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SECTION 4 water Quality Eualuatiou A CP fact sheet for each of these projects is included in Appendix A. It should be noted that at the time of writing of this report, Lane county funding for CPs has not been identified. 3) On- Street Rain Garden Option for Local Streets — The South of Horn Lane drywell cluster includes a relatively large area with many drywells (26 County wells and 1 City well). Almost the entire area within the River Road Santa Clara basin and south of Horn Lane is drained through the use of drywells and informal surface infiltration, except for the area adjacent to and including River Road which is drained through a piped system. In addition, this area reflects a mix of County and City jurisdiction (sometimes on a lot -to -lot basis). As redevelopment and street improvements occur in this area, it is likely that City annexations will also occur. For this area, constructing pretreatment systems and pipes to discharge to the nearest surface drainage was considered to be infeasible due to the flat topography and lack of available capacity in the downstream system. The decommissioning option that was selected for this drywell cluster was to construct street side rain gardens for the storage and infiltration of runoff as local street improvements occur. For this option, individual properties adjacent to the right of way (ROW) would be required to manage their drainage on -site, in accordance with requirements for stormwater in the City of Eugene Code (Chapter 9, Section 9.6791(3)), and the street side rain gardens would be constructed to handle all runoff from the ROW (for a five -year design storm). Six different concept options were evaluated in terms of providing street side rain gardens for handling drainage from local streets. Each option assumes a base 45 -foot ROW width and various initial raingarden configurations. The six initial options were evaluated to determine the amount of additional ROW that would be required to accommodate runoff from the ROW during the 5 -year design storm. The six initial options are described according to the following: 1. Shed Cross - Section, Reduced Parking Bays One Side, Sidewalk Opposite Side 2. Shed Cross - Section, Parking Bays One Side, Sidewalk Opposite Side 3. Crown Cross - Section, Reduced Parking Bays One Side, Sidewalk Opposite Side 4. Shed Cross - Section, On- Street Parking, Sidewalk One Side 5. Crown Cross - Section, On- Street Parking, Sidewalk Both Sides 6. Crown Cross - Section, On- Street Parking, Sidewalk One Side Figures illustrating these six initial options are provided in Appendix F. Each option was evaluated as one ROW unit, which includes four 50 -foot wide residential lots on each side of the street and a base ROW width of 45 feet. For each option, the pervious and impervious areas associated with the ROW were computed, and the Santa Barbara Urban Hydrograph method was used to estimate the volume of runoff that would need to be accommodated by the rain gardens for a 5 -year, 24 -hour design storm of 3.6" using an SCS Type IA rainfall distribution. Rain garden sizing was based on guidance from Eugene's manual (Eugene's Stormwater Management Manual, 2006) for a rain garden facility. The rain gardens were assumed to be 12" deep with a 3:1 horizontal to vertical sideslope. By comparing the volume of runoff generated during the 5 -year design storm with the volume of storage associated with the initial rain garden configurations, the initial rain garden configuration did not accommodate all of the volume of runoff as necessary. Therefore, the additional ROW width 0:\25695978 Eugene RR -SC Final Basin P1an\Master P1anTINAL 2- 2010\Master_Plan 3- 11- 10_FINAL_ Word _Version.doc 4 -13