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<br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />Alternative No. 1 <br /> <br />We feel that the first alternative, reshaping the ditch as an earthen structure, <br /> <br /> <br />violates a majority of the rules we have established. The life span of the <br /> <br />Highland Lateral and Farmers Extension Irrigation Ditch ended many years ago. <br /> <br />This is based on life span being defined as the ditch remaining in the original <br /> <br />shape as when it was built. The years of use have deteriorated the embankments <br /> <br /> <br />and washed away much of the ditch. Much maintenance has been required to keep <br /> <br />the ditch in its present deteriorated state. <br /> <br />We believe the projected life span of an earthen ditch properly compacted and <br /> <br /> <br />with proper amounts of bentonite added to be three (3) to five (5) years. This <br /> <br />average life span was determined through research of existing earthen ditches <br /> <br />in Northern Colorado. <br /> <br />Assume that a ditch is shaped in a trapesoidal channel to carry two hundred (200) <br /> <br /> <br />c.f.s. The cross section of the channel would be similar to that shown in Exhibit <br /> <br /> <br />No.4. This channel will be acted upon by the following hydraulic forces: <br /> <br />a. Hydraulic pressure <br />b. Turbulent flows <br />c. Transitional changes in velocity <br /> <br />This channel will also be affected by the weather, tail waters and storm waters <br /> <br /> <br />flowing into the ditch, and the accumulation of foreign debris. <br /> <br />The hydraulic pressures against the embankments of the ditch should pose no <br /> <br /> <br />problem. This is why standing water sources such as sewage lagoons, water re- <br /> <br />servoirs, etc. can be lined with bentonite or chemical sealants and not deteriorate. <br /> <br />Turbulent flows and velocities are the main problems for channel stability. All <br /> <br /> <br />earthen water channels have suspended sediment and bed load rates. The bed load <br /> <br />rate is caused by water velocities which picks up the dirt that lines a channel <br /> <br /> <br />and carries it downstream to a point where the velocity is slow enough to again <br /> <br />allow the particle to settle. This erosion process is very hard to put an exact <br /> <br />22 <br />