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<br />tagline surveys between cross-section endpoints. Cross-section endpoints were <br />monumented using aluminum caps set on #5 rebar for future monitoring and assessment <br />programs. In addition to cross-section surveys, a thalweg profile, and intermediate cross- <br />sections were surveyed in each reach using a total station or a GPS. The basis for the <br />survey was state plane coordinates obtained from control set for URS aerial mapping <br />(URS, 1998). <br /> <br />Table 7.1 Summary of reach study sites <br /> <br />Site No. Length (ft) No. Monumented Comments <br /> Cross-sections <br />IMl 1170 12 Farthest US reach above the Lake Fork confluence <br /> and DS of Cali fomi a Gulch. <br />1M2 1350 II Site location immediately DS of Lake Fork <br /> confluence. <br />1M3 1010 8 Fairly straight reach located on Dr. Smith's property. <br />IM4 2150 16 Multi-thread channel located US ofHWY 24 Bridge. <br />IM5 1220 10 Single-thread channel DS HWY 24 Bridge. <br />IM6 1260 8 Multi-thread channel in narrow area above valley <br /> terraced neck or constriction <br /> <br />7.2. Hydrologic Influence on Sediment Transport <br /> <br />Hydrology influences sediment transport by the frequency and duration that various <br />discharges are delivered to a stream. At ditIerent discharges, the stream is capable of <br />moving varying sizes of sediment at different rates. In general, the higher the discharge, <br />the larger the bed material in motion and the larger the bed material transport rate. The <br />hydrology used in this study for hydraulic and incipient motion analyses are referred to as <br />annual peak discharges, which are the range of discharges occurring at various yearly <br />recurrence intervals (in contrast to flow duration discharges; Chapter 6). By using the <br />range of annual peak discharges, a variety of hydraulic and sediment transport <br />circumstances were analyzed. <br /> <br />7.2.1. Event Discharges <br />Annual peak discharges used in the hydraulic model and incipient motion analysis were <br />developed based on the Log-Pearson III flood frequency distribution. Data analyzed for <br />1M Site 1 used the gage located on the Upper Arkansas near Leadville, 07081200, having <br />a drainage area of97.2 square miles. The Leadville gage is located approximately 3.0 <br />miles upstream from 1M Site I and 4.0 miles upstream from the Lake Fork and Upper <br />Arkansas confluence. The gage has 23 years of annual peak data, which was considered <br />reasonable for developing a flood frequency curve. <br /> <br />Two locations within the study area provide gage data for 1M Sites 2 through 6. The <br />upstream gage, Upper Arkansas near Malta, 07083700, has a drainage area of 228 square <br />miles. The Malta gage has thirteen years of data, although during five years between <br />1976 and 1980, discharges were considered to have higher than average peak values <br />resulting from transbasin transfers being conveyed from Turquoise Reservoir, The other <br /> <br />May 7, /999 <br /> <br />Fluvial Geomorphological Assessment <br />Upper Arkansas River <br /> <br />Page 48 <br />