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CC - Item 3A - Attachment G - Appendix D - Strathmore Garvey Drainage StudyGarvey & Strathmore Apartments Drainage Study 7849 Garvey Avenue Rosemead, CA 91770 Date Prepared: August 11, 2022 Prepared for: Green Park Property, LLC Attn.: Cindy Lau 120 E. Valley Blvd. San Gabriel, CA 91776 (626) 307-0062 Prepared By: 4340 Viewridge Ave, Suite B San Diego, CA 92113 Ph: (858) 634-8620 Declaration of Responsible Charge: I hereby declare that I am the engineer of work for this project, that I have exercised responsible charge over the design of the project as defined in section 6703 of the business and professions code, and that the design is consistent with current standards. I understand that the check of the project drawings and specifications by the City of Rosemead is confined to a review only and does not relieve me, as an engineer of work, of my responsibilities for project design. _______________________________ Patric T. de Boer RCE 83583 Registration Expires 3-31-2023 ______________________________ Patric T de Boer RCE 835 Table of Contents Site & Project Description ....................................................................................................... 1 Methodology ............................................................................................................................ 1 Existing Conditions ................................................................................................................. 1 Proposed Conditions ............................................................................................................... 2 Existing HydroCalc Analysis................................................................................................... 2 Proposed HydroCalc Analysis ................................................................................................. 3 Results and Conclusions .......................................................................................................... 3 Site Vicinity Map ..................................................................................................................... 4 Existing Hydrology Exhibit .................................................................................................... 5 Proposed Hydrology Exhibit .................................................................................................. 6 Pipe Sizing ............................................................................................................................... 7 HydroCalc Analysis Exhibits .................................................................................................. 8 Appendices 50-Year 24-Hour Isopluvial ...................................................................................... Appendix 1 Soil Type Map ......................................................................................................... Appendix 2 1 Site & Project Description This drainage study has been prepared for the proposed project located at 7849 Garvey Avenue in the City of Rosemead. The project site is located 0.65 south of Interstate 10 at the northwest corner of the intersection of Garvey Avenue and Strathmore Avenue. See figure No.1 for a Vicinity Map. The site is currently occupied by a paved parking lot and three commercial buildings. No existing storm drains or inlets are known to exist on the project site. The proposed project involves the demolition and removal of all existing improvements and structures. A seven story apartment with an integrated parking garage will be constructed. The single building will cover the majority of the site. Methodology This drainage report has been prepared in accordance with current County of Los Angeles regulations and procedures. The analyses of the existing and proposed conditions were performed using HydroCalc (Version 1.02) to calculate runoff flowrates and volumes. Given the area, length of flow path, average slope, design storm depth, imperviousness, and soil type, HydroCalc generates a hydrograph for the existing and proposed conditions. Soil and rainfall inputs were determined using the GIS data provided by maps the Los Angeles Flood Control District. This report analyzes the flow generated by the 25, 50 and 100-year storm events for storm drain sizing and flood control purposes. The following references were used in this report (1) Handbook of Hydraulics, E.F. Brater & H.W. King, 6th Ed., 1976. (2) Los Angeles County Department of Public Works Hydrology Manual, 2006 Existing Conditions The existing 1.21 acre site is 100% impervious and underlain by soil type # 7. The site accepts offsite runoff from the alley and the properties west of the site. The offsite areas surface flow to the site and confluence with the on-site flow before draining to Strathmore Avenue. The entire site and the offsite areas drain east via surface flow to the gutter on Strathmore Ave., thence south to the existing curb inlet, and ultimately to the existing 24” pipe on the public storm drain system. This point is referred to as Discharge Point # 1 in this report. 2 Proposed Conditions The proposed improvements consist of a seven-story apartment building, hardscape and on-site storm drain system. The proposed development will grade the entire site but will keep the same discharge point as the existing conditions. The proposed site will be 100% impervious. The majority of the site will be covered by the building. Catch basins will be installed along the west end of the building and the westerly alley to accept the offsite runoff generated from the westerly properties and bypass via pipe flow to a connection point to the 24” storm drain in Strathmore Avenue. The roof drains of the building will drain directly to storm drain pipes in the ground level parking lot that will be connected to a proposed 8’x16’ Modular Wetland System vault for treatment. Following treatment, the stormwater will drain out via pipe flow to a proposed storm drain pipe that will connect to the existing 24” RCP pipe on Strathmore. This point is referred to as Discharge Point # 1 in this report. Existing HydroCalc Analysis The existing condition was modeled as a single on-site basin and three off-site basins, referred to as E-1, O-1, O-2 and O-3 in this report. Below is a summary of the HydroCalc calculations for the existing conditions. The output data sheets from HydroCalc can be found at the end of this report. Basin # Area (ac) Soil Type Imperv. (%) I25 (in/hr) I50 (in/hr) I100 (in/hr) Q25 (cfs) Q50 (cfs) Q100 (cfs) E-1 1.21 7 100 3.25 3.70 4.15 3.54 4.03 4.52 O-1 0.36 7 100 3.25 3.70 4.15 1.05 1.20 1.35 O-2 0.17 7 100 3.25 3.70 4.15 0.50 0.57 0.64 O-3 0.29 7 45 3.25 3.70 4.15 0.85 0.97 1.08 Total Combined Flow 5.93 6.76 7.58 3 Proposed HydroCalc Analysis The proposed site was modeled as a single on-site basin and three offsite basins, referred to as P-1, O-1, O-2 and O-3 in this report. Below is a summary of the HydroCalc calculations for the proposed conditions. The output data sheets from HydroCalc can be found at the end of this report. Results and Conclusions The proposed improvements result in no change to the peak runoff flowrate for the 25, 50 and 100-year storm events. This is because the site is 100 % impervious for both the existing and proposed conditions. The onsite flowpath was modified, but the time of concentration in both the existing and proposed conditions is below the 5.0 minute minimum allowed by the Rational Method. The offsite flowpath is modified in that runoff from the site will discharge directly to a new connection to the 24” storm drain in Strathmore Ave, rather than flowing to the existing curb inlet first. It is the opinion of Omega Engineering Consultants that the project will not cause adverse effects to the downstream drainage facilities or receiving waters. A separate LID Plan has been prepared to discuss the water quality impacts of the proposed development. Basin # Area (ac) Soil Type Imperv. (%) I25 (in/hr) I50 (in/hr) I100 (in/hr) Q25 (cfs) Q50 (cfs) Q100 (cfs) P-1 1.21 7 100 3.25 3.70 4.15 3.54 4.03 4.52 O-1 0.36 7 100 3.25 3.70 4.15 1.05 1.20 1.35 O-2 0.17 7 100 3.25 3.70 4.15 0.50 0.57 0.64 O-3 0.29 7 45 3.25 3.70 4.15 0.85 0.97 1.08 Total Combined Flow 5.93 6.76 7.58 10 CONDUIT SIZING CALCULATIONS The following chart details the sizing parameters and for conduits that convey runoff on the site. K'= Discharge factor =(Q*n)/(d8/3*s1/2 ) n= Mannings coefficient =0.013 for PVC & HDPE d=diameter of conduit (ft)=per chart Q= Discharge =based off portions of basins tributary to outlet s=Minimum Pipe Slope (ft/ft)=per chart D=depth of flow =From table 7-4 See right Ca= Flow factor = From table 7-14 See right A=Cross sectional area of flow =Ca*d2 V=Velocity =Q/A Pipe Flow Pipe Tributary Areas Q (cfs)S (%)d (in)K'D/d Ca A (sf)V (fps) 1 Half of proposed building roof 2.26 0.5 12 0.4155 0.73 0.614 0.614 3.68 2 Half of proposed building roof 2.26 0.5 12 0.4155 0.73 0.614 0.614 3.68 3 Basin O-1 1.35 0.5 12 0.2482 0.52 0.413 0.413 3.27 4 Basin O-2 0.64 0.5 12 0.1177 0.34 0.236 0.236 2.72 5 Basin O-3 1.08 0.5 12 0.1986 0.45 0.343 0.343 3.15 6 Entire proposed building roof and offsite basns 7.58 0.5 18 0.4727 0.83 0.697 1.568 4.83 Peak Flow Hydrologic Analysis File location: P:/DWG OMEGA/0713 Strathmore and Garvey/STORMWATER/H&H/Calculations/25-Year/Strathmore - 25 Year - E-1.1.pdf Version: HydroCalc 1.0.3 Input Parameters Project Name Strathmore - 25 Year Subarea ID E-1.1 Area (ac)1.21 Flow Path Length (ft)235.0 Flow Path Slope (vft/hft)0.0241 50-yr Rainfall Depth (in)6.2 Percent Impervious 1.0 Soil Type 7 Design Storm Frequency 25-yr Fire Factor 0 LID False Output Results Modeled (25-yr) Rainfall Depth (in)5.4436 Peak Intensity (in/hr)3.2478 Undeveloped Runoff Coefficient (Cu)0.6837 Developed Runoff Coefficient (Cd)0.9 Time of Concentration (min)5.0 Clear Peak Flow Rate (cfs)3.5369 Burned Peak Flow Rate (cfs)3.5369 24-Hr Clear Runoff Volume (ac-ft)0.4899 24-Hr Clear Runoff Volume (cu-ft)21341.0961 Peak Flow Hydrologic Analysis File location: P:/DWG OMEGA/0713 Strathmore and Garvey/STORMWATER/H&H/Calculations/Proposed/25-Year/Strathmore - 25 Year - P-1.1.pdf Version: HydroCalc 1.0.3 Input Parameters Project Name Strathmore - 25 Year Subarea ID P-1.1 Area (ac)1.21 Flow Path Length (ft)100.0 Flow Path Slope (vft/hft)0.005 50-yr Rainfall Depth (in)6.2 Percent Impervious 1.0 Soil Type 7 Design Storm Frequency 25-yr Fire Factor 0 LID False Output Results Modeled (25-yr) Rainfall Depth (in)5.4436 Peak Intensity (in/hr)3.2478 Undeveloped Runoff Coefficient (Cu)0.6837 Developed Runoff Coefficient (Cd)0.9 Time of Concentration (min)5.0 Clear Peak Flow Rate (cfs)3.5369 Burned Peak Flow Rate (cfs)3.5369 24-Hr Clear Runoff Volume (ac-ft)0.4899 24-Hr Clear Runoff Volume (cu-ft)21341.0961 Peak Flow Hydrologic Analysis File location: P:/DWG OMEGA/0713 Strathmore and Garvey/STORMWATER REPORTS/H&H/Calculations/Offsite/25-Year/Strathmore - 25 Year - O-1.pdf Version: HydroCalc 1.0.3 Input Parameters Project Name Strathmore - 25 Year Subarea ID O-1 Area (ac)0.36 Flow Path Length (ft)130.0 Flow Path Slope (vft/hft)0.0154 50-yr Rainfall Depth (in)6.2 Percent Impervious 1.0 Soil Type 7 Design Storm Frequency 25-yr Fire Factor 0 LID False Output Results Modeled (25-yr) Rainfall Depth (in)5.4436 Peak Intensity (in/hr)3.2478 Undeveloped Runoff Coefficient (Cu)0.6837 Developed Runoff Coefficient (Cd)0.9 Time of Concentration (min)5.0 Clear Peak Flow Rate (cfs)1.0523 Burned Peak Flow Rate (cfs)1.0523 24-Hr Clear Runoff Volume (ac-ft)0.1458 24-Hr Clear Runoff Volume (cu-ft)6349.417 Peak Flow Hydrologic Analysis File location: P:/DWG OMEGA/0713 Strathmore and Garvey/STORMWATER REPORTS/H&H/Calculations/Offsite/25-Year/Strathmore - 25 Year - O-2.pdf Version: HydroCalc 1.0.3 Input Parameters Project Name Strathmore - 25 Year Subarea ID O-2 Area (ac)0.17 Flow Path Length (ft)80.0 Flow Path Slope (vft/hft)0.025 50-yr Rainfall Depth (in)6.2 Percent Impervious 1.0 Soil Type 7 Design Storm Frequency 25-yr Fire Factor 0 LID False Output Results Modeled (25-yr) Rainfall Depth (in)5.4436 Peak Intensity (in/hr)3.2478 Undeveloped Runoff Coefficient (Cu)0.6837 Developed Runoff Coefficient (Cd)0.9 Time of Concentration (min)5.0 Clear Peak Flow Rate (cfs)0.4969 Burned Peak Flow Rate (cfs)0.4969 24-Hr Clear Runoff Volume (ac-ft)0.0688 24-Hr Clear Runoff Volume (cu-ft)2998.3358 Peak Flow Hydrologic Analysis File location: P:/DWG OMEGA/0713 Strathmore and Garvey/STORMWATER REPORTS/H&H/Calculations/Offsite/25-Year/Strathmore - 25 Year - O-3.pdf Version: HydroCalc 1.0.3 Input Parameters Project Name Strathmore - 25 Year Subarea ID O-3 Area (ac)0.29 Flow Path Length (ft)90.0 Flow Path Slope (vft/hft)0.0444 50-yr Rainfall Depth (in)6.2 Percent Impervious 1.0 Soil Type 7 Design Storm Frequency 25-yr Fire Factor 0 LID False Output Results Modeled (25-yr) Rainfall Depth (in)5.4436 Peak Intensity (in/hr)3.2478 Undeveloped Runoff Coefficient (Cu)0.6837 Developed Runoff Coefficient (Cd)0.9 Time of Concentration (min)5.0 Clear Peak Flow Rate (cfs)0.8477 Burned Peak Flow Rate (cfs)0.8477 24-Hr Clear Runoff Volume (ac-ft)0.1174 24-Hr Clear Runoff Volume (cu-ft)5114.8082 Peak Flow Hydrologic Analysis File location: P:/DWG OMEGA/0713 Strathmore and Garvey/STORMWATER/H&H/Calculations/50-Year/Strathmore - 50 Year - E-1.1.pdf Version: HydroCalc 1.0.3 Input Parameters Project Name Strathmore - 50 Year Subarea ID E-1.1 Area (ac)1.21 Flow Path Length (ft)235.0 Flow Path Slope (vft/hft)0.0241 50-yr Rainfall Depth (in)6.2 Percent Impervious 1.0 Soil Type 7 Design Storm Frequency 50-yr Fire Factor 0 LID False Output Results Modeled (50-yr) Rainfall Depth (in)6.2 Peak Intensity (in/hr)3.6991 Undeveloped Runoff Coefficient (Cu)0.721 Developed Runoff Coefficient (Cd)0.9 Time of Concentration (min)5.0 Clear Peak Flow Rate (cfs)4.0283 Burned Peak Flow Rate (cfs)4.0283 24-Hr Clear Runoff Volume (ac-ft)0.558 24-Hr Clear Runoff Volume (cu-ft)24306.4876 Peak Flow Hydrologic Analysis File location: P:/DWG OMEGA/0713 Strathmore and Garvey/STORMWATER/H&H/Calculations/Proposed/50-Year/Strathmore - 50 Year - P-1.1.pdf Version: HydroCalc 1.0.3 Input Parameters Project Name Strathmore - 50 Year Subarea ID P-1.1 Area (ac)1.21 Flow Path Length (ft)100.0 Flow Path Slope (vft/hft)0.005 50-yr Rainfall Depth (in)6.2 Percent Impervious 1.0 Soil Type 7 Design Storm Frequency 50-yr Fire Factor 0 LID False Output Results Modeled (50-yr) Rainfall Depth (in)6.2 Peak Intensity (in/hr)3.6991 Undeveloped Runoff Coefficient (Cu)0.721 Developed Runoff Coefficient (Cd)0.9 Time of Concentration (min)5.0 Clear Peak Flow Rate (cfs)4.0283 Burned Peak Flow Rate (cfs)4.0283 24-Hr Clear Runoff Volume (ac-ft)0.558 24-Hr Clear Runoff Volume (cu-ft)24306.4876 Peak Flow Hydrologic Analysis File location: P:/DWG OMEGA/0713 Strathmore and Garvey/STORMWATER REPORTS/H&H/Calculations/Offsite/50-Year/Strathmore - 50 Year - O-1.pdf Version: HydroCalc 1.0.3 Input Parameters Project Name Strathmore - 50 Year Subarea ID O-1 Area (ac)0.36 Flow Path Length (ft)130.0 Flow Path Slope (vft/hft)0.0154 50-yr Rainfall Depth (in)6.2 Percent Impervious 1.0 Soil Type 7 Design Storm Frequency 50-yr Fire Factor 0 LID False Output Results Modeled (50-yr) Rainfall Depth (in)6.2 Peak Intensity (in/hr)3.6991 Undeveloped Runoff Coefficient (Cu)0.721 Developed Runoff Coefficient (Cd)0.9 Time of Concentration (min)5.0 Clear Peak Flow Rate (cfs)1.1985 Burned Peak Flow Rate (cfs)1.1985 24-Hr Clear Runoff Volume (ac-ft)0.166 24-Hr Clear Runoff Volume (cu-ft)7231.6823 Peak Flow Hydrologic Analysis File location: P:/DWG OMEGA/0713 Strathmore and Garvey/STORMWATER REPORTS/H&H/Calculations/Offsite/50-Year/Strathmore - 50 Year - O-2.pdf Version: HydroCalc 1.0.3 Input Parameters Project Name Strathmore - 50 Year Subarea ID O-2 Area (ac)0.17 Flow Path Length (ft)80.0 Flow Path Slope (vft/hft)0.025 50-yr Rainfall Depth (in)6.2 Percent Impervious 1.0 Soil Type 7 Design Storm Frequency 50-yr Fire Factor 0 LID False Output Results Modeled (50-yr) Rainfall Depth (in)6.2 Peak Intensity (in/hr)3.6991 Undeveloped Runoff Coefficient (Cu)0.721 Developed Runoff Coefficient (Cd)0.9 Time of Concentration (min)5.0 Clear Peak Flow Rate (cfs)0.566 Burned Peak Flow Rate (cfs)0.566 24-Hr Clear Runoff Volume (ac-ft)0.0784 24-Hr Clear Runoff Volume (cu-ft)3414.9611 Peak Flow Hydrologic Analysis File location: P:/DWG OMEGA/0713 Strathmore and Garvey/STORMWATER REPORTS/H&H/Calculations/Offsite/50-Year/Strathmore - 50 Year - O-3.pdf Version: HydroCalc 1.0.3 Input Parameters Project Name Strathmore - 50 Year Subarea ID O-3 Area (ac)0.29 Flow Path Length (ft)90.0 Flow Path Slope (vft/hft)0.0444 50-yr Rainfall Depth (in)6.2 Percent Impervious 1.0 Soil Type 7 Design Storm Frequency 50-yr Fire Factor 0 LID False Output Results Modeled (50-yr) Rainfall Depth (in)6.2 Peak Intensity (in/hr)3.6991 Undeveloped Runoff Coefficient (Cu)0.721 Developed Runoff Coefficient (Cd)0.9 Time of Concentration (min)5.0 Clear Peak Flow Rate (cfs)0.9655 Burned Peak Flow Rate (cfs)0.9655 24-Hr Clear Runoff Volume (ac-ft)0.1337 24-Hr Clear Runoff Volume (cu-ft)5825.5218 Peak Flow Hydrologic Analysis File location: P:/DWG OMEGA/0713 Strathmore and Garvey/STORMWATER/H&H/Calculations/100-Year/Strathmore - 100 Year - E-1.1.pdf Version: HydroCalc 1.0.3 Input Parameters Project Name Strathmore - 100 Year Subarea ID E-1.1 Area (ac)1.21 Flow Path Length (ft)235.0 Flow Path Slope (vft/hft)0.0241 50-yr Rainfall Depth (in)6.2 Percent Impervious 1.0 Soil Type 7 Design Storm Frequency 100-yr Fire Factor 0 LID False Output Results Modeled (100-yr) Rainfall Depth (in)6.9564 Peak Intensity (in/hr)4.1504 Undeveloped Runoff Coefficient (Cu)0.7543 Developed Runoff Coefficient (Cd)0.9 Time of Concentration (min)5.0 Clear Peak Flow Rate (cfs)4.5198 Burned Peak Flow Rate (cfs)4.5198 24-Hr Clear Runoff Volume (ac-ft)0.6261 24-Hr Clear Runoff Volume (cu-ft)27271.8791 Peak Flow Hydrologic Analysis File location: P:/DWG OMEGA/0713 Strathmore and Garvey/STORMWATER/H&H/Calculations/Proposed/100-Year/Strathmore - 100 Year - P-1.1.pdf Version: HydroCalc 1.0.3 Input Parameters Project Name Strathmore - 100 Year Subarea ID P-1.1 Area (ac)1.21 Flow Path Length (ft)100.0 Flow Path Slope (vft/hft)0.005 50-yr Rainfall Depth (in)6.2 Percent Impervious 1.0 Soil Type 7 Design Storm Frequency 100-yr Fire Factor 0 LID False Output Results Modeled (100-yr) Rainfall Depth (in)6.9564 Peak Intensity (in/hr)4.1504 Undeveloped Runoff Coefficient (Cu)0.7543 Developed Runoff Coefficient (Cd)0.9 Time of Concentration (min)5.0 Clear Peak Flow Rate (cfs)4.5198 Burned Peak Flow Rate (cfs)4.5198 24-Hr Clear Runoff Volume (ac-ft)0.6261 24-Hr Clear Runoff Volume (cu-ft)27271.8791 Peak Flow Hydrologic Analysis File location: P:/DWG OMEGA/0713 Strathmore and Garvey/STORMWATER REPORTS/H&H/Calculations/Offsite/100-Year/Strathmore - 100 Year - O-1.pdf Version: HydroCalc 1.0.3 Input Parameters Project Name Strathmore - 100 Year Subarea ID O-1 Area (ac)0.36 Flow Path Length (ft)130.0 Flow Path Slope (vft/hft)0.0154 50-yr Rainfall Depth (in)6.2 Percent Impervious 1.0 Soil Type 7 Design Storm Frequency 100-yr Fire Factor 0 LID False Output Results Modeled (100-yr) Rainfall Depth (in)6.9564 Peak Intensity (in/hr)4.1504 Undeveloped Runoff Coefficient (Cu)0.7543 Developed Runoff Coefficient (Cd)0.9 Time of Concentration (min)5.0 Clear Peak Flow Rate (cfs)1.3447 Burned Peak Flow Rate (cfs)1.3447 24-Hr Clear Runoff Volume (ac-ft)0.1863 24-Hr Clear Runoff Volume (cu-ft)8113.9475 Peak Flow Hydrologic Analysis File location: P:/DWG OMEGA/0713 Strathmore and Garvey/STORMWATER REPORTS/H&H/Calculations/Offsite/100-Year/Strathmore - 100 Year - O-2.pdf Version: HydroCalc 1.0.3 Input Parameters Project Name Strathmore - 100 Year Subarea ID O-2 Area (ac)0.17 Flow Path Length (ft)80.0 Flow Path Slope (vft/hft)0.025 50-yr Rainfall Depth (in)6.2 Percent Impervious 1.0 Soil Type 7 Design Storm Frequency 100-yr Fire Factor 0 LID False Output Results Modeled (100-yr) Rainfall Depth (in)6.9564 Peak Intensity (in/hr)4.1504 Undeveloped Runoff Coefficient (Cu)0.7543 Developed Runoff Coefficient (Cd)0.9 Time of Concentration (min)5.0 Clear Peak Flow Rate (cfs)0.635 Burned Peak Flow Rate (cfs)0.635 24-Hr Clear Runoff Volume (ac-ft)0.088 24-Hr Clear Runoff Volume (cu-ft)3831.5863 Peak Flow Hydrologic Analysis File location: P:/DWG OMEGA/0713 Strathmore and Garvey/STORMWATER REPORTS/H&H/Calculations/Offsite/100-Year/Strathmore - 100 Year - O-3.pdf Version: HydroCalc 1.0.3 Input Parameters Project Name Strathmore - 100 Year Subarea ID O-3 Area (ac)0.29 Flow Path Length (ft)90.0 Flow Path Slope (vft/hft)0.0444 50-yr Rainfall Depth (in)6.2 Percent Impervious 1.0 Soil Type 7 Design Storm Frequency 100-yr Fire Factor 0 LID False Output Results Modeled (100-yr) Rainfall Depth (in)6.9564 Peak Intensity (in/hr)4.1504 Undeveloped Runoff Coefficient (Cu)0.7543 Developed Runoff Coefficient (Cd)0.9 Time of Concentration (min)5.0 Clear Peak Flow Rate (cfs)1.0832 Burned Peak Flow Rate (cfs)1.0832 24-Hr Clear Runoff Volume (ac-ft)0.1501 24-Hr Clear Runoff Volume (cu-ft)6536.2355 3 Appendix 1 Esri, NASA, NGA, USGS, FEMA | Esri Community Maps Contributor + −   LA County Hydrology Map  Layers Hydrology GIS 50yr Two Tenths (Rainfall) DPA Zones Soils 2004 Final 85th Percentile, 24-hrRainfall 1-year, 1-hour RainfallIntensity Final 95th Percentile, 24-hrRainfall LA County Parcels About Legend Layers Appendix 2 E + −   LA County Hydrology Map  Layers Hydrology GIS 50yr Two Tenths (Rainfall) DPA Zones Soils 2004 Final 85th Percentile, 24-hrRainfall 1-year, 1-hour RainfallIntensity Final 95th Percentile, 24-hrRainfall LA County Parcels About Legend Layers lacounty.gov | Public Works FAQ | Privacy / Terms of Use | ADA / Accessibility | |   Feedback