Channel Geomorphology and In-Channel Veg Response to RFP

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Bedload sampling wi44 follow standard USGS procedures using a crane mounted BL-84 sampler. Initially, 20 equally space verticals will be sampled throughout the flowing portion of the river cross section on the downstream side of each of the bridge crossings to be sampled. The number of verticals sampled may increase or decrease as the width of the river changes with stage. The wetted width of the river needs to be recorded for each sample in order to compute a transport rate. As a starting point, I would recommend a minimum of 18-22 samples per site, per year, collected over a broad range of discharges (as mentioned in the DMP) in order to get a reasonable transport/discharge relationship. This estimate of sample size is based partially on a"power of test" analysis done on bedload and suspended load data by Troendle, Nankervis, and Ryan (1996 - see my resume section for reference) and partially on my own professional experience. Samples will be composited and taken to the lab for grain size analysis. See grain size analysis (Section I.f.) for description of laboratory procedures. Total (inorganic) bedload transport rate (kg/s) will be calculated for each sample and paired with the appropriate discharge value as measured at the respective gauges. Flexibility is the key to capturing sediment samples over a broad range of discharges. Large sediment transporting flows can occur any month of the year but generally happen in the spring (March-June) as a function of snowmelt from the headwaters. It will be important to monitor, in real-time, the USGS gauges located upstream from the Central Platte River in Colorado, Wyoming, and Nebraska to determine when the best opportunities for measuring sediment will occur and then to act in a timely manner to take advantage those opportunities. I.b. Cross Section Surveys Cross sections will be located based on the criteria set forth in the DMP. Right and left end points of the cross sections (or segments of cross sections, if required) will be monumented with rebar stakes, capped and labeled. Detailed cross sections surveys (using a survey-grade GPS RTK system) will document the topography within the accretion zone for each of the four transects at each Anchor Point identifying the various geomorphic and vegetative features of the channel while recording horizontal and vertical locations relative to NAD 1983 and NGVD 1988 references. All verticals surveyed between the left and right end pins of a cross section will be horizontally corrected to fall exactly on the Left-Right pin vector. I use this correction in my MS Excel template/macro to provide the distance from the left pin for each vertical measured, which facilitates graphing and calculating hydraulic geometry parameters (width, mean and maximum depth, area, wetted perimeter, hydraulic radius, and width/depth ratios). Typically, this correction is very small but in order to obtain accurate and consistent estimates of channel geometry over time, it is a critical step. I.c. Longitudinal Profile Surveys The longitudinal profile survey will be perform as stated in the DMP using a using a survey-grade GPS RTK system. In addition to the thalweg elevation, a water surface elevation at every thalweg point measured may be made. It is often useful to look at these two parameters in tandem when trying to identify trends and would not take much time do, either in the field or the office. It is important to track discharge during water surface measurements. Another suggestion would be to perform the longitudinal profile survey in the second year (2010) which would allow, through the cross sections surveys in the first year, one to actually locate the thalweg throughout the 95 mile reach and provide a "road map" to guide the survey. Effective and efficient execution of the profile survey will probably require the use of a boat. PRRIP - Geomorphic Monitoring 4 of 20 Blue Mountain Consultants