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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />4.0 Methods <br /> <br />4./ Data Collection and Field Work <br /> <br />The first step in delineating a floodplain is to collect as much existing data as possible. The <br />floodplain history is an important first step in assessing the likely extent of the inundation during <br />a flood event as well as determining what data currently exists. This history is obtained through <br />contacting community members. primarily city officials but also other parties interested in the <br />floodplain delineation. that have first person knowledge of the floodplain or any other pa..! over <br />bank flow problems or significant flood events and acquiring word-of-mouth information. These <br />individuals will also be able to provide any data that they have previously collected. In addition. <br />historical data are obtained through archived documentation of historical problems due 10 past <br />flooding from designated cily files, the CWCB. the USGS. past press releases. and olher sources. <br /> <br />In addition to obtaining the history. existing GIS data l.. obtained. GIS data can be found from <br />city. county. state. or federal agency GIS departments. At a minimum. GIS data should include <br />natural contours with hills. depressions. valley. and mountain elevations and slopes; hydrologic <br />fealures with streams. rivers. ponds. lakes, reservoirs. and irrigation canals; and societal <br />struclures including streets. roads. highways. railroads. bridges. culverts. dams. and buildings. <br />Any other GlS data such as vegetation Iype and cover. fences. power lines. property boundaries. <br />and any other man made structures Ihat lS available is beneficial. This methodology assumes that <br />the minimum GIS dala is already available and does not need to be generated. If data is not <br />available it is possible to generate it. That task. however. is outside Ihe scope of Ihls project. <br /> <br />Any other necessary information that is not currently available from previous documentation is <br />obtained from field observations and measurements. Measured dimensions and an inventory of <br />all drainage structures. including bridges and culverts. are obtained. Reference and geographical <br />orientation markings are needed for clarity. All of the field observalions and the objects being <br />measured need to be photographed. In addition. the channel and bankfull of the basin are <br />photographed for a visual reference of the watershed. Bankfull is the extent of the channel that <br /> <br />15 <br />