City Policy on Piping Roadside Ditches
Unimproved streets typically do not have well designed, piped, underground drainage systems consisting of curb and gutter, catch-basins, manholes, clean-outs, and piped lines. Roadside ditches are provided to channel surface water away from the street and roadbed and provide a surface drainage facility for the adjacent properties to reduce the likelihood of localized flooding. Roadside ditches also present a road hazard to vehicles leaving the roadway, especially if the ditch banks are steep, and they present a potential health hazard by providing a breeding area for mosquitoes. However, roadside ditches are easier and less expensive to maintain than piped systems.
Some property owners, desiring to eliminate the roadside and potential health hazards, request that the ditch be piped and back-filled. The City does not have a funding source for this purpose. The Corvallis engineering standards for structured roadside drainage facilities are either a roadside ditch or curb and gutter piped drainage facility including curb inlets or other catch-basin facilities, pipes, manholes, etc. Fully improved drainage facilities consisting of curb and gutter and piped systems are preferred to roadside ditches but typically require full street improvements to urban standards. To accommodate a private property owner's desire to pipe and back-fill roadside ditches and provide road drainage, the Public Works Department administers a permitting process establishing design and material and installation guidelines to be used by the property owner.
The covered pipe/ditch is inferior in function as a roadway drainage system to either a roadside ditch or fully designed piped system and, as permitted by this action, not intended to be used as a parking area or other load-bearing roadway surface. The installation is intended to function as closely as possible as a drainage facility to that of an open ditch. The future maintenance of the filled ditch shall be assumed by the adjacent property owner.
The permit application may be downloaded. Fill out and bring all pages of the application to the Public Works Department office at 1245 NE 3rd Street for approval. The permit application may also be obtained at the Public Works Department office. A permit fee shall be submitted with the permit application. The permit fee is the same as for a plumbing permit (currently $100) and is subject to change.
All costs related to the piping and back-filling shall be paid by the property owner, including the permit fee and all future repair and maintenance of the piped ditch adjacent to the property. The property owner, and any subsequent property owner, shall assume liability for any damages or injuries that may result from improper installation or maintenance of the piped ditch, including localized flooding on private property.
The inspection services shall be performed by Public Works Utilities Division. Two inspections shall be done: the first to inspect pipe type, bedding and back-fill up to the springline; the second after the final back-fill of rock.
The piping material shall be perforated pipe and comply with AASHTO M252 or 294 standards, and/or ODOT Specification 00430.00, as applicable.
Installation shall consist of the properly sized pipe laid at the proper grade and shall comply with:
- manufacturer's recommendations, including using the proper connectors to existing piping, such as concrete driveway culverts;
- direction from Corvallis Public Works;
- and, inasmuch as possible, ASTM D 2321, Standard Practice for Underground Installation of Polyethylene pipe for Sewers and Other Gravity-Flow Applications.
The pipe shall be bedded on a backfill foundation and up to the springline on the pipe (the haunching areas) in Class I, 3/4"minus crushed rock, but the final backfill and cover shall be shall be round, open rock, Class II material (1 ½" to 2 1/2") compacted to a density of approximately 85%, which is typically achieved by hand-tamping. See drawing "Open Ditch Installation" to determine the bedding and fill to the springline. Care shall be exercised to avoid crushing or deforming the pipe. Any exposed end of the pipe shall be anchored with Class 20-25 lb quarry rock to prevent the pipe from moving and to minimize erosion at the pipe end. Optionally, the pipe may also be anchored with mechanical anchors such as bent rebar driven into competent soil or attached to precast weights.
Roof or foundation drains may be connected to the pipe using required fittings, or may be terminated in the ditch without making a connection to the pipe, using the ditch system as a French drain. If these drains are not attached to the pipe, they shall terminate in the trench in such a manner as to minimize erosion of fine aggregates into the pipe (i.e. 90 degree fitting pointing down, or drain end cap, etc.).
Drawings and Specifications
Envelope and Trench Dimensions
STD-102 Open Ditch Installation Typical Cross-Section
STD-601 Dissimilar Materials Adapter
STD-603 Dissimilar Materials Adapter