing berm prevents offsite runon from leaving the multi-family development to the north and entering the subject property . Drainage does not enter the property from the west, as it is downstream of the subject parcel. Lastly, curb, gutter, and sidewalk improvements in the right-of-way along Walnut Avenue -as well as a parkway sloped away from the site -prevent drainage from entering the site to the south. Runoff primarily leaves the site to the west, where it eventually enters the existing curb and gutter in Walnut Avenue. The existing curb and gutter conveys drainage west to a sump inlet located approximately 100 feet away from the property. After entering the curb inlet, the surface storm water enters the public storm drain in Walnut Avenue and is conveyed east to the San Diego Northern Railway (SDNR) right-of-way. Once outletting through a headwall, drainage will head south before ultimately discharging in the Agua Hedionda Lagoon and the Pacific Ocean . The subject property can be assumed to have one discharge location from the site in the existing condition. Basin A is approximately 0.552 acres in size and 15.6% impervious . Per the Web Soil Survey application available through the United States Department of Agriculture, the area is generally categorized to have group B soils. Based upon soil type and the amount of existing impervious area onsite, a runoff coefficient of 0.35 was calculated for Basin A using the methodology described in section 3.1.2 of the San Diego County Hydrology Manual and the formula provided therein. Using the Rational Method Page 1 of 13 .. .. -... ,,.. ... -.. .... ... ----,.. --1111 - -... .. .. -... -.. .. "' .. .. ... ... PLSA 2808-01 Procedure outlined in the San Diego County Hydrology Manual, a peak flow rate and time of concentration was calculated for each basin for the I 00-year, 6-hour storm event. The peak flow rate for the I 00-year, 6-hour storm for Basin A was determined to be 1.27 cfs with a time of concentration of 5.0 minutes (minimum time of concentration per San Diego County Hydrology Manual used to calculate rainfall intensity for drainage basin of this size), discharging to Walnut Avenue to the southwest before entering a storm drain curb inlet where it is conveyed east via an existing public storm drain to the railroad right-of- way . It can be noted that a small strip of the site to the northeast providing access off Washington Street is sloped to drain away from the property. While this portion of the property discharges to a separate location, both flows are eventually conveyed to the railroad right- of-way just downstream and continue south towards Tamarack Avenue and the Agua Hedionda Lagoon. Refer to pre-development hydrology calculations included in Section 3. I of this report for a detailed analysis and the pre-development hydrology map included in Appendix A of this report for existing drainage basin delineation and discharge locations. 1.3 Proposed Project The proposed project includes the demolition of all onsite structures and the construction of eleven multi-family condominium units with a shared access driveway, and various hardscape and landscape. Site grading along with drainage and utility improvements typical of this type ofresidential development will also be constructed. The proposed pad elevations range from elevation 54.0 at the northern end of the property to 55.0 at the southerly end of the subdivision near Walnut Avenue. Runoff from the proposed development will drain from south to north, and will be directed to the proposed bioretention basin located at the northeast comer of the property. A majority of the site and the entirety of the proposed impervious areas will be routed away from proposed structures to a series of storm drain inlets located in the rear yards of each unit. Runoff draining from the roof of structures will be directed over landscaping or the pervious driveway to eliminate any directly connected impervious areas. Private drain pipes will collect all runoff entering each inlet and will route to the storm water treatment facility by means of 6" PVC storm drain pipes. The drive aisle is sloped in an inverse crown to the center of the driveway, where a PCC ribbon gutter will collect and convey drainage on the surface north through the site. Similar to the existing condition, the analyzed watershed can be categorized into one drainage basin with one discharge location from the subject property. As in the pre- developed condition, Basin A is 0.552 acres in size, and is approximately 47% impervious. Based upon soil type and the amount of proposed impervious area onsite, a runoff coefficient of 0.56 was calculated for Basin A using the methodology described in section 3.1.2 of the San Diego County Hydrology Manual and the formula provided therein. Using the Rational Method Procedure outlined in the San Diego County Hydrology Manual, a peak flow rate and time of concentration was calculated for the post-development I 00- Page 2 of 13 ,,,. - -.. --... -,... -,.. -.. ... ---... -... --.. ... ... ... ... ... PLSA 2808-01 year, 6-hour storm event. The peak flow rate for the 100-year, 6-hour storm for Basin A was determined to be 2.02 cfs with a time of concentration of 5.0 minutes (minimum time of concentration per San Diego County Hydrology Manual used to calculate rainfall intensity for drainage basin of this size) discharging from the site to the northeast by means of a PVC outlet pipe from the bioretention basin. Treated storm water leaving the project in the post-developed condition flows on the surface in Washington Street northeast toward Pine A venue, where it reaches a cross gutter that discharges to the railroad tracks. Thus, existing and proposed flows enter the NCTD right-of-way approximately 500 feet apart, and eventually are conveyed to an existing RCP storm drain on the east side of the railroad tracks. Per City of Carlsbad public record drawing DWG 360-5, the existing RCP storm drain in NCTD right-of-way routes water south to the Agua Hedionda Lagoon. Refer to post-development hydrology calculations included in section 3.2 of this report for detailed analysis and the post-development hydrology map in Appendix A of this hydrology report for proposed drainage basin delineation and discharge locations . While the proposed drainage basin A discharges from the site to the northeast toward Washington Street -as opposed to Walnut Avenue to the south -this can be considered a local micro-diversion in the Agua Hedionda Hydrologic Area. Based on a study by Pasco, Laret, Suiter & Associates of the local drainage basin draining to Walnut Avenue, the existing storm drain in Walnut is at or very near capacity in the current condition. By routing existing flows away from Walnut Avenue, the project helps alleviate demand on a system that is at full capacity. Based on a preliminary review of the existing surface infrastructure on Washington Street and the amount of water the system is conveying, it is also our professional opinion that the curb and gutter has the capacity to route peak flows to the designated discharge location on Pine A venue. Lastly, after working with the City of Carlsbad on all possible solutions, it was also deemed infeasible to construct drainage facility "BB-I" as part of the City of Carlsbad's Drainage Master Plan. In an effort to comply with the City of Carlsbad's storm water standards for Standard Development Projects, the project site will implement source control and site design BMP's where feasible and applicable in accordance with the City of Carlsbad's BMP Design Manual, February 20 I 6 edition. All runoff generated from proposed roofs and hardscape areas will be directed to landscaped areas and grassy swales to disperse drainage onto pervious surfaces. A segmented PCC driveway with gravel-filled openings is proposed for the drive aisle to minimize proposed impervious area, soil compaction, and promote dispersion. Partial infiltration and evapotranspiration in landscaped areas will assist in slowing peak discharges and in reducing total volume generated during storm events. The drive aisle and onsite landscaped areas will remove sediment and particulate- bound pollutants from storm water prior to leaving the project site . Page 3 ofl3 ,.. ... .. .. --.. .. ... ... .. .. .. -.. .. .. -.. -"" ... .. ... .. • .. ... .. ... -... .. .. .. PLSA 2808-01 1.4 Conclusions Based upon the analysis included in this report, the proposed onsite drainage design is adequate to capture and convey runoff from the proposed project and discharge to the appropriate discharge locations, while complying with local and state level water quality regulations. The micro-diversion of storm water from the existing to proposed condition helps alleviate an already sub-standard drainage scenario by directing water away from the storm drain system in Walnut Avenue that is currently at capacity . 1.5 References "San Diego County Hydrology Manual", revised June 2003, County of San Diego, Department of Public Works, Flood Control Section . "San Diego County Hydraulic Design Manual", revised September 2014, County of San Diego, Department of Public Works, Flood Control Section "Engineering Standards, Volume 5: Carlsbad BMP Design Manual", revised February 2016, City of Carlsbad Soil Survey Staff, Natural Resources Conservation Service, United States Department of Agriculture. Web Soil Survey. Available online at http://websoilsurvey.nrcs.usda.gov . Page 4 ofl3 ,,.. -.. -.. -.. -... -.. ... ... -... ... -.. --... -... -... -... .. ... .. -... ... ... ... PLSA 2808-01 2.0 METHODOLOGY 2.1 Introduction The hydrologic model used to perform the hydrologic analysis presented in this report utilizes the Rational Method (RM) equation, Q = CIA. The Rational Method formula estimates the peak rate of runoff based on the variables of area, runoff coefficient, and rainfall intensity, and is the preferred method for drainage basins up to one square mile in size. The rainfall intensity (I) is equal to: Where: I=7.44xP6 xo-0645 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: Where: Q=CIA 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. 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. Page 5 of 13 ... ... .. - ,,,. ... ... ... -... .. .. .. --... -... ,.. .. -... -... - .. - - PLSA 2808-01 2.2 County of San Diego Criteria As defined by the County Hydrology Manual dated June 2003, the rational method is the preferred equation for determining the hydrologic characteristics of basins up to approximately one square mile in size. The County of San Diego has developed its own tables, nomographs, and methodologies for analyzing storm water runoff for areas within the county. The County has also developed precipitation isopluvial contour maps that show even lines ofrainfall anticipated from a given storm event (i.e. I 00-year, 6-hour storm). One of the variables of the RM equation is the runoff coefficient, C. The runoff coefficient is dependent only upon land use and soil type and the County of San Diego has developed a table of Runoff Coefficients for Urban Areas to be applied to basin located within the County of San Diego. The table categorizes the land use, the associated development density ( dwelling units per acre) and the percentage of impervious area. Each of the categories listed has an associated runoff coefficient, C, for each soil type class. The County has also illustrated in detail the methodology for determining the time of concentration, in particular the initial time of concentration. The County has adopted the Federal Aviation Agency's (FAA) overland time of flow equation. This equation essentially limits the flow path length for the initial time of concentration to lengths under I 00 feet, and is dependent on land use and slope . 2.3 City of Carlsbad Standards The City of Carlsbad requires a Preliminary Hydrology Study be completed for projects larger than I-acre per Form P-2: Development Permits. The City of Carlsbad has additional requirements for hydrology reports which are outlined in the Grading and Erosion Control Ordinance. Please refer to this manual for further details . 2.4 Runoff Coefficient Determination As stated in section 2.2, the runoff coefficient is dependent only upon land use and soil type and the County of San Diego has developed a table of Runoff Coefficients for Urban Areas to be applied to basin located within the County of San Diego. The table, included at the end of this section, categorizes the land use, the associated development density ( dwelling units per acre) and the percentage of impervious area. Page 6 of 13 ... -.. -.. ... ... ----... --... ---... ----... ... -... -.. ... ... ... -... ... -.. PLSA 2808-01 3.0 HYDROLOGY MODEL OUTPUT 3.1 Pre-Developed Hydrologic Model Output (100 Year Event) Pre-Development: *Rational Method Equation Q=CIA P100= 2.5 in • I 00-Year, 6-Hour Rainfall Precipitation Basin A (Onsite Drainage Basin) Total Area= 24,020 sf-+ 0.552 Acres Impervious Area= 3,742 sf-+ 0.086 Ac Pervious Area= 20,278 sf-+ 0.466 Ac Cn, Weighted Runoff Coefficient, -0.25, Cn value for natural ground, Type B Soils *Per San Diego Hydrology Design Manual (SDHDM) Section 3.1.2 -0.90, Cn value for developed/impervious surface *Per SDHDM Section 3.1.2 Cn = 0.9 x 3,742 sf+ 0.25 x 20,278 sf= 0.35 24,020 sf Tc= ti+ tt ti@65'=1.0% R-23 per Land Use Element=> 6.1 min from Table 3-2 tt => L = 155' .1.E = 1.6' tt= [ { 11.9(L/5,280)"3 }/.1.E]"0.385 tt= [ {11.9(155/5,280)"3 }/l.6]"0.385 = 0.037 0.037 x 60 = 2.2 Min . Tc= 6.1 + 2.2 = 8.3 Min P6= 2.5 r = 7.44 x P6 x D·0645 I= 7.44 X 2.5 X 8.3-0645 "' 4.75 in/hr 1100"' 4.75 in/hr Q100 = C*I*A Q100 = 0.35 x 4.75 in/hr x 0.552 Ac= 0.92 cfs Page 7 of 13 -.. -... -... .. ... -.. - -.. -... -.. .. ... ... .. ,.. -... ... -... -... .. -... ... .. PLSA 2808-01 3.2 Post-Developed Hydrologic Model Output (100-Year Event) Post-Development: *Rational Method Equation Q=CIA P100= 2.5 in * l 00-Year, 6-Hour Rainfall Precipitation Basin A (Onsite Drainage Basin -Draining to Bioretentionl Total Area= 24,020 sf-+ 0.552 Acres Impervious Area= 11,286 sf-+ 0.259 Ac Pervious Pavement = 4,900 sf-+ 0.11 Ac Pervious Area= 7,824 sf-+ 0.18 Ac Cn, Weighted Runoff Coefficient, -0.25, Cn value for natural ground, Type B Soils *Per San Diego Hydrology Design Manual (SDHDM) Section 3.1.2 -0.90, Cn value for developed/impervious surface *Per SDHDM Section 3.1.2 Cn = 0.9 x 16.186 sf+ 0.25 x 7,824 sf= 0.69 24,020 sf Tc= ti+ tt ti@65'=1.0% R-23 per Land Use Element=> 6.1 min from Table 3-2 tt => L = 225' ti.E = 2.7' tt= [{l l.9(L/5,280)"3}/ti.E]I\0.385 tt= [ { 11.9(225/5,280)"3 }/2.7]1\0.385 = 0.046 0.046 x 60 = 2.8 Min. Tc= 6.1 + 2.8 = 8.9 Min P6= 2.5 1 = 7.44 x P6 x D·0645 I= 7.44 X 2.5 X 8.9-0645 "' 4.55 in/hr Q100 = C*I*A Q100 = 0.69 x 4.55 in/hr x 0.552 Ac = 1. 73 cfs Page 8 of 13 - ... .. -... -.. -.. ... --.. ... .. ... ... ... ... ... ... ,,. ... -... -.. -... ,,. .. .. ... ... .. ... .. Basin B (Panhandle Basin -Draining to Washington Street) Total Area= 1,000 sf • 0.02 Acres Impervious Area= 0 sf• 0.00 Ac Pervious Pavement= 1,000 sf• 0.02 Ac Pervious Area= 0 sf • 0.00 Ac Cn = 0.9 x 1,000 sf+ 0.25 x 0 sf= 0.90 1,000 sf Tc= 5.0 min *Minimum Tc per SDCHM Q100 = C*I*A Q100 = 0.90 x 6.59 in/hr x 0.02 Ac = 0.12 cfs PLSA 2808-01 Pre-Development vs. Post-Development (Undetained -Basin A Onsite RunofQ Pre-Development (Basin A) Q100 = 0.92 cfs Post-Development (Basin A) Q100 = 1.73 cfs Delta 0.81 cfs *Total overall site runoff increased in proposed condition from pre-development site . Refer to the following section, Section 3.3, of this report for a discussion of detention system proposed to mitigate site to existing conditions. Also refer to the Appendix of this report for existing and proposed condition hydrology node maps showing discharge locations, as well as the body of this report for justification for the local diversion of storm water. Page 9 of 13 - .... --.. ... .. ... .. .. -.. .. -.. ... ... --... .. --- - "" ,.. ... .. .. .. .. ... ... PLSA 2808-01 3.3 Detention Analysis The HMP bioretention basin provides pollutant control as well as hydromodification management and mitigation of the 100-year, 6-hour storm event peak flow rate. The 100- year, 6-hour storm event detention analysis was performed in accordance with Chapter 6 of the San Diego County Hydrology Manual. The results of the analysis provide a static detention requirement by comparing the total volume produced by the I 00-year, 6-hour storm in the existing and developed conditions. The total volume can be calculated after producing a hydrograph for each event (pre-and post-developed) with the results of the Rational Method analysis. Calculations and results of this analysis can be shown below. This method is considered to be conservative, as it does not take into account the routing characteristics of the bioretention basin . The HMP bioretention facility consists of a basin with an approximately 300 square foot basin bottom, 18 inches of engineered soil and 3 0 inches of gravel. Runoff will be biofiltered through the engineered soil and gravel layers, then collected in a series of small PVC perforated drain pipes and directed to a catch basin located in the northeast corner of the HMP bioretention basin. Once in the catch basin, runoff will be mitigated via a small low-flow orifice to comply with HMP requirements. In larger, high-intensity storm events, runoff not filtered through the engineered soil and gravel layers will be conveyed via an overflow outlet structure consisting of a 36-inch by 36-inch grate located on top of the catch basin. Runoff entering the outlet structure will be conveyed directly to a proposed 12-inch PVC drainpipe and will discharge northeast towards the SDNR right-of-way. Once on the surface in the railroad right-of-way, runoff will eventually enter the large storm drain located on the east side of railroad tracks and continue south towards the Agua Hedionda Lagoon. Refer to Attachment 5 of the project's Storm Water Quality Management Plan (SWQMP) for a general cross-section of the HMP biofiltration basin. 3.3.1 Static (No Routing) Detention Calculation Pre-Development: I 00-Year Event (Basin A) Volume= C*P6* A *Equation 6-1 ofSDCHM Volume= 0.35 * (2.5 in* 1 ft/ 12 in)* (24,020 SF)= 1,751 CF Post-Development: JOO-Year Event (Basin A) Volume= C*P6* A *Equation 6-1 ofSDCHM Volume= 0.69 * (2.5 in* 1 ft/ 12 in)* (24,020 SF)= 3,453 CF Required Detention Volume = Total Post-Development -Total Pre-Development =Prop.Basin A-Pre Basin A = 3,453 CF-1,751 CF= 1,702 CF -> I, 702 CF static storage required for drainage basin A Page 10 of 13 ,,,.. ... -... -.. ---... -... -... -... -.. -... .... ... -... -... -... .. .. .. .. -... ,.. ... PLSA 2808-01 3.3.2 Basin Stage-Storage Volume Calculation BMP Stage Storage -Basin INF-2 Basin Stage Total Elevation Area Volume Volume (sq-ft) (cu-ft) (cu-ft) 47 300 0 0 47.5 300 60 60 48 300 60 120 48.5 300 60 180 49 300 60 240 49.5 300 60 300 50 300 30 330 50.5 300 30 360 51 300 30 390 51.5 391.25 195.63 585.63 52 482.5 241.25 826.88 52.5 573.75 286.88 1113.75 53 665 332.50 1446.25 *Bottom of Gravel Layer (40% Void Ratio) *Top of Gravel Layer/Bot of Soil (20% Void Ratio) *Top of Ponding/ Weir EL *Top of Slope 1,114 CF storage provided at ponding depth (1,446 CF storage total); use detention volume in conjunction with storage provided in gravel layers of concrete driveway with gravel- filled openings. 3.3.3 Pervious Pavement/ Concrete Driveway with Gravel-Filled Openings Volume Detention Volume Provided = Driveway Area x 12" Gravel Layer x 40% Voids =4,900 SF* (12 in* 1 ft/ 12 in)• 0.40 = 1,960 CF EXTEND Ii" THICI< MONOUTHIC VOIDFUER-t' TO i"(N0.8) AGGREGATE fN V0J0S Ii" THICK PCC PCC BEHEi, TH GRAVEL DRJVE~AY LAYER EM8ED6"1NTO COMPACTED SOII.S (TYP.1 BEDDING COURSE-7 THICK OF 1· rot· (N0.8)AGGREGATE ~ CHOKERCOOl!SE4"THICKOFj'~ TO hN0.51) CRUSHED ROCK ___;. Mlti. 8' THICK OF¾' _...-- CRUSiED ROCK :r PVC UNDER DRAIN PIPE O 3' D.C. (TYP.) TO CONNECT BETWEEN GRAVEL !AYERS 1,446 CF storage from BMP basin+ 1,960 CF storage in gravel layers under PCC driveway = 3,406 CF total > 1,702 CF static storage required for drainage basin A per SDCHM. Page 11 of 13 -.. ... -... ... -... ... ... .. .. .. -.. ... .. .. .. ... .. ... ... ... .. ... .. ... .. ,.. .. ... -.. PLSA 2808-01 3.4 Hydromodification Analysis To satisfy the requirements of the MS4 Permit, a hydromodification management strategy has been developed for the project based on the Final Hydromodification Management Plan dated March 2011, (Final HMP). A continuous simulation model, the Environmental Protection Agency (EPA) Storm Water Management Model (SWMM) version 5.1, was selected to size mitigation measures. The SWMM model is capable of modeling hydromodification management facilities to mitigate the effects of increased runoff from the post-development conditions and use changes that may cause negative impacts (i.e . erosion) to downstream channels . 3.4.1 Hydromodification Criteria Pursuant to the MS4 Permit, post-development runoff conditions (flow rates and durations) must not exceed pre-development runoff conditions by more than 10% (for the range of flows that result in increased potential for erosion, or degraded instream habitat downstream of the project. Based on the Final HMP: • For flow rates between the pre-project lower flow threshold (10%, 30%, or 50%) of the pre-project 2-year runoff event (0.1 Q2, 0.3Q2, or 0.5Q2) to the pre-project 10-year event (Q10), the post-project discharge rates and durations may not deviate above the pre- project rates and durations by more than 10% over more than 10% of the length of the flow duration curve . A channel screening analysis may be performed to determine a larger lower flow threshold, however for this project a lower flow threshold of0.IQ2 (high susceptibility) is assumed . 3.4.2 SWMM Model Development SWMM is a rainfall-runoff model used for single event or continuous simulation of runoff quantity from primarily urban areas. SWMM calculates and routes runoff based on user- specified input including precipitation data, subcatchrnent characteristics, soil data, routing information, and BMP configuration. SWMM is capable of modeling various hydrologic processes including but not limited to time-varying precipitation, evaporation, storage, infiltration, and retention LID facilities . 3.4.3 SWMM Input A pre-development and post-development model were created using the following global information: Parameter lnnut Source Precinitation Oceanside Rainfall Data Proiect Clean Water Evanoration Encinitas ETo Zone Data CIMIS ETo Zones Mao Soils B USDA Web Soil Survev Annlication Page 12 of 13 -... ... .. -----.. --... .. -.. -.. -.. -.. -... -.. .. -.. -... .. .. .. PLSA 2808-0 I The HMP biofiltration basin has been designed to comply with both pollutant control and hydromodification management criteria. Refer to Section 3.5 for the pollutant control calculations. The HMP biofiltration portion in the SWMM model is specified as an "LID Control" within the "Subcatchment" to define the ponding depth, biofiltration soil layer and gravel layer. 3.4.4 SWMM Processing and Output The HMP sizing was determined assuming a completely pervious existing site condition. The pre-development project 0.IQ2 and Q,o were determined to be 0.016 cfs and 0.35 cfs, respectively. After routing through the HMP biofiltration basin, the post-development, mitigated project 0. I Q2 and Q,o were determined to be 0.006 cfs and 0.32 cfs leaving the site, respectively. Refer to the SWMM output included in Attachment 5 of the project SWQMP for detailed information and data from the SWMM model including input files, rain gage and evaporation data, and flow duration and frequency curves. Drawdown calculations are also included in Attachment 2 of the SWQMP. 3.5 Storm Water Pollutant Control To meet the requirements of the MS4 Permit, the HMP biofiltration facility is designed to treat onsite storm water pollutants contained in the volume of runoff from a 24-hour, 85th percentile storm event by filtering runoff through an engineered soil layer and gravel layer. 3.5.1 Numeric Sizing Requirements for Pollutant Control BMPs Pursuant to the MS4 Permit, Pollutant Control BMPs shall be designed to retain onsite pollutants contained in the post-development Design Capture Volume (DCV). The DCV is the volume of runoff resulting from the 24-hour, 85th percentile storm event. The DCV calculations for the project are located in Attachment I of the project SWQMP. The Pollutant Control BMP proposed for the project is an HMP biofiltration basin. The proposed HMP biofiltration basin does not provide retention, therefore pursuant to the MS4 Permit, the HMP biofiltration basin is designed to biofilter 1.5 times the DCV and provide non-routed storage volume equal to at least 0.75 times the portion of the DCV not retained onsite . Page 13 of 13 ,.. .. - -.... -.... ---... ,.. ... -... -... ---... .. .. ... -... -... ,.. ... ... ... ... ... -... APPENDIX A Hydrology Support Material I C 0 (") 0 r--. ..--..-- io ... ll ..... ... + • + + + + + + + + + -• t + + . + I ' ,-,-,-- ' t 1- ' G-0 -+ + + 0 ' r--. ' ... ... - t ' + -io v + -0 (0 -... + ... b Cl') co .... in ..-0..... (0 .... ..- 33•30• Orange I ... ' I "' . . I . . .. I . . . .. .. I .. . . .. I . ' County I ..-· .~§ K •-.. I ,-,-r . ,- . . . . .-~ :" ~: ,. ,,.. : ;...... .· , • # •' . ,, , - (j.L:--••.• •·: ••• ·•• : : ...... •· --·v•....... .•• ~ ... •· -~- ,,,. ,••" ' . . . •·a-.o··· _..·· . ,• . . . . . . . . Riverside County .. ·· ......... ........ ··················• .... . . .... . . . ' ~\ Sil: • .. ... !~ ... ·.... ... .. ..... · .. ~ .... ~ . . .. ~ I ,. -----,--------• •\ l· ~~ "'•• "', .... ... .... . .... ..... ··.. ··... ·.... ··. ·•.. ·..... ·... ·.. ',. .. .. . .. ' .-...... . . •,. . .. . . . . ...,°' ••, \_ I •• ••, •, •, r ·· .... ·., ·... .... •• \ ty '\ : --. .. " ·o r '\ ·· .... ··.ti~ .... . .. .... , •••• ·'IQ -• .. .. . ' . . . . .. . . ' . . ' ' .. . . . . . . ..... • ............. •,\ 1 : ..... . . . . .. . . .. ....... . . . .. ... _ .. . I ~ I I . : .. ~ . .. : ----~-...__ L -. o ·, '.., ~ ~ ,' _ • _.. ]I' I I I 1, I I ••• ~ ••••-•-.: 33°30' -33°15 •• • -, ·u:-: ~ ·. ·. ~ ' . .· ~ . .· : ••• •• ••• \ ~ ·! •• •· • .. •••• •• . .: ~-. .._ ... •············1~11s· : ....... _:_~ ~.5· -·· -0 ~ (') ... ·, ""---... , .~ : ·. ~-: ......... · ....... ~---... ·. •, .. 1 + -;;-:-; .\. . - \ /···----· ' ' ••• lX •• •• • •• •• ·-·~:V '"·. ·· .. ' ·• .... ·-~ ..... . . . .,. .----.,-../~.,..,. ~ ....... ·· -.... ' ,,' . . ~ , ., . 33°00' .,. / .. (') ~~~-~ 0 (') ~ ~ ,:, . , . ., . . .. : ., '. ' I • ~ : : ...... . . "'-.... •, .l:R I I ... • . ' . .. .. I .. "'.,. I · .. ·.. ' .. ____ . . . . . . . ', ...... . .. . . . ~ ', -... -.. •, .... # • • ...... _ ..... ·· ...... . . . . cl) -~ .. . . --. . ' . ' I • • . . . I ~ -._, ... .· : : .'.. 32°45' ··•·3-.a•· <I ·• •••• •· • • .. #,-• :u I I I .. # • t . . ' -. . . .......... . . I ' I . ,.· •••. -'~·-:f·'s·· ,• · 1,. . .. ------- .. ........ . .. , ',, ...... . . ,30001 3 -g CD ::::::! • OJ () 0 C :::, <.),-+ . '< 2°45' ·~ <iJ .-···-.. •• --I ~~ .. r-• -· .. m ... J , .. I I , •••• , .. Om• ' .· : .';· :' .L-.. M e X i C I I I I . -0 • LO C"l 32"30' • , . to g " ;' , 1o 0 •+ "' ..-0 (0 ..- (") 0 + ,. r--. ..--,--• ..-0 ' r--. ..-..-r--. ..-..-..--... in ..-0 (0 ..--..- 32°30' County of San Diego Hydrology Manual ••~I ~• ;·: ,, ,, ~ .. ~~?.l.~~.• Rainfall lsopluvials 100 Year Rainfall Event-6 Hours lsopluvial (inches) DPW ~GIS s1.IGIS ~_.,.,olP.Jl:,iic.Wor,;s -~b<fomiJ/J(lrS:rvir:.n We HJ.vs: San Diego Cc,vcrcd! N 4 E s 3 0 3 ~ THIS MAP IS PROVIDED WITHOUT WARRANTY Of ANY KIND, EITHER EXPRESS OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANT ABILITY ANO FrTNESS FOR A PARTICULAR PURPOSE. Copyright SanGIS. M Rights "-"ed. TNs products may contain Information from the SANOAG Regional Information s,.-wtucto ~ be reproduced without the written-olSANDAG. TNs product may contain '1fonnation wt-ich has been reproduced -perm;ssion granled by Thoma, BtolheN; Maps. Miles I 1 10.0 9.0 8.0 70 f I I 1 I 1 I 1 I 1 I I r 1 I I r 1 I 1 1':. """"' ..... ""' I I ,1' ~~ '~ ~*~~*™* ' 6.0 5.0 '-' I • , i,. i,. --;.._ ~ 1m "AA+l-~1+!-11-1+!!+11-, 1 .,,.,,,_ ..... ! , ~ m , '--, !<... i " r,. ...J 'i,. ~ ~ ttt++l+++-H-H++++I+~ EQUATION 1 , I ' ~ ! i--... ~ ! , "~ r ttlittHl+titt,H+l-+++!ll I = 7.44 Ps D-0.645 , 4.0 3.0 ' "{... 1 , ~ ~ I = Intensity (in/hr) '. , I ~ 1 1--, i,.~ iiR-1.Hl+H-i-W~ Ps = 6-Hour Precipitation (in) r-..._ 1 I t 1'-1 = 3.2 in/hr D = Duration (min) 1 I • · ~ rm,m--i-r-r-,-,-,-,n,-,..,..,.,,.,~ I I ! l"'iiio:T ,... ~ti.R'l-1¼+-H.!l~ n , i I ""' ~ ~~ I "'""'"' I 2.0 ..... ' " i-." i , ~ I "'klcffii+H I'-~ ' Q !m!ll:'-+.'':P-,jd1f.ti-++++~l+ll-4 i-.i-. I ~ i ,...,_,_~~~ . l°" ' I• ti-,._ 1,1'-l'i j i i i : r---,-. \ ... ,.... ... ,-,_, I ~ I !•""'~'·~~ ~ 'g,.o ';:o.9 10.B fo.7 i '. ,., i I l!!!l++WH-,.~~!I "-i-... ~ ii-tit-,-. 1 i I 11!+1+1-F!-l,l:I+~ • "'-"'-I ! : ..... I ! il'lt.t-1'+-P!<..H-A~--'-t~, .ffl~ : ! II ~~ : I 0.6 05 I I i ,.. ' . , I I I ,i, ,. i ' 7 ~ l 0.4 0.3 1i--1---t-+-H++-1-+tt+ttt-f-H+++t++~#!+IH-l+lt++H+ I IMI I I, , 1 i I ,... : I I "tr-. j I I . ' ~~ 2t----------+-: ' 0.2 ' ~---rt-t t +- ~-t-1 i 1 1 \:=20min 1 : o. I ---+-+-+ . I ~-t·+ ! i llll!I l I I 5 6 7 8 9 10 15 20 30 40 50 2 3 4 5 8 Minutes Hours Duration r 1 ± ~ Ml ul M~ u~ u~ u~ ao 25 2.0 1.5 1.0 Intensity-Duration Design Chart • Example f 1 I I I 1 r 1 I I I I Dlrac:tlona for Appllcallon: (1) From precipitation maps determine 6 hr and 24 hr amounts for the selected frequency. These maps are included in the County ~rology Manual (10, 50, and 100yrmaps included in the Design and Procedure Manual). (2) Adjust 6 hr precipitation (If necessary) so that it iS within the range of 45% to 65% of the 24 hr precipitation (not applicapie to Desert). (3) Plot 6 hr precipitation on the right side of the chart. (4) Draw a line through the point parallel to the plotted lines. (5) This line iS the intensity-<iuration curve for the location being analyzed. Appllcatlon Fonn: (a) Selected frequency~ year p (b) P5 = 3 in. P24 = 5.5 _§_ = 54.5 %(21 --' --'P24 -- (c) Adjusted p6t21 = _3_ in. (d) t• = ~ min. (e) I= ___1L in./hr. Note: This chart replaces lhe intensity-Duration-Frequency curves used since 1965. 1 . 1.5 2 2.5 3 3.5 . 4 ,1;:g -5 5.5 I I I ,---,----,---,--T ---, --.-~ ·,-i _!t63 :._~.:_Q§i 5:2?._ 6.~_~7.9Q_ 9.~l ~0.54_ 1,.86. T~.1~, 14.4:81_15.'..1]1_1_ _2. 12 , a. ,a).4.24. 5.30. 6.38J ,•2J_ a.48 _ 9.54. 10060. 11,68j_12.72 1.68 -~~f-3-_37_, 4.2_1,5.~ __ 5.9:Q.L~!4. 7.58. B:~-, 9.27_JQ.1_~ _J:30 _ 1.~-2:~. 3.24 0_3._89~ 4:54]_ 5.19. 5.84_. B:~ ~_7.1~---7_.~_ 1.oa 1.&2.2.,s_ 2.:_69 __ !!:~.3.n! 4.31 4.85 s.39_;_~-!3-__ f;;.46 0.93 _1.40; 1.87 __ 2-~.~80~3.27f 3.73. 4.20, 4.67; 5.13_ 5.~ o.83 • 1.24. t.66_ 2.01. 2.49. 2.90j. 3.32 • an • 4.15 ~ •-!!6 __ 4.98 o.69 .t.03~ 1.38 __ 1.n_2.01_2.41 l 2.76. 3.10. 3.45; 3.79. 4.1_3 0.60 0.901 1.19 1.49 1.79 2.091 2.39 2.69 2.98. 3.28 3.58 -~-~ · o.ao; 1.0if 1.33: 1.se· 1.86·! 2.12 -2.39·: 2.65-~_~3~1a- o.•1. o.&1. o.~. 1.02 _ ,.23. 1 . ..a. 1.83 _ 1.~.2.QC.2.2S_2.~ o.:M :o.s1;0.ee. o.as.1.02, 1.19, 1.36 1.sa, 1.10. 1.87, 2.~ 9...:~ ~Q_:44~Q.:591_9~_:_9._~~)_:Q3_,. l.:_18 -_1._32. 1.47. 1._f:2 :. 1.7!i O~~ ~O:~i-0.~_ Q.!35 __ 0,?8:9-91~ 1.~; 1:1~: 1._3_1 __ 1.<M_r 1_._5! 9~ ;o.33 __ o.~~ 0:54 _ ~-85 _o,~. o.87, 0.98, 1.oe. 1.10 _ 1~ o. 19 10.2&;_0.~j ()'.4?_J>.56;_o_:~. 0.1s. Q.85, SJ:~~ 1.03_ ~ 1.1s 0.17 ,0,25,0.3:I_ O.<l!_0.50,0.58 0.87 · 0.75 · 0.84 0.92 1.00 3-2 I I r 1 r 1 r 1 r 1 r 1 r 1 San Diego County Hydrology Manual Date: June 2003 r 1 r 1 r 1 r 1 r 1 Table 3-1 r 1 r I r 1 r 1 r 1 r , , 1 Section: Page: 3 6 of26 RUNOFF COEFFICIENTS FOR URBAN AREAS Land Use I Runoff Coefficient "C" Soil Type NRCS Elements Coun Elements %IMPER. A B 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 IO 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 (LOR) Residential, 2.9 DU/A or less 25 0.38 0.41 0.45 0.49 Medium Density Residential (MOR) Residential, 4.3 DU/A or less 30 0.41 0.45 0.48 0.52 Medium Density Residential (MOR) Residential, 7.3 DU/A or less 40 0.48 0.51 0.54 0.57 Medium Density Residential (MOR) 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 (HOR) 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. Com) Neighborhood Commercial 80 0.76 0.77 0.78 0.79 Commercial/Industrial (G. Com) General Commercial 85 0.80 0.80 0.81 0.82 Commercial/Industrial (O.P. Com) 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). DUI A -dwelling units per acre NRCS -National Resources Conservation Service 3-6 r 1 -... -... -.. -... -... -... -... -... -... -... -... -.. ... .. -... -... -... -... ... ... -.. San Diego County Hydrology Manual Date: June 2003 Section: Page: 3 12 of 26 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 Ti 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/ .5% 1% 2% 3% 5% 10% Acre LM Ti 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 LOR 1 50 12.2 70 11.5 85 10.0 100 9.5 100 8.0 100 6.4 LOR 2 50 11.3 70 10.5 85 9.2 100 8.8 100 7.4 100 5.8 LOR 2.9 50 10.7 70 10.0 85 8.8 95 8.1 100 7.0 100 5.6 MOR 4.3 50 10.2 70 9.6 80 8.1 95 7.8 100 6.7 100 5.3 MOR 7.3 50 9.2 65 8.4 80 7.4 95 7.0 100 6.0 100 4.8 MOR 10.9 50 8.7 65 7.9 80 6.9 90 6.4 100 5.7 100 4.5 MOR 14.5 50 8.2 65 7.4 80 6.5 90 6.0 100 5.4 100 4.3 HOR 24 50 6.7 65 6.1 75 5.1 90 4.9 95 4.3 100 3.5 HOR 43 50 5.3 65 4.7 75 4.0 85 3.8 95 3.4 100 2.7 N.Com 50 5.3 60 4.5 75 4.0 85 3.8 95 3.4 100 2.7 G.Com 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 I. 50 3.7 60 3.2 70 2.7 80 2.6 90 2.3 100 1.9 *See Table 3-1 for more detailed description 3-12 33' 9'23"N 33' 9' 18" N ~ &l /il Hydrologic Soil Group-San Diego County Area, California I I I I i I I I t '67400 tl57400 ~ iR /il N t A '67400 45n'OO 461520 4675<0 <67$) ll5l!BJ 4618ll '67400 45n'OO 461520 4675<0 ,f5l'H) -4618ll Map Scale: 1: 1,140 J printed on A ianckape (11" X 8.5") sheet ----====-------=======Meters 0 15 3'.) 8'.) 9) ----=====-------=======feet o ro m ~ :m Map projection: 1/W?b t-'e'cator Comer aiorcinatEs: WGS84 Edge tics: lJTM Zone llN WGS84 USDA Natural Resources Web Soil Survey National Cooperative Soil Survey --Conservation Service 457&1) 457&1) 4616«) 46l800 <13768) 4616«) 461800 <13768) 45T700 45T700 ~ ~ /il t ~ ~ /il t I I i I I i 12/11/2017 Page 1 of4 33' 9' ZJ"N 33' 9' 18" N Hydrologic Soil Group-San Diego County Area, California MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Solis Soil Rating Polygons D A D AfD DB • s,o oc 0 C/0 oo D Not rated or not available Soil Rating Lines -A -ND -B -B/0 C -CID -D --Not rated or not available Soil Rating Points • A • AfD • B • BID USDA Natural Resources --Conservation Service C C • CID • D • Not rated or not available Water Features Streams and Canals Transportation +++ Rails _,.,; Interstate Highways _,.,; US Routes Major Roads Local Roads Background • Aerial Photography Web Soil Survey National Cooperative Soil Survey The soil surveys that comprise your AOI were mapped at 1:24,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: San Diego County Area, California Survey Area Data: Version 12, Sep 13, 2017 Soil map units are labeled (as space allows) for map scales 1 :50,000 or larger. Date(s) aerial images were photographed: Nov 3, 2014-Nov 22, 2014 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. 12/11/2017 Page 2 of 4 ... 11111 Hydrologic Soil Group-San Diego County Area, California ... ... ... Hydrologic Soil Group .. -.. Map unit symbol Map unit name Rating AcreslnAOI Percent ol AOI -.. ... ... ... .. -.. -... .... ... -... ... ... -.. --... ... -... -.. ... ... -.. iMIC Marina loamy coarse sand, 2 to 9 percent slopes 2.4 ' Totals for Area of Interest 2.4 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, B/D, 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, BID, or CID), 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 D are assigned to dual classes . Rating Options Aggregation Method: Dominant Condition Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 100.0% 100.0% 12/11/2017 Page 3 of 4 ... .., Hydrologic Soil Group-San Diego County Area, California -... -... -... -... -... -... -... -... ---... -... -.. -... ... ... -... -... -.. - Component Percent Cutoff: None Specified Tie-break Rule: Higher USDA Natural Resources ..iii Conservation Service Web Soil Survey National Cooperative Soil Survey 12111/2017 Page 4 of 4 ~ 'i \ ------ \ ~ N:204-132$00~ P©RTION OF TRACT ; OF THUM LANDS MAP NO. 1681 ' POR O O TRACT 218 OF THUM LANDS MAP NO. 1681 I I . 1! I I I -.:::---.._ __ --- -----·· \ \ I I \ \ "' "' I / \ \ \ I I I -- VVP,L.11 -----_( l \ ----------- EXISTING HYDROLOGY EXHIBIT I / \ \ • \ 362 WALNUT AVENUE :'l , , , \ , , , , , , , , , , , \ , , , \ ,~ ! • ''' ''' , __ -_-___ .,..,-- \ \ \ \ APN: 204-132-16-00 PARCEL 1 PM425 ----- _55---- ------ -. I I I I I I . , I I I I \_ "" "" ~--- / - • • NODEA1.2 ·(55i1 F6t· --r'---, 1 : ( • ,--,_....._ / \ i ,, ,/~I ~-,2. ~ ·--\ . ./ "' \/, / ! -(V BAS/NA I :> AREA =24,020S(, ~v (0.55AC) ( ·< ( Cn = 0.35 '-_/1-___!1 /'-.J,-) "'-J • / j ,,,.--.'-,.--, ( . ' \ I,: rJ _; • • • / • ----55---- I • • • -- --__ __..------ ----- \NODEAU (55.6FG) • • • --. .----------54--- \ ~ \J \ ~ \ ~ --+---\ --------------Bt~0G -----~--\ \ \ \ .. \ \,, \ \ \ \ \ \ \ \ \ \ \ \ \._\_( '-- --55--_,; --------. . ,-,---:: -------~ • • • --------------NODE A 1.3 (53.5 FG) Q/00=0.92 CFS • • • .. ----------,--, =-· -=-=----------- \IV,!\LL PORTION OF TRACT 219 OF THUM LANDS MAPN0.1681 ~ \\\ \ \ \ \ \ \\\ \ \ \ \ \, __ -'\\",-,--,,, \ \ \ \\ \ \ \ \ ,-\\\~ BLDG .l ' \ \ PLAN VIEW -EXISTING NODE MAP SCALE: 1' = 10' ---- I I _1 - I ----_ _,..,.. I I /( I /i I" i / t; ! / '1 ! -------_, L ___ l ! ' Ii I I "'-11 I I I I '2, \ / I I , l I I I I \ I I I I I I . I I ! I I ' i I ' I ' i / / ,/ <r,J /. I I I \ \ \ I \ \ \ \ \ 40.0' !I ~ { \\ / ~ as ::::; \, <::( I- :'.:) <: -.I ~ LEGEND SUBDIVISION BOUNDARY PROPERTY LINE I RIGHT-OF-WAY CENTERLINE OF ROAD EXISTING CONTOUR LINE EXISTING PA TH OF TRAVEL -------- -·47-· . ··--···--• EXISTING MAJOR DRAINAGE BASIN BOUNDARY EXISTING IMPERVIOUS AREA BASIN A -AREA CALCULATIONS TOTAL BASIN AREA 24,020 SF (0.55AC) --BA8/N-EXIS-TING.JM/>liR-VIOUSAREA-' -~ BASIN EXISTING PERVIDUS AREA ~-3,742Si=(O.OB6AC) --- 20,278 SF (0.466 AC) 15.6% % IMPERVIOUS Cn 0.35 GRAPHIC SCALE 1" = 10' 10 0 10 20 30 EXISTING HYDROLOGY EXHIBIT WALNUT BEACH HOMES -362 WALNUT AVE CITY OF CARLSBAD PASCO LARET SUITER & ASSOCIATES CIVIL ENGINEERING + LAND Pl.ANNING + LAND SURVEYING 555 North Hlpwlay 101. Ste A. Solaaa Peeeh, CA 92075 ph 858.25!1.8212 I & 858.25!1.41112 I pJ-gln"1'1n1 com PLSA 2808-01 LEGEND ---------- PROPOSED HYDROLOGY EXHIBIT SUBDIVISION BOUNDARY PROPERTY LINE I RIGHT-OF-WAY CENTERLINE OF ROAD EXISTING CONTOUR LINE PROPOSED CONTOUR LINE PROPOSED PA TH OF TRAVEL SEE TO RIGHT THIS SHEET AND PROJECT TENTATIVE MAP FOR OUTLET TO WASHINGTON STREET RIGHT-OF-WAY NODE BU 54.0FG ---. .. ~ \ \ ~on./::i::~= =-= == -------"'-, NODEA1.3 51.0FG APN: 204-132-26-00 PORTION OF TRACT 222 OF THUM LANDS MAPNO.1681 I PO T,O OF CT 218 OF THUM LANDS MAPNO.1681 J <D L[) i I i I i ,,,, o! ~· S:I a \ ::g: co! lOi rg; "'' \ I I I I ' ' \ ' \ \ " fil . \ H • X _..:........:,__, -----~ ·%< \ \ X PARCEL 1 PM425 s=--==.c ' --,:-" ' -~= - -- ----- ·,,'\-Y\\ \ \ \ \ \ \ \ \ \ '\\\,YY\~--\ \ \ \ \ \' BLDG ~ \j ✓ 362 WALNUT AVENUE APN: 204-132-16-00 --------- _,/ ·: ' / c:;'!<,. /.• ~ ! / ,..., ,1 /"' /,~ 'i' PORTION OF TRACT , I 219 OF THUM LANDS MAP NO. 1681 -------- -- > X \ NODEA1.2 54.7 TG 53.7 IE -- BASIN A -AREA CALCULATIONS PLAN VIEW -PROPOSED NODE MAP SCALE: 1" = 10' BASIN B -AREA CALCULATIONS ----------------------- TOTAL BASIN AREA BASIN PROPOSED IMPERVIOUS AREA "BASIN PROPOSED PERVIOUS PAVEMENT BASIN PROPOSED PERVIOUS AREA % IMPERVIOUS Cn 24,020 SF /0.55 AC) 11,286 SF /0.26 AC) 4,900 SF /0.11 AC) 7,824 SF /0.18 AC) 67.4% 0.69 "PERVIOUS PAVEMENT CONSIDERED IMPERVIOUS FOR FLOOD CONTROL CALCULATIONS I DETERMINING PEAK RUNOFF GENERA TED BY THE 100-YEAR, 6-HOUR STORM EVENT TOTAL BASIN AREA BASIN PROPOSED IMPERVIOUS AREA "BASIN PROPOSED PERVIOUS PAVEMENT BASIN PROPOSED PERVIOUS AREA % IMPERVIOUS en 1,000 SF /0.02 AC) 0 SF (0.00 AC) 1,000 SF /0.02 AC) 0 SF (0.00 AC) 100.0% 0.90 ---------------------------- .. ./ ,, [ I t I / ~ I I I t --W---W--+ \ \ ./1-""'1--1 • • > ' I> / . ··--····--~ PROPOSED MAJOR DRAINAGE BASIN BOUNDARY PROPOSED IMPERVIOUS AREA WASHINGTON STREET NODEB12 48.0FS Q100 = 0.12 CFS APN: 204-132-26-00 ------" ---I -,~ ·rR,AS1-i~- Rv"st*.,,,_..,-i'lT-ENCL i -- APN: 204-132-16-00 • 'C:/ ~ ------------. ----------1! /> 1., ' ' i t, . ii' t> / • ; ,.., / A ' r,,".i , i ' i ' I I I I \ ~ \\ m • ' ::,;: <:( I-::::i <: _, ~ I \ \ . f, ' \ \ ' 40.0' Hi I~ , I' , i.' i \ r "PERVIOUS PAVEMENT CONSIDERED IMPERVIOUS FOR FLOOD CONTROL CALCULATIONS I DETERMINING PEAK RUNOFF GENERA TED BY THE 100-YEAR, 6-HOUR STORM EVENT ------------- \ \ \ NODEB1.1 54.0FG ~ ,, ' ' -- -- \ 5,, -· _'\,/1,J_lll,L_L ---~FiiiiiiiW,lif}.~ffi ... &l!llii -· PLAN VIEW -OUTLET TO WASHINGTON SCALE: 1" = 10' GRAPHIC SCALE 1" = 10' 10 0 10 PROPOSED HYDROLOGY EXHIBIT WALNUT BEACH HOMES -362 WALNUT AVE CITY OF CARLSBAD 20 30 PASCO LARET SUITER & ASSOCIATES CML ENGINEERING + LAND PLANNING + LAND SURVEYING 535 North Hlplway 101, Ste A., Solua lltteh, CA 1121175 ph 858.25111.8212 I f: 858.259.4812 I pbaensineedng.com PLSA 2808-01 ----------~-----'