After years of planning and design, the Santa Clara Valley Water District constructed flood protection improvements along Permanente Creek in Mountain View, California. Known as the Permanente Creek Flood Protection Project, this design helped to improve stormwater quality in the area, assist in protecting residents downstream from flooding concerns, all while creating recreational opportunities and enhancing the environment.
The McKelvey Park Detention Basin Project is one of the elements of the Permanente Creek Flood Protection Project. It included the redevelopment of a 0.7-acre mini-park which doubles as a detention basin that will store large volumes of stormwater from Hale and Permanente Creeks during a 50-year flood event or larger.
Another important element of this project was the collection and treatment of stormwater from more than 160 acres of city roads, public spaces, and commercial properties in the area. Because the State of California has adopted trash amendments which require cities to install and maintain full capture trash removal devices or take a multi-tier equivalency approach to removing trash from stormwater runoff, the City of Mountain View opted to install a CDS hydrodynamic separation system to remove sediment and 100% of the trash and debris from stormwater runoff in this area surrounding McKelvey Park.
The City of Mountain View and the Consulting Engineer had several positive experiences with CDS, having installed them on numerous projects in the past. The City examined the long-term lifecycle costs for using multiple individual catch basin screens compared to a smaller number of large devices like the CDS. While the CDS systems are initially more expensive, they have significantly lower maintenance costs, excellent performance history and reliability, making CDS the City’s choice for their ongoing trash control efforts.
The CDS system included a 12-foot diameter manhole with a 9’ diameter, 8’ tall separation screen, and an 8’x16’ diversion vault treating over 47 cfs from 160 acres of high-density urban development.
Installation was completed in less than a week in a crowded urban area and a tight construction site. Large trucks, overhead clearance for the cranes, and street access all had to be managed. Contech played a vital role in the delivery and installation of the system. A Contech Project Coordinator worked on delivery schedules and coordination. Most loads were oversize with a pilot car, which meant they needed to comply with roadway curfews and detailed routing to the job site. A Contech Field Representative was also on-site, providing contractor support during the installation.
While many full capture screening devices require maintenance after every storm, the CDS typically only requires annual maintenance. Additionally, CDS can be maintained from the surface without the need for confined space entry. This allows the City to maintain the CDS with its own crews and equipment.
Contech held a maintenance demonstration of the CDS system in August of 2019. The event was attended by representatives from Contech, the City of Mountain View, Caltrans and other local municipalities. The event allowed attendees to see firsthand just how simple it is to maintain a CDS system. It also demonstrated the system’s ability to capture and hold several cubic yards of sediment, trash and debris, even when experiencing extended periods of time in between maintenance events.
This portion of Mountain View is now covered by this CDS system, and trash within this drainage area will no longer be able to make its way into Permanente Creek and out to the San Francisco Bay.