2017 CASQA Award Winner - Outstanding Regional Sustainable Stormwater Project: Gobernadora Multipurpose Basin
Gobernadora Multi-Purpose Basin is a specialized 26-acre facility developed as a unique opportunity to reclaim an untapped water resource while improving water quality. The facility is located in South Orange County and was conceived through a public-private entity collaboration including Rancho Mission Viejo, Santa Margarita Water District (SMWD) and Orange County Public Works. The basin features many specialized design elements and provides multiple benefits including:
- Groundwater recharge and recovery
- Non-potable water reclamation
- Flood mitigation / storage
- Urban stormwater treatment
- Natural stream stabilization / habitat restoration
The basin is located adjacent to the natural alluvial Cañada Gobernadora Creek draining a fully urbanized watershed area of 7.8 square miles and provides the ability to capture and utilize 350 to 800 acre-feet of urban nuisance runoff annually. There were numerous physical and regulatory constraints on the project site due to wildlife habitat, an active alluvial creek system, high groundwater, topography, existing utilities, adjacent public park and residential area. To manage these constraints, the site was configured into two separate basins, an upper 10.9-acre basin providing stormwater treatment and a lower 15.9-acre basin providing flood protection, which are connected by a spillway system. The combined maximum flood control storage volume is approximately 120 acre-feet.
The upper stormwater treatment basin contains four interconnected water quality wetland treatment cells that receive all urban stormwater runoff diverted from the creek through a hydraulically controlled diversion facility. The treated urban nuisance flows are recharged into the aquifer and the surface flows are captured by SMWD using a pump station located in the upper basin that connects to the non-potable water pipeline. The unique layout of the pump station wet-well was divided into four separate chambers providing multiple functions and allowing flexibility in operations. Two groundwater production wells along the basin perimeter capture a portion of the groundwater and also connect to the pump station.
The lower flood control basin provides flood storage with peak flow attenuation for all storms exceeding a 10-year event through the use of a side-weir adjacent to the upper basin. The side-weir intercepts a portion of the creek flows and allows valuable sediment to continue travel downstream to maintain stream stability.
Two large custom inflatable dams located within the creek control flows and water levels. One dam captures dry-weather flow and the second dam provides flood management by creating variable water levels for the side weir. A unique feature of the basin system is that it can automatically change between dry-weather operation for stormwater reuse/treatment and flood protection during large storms according to the amount of flow in the creek. The dynamic operation of the system reduced the facility size requirement and added water reclamation and flood control benefits. Water level sensors in the creek connect to the facility computer programmable logic control (PLC) which determines inflation timing of the rubber dams. The upper dam is normally inflated to divert all creek nuisance flows during non-storm periods. Storm flows trigger the upper dam to deflate, the diversion structure slide gate to close, and the lower dam to inflate to increase water levels which allows flood flows to spill over the side weir into the upper basin. This project is an excellent example of integrated regional watershed planning involving multiple watershed stakeholders to maximize beneficial water uses and leverage alternative water sources.
Bruce Phillips is Senior Vice President for PACE, a specialized company in environmental water resources and hydraulic research located in Fountain Valley. Bruce has over 30-years of experience in stormwater/flood management/river engineering/hydraulic analysis/hydrology. He has master of science degrees in both Civil Engineering from California State Long Beach and also Petroleum Engineering from USC. He is also a lecturer in a variety of hydrology and hydraulics courses at the California State Long Beach civil engineering department for over 25-years. In addition, Bruce has published over 60 different papers on stormwater water management and river engineering.