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Home My WebLink About3219 Adopting the 2019 Stormwater Management Plan Ordinance 3219 Page I of'3 Ordinance No. 3219 AN ORDINANCE OF THE CITY OF PORT TOWNSEND, WASHINGTON, ADOPTING THE 2019 STORMWATER MANAGEMENT PLAN WHEREAS, the City of Port Townsend adopted the 1987 Comprehensive Storm Water Drainage Plan for Port Townsend to establish the City's municipal stormwater utility; WHEREAS, in 2017 the City hired Parametrix to assist the City in the creation and adoption an updated Stormwater Management Plan; WHEREAS, in 2017 the City in conjunction with Parametrix engaged the public in the formulation of the Stormwater Management Plan through public open houses, public comment periods, and a technical advisory task force committee; WHEREAS, the first Technical Advisory Task Force was formed to provide a wide variety of perspectives on the City's existing stormwater utility and input on the creation and adoption of the Stormwater Management Plan; the Technical Advisory Task Force met on August 30, 2017 and November 2, 2017; WHEREAS,the City held a public open house to solicit input, including known flood areas, from the general public; WHEREAS, the City opened two public comment periods; the first comment period was to gain feedback on what topics to include in the Stormwater Management Plan; the second comment period (2019) was to provide comments on the draft Stormwater Management Plan; WHEREAS, City Council formed an Ad Hoc Council Committee on the Stormwater Management Plan that met four times and covered topics like the stormwater utility, operations and maintenance, proposed capital projects, and proposed regulatory policies; WHEREAS, City staff gave three briefings of the Stormwater Management Plan to the Planning Commission on March 22, 2018, June 7, 2018 and January 24, 2019; WHEREAS, City staff gave two briefings to the Parks, Recreation and Tree Advisory Board regarding the Stormwater Management Plan on March 27, 2018 and February 26, 2019; WHEREAS, City staff gave four briefings to the City Council on the Stormwater Management Plan on December 11, 2017, April 4, 2018, June 11, 2018 and February 19, 2019; WHEREAS,the City's Responsible Official issued on February 20, 2019 a threshold determination of non-significance (DNS) in accordance with Chapter 43.21 C RCW, the State Environmental Policy Act (SEPA). After timely public notice and comment, the threshold DNS became final on March 7, 2019. No appeal of the SEPA threshold determination was received. WHEREAS, the 2019 Stormwater Management Plan will amend and update the 1987 Comprehensive Storm Water Drainage Plan; Ordinance 3219 Page 2 of'3 WHEREAS, the 2019 Stormwater Management Plan provides policy direction for Key Drainageways; however, the City's development of the Key Drainageways regulations will be adopted at a later date. WHEREAS, the Stormwater Management Plan's purpose is to establish best management practices for stormwater management and to adopt a capital improvement program for stormwater projects; WHEREAS, the objectives of the Plan include: • Update and define drainage connectivity and mapping; • Prepare updated policies for protecting the natural and built drainage system; • Describe approaches to protect and improve the existing roadway drainage system; • Prepare standard designs for future road drainage infrastructure; • Assess the existing impacts and potential changes due to new development; and • Prepare concept designs for capital projects to address existing stormwater problem areas. NOW THEREFORE, the City Council of the City of Port Townsend does ordain as follows: Sectiort J. r" tlg fiom. The 2019 Port Townsend Stormwater Management Plan is hereby adopted as outlined in the attached Exhibit"A." The Council declares that the adoption of the Stormwater Management Plan through this Ordinance is necessary for the protection of public health and public safety. Section .., P eparatiort offlie Key, Qraiii�.ig,yay.R g lation. Public Works staff will prepare the Key Drainageway regulations as described in the Stormwater Management Plan Section 6.2 Stormwater Control Standards and Policies and Table 6-3 Summary of Stormwater Control and Drainage Protection Item No. 6.2.5 to implement protection measures for Level 2b Key Drainageways. Section 3. l igaler. The 1987 Comprehensive Storm Water Drainage Plan for Port Townsend is replaced. Section 4. Filing. The Stormwater Management Plan as approved by the City Council shall be filed with the City Clerk and shall be available for public inspection upon the effective date of this Ordinance. SeGtion 5. Severabilit . If any clause, sentence, paragraph, section or part of this Ordinance or the Plan adopted herein, or their application to any person or circumstance is held to be invalid or unconstitutional by a court of competent jurisdiction, such order or judgment shall not affect the validity or constitutionality of the remainder of any part of this Ordinance or Plan. To this end, the provisions of each clause, sentence, paragraph, section or part of this Ordinance and Plan are declared severable. Ordinance 3219 Page 3 of 3 Section 6. Effective Date. This Ordinance shall be effective five days following publication of this Ordinance or a summary thereof. ADOPTED by the City Council of the City of Port Townsend, Washington, at a regular meeting thereof, held this 1 st day of April 2019. 1)ebon li S. Stin ()n Mayor Attest: Approved as to Form: ... m_m................ . _.. -------- Joanna Sanders, MMC � i (j cer, V)od City Clerk City Attorney Ordinance 3219 Exhibit A Page I of 377 Exhibit A Stormwater Management Plan Prepared for City ofPort Townsend January 2019 Prepared by Parametrix Ordinance 3219 Exhibit A Page 2 of 377 Ordinance 3219Exhibit A Page 3 of 377 Stormwater Management Plan Prepared for City of Port Townsend Prepared by Parametrix 719 2nd Avenue,Suite 200 Seattle,WA 98104 T.206.394.3700 F. 1.855.542.6353 www.parametrix.com January 2019 1 553-2836-004 Ordinance 3219Exhibit A Page 4 of 377 CITATION Parametrix. 2019. Stormwater Management Plan. Prepared by Parametrix, Seattle,WA.January 2019. Ordinance 3219 Exhibit A Page S of 377 Stormwater Management Plan City of Port Townsend TABLE OF CONTENTS 1. INTRODUCTION AND PURPOSE............................................................................................. 1-1 1.1 Public Input Process......................................................................................................................1-1 1.2 Introduction .................................................................................................................................. 1-1 1.3 Comprehensive Program Mission.................................................................................................1-2 1.4 Plan Outline................................................................................................................................... 1-2 1.5 Plan Resources.............................................................................................................................. 1-3 2. THE WATERSHEDS AND BASINS............................................................................................2-1 2.1 Project Area Description...............................................................................................................2-1 2.2 Physical Conditions of the Area....................................................................................................2-1 2.2.1 Topography and Drainage................................................................................................2-1 2.2.2 Local Geology...................................................................................................................2-2 2.2.3 Soils..................................................................................................................................2-9 2.3 Area Climate and Hydrology.........................................................................................................2-9 2.3.1 Hydrology.........................................................................................................................2-9 2.4 Water Quality..............................................................................................................................2-10 2.5 Climate Change...........................................................................................................................2-10 3. THE BUILT ENVIRONMENT....................................................................................................3-1 3.1 Land Use........................................................................................................................................3-1 3.1.1 Existing Land Cover..........................................................................................................3-2 3.1.2 Future Land Use and Land Cover.....................................................................................3-9 3.1.3 Estimating Runoff Potential...........................................................................................3-15 3.1.4 Catchments with Largest Increase Potential .................................................................3-25 3.2 Stormwater System Operation and Maintenance......................................................................3-27 3.2.1 Asset Identification........................................................................................................3-28 3.2.2 Level of Service..............................................................................................................3-28 3.2.3 Reporting .......................................................................................................................3-28 4. BASIN PLANNING..................................................................................................................4-1 4.1 Planning Objectives.......................................................................................................................4-1 4.2 Drainage Connectivity...................................................................................................................4-1 4.2.1 Drainage System Hierarchy..............................................................................................4-2 4.2.2 Drainage System Connectivity.........................................................................................4-6 4.2.3 Drainage System Protection ............................................................................................4-6 4.2.4 Evaluating Potential Capacity Needs and Impacts...........................................................4-8 4.2.5 Drainageway Potential Impact Assessment...................................................................4-21 4.2.6 Potential Impacts to Closed System Wetlands..............................................................4-25 4.3 Drainage System Stormwater Improvements ............................................................................4-25 4.4 Roadway Inventory for Upgrade Opportunities.........................................................................4-26 January 2019 1 553-2836-004 i Ordinance 3219 Exhibit A Page 6 of 377 Stormwater Management Plan City of Port Townsend TABLE OF CONTENTS (CONTINUED) 5. CAPITAL PROJECTS PLAN.......................................................................................................5-1 5.1 Proposed Capital Projects.............................................................................................................5-1 5.2 Proposed Recurring Capital Projects ............................................................................................5-5 6. IMPLEMENTATION................................................................................................................6-1 6.1 Capital Plan Priorities and Schedule .............................................................................................6-1 6.1.1 Capital Projects for Existing Flood Control ......................................................................6-1 6.1.2 Non-Capital Recurring Projects........................................................................................6-2 6.2 Stormwater Control Standards and Policies.................................................................................6-3 6.2.1 Stormwater Control from New Development.................................................................6-3 6.2.2 Drainage System Protection ............................................................................................6-4 6.2.3 Drainage System Review and Upgrades ..........................................................................6-7 6.2.4 Other Drainage System Protection Measures.................................................................6-8 6.3 Funding and Resources...............................................................................................................6-10 6.3.1 Capital Projects..............................................................................................................6-10 6.4 Summary Implementation Plan..................................................................................................6-12 7. REFERENCES .........................................................................................................................7-1 LIST OF FIGURES 1 Stormwater Drainage Basins.........................................................................................................2-3 2 Drainage Basins Discharge Locations............................................................................................2-4 3 Topography...................................................................................................................................2-5 4 Flood Hazard Zones.......................................................................................................................2-6 5 Area Geology.................................................................................................................................2-7 6 Annual Water Budget ...................................................................................................................2-8 7 Hydrologic Soil Groups................................................................................................................2-11 8 Drainage Catchment Areas...........................................................................................................3-7 9 Land Use......................................................................................................................................3-11 10 Vacant Lands and Development Potential..................................................................................3-12 11 Catchment Nodes .......................................................................................................................3-17 12 Stormwater Facilities....................................................................................................................4-3 13 Stormwater System Levels............................................................................................................4-4 14a Pipe Capacity„Look Up Table" .....................................................................................................4-9 14b Ditch Capacity„Look up Table" ..................................................................................................4-10 15 Long Paths, CDCs & KDs..............................................................................................................4-11 16 Roadway Drainage for Long Path Conveyance Sizing.................................................................4-19 17 CDCs & KDs High Velocity Reaches.............................................................................................4-23 18 Future Impact Estimate Wetland Footprints..............................................................................4-27 19 Capital Projects .............................................................................................................................5-3 ii January 2019 1 553-2836-004 Ordinance 3219 Exhibit A Page 7 of 377 Stormwater Management Plan City of Port Townsend TABLE OF CONTENTS (CONTINUED) LIST OF TABLES 2-1 Rainfall Depths for 24-Hour Events ..............................................................................................2-9 3-1 Existing Land Cover.......................................................................................................................3-2 3-2 Existing Land Use Model Inputs....................................................................................................3-4 3-3 Future Land Use Model Inputs ...................................................................................................3-13 3-4 Buildable Area—Impervious Comparison...................................................................................3-19 3-5a Peak Runoff at Nodes or for Total Catchment—Existing............................................................3-23 3-5b Peak Runoff at Nodes or for Total Catchment—Future.............................................................3-24 3-6 Potential Change in Peak Flows by Catchment Area..................................................................3-25 3-7 Existing Inventory of Public Facilities..........................................................................................3-29 3-8 Maintenance Frequency and Personnel.....................................................................................3-30 4-1 Basins and Disposition or Discharge Point....................................................................................4-2 4-2a Pipe Capacity for Reaches of Different Slopes..............................................................................4-9 4-2b Ditch Capacity for Reaches of Different Slopes ............................................................................4-9 4-3 Catchment Area Peak flows and Maximum Required Drainage Conveyance............................4-13 4-4 Drainage Facility Size Estimates for Drainage Paths Exceeding Minimum Conveyance Sizing ..4-15 4-5 Peak Flows in Reaches for Structure Sizing.................................................................................4-17 4-6 Peak flows in Reaches for Long-Path Conveyance Sizing ...........................................................4-18 4-7 Peak Flow Increase at Key Nodes due to future Development..................................................4-21 4-8 CDC and KD Velocity Thresholds.................................................................................................4-22 4-9 Potentially Impacted Wetlands...................................................................................................4-25 5-1 Capital Projects.............................................................................................................................5-2 5-2 Other Built Capital Projects...........................................................................................................5-5 6-1 Capital Projects Rankings and Priority..........................................................................................6-1 6-2 Summary of the Roadway Drainage Improvement Plan ..............................................................6-2 6-3 Summary of Stormwater Control and Drainage Protection.........................................................6-6 6-4 Summary of Drainage System Review and Upgrades...................................................................6-7 6-5 Summary of Other Drainage System Protection Measures..........................................................6-9 6-7 Summary Cost Plan—Capital (2019-2024) .................................................................................6-10 6-8 Summary Cost Plan - Resources..................................................................................................6-11 6-9 Summary Implementation Schedule ..........................................................................................6-12 6-10 Updated CIP with $6 Surcharge and Development Fee..............................................................6-15 January 2019 1 553-2836-004 iii Ordinance 3219Exhibit A Page 8 of 377 Stormwater Management Plan City of Port Townsend TABLE OF CONTENTS (CONTINUED) APPENDICES A Kickoff Meetings B Public Input Process C FEMA Flood Mapping D Modeling Analysis E Roadway Inventory F Small-Site Stormwater Management Guide G Capital Projects Worksheets H Stormwater Manual Comparison I Updated Capital Improvements Plan iv January 2019 553-2836-004 Ordinance 3219Exhibit A Page 9 of 377 Stormwater Management Plan City of Port Townsend ACRONYMS AND ABBREVIATIONS BMP best management practice CAO Critical Area Ordinance CDC Critical Drainage Corridors Ecology Washington State Department of Ecology EDS Engineering Design Standards FTE full time equivalent HSG hydrologic soil groups KD Key Drainageway LID low impact development MEP maximum extent practicable NOAA National Oceanic and Atmospheric Administration NPDES National Pollution Discharge Elimination System NRCS Natural Resources Conservation Service PTMC Port Townsend Municipal Code RSL relative sea level SMP Stormwater Management Plan SWMMWW Stormwater Management Manual for Western Washington USDA U.S. Department of Agriculture January 2019 1 553-2836-004 v Ordinance 3219 Exhibit A Page 10 of 377 Ordinance 3219Exhibit A Page 11 of 377 Stormwater Management Plan City of Port Townsend Z. INTRODUCTION AND PURPOSE 1.1 Public Input Process The planning process included public participation via public open house, public comment periods and a technical advisory task force committee.The first SMP Technical Advisory Task Force meeting was held on August 30, 2017.The purpose of the Task Force was to provide a wide variety of perspectives on the City's existing stormwater utility and input on the creation and adoption of the SMP. A second task force meeting was held on November 2, 2017. Materials provided in the two meetings are included in Appendix A. A public open house was held between the two Task Force meetings to present the plan purpose and findings (to date) and solicit input from the general public, such as known flooding problems for capital project. During the SMP adoption process there were two public comment periods. The first comment period was early in the process and the goal was to gain feedback on what topics the public would like to see covered in the SMP and what was important regarding stormwater.The second comment period was to provide comments on the draft version of the SMP The input provided throughout the public participation process was reviewed by the Plan team and included where appropriate in this final draft.The materials and minutes from city council sub- committee meetings, planning commission meetings and workshops, and the city council meetings and workshop are included in Appendix B. 1.2 Introduction The City of Port Townsend is unique in many ways, notably when it comes to climate, landscape, and history of its development.Annual rainfall of about 17 inches is 70 percent of the amount that falls in Port Angeles,just 30 miles to the west, and 25 percent of Quilcene's, 23 miles to the south.There are no "streams" in our common understanding of the term and the City is surrounded on three sides by water: the Strait of Juan de Fuca, Admiralty Inlet, and Port Townsend Bay(all parts of the Salish Sea). Much of the land was platted in the 1890s, with no regard to topography, drainage patterns, or infrastructure. These conditions result in challenges for the City and property owners to follow natural drainage patterns, control changes from new development, and apply western Washington stormwater manual standards that were developed for wetter climates with streams and more traditional land development approaches. In 1986,the City prepared the "Comprehensive Storm Water Drainage Plan for Port Townsend" (CH2MHill et al. 1987)which was used as the basis for establishing the City's municipal stormwater utility. Deficiencies in this plan were noted when preparing the Growth Management Plan in the early 1990s, which resulted in initiating a new comprehensive plan (Port Townsend 1996) and an updated Stormwater Management Plan (SMP) (Port Townsend 1999). Notable in the draft 1999 SMP was the idea of a "natural drainage systems" approach, which included the mapping of"Critical Drainage Corridors".The draft 1999 plan was never adopted; however, the natural drainage systems approach was adopted through the 1996 Comprehensive Plan through policies and goals in both the Land Use and Utility Elements of the 1996 Comprehensive Plan.The Critical Drainage Corridors were protected through regulatory language in the city's Critical Area Ordinance (CAO). January 20191 553-2836-004 1-1 Ordinance 3219Exhibit A Page 12 of 377 Stormwater Management Plan City of Port Townsend This SMP update addresses ongoing management of the existing system and plots a course for the future of the system. While there are many pieces already in place—system mapping, adopted standards, and a recognized need to consider development and protect resources—the SMP includes analyses, approaches, priorities, specific projects, mechanisms, updated performance standards, and an implementation plan. In addition, since stormwater practice and regulations continue to evolve and the approach and responsibility of municipalities to control stormwater discharges and manage infrastructure increases, this Plan recommends policy and regulatory updates. The SMP is an important tool for the City to use for day-to-day development review, operations, and long-term planning. The objectives of the SMP include: • Updating and defining drainage connectivity and mapping; • Preparing updated policies for protecting the natural and built drainage system; • Describing approaches to protect and improve the existing roadway drainage system; • Preparing standard designs for future road drainage infrastructure; • Assessing the existing impacts and potential changes due to new development; • Preparing concept designs for capital projects to address existing stormwater problem areas; and • Preparing site development information and review materials, including low impact development (LID) measures, redevelopment, new site development, and water quality retrofitting. The SMP presents the background objectives existing conditions summary, basin analysis, consideration of future land use, recommended stormwater controls, and capital projects to address existing stormwater problems. 1.3 Comprehensive Program Mission The project kick-off with both the City and Parametrix teams was held on June 20, 2017.The purpose of the kickoff was to develop the Plan vision and team mission to complete the plan, brainstorm the Plan needs and goals, discuss risks and threats to project success, and finalize the schedule and work plan for the adoption of an updated SMP. The team agreed on the following Vision and Mission statement: A fully functional, achievable, and sustainable stormwater system that is integrated into the landscape, supports envisioned growth, protects residents, and nurtures the environment. Additional information to help guide plan preparation was collected by the team.The kick-off meeting day included a field tour of key areas and problem areas in the city. Notes from the meeting brainstorming are provided in Appendix A. 1.4 Plan Outline The Plan structure follows this general outline: Section 2 describes the study area, with a discussion of the physical setting and natural drainage system; Section 3 describes the current built environment in the context of how it affects water resources, such as land cover and stormwater facilities; Section 4 describes the basis for stormwater planning, establishes stormwater control targets, and presents the proposed SMP approaches; Section 5 describes the proposed capital projects; and Section 6 includes the implementation plan. 1-2 January 20191 553-2836-004 Ordinance 3219Exhibit A Page 13 of 377 Stormwater Management Plan City of Port Townsend 1.5 Plan Resources The City prepared the Draft Storm Water Management Plan in 1999 (Port Townsend 1999).This plan was very thorough and provides a strong platform on which this SMP plan update was built. Key material used for a starting point includes the original drainage basin mapping and critical drainage corridors (CDC) map. The existing available GIS mapping from the city was used extensively, including topography, the mapped drainage basins, CDCs, road network, drainage patterns and conveyance, wetlands,floodplains and soils mapping.The City staff also prepared new information for this plan, such as a roadway inventory, new and revised catchment inventory, and updated CDC and key drainageway(KD) mapping. Other information, such as water quality sampling and some rainfall data, was provided by the City. Other geology and climate data were collected from reliable Internet sources. January 20191 553-2836-004 1-3 Ordinance 3219 Exhibit A Page 14 of 377 Ordinance 3219Exhibit A Page 15 of 377 Stormwater Management Plan City of Port Townsend 2. THE WATERSHEDS AND BASINS 2.1 Project Area Description The City is located on the Quimper Peninsula, surrounded on three sides by the Strait of Juan de Fuca, Admiralty Inlet, and Port Townsend Bay, all parts of the Salish Sea. Figure 1 shows the city limits, streets, named receiving waters, wetlands and potential wetlands, CDCs, KDs, and drainage basins. There are no well-defined perennial or named streams.There is a long linear depression that generally drains toward "Chinese Gardens"which contains a connected series of wetlands and a designated floodplain. CDCs are regulated by the City's Critical Areas ordinance. KDs are defined in this Plan and regulated by stormwater codes and design standards. The general disposition of surface waters is shown on Figure 2. Drainage basins in the City drain either to closed depressions or directly to the ocean.The basins that discharge to the ocean are via a storm sewer system, flow through surface ravines or through outlets from the two large named wetlands, Chinese Gardens and Kah Tai Lagoon.The closed basins discharge into groundwater at small wetlands. Additional detailed discussion of the drainage basins is provided in the 1987 Comprehensive Stormwater Drainage Plan (CH2M Hill et al. 1987). 2.2 Physical Conditions of the Area '.1. Topography and Drainage The landscape and general topography of the City indicates irregular and undulating slopes. Figure 3 is a topographic map of the City which shows the location of the low-lying areas, closed depressions and geologic drainage features. Generally, there are relatively flat"plateaus" along the east and west sides of the City with a valley(low lands) going through the middle. High bluffs dominate the ocean edge. Strong erosional drainage patterns are not well-seen and are generally limited to drainage from the plateau, notably in the southwest corner of the city. The formation of the large-scale landforms found are an outcome of many processes, including deposition by advancing and receding glaciers, changing sea levels, isostatic rebound after the glaciers have gone, and other apparent significant land forming events. However,there is little evidence of landscape-level changes due to streams and flowing water over the last several thousand years since the glaciers retreated, other than very local drainage patterns. The topography of the City indicates low-lying areas and subtle drainage paths to form the natural drainage disposition shown on Figures 2 and 3. Topographic maps and the built environment(i.e., both built drainage network and existing roads)were used to define the drainage basins and their discharge location. Figure 3 indicates by shading the location of low-lying drainage patterns within the major drainage basins that lead to receiving water.The drainage patterns described in this section and shown on Figures 1 through 3 form the drainage network on which the stormwater planning is based. As shown on Figure 2, stormwater runoff drains directly to:the ocean either via storm sewers (pipes) or from the two large named wetlands (Chinese Gardens and Kah Tai Lagoon)via an overflow pipe or to closed basins that discharge into the groundwater, often at small wetlands and surface ravines.The flow path and disposition of stormwater is an important factor in the stormwater impact analysis, future control decisions and policies and potential basin retrofitting. January 20191 553-2836-004 2-1 Ordinance 3219Exhibit A Page 16 of 377 Stormwater Management Plan City of Port Townsend Designated floodplains and coastal flood hazard zones as mapped by FEMA exist in the low coastline areas along the entire City shoreline (Figure 4). The only non-coastal floodplain in the City has also been mapped in Drainage Basin 4, for which detailed information can be found in Appendix C (Polaris 1996). Wetlands have also been mapped throughout the city annotated as "wetlands" or"potential wetlands" (Figure 4).A wetland has been delineated by a wetland specialist and documented by a wetland report; a potential wetland is identified through aerial mapping by a topographic depression or wet area in the landscape and does not have a delineation wetland report and has not been field verified. 2.2.2 Local Geology The geology and climate of the area contribute substantially to defining stormwater planning approaches for the City.The relatively poorly defined natural drainage paths are a direct result of the recent geologic past and the lack of rainfall to form drainage patterns and provide perennial streams. The dominant geologic formation that resulted in local landforms is known as the Vashon recessional drift, made up of sediments deposited during and after the last retreat of the Puget Lobe glacier.The landforms are made up of a combination of materials deposited during previous advances as till, outwash coming from the glacier as it retreated, and materials left behind as the ice stagnated and melted. Because the Vashon recessional drift is the last deposit left by the melting glacier, it is relatively undisturbed (Washington State Department of Ecology [Ecology] 1981). No interpretations of the existing smaller-scale landforms in the City were found, and virtually all of the City is mapped as "Vashon Till (Qvt)" on the Surficial Geologic Map of the Port Townsend Quadrangle (Pessl et al. 1989) (Figure 5). Small areas of"Marsh, Swamp, or Bog" (Qm), "Recessional-Continental" deposits (Qvrc) and "Advance Outwash" (Qva) are also found.This mixture of material sources, depositional environments, and geologic processes demonstrates that highly variable landforms. As described earlier, annual rainfall in the City is very low when compared to nearby areas due to the Olympic Mountains rain shadow. In addition,the historical forest cover before the arrival of European settlement resulted in low basin response and runoff from the rain that does fall. Consequently, there was limited water available to carve drainage channels. Low areas that appear to have been created by water are present (see Figure3) and may have resulted from the last processes of the melting glaciers or in the slow response to several thousand years of rainfall since the glaciers melted. Ecology conducted a study of ground water resources in eastern Jefferson County (Ecology 1981) and developed a compelling analysis of the annual water budgets for the Port Townsend area that demonstrates the amount of water typically available for surface water runoff. Figure 6, replicated here from Ecology 1981, shows the relative percentages of average annual rainfall needed to replenish soil moisture and the resultant remaining water surplus available for runoff. The results show that the average annual excess water available (water surplus)for runoff is just 0.6 inches(precipitation minus evapotranspiration), although under seasonally variable infiltration and evapotranspiration or in different locations, it could be more or less. This is a very small amount of water available for runoff. By comparison, the excess available runoff(water surplus) in Quilcene,just 30 miles south of the City, is 29.7 inches (Ecology 1981).This excess runoff in Quilcene is also reflected in local drainage patterns and development of channels in the same glacial materials. As the amount of average annual precipitation increases moving south from Port Townsend, the number of streams also increases to the south (Ecology 1981). 2-2 January 20191 553-2836-004 Ordinance 3219Exhibit A Page 17 of 377 Stormwater Drainage Basins oPJ c�l Figure 1 � 14 53rd St. Chinese Gardens 11 p o 49th St. ooh • • UUUlll�l5 O m a o 19 Drainage Basins p K Wetlands C3 Potential Wetlands G�dt;,,d co ' 100 Year Flood q ve. v 1$ 1s o Critical Drainage Corridors a tin s Ave. cJ�. C m .• ' St e Key Drainageways gab City Limits po 7 �a 17 C/) 1 t St. d C/) U) Q Q� C Lagoon 14th St. 9 (� o C 15 I x N 1� Q � o � 16 o G7 D O � N (6 IL m E 0 0.25 0.5 0.75 1 LL Miles a 2019 Stormwater Management Plan Page 2 - 3 Ordinance 3219Exhibit A Page 18 of 377 (99 (o- AIM �___�- --` \___�f' Drainage Basin ' O Discharge Locations o Figure 2 14 -- g3rq St. Gardens i,- 1 p o 49th St. oo� • • ' kmap i Ago"e O Discharge Locations C3Drains to Salish Sea Q p \ C3 Kah Tai Lagoon (Overflows to Salish Sea) r C3 Chinese Gardens V 4co � (Overflows to Salish Sea) C3 Closed Basin (No Outlet) \ o Hastings Ave. s�. \ \ Drains to Ravines —7 aSt. Drains to County 0 ON � Outfalls 17 \\d \\^ a o,� s Features 1 t St. � �� Drainage Basins 0$ Kah Tai Lagoon Wetlands o 14th St Potential Wetlands N 10 76 100 Year Flood Critical Drainage Corridors Key Drainageways p O City Limits C I a � 1 lI I1 0 0.25 0.5 0.75 1 j LL Miles a 2019 Stormwater Management Plan Page 2 - 4 Ordinance 3219Exhibit A Page 19 of 377 Topography 2 ® Figure 3 D 53rd St. f p o � ardens ',�, 49th St. vv 4 Elevation o 295' � Q -- • ( 6 N 0, 0 ,�? C 07 103 O 18 oa o 19 � o a U J 10 aHastings Ave. a ,. co Fsr. / \`v�% � o Features o a o � D o � o 19 Drainage Basins Wetlands U) 12 R ) 12 C3 Potential Wetlands � 19th St. o D G°Je R � 4� �a` City Limits � Ka at agoon 14th St. J 15 0 � N S� spa o o c �} Q m a 10 o O d 16 g 0 O ----------- f JVl p O O (6 a � E 0 0.25 0.5 0.75 1 LL Miles a 2019 Stormwater Management Plan Page 2 - 5 Ordinance 3219Exhibit A Page 20 of 377 Flood Hazard Zones � Figure 4 14 53rd St. Chinese Gardens p o 49th St. P'A CD o p • r ! O s WULl.:J15 O FEMA Flood Hazard Zones e O� C3 " Zone AE Q C3 Zone VE Ca a i/ co ' � Features �t�dgVe O r � O 1a 19 a 19 a Drainage Basins tings Ave. °® ° cJ� a 0Wetlands gab Q �` i o� a p r� C3 Potential Wetlands ® 5 po c G 17 �aC3 100 Year Flood Area ` — cn 1 U) 1 t St. Critical Drainage Corridors N � a. N �a�e`5 Key Drainageways N a 1 th St. 9 J _ T' '� City Limits © o E q 15 o N S\Na`J CSD R 16 10 _ m o D O N (6 a m E 0 0.25 0.5 0.75 1 now LL Miles a 2019 Stormwater Management Plan Page 2 - 6 Oil Area Geology Figure 5 Surficial Geologic Map of the Port Townsend 30- by 60-Minute Quad- rangle, Puget Sound Region, r' Dethier, D.B. Booth, • J.P Minard 1989 Q. Beach Deposits AM 1i UW Qd: Dune Deposits Qm: Marsh, Bog, or Swamp Q •nal-Conti QVashon Till 4 '0 qW Ordinance 3219Exhibit A Page 22 of 377 PORT TOWNSEND WATER HOLDING CAPACITY OF SOI L 2" 6• Annual Water Budget PRECIPITATION 183 (Ecology 1981 ) POTENTIAL 25,2 TRANSPIRATION A 6 - 14417.7 Figure 6 WATER SURPLUS 3.9 0.6 6 POTENTIAL EVAPOTRANSPIRAT" +� 4 ACTUAL EVAPOTRANSPIRATION a �► � WATER PRECIPITATION DEFICIT 2 � .... .�" 6 � IL MOISTURIn ,,. -SECHARGE {6 ) WATER SURPLUS ,••,• �- O SOIL MOISTURE UTILIZATION JAN FES MAR APR I MAY I JUN I JUL T AUG I SEP OCT NOV DEC Y QUILCENE 2 SW WATER HOLDING 2 6 CAPACITY OF SOI L PRECIPITATION 50.0 PQTENTIA_L APO TRA IRATI N 25.1 TRAUAL PIRATI N- I7.4 203 WATER SURPLUS 32.6 29.7 I0 8 PRECIPITATION N V m 6- x POTENTIAL EVAPOTRANSPIRATION WATER ACTUAL m 4 EVAPOTRANSPIRATION �eY� ►� SURPLUS SURPLUS � WATER-: DEFICIT ��►R SOIL t 2• s OISTURE 6" RECHARGE 0 2 � `.�(5.) N a r .f r• r SOIL MOISTURE UTILIZATION 0 JAN FEB MAR APR MAY JUN JUL AUG SEP OCT N0V DEC~ 0 N (6 a E `o Figure 19. MEAN ANNUAL WATER BUDGETS . LL_ 31 d 2019 Stormwater Management Plan Page 2 - 8 Ordinance 3219Exhibit A Page 23 of 377 Stormwater Management Plan City of Port Townsend 2.2.3 Soils Soils in the area were mapped by the Natural Resources Conservation Service (NRCS), as shown on Figure 7.The NRCS divides soils into four hydrologic soil groups (HSG) defined by the expected rainfall infiltration and runoff response. These soils categories provide information for hydrologic modeling and planning-level information regarding localized infiltration potential (or lack thereof).These data will be used for testing potential impacts described in Section 4 below. Figure 7 has highlighted HSG "A" and HSG "D" which represents the soils most likely to have high infiltration and low infiltration respectively. The hydrologic soil groups will be used to support on-site infiltration feasibility7. 2.3 Area Climate and Hydrology 2.3.1 Hydrology Port Townsend is located in the rain shadow of the Olympic Mountains. The precipitation in the area usually falls as rain, with about 65 percent of the yearly precipitation occurring between October and March. Current hydrological parameters in the City are: • Average annual rainfall: 17.64 inches • Mean storm events: 50 • Mean storm depth': 0.266 inches 1 Data from the Port Townsend Station located at latitude 48.07,longitude 122.45(Perrich 1992). Rainfall depths for selected 24-hour storm events are shown in Table 2-1. Table 2-1. Rainfall Depths for 24-Hour Events 2 Return Frequency Precipitation Depth(inches) 2-year 1.17 10-year 1.72 25-year 2.03 100-year 2.50 Z Data taken from National Oceanic and Atmospheric Administration(NOAA),U.S.Department of Commerce(reference needed) Hydrologic modeling is used to predict runoff from under different land use scenarios. Modeling for this Plan was done using MGSFlood.The predicted runoff rates are used for sizing conveyance structures such as culverts and ditches. Stormwater models use the long-term regional rainfall records which are tailored to the specific location being analyzed (i.e., Port Townsend). The maximum adjustment in the rainfall record allowed by Ecology is a factor of 0.78, which does not fully reflect the reduction needed when comparing Port Townsend rainfall records to nearby stations used in the long-term model record. Consequently, the modeled rainfall amounts used, and the resultant peak flow rates (described in sections below), may be higher than observed amounts. Because of this, conveyance structures may be larger than needed for the design storms used. However, the structure sizing is not that sensitive to modest changes in rainfall extremes, therefore the overall effect on results is expected to be minor. Also, the impact analysis is comparative, using the same rainfall record, which means the existing and future conditions are similarly different (high or low) but the comparative difference is reasonably accurate. The rational method is another appropriate approach for calculating peak flows in for conveyance design. However, the rainfall intensity numbers used in the rational method also rely on location-specific rainfall data.These data have not been calculated for Port Townsend and the available nearby rainfall January 20191 553-2836-004 2-9 Ordinance 3219Exhibit A Page 24 of 377 Stormwater Management Plan City of Port Townsend stations do not have the type of data or length of records needed to be appropriate data sources. Similar adjustments can be made to nearby available rainfall data if this method is used but is also expected to over-predict runoff rates. 2.4 Water Quality No stormwater quality data has been collected by the City at city outfalls.The Jefferson County Health Department collected dry and wet weather samples to evaluate e coli from storm sewer outfalls in 2013 and 2014.The samples can inform some elements of stormwater planning which would be focused on education (usually pet waste), source controls, and illicit discharges.There is insufficient available data to inform a basin or outfall-specific stormwater quality retrofit prioritization plan,which is the norm, not the exception, in most of Puget Sound communities. However, stormwater is a presumptive practice; therefore, a surrogate such as the percentage of roadways and intensity of development in a basin can be used to prioritize locations for stormwater treatment retrofits to improve water quality. 2.5 Climate Change Change in climate is expected to result in more extreme weather such as larger storms of greater intensity, changes in seasonal rainfall patterns, more extreme difference between wet and dry years, or changes in snow and snow melt patterns. In addition, warming weather is resulting in higher sea levels which can impact coastal communities, such as Port Townsend. Change in the global climate is expected to increase temperatures in western Washington 4.2° F to 5.40 F by 2050 in the Puget Sound Region and more extreme weather may be expected. For example, according to a study done by University of Washington (Mauger et al. 2015),the wettest days (99th percentile of 24-hour precipitation totals) in the Pacific Northwest are projected to increase in precipitation by 22 percent by the 2080s and the frequency of those events are predicted to increase from 2 days per year historically(1970-1999)to 7 days per year in the future (2070-2099).According to some models, around the Puget Sound watershed and Port Townsend, the maximum 24-hour precipitation event is projected to have an increase precipitation of 6 percent to 10 percent by 2040, and 10 percent to 11.5 percent by 2080. Precipitation in general is projected to increase in fall, winter and spring and decrease in summer. Around the Puget Sound watershed and Port Townsend, it is projected that winter precipitation will increase on average of 7 percent to 8.5 percent by 2040,while summer precipitation will decrease on average by 10 percent to 11.5 percent. Additionally, the average snowpack is predicted to decline in the Puget Sound region, causing the spring peak in streamflow to occur earlier in the year and decreasing summer minimum flows. In addition, warming weather is resulting in higher sea levels which can impact coastal communities such as Port Townsend. Based on a University of Washington study on projected sea level rise (Miller et al. 2018), around Port Townsend there is a 99 percent probability that relative sea level (RSL) will increase by 0.1 feet by 2030 and a 50 percent probability that RSL will increase by 0.4 feet. By 2070, that increases to a 99 percent probability that the RSL will rise by 0.4 feet and 50 percent probability of over 1.3 feet.These projections all assume high greenhouse gas scenario. In a low greenhouse gas scenario,the projections remain the same for 2030, and decrease slightly to a 99 percent probability of RSL rises by 0.3 feet and 50 percent probability of over 1.1 feet in 2070. Looking farther ahead, in 2150 there is a 99 percent probability that RSL will increase by 0.3 feet and 50 percent probability that RSL will increase by 2.8 feet. Furthermore, in the event of a subduction zone earthquake, some parts of Washington coast may be subject to land level changes, based on multiple seismic deformation models, of 0 to 0.3 feet subduction. 2-10 January 20191 553-2836-004 Ordinance 3219Exhibit A Page 25 of 377 r , Hydrologic Soil Groups O Figure 7 53rq St. 1 49th St. f o� W St. O 4 Runoff Potential (') CD C3 C-3 Q A - Low C - Moderate -r C:�3 C/D - Moderate to High 1 � �� " G�'dtiid � D - High q ve . C3 1s 1s Variable �I Hastin s e. St.F cJ�. e o� C3 Cut and Fill, Rough Broken, � Water, Reservoir �c 5 (')Hydrologic Soil Groups per 2005 Stormwater Management Manual 17 0 for Western Washington CO 1)th St. �a�e�5 19 Drainage Basins 14th St. 9 J City Limits a E N ��. c0 o 0 LL O N (6 a ' 0 0.25 0.5 0.75 1 NNNNNNr LL Miles a 2019 Stormwater Management Plan Page 2 - 11 Ordinance 3219 Exhibit A Page 26 of 377 Ordinance 3219Exhibit A Page 27 of 377 Stormwater Management Plan City of Port Townsend 3. THE BUILT ENVIRONMENT Stormwater plans are prepared to address both current and proposed conditions: the effects of land conversion on stream hydrology and the impacts of pollution-generating activities on water quality. Land drainage has been included in design for centuries; stormwater management has been the norm for the past several decades in Washington and continues to evolve as the practice learns from the past and new issues come to the forefront. Existing land use and land cover have created drainage conditions observed today, including some localized flooding and erosion impacts. Development of vacant undeveloped lands, redevelopment, and infill will bring future potential impacts, if not properly controlled. The measures and standards for control to be used in Port Townsend will follow the general approach for stormwater management used elsewhere in western Washington, with adjustments due to local conditions found in Port Townsend. As described before, the City will be unique in its approach to addressing stormwater management because of the following unique local conditions: there are no natural streams but there are obvious pathways, drainage basins, and receiving waters; new development will be predominantly infill into pre- platted areas with or without existing opened rights-of-way; rainfall is relatively low; and the road system is the dominant drainage conveyance network. In this section, existing land use (as defined by imperviousness) is estimated to evaluate existing drainage needs, primarily in the road system, and identify areas with potentially high stormwater quality impacts.There are no reliable mapped data for determining existing imperviousness,therefore estimates were made using approaches described below. Future land use is estimated by both the development potential and estimated allowable development.This generally tends to over predict future impacts,which means the planning outcomes tend to be reliably protective. Runoff modeling requires soils and land cover data. Figure 7 provides the source for soils data. Land cover refers to the general type and condition of vegetated surfaces, such as forests, pastures, and open landscapes, each of which has a different runoff response to precipitation. The City used visual estimates for land cover data. In low precipitation areas with moderate soil runoff response such as Port Townsend, runoff rates are relatively insensitive to land cover. In addition, for purposes of hydrologic modeling, each drainage basin in the City was further divided into subbasins, referred to as "catchment" areas as shown on Figure 8. The catchment boundaries are defined by both topography and the built environment—existing roads and stormwater infrastructure. 3.1 Land Use An inventory of impervious area and land cover, described in terms of aerial coverage within a catchment, is needed to prepare modeling or characterization analyses that relate runoff potential or quality characteristics to a point in the conveyance system. Impervious land cover can include amounts and types of impervious surface, for example roads, sidewalks, rooftops, or parking lots, or a stormwater management description like pollution generating or"effective" impervious surface. Available data to make these characterizations varies widely between different jurisdictions. Fortunately, there are a number of approaches to either translate available data into categories that are useful for stormwater management or basin planning evaluations. Data are needed to characterize existing conditions and to project the changes that could occur due to new development. January 20191 553-2836-004 3-1 Ordinance 3219Exhibit A Page 28 of 377 Stormwater Management Plan City of Port Townsend 3.1.1 Existing Land Cover Existing land use and imperviousness is estimated to evaluate existing conditions to determine drainage needs, primarily in the road system, identify areas with potentially high stormwater quality impacts, and provide a baseline for modeling existing runoff conditions. For the modeling analysis, imperviousness is calculated for each catchment within a drainage basin. The approach for estimating existing imperviousness is described below. For rights-of-way,two categories were identified: opened rights-of-way(which means an existing public road is present) and unopened rights-of-way(an undeveloped, platted right-of-way with no public road). For opened rights-of-way, the length of roadways in the catchments were measured and multiplied by 22-feet to estimate the area of impervious surface.The right-of-way per catchment is shown in Table 3- 1.The opened rights-of-way are an estimated 40 percent imperviousness based on a typical roadway width of 22-feet of pavement in a 60-foot wide platted right-of-way, plus some consideration of sidewalks and driveways in the right-of-way. For unopened rights-of-way, imperviousness is assumed to be zero. The remaining land (i.e., not platted rights-of-way)was classified into developed land, critical areas (undevelopable land including steep slopes, wetlands, and CDCs), or vacant land. For developed land, the estimated imperviousness is 37 percent of the developed land area. Vacant land was further divided into conservation or public lands (which are assumed will remain undeveloped) underdeveloped land (which are large tracts with little development or a single house) and undeveloped (developable land either platted land or not). For vacant land, the estimated imperviousness was assumed to be zero for current baseline conditions. Runoff modeling requires land cover data and soils types. Land cover refers to the general type and condition of vegetated surfaces, such as forests, pastures, and open landscapes, each of which has a different runoff response to precipitation. Visual estimates were used to provide data for land cover. In low precipitation areas with moderate soil runoff response such as Port Townsend, runoff rates are relatively insensitive to land cover. Figure 7 provides the source for soils data.Tables 3-1 and 3-2 provides a breakdown of total catchment area breakdown (see Figure 8), rights-of-way impervious area, rights-of-way unopened area, developed area, critical areas, vacant conservation/public land and vacant underdeveloped/developable land. Table 3-1. Existing Land Cover Remaining Land Total Right-of-Way Vacant Area Open Unopened Developed Critical Areas Underdeveloped/ Catchment (ac.) (ac.) (ac.) (ac.) (ac.) Conservation/public Developable 1 12.8 0.0 0.0 0.0 12.8 0.0 0.0 2 62.7 13.7 4.8 15.1 2.0 24.1 3.4 3 19.1 0.0 0.0 0.0 10.9 0.0 8.1 4a 46.5 0.0 0.0 0.0 46.5 0.0 0.0 4b 80.3 0.1 0.2 0.9 7.1 0.8 71.2 4c 122.4 15.0 4.2 7.4 8.9 21.9 65.0 4d 47.4 0.1 0.0 0.0 8.6 0.1 38.6 4e 26.7 4.6 1.0 5.2 1.5 7.9 6.7 M 83.7 8.5 2.3 13.3 6.3 52.5 1.0 4g 107.6 17.5 15.2 27.6 19.8 25.4 2.2 3-2 January 2019 553-2836-004 Ordinance 3219 Exhibit A Page 29 of 377 Stormwater Management Plan City of Port Townsend Table 3-1. Existing Land Cover (continued) Remaining Land Total Right-of-Way Vacant Area Open Unopened Developed Critical Areas Underdeveloped/ Catchment (ac.) (ac.) (ac.) (ac.) (ac.) Conservation/public Developable 4h 46.4 2.8 4.2 8.2 3.0 1.2 27.0 4i 114.2 7.2 26.8 43.3 11.3 9.9 15.7 4j 38.0 2.3 0.2 33.5 2.0 0.0 0.0 4k 129.9 13.9 24.1 66.3 11.2 13.6 0.8 41 314.8 22.9 45.7 160.2 37.3 25.6 23.2 4m 38.4 3.7 8.6 16.3 1.7 8.1 0.0 5a 85.7 1.5 14.0 65.5 1.2 1.7 1.9 5b 54.8 2.6 1.9 17.8 9.5 23.0 0.0 5c 36.9 3.1 4.3 8.0 9.5 4.7 7.3 5d 61.4 1.8 17.9 34.4 2.4 1.8 3.1 6a 80.4 18.4 6.7 25.0 2.9 26.9 0.5 6b 14.6 3.6 1.3 5.7 0.0 4.0 0.0 6c 5.8 0.9 1.0 0.3 1.2 2.3 0.0 7a 19.6 3.4 2.0 4.6 3.1 6.4 0.0 7b 7.4 0.0 0.0 0.2 0.0 7.2 0.0 7c 48.5 16.5 3.1 5.8 0.7 22.4 0.0 7d 26.0 7.1 1.0 3.9 1.6 11.0 1.3 7e 18.8 1.4 0.5 13.0 0.1 3.9 0.0 7f 6.6 0.1 0.0 4.9 0.9 0.6 0.0 8a 70.8 13.7 4.2 11.7 0.9 40.1 0.2 8b 107.3 14.2 3.6 14.3 9.6 37.8 27.9 8c 61.9 12.3 6.3 18.4 3.3 21.2 0.5 8d 8.0 3.4 0.3 1.9 0.2 2.2 0.0 8e 2.7 0.6 0.0 1.1 0.0 0.9 0.0 8f 31.9 9.6 4.5 4.0 0.0 13.8 0.0 8g 13.9 3.1 0.9 3.3 0.2 5.6 0.8 8h 5.7 0.3 0.1 4.4 0.0 0.9 0.0 8i 50.6 4.7 8.3 30.1 0.4 6.6 0.4 8j 18.4 4.3 2.0 7.4 0.5 4.2 0.0 8k 32.6 2.8 4.3 13.8 8.4 3.0 0.2 9a 46.4 0.0 0.0 0.0 46.4 0.0 0.0 9b 137.7 34.6 16.2 33.5 1.3 52.0 0.0 9c 30.5 8.6 3.3 5.0 1.0 12.4 0.1 9d 39.0 13.6 1.0 2.0 0.1 22.2 0.0 9e 13.8 5.8 1.1 0.8 1.7 3.4 1.7 9f 108.8 24.2 16.3 11.5 7.7 35.2 21.4 9g 26.2 0.4 0.0 0.0 0.0 0.0 25.7 9h 39.9 7.4 0.5 6.6 0.0 25.4 0.0 9i 25.1 7.2 2.3 2.9 0.0 12.4 0.2 9j 99.6 16.3 6.3 35.0 13.2 28.7 0.0 9k 15.9 3.3 1.2 1.4 0.0 10.0 0.0 91 49.3 16.4 4.1 10.4 0.2 18.2 0.0 January 20191 553-2836-004 3-3 Ordinance 3219 Exhibit A Page 30 of 377 Stormwater Management Plan City of Port Townsend Table 3-1. Existing Land Cover (continued) Remaining Land Total Right-of-Way Vacant Area Open Unopened Developed Critical Areas Underdeveloped/ Catchment (ac.) (ac.) (ac.) (ac.) (ac.) Conservation/public Developable 9m 17.1 7.0 0.1 0.8 0.2 9.1 0.0 10a 103.9 24.7 6.3 15.1 12.0 45.7 0.1 10b 23.5 3.9 0.7 5.3 3.8 9.8 0.0 10c 51.0 2.2 1.3 0.0 1.0 46.5 0.0 10d 21.4 5.2 0.8 0.0 0.3 15.1 0.0 11a 72.1 2.0 9.8 41.2 14.9 3.5 0.7 11b 76.7 17.8 6.5 10.4 5.4 33.6 3.0 11c 28.8 5.5 1.5 7.4 6.8 7.7 0.0 11d 3.7 0.0 0.0 0.0 3.7 0.0 0.0 11e 26.7 4.4 1.5 4.7 9.3 6.2 0.6 11f 33.6 6.3 2.7 10.3 1.4 12.9 0.0 12a 86.6 32.9 3.8 4.4 2.0 43.5 0.1 12b 20.1 4.3 1.2 0.5 3.1 10.5 0.4 12c 26.9 10.9 0.5 0.4 1.6 13.4 0.1 12d 30.8 13.0 0.4 2.1 1.2 13.4 0.7 12e 13.5 3.6 0.4 0.6 1.3 6.7 0.9 12f 112.2 38.6 0.7 9.5 1.6 57.2 4.6 12g 14.3 2.0 0.1 1.3 0.5 10.5 0.0 13a 44.8 5.4 0.8 3.4 2.1 30.0 3.1 13b 51.9 15.9 1.1 4.1 1.6 24.5 4.6 13c 18.8 0.6 0.8 1.8 10.7 4.4 0.5 14 193.6 10.3 4.9 11.6 21.9 13.0 131.8 15a 131.7 5.1 7.8 77.8 30.1 10.9 0.0 15b 24.6 4.0 1.3 13.8 0.6 4.4 0.6 15c 24.0 1.3 0.3 12.0 2.3 4.2 3.8 16a 42.9 6.7 5.8 14.5 6.1 9.3 0.5 16b 62.7 8.3 5.4 22.5 6.6 19.9 0.0 16c 7.5 1.6 1.1 0.9 0.1 3.7 0.0 17a 53.7 7.0 5.5 34.1 0.7 6.4 0.0 17b 46.4 5.8 1.2 15.7 6.4 16.4 0.9 18a 141.6 5.0 4.4 105.0 15.1 12.1 0.0 18b 84.6 2.9 7.7 61.8 9.4 0.3 2.7 Table 3-2. Existing Land Use Model Inputs Pervious(ac.) Total Area Impervious Percent Hydrologic Soil Hydrologic Soil Hydrologic Soil Catchment (ac.) (ac.) Impervious Type A-Forest Type C-Forest Type D-Forest 1 12.8 0.00 0.0% 11.5 1.3 0.0 2 62.7 11.1 17.7% 35.1 16.5 0.0 3 19.1 0.01 0.1% 19.0 0.00 0.0 4a 46.5 0.00 0.0% 2.1 2.1 42.3 3-4 January 20191 553-2836-004 Ordinance 3219 Exhibit A Page 31 of 377 Stormwater Management Plan City of Port Townsend Table 3-2. Existing Land Use Model Inputs(continued) Pervious(ac.) Total Area Impervious Percent Hydrologic Soil Hydrologic Soil Hydrologic Soil Catchment (ac.) (ac.) Impervious Type A-Forest Type C-Forest Type D-Forest 4b 80.3 0.3 0.3% 66.8 11.80 1.4 4c 122.4 18.2 14.8% 47.9 53.35 2.9 4d 47.4 0.2 0.4% 16.3 22.0 8.9 4e 26.7 3.7 13.7% 17.7 3.6 1.8 4f 83.7 10.4 12.4% 40.1 32.5 0.8 4g 107.6 13.8 12.8% 27.1 66.7 0.0 4h 46.4 1.2 2.5% 32.8 12.4 0.0 4i 114.2 5.4 4.7% 87.3 21.6 0.0 4j 38.0 1.9 4.9% 10.7 25.5 0.0 4k 129.9 7.5 5.8% 107.1 15.3 0.0 41 314.8 15.1 4.8% 274.0 0.0 25.8 4m 38.4 2.8 7.3% 14.7 20.9 0.0 5a 85.7 1.0 1.2% 30.5 54.3 0.0 5b 54.8 4.3 7.9% 12.5 38.0 0.0 5c 36.9 2.7 7.4% 20.6 10.1 3.5 5d 61.4 1.3 2.1% 23.8 36.4 0.0 6a 80.4 13.8 17.2% 33.9 32.7 0.0 6b 14.6 2.3 16.0% 5.6 6.7 0.0 6c 5.8 0.9 14.7% 0.0 5.0 0.0 7a 19.6 2.5 12.9% 13.7 3.3 0.0 7b 7.4 1.5 20.2% 0.0 5.9 0.0 7c 48.5 11.5 23.7% 26.4 10.6 0.0 7d 26.0 5.6 21.5% 8.7 12.1 0.0 7e 18.8 1.5 8.1% 4.6 12.7 0.0 7f 6.6 0.2 3.1% 0.0 6.4 0.0 8a 70.8 10.5 14.9% 60.1 0.2 0.0 8b 107.3 11.0 10.3% 42.2 54.1 0.0 8c 61.9 10.2 16.4% 42.4 9.4 0.0 8d 8.0 2.1 26.6% 3.7 2.1 0.0 8e 2.7 0.6 21.4% 0.0 2.1 0.0 8f 31.9 6.0 18.7% 22.3 3.6 0.0 8g 13.9 2.1 15.0% 0.4 11.5 0.0 8h 5.7 1.2 21.4% 0.0 4.5 0.0 8i 50.6 3.6 7.1% 0.0 47.1 0.0 8j 18.4 3.6 19.7% 14.8 0.0 0.0 8k 32.6 2.1 6.5% 30.2 0.0 0.3 9a 46.4 0.0 0.0% 0.0 5.5 40.9 9b 137.7 23.5 17.1% 102.6 11.6 0.0 9c 30.5 5.6 18.3% 22.7 2.2 0.0 9d 39.0 9.4 24.2% 25.6 4.0 0.0 9e 13.8 3.2 23.1% 3.5 7.1 0.0 9f 108.8 16.1 14.8% 46.4 44.8 1.5 9g 26.2 7.2 27.6% 8.0 11.0 0.0 January 20191 553-2836-004 3-5 Ordinance 3219 Exhibit A Page 32 of 377 Stormwater Management Plan City of Port Townsend Table 3-2. Existing Land Use Model Inputs(continued) Pervious(ac.) Total Area Impervious Percent Hydrologic Soil Hydrologic Soil Hydrologic Soil Catchment (ac.) (ac.) Impervious Type A-Forest Type C-Forest Type D-Forest 9h 39.9 6.6 16.6% 33.3 0.0 0.0 9i 25.1 8.3 32.9% 0.0 16.9 0.0 9) 99.6 9.5 9.5% 90.2 0.0 0.0 9k 15.9 6.3 39.2% 9.5 0.2 0.0 91 49.3 9.0 18.2% 19.8 20.5 0.0 9m 17.1 13.3 77.9% 3.5 0.3 0.0 10a 103.9 11.5 11.0% 91.5 1.0 0.0 10b 23.5 4.6 19.7% 9.2 9.7 0.0 10c 51.0 6.1 12.0% 44.9 0.0 0.0 10d 21.4 2.3 10.7% 19.1 0.0 0.0 11a 72.1 9.6 13.3% 62.4 0.0 0.0 11b 76.7 8.6 11.2% 68.1 0.0 0.0 11c 28.8 2.9 10.0% 25.9 0.0 0.0 11d 3.7 1.1 30.6% 2.6 0.0 0.0 11e 26.7 6.0 22.3% 20.6 0.2 0.0 11f 33.6 13.7 40.9% 19.6 0.3 0.0 12a 86.6 15.5 17.9% 68.4 2.7 0.0 12b 20.1 6.1 30.3% 14.0 0.0 0.0 12c 26.9 8.1 30.0% 18.8 0.0 0.0 12d 30.8 6.0 19.5% 24.8 0.0 0.0 12e 13.5 15.21 112.7%1 -1.72 0.0 0.0 12f 112.2 17.5 15.6% 90.7 4.1 0.0 12g 14.3 5.5 38.6% 3.7 5.2 0.0 13a 44.8 9.3 20.7% 35.5 0.0 0.0 13b 51.9 8.1 15.5% 43.9 0.0 0.0 13c 18.8 6.0 32.0% 12.5 0.3 0.0 14.00 193.6 12.2 6.3% 161.7 19.7 0.0 15a 131.7 3.2 2.4% 102.4 25.3 0.8 15b 24.6 2.8 11.2% 15.3 6.6 0.0 15c 24.0 2.6 10.7% 12.5 9.0 0.0 16a 42.9 8.6 20.0% 34.3 0.0 0.0 16b 62.7 4.0 6.4% 58.7 0.0 0.0 16c 7.5 2.4 32.1% 5.1 0.0 0.0 17a 53.7 6.8 12.7% 46.9 0.0 0.0 17b 46.4 5.6 12.0% 40.8 0.0 0.0 18a 141.6 2.6 1.8% 119.8 19.2 0.0 18b 84.6 1.6 1.9% 83.0 0.0 0.0 1 The approach used to calculate existing impervious area resulted in an area larger than the basin.These numbers were adjusted to show the maximum area possible. 3-6 January 20191 553-2836-004 Ordinance 3219Exhibit A Page 33 of 377 Drainage Catchment Areas 0 4b Figure 8 4D 14 O 4a 4d 0 4h 4 o �1 Orr 4i 4m 4c . . oao V 00 4.f �o f b oo Sd • 6c; 19 Drainage Basins xi �r Q p o 5 O 18G 5a 7 5a Catchments - 13c C�3 Wetlands D, Gi, 8i _ _ � /a �b 7e 7 a Potential Wetlands 4k _� q ve.0 8b 1 -3 18 o a g �/ �� CityLIrTIItS °° 8d ® ° o 09 j 8b o 2 o ° ° 1 b 17a 8a 12 .�L.�8a-o' 99 9 d I b c e 1 � Ila g 9a a a E ° o 15 ° 9k o _ ° 1a q Q 15b ) 1m �b Ile- o o 15c 10 16c a � m E 0 0.25 0.5 0.75 1 LL Miles a 2019 Stormwater Management Plan Page 3 - 7 Ordinance 3219 Exhibit A Page 34 of 377 Ordinance 3219Exhibit A Page 35 of 377 Stormwater Management Plan City of Port Townsend I1_2 Future Land Use and Land Cover Existing land use, as described above, is used in runoff models to evaluate existing drainage conditions and needs and identify areas with potential stormwater impacts. Future land use, mainly in the form of new impervious surfaces and converted land cover, is used to predict future potential runoff impacts. Future potential impact areas are the focus of the SMP. The unopened rights-of-way and the "developable land" categories are where the potential runoff changes will occur. For planning purposes, potential land conversion estimates are made for full build- out to predict where impacts could occur which then point to the need for measures to minimize or manage those impacts. For unopened rights-of-way,the total potential conversion of land area is estimated to be 40 percent impervious, following the assumption used for existing opened rights-of-way in Section 3.1.1. Some of the unopened rights-of-way are located adjacent to public and conservation lands and may never be opened, resulting in an over-estimation of future imperviousness, thus the modeling results can be considered conservative. For vacant land, public and conservation lands are expected to remain pervious and undeveloped. Underdeveloped and remaining developable lands are assumed to be developed to their full, allowable potential.The estimated future fully developed impervious percentage is 37 percent, which was provided by City staff to use in runoff modeling.This is a typical approach in stormwater planning, although it has been found to overpredict actual development that occurs. Larger tracts that will construct new roads within new rights-of-way use an estimate of 37 percent future impervious (which is the same percent used for future developable land), while existing unopened rights-of-way will use 40 percent imperviousness.The 3 percent difference is small and is not expected to result in significantly different modeling outcomes. Land cover conversion will assume that the remaining uncovered pervious lands will be "pasture" (which includes lawns and non-forested open spaces; this is a modeling convention term) and or remain in part forest.The land cover is visually estimated from recent aerial photos. For the model it will be assumed that 50 percent of the forest in developable land will convert to pasture, and that pasture will remain pasture. The potential development and conversion to impervious surfaces described here are used to model and predict the highest potential for future impacts to the natural drainage ways, drainage systems, and existing wetlands. However, the reality is that runoff would be controlled to some extent at each site, with full control following the stormwater manual at larger sites and to the maximum extent practicable at small sites or individual platted lots.The amount of control or runoff reduction is catchment-specific, considering soils conditions and developable tract types. In the modeling results, if the potential for future impacts is found or exceeds thresholds, a closer catchment-specific analysis and adjustment may be made if the conservative assumptions (developable and underdeveloped lands developed to their full, allowable potential with no stormwater controls) result in an impact. Catchments that still could have impacts after these adjustments are applied may become candidates for regional control facilities. Existing Land Use is shown on Figure 9. Vacant lands and development potential are shown in Figure 10. Soils mapping and potential for good infiltration conditions are shown in Figure 7. Using this information, the estimates for future conditions for full buildout for the MGSFlood model are shown in Table 3-3. January 20191 553-2836-004 3-9 Ordinance 3219 Exhibit A Page 36 of 377 Ordinance 3219Exhibit A Page 37 of 377 Land-Use Figure 9 ❑❑❑❑a❑- o ❑❑ ❑ 14 ❑❑❑❑ ❑❑❑ Chinese =❑❑❑0❑❑❑ ❑D�❑ ❑i❑❑ 0❑❑❑ ❑Oa Gardens El' H o Elth St. Residential Districts L 0❑ R-I Min. 10,000 sq. ft. lot I TIT ° ❑❑❑❑ R-11 Min. 5,000 sq. ft. lot El El El El El El El El o p ❑❑❑❑❑❑❑❑❑❑ I ❑ ❑❑ ❑El ❑�- R-111 10 to 16 d.0 per 40,000 s.f. �� ° T❑❑❑ ❑�❑o❑ Oa o❑ ❑ (❑ o OHO R IV 15 to 24 d.0 per 40,000 s.f. �� ❑ ❑❑ �E ❑❑ a ❑ O❑ a = ❑❑000❑❑❑❑ -7n' 1:11:1 ❑ o ❑000❑ ❑ ❑❑❑❑❑°� �• ° Mixed Use Districts ❑❑❑❑❑_❑ ❑❑❑ ° �❑ og ❑ ❑ ❑ ... P' ❑ C-I/MU Neighborhood Mixed Use ❑❑�/❑❑ ❑ O ❑❑ ❑< ��00 �o CII/MU Community Mixed Use El El El� 000❑�❑❑]❑❑ __ ❑' Commercial Districts 0 0 0 0❑❑❑ _ ❑ q V ❑ ❑❑❑ �� ooE_::�U❑'� �FRI � O C-1 Neighborhood Commercial El EJ o 0 stirs sA Roo�j ❑o❑❑❑❑� �O❑ �O� �O�>" C-11 General Commercial C o o a o o❑ o o �❑0❑jam OODODOO' O C-I I(H) Hospital Commercial LiC-111 Historic Commercial a � 0 R � �C� ODOi► ! ° � DIJD �� ° a❑❑❑ ��0�-� � X0000 � a • 1 O ❑❑ 0 D ❑❑��°° �O� ��DOO � Marine-Related and Manufacturing Districts ❑❑❑❑❑1�❑❑❑❑ -❑ oD�� 0�� DO��®��0�� 0 0 0 �,� M C Commercial/ Light Manufacturing i0 ❑ �a❑❑o��o❑ O� �00 �O 0�-�® ❑0 El ❑ 0 � OOODOO��' M-I I(A) Marine Related Uses 0 a a 10 ❑❑❑ ❑❑ElLagoonO ^ O O M I I(B) Marine Related Uses ❑❑❑❑❑ ❑❑❑❑ O�❑❑❑❑❑� 1 th 8t ❑❑❑❑ 9 A �� D ❑EK]1� a�° °°❑0❑❑❑❑❑° ❑� 0❑0 �;��.' Public, Park and Open Space Districts 0 4 15 ❑® �Ln�� °°°°❑❑°D�� \ P/OS Existing Park or Open Space ❑l/I El El ❑■ ❑ P/OS(B) Public/ Mixed Use DDDR El El E❑❑❑ DO 10 w P-1 Public/ Infrastructure ❑D.l■ �� ❑❑❑■ o f.�■ I� Wetlands and Stormwater Basins ET Wetlands 0 0 0 ❑ �❑ ❑❑ Potential Wetlands a 19 Drainage Basins 0 0.25 0.5 0.75 1 LL Miles a 2019 Stormwater Management Plan Page 3 - 11 Ordinance 3219 Exhibit A Page 38 of 377 Vacant Lands & ° 1E ❑ Development Potential rim o❑ ❑ � "'�0 Figure 10 o m❑ [1014' .a H T 11 0 Chinese v� e❑❑❑ ❑e Gardens ❑ ❑❑ EEll' 00 m �' oo 1, o �❑ ❑� opo coq � ' P . a 0 o I ❑ D ❑ � i � e_ d a D I4 El � 0� ��i \ LI a °❑ ❑ �❑ 11-1 ❑SMlE❑ ' El o z ❑ ❑❑ Lb C❑ 0 tl4 ❑ ° • 0 --- -' ° Development ❑�❑ ❑ ��❑�� ; o��& ��o� ! Vacant & Underdeveloped ❑❑ �❑❑0 ` Cin ��° Residential Properties 11 Ell El oo �� .., 0: ,e'4 � � m Parks, Open-Space, & Cemeteries B ❑❑' � -�� _ moi—� IL�� ° � 'a_ , LLand Trust Properties ❑ o 0 ,. o m � Qo q� �' ° Developed Land $ oho �]�7❑❑ ❑ ❑� D 0 o oo m Zrs�__ _a_ , •� Udo zo .00 j o �, , m _ =000� 0El _ / gabL ,I � Features a o - o O L7 �! D IO ®'�A ° / r Drainage Basins ;e ° o❑ e � ` 9 9 El El 5JI , 0 m nn Jho❑�� ❑0❑ Catchments 110 A N u�❑9 ELI Slopes ® o � opes > 40% El El� ❑ e-a 4 El ❑ ❑ �� ❑❑ e _ Wetlands ❑mm o ❑❑Lh o o ❑ ❑ ao° Potential Wetlands ❑�� m �❑ ` ------E" ! - - LHH [TT 100 Year Flood /\ ❑ Critical Drainage Corridors 0❑ Q d ❑ F_ ' �_ ❑ P q Key Drainageways �El o o; ❑0 City Limits p , ,D] a � Elin E_ )l 0 0.25 0.5 0.75 1 �0 LL Miles a 2019 Stormwater Management Plan Page 3 - 12 Ordinance 3219 Exhibit A Page 39 of 377 Stormwater Management Plan City of Port Townsend Table 3-3. Future Land Use Model Inputs Pervious(ac.) Total Area Impervious Percent Hydrologic Soil Hydrologic Soil Hydrologic Soil Catchment (ac.) (ac.) Impervious Type A-Forest Type C-Forest Type D-Forest 1 12.8 0.1 7.6% 10.6 1.2 0.0 2 62.7 27.7 44.2% 23.8 11.2 0.0 3 19.1 0.00 0.1% 19.0 0.0 0.0 4a 46.5 0.1 0.3% 2.1 2.1 42.2 4b 80.3 0.1 1.2% 66.2 11.7 1.4 4c 122.4 30.7 25.1% 42.2 46.9 2.6 4d 47.4 0.2 0.5% 16.3 21.1 8.9 4e 26.7 8.9 33.3% 13.7 2.8 1.4 4f 83.7 35.8 42.8% 26.2 21.2 0.5 4g 107.6 41.6 38.7% 19.1 46.9 0.0 4h 46.4 6.3 13.7% 29.1 10.1 0.0 4i 114.2 36.5 31.9% 62.4 15.4 0.0 4j 38.0 14.4 37.7% 7.0 16.7 0.0 4k 129.9 48.1 37.0% 71.6 10.2 0.00 41 314.8 106.8 33.9% 190.2 0.0 17.9 4m 38.4 15.3 39.8% 9.5 13.6 0.0 5a 85.7 31.5 36.8% 19.5 34.7 0.0 5b 54.8 20.2 36.8% 8.6 26.0 0.0 5c 36.9 9.9 26.8% 16.3 7.1 2.8 5d 61.4 21.1 35.8% 15.6 23.9 0.0 6a 80.4 35.1 44.7% 22.6 21.9 0.0 6b 14.6 6.4 44.1% 3.8 4.4 0.0 6c 5.8 2.4 40.5% 0.0 3.5 0.0 7a 19.6 7.6 38.9% 9.6 2.3 0.0 7b 7.4 4.2 57.1% 0.0 3.2 0.0 7c 48.5 23.2 47.9% 18.0 7.3 0.0 7d 26.0 11.5 44.4% 5.8 8.6 0.0 7e 18.8 7.7 42.3% 2.9 8.0 0.0 7f 6.6 2.3 34.3% 0.0 4.3 0.0 8a 70.8 31.4 44.3% 39.3 0.2 0.0 8b 107.3 32.1 29.9% 32.1 42.3 0.0 8c 61.9 27.5 44.4% 28.2 6.3 0.0 8d 8.0 3.8 47.4% 2.7 1.5 0.0 8e 2.7 1.3 49.7% 0.0 1.4 0.0 8f 31.9 14.4 45.0% 15.1 2.5 0.0 3-13 January 2019 553-2836-004 Ordinance 3219 Exhibit A Page 40 of 377 Stormwater Management Plan City of Port Townsend Table 3-3. Future Land Use Model Inputs (continued) Pervious(ac.) Total Area Impervious Percent Hydrologic Soil Hydrologic Soil Hydrologic Soil Catchment (ac.) (ac.) Impervious Type A-Forest Type C-Forest Type D-Forest 8g 13.9 5.8 41.5% 0.3 7.9 0.0 8h 5.7 3.2 56.2% 0.0 2.5 0.0 8i 50.6 20.5 40.5% 0.0 30.1 0.0 8j 18.4 8.8 47.7% 9.6 0.0 0.0 8k 32.6 10.5 32.1% 21.9 0.0 0.2 9a 46.4 1.9 4.1% 0.0 5.3 39.2 9b 137.7 61.6 44.8% 68.3 7.7 0.0 9c 30.5 13.6 44.5% 15.5 1.5 0.0 9d 39.0 18.8 48.3% 17.5 2.7 0.0 9e 13.8 5.3 38.6% 2.8 5.7 0.0 9f 108.8 41.2 37.9% 33.9 32.7 1.1 9g 26.2 7.2 27.7% 7.1 10.1 0.0 9h 39.9 18.7 46.8% 21.2 0.0 0.0 9i 25.1 14.9 59.2% 0.0 10.2 0.0 9j 99.6 36.1 36.2% 63.6 0.0 0.0 9k 15.9 10.9 68.7% 4.9 0.1 0.0 91 49.3 21.2 43.0% 13.8 14.3 0.0 9m 17.1 17.0 99.5% 0.1 0.0 0.0 10a 103.9 37.3 35.9% 65.9 0.7 0.0 10b 23.5 10.5 44.6% 6.3 6.7 0.0 10c 51.0 23.9 46.8% 27.2 0.0 0.0 10d 21.4 8.2 38.4% 13.2 0.0 0.0 11a 72.1 31.4 43.6% 40.6 0.0 0.0 11b 76.7 27.8 36.2% 48.9 0.0 0.0 11c 28.8 9.4 32.7% 19.4 0.0 0.0 11d 3.7 1.2 30.7% 2.6 0.0 0.0 11e 26.7 11.5 42.9% 15.2 0.2 0.0 11f 33.6 23.4 69.7% 10.1 0.2 0.0 12a 86.6 34.9 40.3% 49.7 1.1 0.0 12b 20.1 10.9 54.1% 9.2 0.0 0.0 12c 26.9 13.5 50.3% 13.3 0.0 0.0 12d 30.8 11.1 38.8% 18.8 0.0 0.0 12e 13.5 13.5 100.0% 0.0 0.0 0.0 12f 112.2 42.5 37.9% 66.7 3.0 0.0 12g 14.3 9.9 69.1% 1.8 2.6 0.0 13a 44.8 22.2 49.5% 22.7 0.0 0.0 13b 51.9 19.1 36.8% 32.8 0.0 0.0 3-14 January 2019 553-2836-004 Ordinance 3219Exhibit A Page 41 of 377 Stormwater Management Plan City of Port Townsend Table 3-3. Future Land Use Model Inputs(continued) Pervious(ac.) Total Area Impervious Percent Hydrologic Soil Hydrologic Soil Hydrologic Soil Catchment (ac.) (ac.) Impervious Type A-Forest Type C-Forest Type D-Forest 13c 18.8 9.9 52.6% 8.7 0.2 0.0 14.00 193.6 23.6 12.2% 151.5 18.5 0.0 15a 131.7 40.3 30.6% 72.8 17.1 0.6 15b 24.6 10.1 40.9% 10.2 4.4 0.0 15c 24.0 8.7 36.2% 8.9 6.4 0.0 16a 42.9 20.3 47.1% 22.7 0.0 0.0 16b 62.7 22.1 35.2% 40.6 0.0 0.0 16c 7.5 4.6 61.2% 2.9 0.0 0.0 17a 53.7 24.1 44.9% 29.6 0.0 0.0 17b F 46.4 18.0 38.9% 28.3 0.0 0.0 18a 141.6 47.7 33.7% 80.9 13.0 0.0 18b 84.6 28.1 33.2% 56.5 0.0 0.0 3.1.3 Estimating Runoff Potential As described in previous sections, the City has: low rainfall depth and intensity when compared to elsewhere in western Washington, areas of relatively low runoff soils and land cover, and small catchments with poorly defined natural drainage paths. These factors converge to result in a relatively narrow range of peak flow rates, which often means that similar drainage infrastructure is needed in many different locations. Modeling the entire system would be costly; a generalized modeling approach can address much of the City's system need.To define this need and confirm the expectation that similar runoff results can be found across the city, some generalized runoff modeling was performed. The land cover conversion analysis results, previously described in this section, are input into the hydrologic model to find future peak runoff potential from the basin. The location at which this peak flow rate occurs is described as "key locations" in the drainage system. In some catchments, the peak flow rate is the entire runoff potential from the catchment, with no specific geographic location.An example would be in Catchment 1,which has runoff that generally flows toward the Strait of Juan de Fuca and discharges at multiple points. In the catchments where there is a defined location at which all of the runoff is directed, a "node" is defined as the specific location of the calculated peak flow rate, as shown on Figure 11.Table 3-4 lists the catchment area name, total catchment area in acres, percentage of existing and future impervious area, and distribution of land cover. Existing and future peak runoff for the 2-, 10-, 25-, and 100-year events were determined at the catchment nodes shown on Figure 11 (unless there is no node, which means that the peak runoff rate is total runoff potential from the entire basin). These modeling results will be used to define potentially impacted areas.The future peak flows for the 25-year event will be used to assess drainage conveyance needs in the roadway system, notably where the road drainage becomes the main flow path in the basin. The 25-year peak flows will be used to assess potential impacts from future development to CDCs and KDs as defined in Section 4.A comparison between existing (Table 3-5a) and future (Table 3-5b) conditions for selected events (2-, 10-, 25-, and 100-year storm events) is also used to assess wetland receiving waters, notably in Basins 4 through 9.The peak runoff modeling results for Existing and Future Conditions are shown in Tables 3-5a and Table 3-5b, respectively. January 20191 553-2836-004 3-15 Ordinance 3219 Exhibit A Page 42 of 377 Ordinance 3219Exhibit A Page 43 of 377 3 Catchment Nodes 4b Figure 11 4� 5g St. ineGar• 4d 0 4h 9 St. 4 4�n w 4c • 41 op 4f c� 7 17 CD O Catchment Nodes 1 Q p 5d 51 98� \ 5a � ••• 7 Features a a ce Catchments 7 7c k 8i Wetlands O 4 8 dq � 8 � � \ ve. (� o 19 0 g C:3 Potential Wetlands 11 stin s Ave. °° o ° c� a ° •. St 0�a�e o a \ 100 Year Flood 9 � � 8b 2 a p o 3 Critical Drainage Corridors ° 1 h 8a d > Key Drainageways 99 a) City Limits b c N g 2 9a 1 th St. �\ a x E ami o 4 � a 0 E Y D 15b 16 r 1 e ° 15c � 70 11 1 c 0 0.25 0.5 0.75 1 0 LL Miles a 2019 Stormwater Management Plan Page 3 - 17 Ordinance 3219 Exhibit A Page 44 of 377 Ordinance 3219 Exhibit A Page 45 of 377 Stormwater Management Plan City of Port Townsend Table 3-4. Buildable Area-Impervious Comparison Existing Impervious(ac.) Future Impervious(ac.) Total Area Buildable Total Impervious Buildable Total Impervious Catchment (ac.) ROW Area Percent ROW Area Percent 1 12.8 0.0 0.0 0.0% 1.0 0.0 7.6% 2 62.7 13.7 5.6 30.7% 15.8 20.0 57.2% 3 19.1 0.0 0.0 0.1% 0.0 0.0 0.1% 4a 46.5 0.0 0.0 0.0% 0.1 0.0 0.3% 4b 80.3 0.1 0.3 0.5% 0.2 0.9 1.3% 4c 122.4 15.0 7.8 18.7% 16.7 18.6 28.9% 4d 47.4 0.1 0.1 0.4% 0.1 0.1 0.5% 4e 26.7 4.6 1.6 23.2% 5.0 6.4 42.7% 4f 83.7 8.5 6.1 17.4% 9.6 30.4 47.7% 4g 107.6 17.5 5.7 21.5% 25.7 25.3 47.3% 4h 46.4 2.8 0.3 6.6% 4.5 3.7 17.7% 4i 114.2 7.2 2.6 8.6% 18.6 22.3 35.8% 4j 38.0 2.3 0.6 7.8% 2.4 13.0 40.7% 4k 129.9 13.9 1.7 12.0% 24.9 31.3 43.2% 41 314.8 22.9 5.6 9.1% 45.8 74.4 38.2% 4m 38.4 3.7 1.3 12.9% 7.2 10.3 45.4% 5a 85.7 1.5 0.3 2.1% 7.2 25.2 37.7% 5b 54.8 2.6 2.8 9.9% 3.4 17.9 38.8% 5c 36.9 3.1 1.4 12.1% 5.5 6.1 31.5% 5d 61.4 1.8 0.4 3.6% 9.1 13.8 37.3% 6a 80.4 18.4 6.3 30.6% 21.3 25.5 58.1% 6b 14.6 3.6 1.2 32.8% 4.2 4.7 60.8% 6c 5.8 0.9 0.5 23.2% 1.4 1.4 48.9% 7a 19.6 3.4 1.1 23.2% 4.4 5.2 49.2% 7b 7.4 0.0 1.1 15.5% 0.0 3.9 52.4% 7c 48.5 16.5 4.6 43.4% 17.8 15.0 67.6% 7d 26.0 7.1 2.5 36.6% 7.5 8.0 59.6% 7e 18.8 1.4 1.0 12.8% 1.6 7.2 47.0% 7f 6.6 0.1 0.2 4.2% 0.1 2.2 35.4% 8a 70.8 13.7 4.4 25.6% 15.4 23.6 55.0% 8b 107.3 14.2 5.9 18.7% 16.0 25.1 38.3% 8c 61.9 12.3 4.2 26.6% 14.9 18.9 54.6% 8d 8.0 3.4 0.5 48.0% 3.5 2.0 68.8% 8e 2.7 0.6 0.3 35.8% 0.6 1.1 64.1% 8f 31.9 9.6 2.6 38.3% 11.4 9.2 64.6% January 20191 553-2836-004 3-19 Ordinance 3219 Exhibit A Page 46 of 377 Stormwater Management Plan City of Port Townsend Table 3-4. Buildable Area-Impervious Comparison (continued) Existing Impervious(ac.) Future Impervious(ac.) Total Area Buildable Total Impervious Buildable Total Impervious Catchment (ac.) ROW Area Percent ROW Area Percent 8g 13.9 3.1 1.1 29.9% 3.5 4.4 56.5% 8h 5.7 0.3 1.1 25.2% 0.4 3.1 60.0% 8i 50.6 4.7 1.4 12.2% 8.1 15.0 45.7% 8j 18.4 4.3 1.3 30.0% 5.1 5.6 58.0% 8k 32.6 2.8 1.0 11.9% 5.0 7.3 37.5% 9a 46.4 0.0 0.0 0.0% 1.9 0.0 4.1% 9b 137.7 34.6 10.3 32.6% 41.1 41.9 60.3% 9c 30.5 8.6 2.5 36.2% 10.1 9.0 62.3% 9d 39.0 13.6 3.8 44.6% 14.0 12.8 68.7% 9e 13.8 5.8 0.7 47.0% 6.4 2.3 62.5% 9f 108.8 24.2 7.6 29.2% 32.0 24.9 52.3% 9g 26.2 0.4 6.7 27.2% 0.4 6.7 27.2% 9h 39.9 7.4 2.8 25.7% 7.6 14.6 55.8% 9i 25.1 7.2 5.9 52.5% 8.2 11.6 78.9% 9j 99.6 16.3 2.1 18.5% 19.3 25.7 45.2% 9k 15.9 3.3 4.9 51.4% 3.8 9.1 80.8% 91 49.3 16.4 2.7 38.8% 18.0 13.3 63.6% 9m 17.1 7.0 10.1 99.9% 7.1 13.7 121.5% 10a 103.9 24.7 2.5 26.2% 28.1 25.0 51.1% 10b 23.5 3.9 3.1 29.8% 4.2 8.7 54.8% 10c 51.0 2.2 2.3 8.9% 2.8 19.5 43.6% 10d 21.4 5.2 0.2 25.3% 5.5 5.8 52.9% 11a 72.1 2.0 8.1 14.1% 7.3 24.6 44.4% 11b 76.7 17.8 1.8 25.6% 20.7 18.1 50.6% 11c 28.8 5.5 0.0 19.0% 6.4 5.6 41.7% 11d 3.7 0.0 1.1 30.6% 0.0 1.1 30.7% 11e 26.7 4.4 3.8 30.8% 5.8 7.9 51.3% 11f 33.6 6.3 11.2 52.2% 7.4 19.8 81.0% 12a 86.6 32.9 4.3 42.9% 34.5 22.0 65.3% 12b 20.1 4.3 4.7 44.8% 5.0 8.8 68.5% 12c 26.9 10.9 4.1 55.9% 11.2 9.2 76.2% 12d 30.8 13.0 1.4 46.9% 13.2 7.2 66.2% 12e1 13.5 3.6 13.5 100.0% 3.8 16.6 151.6% 12f 112.2 38.6 1.5 35.7% 38.9 26.2 58.0% 12g 14.3 2.0 4.3 44.5% 2.1 8.7 74.9% 13a 44.8 5.4 5.5 24.3% 5.9 17.9 53.0% 3-20 January 2019 553-2836-004 Ordinance 3219 Exhibit A Page 47 of 377 Stormwater Management Plan City of Port Townsend Table 3-4. Buildable Area-Impervious Comparison (continued) Existing Impervious(ac.) Future Impervious(ac.) Total Area Buildable Total Impervious Buildable Total Impervious Catchment (ac.) ROW Area Percent ROW Area Percent 13b 51.9 15.9 0.9 32.5% 16.4 11.5 53.8% 13c 18.8 0.6 5.9 34.7% 2.2 8.2 55.4% 14.00 193.6 10.3 0.9 5.8% 12.5 10.0 11.7% 15a 131.7 5.1 0.3 4.1% 9.5 33.1 32.3% 15b 24.6 4.0 0.2 17.1% 4.6 7.0 46.8% 15c 24.0 1.3 1.6 12.4% 1.5 7.6 37.9% 16a 42.9 6.7 4.6 26.3% 9.5 13.4 53.4% 16b 62.7 8.3 0.5 14.1% 10.6 16.2 42.9% 16c 7.5 1.6 2.1 48.8% 2.0 3.8 77.9% 17a 53.7 7.0 3.8 20.1% 9.3 18.7 52.2% 17b 46.4 5.8 2.6 18.0% 6.4 14.4 44.9% 18a 141.6 5.0 0.5 3.9% 6.7 43.9 35.7% 18b 84.6 2.9 0.0 3.4% 6.5 23.0 34.8% 1 Impervious area and impervious percent were changed to full basin area. January 20191 553-2836-004 3-21 Ordinance 3219 Exhibit A Page 48 of 377 Ordinance 3219 Exhibit A Page 49 of 377 Stormwater Management Plan City of Port Townsend Table 3-5a. Peak Runoff at Nodes or for Total Catchment-Existing' Existing Runoff(cfs) Storm Event Basin 1 Basin 2 Basin 3 Basin 4a Basin 4b Basin 4c Basin 4d Basin 4e Basin 4f Basin 4g Basin 4h Basin 4i Basin 4j JL Basin 4k Basin 41 Basin 4m jL Basin 5a Basin 5b Basin 5c Basin 5d 2-Year 0.02 2.25 0.06 0.01 0.23 3.68 0.08 0.78 2.12 2.77 0.30 1.32 0.40 1.83 3.70 0.60 0.24 0.82 0.53 0.28 10-Year 0.11 3.45 0.30 0.01 1.13 5.65 0.33 1.19 3.24 4.24 0.72 2.35 0.61 3.10 7.13 0.92 0.45 1.26 0.85 0.47 25-Year 0.15 3.94 0.43 0.02 1.65 6.56 0.50 1.41 3.84 4.57 1.09 3.54 0.75 4.63 10.80 1.10 0.61 1.41 0.97 0.57 100-Year 0.20 4.65 0.56 0.09 2.12 7.76 0.62 1.68 4.55 5.43 1.22 3.77 0.90 4.98 11.34 1.31 0.98 1.78 1.18 0.89 Storm Event Basin 6a Basin 6b Basin 6c Basin 7a Basin 7b Basin 7c Basin 7d Basin 7e Basin 7f Basin 8a Basin 8b Basin 8c Basin 8d Basin Be Basin 8f Basin 8g Basin 8h Basin 8i Basin 8j Basin 8k 2-Year 2.62 0.44 0.16 0.54 0.23 2.32 1.11 0.31 0.04 2.25 2.24 2.10 0.43 0.11 1.21 0.41 0.24 0.71 0.74 0.49 10-Year 4.05 0.68 0.26 0.83 0.34 3.54 1.70 0.48 0.06 3.44 3.43 3.20 0.65 0.17 1.85 0.62 0.36 1.06 1.13 0.82 25-Year 4.86 0.78 0.30 1.00 0.36 3.90 1.84 0.54 0.07 4.20 4.06 3.80 0.70 0.18 2.19 0.66 0.39 1.13 1.35 1.21 100-Year 5.67 0.96 0.35 1.19 0.41 4.63 2.15 0.64 0.07 5.03 4.82 4.51 0.83 0.20 2.59 0.75 0.44 1.27 1.60 1.32 Storm Event Basin 9a Basin 9b Basin 9c Basin 9d Basin 9e Basin 9f Basin 9g Basin 9h Basin 9i Basin 9j Basin 9k Basin 91 Basin 9m Basin 10a Basin 10b Basin 10c Basin 10d Basin 11a Basin 11b Basin 11c 2-Year 0.01 4.90 1.15 1.91 0.63 3.26 1.44 1.42 1.63 2.07 1.25 1.81 2.63 2.44 0.94 1.31 0.49 2.05 1.84 0.62 10-Year 0.02 7.53 1.75 2.93 0.97 5.01 2.19 2.17 2.44 3.20 1.91 2.76 3.97 3.75 1.43 2.00 0.76 3.14 2.82 0.95 25-Year 0.02 8.86 2.08 3.29 1.05 5.91 2.37 2.58 2.61 4.48 2.06 3.03 4.25 4.95 1.58 2.55 1.03 3.90 3.75 1.30 100-Year 0.19 10.54 2.47 3.89 1.20 7.00 2.73 3.07 2.92 5.22 2.42 3.59 4.79 5.95 1.88 3.07 1.22 4.67 4.50 1.54 Storm Event Basin 11d Basin 11e Basin 11f Basin 12a Basin 12b Basin 12c Basin 12d Basin 12e Basin 12f Basin 12g Basin 13a Basin 13b Basin 13c Basin 14 Basin 15a Basin 15b Basin 15c Basin 16a Basin 16b Basin 16c 2-Year 0.23 1.21 2.74 3.24 1.23 1.63 1.24 1.29 3.72 1.09 1.88 1.72 1.22 2.91 0.82 0.59 0.55 1.75 0.98 0.49 10-Year 0.35 1.86 4.19 5.00 1.88 2.49 1.89 1.97 5.70 1.67 2.89 2.63 1.85 4.90 2.04 0.90 0.84 2.68 1.68 0.74 25-Year 0.39 2.16 4.53 5.87 2.07 2.75 2.24 2.13 6.83 1.79 3.37 3.17 2.01 7.29 3.09 1.09 0.99 3.18 2.51 0.81 100-Year 0.46 2.56 5.28 6.98 2.46 3.26 2.66 2.41 8.15 2.04 3.98 3.79 2.39 7.90 3.47 1.31 1.18 3.77 2.70 0.96 Storm Event Basin 17a Basin 17b Basin 18a Basin 18b 2-Year 1.46 1.19 0.78 0.50 10-Year 2.23 1.82 2.29 1.52 25-Year 2.86 2.34 3.48 2.30 100-Year 3.43 2.82 4.10 2.75 'Note:The peak rates shown are for the total runoff generated by the catchment only.The actual peaks at the nodes that include upstream accumulated and routed drainage are not included in this table. January 20191 553-2836-004 3-23 Ordinance 3219Exhibit A Page 50 of 377 Stormwater Management Plan City of Port Townsend Table 3-5b. Peak Runoff at Nodes or for Total Catchment-Future' Future Runoff(Full Buildout,cfs) Storm Event Basin 1 Basin 2 Basin 3 Basin 4a Basin 4b Basin 4c Basin 4d Basin 4e Basin M Basin 4g Basin 4h Basin 4i Basin 4j Basin 4k Basin 41 Basin 4m Basin 5a Basin 5b Basin 5c Basin 5d 2-Year 0.21 4.39 0.06 0.01 0.27 5.65 0.08 1.41 6.11 6.20 0.73 4.14 0.42 4.80 10.14 1.84 1.39 2.52 1.31 1.75 10-Year 0.32 6.71 0.30 0.01 1.16 8.60 0.34 2.14 9.37 9.45 1.13 6.36 0.64 7.33 15.51 2.82 2.14 3.90 2.01 2.69 25-Year 0.39 7.27 0.43 0.02 1.74 9.32 0.50 2.35 10.07 10.14 1.59 7.45 0.77 8.71 18.52 3.05 2.56 4.42 2.25 3.01 100-Year 0.47 8.38 0.56 0.09 2.17 11.09 0.62 2.79 11.55 11.54 1.84 8.81 0.92 10.33 22.10 3.53 3.00 5.57 2.84 3.80 Storm Event Basin 6a Basin 6b Basin 6c Basin 7a Basin 7b Basin 7c Basin 7d Basin 7e Basin 7f Basin 8a Basin 8b Basin 8c Basin 8d Basin 8e Basin 8f Basin 8g Basin 8h Basin 8i Basin 8j Basin 8k 2-Year 5.03 0.82 0.42 1.19 0.75 4.17 1.99 0.63 0.08 5.42 5.34 4.14 0.61 0.18 2.56 0.90 0.32 1.85 1.22 1.11 10-Year 7.76 1.26 0.64 1.81 1.13 6.40 3.03 0.96 0.13 8.27 8.16 6.32 0.94 0.27 3.91 1.35 0.48 2.77 1.86 1.71 25-Year 8.69 1.41 0.72 1.95 1.20 6.88 3.25 1.04 _0.14 8.94 8.83 6.83 1.01 0.29 4.24 1.44 0.51 2.96 2.02 2.02 100-Year 10.94 1.78 0.91 2.32 1.34 7.88 3.70 1.20 0.15 10.51 10.24 8.04 1.16 0.32 4.90 1.62 0.57 3.31 2.40 2.40 Storm Event Basin 9a Basin 9b Basin 9c Basin 9d Basin 9e Basin 9f Basin 9g Basin 9h Basin 9i Basin 9j Basin 9k Basin 91 Basin 9m Basin 10a Basin 10b Basin 10c Basin 10d Basin 11a Basin 11b Basin 11c 2-Year 0.01 9.86 2.34 3.58 1.00 7.36 1.44 3.24 2.72 4.68 2.06 3.42 3.31 6.42 1.69 4.73 1.65 3.28 4.84 1.35 10-Year 0.02 15.05 3.57 5.48 1.52 11.25 2.20 4.95 4.08 7.18 3.13 5.25 4.96 9.76 2.58 7.24 2.51 5.03 7.37 2.07 25-Year 0.02 16.26 3.86 5.90 1.63 12.18 2.38 5.35 4.35 8.25 3.35 5.64 5.29 10.66 2.78 7.81 2.71 5.80 8.06 2.37 100-Year 0.19 19.12 4.51 6.78 1.85 14.08 2.73 6.25 4.88 9.73 3.81 6.46 5.93 12.66 3.20 8.98 3.19 6.85 9.57 2.79 Storm Event Basin 11d Basin 11e Basin 11f Basin 12a Basin 12b Basin 12c Basin 12d Basin 12e Basin 12f Basin 12g Basin 13a Basin 13b Basin 13c Basin 14 Basin 15a Basin 15b Basin 15c Basin 16a Basin 16b Basin 16c 2-Year 0.23 1.94 3.87 6.66 2.11 2.65 2.24 2.07 7.81 1.86 4.14 3.55 1.83 4.11 2.47 1.01 0.86 2.98 2.77 0.84 10-Year 0.35 2.97 5.92 10.16 3.24 4.06 3.42 3.10 11.95 2.81 6.34 5.41 2.80 6.33 3.79 1.55 1.32 4.56 4.26 1.28 25-Year 0.39 3.21 6.34 10.98 3.47 4.37 3.70 3.33 12.90 3.00 6.84 5.85 3.02 8.63 4.96 1.74 1.48 4.92 4.99 1.37 100-Year 0.46 3.80 7.23 12.87 3.98 5.02 4.37 3.72 15.29 3.38 7.86 6.96 3.46 10.25 5.97 2.06 1.75 5.84 5.91 1.57 Storm Event Basin 17a Basin 17b Basin 18a Basin 18b 2-Year 2.33 2.47 2.06 1.29 10-Year 3.58 3.79 3.45 2.19 25-Year 4.21 4.24 5.11 3.28 100-Year 4.99 5.02 5.57 3.52 'Note:The peak rates shown are for the total runoff generated by the catchment only.The actual peaks at the nodes that include upstream accumulated and routed drainage are not included in this table. 3-24 January 2019 1 553-2836-004 Ordinance 3219 Exhibit A Page 51 of 377 Stormwater Management Plan City of Port Townsend Catchments with Largest Increase Potential The existing and future peak runoff determined in Table 3-5a and Table 3-5b above provide an indicator of where the highest potential impacts could occur or where there are priorities for further evaluation or improvements. Table 3-6 shows the peak 25-year runoff rates under existing and future conditions and the percent change. The highest potential changes shown can provide a basis for prioritizing other improvements that may be identified in Section 4. Table 3-6. Potential Change in Peak Flows by Catchment Area Existing Peak 25-year Future Peak 25-year Rank(highest Catchment Number Flow(cfs) Flow(cfs) Percent Change change) 1 0.2 0.4 160% 10 2 3.9 7.3 84% 33 3 0.4 0.4 0% 82 4a 0.0 0.0 0% 83 4b 1.7 1.7 5% 77 4c 6.6 9.3 42% 72 4d 0.5 0.5 2% 79 4e 1.4 2.3 67% 52 4f 3.8 10.1 162% 8 4g 4.6 10.1 122% 13 4h 1.1 1.6 45% 69 4i 3.5 7.4 111% 19 4j 0.7 0.8 3% 78 4k 4.6 8.7 88% 29 41 10.8 18.5 71% 46 4m 1.1 3.0 177% 6 5a 0.6 2.6 317% 2 5b 1.4 4.4 214% 4 5c 1.0 2.3 133% 12 5d 0.6 3.0 427% 1 6a 4.9 8.7 79% 42 6b 0.8 1.4 81% 39 6c 0.3 0.7 140% 11 7a 1.0 2.0 96% 25 7b 0.4 1.2 233% 3 7c 3.9 6.9 76% 44 7d 1.8 3.3 77% 43 7e 0.5 1.0 90% 27 7f 0.1 0.1 106% 22 8a 4.2 8.9 113% 18 8b 4.1 8.8 117% 15 8c 3.8 6.8 80% 40 8d 0.7 1.0 43% 70 January 20191 553-2836-004 3-25 Ordinance 3219 Exhibit A Page 52 of 377 Stormwater Management Plan City of Port Townsend Table 3-6. Potential Change in Peak Flows by Catchment Area (continued) Existing Peak 25-year Future Peak 25-year Rank(highest Catchment Number Flow(cfs) Flow(cfs) Percent Change change) 8e 0.2 0.3 59% 56 8f 2.2 4.2 93% 26 8g 0.7 1.4 118% 14 8h 0.4 0.5 31% 74 8i 1.1 3.0 162% 9 8) 1.3 2.0 50% 62 8k 1.2 2.0 67% 51 9a 0.0 0.0 0% 84 9b 8.9 16.3 84% 36 9c 2.1 3.9 86% 32 9d 3.3 5.9 79% 41 9e 1.0 1.6 55% 60 9f 5.9 12.2 106% 21 9g 2.4 2.4 0% 81 9h 2.6 5.4 108% 20 9i 2.6 4.4 67% 50 9) 4.5 8.2 84% 35 9k 2.1 3.4 63% 54 91 3.0 5.6 86% 31 9m 4.2 5.3 25% 75 10a 4.9 10.7 115% 16 10b 1.6 2.8 76% 45 10c 2.6 7.8 206% 5 10d 1.0 2.7 164% 7 11a 3.9 5.8 49% 65 11b 3.8 8.1 115% 17 11c 1.3 2.4 82% 37 11d 0.4 0.4 0% 80 11e 2.2 3.2 48% 66 11f 4.5 6.3 40% 73 12a 5.9 11.0 87% 30 12b 2.1 3.5 67% 49 12c 2.7 4.4 59% 57 12d 2.2 3.7 65% 53 12e 2.1 3.3 56% 59 12f 6.8 12.9 89% 28 12g 1.8 3.0 68% 48 13a 3.4 6.8 103% 23 13b 3.2 5.8 84% 34 13c 2.0 3.0 50% 64 14 7.3 8.6 18% 76 15a 3.1 5.0 61% 55 15b 1.1 1.7 59% 58 3-26 January 20191 553-2836-004 Ordinance 3219Exhibit A Page 53 of 377 Stormwater Management Plan City of Port Townsend Table 3-6. Potential Change in Peak Flows by Catchment Area (continued) Existing Peak 25-year Future Peak 25-year Rank(highest Catchment Number Flow(cfs) Flow(cfs) Percent Change change) 15c 1.0 1.5 50% 63 16a 3.2 4.9 55% 61 16b 2.5 5.0 99% 24 16c 0.8 1.4 70% 47 17a 2.9 4.2 47% 67 17b 2.3 4.2 81% 38 18a 3.5 5.1 47% 68 18b 2.3 3.3 42% 71 3.2 Stormwater System Operation and Maintenance Proper operation and maintenance of the stormwater system is necessary to prolong life and effectiveness of the system as well as reduce the potential for flooding and improve water quality.There are several sources and guidelines as well as direct experience used to develop the City's stormwater practices. Ecology provides guidance on best management practices (BMPs)for municipal operations in the Stormwater Management Manual for Western Washington (SWMMWW).This manual was developed in response to federal requirements and tailored to conditions in the Pacific Northwest. Below are the recommended BMPs from the SWMMWW the City of Port Townsend uses for guidance for stormwater system maintenance. • Maintenance of Public and Private Utility Corridors and Facilities • Maintenance of Roadside Ditches • Maintenance of Stormwater Drainage and Treatment Systems • Spills of Oil and Hazardous Substances • Urban Streets • Recommendations for Management of Street Wastes. The operation and maintenance of the stormwater system is funded by a stormwater utility fund and includes 3.55 full time equivalents (FTEs) distributed amongst several employees. This number is likely to increase as the stormwater system is extended or enhanced, increasing the need for maintenance. January 20191 553-2836-004 3-27