PACE performed an extensive hydrologic and hydraulic analysis to develop a series of flood control channel improvements designed to increase the conveyance capacity of the existing creek system in order to provide flood protection, creek stabilization, and removal of existing flood hazard designations within portions of Conejo and Calleguas Creeks. One of the objectives of the project is to minimize the impacts on the existing environmental resources in the creeks and adjacent properties caused by the proposed channel improvements. Naturalized flood protection methods have been developed including a restored creek corridor and a manmade lake system to support conveyance and detention during major storm events. Major benefits of the proposed channel improvement techniques include improved flood protection levels, elimination of flood hazard zones from adjacent property, and enhancement of riparian vegetation and public recreational elements.
The hydraulic issues associated with the project are (1) downstream hydraulic control, (2) existing channel elevations at project limits, (3) physically constrained channel top width, (4) horizontal alignment constraints, (5) exposed bedrock locations, (6) existing floodplain vegetated corridors, and (7) wide/shallow floodplain limits. For the Calleguas Creek channel, the recommended project channel improvements along Calleguas Creek generally consists of (1) widening the existing channel on the east side of the channel through the excavation of a large terrace or bench elevated slightly above the existing channel flowline and (2) the installation of a soil cement revetment along the entire relocated eastern channel bank. The proposed channel improvements along Conejo Creek vary according to channel reach, but in general, the modified channel will function by conveying the flows in a widened channel in the upstream reaches, and then an engineered bypass channel will join the existing channel downstream in a widened terraced channel system. Portions of the channel will be widened with soil cement revetment along both banks. The channel’s third reach includes a newly excavated earthen bypass channel that is completely incised and vegetated. The bypass channel will be landscaped to create a restored riparian channel corridor with different water quality treatment elements, including multiple ponds and meandering low-flow creek feature. The bypass channel is intended to have multiple project benefits including a passive landscaped feature with walking trails as well as a portion of the water quality treatment for the project.