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Home My WebLink AboutMS 2021-0001; GARFIELD HOMES; HYDROLOGY STUDY; 2022-05-12 HYDROLOGY STUDY FOR GRADING PERMIT / PARCEL MAP GARFIELD HOMES 4008 GARFIELD STREET PUD 2021-0001 / SDP 2021-0002 / CDP 2021-0003 / MS 2021-0001/ GR 2021-0035 DWG 533-6A CITY OF CARLSBAD, CA PREPARED FOR: RREG INVESTMENTS SERIES, LLC SERIES I038 5315 AVENIDA ENCINAS, SUITE 200 CARLSBAD, CA 92008 PREPARED BY: PASCO LARET SUITER & ASSOCIATES, INC. 535 N. HIGHWAY 101, SUITE A SOLANA BEACH, CA 92075 PH: (858) 259-8212 Prepared: September 2021 Revised: May 2022 __________________________________________________ Bryan Knapp, PE 86542 DATE TABLE OF CONTENTS SECTION Executive Summary 1.0 Introduction 1.1 Existing Conditions 1.2 Proposed Project 1.3 Conclusions 1.4 References 1.5 Methodology 2.0 Introduction 2.1 County of San Diego Criteria 2.2 Runoff Coefficient Determination 2.3 Hydrology & Hydraulic Model Output 3.0 Pre-Developed Hydrologic Calculations (100-Year Event) 3.1 Post-Developed Hydrologic Calculations (100-Year Event) 3.2 Pre-Developed vs. Post-Developed Peak Flows (100-Year Event) 3.3 Appendix 4.0 Isopluvial Maps Intensity Duration Design Charts Runoff Coefficients Hydrologic Soil Group - USDA Web Soil Survey Pre-Development Hydrology Node Map Post-Development Hydrology Node Map PLSA 3391-01 Page 1 of 11 1.0 EXECUTIVE SUMMARY 1.1 Introduction This Hydrology Study for the proposed development at 4008 Garfield Street, known as the Garfield Homes, has been prepared to analyze the hydrologic 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 along Garfield Street, southeast of the Garfield Street and Chinquapin Avenue intersection, in the City of Carlsbad. The site is bound by Garfield Street to the west, Chinquapin Avenue to the north, and residential development to the south and east. The existing site consists of a single-family residential structure, detached garage, and other hardscape and landscape improvements typical to the surrounding residential sites. The project site is located in the Carlsbad Watershed, the Agua Hedionda Hydrologic Area, and, more specifically, the Los Monos Hydrologic Sub-Area (904.31). The subject property has an approximate area of 0.138 acres and is approximately 51% impervious in the existing condition. Per the Web Soil Survey application available through the United States Department of Agriculture, the basin is generally categorized to have type B hydrologic soils. Based on the existing impervious area and land use type, a pre-development weighted runoff coefficient of 0.58 was calculated for the subject property using the methodology described in section 3.1.2 of the San Diego County Hydrology Manual and the formula provided therein. The existing site can be categorized into a single drainage basin designated as basin EX-1, which comprises the entire property. Drainage basin EX-1 primarily drains from west to east, discharging onto Chinquapin Avenue by surface and sheet flow methods. Once on Chinquapin Avenue, runoff leaving the site travels east along Chinquapin Avenue and enters an existing storm drain inlet at the end of the public street. Storm water collected in the drain at the end of Chinquapin Avenue continues to be conveyed through public storm water facilities until ultimately reaching the Pacific Ocean. Using the Rational Method Procedure outlined in the San Diego County Hydrology Manual, a peak flow rate and time of concentration were calculated for the 100-year, 6- hour storm event for the onsite drainage basins. Table 1 below summarizes the results of the Rational Method calculations. PLSA 3391-01 Page 2 of 11 EXISTING DRAINAGE FLOWS DRAINAGE AREA DRAINAGE AREA (ACRES) Q100 (CFS) I100 (IN/HR) EX-1 0.138 0.51 6.42 Table 1. Existing Condition Peak Drainage Flow Rates Refer to pre-development hydrology calculations included in Section 3.1 of this report for a detailed analysis of the existing drainage basin, as well as a pre-development hydrology node map included in the appendix of this report for pre-development drainage basin delineation and discharge locations. 1.3 Proposed Project The proposed project includes the demolition of all existing onsite improvements and the construction of three (3) new multi-family residential condominiums. Construction activities such as grading and onsite hardscape improvements are also proposed. Hardscape improvements include the construction of concrete driveways and walkways. The development project also includes offsite improvement in the right-of-way such as public concrete walkways, new curb and gutter, and driveway aprons. Miscellaneous landscape improvements typical to residential development are also being proposed. As in the existing condition, storm water will flow from west to east in the post-development condition. Storm water collection from structures and other onsite hardscape features will be dispensed into landscaped areas located around proposed buildings and conveyed via landscaped swales to area drains located in the front yards of the onsite units. Outletting from the area drains will be 3” PVC underdrain pipes directing water through the curb face onto Chinquapin Avenue. As in the pre-development condition, water will then continue east through public facilities until ultimately reaching the Pacific Ocean. The subject property is approximately 70% impervious in the proposed condition. Based on the proposed impervious area and land use type, a post-development weighted runoff coefficient of 0.71 was calculated for the subject property using the methodology described in section 3.1.2 of the San Diego County Hydrology Manual and the formula provided therein. The proposed site consists of a single drainage basin designated as PR-1. Drainage basin PR-1 consists of the entire project property, and as previously discussed will all drain into the Chinquapin right-of-way. Within basin PR-1 there are three subbasins based on the points of discharge onto Chinquapin Avenue by means of sidewalk under drain pipe. These have been delineated as well to determine peak runoff at each minor point of discharge to size proposed private drainage infrastructure. These all confluence at the northeast corner of the property along Chinquapin Avenue and combine for the peak flow generated by the entire property. Sizing calculations for this infrastructure can be seen in section 3.2.1 of this report. By PLSA 3391-01 Page 3 of 11 virtue of grading pads for construction and the proposed private drainage swales at 1.0% through the site, the time of concentration in the post-development condition has increased from the pre-project rate. This promotes incidental infiltration, evapotranspiration, and serves to mitigate peak runoff leaving the site due to the slight increase in proposed impervious area. Using the Rational Method Procedure outlined in the San Diego County Hydrology Manual, a peak flow rate and time of concentration were calculated for the 100-year, 6- hour storm event for the onsite drainage basins. Table 2 below summarizes the results of the Rational Method calculations in the post-developed condition. PROPOSED DRAINAGE FLOWS DRAINAGE AREA DRAINAGE AREA (ACRES) Q100 (CFS) I100 (IN/HR) PR-1 0.138 0.53 5.45 Table 2. Proposed Condition Peak Drainage Flow Rates Refer to post-development hydrology calculations included in Section 3.2 of this report for a detailed analysis of the proposed drainage basin, as well as a post-development hydrology node map included in the appendix of this report for post-development drainage basin delineation and discharge locations. In an effort to comply with the City of Carlsbad storm water standards, the proposed site has incorporated LID design techniques to optimize the site layout. Runoff from proposed roofs and new or removed and replaced hardscape areas will be directed to landscaped areas in an effort to disperse drainage to pervious surfaces. The landscaped areas will assist to remove sediment and particulate-bound pollutants from storm water. 1.4 Conclusions Based upon the analysis included in this report, there is a difference of ~0.02 cfs in peak runoff between the proposed development and the existing condition. Similar to the existing condition, the project will discharge onto Chinquapin Avenue. Water will not be diverted away from existing drainage patterns, and the difference in runoff can be considered negligible and will not have any adverse effect on the downstream watershed. The proposed project will be exempt from hydromodification compliance requirements as it does not qualify as a Priority Development Project as defined in the Regional Municipal Separate Storm Sewer System (MS4) Permit and the Carlsbad BMP Design Manual. An additional detention analysis was not performed at this time as it was determined that the project increases runoff in the proposed condition from the pre- project condition. PLSA 3391-01 Page 4 of 11 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 “City of Carlsbad Engineering Standards, Volume 5: Carlsbad BMP Design Manual (Post Construction Treatment BMPs)”, revised September 2021 “Low Impact Development Handbook – Stormwater Management Strategies”, revised July 2014, County of San Diego, Department of Public Works Soil Survey Staff, Natural Resources Conservation Service, United States Department of Agriculture. Web Soil Survey. Available online at http://websoilsurvey.nrcs.usda.gov. Accessed May 20, 2020 PLSA 3391-01 Page 5 of 11 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 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 D-0.645 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. 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. PLSA 3391-01 Page 6 of 11 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 of rainfall anticipated from a given storm event (i.e. 100-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 100 feet, and is dependent on land use and slope. The time of concentration minimum is 5 minutes for purposes of calculating rainfall intensity per the County of San Diego Hydrology Manual requirements. 2.3 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 in the Appendix of this report, categorizes the land use, the associated development density (dwelling units per acre) and the percentage of impervious area. For this study, a weighted runoff coefficient was used for both the pre-project and post- developed site in accordance with the equation provided in Section 3.1.2 of the County of San Diego Hydrology Manual. The weighted runoff coefficient is a function of the total impervious and pervious surface areas in the existing and proposed conditions. PLSA 3391-01 Page 7 of 11 3.0 HYDROLOGY MODEL OUTPUT 3.1 Pre-Developed Hydrologic Model Output (100-Year Event) Pre-Development: Q = CIA *Rational Method Equation P100 = 2.5 *100-Year, 6-Hour Rainfall Precipitation Basin EX-1 (Total Site) Total Area = 6,001 sf  0.138 Acres Impervious Area = 3,032 sf  0.070 Acres Pervious Area = 2,969 sf  0.068 Acres 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 - 0.9, C value for developed / impervious surface * Per SDHDM Section 3.1.2 Cn = 0.9 x 3,032 sf + 0.25 x 2,969 sf = 0.58 6,001 sf Tc = ti + tt ti @ 100’=8.3% => 4.0 min from Table 3-2 tt => L=156’-100’= 56’ ΔE=58.5-57.6=0.9’ tt= [{11.9(L/5,280)^3}/ΔE]^0.385 tt= [{11.9(56/5,280)^3}/0.9]^0.385 = 0.02 0.02 x 60 = 1.2 Min. Tc = 4.0 + 1.2 = 5.2 Min Tc = 5.2 Min I = 7.44 x P6 x D-0.645 *Rainfall Intensity Equation I = 7.44 x 2.5 x 5.2-0.645 ≈ 6.42 in/hr Q100 = 0.58 x 6.42 in/hr x 0.138 Ac = 0.51 cfs PLSA 3391-01 Page 8 of 11 3.2 Post-Developed Hydrologic Model Output (100-Year Event) Post-Development (without considering HMP/BMP treatment): Q = CIA *Rational Method Equation P100 = 2.5 *100-Year, 6-Hour Rainfall Precipitation Basin PR-1 (Total Site) Total Area = 6,001 sf ➔ 0.138 Acres Impervious Area = 4,205 sf ➔ 0.097 Acres Pervious Area = 1,796 sf ➔ 0.041 Acres 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 - 0.9, C value for developed / impervious surface * Per SDHDM Section 3.1.2 Cn = 0.9 x 4,205 sf + 0.25 x 1,796 sf = 0.71 6,001 sf Tc = 6.7 Min I = 7.44 x P6 x D-0.645 *Rainfall Intensity Equation I = 7.44 x 2.5 x 6.7-0.645 ≈ 5.45 in/hr Q100 = 0.71 x 5.45 in/hr x 0.056 Ac = 0.53 cfs **Total peak discharge leaving the property in the proposed condition Sub-Basin 1 (Peak Flow at Northeast Catch Basin) Total area = 2,891 sf ➔ .066 Acres Tc = ti + tt ti @ 65’=1.0% => 6.1 min from Table 3-2 tt => L=127’-65’= 62’ ΔE=60.1-56.9=3.2’ tt= [{11.9(L/5,280)^3}/ΔE]^0.385 tt= [{11.9(62/5,280)^3}/3.2]^0.385 = 0.02 0.01 x 60 = 0.6 Min. Tc = 6.1 + 0.6 = 6.7 Min Tc = 6.7 Min I = 7.44 x P6 x D-0.645 *Rainfall Intensity Equation I = 7.44 x 2.5 x 6.7-0.645 ≈ 5.45 in/hr Q100 = 0.71 x 5.45 in/hr x 0.066 Ac = 0.25 cfs PLSA 3391-01 Page 9 of 11 Sub-Basin 2 (Peak Flow at North Catch Basin) Total area = 2,412 sf ➔ 0.55 Acres Tc = ti + tt ti @ 65’=1.0% => 6.1 min from Table 3-2 tt => L=102’-65’= 37’ ΔE=64.7-62.4=2.3’ tt= [{11.9(L/5,280)^3}/ΔE]^0.385 tt= [{11.9(37/5,280)^3}/2.3]^0.385 = 0.02 0.02 x 60 = 0.4 Min. Tc = 6.1 + 0.4 = 6.5 Min Tc = 6.5 Min I = 7.44 x P6 x D-0.645 *Rainfall Intensity Equation I = 7.44 x 2.5 x 6.5-0.645 ≈ 5.56 in/hr Q100 = 0.71 x 5.56 in/hr x 0.055 Ac = 0.22 cfs PLSA 3391-01 Page 10 of 11 3.2.1 Capacity check for D-27 PVC Sidewalk Underdrain Cpvc = 0.125 cfs** **Capacity of 3” PVC pipe sloped at 2% QSB1 = 0.25 cfs *Flowrate of Sub-Basin 1 QSB2 = 0.22 cfs *Flowrate of Sub-Basin 2 Capacity of two 3” PVC pipes sloped at 2% Cpvc * 2 = 0.125 * 2 = 0.25 cfs = C2pvc Capacity check for two 3” PVC pipes sloped at 2% onto Chinquapin Avenue for sub- basins 1 and 2. C2pvc – QSB1= 0.25 - 0.25 = 0.00 cfs Cpvc – QSB2 = 0.25 – 0.22 = +0.03 cfs Two 3” PVC pipes sloped at 2% will handle the 100-year storm flowrates for sub basin 1 and sub basin 2. **See Appendix for capacity calculations for 3” PVC pipe sloped at 2% 3.3 Pre-Developed vs. Post-Developed Peak Flows (100-Year Event) Pre-Development vs. Post-Development (Discharge Leaving Site): Pre-Development Post-Development Delta Q100 = 0.51 cfs Q100 = 0.53 cfs 0.02 cfs increase *Increase of < 0.05 cfs can be considered negligible PLSA 3391-01 Page 11 of 11 4.0 APPENDIX San Diego County Hydrology Manual Section: 3 Date: June 2003 Page: 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 (Ti) .5% 1% 2% 3% 5% 10% Element* DU/ 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 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 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. 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 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 TypeNRCS Elements County Elements % IMPER. A B C D Undisturbed Natural Terrain (Natural) Permanent Open Space 0* 0.200.250.300.35Low 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. 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). DU/A = dwelling units per acre NRCS = National Resources Conservation Service 3-6 Hydrologic Soil Group—San Diego County Area, California Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11/16/2020 Page 1 of 436676183667625366763236676393667646366765336676603667618366762536676323667639366764636676533667660468020468027468034468041468048468055468062468069468076468083468090 468020 468027 468034 468041 468048 468055 468062 468069 468076 468083 468090 33° 8' 50'' N 117° 20' 34'' W33° 8' 50'' N117° 20' 31'' W33° 8' 48'' N 117° 20' 34'' W33° 8' 48'' N 117° 20' 31'' WN Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 11N WGS84 0 15 30 60 90 Feet 0 4 9 18 27 Meters Map Scale: 1:333 if printed on A landscape (11" x 8.5") sheet. Soil Map may not be valid at this scale. MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Soils Soil Rating Polygons A A/D B B/D C C/D D Not rated or not available Soil Rating Lines A A/D B B/D C C/D D Not rated or not available Soil Rating Points A A/D B B/D C C/D D Not rated or not available Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Roads Local Roads Background Aerial Photography 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 15, May 27, 2020 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Jan 23, 2020—Feb 13, 2020 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. Hydrologic Soil Group—San Diego County Area, California Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11/16/2020 Page 2 of 4 Hydrologic Soil Group Map unit symbol Map unit name Rating Acres in AOI Percent of AOI MlC Marina loamy coarse sand, 2 to 9 percent slopes B 0.2 100.0% Totals for Area of Interest 0.2 100.0% 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 (A/D, 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 (A/D, B/D, or C/D), 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 Hydrologic Soil Group—San Diego County Area, California Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11/16/2020 Page 3 of 4 Component Percent Cutoff: None Specified Tie-break Rule: Higher Hydrologic Soil Group—San Diego County Area, California Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11/16/2020 Page 4 of 4 Channel Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc.Friday, Nov 12 2021 3-in PVC @ 2.0% Circular Diameter (ft) = 0.25 Invert Elev (ft) = 53.15 Slope (%) = 2.00 N-Value = 0.013 Calculations Compute by: Known Depth Known Depth (ft) = 0.25 Highlighted Depth (ft) = 0.25 Q (cfs) = 0.125 Area (sqft) = 0.05 Velocity (ft/s) = 2.54 Wetted Perim (ft) = 0.79 Crit Depth, Yc (ft) = 0.22 Top Width (ft) = 0.00 EGL (ft) = 0.35 0 1 Elev (ft)Section 52.75 53.00 53.25 53.50 53.75 54.00 Reach (ft)