Tie channels connect rivers to off-river water bodies along many lowland river systems across the globe. In addition to transferring water and sediment to floodplain lakes, tie channels serve as a critical ecological links. Floodplain lakes provide refuge, breeding and food to many fish species. The alterations of many river systems by levee construction and agriculture have eliminated this vital connection. Field studies of tie channels indicate that these channels are long-lived (100s to 1000s of years) stable channels that steadily propagate into these lakes by deposition from sediment-laden jets. For tie channels, as well as all forms of deltaic channels, the mechanism by which these channels form and evolve is poorly understood. Restoration efforts to re-establish connectivity between rivers and floodplains would be greatly enhanced by understanding the morphodynamics that produce these stable, self-maintaining channels. Additionally, efforts to divert sediment into eroding coastal regions will require the ability to predict how channel systems will develop and sediment will be distributed in response to these efforts.

Our work relies on scaled laboratory models of leveed channel formation using tie channels as prototypes. Our experiments consist of a large (3 x 8 x 0.6 m) basin into which we introduce a jet laden with plastic particles. We observe that the interaction of the inflowing jet and the still basin water leads to intense shear zones along the margins of the jet and the development of “quasi-“ two dimensional large scale turbulent structures. Our results to date indicate that levee development is maximized in the transition zone to quasi-2D turbulence. Once distinct lateral shear zones break down, however, the large-scale turbulent structures are no longer constrained to a narrow portion of the basin and sediment deposition occurs across a broad area and levee development ceases. Ongoing work focuses on developing a prograding channel system and making detailed measurements of the flow-field interaction with the evolving channel morphology. Using particle image velocimetry (PIV) we will look at the spatial patterns of sediment entrainment and deposition by large scale turbulent structures across the inflowing jet.

Major accomplishments:

So far: Resolved scaling issues, achieved formation of subaqueous levees, related initial deposition to hydrodynamics.

Papers
Rowland, J. (2007), Tie channels, PhD thesis, Dept. of Earth and Planetary Science, advisor B. Dietrich, University of California, Berkeley.

Rowland, J.C., and W. E. Dietrich (2005), Two-dimensional turbulence of shallow, plane, jets and the development of subaqueous levees, EOS Trans., AGU, 86: 52, Fall Meeting Supplement, Abstract  H44D-08.

Rowland, J.C., and W.E. Dietrich (2004), Laboratory modeling of self-formed leveed channels from sediment-laden flows entering still water. EOS Trans., AGU, 85: 47, p. F925.