Loading...
HomeMy WebLinkAbout11.UP23-0009_Stormwater_Management_PlanButte County C-1 June 2022 Stormwater Management and Discharge Control Manual Post-Construction Stormwater Management Plan for Project Name Post-Construction Stormwater Management Plan Butte County C-2 June 2022 Stormwater Management and Discharge Control Manual Section 1: Basic Project Information This worksheet must be filled out for all projects required to implement the Stormwater Management and Discharge Control Manual. A licensed professional engineer or landscape architect is not required for the development of the project plan for Small Projects. Project Site Address Owner Information Name Title, if applicable Company or Affiliation Address Telephone Number Email Address Professional Engineer/Landscape Architect Information (not required for Small Projects) Name Title Company or Affiliation Address Telephone Number Email Address Professional Engineer/ Landscape Architect Stamp and Signature Post-Construction Stormwater Management Plan Butte County C-3 June 2022 Stormwater Management and Discharge Control Manual Project Type Is the proposed project: □ A linear underground/overhead utility project (LUP) that creates and/or replaces at least 2,500, but less than 5,000 square feet of impervious surface? □ A detached single-family home that is not part of a common plan of development? □ A routine maintenance or repair project that maintains the original line and grade, hydraulic capacity, and original purpose of the facility? □ Exterior wall surface replacement □ Pavement resurfacing within an existing footprint □ Replacement of damaged pavement (e.g., pothole repair, short-non-contiguous sections of roadway) □ Re-roofing regardless of whether it is a full roof replacement or an overlay □ Interior remodels that do not modify the existing footprint? □ Excavation, trenching, and resurfacing associated with LUPs? □ Pavement grinding and resurfacing of existing roadways and parking lots? □ Construction of new sidewalks, pedestrian ramps, or bicycle lanes on existing roadways? □ Construction of sidewalks and bicycle lanes built as part of new streets or roads that are graded to runoff to adjacent vegetated areas? □ Construction of impervious trails that are graded to runoff to adjacent vegetated areas or other non-erodible areas? □ Construction of sidewalks, bicycle lanes, and trails with permeable surfaces? The above projects are exempt from the requirements of the Stormwater Management and Discharge Control Manual. See Chapter 2.5 of the Manual for details on project exceptions. Submit Section 1 of the Post-Construction Stormwater Management Plan as part of the application submittal. Post-Construction Stormwater Management Plan Butte County C-4 June 2022 Stormwater Management and Discharge Control Manual Project Type If the proposed project is not exempt as identified above, identify the type of project below. See Chapter 2 of the Stormwater Management and Discharge Control Manual for more information on project types. Note: you may need to check more than one box. □ Small Project – Projects that create and/or replace at least 2,500, but less than 5,000 square feet of impervious surface; or detached single-family homes that create and/or replace a minimum of 2,500 square feet of impervious surface and are not part of a larger plan of development. Complete Section 2 worksheet. □ Regulated Project – Projects that create and/or replace greater than or equal to 5,000 square feet of impervious surface and LUPs that create 5,000 square feet or more of newly constructed contiguous impervious surfaces. Complete Section 3 worksheet. □ New development □ Redevelopment that increases the impervious surface area by 50 percent or more of the existing development □ Redevelopment that increases the impervious surface area by less than 50 percent of the existing development □ Hydromodification Management Project – Projects that create and/or replace one acre or more of impervious surface and result in a net increase of impervious surface. Complete Section 3 and Section 4 worksheets. □ Project in a Priority Land Use Area – Projects in a high-density residential, industrial, commercial, or mixed used area, or at public transportation facilities. Complete Section 4 worksheet. Description of the Project Provide a brief description of the proposed project. Owner Certification and Signature The undersigned owner of the subject property is responsible for the implementation of the provisions of this Post-Construction Stormwater Management Plan consistent with the requirements of the Stormwater Management and Discharge Control Manual, the Stormwater Ordinance of Butte County, and Provision E.12 of the California State Water Resources Control Board Phase II Permit (Order No. 2013-0001-DWQ). If the undersigned transfers its interest in the property, its successors-in-interest shall bear the aforementioned responsibility to implement the Post-Construction Stormwater Management Plan. A copy of the final signed and fully approved Post-Construction Stormwater Management Plan shall be available on the subject site throughout the course of the development. Owner Signature Date Post-Construction Stormwater Management Plan Butte County C-5 June 2022 Stormwater Management and Discharge Control Manual Section 2: Small Projects This worksheet is applicable to Small Projects only. Small Projects are required to implement at least one site design measure and calculate the change in the pre-project and post-project stormwater runoff using the State Water Resources Control Board’s Post-Construction Calculator, which is available at: http://www.swrcb.ca.gov/water_issues/programs/stormwater/phase_ii_municipal.shtml. More information is available in Chapter 5 of the Stormwater Management and Discharge Control Manual. For the proposed project, identify the following information: Pre-Project Stormwater Runoff Volume (ft3) Post-Project Stormwater Runoff Volume without credits(ft3) Proposed Site Design Measure Stormwater Runoff Volume Credit (ft3) □ Stream setbacks and buffers □ Soil quality improvement and maintenance □ Tree planting and preservation □ Rooftop and impervious area disconnection □ Porous pavement □ Green Roof □ Vegetated swales □ Rain barrels/cisterns Total Stormwater Runoff Volume Credit (ft3) The project applicant must include a printout of the Post-Construction Calculator results as part of the Post-Construction Stormwater Management Plan. If the Small Project is located in a Priority Land Use Area, the project applicant must also complete the Section 4 worksheet. Post-Construction Stormwater Management Plan Butte County C-6 June 2022 Stormwater Management and Discharge Control Manual Section 3: Regulated and Hydromodification Management Projects The following worksheets are applicable to Regulated Projects. Site Assessment Worksheet Regulated and Hydromodification Management Projects are required to assess conditions at the project site. This information is used to plan the project site layout and identify potential sources of pollutants of concern. Complete the Site Assessment Worksheet as part of the Post-Construction Stormwater Management Plan submittal. More information is available in Chapter 4 of the Stormwater Management and Discharge Control Manual. Site Planning Worksheet Regulated and Hydromodification Management Projects are required to consider, and implement if feasible, site planning principles to maximize the effectiveness of stormwater management for the project site. Complete the Site Planning Worksheet as part of the Post-Construction Stormwater Management Plan submittal. More information is available in Chapter 4 and Chapter 5 of the Stormwater Management and Discharge Control Manual. Source Control Measures Regulated and Hydromodification Management Projects are required to implement source control measures to prevent pollutants from contacting stormwater runoff or prevent discharge of contaminated stormwater runoff from the project site. All proposed projects that include landscape irrigation must implement the source control measure for landscape irrigation described in Chapter 6 of the Stormwater Management and Discharge Control Manual. Complete a Source Control Measures Worksheet as part of the Post-Construction Stormwater Management Plan submittal. Drainage Management Area Worksheet Regulated and Hydromodification Projects are required to delineate discrete drainage management areas for a project site and manage stormwater runoff according to those drainage management areas (DMA). Complete a Drainage Management Area Worksheet for each DMA at the project site. More information is available in Chapter 6.1.1 of the Stormwater Management and Discharge Control Manual. Site Design Measures Regulated and Hydromodification Management Projects are required to implement site design measures to the extent technically feasible and calculate the stormwater runoff volume credit using the State Water Resources Control Board’s Post-Construction Calculator for each DMA. The Post-Construction Calculator is available at: http://www.swrcb.ca.gov/water_issues/programs/stormwater/phase_ii_municipal.shtml. More information is available in Chapter 5 and Chapter 7 of the Stormwater Management and Discharge Control Manual. Complete a Site Design Measure Worksheet for each DMA as part of the Post-Construction Stormwater Management Plan submittal. Post-Construction Stormwater Management Plan Butte County C-7 June 2022 Stormwater Management and Discharge Control Manual Stormwater Treatment and Baseline Hydromodification Control Measures Regulated Projects are required to implement stormwater treatment control measures to manage the portion of the stormwater runoff not mitigated by site design measures. More information is available in Chapter 8 of the Stormwater Management and Discharge Control Manual. Complete a Stormwater Treatment Control Measure Worksheet for each DMA where proposed site design measures do not manage the fully manage stormwater runoff of the DMA and submit as part of the Post-Construction Stormwater Management Plan. Other Requirements of the Post-Construction Stormwater Management Plan In addition to completing the applicable worksheets, Regulated and Hydromodification Management Projects must also include the following information: • Site Conditions Report, prepared by or under the supervision of a competent, licensed professional, that addresses and discusses relevant findings of the geotechnical evaluation. Geotechnical evaluations must be conducted in accordance with local standards, including, but not limited to, approved investigation, evaluation, and testing methodologies. • Site Layout Plan that, at a minimum, illustrates: o Existing natural hydrologic features (e.g., depressions, watercourses, wetlands, riparian corridors, undisturbed areas) and significant natural resources); o Proposed locations and footprints of improvements creating new, or replaced impervious surfaces; o Existing and proposed site drainage system and connections to off-site drainage; o Proposed locations and footprints stormwater control measures (e.g., site design measures, source control measures, stormwater treatment control measures) implemented to manage stormwater runoff; o All DMAs with unique identifiers; and o Maintenance areas of the project site. • Operations and Maintenance Plan (See Template in Appendix G) Post-Construction Stormwater Management Plan Butte County C-8 June 2022 Stormwater Management and Discharge Control Manual Site Assessment Worksheet General Project Site Information Latitude Longitude Elevation Total Project Area (AT) (ft2) Total Existing Impervious Area (ft2) Total Post-Project Impervious Area (ft2) Receiving Water(s) Describe location(s) of discharge from the project site. Describe Environmentally Sensitive Areas, if applicable. Pollutants of Concern Post-Project Land Use Type(s) Describe expected pollutant-generating activities. Pre-project Post-project Identify pollutants of concern. Post-Construction Stormwater Management Plan Butte County C-9 June 2022 Stormwater Management and Discharge Control Manual Site Planning Worksheet Describe how the following site planning principles were considered and implemented in developing and optimizing the site layout for the project. Define the development envelope and protected areas, identifying areas that are most suitable for development and areas to be left undisturbed. Concentrate development on portions of the site with less permeable soils and preserve areas that can promote infiltration. Limit overall impervious coverage of the site with paving and roofs. Set back development from creeks, wetlands, and riparian habitats. Preserve significant trees. Conform the site layout along natural landforms. Avoid excessive grading and disturbance of vegetation and soils. Replicate the site’s natural drainage patterns. Detain and retain stormwater runoff throughout the site. Post-Construction Stormwater Management Plan Butte County C-10 June 2022 Stormwater Management and Discharge Control Manual Source Control Measures Worksheet Describe source control measures to be implemented for each potential pollutant generating activity or source present at the project site. If a potential pollutant generating activity or source is not present at the project site, indicate it as “N/A”. Parking/storage areas and maintenance Landscape/outdoor pesticide use Building and grounds maintenance Refuse areas Outdoor storage of equipment or materials Vehicle and equipment cleaning Vehicle and equipment repair and maintenance Fuel dispensing areas Pools, spas, ponds, decorative fountains, and other water features Post-Construction Stormwater Management Plan Butte County C-11 June 2022 Stormwater Management and Discharge Control Manual Source Control Measures Worksheet (cont’d) Indoor and structural pest control Accidental spills or leaks Restaurants, grocery stores, and other food service operations Interior floor drains Industrial processes Loading docks Fire sprinkler test water Drain or wash water from boiler drain lines, condensate drain lines, rooftop equipment, drainage sumps, and other sources Unauthorized non-stormwater discharges Post-Construction Stormwater Management Plan Butte County C-12 June 2022 Stormwater Management and Discharge Control Manual Drainage Management Area Worksheet Drainage Management Area (DMA) # Type of DMA: □ Self-treating area □ Areas draining to self-retaining areas □ Self-retaining area □ Areas draining to bioretention facility Describe the DMA Total Drainage Area (ft2) Existing Impervious Area (ft2) Soil Type Post-Project Impervious Area (ft2) Infiltration Rate (in/hr) Mean Annual Runoff-Producing Rainfall Depth (P6) (in) Drawdown time (tmax) (hr) (24 or 48) Regression constant (a) (1.582 for 24-hr drawdown, 1.963 for 48-hr drawdown) Pre-Project Condition: Imperviousness ratio (i) = Existing Impervious Area ÷ Total Drainage Area (decimal) Stormwater runoff coefficient (C) = 0.858 x i3 – 0.78 x i2 +0.774 x i + 0.04 Unit stormwater volume (P0) (in) = a x C x P6 Stormwater Runoff Volume for the DMA (ft3) Post-Project Condition: Imperviousness ratio (i) = Post-Project Impervious Area ÷ Total Drainage Area (decimal) Stormwater runoff coefficient (C) = 0.858 x i3 – 0.78 x i2 +0.774 x i + 0.04 Unit stormwater volume (P0) (in) = a x C x P6 Stormwater Design Volume for the DMA (SDV) (ft3) = A x P0 ÷ 12 Post-Construction Stormwater Management Plan Butte County C-12 June 2022 Stormwater Management and Discharge Control Manual Drainage Management Area Worksheet Drainage Management Area (DMA) # Type of DMA: □ Self-treating area □ Areas draining to self-retaining areas □ Self-retaining area □ Areas draining to bioretention facility Describe the DMA Total Drainage Area (ft2) Existing Impervious Area (ft2) Soil Type Post-Project Impervious Area (ft2) Infiltration Rate (in/hr) Mean Annual Runoff-Producing Rainfall Depth (P6) (in) Drawdown time (tmax) (hr) (24 or 48) Regression constant (a) (1.582 for 24-hr drawdown, 1.963 for 48-hr drawdown) Pre-Project Condition: Imperviousness ratio (i) = Existing Impervious Area ÷ Total Drainage Area (decimal) Stormwater runoff coefficient (C) = 0.858 x i3 – 0.78 x i2 +0.774 x i + 0.04 Unit stormwater volume (P0) (in) = a x C x P6 Stormwater Runoff Volume for the DMA (ft3) Post-Project Condition: Imperviousness ratio (i) = Post-Project Impervious Area ÷ Total Drainage Area (decimal) Stormwater runoff coefficient (C) = 0.858 x i3 – 0.78 x i2 +0.774 x i + 0.04 Unit stormwater volume (P0) (in) = a x C x P6 Stormwater Design Volume for the DMA (SDV) (ft3) = A x P0 ÷ 12 Post-Construction Stormwater Management Plan Butte County C-12 June 2022 Stormwater Management and Discharge Control Manual Drainage Management Area Worksheet Drainage Management Area (DMA) # Type of DMA: □ Self-treating area □ Areas draining to self-retaining areas □ Self-retaining area □ Areas draining to bioretention facility Describe the DMA Total Drainage Area (ft2) Existing Impervious Area (ft2) Soil Type Post-Project Impervious Area (ft2) Infiltration Rate (in/hr) Mean Annual Runoff-Producing Rainfall Depth (P6) (in) Drawdown time (tmax) (hr) (24 or 48) Regression constant (a) (1.582 for 24-hr drawdown, 1.963 for 48-hr drawdown) Pre-Project Condition: Imperviousness ratio (i) = Existing Impervious Area ÷ Total Drainage Area (decimal) Stormwater runoff coefficient (C) = 0.858 x i3 – 0.78 x i2 +0.774 x i + 0.04 Unit stormwater volume (P0) (in) = a x C x P6 Stormwater Runoff Volume for the DMA (ft3) Post-Project Condition: Imperviousness ratio (i) = Post-Project Impervious Area ÷ Total Drainage Area (decimal) Stormwater runoff coefficient (C) = 0.858 x i3 – 0.78 x i2 +0.774 x i + 0.04 Unit stormwater volume (P0) (in) = a x C x P6 Stormwater Design Volume for the DMA (SDV) (ft3) = A x P0 ÷ 12 Post-Construction Stormwater Management Plan Butte County C-13 June 2022 Stormwater Management and Discharge Control Manual Site Design Measure Worksheet Drainage Management Area (DMA) # For this DMA, identify the following information: Stormwater Design Volume without credits (ft3) = SDV Stormwater Design Volume with credits (ft3) = SDVadj = SDV - SDMcredit (This volume must be treated by stormwater treatment control measures.) Do proposed site design measures completely manage the SDV for this DMA? □ Yes, stormwater management requirement met for this DMA. □ No, proceed to Stormwater Treatment and Baseline Hydromodification Measure Worksheet. Proposed Site Design Measure Stormwater Runoff Volume Credit (ft3) □ Stream setbacks and buffers □ Soil quality improvement and maintenance □ Tree planting and preservation □ Rooftop and impervious area disconnection □ Porous pavement □ Vegetated swales □ Rain barrels/cisterns Total Stormwater Runoff Volume Credit (SDMcredit) For site design measures not implemented for this DMA, describe why they are not selected. Post-Construction Stormwater Management Plan Butte County C-13 June 2022 Stormwater Management and Discharge Control Manual Site Design Measure Worksheet Drainage Management Area (DMA) # For this DMA, identify the following information: Stormwater Design Volume without credits (ft3) = SDV Stormwater Design Volume with credits (ft3) = SDVadj = SDV - SDMcredit (This volume must be treated by stormwater treatment control measures.) Do proposed site design measures completely manage the SDV for this DMA? □ Yes, stormwater management requirement met for this DMA. □ No, proceed to Stormwater Treatment and Baseline Hydromodification Measure Worksheet. Proposed Site Design Measure Stormwater Runoff Volume Credit (ft3) □ Stream setbacks and buffers □ Soil quality improvement and maintenance □ Tree planting and preservation □ Rooftop and impervious area disconnection □ Porous pavement □ Vegetated swales □ Rain barrels/cisterns Total Stormwater Runoff Volume Credit (SDMcredit) For site design measures not implemented for this DMA, describe why they are not selected. Post-Construction Stormwater Management Plan Butte County C-13 June 2022 Stormwater Management and Discharge Control Manual Site Design Measure Worksheet Drainage Management Area (DMA) # For this DMA, identify the following information: Stormwater Design Volume without credits (ft3) = SDV Stormwater Design Volume with credits (ft3) = SDVadj = SDV - SDMcredit (This volume must be treated by stormwater treatment control measures.) Do proposed site design measures completely manage the SDV for this DMA? □ Yes, stormwater management requirement met for this DMA. □ No, proceed to Stormwater Treatment and Baseline Hydromodification Measure Worksheet. Proposed Site Design Measure Stormwater Runoff Volume Credit (ft3) □ Stream setbacks and buffers □ Soil quality improvement and maintenance □ Tree planting and preservation □ Rooftop and impervious area disconnection □ Porous pavement □ Vegetated swales □ Rain barrels/cisterns Total Stormwater Runoff Volume Credit (SDMcredit) For site design measures not implemented for this DMA, describe why they are not selected. Post-Construction Stormwater Management Plan Butte County C-14 June 2022 Stormwater Management and Discharge Control Manual Stormwater Treatment and Baseline Hydromodification Control Measure Design Worksheet For each drainage management area (DMA), in which proposed site design measures did not fully manage the difference in pre- and post-project stormwater runoff volume, complete this worksheet. Drainage Management Area (DMA) # Design bioretention facility to manage the adjusted stormwater design volume (SDVadj). Calculate the bottom surface area of a bioretention facility: Stormwater Design Volume for the DMA (SDV) (ft3) See Drainage Management Area Worksheet. Total Stormwater Runoff Credit Volume (SDMcredit) (ft3) See Site Design Measure Worksheet. Adjusted Stormwater Design Volume (SDVadj) (ft3) = SDV - SDMcredit Design infiltration rate of underlying soils (fdesign) (in/hr) Ponding zone depth (dpz) (ft) (0.5-1.5 ft) Planting media layer depth (dpm) (ft) (min 1.5 ft) Planting media porosity (ηpm) Gravel layer depth (dgl) (ft) (min 1 ft) Gravel layer porosity (ηgl) Bottom surface area of a bioretention facility (ft2) = 𝑆𝑆𝑆𝑆𝑆𝑆𝑎𝑎𝑎𝑎𝑎𝑎𝑑𝑑𝑝𝑝𝑝𝑝+�𝜂𝜂𝑝𝑝𝑝𝑝×𝑑𝑑𝑝𝑝𝑝𝑝�+�𝜂𝜂𝑔𝑔𝑔𝑔×𝑑𝑑𝑔𝑔𝑔𝑔� Verify that: 𝑑𝑑𝑝𝑝𝑝𝑝+�𝜂𝜂𝑝𝑝𝑝𝑝× 𝑑𝑑𝑝𝑝𝑝𝑝�+�𝜂𝜂𝑔𝑔𝑔𝑔× 𝑑𝑑𝑔𝑔𝑔𝑔�≤ 𝑓𝑓𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑔𝑔𝑑𝑑× 𝑡𝑡𝑝𝑝𝑚𝑚𝑚𝑚÷ 12. If not, redesign factors above. Verify that the DMA has adequate space to implement bioretention facility sized above. If not, redesign factors above or provide additional stormwater treatment control measures to manage remaining portion of the SDV. Describe and provide justification for any variations to the bioretention design for site-specific conditions. See Appendix E Fact Sheet LID-1 of the Stormwater Management and Discharge Control Manual for more information. Post-Construction Stormwater Management Plan Butte County C-15 June 2022 Stormwater Management and Discharge Control Manual Describe and provide justification if an alternative stormwater treatment control measure is proposed in lieu of a bioretention facility, such an infiltration trench, infiltration basin, dry well, or detention basin. Such a stormwater treatment control measure must meet the bioretention equivalency criteria in Provision E.12.e.(g) of the Phase II Stormwater Permit. Describe and provide justification for any exceptions to the requirements for bioretention or bioretention-equivalent measures. Exception to bioretention must meet all the requirements of Chapter 8.2 of the Stormwater Management and Discharge Control Manual. Identify and describe the proposed biotreatment or media filter system that will be used in lieu of bioretention. Summary of Stormwater Treatment and Baseline Hydromodification Control Measure Design Stormwater Design Volume for DMA (SDV) (ft3) 1. Total Stormwater Runoff Credit Volume (SDMcredit) (ft3) 2. Volume of Stormwater Runoff Managed by Bioretention Facility (ft3) 3. Volume of Stormwater Runoff Managed by Other Stormwater Treatment Control Measure (identify each control measure) a. b. Total Stormwater Runoff Volume Managed for DMA (ft3) = sum of items 1-3 above. If Total Stormwater Runoff Volume Managed for this DMA equals or exceeds the Stormwater Design Volume for this DMA, then design for stormwater management for this DMA is complete. If the Total Stormwater Runoff Volume Managed for this DMA is less than the Stormwater Design Volume for this DMA, redesign site design measures and stormwater treatment control measures until the entire Stormwater Design Volume for this DMA has been managed. Complete this exercise for each DMA. Post-Construction Stormwater Management Plan Butte County C-14 June 2022 Stormwater Management and Discharge Control Manual Stormwater Treatment and Baseline Hydromodification Control Measure Design Worksheet For each drainage management area (DMA), in which proposed site design measures did not fully manage the difference in pre- and post-project stormwater runoff volume, complete this worksheet. Drainage Management Area (DMA) # Design bioretention facility to manage the adjusted stormwater design volume (SDVadj). Calculate the bottom surface area of a bioretention facility: Stormwater Design Volume for the DMA (SDV) (ft3) See Drainage Management Area Worksheet. Total Stormwater Runoff Credit Volume (SDMcredit) (ft3) See Site Design Measure Worksheet. Adjusted Stormwater Design Volume (SDVadj) (ft3) = SDV - SDMcredit Design infiltration rate of underlying soils (fdesign) (in/hr) Ponding zone depth (dpz) (ft) (0.5-1.5 ft) Planting media layer depth (dpm) (ft) (min 1.5 ft) Planting media porosity (ηpm) Gravel layer depth (dgl) (ft) (min 1 ft) Gravel layer porosity (ηgl) Bottom surface area of a bioretention facility (ft2) = 𝑆𝑆𝑆𝑆𝑆𝑆𝑎𝑎𝑎𝑎𝑎𝑎𝑑𝑑𝑝𝑝𝑝𝑝+�𝜂𝜂𝑝𝑝𝑝𝑝×𝑑𝑑𝑝𝑝𝑝𝑝�+�𝜂𝜂𝑔𝑔𝑔𝑔×𝑑𝑑𝑔𝑔𝑔𝑔� Verify that: 𝑑𝑑𝑝𝑝𝑝𝑝+�𝜂𝜂𝑝𝑝𝑝𝑝× 𝑑𝑑𝑝𝑝𝑝𝑝�+�𝜂𝜂𝑔𝑔𝑔𝑔× 𝑑𝑑𝑔𝑔𝑔𝑔�≤ 𝑓𝑓𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑔𝑔𝑑𝑑× 𝑡𝑡𝑝𝑝𝑚𝑚𝑚𝑚÷ 12. If not, redesign factors above. Verify that the DMA has adequate space to implement bioretention facility sized above. If not, redesign factors above or provide additional stormwater treatment control measures to manage remaining portion of the SDV. Describe and provide justification for any variations to the bioretention design for site-specific conditions. See Appendix E Fact Sheet LID-1 of the Stormwater Management and Discharge Control Manual for more information. Post-Construction Stormwater Management Plan Butte County C-15 June 2022 Stormwater Management and Discharge Control Manual Describe and provide justification if an alternative stormwater treatment control measure is proposed in lieu of a bioretention facility, such an infiltration trench, infiltration basin, dry well, or detention basin. Such a stormwater treatment control measure must meet the bioretention equivalency criteria in Provision E.12.e.(g) of the Phase II Stormwater Permit. Describe and provide justification for any exceptions to the requirements for bioretention or bioretention-equivalent measures. Exception to bioretention must meet all the requirements of Chapter 8.2 of the Stormwater Management and Discharge Control Manual. Identify and describe the proposed biotreatment or media filter system that will be used in lieu of bioretention. Summary of Stormwater Treatment and Baseline Hydromodification Control Measure Design Stormwater Design Volume for DMA (SDV) (ft3) 1. Total Stormwater Runoff Credit Volume (SDMcredit) (ft3) 2. Volume of Stormwater Runoff Managed by Bioretention Facility (ft3) 3. Volume of Stormwater Runoff Managed by Other Stormwater Treatment Control Measure (identify each control measure) a. b. Total Stormwater Runoff Volume Managed for DMA (ft3) = sum of items 1-3 above. If Total Stormwater Runoff Volume Managed for this DMA equals or exceeds the Stormwater Design Volume for this DMA, then design for stormwater management for this DMA is complete. If the Total Stormwater Runoff Volume Managed for this DMA is less than the Stormwater Design Volume for this DMA, redesign site design measures and stormwater treatment control measures until the entire Stormwater Design Volume for this DMA has been managed. Complete this exercise for each DMA. Post-Construction Stormwater Management Plan Butte County C-14 June 2022 Stormwater Management and Discharge Control Manual Stormwater Treatment and Baseline Hydromodification Control Measure Design Worksheet For each drainage management area (DMA), in which proposed site design measures did not fully manage the difference in pre- and post-project stormwater runoff volume, complete this worksheet. Drainage Management Area (DMA) # Design bioretention facility to manage the adjusted stormwater design volume (SDVadj). Calculate the bottom surface area of a bioretention facility: Stormwater Design Volume for the DMA (SDV) (ft3) See Drainage Management Area Worksheet. Total Stormwater Runoff Credit Volume (SDMcredit) (ft3) See Site Design Measure Worksheet. Adjusted Stormwater Design Volume (SDVadj) (ft3) = SDV - SDMcredit Design infiltration rate of underlying soils (fdesign) (in/hr) Ponding zone depth (dpz) (ft) (0.5-1.5 ft) Planting media layer depth (dpm) (ft) (min 1.5 ft) Planting media porosity (ηpm) Gravel layer depth (dgl) (ft) (min 1 ft) Gravel layer porosity (ηgl) Bottom surface area of a bioretention facility (ft2) = 𝑆𝑆𝑆𝑆𝑆𝑆𝑎𝑎𝑎𝑎𝑎𝑎𝑑𝑑𝑝𝑝𝑝𝑝+�𝜂𝜂𝑝𝑝𝑝𝑝×𝑑𝑑𝑝𝑝𝑝𝑝�+�𝜂𝜂𝑔𝑔𝑔𝑔×𝑑𝑑𝑔𝑔𝑔𝑔� Verify that: 𝑑𝑑𝑝𝑝𝑝𝑝+�𝜂𝜂𝑝𝑝𝑝𝑝× 𝑑𝑑𝑝𝑝𝑝𝑝�+�𝜂𝜂𝑔𝑔𝑔𝑔× 𝑑𝑑𝑔𝑔𝑔𝑔�≤ 𝑓𝑓𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑔𝑔𝑑𝑑× 𝑡𝑡𝑝𝑝𝑚𝑚𝑚𝑚÷ 12. If not, redesign factors above. Verify that the DMA has adequate space to implement bioretention facility sized above. If not, redesign factors above or provide additional stormwater treatment control measures to manage remaining portion of the SDV. Describe and provide justification for any variations to the bioretention design for site-specific conditions. See Appendix E Fact Sheet LID-1 of the Stormwater Management and Discharge Control Manual for more information. Post-Construction Stormwater Management Plan Butte County C-15 June 2022 Stormwater Management and Discharge Control Manual Describe and provide justification if an alternative stormwater treatment control measure is proposed in lieu of a bioretention facility, such an infiltration trench, infiltration basin, dry well, or detention basin. Such a stormwater treatment control measure must meet the bioretention equivalency criteria in Provision E.12.e.(g) of the Phase II Stormwater Permit. Describe and provide justification for any exceptions to the requirements for bioretention or bioretention-equivalent measures. Exception to bioretention must meet all the requirements of Chapter 8.2 of the Stormwater Management and Discharge Control Manual. Identify and describe the proposed biotreatment or media filter system that will be used in lieu of bioretention. Summary of Stormwater Treatment and Baseline Hydromodification Control Measure Design Stormwater Design Volume for DMA (SDV) (ft3) 1. Total Stormwater Runoff Credit Volume (SDMcredit) (ft3) 2. Volume of Stormwater Runoff Managed by Bioretention Facility (ft3) 3. Volume of Stormwater Runoff Managed by Other Stormwater Treatment Control Measure (identify each control measure) a. b. Total Stormwater Runoff Volume Managed for DMA (ft3) = sum of items 1-3 above. If Total Stormwater Runoff Volume Managed for this DMA equals or exceeds the Stormwater Design Volume for this DMA, then design for stormwater management for this DMA is complete. If the Total Stormwater Runoff Volume Managed for this DMA is less than the Stormwater Design Volume for this DMA, redesign site design measures and stormwater treatment control measures until the entire Stormwater Design Volume for this DMA has been managed. Complete this exercise for each DMA. Post-Construction Stormwater Management Plan Butte County C-16 June 2022 Stormwater Management and Discharge Control Manual Section 4: Hydromodification Management Projects (only) For projects that create and/or replace one acre or more of impervious surface and result in a net increase of impervious surface, full hydromodification is required. For these projects, the post-construction stormwater runoff flow rate shall not exceed the pre-construction stormwater runoff flow rate for the 2-year, 24-hour design storm event. Hydrologic routing modeling for the drainage management areas (DMAs) must be conducted to calculate the peak stormwater runoff response time and the peak project stormwater runoff flow rate for the entire project site. Precipitation for 2-year, 24-hour storm event (in) From hydrologic routing modeling: Pre-Project Total Stormwater Runoff Response Time (Tc,pre) (min) Pre-Project Peak Stormwater Runoff Flow Rate (Qp,pre) (ft3/s) Post-Project Total Stormwater Runoff Response Time (Tc,post) (min) Post-Project Peak Stormwater Runoff Flow Rate (Qp,post) (ft3/s) Describe and provide justification for proposed hydromodification management control measures to be implemented to meet the full hydromodification requirements. Does the project meet the full hydromodification requirements? □ Yes □ No. Re-evaluate proposed hydromodification management control measure and provide additional capacity or implement additional hydromodification management control measure(s) to meet the full hydromodification requirements. D–3(210-VI-TR-55, Second Ed., June 1986) Worksheet 3: Time of Concentration (Tc) or travel time (Tt) Project By Date Location Checked Date Check one: Present Developed Sheet flow (Applicable to Tc only) 1. Surface description (table 3-1) ................................... 2. Manning’s roughness coefficient, n (table 3-1) .......... 3. Flow length, L (total L † 300 ft) ................................. ft 4. Two-year 24-hour rainfall, P2 .................................. in 5. Land slope, s ........................................................ ft/ft 6. Check one: Tc Tt through subarea Segment ID 7. Surface description (paved or unpaved) ..................... 8. Flow length, L ...........................................................ft 9. Watercourse slope, s ............................................ ft/ft 10. Average velocity, V (figure 3-1) ............................. ft/s 11. Compute Tt ........... hr Segment ID 12. Cross sectional flow area, a ................................. ft 2 13. Wetted perimeter, pw .............................................. ft 14. Hydraulic radius, r= Compute r ......................... ft 15 Channel slope, s ..................................................... ft/ft 16. Manning’s roughness coefficient, n ............................ 17. Compute V ................ft/s 18. Flow length, L .......................................................... ft 19. Compute Tt .............. hr 20. Watershed or subarea Tc or Tt (add Tt in steps 6, 11, and 19) ....................................................... Hr Shallow concentrated flow Channel flow 0.007 (nL) 0.8Tt = _____________ P2 0.5 s0.4 LTt = _______ 3600 V Compute Tt ......... hr += 1.49 r 2/3 s 1/2 n V = __________ ____ L 3600 V Tt = _________ Segment ID += Notes: Space for as many as two segments per flow type can be used for each worksheet. Include a map, schematic, or description of flow segments. += a pw Type I 24-hr 2 YR Rainfall=2.75"23005_Hydrology Printed 10/26/2023Prepared by {enter your company name here} Page 1HydroCAD® 10.00-26 s/n 03026 © 2020 HydroCAD Software Solutions LLC Summary for Subcatchment 6S: Existing Site Runoff = 12.65 cfs @ 10.00 hrs, Volume= 2.007 af, Depth> 1.04" Runoff by SBUH method, Split Pervious/Imperv., Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Type I 24-hr 2 YR Rainfall=2.75" Area (sf) CN Description 4,590 98 Unconnected roofs, HSG C 1,005,035 82 Woods/grass comb., Poor, HSG C 1,009,625 82 Weighted Average 1,005,035 82 99.55% Pervious Area 4,590 98 0.45% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 15.0 Direct Entry, Subcatchment 6S: Existing Site Runoff Hydrograph Time (hours) 201918171615141312111098765Flow (cfs)14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Type I 24-hr 2 YR Rainfall=2.75" Runoff Area=1,009,625 sf Runoff Volume=2.007 af Runoff Depth>1.04" Tc=15.0 min CN=82/98 12.65 cfs Type I 24-hr 2 YR Rainfall=2.75"23005_Hydrology Printed 10/26/2023Prepared by {enter your company name here} Page 3HydroCAD® 10.00-26 s/n 03026 © 2020 HydroCAD Software Solutions LLC Summary for Subcatchment 7S: DMA A Runoff = 2.58 cfs @ 10.00 hrs, Volume= 0.405 af, Depth> 1.14" Runoff by SBUH method, Split Pervious/Imperv., Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Type I 24-hr 2 YR Rainfall=2.75" Area (sf) CN Description 16,715 98 Unconnected pavement, HSG C 169,015 82 Woods/grass comb., Poor, HSG C 185,730 83 Weighted Average 169,015 82 91.00% Pervious Area 16,715 98 9.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 15.0 Direct Entry, Subcatchment 7S: DMA A Runoff Hydrograph Time (hours) 201918171615141312111098765Flow (cfs)2 1 0 Type I 24-hr 2 YR Rainfall=2.75" Runoff Area=185,730 sf Runoff Volume=0.405 af Runoff Depth>1.14" Tc=15.0 min CN=82/98 2.58 cfs Type I 24-hr 2 YR Rainfall=2.75"23005_Hydrology Printed 10/26/2023Prepared by {enter your company name here} Page 7HydroCAD® 10.00-26 s/n 03026 © 2020 HydroCAD Software Solutions LLC Summary for Subcatchment 14S: DMA B Runoff = 0.77 cfs @ 10.00 hrs, Volume= 0.118 af, Depth> 1.39" Runoff by SBUH method, Split Pervious/Imperv., Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Type I 24-hr 2 YR Rainfall=2.75" Area (sf) CN Description 13,375 98 Unconnected pavement, HSG C 31,310 82 Woods/grass comb., Poor, HSG C 44,685 87 Weighted Average 31,310 82 70.07% Pervious Area 13,375 98 29.93% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 15.0 Direct Entry, Subcatchment 14S: DMA B Runoff Hydrograph Time (hours) 201918171615141312111098765Flow (cfs)0.85 0.8 0.75 0.7 0.65 0.6 0.55 0.5 0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 Type I 24-hr 2 YR Rainfall=2.75" Runoff Area=44,685 sf Runoff Volume=0.118 af Runoff Depth>1.39" Tc=15.0 min CN=82/98 0.77 cfs Type I 24-hr 2 YR Rainfall=2.75"23005_Hydrology Printed 10/26/2023Prepared by {enter your company name here} Page 5HydroCAD® 10.00-26 s/n 03026 © 2020 HydroCAD Software Solutions LLC Summary for Subcatchment 12S: DMA C Runoff = 11.70 cfs @ 10.00 hrs, Volume= 1.824 af, Depth> 1.22" Runoff by SBUH method, Split Pervious/Imperv., Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Type I 24-hr 2 YR Rainfall=2.75" Area (sf) CN Description 126,030 98 Unconnected pavement, HSG C 653,180 82 Woods/grass comb., Poor, HSG C 779,210 85 Weighted Average 653,180 82 83.83% Pervious Area 126,030 98 16.17% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 15.0 Direct Entry, Subcatchment 12S: DMA C Runoff Hydrograph Time (hours) 201918171615141312111098765Flow (cfs)13 12 11 10 9 8 7 6 5 4 3 2 1 0 Type I 24-hr 2 YR Rainfall=2.75" Runoff Area=779,210 sf Runoff Volume=1.824 af Runoff Depth>1.22" Tc=15.0 min CN=82/98 11.70 cfs Type I 24-hr 2 YR Rainfall=2.75"23005_Hydrology Printed 10/26/2023Prepared by {enter your company name here} Page 9HydroCAD® 10.00-26 s/n 03026 © 2020 HydroCAD Software Solutions LLC Summary for Pond 15P: BioRet 1 Inflow Area = 5.290 ac, 13.06% Impervious, Inflow Depth > 1.19" for 2 YR event Inflow = 3.35 cfs @ 10.00 hrs, Volume= 0.523 af Outflow = 1.98 cfs @ 10.31 hrs, Volume= 0.510 af, Atten= 41%, Lag= 18.3 min Primary = 1.98 cfs @ 10.31 hrs, Volume= 0.510 af Routing by Stor-Ind method, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Peak Elev= 362.89' @ 10.31 hrs Surf.Area= 1,600 sf Storage= 2,612 cf Plug-Flow detention time= 26.1 min calculated for 0.510 af (98% of inflow) Center-of-Mass det. time= 15.2 min ( 764.8 - 749.6 ) Volume Invert Avail.Storage Storage Description #1 359.40' 3,584 cf Custom Stage Data (Prismatic) Listed below (Recalc) Elevation Surf.Area Voids Inc.Store Cum.Store (feet) (sq-ft) (%) (cubic-feet) (cubic-feet) 359.40 1,600 0.0 0 0 359.50 1,600 40.0 64 64 361.50 1,600 10.0 320 384 363.00 1,600 100.0 2,400 2,784 363.50 1,600 100.0 800 3,584 Device Routing Invert Outlet Devices #1 Primary 361.50'8.0" Horiz. Orifice/Grate C= 0.600 Limited to weir flow at low heads Primary OutFlow Max=1.98 cfs @ 10.31 hrs HW=362.89' (Free Discharge) 1=Orifice/Grate (Orifice Controls 1.98 cfs @ 5.68 fps) Type I 24-hr 2 YR Rainfall=2.75"23005_Hydrology Printed 10/26/2023Prepared by {enter your company name here} Page 10HydroCAD® 10.00-26 s/n 03026 © 2020 HydroCAD Software Solutions LLC Pond 15P: BioRet 1 Inflow Primary Hydrograph Time (hours) 201918171615141312111098765Flow (cfs)3 2 1 0 Inflow Area=5.290 ac Peak Elev=362.89' Storage=2,612 cf 3.35 cfs 1.98 cfs Type I 24-hr 2 YR Rainfall=2.75"23005_Hydrology Printed 10/26/2023Prepared by {enter your company name here} Page 12HydroCAD® 10.00-26 s/n 03026 © 2020 HydroCAD Software Solutions LLC Summary for Pond 16P: BioRet 1 Inflow Area = 17.888 ac, 16.17% Impervious, Inflow Depth > 1.22" for 2 YR event Inflow = 11.70 cfs @ 10.00 hrs, Volume= 1.824 af Outflow = 6.27 cfs @ 10.37 hrs, Volume= 1.775 af, Atten= 46%, Lag= 21.9 min Primary = 6.27 cfs @ 10.37 hrs, Volume= 1.775 af Routing by Stor-Ind method, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Peak Elev= 363.04' @ 10.37 hrs Surf.Area= 6,020 sf Storage= 10,739 cf Plug-Flow detention time= 30.8 min calculated for 1.774 af (97% of inflow) Center-of-Mass det. time= 18.6 min ( 764.2 - 745.7 ) Volume Invert Avail.Storage Storage Description #1 359.40' 13,485 cf Custom Stage Data (Prismatic) Listed below (Recalc) Elevation Surf.Area Voids Inc.Store Cum.Store (feet) (sq-ft) (%) (cubic-feet) (cubic-feet) 359.40 6,020 0.0 0 0 359.50 6,020 40.0 241 241 361.50 6,020 10.0 1,204 1,445 363.00 6,020 100.0 9,030 10,475 363.50 6,020 100.0 3,010 13,485 Device Routing Invert Outlet Devices #1 Primary 361.50'8.0" Horiz. Orifice/Grate X 3.00 C= 0.600 Limited to weir flow at low heads Primary OutFlow Max=6.26 cfs @ 10.37 hrs HW=363.04' (Free Discharge) 1=Orifice/Grate (Orifice Controls 6.26 cfs @ 5.98 fps) Type I 24-hr 2 YR Rainfall=2.75"23005_Hydrology Printed 10/26/2023Prepared by {enter your company name here} Page 13HydroCAD® 10.00-26 s/n 03026 © 2020 HydroCAD Software Solutions LLC Pond 16P: BioRet 1 Inflow Primary Hydrograph Time (hours) 201918171615141312111098765Flow (cfs)13 12 11 10 9 8 7 6 5 4 3 2 1 0 Inflow Area=17.888 ac Peak Elev=363.04' Storage=10,739 cf 11.70 cfs 6.27 cfs Hydrologic Soil Group—Butte Area, California, Parts of Butte and Plumas Counties Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 10/25/2023 Page 1 of 44367760436783043679004367970436804043681104367760436783043679004367970436804043681104368180627390627460627530627600627670627740627810627880627950628020 627390 627460 627530 627600 627670 627740 627810 627880 627950 628020 39° 27' 13'' N 121° 31' 10'' W39° 27' 13'' N121° 30' 42'' W39° 26' 59'' N 121° 31' 10'' W39° 26' 59'' N 121° 30' 42'' WN Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 10N WGS84 0 100 200 400 600 Feet 0 40 80 160 240 Meters Map Scale: 1:3,030 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: Butte Area, California, Parts of Butte and Plumas Counties Survey Area Data: Version 21, Aug 28, 2023 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Dec 6, 2018—Dec 12, 2018 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—Butte Area, California, Parts of Butte and Plumas Counties Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 10/25/2023 Page 2 of 4 Hydrologic Soil Group Map unit symbol Map unit name Rating Acres in AOI Percent of AOI 317 Thompsonflat loam, 2 to 15 percent slopes C 27.2 99.9% 565 Dunstone-Argonaut taxadjunct- Sunnyslope , 2 to 15 percent slopes D 0.0 0.1% Totals for Area of Interest 27.3 100.0% 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. Hydrologic Soil Group—Butte Area, California, Parts of Butte and Plumas Counties Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 10/25/2023 Page 3 of 4 Rating Options Aggregation Method: Dominant Condition Component Percent Cutoff: None Specified Tie-break Rule: Higher Hydrologic Soil Group—Butte Area, California, Parts of Butte and Plumas Counties Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 10/25/2023 Page 4 of 4 NOAA Atlas 14, Volume 6, Version 2 Location name: Oroville, California, USA* Latitude: 39.4516°, Longitude: -121.5148° Elevation: 376 ft** * source: ESRI Maps ** source: USGS POINT PRECIPITATION FREQUENCY ESTIMATES Sanja Perica, Sarah Dietz, Sarah Heim, Lillian Hiner, Kazungu Maitaria, Deborah Martin, Sandra Pavlovic, Ishani Roy, Carl Trypaluk, Dale Unruh, Fenglin Yan, Michael Yekta, Tan Zhao, Geoffrey Bonnin, Daniel Brewer, Li-Chuan Chen, Tye Parzybok, John Yarchoan NOAA, National Weather Service, Silver Spring, Maryland PF_tabular | PF_graphical | Maps_&_aerials PF tabular PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches)1 Duration Average recurrence interval (years) 1 2 5 10 25 50 100 200 500 1000 5-min 0.147 (0.126‑0.172) 0.189 (0.162‑0.222) 0.247 (0.212‑0.292) 0.298 (0.252‑0.355) 0.370 (0.301‑0.460) 0.430 (0.341‑0.547) 0.494 (0.380‑0.648) 0.562 (0.418‑0.763) 0.660 (0.467‑0.942) 0.740 (0.503‑1.10) 10-min 0.210 (0.181‑0.247) 0.271 (0.233‑0.318) 0.355 (0.304‑0.418) 0.427 (0.362‑0.508) 0.531 (0.432‑0.659) 0.616 (0.489‑0.785) 0.707 (0.545‑0.928) 0.806 (0.600‑1.09) 0.947 (0.670‑1.35) 1.06 (0.720‑1.58) 15-min 0.254 (0.219‑0.298) 0.327 (0.281‑0.385) 0.429 (0.367‑0.506) 0.516 (0.438‑0.615) 0.642 (0.522‑0.797) 0.745 (0.591‑0.949) 0.856 (0.659‑1.12) 0.975 (0.725‑1.32) 1.14 (0.810‑1.63) 1.28 (0.871‑1.91) 30-min 0.357 (0.307‑0.419) 0.460 (0.395‑0.540) 0.603 (0.516‑0.711) 0.725 (0.615‑0.864) 0.902 (0.734‑1.12) 1.05 (0.830‑1.33) 1.20 (0.925‑1.58) 1.37 (1.02‑1.86) 1.61 (1.14‑2.30) 1.80 (1.22‑2.68) 60-min 0.443 (0.381‑0.520) 0.570 (0.490‑0.670) 0.747 (0.640‑0.881) 0.899 (0.762‑1.07) 1.12 (0.910‑1.39) 1.30 (1.03‑1.65) 1.49 (1.15‑1.96) 1.70 (1.26‑2.30) 1.99 (1.41‑2.84) 2.23 (1.52‑3.32) 2-hr 0.639 (0.550‑0.750) 0.786 (0.675‑0.924) 0.988 (0.847‑1.16) 1.16 (0.985‑1.38) 1.41 (1.15‑1.75) 1.61 (1.28‑2.05) 1.82 (1.40‑2.39) 2.06 (1.53‑2.79) 2.38 (1.69‑3.40) 2.65 (1.80‑3.94) 3-hr 0.776 (0.668‑0.911) 0.942 (0.810‑1.11) 1.17 (1.00‑1.38) 1.36 (1.16‑1.62) 1.64 (1.33‑2.03) 1.86 (1.47‑2.36) 2.09 (1.61‑2.74) 2.34 (1.74‑3.17) 2.69 (1.90‑3.84) 2.97 (2.02‑4.42) 6-hr 1.12 (0.964‑1.31) 1.35 (1.16‑1.58) 1.65 (1.41‑1.94) 1.90 (1.61‑2.27) 2.26 (1.84‑2.80) 2.54 (2.01‑3.23) 2.83 (2.18‑3.71) 3.14 (2.33‑4.26) 3.56 (2.52‑5.08) 3.90 (2.65‑5.80) 12-hr 1.52 (1.31‑1.79) 1.90 (1.63‑2.23) 2.39 (2.05‑2.82) 2.79 (2.36‑3.32) 3.32 (2.70‑4.13) 3.73 (2.96‑4.75) 4.14 (3.19‑5.44) 4.56 (3.39‑6.19) 5.12 (3.62‑7.31) 5.55 (3.77‑8.25) 24-hr 2.08 (1.82‑2.43) 2.75 (2.40‑3.22) 3.59 (3.12‑4.21) 4.24 (3.66‑5.02) 5.10 (4.28‑6.22) 5.74 (4.72‑7.13) 6.37 (5.12‑8.09) 6.99 (5.47‑9.11) 7.80 (5.88‑10.6) 8.40 (6.13‑11.8) 2-day 2.74 (2.39‑3.20) 3.65 (3.18‑4.27) 4.78 (4.16‑5.61) 5.67 (4.89‑6.70) 6.80 (5.70‑8.29) 7.64 (6.27‑9.48) 8.44 (6.78‑10.7) 9.24 (7.23‑12.0) 10.3 (7.73‑13.9) 11.0 (8.04‑15.4) 3-day 3.20 (2.79‑3.74) 4.24 (3.70‑4.97) 5.55 (4.83‑6.52) 6.57 (5.67‑7.76) 7.88 (6.60‑9.60) 8.83 (7.25‑11.0) 9.75 (7.83‑12.4) 10.7 (8.35‑13.9) 11.8 (8.91‑16.0) 12.7 (9.26‑17.7) 4-day 3.58 (3.12‑4.18) 4.72 (4.12‑5.52) 6.15 (5.35‑7.21) 7.26 (6.27‑8.58) 8.69 (7.28‑10.6) 9.73 (8.00‑12.1) 10.7 (8.63‑13.7) 11.7 (9.20‑15.3) 13.0 (9.82‑17.6) 14.0 (10.2‑19.5) 7-day 4.56 (3.98‑5.33) 5.85 (5.10‑6.84) 7.49 (6.52‑8.79) 8.79 (7.59‑10.4) 10.5 (8.79‑12.8) 11.8 (9.66‑14.6) 13.0 (10.4‑16.5) 14.2 (11.1‑18.6) 15.9 (11.9‑21.5) 17.1 (12.5‑23.9) 10-day 5.23 (4.56‑6.11) 6.60 (5.76‑7.73) 8.37 (7.28‑9.82) 9.78 (8.44‑11.6) 11.6 (9.75‑14.2) 13.0 (10.7‑16.2) 14.4 (11.6‑18.3) 15.8 (12.4‑20.6) 17.6 (13.3‑23.9) 19.0 (13.9‑26.6) 20-day 7.04 (6.14‑8.23) 8.81 (7.68‑10.3) 11.1 (9.62‑13.0) 12.8 (11.1‑15.2) 15.2 (12.7‑18.5) 16.9 (13.9‑21.0) 18.6 (14.9‑23.6) 20.3 (15.9‑26.4) 22.5 (16.9‑30.4) 24.1 (17.6‑33.7) 30-day 8.53 (7.45‑9.97) 10.7 (9.31‑12.5) 13.4 (11.6‑15.7) 15.5 (13.4‑18.3) 18.2 (15.2‑22.2) 20.2 (16.6‑25.0) 22.1 (17.7‑28.0) 24.0 (18.8‑31.2) 26.3 (19.8‑35.7) 28.1 (20.5‑39.3) 45-day 10.6 (9.25‑12.4) 13.3 (11.6‑15.6) 16.6 (14.4‑19.5) 19.1 (16.5‑22.6) 22.3 (18.7‑27.2) 24.6 (20.2‑30.6) 26.8 (21.5‑34.0) 28.9 (22.6‑37.6) 31.5 (23.7‑42.6) 33.3 (24.3‑46.6) 60-day 12.6 (11.0‑14.7) 15.8 (13.7‑18.4) 19.6 (17.0‑23.0) 22.5 (19.4‑26.6) 26.1 (21.9‑31.8) 28.7 (23.5‑35.6) 31.1 (25.0‑39.5) 33.3 (26.1‑43.4) 36.1 (27.2‑48.9) 38.0 (27.7‑53.2) 1 Precipitation frequency (PF) estimates in this table are based on frequency analysis of partial duration series (PDS). Numbers in parenthesis are PF estimates at lower and upper bounds of the 90% confidence interval. The probability that precipitation frequency estimates (for a given duration and average recurrence interval) will be greater than the upper bound (or less than the lower bound) is 5%. Estimates at upper bounds are not checked against probable maximum precipitation (PMP) estimates and may be higher than currently valid PMP values. Please refer to NOAA Atlas 14 document for more information. Back to Top PF graphical Back to Top Maps & aerials Small scale terrain Large scale terrain Large scale map Large scale aerial + – 3km 2mi + – 100km 60mi + – 100km 60mi Post-Construction Stormwater Management Plan Butte County C-17 June 2022 Stormwater Management and Discharge Control Manual Section 5: Projects in Priority Land Use Areas This worksheet is applicable to all Projects in PLU Areas. Priority Land Use (PLU) areas, as defined in the Statewide Trash Amendments, include high-density residential, industrial, commercial, mixed urban, and public transportation stations (see Chapter 2.3 of the Stormwater Management and Discharge Control Manual). All development and redevelopment projects subject to the Stormwater Management and Discharge Control Manual (Small Projects, Regulated Projects, and Hydromodification Projects) within these PLU areas are required to implement trash controls consistent with the Trash Amendment criteria. Trash controls are either standalone Full-Capture Devices or Multi-Benefit Trash Treatment Systems whereas certain stormwater treatment facilities (e.g., bioretention) are enhanced to include trash controls. See Chapter 9 of the Stormwater Management and Discharge Control Manual for detailed requirements. For the proposed project, identify the following information: Proposed Trash Control Measure □ Full Capture System Brand _____________ Model _____________ Capacity ___________ □ Multi-Benefit Trash Treatment System □ Bioretention □ Infiltration Trench □ Infiltration Basin □ Detention Basin The proposed Trash Control Measure(s) must clearly be identified on the Site Layout Plan as part of the Post-Construction Stormwater Management Plan.