20B - AA - AGMT - DELHI DIVERSION

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(Element 3) could be modified, including pumping for a shorter duration, or if necessary shutting down the pumps at certain times to provide low flows that the USFWS and the SARWQCB find agreeable for discharge into the Upper Newport Bay. 2. Comment: Project implementation could result in increased erosion in the earthen downstream sections of the channel. The project would remove sediment from dry weather flows along the earthen section of the channel from Mesa Street to Upper Newport Bay. The lack of sediment deposition could encourage greater scouring during wet weather flows. Board recommends conducting a hydraulic study of the channel examining sediment transport prior to determining whether to construct the project. Response: OCFCD is currently aware of erosion issues along the earthen section of the channel from Mesa Street to Upper Newport Bay and is currently developing a channel restoration project to address these issues. Erosion issues result from upstream portions of the channel that are fully hardened in a fully urbanized watershed with comparatively minor sediment loading from the Delhi Watershed to Newport Bay Watershed (Shibberu, 2009). It is estimated that of the 74.7 tons of combined material removed annually from Santa Ana Delhi sub -watershed based on period 2012-2014 (OCFCD), 33.3% consisted of sediment which amounts to 24.6 tons of sediment. It is possible that 24.6 tons of sediment may be fully retained by the proposed diversion structure and removed by maintenance operations. This retained 24.6 tons of sediment constitutes 0.04% of the overall TMDL limit of 62,500 ton per annum for the Newport Bay Watershed (Shibberu, 2009) and would not require a hydraulic study of the channel examining sediment transport. During wet weather, water is not capable of pooling several feet deep behind the diversion structure before it is released downstream. Flows less than 20 cfs will be diverted through an off -channel diversion facility for screening treatment and returned to channel via a Bypass Culvert. Flows exceeding 20 cfs, but less than that of a 2-year water surface will pass through both the off -channel diversion facility trash nets, and main channel. Only the top 18 inches of flows are to be skimmed for floating litter and debris by a floating boom that rises to match the 2-year water surface. The boom will partially release after a 2-year water surface has been reached to maintain the 100-yearflood control capacity of the channel provided by both the off -channel diversion facility and the main channel at the proposed project site. At no point are flows fully contained by the facility, only 3 cfs of dry -weather flows may be pumped from the Bypass Culvert if not returned to channel. 2.3 COMMENTS FROM ORANGE COUNTY WATER DISTRICT (OCWD) — FEBRUARY 25, 2016 1. Comment: OCWD operates a non -potable recycled water supply system called the Green Acres Project that delivers recycled water to irrigation and industrial users. A portion of the Green Acres Project pipeline is located in the vicinity of the proposed Santa Ana Delhi Channel Diversion Project area. OCWD requests that the applicant consider potential impacts to this pipeline as the project is designed and constructed. Response: Comment noted. Project design plans include provisions for maintaining clearance of the Green Acres Project pipeline. 20B-15