E 350 Drainage Controls and Criteria

One of the factors that may exert a controlling influence on the street design is drainage and its disposal. Although this phase is normally handled by the Storm Drain Design Division or the Storm Drain Sections of the Districts, it is essential for the street designer to have some basic knowledge of the problems, responsibilities, and liabilities, etc. of the City, the property owner, and the storm drain designer.

One of the controlling factors of immediate concern to the street designer is the City’s policy of not permitting a street or alley to be improved or partially improved without providing a means for adequate drainage.

For example, it is not permitted to design a street improvement so that the water from the abutting property and the proposed improvement drains onto an unimproved street, or a partially improved street without drainage control, or other private property.

However, if it can be established that the amount of water involved is negligible and will not damage, erode, or otherwise worsen the existing drainage conditions of the existing street section or of private property, construction may be permitted.

If a considerable amount of water is involved which drains onto private property, and a drainage easement or a waiver is obtained from the property owners, the proposed street improvement may be permitted.

Other controlling factors as dictated by drainage are based on studies that have to be made by the storm drain designer, such as a joint analysis of rainfall frequency and duration, the longitudinal street grade, pavement cross-slopes, curb and inlet types, and spacing of inlets or discharge points. This intonation is needed to determine whether the width of water on the pavement during selected storm frequencies is great enough to unduly interfere with traffic flow.

Since the controls and criteria involved for the above studies require extensive treatment, reference is made in this regard to the Storm Drain Design Manual.  In addition, other aspects of drainage control and criteria as directly related to street design are covered in various sections of this Street Design Manual, such as Chapters E 400, Cross-Section Elements, and E 500, Grade Determination, etc., and under subsections such as butters, Curbs, Cross-Sections, etc.