Cyclic Fluvial Processes and Bias in Environmental Monitoring, Colorado River in Grand Canyon

Abstract

The Colorado River in Grand Canyon is one of the most intensively studied regulated rivers in the world where discharge is controlled to optimize peak load hydropower production. Sandy channel margin deposits that occur along the Colorado River have been monitored for nearly three decades to determine the effects of flow regulation by Glen Canyon Dam. Recent results from remote daily monitoring show that it is common for large areas of fluvial sand deposits to be eroded in less than one day, followed by redeposition of the area within a few weeks or months. These remote observations were confirmed directly. A review of the maximum erosion and deposition measurements from all sources shows that the recently measured daily changes equal or exceed the magnitude of changes measured over time spans from 2 weeks to 10 years. Consequently, erosion and deposition rates are significantly greater than previously reported because erosion and deposition occur in cycles that repeat several times each year at individual sites, each with unique recurrence intervals. These findings show that monitoring environmental changes downstream of a peaking power dam such as at Glen Canyon presents temporal and spatial sampling problems that lead to data biasing. This has implications for past interpretations as well as for future investigations on this and other regulated rivers.