GCDAMP- Questions and Answers Page

UNDER CONSTRUCTION:

• To be added: From Knowledge Assessment_"Assessing what we know and don't know_8-22-2011"- USGS

1. The food web on which fish depend is very simple
2. Availablitity of high-quality food resources limits fish populations- Black Flies and midges are the most important parts of the present food web.
3. The mainstem Colorado River water temperature is typically well velow the termal optimum for native fishes, but recently has been warmer.
4. Warming increases growth/ production of algae and invertebrates.
5. Warming increases the growth rate of humpback chub.
6. We don't understand the decline in RBT between 2001 and 2007.
7. Rainbow and brown trout disproportionately prey on native fish.

WHAT WE DON'T KNOW--

1. Will warmer mainstem temperatures alone allow for increased survival of humpback chub?
2. Do trout have substantial population-level effects on humpback chub?
3. What ages of HBC are most impacted, and by what mechanisms? Competition, predation...

RAFTING RELATED

• Do rafting groups get told not to cave-in sandbars?

SEDIMENT RELATED

• Sediment Retention:

1. How do intervening flows effect retention of sand bars?
2. Riprap, HFE, Sandbars erosion: Q: In order to retain sandbar life following an HFE, what consideration of utilizing riprap as a possible action against erosion in the Grand Canyon?

A: The park system was created to conserve unimpaired the resources and values that the park was set aside to protect. Natural landscapes disturbed by natural phenomena will be allowed to recover naturally (where possible). Landscape and vegetation conditions altered by human activity may be manipulated where the park management plan provides for restoring the lands to a natural condition. This usually entails removing the man-made objects (like a fence, structure, or even a dam) to bring the area back to a natural state. If the use of man-made objects or non-native species proves worthy in restoring a landscape, it can be used to a limited degree, and as long as it is done on a temporary basis and does not impair the resources.

The second aspect to the answer relates to wilderness management (which applies to the lands along the river). Because the beaches are within NPS proposed wilderness recommendation, They are required to manage the area as Wilderness; including the values of naturalness, primitive and unconfined recreation, solitude, and special values. No action can be taken that would diminish the area's wilderness eligibility until after Congress and the President have taken action. This aspect takes us back to the "as natural as possible" discussion and would be a prohibitive factor for such actions as rip-wrapping and other such man-made structures.

-- Also consider-- the cost of doing such work in the Grand Canyon may even exceed that of sediment augmentation.

FISH RELATED

• How often do native fish get handled?

DAM- General Overview

• What resources have been improved because of the dam?
• Was there more or less vegetation along the river after GC Dam was built?

Monitoring

• How far back does the readings of the gauges go? Pre-dam?

Flow Regimes

• Do steady flows produce more trout?
• Do steady flows lead to increases in vegetation encroachment?