2012-01-17_REVISION - M2005050 (2)

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Cazier, Tim From: Cazier, Tim Sent: Friday, February 03, 2012 2:45 PM To: 'jamespirc @aol.com' Cc: Means, Russ Subject: RE: JBird /Prince Albert Spillway Mr. Pierce, I have reviewed you latest rationale and though your argument that the velocity in the horizontal spillway section should be limited by the calculated interstitial velocity in the sloped riprap section has merit, I differ with your two other assertions: 1. 2 -inch minus gravel is functionally equivalent to Pennsylvania's class R -2 riprap: The R -2 riprap has a D100 of 3 inches, 50% larger than the 2 -inch minus material proposed. I would argue that the Pennsylvania equivalent is closer to the R -1 (D100 = 1.5 in). As such the Vmax is 2.5 fps and the allowable shear stress (ia) is 0.25 psf. 2. Elimination of the need to compare the estimated shear stress with the allowable shear stress. My rough calculations indicate the maximum gradient /slope of the accelerating flow is 1.2 % for the upper pond spillway and 0.65 % for the lower pond spillway. I would expect the surface gradient of the accelerating flow to exceed those numbers. You'll need to demonstrate that the shear stress is below the allowable value in Table 6. Also, the Mirafi FW 700 geotextile shown in the design detail you sent is a woven geotextile. The preferred geotextile for riprap filter (when acceptable) is a non -woven geotextile (12 -oz minimum unit weight). The reason for this is that the sharp points of angular riprap tend to spread the open weave in woven geotextiles during the installation process. Tim Cazier, P.E. Environmental Protection Specialist Colorado Division of Reclamation, Mining and Safety 1313 Sherman Street, Room 215 Denver, CO 80203 ph: 303 - 866 -3567 x8169 fax: 303 - 832 -8106 tim.cazier(j�state.co.us From: jamespirc @aol.com [mailto:jamespirc(daol.com] Sent: Wednesday, January 25, 2012 3:28 PM To: Cazier, Tim Subject: ]Bird/Prince Albert Spillway Mr. Cazier - Appreciate your taking the time to prepare the graphic and your explication of what you perceive as the problems. I therefore have attached a snapshot of the spillway design detail for the JBird (and Prince Albert) to provide a graphic of the design. As noted previously, rather than using an earth cutoff and attempting to cultivate a vegetative cover, I have continued the geotextile to the interior face of the berm with a gravel layer as protection for the geotextile. In looking at the Pennsylvania channel criteria, I believe that this 3 inch layer of 2 inch minus gravel will be, at least, the functional equivalent of Pennsylvania's class R -2 riprap. As the velocity through the berm is 2fps or less and the class R- 2 riprap has a Vmax of 4.5 fps this should suffice.