Laserfiche WebLink
<br />!".,: '<'.: \t.) (:i ~,! <br />V..~ _~ ,"",0 <br /> <br />a FEMA model, the appearance is created that the FEMA water surface elevations <br />were lower than FEMA had previously thought. Using his modified lower <br />baseline, Mr. Browning concludes that the Charlie's Hole and D-Hole structures <br />created a greater flood risk than was apparent in the previous FEMA model study. <br /> <br />Appendix 1 of this letter shows that the Boating Park was designed below the <br />existing channel invert and that pools were excavated below each structure. The <br />CWCB's own survey shown in attachments C, F, and G confirm the structures <br />were in fact constructed below the existing channel invert. Changes in cross- <br />section at station 997000 are a result of the lowered chamiel invert at the crest of <br />the D-Hole. If the crest of this structure is placed beneath the existing channel <br />invert at station 996960, then the channel upstream of this structure must also be <br />lowered to blend the changes in channel invert into the existing riverbed. <br /> <br />Therefore, in contrast to Mr. Browning's conclusion, I have come to the <br />conclusion that Mr. Browning's own work implies that the Charlie's Hole andD- <br />Hole structures may actually lower the flood elevations. I base this on the fact <br />that the RlCD water surface elevations shown in his figure G are based on a more <br />accurate survey that includes structures that were not created for the Boating Park. <br />In attachment F, the FEMA water surface elevation is made with historical data. <br />According toMr. Browning, the FEMA water surface elevation in Attachment G <br />are made with current Boating Park improvements taken into account and these <br />improvements have caused a decrease in the expected FEMA water surface <br />elevation. <br /> <br />Mr. McLaughlin states that the "Deposition of bed material and elevation of the river bed <br />is likely to occur upstream ofthe.in-channel structures due to lower velocities and related <br />riverbed shear stress" and opines this may increase the risk of flood. (McLaughlin at <br />Topic #'s 3, 4.) Mr. McLaughlin cites a purported sandbar formation, shown as Figure 2 <br />of his letter, upstream of Charlie's Hole as evidence that this increase of deposition has <br />already begun. Figure 3 of this report, shown below, shows this same sandbar at this <br /> <br />14 <br />