6-Attachment E-Stormwater ComprehensivePlan 2020.pdf

CITY OF OAK HARBOR

ISLAND COUNTY WASHINGTON

COMPREHENSIVE STORMWATER PLAN

G&O #16625

MARCH 2020

i

TABLE OF CONTENTS

CHAPTER 1 – INTRODUCTION

PURPOSE ........................................................................................................................... 1-2

Authorization ....................................................................................................... 1-2

GOALS .............................................................................................................................. 1-3

CHAPTER 2 – DRAINAGE AREA CHARACTERISTICS

LOCATION ......................................................................................................................... 2-1

TOPOGRAPHY .................................................................................................................... 2-1

CLIMATE ........................................................................................................................... 2-2

WATERWAYS AND WATERBODIES .................................................................................... 2-2

TIDAL DATA ..................................................................................................................... 2-3

SOILS ................................................................................................................................ 2-3

CRITICAL AREAS ............................................................................................................... 2-4

Frequently Flooded Areas .................................................................................... 2-5

Wetlands .............................................................................................................. 2-5

Critical Aquifer Recharge Areas .......................................................................... 2-6

Fish and Wildlife Habitat Conservation Areas .................................................... 2-6

Geological Hazard Areas ..................................................................................... 2-6

Garry Oak Tree Protection ................................................................................... 2-7

ZONING AND LAND USE .................................................................................................... 2-7

DRAINAGE BASINS ............................................................................................................ 2-9

CHAPTER 3 – STORMWATER SYSTEM ANALYSIS

INTRODUCTION ................................................................................................................. 3-1

EXISTING STORMWATER CONVEYANCE SYSTEM .............................................................. 3-1

IDENTIFIED STORMWATER CONVEYANCE PROBLEMS ....................................................... 3-1

HYDROLOGIC MODEL ....................................................................................................... 3-2

HYDRAULIC MODEL ......................................................................................................... 3-2

Design Storm ....................................................................................................... 3-2

MODELING RESULTS AND SYSTEM DEFICIENCIES ............................................................. 3-3

Upper Dry Creek .................................................................................................. 3-3

UDC-1: Undersized Stormwater Pipes Along North Oak Harbor

Street .................................................................................................. 3-3

UDC-2/UDC-4: Flooding at NE 7th Avenue and NE Ellis ..................... 3-4

UDC-3: Retrofit Flow Control/Treatment Project at NE Goldie

Street and Easy Street ........................................................................ 3-4

Midway ................................................................................................................ 3-5

M-1: Stormwater Infrastructure Along NE Ronhaar Street and NE

6th Avenue .......................................................................................... 3-5

M-2: Undersized Pipe Along NE 7th Avenue ......................................... 3-5

M-3: Undersized Stormwater Pipes Along SE 4th Avenue, SE

5th Avenue, and SE Ely Street ............................................................ 3-5

M-4: Corrugated Stormwater Pipe Restricting Flow North of

Home Depot (South Cabot Drive) ..................................................... 3-6 ii

M-5: Undersized Pipe Along SE Bayshore Drive .................................. 3-6

M-6: Flooding at SW Bayshore Drive and SW Beeksma Drive ............ 3-6

M-7: SE City Beach Outfall Clogging .................................................... 3-7

High School ......................................................................................................... 3-7

HS-1: Corrugated and Undersized Stormwater Pipe Along West

Whidbey Avenue ............................................................................... 3-7

Oak Prairie ........................................................................................................... 3-7

OP-1: Corrugated Stormwater Pipe Restricting Flow Along SE

Pasek Street ........................................................................................ 3-7

OP-2: Retrofit Treatment Vault at SE Pasek Street and Pioneer Way ... 3-7

Dry Creek ............................................................................................................. 3-8

DC-1: Flooding Near SW 6th Avenue ..................................................... 3-8

DC-2: Flooding Near Oak Harbor Street and SW 6th Avenue ................ 3-8

DC-3: Undersized Stormwater Pipe Along Oak Harbor Street .............. 3-8

DC-4: Freund Marsh Regional Treatment Facility ................................. 3-9

Golf Course .......................................................................................................... 3-9

GC-1: Undersized Culvert at West Fort Nugent Road and Loer’s

Pond ................................................................................................... 3-9

Freund Marsh ....................................................................................................... 3-9

FM-1: Road Runoff Drainage to Scenic Heights Trailhead Area ........... 3-9

Eagle Vista ........................................................................................................... 3-9

ADDITIONAL DRAINAGE CONCERNS ............................................................................... 3-10

Predevelopment Flow Requirements ................................................................. 3-10

Detention Exempt Areas Upstream of Over Capacitated Areas ........................ 3-10

Golf Course Basin .............................................................................................. 3-10

Low Impact Development (LID) ....................................................................... 3-11

CHAPTER 4 – WATER QUALITY

INTRODUCTION ................................................................................................................. 4-1

HISTORICAL WATER QUALITY DATA ................................................................................ 4-1

Nationwide Urban Runoff Program (NURP) ...................................................... 4-1

National Water Quality Inventory ....................................................................... 4-2

Clean Water Act, Section 303d ............................................................................ 4-3

WATER QUALITY STANDARDS .......................................................................................... 4-3

Parameters of Concern ......................................................................................... 4-4

Dissolved Oxygen .................................................................................... 4-4 pH ............................................................................................................ 4-5

Temperature ............................................................................................. 4-5

Turbidity .................................................................................................. 4-5

Nutrients ................................................................................................... 4-5

Pathogens/Bacteria ................................................................................... 4-6

Oil and Grease.......................................................................................... 4-6

Total Suspended Solids ............................................................................ 4-6

Heavy Metals ........................................................................................... 4-7

Toxic Organic Compounds ...................................................................... 4-7

Organic Material ...................................................................................... 4-7 iii

Criteria ................................................................................................................. 4-7

Sources of Nonpoint Pollutants ......................................................................... 4-10

Urban Development ............................................................................... 4-10

Highways and Roads.............................................................................. 4-11

Domestic Activities ................................................................................ 4-12

Additional Pollutant Sources ................................................................. 4-12

Water Quality Control: Source Control vs. Treatment ......................... 4-12

Structural Quality Control.................................................................................. 4-13

Biofiltration ............................................................................................ 4-13

Wet Pools ............................................................................................... 4-13

Media Filtration ..................................................................................... 4-14

Oil/Water Separation ............................................................................. 4-14

Regional Treatment Facility .................................................................. 4-15

CHAPTER 5 – OPERATION AND MAINTENANCE

FACILITY OPERATION AND MAINTENANCE PROGRAM ...................................................... 5-1

MAINTENANCE STANDARDS ............................................................................................. 5-2

Infiltration Ponds ................................................................................................. 5-2

Street Sweeping ................................................................................................... 5-2

Catch Basin Cleaning ........................................................................................... 5-3

Pipe Cleaning ....................................................................................................... 5-3

Open Ditch Mowing and Cleaning ...................................................................... 5-3

Detention System Cleaning.................................................................................. 5-4

Culverts ................................................................................................................ 5-4

RECOMMENDED MAINTENANCE PROGRAM ...................................................................... 5-4

Staff Requirements............................................................................................... 5-8

Equipment Needs ................................................................................................. 5-8

Inspection ............................................................................................................. 5-8

Staff Training ....................................................................................................... 5-8

Enforcement ......................................................................................................... 5-9

PUBLIC EDUCATION AND OUTREACH ................................................................................ 5-9

Best Management Practices (BMPs) ................................................................. 5-10

Phase II NPDES Permit Related Activities ....................................................... 5-12

CHAPTER 6 – CAPITAL IMPROVEMENT PLAN

INTRODUCTION ................................................................................................................. 6-1

CAPITAL IMPROVEMENT PROJECTS ................................................................................... 6-1

Upper Dry Creek Projects .................................................................................... 6-2

UDC-1: Stormwater Pipe Replacement (North Oak Harbor Street) ....... 6-2

UDC-2: Stormwater Pipe Replacement (NE 7th Avenue and

NE Ellis)............................................................................................. 6-3

UDC-3: Conveyance, Flow Control and Treatment Improvements in the

Vicinity of Goldie Street, Koetje Street, and Easy Street .................. 6-3

UDC-4: 7th Avenue Wetland BMP Study ............................................... 6-3

Midway Projects .................................................................................................. 6-4 iv

M-1: New Stormwater Infrastructure (NE Ronhaar Street and NE

6th Avenue) ......................................................................................... 6-4

M-2: Stormwater Pipe Replacement (NE 7th Avenue) .......................... 6-4

M-3: Stormwater Pipe Replacement (SE 4th Avenue, SE 5th Avenue, SE Ely Street) ..................................................................................... 6-4

M-4: Replace Corrugated Stormwater Pipe (South of Cabot Drive) ...... 6-5

M-5: Stormwater Pipe Replacement (SE Bayshore Drive) .................... 6-5

M-6: Pump Station with Treatment Vault (SW Bayshore Drive and

SW Beeksma Drive) .......................................................................... 6-6

M-7: Extend Outfall at SE City Beach ................................................... 6-6

High School Basin Projects ................................................................................. 6-7

HS-1: Stormwater Pipe Replacement (West Whidbey Avenue) ............ 6-7

Oak Prairie Projects ............................................................................................. 6-7

OP-1: Stormwater Pipe Replacement (SE Pasek Street) ........................ 6-7

OP-2: Retrofit Treatment Vault (SE Pasek Street and Pioneer Way) ..... 6-8

Dry Creek Projects ............................................................................................... 6-8

DC-1: Flow Control Facility and Stormwater Pipe Replacement

(SW 6th Avenue) ................................................................................ 6-8

DC-2: Flow Control Facility (Oak Harbor Street and SW 6th Avenue) .. 6-9

DC-3: Stormwater Pipe Replacement (Oak Harbor Street) .................... 6-9

DC-4: Freund Marsh Regional Constructed Wetland ........................... 6-10

Golf Course Projects .......................................................................................... 6-10

GC-1: Culvert Replacement (West Fort Nugent Road/Loer’s Pond) ... 6-10

Freund Marsh Projects ....................................................................................... 6-11

FM-1: Catch Basin Replacement/Drainage Analysis ........................... 6-11

Retrofit Projects ................................................................................................. 6-11

RET-1: Future Retrofit Project ............................................................. 6-11

CAPITAL IMPROVEMENT PLAN ........................................................................................ 6-11

CHAPTER 7 – FINANCIAL ANALYSIS

FINANCIAL PLAN .............................................................................................................. 7-1

Current Charges and Connections ....................................................................... 7-1

Service Charge Determination ............................................................................. 7-2

Preliminary Rate Analysis ................................................................................... 7-3

FUNDING ALTERNATIVES .................................................................................................. 7-9

Service Connection Charge .................................................................................. 7-9

Grant and Loan Programs .................................................................................... 7-9

Public Works Trust Fund ......................................................................... 7-9

Department of Ecology Water Quality Combined Funding Program ..... 7-9

Debt Financing ................................................................................................... 7-10 v

LIST OF TABLES

No. Table Page

2-1 Average Monthly Climate Data ........................................................................... 2-2

2-2 Soil Characteristics .............................................................................................. 2-4

2-3 Land Use .............................................................................................................. 2-8

3-1 Cumulative Rainfall for Design Storms ............................................................... 3-2

3-2 Recommended Upgrades Along SE 4th Avenue, SE 5th Avenue, and SE

Ely Street ........................................................................................................ 3-5

4-1 303(d) Categories for Water Bodies In or Tributary to Oak Harbor ................... 4-3

4-2 Water Quality Criteria for Marine Surface Water (WAC 173-201A-210) .......... 4-9

4-3 Freund Marsh Treatment Options ...................................................................... 4-16

4-4 Freund Marsh Water Quality Treatment Flow Rates and Volume .................... 4-19

5-1 Inventory of Stormwater Facilities ...................................................................... 5-5

5-2 Annual Maintenance Expenses ............................................................................ 5-6

5-3 Sample Phase II Audit Items Requested by Ecology......................................... 5-14

6-1 Stormwater Pipe Replacements (North Oak Harbor Street) ................................ 6-2

6-2 Stormwater Pipe Replacements (NE 7th Avenue and NE Ellis) .......................... 6-3

6-3 Stormwater Pipe Replacements (NE 7th Avenue) ................................................ 6-4

6-4 Stormwater Pipe Replacements (SE 4th Avenue, SE 5th Avenue, SE

Ely Street) ...................................................................................................... 6-5

6-5 Stormwater Pipe Replacements (South of Cabot Drive) ..................................... 6-5

6-6 Stormwater Pipe Replacements (SE Bayshore Drive) ......................................... 6-6

6-7 Stormwater Pipe Replacements (West Whidbey Avenue) .................................. 6-7

6-8 Stormwater Pipe Replacements (SE Pasek Street) .............................................. 6-8

6-9 Stormwater Pipe Replacements (SW 6th Avenue) ............................................... 6-9

6-10 Stormwater Pipe Replacements (Oak Harbor Street) ........................................ 6-10

6-11 Capital Improvement Plan (2020 to 2027) ......................................................... 6-12

7-1 Stormwater Utility Monthly Billing Charges ...................................................... 7-2

7-2 Financial Forecast Assumptions .......................................................................... 7-3

7-3 Preliminary Monthly Rate Increases .................................................................... 7-4

7-4 Rate Increases Necessary for a Freund Marsh Wetland Loan in 2022 ................ 7-4

7-5 10-Year Financial Forecast Analysis (2020-2029) .............................................. 7-5

7-6 20-Year Financial Forecast Analysis (2030-2039) .............................................. 7-7 vi

LIST OF FIGURES

No. Figure On or Follows Page

2-1 Vicinity Map ........................................................................................................ 2-2

2-2 Topographic Map ................................................................................................. 2-2

2-3 Wetlands and Waterbodies Map .......................................................................... 2-2

2-4 Critical Areas Map ............................................................................................... 2-4

2-5 Soil Map ............................................................................................................... 2-4

2-6 Water Services Map ............................................................................................. 2-6

2-7 Land Use Map ...................................................................................................... 2-8

2-8 Drainage Basin Map .......................................................................................... 2-10

3-1 Drainage Base Map .............................................................................................. 3-2

3-2 Ault Field & Upper Dry Creek Basin Map .......................................................... 3-2

3-3 High School & Northwest Basin Map ................................................................. 3-2

3-4 Midway and Oak Prairie Basin Map .................................................................... 3-2

3-5 Dry Creek Basin Map .......................................................................................... 3-2

3-6 Golf Course Basin Map ....................................................................................... 3-2

3-7 Freund Marsh Basin Map..................................................................................... 3-2

3-8 Waterloo Marsh & Eagle Vista Basin Map ......................................................... 3-2

3-9 System Deficiencies ............................................................................................. 3-4

3-10 Upper Dry Creek Basin Results ........................................................................... 3-4

3-11 Midway (North) Basin Results ............................................................................ 3-6

3-12 Midway (South) Basin Results ............................................................................ 3-6

3-13 Midway (City Beach) Basin Results .................................................................... 3-6

3-14 Highschool Basin Results .................................................................................... 3-8

3-15 Oak Prairie Basin Results .................................................................................... 3-8

3-16 Dry Creek Basin Results ...................................................................................... 3-8

3-17 Golf Course Basin Results ................................................................................. 3-10

3-18 Freund Marsh Basin Results .............................................................................. 3-10

3-19 Garry Oak Delineation Map ............................................................................... 3-10

3-20 Site Suitability Map for LID Facilities .............................................................. 3-12

4-1 Freund Marsh Regional Treatment Facility Area Subbasin .............................. 4-20

4-2 Potential Regional Treatment Facility Area ...................................................... 4-20

4-3 Landscape Media Alternative ............................................................................ 4-20

4-4 Potential Wetland Treatment Area ..................................................................... 4-20

6-1 Capital Improvement Projects.............................................................................. 6-2

6-2 Upper Dry Creek CIPs ......................................................................................... 6-2

6-3 Midway (North) CIPs .......................................................................................... 6-4

6-4 Midway (South) CIPs .......................................................................................... 6-6

6-5 Midway (City Beach) CIPs .................................................................................. 6-6

6-6 High School Basin CIPs....................................................................................... 6-8

6-7 Oak Prairie CIPs .................................................................................................. 6-8

6-8 Dry Creek CIPs .................................................................................................... 6-8

6-9 Golf Course Basin CIPs ..................................................................................... 6-10

6-10 Freund Marsh CIPs ............................................................................................ 6-12 vii

APPENDICES

Appendix A – NOAA Tidal Information

Appendix B – Stormwater Base Map

Appendix C – Model Background Information and Results

Appendix D – Infiltration Trench and Raingarden Sizing Memorandum/Calculations

Appendix E – Maintenance Guidelines

Appendix F – Draft 2019 Rate Study

Appendix G – Sample NPDES Phase II Permit Schedule

Appendix H – Cost Estimates

Appendix I – SEPA Checklist

City of Oak Harbor 1-1

Comprehensive Stormwater Plan March 2020

CHAPTER 1

INTRODUCTION

As Whidbey Island’s largest incorporated city, Oak Harbor has been developed and continues to grow, contributing to the need for effective stormwater management. The

2006 Stormwater Comprehensive Plan identified 36 existing flooding problem areas, two existing maintenance and erosion problem areas, and 59 potential future flooding problem areas. The 2006 Plan presented a solution with 20 capital projects, of which the

City has completed or begun six projects. The City’s 2016 Comprehensive Plan identifies development projections through the year 2036, including a population increase from 22,693 (2015) to 25,814. The 2016 Plan also presents the goal to “Preserve and enhance water quality in conformance with the Puget Sound Partnership’s Action Agenda for Puget Sound and other Clean Water Act and Growth Management Act requirements” which will be supported by this Stormwater Comprehensive Plan.

Prior to the late 1970s, stormwater management in the U.S. and specifically the Puget

Sound region consisted primarily of conveying runoff away from developed areas in order to preserve the health and safety of citizens and protect property, both public and private. Drainage improvement projects addressed large storm events and local flooding with little thought for upstream, downstream, or environmental impacts. With the passage of the Clean Water Act in 1972, completion of the Nationwide Urban Runoff

Program in 1983, and subsequently other federal and state laws, the cumulative effects of smaller storms in developed/urbanized areas were formally recognized as a major contributor to water quality and habitat degradation.

Stormwater runoff collects sediment and pollutants from exposed construction sites and agricultural areas as well as pollutants from the street network, residential, commercial, and industrial developments. Pollutants in stormwater runoff include metals such as lead, cadmium, and copper; oil and grease; pesticides and fertilizers; nutrients; suspended solids; and harmful bacteria. In addition, urbanization increases the amount of impervious surfaces such as rooftops, streets, and parking areas. Impervious surfaces directly relate to an increase in runoff volumes and peak flow rates. The pollutant loads and increased volumes of stormwater runoff result in negative impacts to downstream properties and surface water bodies such as lakes, streams, and wetlands and reduced infiltration to groundwater. Due to regulations required under the Clean Water Act and the listing of anadromous (salmon, trout, char) species under the Endangered Species

Act, it has become increasingly important for municipalities to implement stormwater quality and quantity (flow) control measures.

Gray & Osborne, Inc., Consulting Engineers

1-2 City of Oak Harbor

March 2020 Comprehensive Stormwater Plan

PURPOSE

The City of Oak Harbor Stormwater Comprehensive Plan (Plan) is a planning document that provides guidance to minimize adverse effects of stormwater runoff on ground and surface water. It is also a document to help ensure the City maintain compliance with government regulations such as the Clean Water Act and the City’s NPDES Phase II

Permit. It identifies water quality and quantity problems associated with stormwater runoff that may affect the environment and community, and provides recommendations for improvements and programs including a cost analysis and implementation schedule.

The Plan identifies specific structural and non-structural solutions to quantity and water quality problems within the City. Structural solutions include construction of capital projects such as stormwater detention and treatment facilities, infiltration facilities, pipelines, and culverts. Nonstructural solutions include stormwater management facility inspection and maintenance, public education and outreach, water quality monitoring, implementation of best management practices, and regulations encouraging vegetation preservation and low impact development.

AUTHORIZATION

The City of Oak Harbor contracted with Gray & Osborne, Inc. to complete the update to the Plan. Specific components in the Scope of Work include:

• Provide overall project management and oversight services;

• Update GIS information with data collected as part of the Plan;

• Identify drainage basins and describe hydrologic characterizations and existing stormwater facilities;

• Evaluate the impact of runoff to the existing conveyance systems under both current and future land use conditions;

• Evaluate the overall condition of the system by creating a map of aging stormwater facilities based upon GIS data or City staff knowledge;

• Identify the current level of maintenance of public and privately owned systems through discussions with maintenance personnel;

• Develop a maintenance schedule and associated costs for performing facility maintenance;

• Identify conveyance problems;

City of Oak Harbor 1-3

• Identify water quality problems;

• Identify potential structural and non-structural solutions to conveyance system and water quality problems;

• Review the City’s NPDES Phase II Program for compliance with the current permit requirements and timelines;

• Propose a schedule and priority of capital improvements for the 6- and

20-year planning horizons;

• Review the current revenue and expenses to assist the City’s budget development;

• Provide a draft Comprehensive Stormwater Plan for review by City staff;

and

• Provide a final Plan to the City.

GOALS

As additional development and redevelopment occurs within the City, the amount of naturally vegetated areas will decrease while the amount of impervious surfaces will increase, leading ultimately to increased peak runoff rates and transport of more pollutants to the City’s streams, wetlands, and the bay.

The primary goal of the Oak Harbor Comprehensive Stormwater Plan is to provide guidance to the City Council, staff, and citizens to preserve and protect the water quality and hydraulic regime within the City’s natural and manmade stormwater drainage system, and the major receiving waters, Oak Harbor and Puget Sound.

To this end, the City intends to manage land development and stormwater programs to preserve natural areas, minimize water borne pollutants, mitigate the impacts of increased runoff, enforce permit conditions and erosion control BMPs on construction sites, and to preserve fish and wildlife habitat. Through careful planning of funds generated from the existing Stormwater Utility, the City’s implementation of the Plan will meet the goals to protect the health, safety, and welfare of the local citizenry and to preserve surface water resources within, and downstream of, the City.

City of Oak Harbor 2-1

CHAPTER 2

DRAINAGE AREA CHARACTERISTICS

LOCATION

The City of Oak Harbor (City), Washington was incorporated in 1915. The City’s current boundary and Urban Growth Area (UGA) encompass approximately 6.5 square miles (see Figure 2-1). The City is located in north central Whidbey Island in Island

County, approximately 40 miles northwest of Everett. State Route 20 (SR 20) passes through the City, splitting the City into distinct east and west sections. Naval Air Station

Whidbey Island (NAS Whidbey) is located about three miles north of Oak Harbor, with the secondary Seaplane Base is located on the east side of the City, above Crescent

Harbor. There are three main access routes to the Island; the Deception Pass Bridge to the north, the Port Townsend-Coupeville ferry near the center of the Island, and the

Clinton-Mukilteo ferry near the south end of the Island. This Plan will focus on stormwater issues within the city limits (excluding the Navy base located on the east side) and areas within the City’s UGA. Island County has designated a joint planning area

(JPA) just outside of the City’s UGA. The JPA serves as a method to help facilitate joint planning efforts between the County and City including where UGA areas could potentially expand if needed, where coordination of joint planning efforts would occur such as shared transportation corridors and where land designated for protection would be secured between the two agencies.

Projections from the Washington State Office of Financial Management estimate the

2019 population at 22,970, representing 27 percent of the total population of Island

County. Oak Harbor is a combination of residential and commercial communities. The commercial land use is mostly located along SR 20, with a mix of residential and commercial use to the east and newer residential areas to the west. Low density residential constitutes a major portion of the city and UGA, making up approximately

47 percent of the land.

TOPOGRAPHY

The City of Oak Harbor lies in a topographic bowl facing southeast towards the bay.

Portions of the City are outside this bowl and instead slope down to the west towards the

Strait of Juan de Fuca. The City is approximately 7 miles south of Deception Pass, connecting Whidbey Island to Fidalgo Island and subsequently the mainland. Elevations within the City range from sea level at the south end to 307 feet towards the north.

Slopes range from zero to over 14 percent, with 3 to 6 percent being more typical. The topography of the City is shown in Figure 2-2.

2-2 City of Oak Harbor

CLIMATE

The climate of Oak Harbor is heavily influenced by Puget Sound and the Olympic

Mountain Range to the west. The surrounding waters moderate the temperature fluctuations, keeping the average summer highs below 75 degrees F and average winter lows above freezing. The City lies within the Olympic Mountain Range rain shadow which reduces precipitation to an average of 21 inches annually, compared to a State average of 38 inches. Precipitation is lowest during the summer months and moderate during the winter months. Table 2-1 summarizes the historical monthly average temperature and rainfall data for the City.

TABLE 2-1

Average Monthly Climate Data

Month

High Temp.

(°F)

Low Temp.

(°F)

Precipitation

(in)

January 45 34 2.5

February 48 35 1.8

March 52 37 1.8

April 57 40 1.6

May 63 44 1.6

June 67 48 1.3

July 72 51 0.8

August 72 51 0.9

September 68 47 1.3

October 58 42 1.8

November 50 38 2.7

December 45 35 2.7

Total 20.7 Source: www.wrcc.dri.edu, NOAA Cooperative Climatology Data

Summaries for Coupeville, 1948 to 2005.

WATERWAYS AND WATERBODIES

Both marine and fresh waterbodies exist within the Oak Harbor city limits as shown in

Figure 2-3. The largest fresh waterbody within the City is Loers Pond, located within the

Whidbey Island Golf and Country Club golf course. Loers Pond receives surface water from the Golf Course and Waterloo Marsh basins and discharges to an unnamed stream.

This unnamed stream, draining west to Swan Lake, has been added to the Department of

Ecology 303(d) list due to bacteria and dissolved oxygen. Sampling locations for the unnamed stream are believed to be outside of the City limits, but exact locations are unknown.

Oak Harbor

S t r a i t o f J u a n d e F u c a

S a r a t o g a P a s s a g e

C r e s c e n t H a r b o r

NAS Whidbey

Camano Island

Deception Pass

Fidalgo Island

NAS Whidbey

P e n n C o v e

M:\Oak Harbor\16625.00 Storm Comp Plan\GIS\Oak Harbor Vicinity map.mxd

CITY OF OAK HARBOR

COMPREHENSIVE STORMWATER

MANAGEMENT PLAN

VICINITY MAP

FIGURE 2-1

LEGEND:

Water Bodies

Urban Growth Area (UGA)

Joint Planning Area (JPA)

Oak Harbor

City Limits

Coupeville

Anacortes

Island County

Skagit County ³ 0 5,000 10,000

Feet

NAS Whidbey

O a k H a r b o r

S a r a t o g a P a s s a g e

S t r a i t o f J u a n d e F u c a

150 175

200 15

State Rte 2

N Bo on R d

He lle r R d

W Ault Field Rd

Sw an tow n R d

He lle r S t

W Fort Nugent Rd

NE

M idw ay

B lvd

SE Pioneer Way

N Oa k H arb or St

E Pioneer Way

E Whidbey Ave

Coral Sea Ave

Pio nee r W ay

W Waterloo Rd

W Whidbey Ave

W Sleeper Rd

W Clover Valley Rd

W Crescent Harbor Rd

M:\Oak Harbor\16625.00 Storm Comp Plan\GIS\working maps\Oak Harbor Topo map.mxd

CITY OF OAK HARBOR

COMPREHENSIVE STORMWATER

MANAGEMENT PLAN

TOPOGRAPHIC MAP

FIGURE 2-2

LEGEND:

City Limits

UGA

JPA

25 ft. Contours

Parcels ³ 0 5,000

Feet

State Rte 2

N Bo on R d

He lle r R d

W Ault Field Rd

He lle r S t

NE

M idw ay

Bl vd

Swantown Rd

SE Pioneer Way

N Oa k H arb or St

E Pioneer Way

E Whidbey Ave

Coral Sea Ave

Pio ne er Way

W Waterloo Rd

W Whidbey Ave

W Clover Valley Rd

W Fort Nugent Rd

W Crescent Harbor Rd

M:\Oak Harbor\16625.00 Storm Comp Plan\GIS\2-3 Wetlands and Waterbodies.mxd

LEGEND:

Private Detention Pond

City Owned Detention Pond

Freshwater Emergent Wetland

Estuarine and Marine Wetland

Water Bodies

City Limits

UGA

JPA

0 2,000 4,000

Feet ³

CITY OF OAK HARBOR

COMPREHENSIVE STORMWATER

MANAGEMENT PLAN

WETLANDS AND WATERBODIES MAP

FIGURE 2-3

O a k H a r b o r

S a r a t o g a P a s s a g e

L o e r ' s P o n d

F r e u n d M a r s h

City of Oak Harbor 2-3

Comprehensive Stormwater Plan March 2020

Numerous smaller ponds and wetlands are located throughout the City, as shown in

Figure 2-3.

Freund Marsh is a freshwater wetland located along the Oak Harbor waterfront, just west of Windjammer Park (also known as City Beach). It receives surface runoff from the

City before discharging to the Bay. The marsh is classified as a 100-year floodplain by

FEMA.

The primary marine waterway is Oak Harbor Bay which borders the city to the south, leading to Saratoga Passage. A portion of the Bay along Windjammer Park is listed on the Department of Ecology 303(d) list due to bacteria. The Whidbey Island Marina is located on the east end of the bay, adjacent to Crescent Harbor.

TIDAL DATA

Tidal fluctuations play an important role in the City’s stormwater management. With most drainage within the City discharging to Oak Harbor, high tides can submerge the outfalls. This reduces drainage capacity, resulting in surcharging of pipes. Tidal conditions must be established in combination with extreme rainfall events to understand the effects on upstream drainage.

The National Oceanic and Atmospheric Administration (NOAA) Crescent Harbor station gives tidal data, shown in Appendix A. Based on NOAA extreme water levels data for nearby Seattle, the 1 percent annual exceedance probability (AEP) level is 3.2 feet above mean higher high water (MHHW), equal to 12.4 feet (NAVD88).

The Federal Emergency Management Agency (FEMA) provides floodplain maps depicting 100-Year floodplain elevations for Oak Harbor (FEMA, 2017). These floodplains are shown in Figure 2-4.

SOILS

The soils of Island County were surveyed by the United States Department of Agriculture

(USDA) National Resources Conservation Service (NRCS). The NRCS website indicates 10 soil types (e.g., silt loam, gravelly sandy loam, muck, etc.,) within the general UGA of Oak Harbor, as shown in Figure 2-5 and Table 2-2. The NRCS classifies soils, from A to D, according to runoff potential. Type A has low runoff potential and type D has high runoff potential. The NRCS also provides information pertaining to the physical and chemical properties of the soils, including drainage class. Table 2-2 summarizes the significant soil groups and drainage class of the soils found within Oak

Harbor’s UGA.

2-4 City of Oak Harbor

TABLE 2-2

Soil Characteristics

Soil

Hydrologic

Soil Group Drainage Class Rating

Alderwood gravelly sandy loam B Moderately well drained

Coupeville loam D Poorly drained

Coastal beaches B Well drained

Coveland loam D Somewhat poorly drained

Dugualla muck D Very poorly drained

Elwha loam B Moderately well drained

Everett very gravelly sandy loam A Somewhat excessively drained

Frostad loam D Poorly drained

Hoypus sandy loam A Somewhat excessively drained

Indianola loamy sand A Somewhat excessively drained

Limepoint mucky silt loam D Poorly drained

Mitchellbay gravelly sandy loam C Somewhat poorly drained

Morancreek sandy loam B Moderately well drained

Puget silty clay loam C Poorly drained

Semiahmoo muck D Very poorly drained

Shalcar muck D Very poorly drained

Sholander gravelly loam C Somewhat poorly drained

Spieden mucky silt loam D Poorly drained

Sucia loamy sand B Moderately well drained

Whidbey gravelly loam B Moderately well drained

Zylstra loam C Somewhat poorly drained

CRITICAL AREAS

Discussed below are types of critical areas found within the City and which are identified by the Growth Management Act. Their presence can dictate where facilities should or should not be located. These areas include: shorelines and tidal flats, wetlands, fish and wildlife habitat conservation areas, geologically hazardous areas, frequently flooded areas, critical aquifer recharge areas, urban forests, surface water quality, air quality, stormwater management, and cultural resources. In addition, Oak Harbor Municipal

Code designates and regulates the following critical areas:

• Frequently Flooded areas

• Wetlands

• Critical Aquifer Recharge areas

• Rivers and Streams

• Fish and Wildlife Habitat Conservation areas

• Geological Hazard areas

N Bo on R d

He lle r R d

W Ault Field Rd

He lle r S t

NE

M idw ay

Bl vd

Swantown Rd

SE Pioneer Way

N Oa k H arb or St

E Pioneer Way

E Whidbey Ave

Coral Sea Ave

Pio ne er Way

W Waterloo Rd

W Whidbey Ave

W Clover Valley Rd

W Fort Nugent Rd

W Crescent Harbor Rd

M:\Oak Harbor\16625.00 Storm Comp Plan\GIS\2-4 Critical Areas Map.mxd

LEGEND:

Critical Aquifer Recharge Area

High Susceptibility Moderate Susceptibility < 40% Slope

City Limits

UGA

JPA

100 Year Flood Zone

0 2,000 4,000 Feet

³

CITY OF OAK HARBOR

COMPREHENSIVE STORMWATER

MANAGEMENT PLAN

CRITICAL AREAS MAP

FIGURE 2-4

S a r a t o g a P a s s a g e

Sta te R te 2

N Bo on R d

He lle r R d

W Ault Field Rd

He lle r S t

Swantown Rd

NE

M idw ay

B lvd

SE Pioneer Way

N Oa k H arb or St

E Pioneer Way

E Whidbey Ave

Co ral

Se a A ve

Pio nee r W ay

W Waterloo Rd

W Whidbey Ave

W Fort Nugent Rd

W Clover Valley Rd W Fakkema Rd

W Crescent Harbor Rd

M:\Oak Harbor\16625.00 Storm Comp Plan\GIS\2-5 Soils Map.mxd

0 2,000 4,000 Feet

³

CITY OF OAK HARBOR

COMPREHENSIVE STORMWATER

MANAGEMENT PLAN

SOIL MAP

FIGURE 2-5

LEGEND:

Parcels City Limits

UGA

JPA

Water Bodies Streams

Soils:

City Limits

Areas

UGA

Hydrologic Soil Group A Beaches-Endoaquents Hoypus Sandy Loam Indianola Loamy Sand

Hydrologic Soil Group B Elwha-Zylstra-Morancreek Complex Everett-Alderwood Complex Morancreek-Limepoint Complex Sucia Loamy Sand Sucia-Sholander Complex Whidbey Gravelly Loam Whidbey-Hoypus Complex

Hydrologic Soil Group C Mitchellbay Gravelly Sandy Loam Puget Silty Clay Loam Sholander-Spieden Complex Zylstra-Frostad Complex Zylstra-Mitchellbay Complex

Hydrologic Soil Group D Coupeville Loam Coupeville-Mitchellbay Complex Coveland Loam Dugualla Muck Semiahmoo Muck Shalcar Muck Urban Land

Non-Soil Features Dumps Pits Urban Land Water

City of Oak Harbor 2-5

• Garry Oak Tree Protection

FREQUENTLY FLOODED AREAS

The City of Oak Harbor is located in a topographic bowl that drains to Oak Harbor Bay.

Within this bowl, certain areas lack adequate drainage to prevent flooding. In accordance with the federal National Flood Insurance Program and Oak Harbor Municipal Code, land development is regulated to prevent and/or discourage development within the flood plain, in order to avoid future losses due to flood events.

The Federal Emergency Management Agency (FEMA) documented areas that are subject to 100-year floods within the City, updated in 2007. The 100-year flood has been adopted as the base flood for purposes of floodplain management. A 100-year flood area is defined as those lands, which are subject to a one percent or greater chance of flooding in any one year. Figure 2-4 delineates the 100-year floodplain boundaries within the City of Oak Harbor.

WETLANDS

Wetlands and riparian corridors perform valuable functions within the ecosystem.

Clearing of vegetation, grading, filling, draining, and other activities associated with land development may decrease the ability of the riparian zone to provide drainage, stabilize stream banks, provide wildlife habitat, and filter pollutants from runoff. Wetlands receiving surface water from surrounding areas can filter entering pollutants by a combination of physical, chemical, and biological processes.

Wetlands also play a major role in flood control. During flooding, rivers and streams overflow their banks and spread out across the flood plain. Wetlands attenuate the peak flows from storm events by storing water during wet periods and discharging this stored water later during drier periods.

According to the National Wetlands Inventory, there are large wetland areas located at

Freund Marsh Park and north of NE 7th Avenue between NE Goldie Road and North Oak

Harbor Street. Smaller wetlands are located at the Whidbey Golf and Country Club and other areas of the City. Figure 2-3 shows the approximate location of wetlands within the

City as identified by the National Wetlands Inventory. The inventory (completed in the early 1980s) only identified large wetlands and the map is not intended to show all such areas. Smaller wetlands throughout the City continue to provide varying degrees of ecological functions such as peak flow attenuation, natural water quality treatment, and wildlife habitat.

2-6 City of Oak Harbor

CRITICAL AQUIFER RECHARGE AREAS

The City receives 99 percent of its water from the City of Anacortes Water Treatment

Plant, which sources its water from the Skagit River. In addition to supplying residential and commercial customers in Oak Harbor, the City also supplies water to NAS Whidbey

Island, Deception Pass State Park, and North Whidbey Water District. The City has four reservoirs capable of storing 7.15 million gallons of water and maintains three deep wells as an emergency source.

The Growth Management Act requires that potable water sources such as wells be mapped and assessed for vulnerability to ground or surface water contamination.

Depending on the depth of the aquifer, soil porosity, and other parameters, certain land uses or stormwater management practices may cause contaminants to percolate down into groundwater, having a negative effect on water quality for a specific well or an entire aquifer. These critical aquifer recharge areas have been delineated by the Island County

Health Department through the 2514 Watershed Planning process and are included in

Figure 2-4.

Swantown Water District, serving approximately 92 customers bordering the Oak Harbor

City limits northwest of Whidbey Golf and Country Club, sources water from two wells at a depth of 130 feet. This water source is not treated. Other active drinking water wells, according to Ecology Well Logs, are located mostly to the north or west of the

City. Water service providers and wells are shown in Figure 2-6.

FISH AND WILDLIFE HABITAT CONSERVATION AREAS

The main areas of habitat within the city are associated with Oak Harbor Bay. The entire shoreline of Oak Harbor is a critical area for recovery of Puget Sound Chinook ESU

(evolutionarily significant unit). There are also forage fish spawning areas along the waterfront and, at the south end of the city, bald eagle habitat. A critical area for Heron is located near the UGA boundary just north of West Ault Field Road. Other aquatic environment critical areas exist just outside of Oak Harbor Bay, including eelgrass, geoduck, harlequin duck, and shellfish areas.

The namesake for the City, the Garry Oak, has a concentration area south of East

Whidbey Avenue, west of SE Regatta Drive, and east of SR 20. Preservation of Garry

Oaks, as well as other urban components, is a major goal presented in the City’s

Comprehensive Plan.

GEOLOGICAL HAZARD AREAS

The City’s Comprehensive Plan identifies geologically sensitive areas such as steep slopes, primarily those associated with the bluffs along the shoreline. Steep (>15%), potentially unstable slopes exist above the waterfront east of SW Scenic Heights Road and south of SE Pioneer Way. Areas of moderate to high liquefaction susceptibility are

O a k H a r b o r

S a r a t o g a P a s s a g e

Oak Harbor, City Of

Naval Air Station/Whidbey Island

Swantown Water District

Hillc res t V illa ge Wate r C o In c

North Boon Water System Waterloo Acres Community Water Sys

Wagon Wheel

Crosswoods Water Company

Fairway Estates Inc

Timaru Community Water Association

West Ridge Water System

Naval Air Station/Whidbey Island Parkwood Manor Mhp

Suburban Hills Community Association

Westview Community Association

Suburban Mobile Park

Valley High Park

Pine Terrace Water Association

Highland Trace Water Co Inc

Bets Water System

Eastgate

Windmill Court

Indian Ridge Water Company

Evergreen Park

Heathrow Water System

Little Valley Apts.

Fir Grove Mobile Park

Lighthouse Christian Center M & M Mobile Park

Eastgate

Veterans of Foreign Wars, Post 7392

State Rte 2

N Bo on R d

He lle r R d

W Ault Field Rd

He lle r S t

Swantown Rd

NE

M idw ay

B lvd

SE Pioneer Way

E Pioneer Way

E Whidbey Ave

Coral Sea Ave

Pio nee r W ay

W Waterloo Rd

W Whidbey Ave

W Fort Nugent Rd

W Clover Valley Rd W Fakkema Rd

W…