Chapter 19.50


19.50.010    Purpose and intent.

19.50.020    General provisions.

19.50.030    Ditches – Ditch section.

19.50.040    Stormwater pipes – Curb and gutter section.

19.50.050    Catch basins, manholes and inlets.

19.50.060    Frames, grates and covers.

19.50.070    Materials and installation standards.

19.50.010 Purpose and intent.

This chapter describes the type, dimension, and size of materials associated with stormwater facilities as well as the methods of installation. Except where noted, all elements shall be as provided for by Washington State Department of Ecology regulations. All materials and installations standards for stormwater facilities shall conform to the following standard specifications. (Ord. 2007 § 1, 2017; Ord. 1978 § 1 (Exh. 6), 2016. DS § 1001)

19.50.020 General provisions.

A stormwater site plan prepared in accordance with the provisions of Chapter 19.45 FMC shall be prepared and reviewed by the Public Works Director prior to the commencement of any stormwater drainage construction. (Ord. 2007 § 1, 2017; Ord. 1978 § 1 (Exh. 6), 2016. DS § 1002)

19.50.030 Ditches – Ditch section.

A.    General. In general, ditches may be used for the stormwater conveyance requirement. The engineer shall provide a design subject to the approval of the Public Works Director. (Ord. 2007 § 1, 2017; Ord. 1978 § 1 (Exh. 6), 2016. DS § 1003)

19.50.040 Stormwater pipes – Curb and gutter section.

A.    General. Underground stormwater drainage shall be provided for curb street sections whenever the length of surface drainage exceeds 300 feet on road grades extending either direction from crest or sag on vertical curves.

B.    Stormwater Pipe – Mains. Other than pipes connecting street inlets to main stormwater pipes, stormwater pipe shall be a minimum of 12 inches in diameter and in accordance with standard specifications. Runoff shall be computed and, if the flow requires it, larger pipe shall be used.

C.    Stormwater Pipe – Connectors with Structures. Stormwater pipe connecting street inlets to main stormwater pipes by structure, i.e., catch basin or manhole, shall be a minimum of eight inches in diameter with a maximum length of 48 feet.

D.    Stormwater Pipe – Connectors without Structures. Connections of stormwater pipe leading from a street inlet location may be made into a main stormwater pipe without structure, subject to the approval of the Public Works Director and subject to the following requirements:

1.    The inletting structure shall be a catch basin and not a simple inlet lacking a catch or drop section.

2.    Outside diameter of inlet pipe shall not exceed one-half the inside diameter of the main stormwater pipe, or a minimum of eight inches, whichever is greater.

3.    Standard shop-fabricated tees, wyes, and saddles shall be used.

4.    Field tap connections require approval by the Public Works Director.

E.    Stormwater Pipes under Roads and Driveways (Culverts).

1.    Stormwater pipe under public roads shall have a minimum of two feet of cover.

2.    Culverts under driveways shall have a minimum of one foot of cover. Driveway culverts shall also be in accordance with these standards and shall have a minimum diameter of 12 inches and minimum length of 20 feet. Refer to Standard Detail ST-9 for culvert inlet/outlet information. (Ord. 2007 § 1, 2017; Ord. 1978 § 1 (Exh. 6), 2016. DS § 1004)

19.50.050 Catch basins, manholes and inlets.

A.    Spacing. Maximum spacing on stormwater conveyance between inlets or catch basins shall be 200 feet on road grades up to 3.0 percent. When road grade is 3.0 percent or greater, maximum spacing shall be 300 feet.

B.    Drainage Access Structures. Drainage access structures are required at:

1.    All changes in horizontal or vertical alignment.

2.    All connections to a main line pipe.

3.    All changes in pipe size.

4.    At a spacing no greater than 400 feet.

C.    Catch Basins – Shallow Pipes. Refer to the following table for stormwater pipes with depths less than five feet to flow line:

1.    Catch Basin Type 1

Standard Detail ST-4 (DOT B-1)

2.    Catch Basin Type 2 – 48"

Standard Detail ST-5 (DOT B-1e)

D.    Catch Basins – Deep Pipes. Refer to the following table for stormwater pipes with depths five feet and over to flow line to select the appropriate detail for joining or inletting structures:

1.    Catch Basin Type 2 – 48"

Standard Detail ST-2 (DOT B-1e)

2.    Catch Basin Type 2 – 54"

Standard Detail ST-2 (DOT B-1e)

3.    Catch Basin Type 2 – 72"

Standard Detail ST-3 (DOT B-1f)

4.    Catch Basin Type 2 – 96"

Standard Detail ST-3 (DOT B-1f)

E.    Manholes. Where a structure is needed for access or for juncture of stormwater pipes, but not for catchment of silt, the structure shall be one of the following types of manhole:

1.    MH Type 1 – 48"

Standard Detail SS-3

2.    MH Type 2 – 48"

Standard Detail SS-3A

3.    MH Type 3 – 48" to 96"

Standard Detail SS-4

F.    Specifications – Catch Basins, Manholes and Inlet Structures. Provisions contained in the state standard or APWA standard specifications shall apply, unless otherwise specified, to catch basins and curb inlets as well as manholes. Concrete inlets shall conform to Standard Detail ST -7 (B-26). Catch basin appurtenances shall conform to Standard Detail ST-1, ST-2 or ST-3.

    Subject to approval by the Public Works Director, drainage structure materials other than reinforced concrete may be used; provided, that required specifications are available to control quality and acceptable user experience with the product can be shown.

G.    Curb Inlets without Drop Sections. Curb inlets without drop section or catch may be used provided they are connected to a main stormwater pipe by a catch basin.

H.    Yards and Roof Drainage. Adequate measures shall be taken to limit stormwater drainage from yards and roof drains so as to prevent water damage or nuisance within the right-of-way. Design must conform to Standard Detail ST-16 unless no existing stormwater system is in place, in which case such measures may include the following:

1.    Four-inch pipe laid subsurface from yard into nearest catch basin or curb inlet.

2.    Three-inch pipe laid from yard inlet under sidewalk and out through curb face. This method is not permissible when curb is on high side of superelevation or in any situation in which street stormwater drainage cannot be confined to gutter receiving yard stormwater.

I.    Non-Main Stormwater Pipes. Designated stormwater pipes shall be connected to main pipes through a catch basin or manhole to collect stormwater from lots, yards, and isolated impervious areas such as houses. Pipes shall conform to the following criteria:

1.    The minimum diameter shall be eight inches.

2.    Tees are acceptable as connections to downspouts and other small drainage structures. (Ord. 2007 § 1, 2017; Ord. 1978 § 1 (Exh. 6), 2016. DS § 1005)

19.50.060 Frames, grates and covers.

A.    Catch Basin Frames, Grates and Covers. Catch basin frames, grates and covers shall conform to City of Ferndale Standard Details ST-5, ST-6, ST-9, ST-10 and ST-11.

B.    Flat Surface Inlet. On drainage structures under vertical curb and gutter, under average conditions, the frame and grate shall be as shown in the drawings or equal. When the structure does not serve as an inlet, a solid cover, or equal, shall be used. Frame and grate or lid shall be incorporated into curb and gutter sections.

C.    Through Curb Inlets. On drainage structures under vertical curb and gutter, a through curb inlet frame shall be used where conditions limit the effectiveness of a flat surface inlet. This will reduce problems such as clogging from leaf fall or other debris, especially in sag vertical curves.

    When used with this through curb inlet frame, the standard grate shall, in all cases, be ductile iron. Installation of the through curb inlet shall be as shown in the City of Ferndale Standard Detail R-8. Through curb inlets shall be preferred over flat surface inlets.

D.    Lock Bolts. Locking bolts shall be provided on frames and grates or covers unless otherwise approved by the Public Works Director.

E.    Specifications – Cast and Ductile Iron Components. Unless otherwise specified, cast-iron products shall conform to ASTM Designation A 48 Class 30 and ductile iron to ASTM Designation A 536 Grade 80-55-06. (Ord. 2007 § 1, 2017; Ord. 1978 § 1 (Exh. 6), 2016. DS § 1006)

19.50.070 Materials and installation standards.

A.    General. Drain pipe materials and installation shall be in accordance with the current edition of WSDOT or APWA standard specifications and with the following:

1.    Bedding and Backfill. Pipe bedding and trench backfill requirements shall be as shown in City of Ferndale Standard Detail SS-1 (DOT B-18c) and as specified in the state standard specifications.

2.    Cross Culvert Sizing. Where open channels intersect public streets, the minimum diameter cross culvert shall be 18 inches, unless otherwise approved. Cross culverts shall be designed to carry the design runoff with a headwater depth not greater than two times the culvert diameter for culverts 18 inches or under, or one and one-half times the culvert diameter for culverts greater than 18 inches.

3.    Pipe Anchors. Pipe anchors may be required when pipe slopes exceed 15 percent, or when drainage structures are constructed in, or placed on, unstable soils unless the stability of the soils and the placement of the pipe are certified by a licensed geotechnical engineer.

4.    Catch Basins. Catch basin materials shall conform to Standard Details ST-1, ST-2, ST-3, ST-4 and ST-7.

5.    Design of Cross-Sections. Street ditch cross-sections may be “V” shaped or trapezoidal.

6.    Rock Channel Liners. Rock lining shall meet the following requirements:

a.    Rock gradient shall be as follows, at a minimum:

    Passing eight-inch square sieve: 100 percent.

    Passing two-inch square sieve: zero to 10 percent.

b.    Rock shall be placed so as to form a firm, dense protective mat and conform to the design surface of the ditch. Individual rocks shall not protrude more than three inches from that surface. Actual ditch dimensions shall be based on calculated stormwater flows. (Ord. 2007 § 1, 2017; Ord. 1978 § 1 (Exh. 6), 2016. DS § 1007)