Admin Order 58-12-14 - Laserfiche WebLink

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for future discussions and a separate public process which will take into account other non - stormwater related concerns before they are implemented. The green street concepts, once finalized, would most likely be utilized in areas annexed to the City of Eugene. Generally speaking, with respect to financing, if a local street improvement is developer driven, it would be paid for by the developer. If it is initiated by the property owners through the formation of a local improvement district, it would be paid for by assessments to the abutting property owners. The UIC decommissioning elements (e.g. rain gardens and appurtenances) would most likely be funded by the City's stormwater utility fund capital improvement budget. Improvements to arterials and collectors streets may follow the City's "context sensitive" collaborative design process which incorporates significant opportunities for public input on road design, stormwater management, preservation of trees, funding options, and safety. Topic; Modeling and Capital Projects Modeled and observed conditions do not match up. Model does not extend far enough. Limited data upon which the model was based and the adjustment of the model to fit observed conditions [model calibration] is inadequate as the basis for major capital projects, and may result in oversized capital projects. [RR -4], [RR -6], [SC -41, [SC -61, [SC -7j The stormwater model used to evaluate the capacity of the public drainage system is a generalized representation of the system. Calibrating the model to match measured or observed conditions is an iterative process involving adjusting certain variables (within realistic ranges) and comparing results, adjusting again, and comparing results, until a best fit is obtained. The computer model for the RR -SC basin planning evaluated the capacity of approximately 160 open waterway and pipe segments under existing and future land use conditions. The models were updated using survey data collected by Lane County between October and December 2005. The model was validated and adjusted in response to historic photos and observed freeboard elevations provided by the City and through comparison of actual conditions at the Willamette Overflow using real rainfall data for the period from December 27, 2005 to January 3, 2006. Through the RR -SC model calibration process, the impervious surface area percentages were modified to reflect "effective impervious area" as opposed to mapped impervious area. This adjustment is realistic because of the relatively disconnected nature of the stormwater system in RR -SC, but it is still somewhat conservative (as evidenced by the fact that the surface water elevations predicted by the model are somewhat higher than observed values). See page 3 -7 of the basin plan for a more detailed discussion of the adjustment to ISA factors, and rationale. The current model is the best fit based upon best available information and professional engineering judgment of the engineering consultants, and the City's engineering staff. It is acknowledged that further refinement to the model based upon measured flow data would be RR -SC Stormwater Basin Plan Comments Pg.14 of 17