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<br />, <br /> <br />9. Using geophysical technique~ to obser~e channel subbottom scour <br />phenomena and provide an insight to scour conditions prior to high <br />flow data collection at the [..>nUllltler<..] br'idge sites. These <br />data may be collected during the site establishment (if the <br />equipment is availablel,or shortly thereafter when the equipment <br />is available. The geophysical equipment is to be (..>borrowedl <br />rented<..) therefore exact timing of Obtaining the equipment is <br />not defined. Two geophysical techniques, ground-penet.rating radar' <br />and continuous low-frequency subbottom seismic profiling, are to be <br />used with respect to each technique's capabilites to provide useful <br />data in different channel subbottolll mater'ials. These teChniques kill, <br />in most cases, identify locations where scour has occurred, maximum <br />depth of the scour hol ell, and sediment backfill (i f present), and <br />will Indicate the type of subbottom material present in the channel. <br /> <br />Phase II <br /> <br />Annual Data Collection <br /> <br />Data will be collected over a r"'?-year,..) perioo, and assuming proper <br />hydrologic conditions should consist of 50 total measureaents and two <br />measurements at each site. Attempts will be made to collect onsite-highflow <br />data at about 10 of the 20 sites per year'. During the 5 years of data <br />collection, cross sections will be surveyed annually at the approach section <br />and at the bridge opening at all 20 sites in the late summer during low-flow <br />conditions. Photographs will also be taken at this time. <br /> <br />Onsite high-flow event-data collection will include: <br /> <br />1. Making one or more standard discharge measurements, with extra <br />soundings near piers, Obtaining water temperature, and recording <br />the gage height. <br /> <br />2. Obtaining cross-section measurement(ll) at the upstream side of <br />the bridge, including scour depths in front of and close to the <br />, , <br />Sides of the pier. <br /> <br />3. Collecting bed-material samples In local scour holes near the pie,.. <br /> <br />4. Setting high-water marks at the approach section, near the <br />upstream side of the bridge, and downstream of the bridge to help <br />define the water-surface profile, <br /> <br />5. Taking photographs of the flow conditions around the bridge and in <br />the upstream and downstream channel. <br /> <br />6. If the runoff event measured exceeds a 2-year flood, a follow-up <br />site visit will be made to collect more data to include surveying <br />high-water marks, obtaining cross-section measurements at the <br />approach section and at the upstream bridge opening, and taking <br />photographS If necessary. <br /> <br />A-6 <br /> <br />.1 <br />I <br />(I <br />I <br />I <br />I <br />I <br />I <br />I <br />II <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />