Determining Large Flood Events on the Paria River for a Rapid Response Alternative High Flow Experiment. Colorado River Storage Project. Glen Canyon Dam, Arizona. Upper Colorado Region.

摘要

At the request of Bureau of Reclamations (Reclamation) Upper Colorado (UC) Regional Office, analyses were performed on the Paria River by Reclamations Technical Service Center (TSC) to evaluate an alternative High Flow Experiment (HFE) protocol for Glen Canyon Dam operations, proposed by the Western Area Power Administration (WAPA). The alternative HFE proposes to coordinate controlled releases from Glen Canyon Dam with sediment-rich flood events in the Paria River. One goal of the coordinated releases is to increase the ecological benefits downstream of Glen Canyon Dam through Marble Canyon. As part of the evaluation process, this study investigated various types of water and sediment related data sources to determine the feasibility of predicting the occurrence of a large flood event in the Paria River. As a surrogate for continuous sediment data, continuous hydraulic discharge data from two different United States Geological Survey (USGS) gages in the Paria River Basin were statistically analyzed to determine if a relationship between the upstream USGS discharge gage near Kanab (Kanab gage), Utah (UT), and the downstream USGS discharge gage at Lees Ferry (Lees Ferry gage), Arizona (AZ), could be developed to predict large flood events. The Kanab gage is identified as the indicator gage and the Lees Ferry gage is designated as the resultant gage. This report documents the steps taken to determine the relationship between the two gages, and the threshold magnitude of resultant flood events that could be statistically predicted at the Lees Ferry gage. The analyses presented in this document do not address any of the sediment processes that will occur in the Colorado River if a HFE is coordinated with a flood in the Paria River. There are several important sediment related issues that will be important to the benefits that would result from this action. One important consideration is that the sediment concentration, storage, and river bed evolution are not perfectly correlated with flow discharge. There will be hysteresis in the relationship between sediment concentration and flow discharge meaning that sediment concentration is not only dependent upon the current discharge, but also on the flow history. Also, the sediment available for transport near the confluence of the Paria and Colorado River will be a complex function of flow history of not only the Paria, but also the Colorado River. Therefore, the instantaneous flow in the Paria may be insufficient information to determine the timing and magnitude of a HFE.