Technical Work Group Meetings 2009

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' Glen Canyon Dam Technical Work Group Page 22 DRAFT Minutes of March 16 -17, 2009, Meeting choices of sites to be monitored and are impacts mitigated to the AMWG at its next meeting with the provision that any recommendation will not alter the choice of sites selected for impact mitigation in 2009. She said the HEC -RAS model is the flow line model that shows where flow lines are in Grand Canyon. It ' was peer reviewed and published and there were a series of flow lines that were run and made available so they chose to use those rather than run any new model flow lines. It ran flow lines of 25, 45, 97, 125, 170, and 210K cfs. Hoda ran the model against those sites and actually ran them against 132 sites that are proposed for monitoring and /or mitigation. She said some of the overheads have some of the data that came out of that effort. She said related to that sites up to 60,000 cfs have been mitigated so they're done with all the sites that are up to 60,000 cfs. The flows in Grand Canyon run up 45,000 cfs and historically they've run up as high as 95,000 cfs when they ran an earlier test in 1983. She said Mike Berry decided to run a model of an evaluation to look at what are the factors that affect condition of sites in Grand Canyon because condition was the decision cutoff of information potential in an archaeological sense as well as condition of sites to determine treatment. The results of that statistical model is that it wasn't a significant ' factor in determining condition, that it didn't seem to make any difference as to what the flow is and to the condition of the site. The CRAHG took a look at Mike's model and Hoda's presentation and discussed what should be done and there wasn't agreement on what should be done with the data because the intent was ' how would you use that information to decide which sites should be excavated or treated for other reasons as well as monitoring. They came up with a motion (printed on the AIF) and said the HEC -RAS model probably has some utility because it does a good job of virtual shorelines. She said some of the sites are ' pretty good sized because they may be on bench that slopes and that site could be a 97,000 cfs and 125,000 cfs, etc., so many of the sites lie within multiple flow lines. She said there is an error with the HEC - RAS model and it varies but it goes from .4 meters to 1.5 meters at the upper level. She said some of the ' error bars appear on Hoda's document. Mike Berry said there were two classes of highest erosion versus the three classes of lowest erosion so they had two dependent variables. The used the interval scale of variables on the Park Service database which was river mile elevation, distance from the river and slope, along with the HEC -RAS. For the HEC - RAS, they used a minimum inundation level for each individual site as considered. The analysis was not robust in whole; it did not explain a great deal though it did correctly classify 77% on reclassification ' statistics. The HEC -RAS was the least discriminating of the five variables considered. After discussing this with Reclamation staff, they would like to work their way back up from the bottom, the bathtub ring, as they determine which sites will be excavated in any given year. They still don't know what causes erosion of the sites but will use the HEC -RAS model as one of the criteria to determine which sites will be excavated in any given year. Mary said that WAPA feels the HEC -RAS model should be used to the decision related to sites in terms of prioritization and monitoring based on their location in the canyon and flow lines. The CRAHG was not able to make a definitive decision on how best that should be used. It basically says another look should be done in detail. ' Helen said if there were time she would've like to have talked about the limitations but said in a PPT she passed around, "Analysis of Virtual Shorelines in Relation to Archaeological Sites in the Colorado River Ecosystem" (Attachment 13), it contains concerns about using such a simplistic approach to assess dam effects. The directed the members to the diagram on page 3 which depicts some sites in the second graph that suggests there are sites that are well above the 210,000 cfs line. They have similar situations as shown in the diagram where there are sites up on a terrace and because the GIS analyzes the surface of the sites relative to some point of inundation, it won't show effects from lower flows. She feels that's an important ' caveat to keep in mind but also said there could be a reverse scenario where there is a site actually up on the terrace surface and isn't being effected directly and may be showing inundation when, in fact, there is very little of it. 11