The primary goals of the workshop were to:

1. Bring together group with lots of experience; and
2. Define the state of the art in dam removal: what do we know and what can we do with that, and what do we need to know and how soon can we know it.

In addition, the group accomplished the re-defining of the problem in teams of upstream and downstream components, identifying the key knowns and unknowns for each, and identifying the handoff between the two as the rate, timing and size of sediment release from the reservoir. With this handoff defined, people working on the reservoir side of things know what it is they need to focus on telling the downstream people, and the downstream people have a defined boundary condition for their models.

In what appears to be a growing theme in stream restoration efforts, attendees emphasized that success in modeling dam removal processes will not be possible without bringing together research from different disciplines (geology, ecology, hydrology), different perspectives (theoretical and applied), and different research approaches (field studies, laboratory experiments and numerical modeling).

After a day of presentations on the state of the art, and a day-long field trip to observe the emerging delta in Lake Powell, attendees spent a day divided into upstream and downstream working groups. Results from these working sessions will be published in the near future. Below is an overview of these discussions, and a more detailed outline of each group’s findings can be found by clicking on the group’s name:

Upstream group

The major issues relating to reservoir dynamics during and after dam removal are (1) what are the controls on sediment release, and (2) given a pattern of sediment release, what does the residual sediment in the reservoir look like in terms of habitat and channel configuration.

The consensus of the upstream group was that we have already done a good job of identifying the various delta erosion mechanisms that can occur (head cuts, dispersion and translation of the channel, incision) – what’s lacking is the ability to predict the type and magnitude of mechanism(s) that will occur with a given stratigraphy, reservoir geometry and grain size mix. We also have very little idea yet as to the impact of various techniques for dam removal (blow-and-go, staged removal, draining and digging out the reservoir) on these questions.

The upstream group produced a list of needed research, grouped around three overarching questions:

• What controls the rate and timing of sediment removal from reservoirs following dam removal (time scale: weeks to months)?
• What is the stability of reservoir sediment during and after dam removal (time scale: years to decades)?
• What controls the ultimate geometry of the channel in the reservoir?

For a detailed look at the research needs identified by the upstream group, click here.

Downstream group

Similarly, the downstream group felt like the menu of possible outcomes was fairly well known, and the major controls identified (besides those created by removing the dam, the existing valley slope and streambed sediment mix are major controls). What was needed was to take these existing conditions and predict:

1. The transport and fate of the sediment released from the reservoir;
2. The effect of that release configuration on the downstream channel (in terms of changes in deposition patterns, geometry and/or planform); and
3. The response of the ecosystem(s) to these perturbations.

Two of the interesting question that emerged from these discussions were:

1. Is the channel change caused by construction of the dam reversible? And if so, over what time period? Or are there some changes that are not reversible?
2. How do we go about modeling the downstream system given the tradeoffs between 1-dimensional models, which are highly practical, and 2- and 3-dimensional models, which can provide a lot of local detail, but which to work well require a great deal of information? We need better 1D models, which can route water and sediment over long distances. But we also need to be able to connect those 1D results to models which can predict local channel configuration, chemical and biological changes that result from the removal of the dam.

For a detailed look at the research needs identified by the downstream group, click here.