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<br />- 24 - <br /> <br />damage from the force of floodwater and floating debris. <br />The culverts are more likely to be plugged by debris. It is <br />very probable that once these structures are overtopped by <br />the rapidly moving floodwaters, erosion and washout will <br />occur. <br /> <br />Two new crossings on the Blue River are proposed by the <br />town; one between Lincoln Ave. and Village Road and the other <br />downstream from Watson Road. The two crossings were assumed <br />capable of passing both the Intermediate Regional and <br />Standard Project Floods. These crossingswere in the planning <br />stage and no engineering designs were available at the time <br />of this report. <br /> <br />URBANIZATION <br /> <br />Urbanization without regard to proper drainage design <br />can cause a considerable increase in flood flows. Urbaniz- <br />ation within and immediately adjacent to the flat valley <br />floor of both the Blue River and the tributary gulches has <br />the greatest affect on increasing runoff. The increase in <br />runoff will be greatest if the development has a consider- <br />able amount of impervious ground cover, such as parking lots, <br />sidewalks and roofs. Proper land use control and city <br />planning can prevent this from occurring. Development can <br />continue in an orderly and planned manner with due regard to <br />the drainage function such that increased peak flows do not <br />add appreciably to the damage potential. Keeping the amount <br />of impervious ground cover to a minimum, detaining the water <br />at its source, and proper design of streets, culverts and <br />other drainage facilities are key elements in preventing <br />increased flood damages due to urbanization. <br /> <br />SUMMARY <br /> <br />This report has identified the probable flooding limits <br />of an Intermediate Regional Flood and Standard Project Flood. <br />As mentioned previously, floods of greater magnitude could <br /> <br />~ Leonard Rice Consulting Water Engineers, Inc. <br />