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Home My WebLink AboutPA2020103 - HYDRO (2)JN 2019.1995 R:\19\1994\PRELIM\REPORTS\HYDRO\1994 Prelim Hydrostudy.doc PREPARED FOR: PREPARED BY: KWC Engineers 1880 Compton Avenue, Suite 100 Corona, CA 92881 Tel: (951) 734-2130 www.kwcengineers.com RIVERSIDE LEGACY IV NICHOLS ROAD, LLC 1505 Bridgeway, Suite 107 Sausalito, CA 94965 (617) 877-7637 Baker Industrial City of Lake Elsinore, County of Riverside, California P R E L I MIN A RY DRAINAGE REPORT January 2024 Preliminary Drainage Report 2 TABLE OF CONTENTS Section Name Page Number LIST OF TABLES .......................................................................................................... 3 LIST OF FIGURES ........................................................................................................ 3 LIST OF APPENDICES ................................................................................................. 4 Section 1 - Introduction ................................................................................................. 5 1.1 Purpose of Study .......................................................................................... 5 1.2 Project Description ........................................................................................ 5 1.3 Floodplain Mapping ...................................................................................... 6 1.4 Design Criteria .............................................................................................. 6 Section 2 – Hydrologic Data and Model Development .................................................. 7 2.1 Existing Condition Model .............................................................................. 7 2.2 Proposed Condition Model ........................................................................... 8 Section 3 – Unit Hydrograph Analysis Existing and Proposed Conditions .................... 9 3.1 Introduction ................................................................................................... 9 3.2 Approach and Methodology .......................................................................... 9 3.3 On-site Unit Hydrograph Results ................................................................ 11 Section 4 – Hydraulic Analysis .................................................................................... 12 4.1 Onsite Drainage Facilities ........................................................................... 12 4.2 Street Capacity Analysis ............................................................................. 12 4.3 Outlet Analysis ............................................................................................ 12 4.4 Detention Analysis ...................................................................................... 12 Preliminary Drainage Report 3 Section 5 – Debris Basin Analysis ............................................................................... 14 5.1 Design Criteria ............................................................................................ 14 Section 6 – Conclusions .............................................................................................. 15 Section 7 – References ............................................................................................... 16 LIST OF TABLES Table 1. Existing Condition Peak Flow Summary ......................................................... 7 Table 2. Proposed Condition Peak Flow Summary ...................................................... 8 Table 3. Proposed vs Existing Condition Peak Flow Summary .................................... 8 Table 4. Precipitation Depth-Duration-Frequency Summary ......................................... 9 Table 5. Existing Condition Watershed Lag Time Parameters .................................... 10 Table 6. Proposed Condition Watershed Lag Time Parameters ................................. 10 Table 7. Proposed vs Existing Unit Hydrograph Peak Flow Summary ........................ 11 LIST OF FIGURES Figure 1: Vicinity Map Figure 2: Existing Condition Hydrology Key Map Figure 3: Proposed Condition Hydrology Key Map Figure 4: Existing Unit Hydrograph Key Map Figure 5: Proposed Unit Hydrograph Key Map Figure 6: FEMA FIRM Panel Preliminary Drainage Report 4 LIST OF APPENDICES Appendix A: Vicinity Map Appendix B: RCFC Precipitation Data & NRCS Soils Report Appendix C: Existing Condition Hydrology Rational Method & Key Map Appendix D: Proposed Condition Hydrology Rational Method & Key Map Appendix E: FEMA Flood Insurance Rate Map Appendix F: Existing Condition Unit Hydrograph & Key Map Appendix G: Proposed Condition Unit Hydrograph & Key Map Appendix H: Storm Drain Hydraulics WSPG Analysis Preliminary Drainage Report 5 Section 1 INTRODUCTION 1.1 PURPOSE OF STUDY The purpose of this study is to hydrologically model the project site’s onsite tributary watersheds to determine the existing and proposed peak runoffs. The hydrologic analysis was prepared using the Rational Method as specified in the Riverside County Hydrology Manual. The flows are used to estimate the size of the proposed drainage facilities that support the proposed project development. 1.2 PROJECT DESCRIPTION The Baker Industrial project is comprised of 66.23 acres of developed land along Baker Street in the City of Lake Elsinore in Riverside County, California, adjacent to Pierce Street. Appendix A shows a vicinity map of the area illustrating the location of the project. The Baker Industrial project is generally bounded to the northeast by Baker Street. Bounded on the northwest by Pierce Street. To the southeast and southwest of the site, the area is bounded by undeveloped hills. The project site existing conditions is generally flat with some hills coming onto the site along the southern boundary. The existing project gross acreage is 66.23 acres. The site’s drainage area flows from the south and southwest to the north and northeast to the north side of Baker Street. Two new buildings are proposed, building 1 is 206,982 sf and building 2 is 778,423 sf, landscape areas, driveways, and parking lots. The proposed buildings will consist of a warehouse and connected office space with the necessary improvements to facilitate business. The offsite drainage areas will be captured with a flow-by basin and a debris basin routed through storm drain before discharging at their historical locations on the north side of baker street. The onsite drainage areas will be captured by CMP Detention System and treated by MWS Units. Baker Street will be improved on the project frontage. The full width drainage of the street will be captured within the catch basin at the low points of Baker Street. The flows will continue into MWS units within Baker Street. Preliminary Drainage Report 6 1.3 FLOODPLAIN MAPPING The National Flood Insurance Act (1968) established the National Flood Insurance Program, which is based on the minimal requirements for floodplain management and is designed to minimize the flood damage within Other Flood Areas. The Federal Emergency Management Agency (FEMA) is the agency which administrates the National Flood Insurance Program. Other Flood Areas are defined as areas of 0.2% annual chance flood; areas of 1% annual chance flood with average depths of less than 1 foot or with drainage areas less than 1 square mile; and areas protected by levees from 1% annual chance flood. Flood Insurance Rate Maps (FIRMs) were developed to identify areas of flood hazards within a community. According to the Flood Insurance Rate Map (FIRM) catalog, there are FIRMs produced by FEMA for the project site: MAP Number: 06065C2028G MAP Revised: August 28, 2008 FEMA FIRM Panel (Figure 4) is attached in Appendix E shows the floodplain limits and mapped flood zones for the Baker Industrial project area. The project is located within Zone AE, which is an area within the flood hazard areas subject to inundation by the 1% annual chance flood. 1.4 DESIGN CRITERIA The following are design criteria for this project, based on the Riverside County Hydrology Manual. Protection Levels 1. The 100-year flood shall be contained 1’ below the building pads. 2. The 10-year flood shall be contained within the top of curbs. 1) Loss rates are to be determined for the 2- and 5-year events using an AMC I condition, while an AMC II are used for the 10-year event and 100-year event. Preliminary Drainage Report 7 Section 2 HYDROLOGIC DATA AND MODEL DEVELOPMENT 2.1 EXISTING CONDITION MODEL The project site existing condition consists of undeveloped land and characterized by steep topography, generally decreasing in elevation from the south to the north. Several ravines are present which will convey natural drainage across the project site washing towards the north side of Baker Street. The site is comprised of four (4) major drainage areas and four (4) offsite drainage areas to describe the existing drainage conditions. Refer to Existing Condition Hydrology Key Map Figure 2 in Appendix C for locations of the drainage sub-areas and peak flows. Hydrologic calculations to evaluate surface water runoff associated with the 10-year and 100-year storm frequency were performed for the on-site drainage areas. The Riverside County Rational Method Hydrologic calculations (as described in the RCHM) were performed using the CivilDesign Hydrology / Hydraulics computer program package 2005 by Bonadiman and Associates, Inc. Precipitation point values for the 10-year and 100-year durations obtained from Riverside County Flood Control Plate D-4.3, D-4.4, and Plate D-4.6 (see Appendix B). In order to proceed with analysis of the proposed developed condition, it is necessary to first establish the pre-developed peak runoff rates. Table 1 summarizes the data and results for the 10-year and 100-year storm event for on-site and off-site flows. All calculations can be found in Appendix C of the report. Table 1. Existing Condition Peak Flow Summary Drainage Area Area (AC) Q100 (CFS) Q10 (CFS) Q5 (CFS) Q2 (CFS) A 168.50 332.50 197.59 132.10 84.23 B 29.87 77.05 46.47 32.46 21.19 C 24.19 58.01 35.01 24.29 15.83 D 194.30 428.57 258.99 166.04 106.37 2.2 PROPOSED CONDITION MODEL In the proposed condition, the proposed improvements are to add two large industrial/warehouse type buildings, parking area with asphalt pavements, concrete slabs, landscape areas, and improvements to Baker Street. Refer to Appendix B for a preliminary soils report demonstrating soil type and hydrologic group classification. Two new buildings are proposed, building 1 is 206,982 sf and building 2 is 778,423 sf, landscape areas, driveways, and new drainage systems will all drain to Baker Street. Street improvements are proposed for Baker Street. Preliminary Drainage Report 8 The developed condition site consists of four (4) major drainage areas and four (4) offsite drainage areas. The project site runoff will be picked up by a system of gutters and inlets that will discharge through a storm drain system that outlets to Baker Street. The offsite flows will discharge in desilting basins to the south of the property and continue as it does in its current existing conditions through proposed dual 48” storm drains and dual 5x4’ storm drain box. Offsite drainage area will not comingle with onsite flows. Refer to Proposed Condition Hydrology Key Map Figure 3 in Appendix D for locations of the drainage sub-areas and peak flows. Hydrologic calculations were evaluated for surface water runoff associated with the 10- year and 100-year storm frequency. The proposed condition watershed boundaries were delineated using the project’s conceptual grading plan. Hydrologic land cover for the development is considered commercial. Table 2 summarizes the proposed condition 10 and 100-year rational method results. Proposed condition rational method calculations can be found in Appendix D of the report. Table 2. Proposed Condition Peak Flow Summary Drainage Area Area (AC) Q100 (CFS) Q10 (CFS) Q5 (CFS) Q2 (CFS) A 150.09 272.50 154.35 120.18 76.87 B 41.42 105.27 63.26 50.84 34.79 C 39.22 97.19 59.73 48.78 34.26 D 175.52 391.60 237.02 151.53 97.18 Table 3 summarizes the comparison between the Existing Condition and Proposed Condition Hydrology results. Table 3. Existing vs. Proposed Condition Peak Flow Summary Existing Condition Proposed Condition Note Drainage Area Area (Acres) Q100 (CFS) Q10 (CFS) Area (Acres) Q100 (CFS) Q10 (CFS) A 168.50 332.50 197.59 150.09 272.50 154.35 △ Q100 = 60.00 QProposed < QExisting △ Q10 = 43.24 QProposed < QExisting B 29.87 77.05 46.47 41.42 105.27 63.26 △ Q100 = 28.22 QProposed > QExisting △ Q10 = 16.79 QProposed > QExisting C 24.19 58.01 35.01 39.22 97.19 59.73 △ Q100 = 39.18 QProposed > QExisting △ Q10 = 19.72 QProposed > QExisting D 194.30 428.57 258.99 175.52 391.60 237.02 △ Q100 = 36.97 QProposed < QExisting △ Q10 = 21.97 QProposed < QExisting