Supplemental Materials - Laserfiche WebLink

UO North Campus June 15, 2018 Conditional Use Permit Stormwater, Sanitary Sewer, and Water Analysis Report flooding concerns. However, future modification to the control structure may be required depending on the grading and hydraulic requirements for future projects adjacent to the Millrace. The conveyance system downstream from the control structure consists of dual box culverts extending under the railroad tracks. The Millrace continues as an open channel downstream from the railroad tracks and passes through another culvert at the bike path crossing prior to discharging to the Willamette River. It is anticipated that future development within Basin A will maintain similar drainage patterns and will continue to drain to Destination Point A. Redevelopment may include new or reconfigured piped conveyance systems and new outfalls to the Millrace, and the delineation of Basin A may change over time. However, the existing piped conveyance systems and outfalls will remain intact to some degree. There are no known capacity issues with the public drainage system for Destination Point A, but redevelopment projects within Basin A will need to assess capacity issues within the existing private storm drain system on a project-by-project basis. New outfalls to the Millrace may be subject to additional stormwater management requirements under the Endangered Species Act. Refer to Destination Point D for further discussion. Riverfront Pump Station (Basin B / Destination Point B): Destination Point B is Riverfront Pump Station, and is the destination point for the Basin B. The public storm drain systems within Riverfront Parkway and Millrace Drive are expected to have adequate capacity and depth to fully accommodate redevelopment within Basin B on the south side of the railroad tracks. The public storm drain system extending north of the railroad tracks is expected to accommodate future development within the existing limits of Basin B north of the railroad tracks, and may be capable of serving a larger basin area east and west of the existing limits of Basin B. Future projects north of the railroad tracks will need to assess pump station limitations with City staff if the limits of Basin B are expanded with redevelopment. It should be noted that the Riverfront Parkway pump station and the surrounding land surface is within a depression. This area is below the base flood elevation at the adjacent Willamette River and below the water surface elevation of the Millrace. Drainage for this area relies entirely on the pumping systems and there is no overland conveyance route for floodwater to escape. Because of this, special care should be taken when extending the Riverfront Parkway storm drain system to the area north of the railroad tracks, to ensure that flood risks are considered. Grading modifications north of the railroad tracks should be designed with similar precautions. North Athletic Field Basin (Basin C / Destination Point C): private piped outfall to the Willamette River located just west of Autzen footbridge and is the destination point for Basin C. Redevelopment projects within the Riverfront area may utilize the existing piped conveyance system upstream from Destination Point C. Depending on stormwater management strategies, it may be possible to expand the contributing basin area for Destination Point C, however, this system is relatively shallow and may not be suitable for extension significantly beyond the existing basin area. North Millrace / Willamette Basin (Basin D / Destination Point D): Proposed development within the area north of the railroad tracks (Riverfront area) will utilize onsite infiltration and will maintain sheet flow drainage patterns to the Millrace and Willamette River where practical. Where onsite infiltration and sheet flow are not practical, piped conveyance will be required. It may be possible to extend piped conveyance systems from Destination Points B, C, and E, but those systems |5