Chapter 9
GREEN COVE BASIN

Chapter 9

9.000    GENERAL CONSIDERATIONS

9.010    General

9A    STREETS - GREEN COVE BASIN

9A.010    Streets

9B    DRIVEWAYS - GREEN COVE BASIN

9B.010    Driveways

9C    SIDEWALKS - GREEN COVE BASIN

9C.010    Sidewalks

9D    ROADSIDE FEATURES - GREEN COVE BASIN

9D.010    General Vegetation Coverage Standards

9D.020    Species, Cultivars, or Varieties

9D.030    Spacing and Location

9D.040    Parking Lots

9E    STORMWATER - GREEN COVE BASIN

9E.010    General

9E.020    Full Dispersion

9E.030    Applications and Limitations

9E.040    Design Standards

Appendix 1:        List of Standard Drawings

9.000 GENERAL CONSIDERATIONS

9.010 General

The development standards and Standard Drawings in Chapter 9 provide street and stormwater designs required in the Green Cove Basin. Design guidelines and standards not addressed in Chapter 9 are provided in Chapters 1 through 8 of the Engineering Design and Development Standards.

9A STREETS - GREEN COVE BASIN

9A.010 Streets

A.    Streets and Alleys: Residential blocks bounded by streets will not exceed a walking perimeter of 1,700 feet. Commercial blocks will not exceed a walking perimeter of 2,200 feet. Where larger blocks are necessary due to topography, existing development, or other constraints, intervening public cross-block pedestrian, bicycle, and emergency access will be provided.

B.    Design Standards: Green Cove Basin street design standards are provided in Tables 1 and 2.

C.    Surfacing, Permeable Pavement: Permeable pavement materials may be permitted or required at the discretion of the Director of Public Works.

9B DRIVEWAYS - GREEN COVE BASIN

9B.010 Driveways

Permeable pavement materials may be permitted or required in place of cement concrete at the discretion of the Public Works Director.

Table 1: Green Cove Basin Minimum Street Design Standards(1)

Design Standard

FUNCTIONAL CLASSIFICATION

Low-Impact Neighborhood Collector

Local Access Block Spacing (5) >350 Feet

Local Access Block Spacing (5) < 350 Feet

Low-Impact Local Access

Commercial Alleys

Residential Alleys

Minimum Structural Design

See Standard Drawing 4-6A

ADT

500-3,000

0-500

0-500

0-500

N/A

N/A

Sidewalks

5' Both Sides

5' Both Sides

5' Step Side

5' One Side

None

None

Planting Strips (3)

25' Strip Optional, 8' Between Curb & Walk Both Sides (2)

8' Between Curb and Walk Both Sides (2)

8' Between Curb and Walk Both Sides (2)

25' Strip Optional, 8' Between Curb & Walk Both Sides (2)

N/A

N/A

Street Tree Spacing (4)

40' On Center

40' On Center

40' On Center

40' On Center

None

None

Parking Lanes

7' One Side

7' One Side

7' One Side

7' One Side

None

None

Curbs (6)

Both Sides

Both Sides

Both Sides

Both Sides

None

None

Lane Widths

Two-9'

Two-9'

One-13'

One-11'

12'

Two-36" Ribs

R-O-W

53'

2 Lanes 53'

2 Lanes with swale 49'

1 Lane 48'

Lane with swale 44'

41'

12'

12'

No Dead Ends

Intersection Radii

25'

25'

30'

25'

N/A

N/A

Cul-de-sac Radii

N/A

47' w/22' Landscaped Island

47' w/22' Landscaped Island

N/A

N/A

N/A

Grades

0.5-12%

0.5-15%

0.5-15%

0.5-15%

0.5-15%

0.5-15%

Maximum Design Speeds

20 mph

20 mph

20 mph

20 mph

10 mph

10 mph

Site Access

N/A

N/A

N/A

N/A

N/A

N/A

Streetlights

High-mast decorative

Pedestrian Scale

Pedestrian Scale

Pedestrian Scale

N/A

N/A

Access Width

10' at PL

15' at PL Curb

10' at PL

15' at PL Curb

10' at PL

15' at PL Curb

10' at PL

15' at PL Curb

N/A

N/A

Bicycle Facilities

Class II or III as designated on Bike Map

Class II or III as designated on Bike Map

Class II or III as designated on Bike Map

Class II or III as designated on Bike Map

N/A

N/A

(1)    Design standards for street classifications other than those listed in this table shall be per Table 2 in Chapter 4.

(2)    Swale will only be used as an alternative design based on environmental consideration. When swale is required, swale width = 12 feet between curb and sidewalk, 6 feet tree easement opposite side of swale.

(3)    Unless otherwise agreed upon by the City of Olympia, maintenance of street trees, turf, or other landscaping within the planting strips is the responsibility of the adjacent landowner.

(4)    Exact spacing and species to be determined by Urban Forester or City Engineer. Spacing approximate, except spacing will depend on locations of streetlights, fire hydrants, driveways, sight-clearance triangles, etc.

(5)    This distance is measured along the development frontage property lines

(6)    Curbs may be omitted from designs if necessary to facilitate stormwater sheet flow from roadways into roadside dispersion areas. Where curbs are omitted, alternate practices shall be employed to deter vehicles from driving off-road.

Table 2: Green Cove Basin Street Characteristics(1)

Street Characteristics

Low-Impact Neighborhood Collector

Local Access Street

Low-Impact Local Access Street

Types of Traffic Served

Sub-area and local traffic; feed major collector traffic

Local traffic; feed neighborhood/major collector or arterial traffic

Local traffic; feed neighborhood/major collector or arterial traffic

Traffic Volumes

500-3,000 average daily traffic

0-500 average daily traffic

0-500 average daily traffic

Percent Local Traffic

70-100% of origins and destinations are within a 1-mile radius of the street.

80-100% of origins and destinations are within a 1-mile radius of the street.

80-100% of origins and destinations are within a 1-mile radius of the street.

Average Travel Length

1-2 miles

Minimum 2 miles

Minimum 2 miles

Street Spacing(2)

1000'-1500'

350'-500'

250'-350'

Intersection Spacing (3)

200'-700'

250'-350'

200'-700'

Design Speeds

25 miles per hour

20-25 miles per hour

20-25 miles per hour

On-street Parking

Yes

Yes

Yes

Driveway Access

Yes

Yes

Yes

Bike Lanes (Class II or III)

No

No

No

Planting Strips (between sidewalk & curb)

Yes

Yes

Yes

Sidewalks

Yes

Yes

Yes

Traffic Calming

Yes, incorporated into Standard.

Yes, if problem is anticipated or determined through an engineering study.

Yes, incorporated into Standard

Transit Shelters

None

None

None

Transit Pullouts

None

None

None

(1)    Street characteristics for street classifications other than those listed in this table shall be per Table 3 in Chapter 4.

(2)    Street spacing means the frequency of street types within the street network.

(3)    Intersection spacing means how often a cross street occurs on a particular class of street.

9C SIDEWALKS - GREEN COVE BASIN

9C.010 Sidewalks

A.    Sidewalks will be 4 inches thick and constructed of pervious concrete meeting the requirements of Appendix 5 of Chapter 4. Impermeable Portland Cement concrete sidewalks may be approved for a project, if site conditions limit or prohibit the use of pervious concrete. A deviation request for the use of impermeable concrete shall be submitted to the City Engineer, per section 1.050 of the EDDS. When the sidewalk and curb are contiguous, the width of the sidewalk will be measured from face of curb to back of sidewalk. Curbs integral or permeable sidewalks are not allowed.

1.    Base: 2-inch crushed surfacing top course or well-graded sand.

2.    Surfacing: Asphalt. Asphalt sidewalks will not be permitted unless otherwise approved by the Public Works Director.

B.    Sidewalks on local access streets: Sidewalks will be required on one side of local access street’s interior to the development and on the development side of local access streets abutting the exterior of said development, including cul-de-sacs.

9D ROADSIDE FEATURES - GREEN COVE BASIN

9D.010 General Vegetation Coverage Standards

When the optional street cross section (Standard Drawing 9-4) is to be constructed, the Urban Forester shall require trees and shrubs to be planted at a density to ensure the following minimum vegetation coverage standards are achieved:

A.    Coverage: 60% conifer and 40% deciduous;

B.    Achieve 75% tree and shrub canopy coverage in 7 years; and

C.    Achieve 100% tree canopy in 25 years.

9D.020 Species, Cultivars, or Varieties

A.    Recommended plant material palette: Final species selection shall be subject to the discretion of the Urban Forester.

1.    Large trees (coniferous): Western Red Cedar, Douglas Fir, Shore Pine, Alaskan Yellow Cedar.

2.    Large trees (deciduous): Green Ash, Big Leak Maple, Oregon White Oak, Swamp White Oak, Jaquomontii Birch.

3.    Small trees: Vine Maple, Serviceberry, Mountain Ash, Beaked Hazelnut.

4.    Shrubs: Red Flowering Current, Evergreen Huckleberry, Elderberry, Oregon Lilac, Snowberry, Myrica, Hairy Manzanita, Oregon Grape, Nootka Rose, Red-Osier Dogweed, Indian Plum, Ocean Spray, Mock Orange.

B.    Grade. Unless otherwise specified by the Urban Forester, all trees shall have comparatively straight trunks, well-developed leaders and crowns, and shall exhibit evidence of proper nursery pruning practices. At the time of planting, all trees must be free of mechanical injuries and other objectionable features that affect the future form and beauty of the plant.

9D.030 Spacing and Location

The Urban Forester may vary the following standards as necessary to ensure public safety and consistent streetscape design. Final spacing and location of plant materials shall be determined by the Urban Forester in accordance with local conditions; the species, cultivars, or varieties used; and their mature height, spread, and form.

A.    Large trees shall be spaced 20 feet on center in a multiple row-alternating pattern.

B.    Small trees 10 feet on center in a multiple row-alternating pattern.

C.    Shrubs 4 to 6 feet on center in a multiple row-alternating patterns.

D.    Trees shall be planted at least 10 feet from driveways and alleys and at street intersection; the distance shall be that specified in Chapter 4, Section 4B.150, Site Clearance Triangle.

E.    No tree shall be planted closer than 20 feet to a utility pole or a streetlight to allow for maintenance and light penetration.

9D.040 Parking Lots

A parking lot construction permit is required prior to surfacing any unsurfaced designated parking area.

Stormwater retention will be provided and will follow the criteria as set forth in Chapter 5 of these Standards.

Number of plans and specifications will be as required by the Community Planning and Development Department and be submitted for review and approval by the City with respect to stormwater discharge and on-site retention or detention, matching street and/or sidewalk grades, access locations, parking layout, and to check for future street improvement conformity and City zoning regulations.

Parking lot surfacing materials will be permeable and satisfy the requirement for a permanent all-weather surface. Traditional impervious asphalt concrete pavement and cement concrete pavement do not satisfy this requirement. Gravel surfaces are not acceptable or approved surface material types. Combination grass/paving systems are approved surface material types; however, their use requires submittal of an overall parking lot paving plan showing the limits of the grass/paving systems and a description of how the systems will be maintained. If the City determines the grass/paving system is not appropriate for the specific application, alternate permeable surfacing materials will be utilized.

9E STORMWATER - GREEN COVE BASIN

9E.010 General

The standards established by this chapter are intended to represent the minimum standards for the design and construction of stormwater facilities. Requirements for the Green Cove Basin place additional emphasis on stormwater minimization and infiltration.

9E.020 Full Dispersion

All developments shall be designed to achieve full dispersion of stormwater. “Full dispersion” is defined as managing runoff from the specified design event near its point of origin by distributing and infiltrating it into the surface soils. This takes advantage of the soil moisture-holding capacity, while increasing interflow and groundwater recharge, decreasing or eliminating runoff, and greatly flattening and extending the discharge hydrograph.

Full dispersion is achieved when the post-development runoff rate and duration is less than or equal to the predevelopment runoff rate and duration for half of the 2-year event up to the 50-year event and the post-development runoff volume is equal to or less than the runoff volume from the entire area with 10% impervious cover. The post development effective impervious coverage from a hydrologic modeling perspective of the entire area shall be less than or equal to 10 percent.

The City requires hydrologic model verification of design compliance. Full dispersion is achieved when post-development runoff is less than or equal to the predevelopment runoff for the specified design event.

To the extent it is demonstrated that achieving full dispersion is impracticable, the City may allow a development to use conventional stormwater detention, treatment, and conveyance practices.

9E.030 Applications and Limitations

All dispersion areas must be permanently protected from development or conversion to incompatible uses in a manner acceptable to the City and be maintained by their owners in such a manner as to preserve the hydrologic characteristics of the design or native condition.

Dispersed runoff from one threshold discharge area may not overlap with dispersed runoff from any other threshold discharge area. Each threshold discharge area shall have its own dedicated dispersion area.

Employing the below-described practices, and others that are functionally equivalent and appropriate to the development setting, is expected to achieve full dispersion.

9E.040 Design Standards

To achieve full dispersion as defined above, use the following techniques or develop site-specific approaches that will achieve a functionally equivalent result.

A.    Building lots: Stormwater generated on building lots shall be considered fully dispersed if the following conditions are met:

1.    Driveways, walkways, patios, and other small paved areas: Implement one or more of the following:

a.    Use permeable paving surfaces: Design permeable paving surfaces to City guidelines.

b.    Install impervious paving surfaces a minimum of 3 inches above surrounding grass/soil grade and slope them to drain onto the grass/soil surface. Install washed rock-filled, open-topped infiltration trenches (no soil backfill; no geotextile) alongside all paved surfaces. Size the trenches to City guidelines.

2.    Lawns/yards/landscaped areas: All such areas are to receive compost-amended soil. Prepare and install the soils to City guidelines.

B.    Roofs: Stormwater generated from roofs shall be considered fully dispersed if one or more of the following conditions are met:

1.    Install a vegetated roof with 8 inches or more of soil media, or one of equivalent hydrologic performance, designed to City guidelines.

2.    Install a cistern/rainwater harvesting system and provide a use plan for 100% of average annual rainfall. Design rainwater harvesting systems to City guidelines.

3.    Install a drywell to infiltrate roof water sized to City guidelines.

4.    Disperse roof runoff onto compost-amended soils where a minimum flow path of 50 feet is available. Where flow paths are shorter, this alternative may be used in conjunction with a bioretention area (or “rain garden”) constructed downhill of the downspout. Design compost-amended soils and bioretention areas to City guidelines.

C.    Roads and parking lots: Stormwater generated from roads and parking lots shall be considered fully dispersed if one or more of the following conditions are met:

1.    All runoff is collected, treated, and infiltrated, and the stormwater design satisfies applicable City stormwater standards.

2.    All runoff is infiltrated through permeable pavement surfaces as may be permitted or required at the discretion of the Public Works Director.

3.    Runoff is dispersed into forested/native areas or engineered areas according to Drainage Manual criteria.

D.    Stormwater detention facilities: Stormwater detention may be necessary, based on hydrologic modeling results, to manage excess development runoff.

Appendix 1: List of Standard Drawings

Title

Drawing No.

File Type
(DWG includes all drawings in chapter)

 

Chapter 9 – All

PDF DWG

Residential Low-Impact Neighborhood Collector, Sheet 1 of 2

9-1A

PDF DWG

Residential Low-Impact Neighborhood Collector, Sheet 2 of 2

9-1B

PDF DWG

Residential Low-Impact Local Access, Sheet 1 of 2

9-2A

PDF DWG

Residential Low-Impact Local Access, Sheet 2 of 2

9-2B

PDF DWG

Residential Low-Impact Angle Point Details

9-3

PDF DWG

Residential Low-Impact Optional Tree Tract, Neighborhood Collector/Local Access

9-4

PDF DWG

Residential Low-Impact Typical Section - Pipe/Rock Gallery

9-5

PDF DWG

Residential Low-Impact Plan and Profile of Pipe/Rock Gallery

9-6

PDF DWG