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<br />Page 14 <br /> <br />ItO r j:: <br /> <br />9f. <br /> <br />~ .' <br /> <br />. <br /> <br />horizontal widths shall be computed. The 100-year <br />flood boundaries shall be delineated between these <br />cross sectional locations by transposing the water <br />surface elevations to a one or two foot contour <br />topographic base map. These intermediate locations <br />must be correlated to the reference line and the <br />IOO.year flood profile as to their specific location <br />and elevation. <br /> <br />BloclcaQe. All culverts and, bridges shall be considered <br />for the potential to become blocked by floating debris. In <br />determining if there is a potential for blockage, and <br />subsequent reduction in conveyance, old photographs, the <br />history of maintenance during high flows, watershed <br />characteristics such as erodibility of channel banks, <br />amount and type of vegetation along stream, and size and <br />character of the waterway shall be evaluated. Blockage <br />may be accounted for in computer runs by increasing width <br />of piers, raising streambed elevation or reducing waterway <br />opening by a percentage. Where the potential for blockage <br />can be shown, human intervention (e.g., snagging) shall be <br />considered only if such flood fighting activities are <br />speCifically included in the community's adopted emergency <br />response plan. <br /> <br />6. R'ouQhness Coefficients. Values for the' roughness <br />coefficient at valley cross sections shall be based on <br />assumed worst case vegetation conditions along the stream <br />and floodplain. Past flood data, if available, shall be <br />used to verify the adopted roughness coefficients, taking <br />into consideration any alteration in the channel subsequent <br />to the floods. Photographs shall be taken of the study <br />reaches of th~.~t~eam channel and fl~odplain to support <br />.". ,.. .~" ,~,~".. U.~Y 'uo "J'" QU"~ ~, <br /> <br />5. <br /> <br />7. Consistency. A comparison of any proposed IOO-year flood <br />profile with all previously designated and approved <br />information shall be orovided to the Board. Except where a <br />clearly identified change in flooding characteristics or <br />error in the existing data can be shown, the proposed <br />IOO-year flood elev.+ions shall agree with those of other <br />contiguous studies on the same stream. Elevations of cross <br />sections shall be computed to match within !O.5 foot of an <br />existing valid elevation; however, the final published <br />IOO-year flood water surface profile shall be shown to <br /> <br />-~ <br />/~, <br />;6~' <br />" ~ ;;il( ~ (- <br />,"Y'" <br />THE CODE OF COLORADO REGULATIONS -~\ <br /> <br />2 CCR 408-1 <br />