Improved Monitoring at Upper Highline Dam to meet Colorado’s Early Warning System Program Requirements

The Early Warning System Program (EWSP), recently developed by Colorado Dam Safety, is used to reduce the hydrologic hazard category for a dam and thereby reduce the required Inflow Design Flood (IDF) by providing advanced warning of an impending hydrologic event that could lead to a dam failure. Upper Highline Dam, owned and operated by Colorado Parks and Wildlife, currently has an ‘extreme’ hydrologic hazard classification and the existing spillway is inadequate to pass the required PMP before the orifice wall over the spillway is overtopped. Meeting the requirements of the EWSP for Upper Highline Dam would reduce the risk of downstream impacts from a potential dam beach and allow the hydrologic hazard classification to be reduced to ‘high’ and the required IDF would be within the current spillway capacity. As a result, dam safety risks are decreased, and potential design and rehabilitation costs are minimized.
We present the design and analyses used to meet the EWSP requirements at Upper Highline Dam, which includes an automated data acquisition system (ADAS), real-time data-based alerts, and life loss reduction analysis. Elements of the ADAS include a reservoir level sensor with float switches at key elevations for redundancy, water level monitoring at the first downstream road crossing, and other geotechnical monitoring such as foundation drain flow monitoring, embankment and foundation piezometric levels, and spillway wall deflection monitoring. Data from the ADAS is remotely viewed via an online data platform with automated alerts set at critical threshold levels. Implementation of the ADAS was completed in the early spring of 2022 and Upper Highline Dam is one of the first dams in Colorado to meet the requirements of the EWSP.