Drainage facilities on city roads shall conform to the surface water design manual adopted in Chapter 15.18 SMC. Requirements for drainage plan submittals are also included in the surface water design manual adopted in Chapter 15.18 SMC.
(Ord. 483 § 5.1, 1980; Ord. 1198 § 8, 2017)
A. 
Storm drainage shall be provided for curb street section whenever the length of surface drainage exceeds 300 feet on road grade extending either direction from the crest or sag of vertical curves.
B. 
Storm drain pipe other than pipe connecting inlets to the main storm drain shall be a minimum 12-inch diameter and of specified rubber-gasketed corrugated metal or rubber-gasketed concrete pipe. Runoff shall be computed and, if the flow requires it, larger pipe shall be used.
C. 
Storm drain pipe connecting inlets to the main storm drain by structure, i.e., catch basin or manhole, shall be minimum eight-inch diameter rubber-gasketed corrugated metal or rubber-gasketed concrete pipe, with a maximum length of 55 feet.
D. 
Connections of storm drain pipe leading from an inlet location may be made into a main storm drain without structure, subject to case-by-case approval by the engineer 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. 
Inlet-connection and main storm drain pipes shall be of same material and type, either rubber-gasketed corrugated metal or rubber-gasketed concrete pipe.
3. 
Length of the inlet connection shall not exceed 55 feet.
4. 
Standard shop-fabricated tees, wyes, and saddles shall be used, except that connections with concrete pipe may be field-tapped.
E. 
Zinc-coated (galvanized) corrugated iron or steel pipe shall be coated with protective Treatment 1 in accordance with Section 9-05.4(3) of the State Standard Specifications.
F. 
Subject to approval by the engineer, other pipe materials and methods, such as but not limited to plastic or cast-in-place concrete pipe, may be used; provided, that conditions make it feasible, recognized specifications are available to control quality, and acceptable user experience with the product is shown.
G. 
The rubber gasket requirement above may be waived by the engineer if it can be shown that joint leakage will not be an adverse factor.
H. 
Storm drain gradients shall be such as to assure minimum flow velocity of three feet per second when flowing full.
I. 
Closed (underground) drain lines shall not be located with the centerline closer than five feet to any property line separating adjacent lots or tracts. A drainage easement shall be located entirely within a single lot or tract, except where linear extent of the drain line may involve additional properties.
(Ord. 483 § 5.2, 1980; Ord. 1198 § 8, 2017)
A. 
Maximum space on surface drainage courses between inlets or catch basins shall be 200 feet on road grades up to one and one-half percent. When the road grade is one and one-half percent to three percent, maximum spacing shall be 300 feet; when the grade is three percent or greater, maximum spacing shall be 400 feet.
B. 
Maximum spacing on main storm drains between access structures, whether catch basins or manholes, shall be 600 feet.
C. 
Curb inlets without drop section or catch may be used provided they are connected to a main storm drain by catch basin.
D. 
Adequate measures shall be taken to limit surface drainage from yards and roof drains so as to prevent water damage or nuisance within the right-of-way. Such measures may include but are not limited to the following:
1. 
Three-inch pipe laid subsurface from yard inlet to 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 drainage cannot be confined to gutter receiving yard runoff;
3. 
Eight-inch pipe stubbed from catch basin or curb inlet structure to back of sidewalk and plugged, to provide future connection to one or more yard drains.
(Ord. 483 § 5.3, 1980; Ord. 1198 § 8, 2017)