Grand Canyon Recirculation Eddy Beaches

Grand Canyon Recirculation Eddy Project

Sand beaches in the Grand Canyon exist along the banks of the Colorado River in zones where there is a rapid downstream expansion of the river width. When the width of the river increases rapidly in the downstream direction, the flow separates from the bank and forms a recirculation eddy, in which the near-bank water actually flows upstream. During a flood sand is carried into these recirculation eddies and deposited, thus, revealing a sand beach when the flood subsides. These sand beaches are used for camping and form an important habitat for Grand Canyon flora and fauna. The humpback chub is an endangered species that is believed to utilize the backwater areas created by the sand beaches.
This is a collaborative project funded by the USGS Grand Canyon Monitoring and Research Center and the National Science Foundation. All results in this page are preliminary. This work has greatly benefited from visualizations at the Decision Theater.

Unfortunately, the area and volume of these beaches has steadily declined since the blockage of sediment behind Glen Canyon Dam since 1963. Efforts to restore recirculation eddy beaches utilizing inputs of sediment from two tributaries, the Paria and Little Colorado Rivers, which enter the Colorado River downstream of the dam, have been only limitedly successful.
My graduate students and I are trying to understand the process of erosion and deposition of sand in eddy recirculation zones. The intensity of turbulence in flow expansion zones is extreme. For instance boaters often encounter surface boils in these zones that push them a number of meters off course. These boils also transport sand in the water column and into the recirculation eddies. Previous sand transport theory simply doesn’t work in these areas. Starting with the fundamental mathematical equations of fluid motion (the Navier-Stokes equations), Geography Ph.D. student Ryosuke Akahori is using computers to directly simulate (via the Large Eddy Simulation technique) the motion of these boils and the sand that they carry.

Time-average near-surface velocity	Suspended sediment Flux

<>The simulations include the motion of all of the fluid in the river and a representative amount of sand, and thus the amount of data output in a single simulation is daunting. Without a method of sorting through the data, the simulations by themselves provide little new information about the beach formation process.<>
Programmers from the Decision Theater at ASU have allowed us to explore this data visually in 3-D and, perhaps most importantly, interactively in real time. In one visualization, many virtual particles marked the fluid motion in all parts of the river section over time. By interactively moving around the river on the Decision Theater’s screens we were able to find positions along the bottom of the river in which there are large periodic inward then outward motions of fluid. We think that these might by the key zones in which much of the sand enters or leaves the sand beach. As a result, during future flood experiments in the Grand Canyon these critical zones will be monitored. If we are able to validate our simulations of the turbulence and sediment movement during a flood, we will be much closer to being able to manage flow at the dam to maximize the volume of Grand Canyon beaches.
Download some preliminary animations of our simulations of turbulence in 30 Mile Eddy. Click the picture to Download these animations.

Flow tracer of LES simulations in 30 Mile Eddy (47 Meagabytes!)	Cross-stream velocity and vorticity core using the lambda 2 technique. (78 Mb!!!)