Laserfiche WebLink
<br />2012 <br /> <br />dam was abOut 3000 cfs~ . A frequent}' curve should be checked to See if this is a reasonable <br />value. The analysis suggests that post-dam conditions have produced a much smaller channel- <br />fonning discharge of 800 cfs. A second peak in the sediment yield curve occurs at 3000 cfs. <br />This could help explain the formation of the two stage compound channel at Range 8 and at <br />other ranges. <br /> <br />14. Hydraulic geometry theory states that the bankfull width varies directly with the <br />channel- forming discharge according to the following relationship. <br /> <br />Width = a Q 0.' <br /> <br />Where a is a coefficient governed by the bank characteristics. Assuming that bank <br />characteristics are not influenced by the dam, the hydraulic geometry relationship indicates that <br />reducing the channel-fonning discharge would also result in a reduction in channel width. <br /> <br />15. The formation of a two-stage channel complicates the preceding analysis. If it is <br />determined that~ent transport occurs on the bar of the existing channel then separate <br />hydraulic and sedimeiit'~sport calculations are needed for the channel and the bar which <br />then need to be combined to obtain a total bed-material sediment discharge rating curve for the <br />cross-section. Bed-material gradation, roughness, and hydraulic parameters will be different <br />for the two sections of the channel. <br /> <br />Recommendations <br /> <br />16. Additional data collection is recommended to update existing information. A new <br />reservoir survey is recommended to determine sediment accumulation behind John Martin <br />Dam since 1980. It is recommended that the survey ranges downstream from John Martin <br />Dam be resurveyed to determine changes since 1987. In addition, an attempt should be made <br />to locate the cross-sections identified by Nadler in his thesis and determine existing channel <br />widths. This is especially important for documenting conditions upstream from John Martin <br />Reservoir and downstream from the Lamar bridge. It is reCommended that bed-material <br />gradations be collected when the surveys are conducted to supplement the data collected during <br />the field reconnaissance. It is recommended that bank conditions also be recorded at each <br />surveyed cross-section. This would include a sample of the bank material to determine the <br />percentage of clay and silt in each bank and a visual determination of the quantity and type of <br />vegetative cover in the vicinity. <br /> <br />Arkansas River, Colorado <br />Geomorphological Assessment <br /> <br />14 <br /> <br />August 8, 1997 <br />