![]() ![]() If you are considering modifying the ditches within a creek watershed, the City encourages use of a natural drainage system approach. A reasonable use of the adjacent property is not possible unless the exception is approved or harm or threat of harm to public health, safety and welfare, the environment, or public and private property is at risk unless the exception is approved.Įxceptions to the ditch filling moratorium policy include culvert installations that are necessary to implement driveway permits, and required street improvements.An emergency situation necessitates approval of the exception.If the proposed modification is not equally protective, the Director may approve a requested exception if substantial reasons are documented such as: After consultation with SPU, the SDOT Director may approve a requested exception per the Street Use Code SMC 15.04.112 (Decisions–review or reconsideration) if the Director determines that the modification is likely to be equally protective of public health, safety and welfare, the environment, or public and private property. The City does not permit the replacement of an existing ditch with a culvert where the ditch functions as part of the City’s informal drainage system in the street right of way. Additional information is included in SPU CAM 1180 Design Guidelines for Public Storm Drain Facilities (2012). The engineer shall provide the hydraulic calculations used in the pipe design for review by SPU. They shall be designed to be continuous with existing and future storm drain pipes that are, or will be part of the storm drainage system. New public storm drains shall be sized to handle all upstream tributary area from the drainage basin in which they are located. When there is no available public storm drain or public combined sewer, and there is no acceptable discharge point, and/or.Public Storm DrainsĪ new public storm drain may be required: Design information is provided in Section 5.8.3 of Stormwater Manual: Volume 3 – Project Stormwater Control and Standard Plan 294, in the Amendments section. Biofiltration swales are typically configured as flow-through systems, with little or no detention or storage. This combined use can reduce development costs by eliminating the need for separate conveyance and treatment systems. A swale can be designed for both treatment and conveyance of stormwater flow. Biofiltration swales are designed so that stormwater will flow evenly across the entire width of a densely vegetated channel. Pollutant removal occurs by filtration as stormwater moves through the grass blades, which enhances sedimentation, and trapping and adhesion of pollutants to the grass and thatch. ![]() A biofiltration swale is an open, gently sloped, vegetated channel designed to treat stormwater. Instead of using conveyance swales, a biofiltration swale may be proposed. Stormwater is conveyed along a gutter line or along road side conveyance swales. Stormwater conveyance must be considered and included in all ROW project designs. SPU CAM 1180: Design Guidelines for Public Storm Drain Facilities. Standard Specifications Division 7: Storm Drain, Sanitary and Combined Sewers, Water Mains and Related Structures Standard Plans 200 Series: Sewer / Drainage Appurtenance, For alternative street grading concepts, designers have looked to the WSDOT Hydraulics manual for guidance on evaluating flow spread along the gutter line. Streets shall generally have a centerline crown elevation, with some exceptions, such as super-elevated streets. Cross slope of street shall ensure surface drainage flows to the gutter or flow line and is conveyed to drainage pickup points. Standards for cross slopes and longitudinal slopes are important for vehicular and pedestrian safety as well as surface water conveyance. 4.8 Other Street Right-of-Way Improvement Activitiesĭrainage infrastructure shall be provided for improved streets and alleys and shall include catch basins and inlets that discharge to a public combined sewer, public storm drain, or other discharge point approved by SPU.Street and Sidewalk Right of Way Opening and Restoration Rule.Excavation, Shoring, and Safety Systems During Construction.Demolition and Grading During Construction.Construction Inspection and Testing Procedures.4.3 County, State and Federal Permits and Approvals.4.2 City of Seattle Environmental Review and Approvals.Neighborhood Greenways and Trail/Shared Use Path Crossings.1.4 Departmental Roles and Responsibilities.1.3 Other Policy Standards and Guidelines. ![]()
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