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26 n Flooded Areas The lOO-year frequency flood has been selected by the State of Colorado as the flood event to be used for floodplain delineation and regulati on. Thus, the flooded area sheets show only the boundary of the IOO-year floodplain. Flood Elevations The flood frequency elevation and dischargcdata table, Table 3, 11ststhe 10, 50, 100, andSOO-year Flood elevations at selected reference points. The flooded area sheets give the plan view of the flooded area on a contour base map and the high water elevations for the lOO-year flood can be Inter- polated from tnis. The flood profile plates show the streambed elev<ltlon ..ncl the hlgowater elevations for all four frequency floods. Also, the cross section fIgures snow a graphical representation of the high water elevations at typical valley cross sections throughout the study reach. The area delineated on the fioodedarea sheets as the lOO-yearfloodplain meets the requirementsofH.B. 1041 as an area of State interest. Also, upon official approval of this report by the Colorado ~ater Conservation Board, the area outlined by the laO-year flood boundary can be designated a floodplain area and may be regulated accordTngly by the local officials. A portion of the lOa-year floodplain between Stations 57+55 and 80+~o. and Stations 280+00 and 300+60 is subject to floodTng due to upstream condit Tons, such as irrigationditchesandtopographlcalcharacteristicswhichdivert floi>d w..ters to said lands. These areas are designated with sh<Jdingand represent areaS of shallow overland flooding for the 100-year fiood. Be- cause these waters are not hydraulically connected to the channel, the actual The flood profiles may be used Tn areas where controversy arises Over the lOa-year flood boundary on the flooded area sheets. Since the flood profile plates give the elevatIon and dTstance or stationing from a known point, the high water elevations can be surveyed on the ground to alleviate any discrepancies on the base map. tho,,' surface elevation, in the overb'n~ " ' ~ ~ ar~a are genera y higher than in the main channel (shown In Table 3). To determine the depth of floodTng or the floodplain limits at any 1 ocation in th~ fie Id, th~ following procedures should be used: w"ter 1. Locate the ground point at Which the depth of flooding or the flood- plain limit is to be established on the 1"-400' flooded.,ream"p. 2. Oetermine the elevation of the water surface;)t the selected grou nd poTnt from Table 3 by Interpolating between the water surface eleva- tions given for two adjacent cross sections and referrlng to the pro' flledrawings. 3. Using the closest monument for ..ievation control, determine the water surface elevation at the ground point by stand~rd surveying techniques. The floodplain limit is established when the water surfaceeievation intercepts the ground surface. An "ppro~i",ate depth of flood ing can be establ i shed by subtract ing the ground el~vdti"n estimated from the contour map from the previously determined wdter 'urface elevation.