Bear Gulch

Bear Gulch

Background:

The Bear Gulch site is in the Wunderlich County Park and nature preserve in Woodland, CA. This gravity diversion is one of two that feed Bear Gulch Reservoir which is managed by the California Water Service. Bear Gulch Reservoir holds up to 215 million gallons of water which serves as drinking water to approximately 55,000 residents of Menlo Park, Atherton, Portola Valley, and Woodland.

The Bear Gulch retrofit project involved an upgrade to an existing diversion dam to bring it up to modern specifications and fish protection requirements. A temporary earthen dike was installed upstream to dewater the site so that demolition crews could remove the existing diversion dam, intake box/grate, shotcrete, and much of the existing structure. The upgrade included installation of an air-filled bladder activated Obermeyer dam, touch screen interface, a sediment sluicing system, and a fishway with two ISI fish screens. These screens are used to divert water to Bear Gulch Reservoir.

The conical ISI fish screens are each 66 inches (1,676 mm) in diameter and 18-inches (457-mm) tall with 1.75 mm slot openings and a 50 percent open area. The screens are in a bar rack protected forebay at the top of the fishway and include a raised pedestal design and sluicing system to remove sediment. Each screen has a hydraulic drive mechanical brush-cleaning system and a capacity of 8.3 cfs (5.4 MGD, 846 m³/h) per screen at an approach velocity of 0.33 fps (10 cm/s).The cones keep the resident and anadromous fish safe as they move through the screen bay while also acting as a barrier to prevent sediment or debris from ending up in the diverted water.

Benefit of ISI System

The following are the key benefits of the ISI screen system design at this site:

1. The conical screen shape maximizes diversion capacities during low water elevations while maintaining compliance with stringent fish protection requirements.
2. The placement of the screens in the fishway reduces the total project footprint and keeps the screens out of the path of flood waters when they occur.
3. The raised pedestal design maintains natural sediment transport processes in the fishway which includes the sluicing system that is designed to perform a cleaning flush during high water events to remove sediment build up.
4. ISI’s mechanical brush-cleaning system maintains a clean screen surface which ensures compliance with fish protection requirements and ensure reliable diversion of water into the reservoir.

Owner:

California Water Service Co.

Engineer(s):

GHD

General Contractor:

Syblon Reid

Location:

Bear Gulch, Woodside, CA, San Mateo County