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<br />k lot z 4~. ass 0 cia t e 5 <br /> <br />water surface profiles for the design discharge for the FEMA-modeled channels <br />indicated no significant (in comparison to channel widening) impacts on water <br />surface levels. Thus for FEMA-modeled channels, reduction of structure impact <br />by bridge or culvert improvement was not considered as an improvement option. <br /> <br />For non-FEMA-modeled channels for which channel and structure information <br />was limited, it was concluded that bridges, if any, as in the FEMA-model <br />channels, were not a significant factor in estimating channel capacity. <br /> <br />On the other hand, culverts might be a significant constriction in the non-FEMA- <br />modeled channels. To assess whether culverts might or might not be a significant <br />factor in the capacity of the channel, the estimated capacity of the existing <br />channel was determined using the approximate methods discussed in Section 3. <br />The capacity of any culvert system along the channel was assumed to be roughly <br />the same as the capacity of the channel. If, then, the estimated existing channel <br />capacity were in excess of an approximately 1 DO-year frequency stonn event, it <br />was concluded that the capacity of any culvert system in the channel would not be <br />a significant limitation on the capacity of the channel if the channel were to be <br />improved by widening or lining. <br /> <br />On the other hand, if the estimated existing channel capacity was less than that for <br />an approximately 1 DO-year storm, it was assumed that the existing culverts would <br />have a significant impact on the capacity if widening or lining were undertaken, <br />and, therefore, culvert improvements would be required at all culvert systems <br />along the channel where the widen or lining was to take place. For planning <br />purposes (and specifically for costing purposes), the nominal improved culvert <br />system was assumed to be a 5- foot square concrete box culvert with a typical <br />velocity (at the design flow) of 6 feet per second, so that the capacity of a single <br />culvert would be approximately 150 cubic feet per second. The number of barrels <br /> <br />4-4 <br /> <br />Klotz Associates Project No. 0127.008.000 <br />January 2009 <br /> <br />La Porte Citywide Drainage Study <br />City of La Porte <br />