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I I I I I I I I I I I I I I I I I I I 9 reported on Figure 17 for the 10-, 50- and lOa-year flood frequencies represent the relative extent and impact of each flood event. The discharge information is usable not only for flood plain regulation but also for planning, engineering and flood plain improvement. of failure or damage is economically feasible and the hazard to life and property is lower or non-existent. The lOa-year flood event, which can be expected to occur at any time in a given area, based upon recorded historical precipita- tion and other valid data, has a one percent chance of being equalled or exceeded during anyone year. The lOa-year flood event provides a lower risk of failure than the la-year or 50-year flood event, when considering structural flood plain improvements. Flood magnitudes greater than the lOa-year flood magnitude can and will occur. Land improvement adjacent to the lOa-year flood plain limit should consider the remote chance for possible flood damage. The lOa-year flood event is considered by the Urban Drainage & Flood Control District, the Colorado Water Conservation Board, and the Federal Insurance Administration as the flood magnitude for which flood plains should be designated for regulatory and improvement purposes. In Colorado, the lOa-year flood plain represents an area of state interest as defined in H.B. 1041. The lOa-year flood discharges on Second and Third Creeks are greatly affected by the Fulton Ditch, the Union Pacific Railroad and U.s. 85. At each of these locations, flood flows from Second Creek are diverted into Third Creek because of insufficient capacity and obstructions at these crossings. A summary of the lOa-year flow diversion used in this flood plain analysis is provided in Tables 4, 5, and 6. The 10- and 50-year recurrence flood magnitudes have also been calculated at various design points along each creek. These flood magnitudes represent events which can cause severe damage but would not inundate the area characteristic of a lOa-year event. The peak flows for these events should be used in the planning and engineering of improvements where the higher risk Theoretically, it is conceivable that flood waters, once diverted north along the Union Pacific Railroad and U.S. 85 embankments, could continue flowing north into the southern limits of Brighton. However, the flatness of the area, the many county road embank- ments and irrigation ditches which cross the path of such an extreme flood plain, and the agricultural use of the potential flood plain land with a permeable surface would tend to dispute the possibility of such a circumstance. Regardless, future county and city planning should consider possible ground contouring revisions north of Third Creek to eliminate any possibility of such a flood occurrence.