Res-2022-075 - Laserfiche WebLink

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1.4 Field lnvestigation The consultant shall conduct a field investigation to determine avulsion and channel migration characteristics of the project reach that may not be well captured by remote sensing (i.e. L|DAR) data. This will include observing: o Channel geometry (width, depth, slope) and planform. . Channel bed, bank, and floodplain substrate, including shallow (< 4 ft) hand soil probing as needed to determine the erodibility of floodplain substrate, following methods for channel migration and fluvial hazard assessment (Blazewicz et a|.,2020; Olson et al., 2014). . Deposited wood characteristics, such as porosity, blockage of channels, potential stability, and evidence of wood effects on channel evolution that could affect avulsion or channel migration potential, following published guidance on such characterization (Brummer et al., 2006; Livers et al., 2020; Scott et al.,2019; Wohl et al., 2010). The consultant shall utilize an unpersonned aerial vehicle (UAV), as needed, to collect low- altitude, high-resolution imagery of portions of the floodplain to supplement ground-based assessment. Assumptions: . County will obtain right of entry to private parcels as needed 1.5 Channel Survey Consultant will perform an in-water bathymetric survey within the upper 6 miles of the project reach to provide bathymetric data to support hydraulic model development. Cross sections will be collected at spacings of approximately 500 feet to provide a sufficient density to create a ground surface model and 1-foot interval contours. Survey will include key specific cross sections at controlling points along the river such as bridge structures. Consultant will combine the topographic surface derived from the LiDAR data and the bathymetric surface into one seamless digital terrain model (DTM) of the study reach, which will be used in Task 2.2. ln channel data for the lower 5 miles of the study reach will be based on channel data from the effective FEMA Flood lnsurance Study hydraulic model. Assumptions: o Surv€y will be completed between July and September, at a time when flows are low enough to support river wading. . The channel will be accessible by boat/wading. lf bathymetric data are required in areas not accessible by boat a change of scope and budget may be needed.o County will obtain right of entry to private parcels as needed Deliverables o Full topographic surface created by merging the bathymetric surface with the LiDAR data. . Surface will be provided in GIS format 3 1+ w,#lFn"?I'sR