Two-Dimensional Modeling of Paonia Reservoir Drawdown Flushing

Reservoir sedimentation is impacting all Bureau of Reclamation (and other public and private) facilities as water storage and supply become increasingly threatened with the aging infrastructure. Drawdown flushing can be used to remove reservoir sediment in small gorge-shaped reservoirs and to extend the reservoir life span. The efficiency of the sediment removal during drawdown flushing depends on many factors, including timing, duration, and reservoir shape, among others.

In this study the efficiency of reservoir drawdown flushing with different reservoir shapes will be studied using a two dimensional hydraulic and sediment transport model. The research includes two parts: (1) calibration of the numerical model to a real reservoir sediment flush event, and (2) application of the calibrated numerical model to a set of reservoir types modified from the real reservoir geometry. This paper will focus on the calibration process.

For the first task, Paonia Reservoir will serve as the example case. Paonia Dam and Reservoir are located on Muddy Creek, a tributary of the North Fork Gunnison River in western Colorado. Based on the bathymetric survey of the entire reservoir, conducted in June 2013, the estimated average annual rate of sedimentation has been 101 acre-ft per year. The as-built storage capacity of Paonia Reservoir is 20,950 acre-feet, meaning nearly 25% of the reservoir’s original capacity has been lost.

During spring of 2014, drawdown flushing was performed at Paonia Reservoir. The SRH 2D numerical model will used to simulate this drawdown flushing event. During model calibration, sediment concentration of reservoir release will be used for comparison.