Los Gatos Stream Gauge 5119 Modification Project

Located in Los Gatos Creek County Park in the town of Los Gatos, Los Gatos Stream Gauge 5119 (Gauge 5119) is used to measure instream bypass flows at the Kirk Diversion Dam established by the Lake and Streambed Alteration Agreement (LSAA) for the Kirk Diversion Operation and Maintenance Project (Notification No. 1600-2018-0386) to support downstream aquatic habitat. Gauge 5119 is located below a pedestrian bridge and on top of a concrete drop structure on Los Gatos Creek. The existing concrete drop structure is 53 feet long, extends 100 feet across the entire width of Los Gatos Creek, and serves as the weir for Gauge 5119. Flow over the top of the drop structure occurs as shallow sheet flow, and the Gauge 5119 flow readings correlate to the depth of the water on top of the concrete drop structure. Due to the shallow depth of water on top of the concrete drop structure, minor variations in stage (i.e., water surface elevation) result in large changes in flow readings, adversely affecting the accuracy of the flow measurements. Valley Water proposes installing a 1-foot-tall, 3/8-inch-thick steel weir plate over the top of the existing concrete drop structure. A v-notch in the center of the weir plate would concentrate low flows and produce larger changes in water depth for small variations in flow. This modification would improve the resolution and accuracy of the low flow measurements at Gauge 5119. A weir box would be affixed to the upstream face of the drop structure at the center of the weir. The weir box would provide hydrographers with a suitable cross section to take accurate discharge measurements for calibrating the stream gauge while reducing field safety hazards and streamlining data collection. A bubbler-type, differential pressure stream gauge enclosed in 1.5-inch-diameter galvanized pipe conduit would extend from the new gauge to an enclosed gauge house with a data logger above the right top of bank immediately upstream of the drop structure. Solar panels mounted on top of the enclosure would power the system. Valley Water Standard Best Management Practices (BMPs) and Santa Clara Valley Habitat Plan Aquatic Avoidance and Minimization Measures (Aquatic AMMs) have been incorporated into the project. The BMPs and Aquatic AMMs would protect riparian and aquatic habitat and prevent sedimentation and degradation of water quality in Los Gatos Creek. The project is anticipated to take 3 weeks to complete.