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<br />, .
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<br />,5,
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<br />said this might allow for an open discussion on issues that are not agreed wholly upon, He added that Mr, Schreiner's pointE
<br />are very good, He also stated that the A W A storms are maximized and transpositioned using some of the same NWS
<br />procedures, as found in other NWS PMP studies completed for sites around the nation, such as with the Harriman Dam, Thi
<br />study, he mentioned, was one of five studies that were completed for the Harriman Dam, but it was the study that was
<br />completed by an independent Board of Consultants (BOC) that was accepted eventually - not the one completed by the
<br />NWS, As a fmal note on the subject, Mr, Schreiner stated that all PMP studies and their differences, whether accepted or no
<br />are based solely on the money needed to modify the dam in question, Of course, he stated, the dam owner will chose the
<br />lesser PMP values if it means that he can save money in dam re,mediation,
<br />
<br />Presentation #3 bv Dr. Ed Tomlinson
<br />The following presentation by Dr. Tomlinson dealt with the sensitivity analysis portion of the PMP study, These are excerp
<br />from his presentation:
<br />. Dew point temperature: There is an approximately 5% change in maximization factors for every I degree of change in
<br />the storm representative dew point. New dew point analyses measure dew points to the nearest half-degree,
<br />. Storm duration: For the Cherry Creek drainage basin, the PMF is a volume,based issue, and therefore the n,hour
<br />storm duration will be a key value in this study,
<br />. Storm positioning over the basin: the local topography influences greatly the location of storm centers in the Cherry
<br />Creek basin, Historic storms are much closer to the Palmer Divide at the top of the basin than they are to the middle, or
<br />critical center. Positioning the storm along a north,south axis within the basin is not as critical an issue and the east-weE
<br />positioning, as discovered by hydrologic analysis previously completed by Mr, Trieste, in which a runoff was calculated
<br />for the same storm placed at different locations along the north,south axis - differences were minimal. East,west
<br />positioning, on the other hand, would result in much different PMF values, but for this study, and due to a lack of
<br />evidence to support an east-west movement of the storm location, the storm will be critically centered over the basin,
<br />. Incremental Time Distribution: The primary flood issue is based upon rainfall volume, so the n,hour PMP event is oj
<br />primary concern for this study,
<br />. The One Percent Chance of Rainfall Correlation is not going to be used in this study since point rainfall is not a
<br />driving issue for this basin,
<br />. Orographic Effects: Will be determined by "scientific and historic logic," For this study, A W A is determining the
<br />effects of orography on storm location and rainfall enhancement, as well as studying the upwind moisture inflow barrier
<br />. Storm Location: Based on scientific logic, there is more moisture available to the storm on the upwind sides of ridges,
<br />---rhese upslope winds enhance atmospheric vertical motion and rainfall production within the storm, Down slope winds
<br />tend to decrease vertical motion and thereby have a negative effect on rainfall production,
<br />. Barrier Effects of the Palmer Divide: Moisture is removed from the atmosphere by the Palmer Divide on the upwind
<br />(south) side of the ridge, The Palmer Divide could best be described as a sort of cone rather than a ridge, with multiple
<br />ridgelines radiating out from the highest elevations, The primary ridge is oriented west-southwest to east,northeast,
<br />while the ridges on the north side of the Divide playa significant role in depleting moisture from easterly wind
<br />directions,
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<br />At this time, Dr. Tomlinson displayed a colorful terrain map of the Palmer Divide in order to show the significance of the
<br />various ridges, He stated that the north side of the Palmer Divide is going to be considered non.orographic in nature and
<br />therefore, there will be no increases in rainfall over the down slope region of the ridge,
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<br />Using 2-D and 3-D images from TopoUSA, Dr. Tomlinson further emphasized the ridgeline issue of the Palmer Divide
<br />region, Mr, Schreiner mentioned that the NWS would have a problem with the fact that there is not enough of an orographic
<br />influence with only a 600,foot elevation difference between the basin floor and the adjacent basin boundary ridgelines, Mr,
<br />Miller added that there is only an average of a I % slope over 22 miles for the profile that runs from the basin center to a poir
<br />east of the basin, Dr. Tomlinson replied that this assumption is correct on Mr, Miller's part, but that the elevation change sti
<br />falls within the NWS definition, as defmed in HMR-57 (for the Columbia River Basin), for what the NWS considers an
<br />orographic region, He went on to point out how the low section of the Palmer Divide at Palmer Lake, Colorado, acts as a
<br />pass, so south winds and moisture inflow can get into the Plum Creek basin, This creates the type of rainfall that was
<br />observed around Raspberry and Dawson Buttes during the June 16th, 1965 storm event.
<br />
<br />Flood Protection. Water Project Planning and Financing. Stream and Lake Protection
<br />Water Supply Protection. Conservation Planning
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