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Roughness coefficients (Manning's "n") used in the hydraulic computations (shown in Table 4) were chosen by engineering judgment, based on both aerial photographs and field ohservation of the channels and floodplain areas, Starting water-surface elevations were either based on coincident condition elevations, the slope-area method, or elevations of an adjacent study, Generally, the distances on the flood profiles correspond to distances measured along the centerline of the designated watercourses, Along Williams Canyon, however, the low-flow is carried through a I, ]OO-foot concrete box culvert under Canon Avenue near to the confluence with Fountain Creek, In this area, the divergence of the low-flow drainage necessitated the use of distances measured along the centerline of the lOO-year flood path, On the maps, this flow line. used to establish profile distances, is delineated and labeled as the Profile Base Line, The hydraulic analysis for Fountain Creek as developed by the USACE is based on an assumption of limited clogging, The USACE considers limited clogging to be 10 percent of culvert areas and I foot on each side of bridge piers, These values may vary from structure to structure, depending on field elevation of structure configuration, The hydraulic analyses for the remainder of this study were based on unobstructed flow, The flood elevations shown on the profiles are thus considered valid only if hydraulic structures remain unobstructed, operate properly, and do not fail. Supercritical and critical flow conditions predominate in the Upper Monument Creek reach and the Monument Creek Tributary due to steep channels, Water-surface elevations at cross sections in these reaches are based on critical depth, Starting water-surface elevations are based on critical depth or the corresponding water-surface elevations at the confluence of two streams (Reference 6), A split flow occurs on Pine Creek at the Colorado State Highway 83 crossing due to the limited capacity of the culvert. Because the roadway embankment is sufficiently high to divert flows above 1,200 cfs to the south, all recurrence intervals coincide with the ]OO-year flood on the Pine Creek Overflow profile, Flow breakouts for floods greater than the lO-year discharge on Fountain Creek occur at the U ,S, Highway 24 bridge crossing in Manitou Springs, These breakouts flow through the Manitou Avenue underpass and rejoin Fountain Creek at Cross Section C. As a result, the peak discharges for the 50-, 100-, and 500-year floods were reduced 700, 2,100, and 9,250 cfs. respectively, For Crystal Creek and Dirty Woman Creek, culvert capacities are sufficient to pass the ]00- year flow at all but two stream crossings, Both Beacon Light Road over Crystal Creek and the Denver Road over Dirty Woman Creek are inadequately sized, The backed-up water temporarily floods only unused barren land and the peak flows downstream from these roads are attenuated to a certain degree during high frequency flooding events (common flood events), Should the land upstream from either road be developed, the culvert size should be increased. 32