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<br /> <br />deep the head cut would be and Prow long it would Lake to occur. <br />The bed of the present cktannel at the nur•t!r end of tl~e bridge <br />which is presentl,r' carrying the flow of the river tras already <br />degraded to the top of the footing on the pier at the north end <br />of the bridge. Also, The contour map of the area with 1 ft <br />contours shows that there is a 2 ft. r_hange in elevation over a <br />distance 155 ft. just downstream of the bridge. This is a slope <br />of 0.013 ft./ft. ur 68.8 ft. / mile. 'fhe rrot•mal slop~f the <br />River at Lamar is O,U011 ft.lft. or 5.8 ft / mile. This means <br />that the bed of the present channel will Lowr.r a couple of feet <br />over the next few years. r1+'"'°ar X15 ~~/n I 5~o~,c - LD.~i~ I $/ice/ <br />The above degradation of the channel both actual and potential <br />does not take into account the local scour that carr occur at the <br />pier during a flood event. The local scour at a pier would range <br />from 10 to 20 ft. depending on the magnitude and duration of a <br />flood. <br />FUTURE ENLARGEMENT OF THE GRAVEL PIT <br />Enlarging the gravel pit to the north into the present channel <br />and moving it farther north as altown irr fig. 1 increases the risk <br />to the bridge from head cutting. The attack of the water as it <br />bends around the abutment to the north will increase the erosion <br />to it. <br />rw <br />I have evaluatedd Valco, Inc. proposal as presented ~n there <br />Section 404 Permit Application, CO-OYT-0501. Their prupo:;al will <br />noternsure the safety of the bridge. The plans still shift ttte <br />channel to the north. The dike is still so high that it ~t-id-1 <br />concentrates flood flow in a narrow channel until their dike is (a, <br />overtopped. This concentration of the flow will erode this ' <br />channel so that its lowering will expose the piling on the nurthec" <br />most piers and erode the north abutment. Ttre rubble core as <br />shown on the plans will not withstand Lhe high velocity flow ~,t/~; <br />that would occur on the downstream side of the embankment as it ,,~~~ <br />is overtopped. The proposed concrete rubble core if' cemented too <br />r`YVj;,~,l tight will not withL,stand the pore pressure that could occur with <br />\O~s high water on one side and low caater on the other. The dike area <br />that is out` side of the concrete rubble core will erode, <br />especially at the downstream curve. <br />If flow breaks through the dike at any place a head cut will <br />move up the channel exposing the pier footings and piles and <br />eroding the abutments. If the duce is not over topped then it <br />concentrates high Y•low in a narrow channel. This will result in <br />high velocities, scour and endanger the bridge. As stated <br />earlier one of• the footings is now exposed. <br />3 <br />