Hearings Official Decision - Laserfiche WebLink

detained onsite; or, discharged into a new stormwater flood control facility constructed by the applicant. Proposed and required stormwater flood control facilities shall be designed and constructed in compliance with code requirements. The applicant calculated the stormwater runoff using software which utilizes the Santa Barbara Unit Hydrograph Method. This method is acceptable and is considered an equivalent hydrological analysis to the Rational Method. Per the applicant's Stormwater Management Plan and Drainage Study, dated March 3, 2017, and stamped by Nathan Patterson, P.E., the stormwater treatment and management plan for the development includes the widening of a public street, the construction of a private street, and underground treatment and detention tanks. This report has identified five existing points of connection/discharge: (1) the eastern gutter line on Capital Drive, (2) Hendricks Park east of the development, (3) a shallow channel north of the site, (4) the western gutter line on Capital Drive, and (5) the adjacent neighboring properties to the west of Capital Drive. The applicant has broken the proposed stormwater management up into three initial components: (1) Capital Drive runoff, (2) private roadway runoff, and (3) individual lot runoff. The majority of Capital Drive currently sheet flows to the west where intermittent curb exists. In areas where curb does not exist, runoff drains to discharge point (5), which are the neighboring properties to the west of Capital Drive. Capital Drive The applicant has proposed to construct a flush curb on the west side of Capital Drive in the areas where a functioning curb currently does not exist. The proposal for a flush curb is consistent with existing drainage patterns. The applicant is proposing to reconstruct Capital Drive to City of Eugene local street standards, which includes constructing the road to a width of 21 feet. The road is proposed to be constructed in a fashion that mimics existing drainage patterns and quantities, with any additional street width draining to the east gutter. There is a high point in Capital Drive at approximately the middle of the site. Runoff south of the high point on the east side of Capital Drive will be collected into catch basins and directed to a mechanical treatment device near the southern intersection with the private roadway. The runoff will then exit the underground system via a bubbler and continue down the curb line at a rate less than or equal to existing rates. Runoff north of the high point on the east side of Capital Drive will be collected into a proposed catch basin and underground detention tank system that will discharge into an existing drainage ditch north of the site. Runoff on the west side of Capital Drive will drain at rates and locations that match existing conditions - either to the western gutter line or the adjacent neighboring properties to the west. Private Roadway The applicant has proposed three discharge locations for the runoff of the proposed private roadway. The first discharge point is for the southern portion of the private roadway, which will be collected by catch basins or a trench drain and will enter an underground detention tank. From here, the runoff will then be discharged into the eastern gutter line south of the intersection via a bubbler. The second discharge point for the private roadway is located at the bottom of the conservation area between Lots 13 and 14. Runoff for this drainage basin will be collected into various underground storage tanks that will reduce the peak discharge rate and release into the eastern conservation area west of the Ribbon Trail, via level spreaders. The third discharge point Hearings Official Decision (PDT 17-1) 72