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I I I I I I I I I I I I I I I I I I I 3 FLOOD HISTORY "2, The most upstream report of high water cal'1e from a resident at 6200 Nevada Place, This person said water had flowed as high as the sidewalk on both sides of the street. 4, Immediately upstream of So, Eaton St. the flood channel is ter- minated and a 42-inch diameter pipe is orovided for conveyance (see sheet 7). The inlet of this pipe was free of debris, but the City of Lakewood was in the area that morning and could have cleaned the inlet. Evidence of hiah water on fences across So, Eaton St. was as high as 1.5 feet." The lady livinq north of the drainageway on So, Eaton St, showed where her vegetable garden nad washed away, She experienced no other property damage. 7, Deposits of sediment and debris showed where water left the banks of the channel between secti ons 26 + 00 and 20 + 40 on sheet 8." Flood history on record for the two tributaries is limited to occasional complaints filed by telephone with the City of Denver, Centennial Engineerir;, Inc" staff conducted interviews with residents in areas where calculations indicated a potential flooding problem exists. Along the 1st Avenue Tributary, no specific problems were reported for the a'~a west of Sheridan Boulevard, The lower lying areas east of Sheridan Boulevarc seem to be subject to flooding on a more frequent than annual basis, Resi- dents reported having water in their yards and basements during or after any heavy rainstorm and complained about "sewage-like odors" coming from the oper channel portion located close to the mouth of the tributary. The lack of maintenance on these channels is the apparent reason for the growth in the channel to generate enough resistance to cause overtopping even at low-intensity Flood experience seems less frequent and not as severe as on 1st Avenue Tributary. HYDROLOGY The two tributaries were each divided into subbasins. The Colorado Urban Hydrograph Procedure was used to develop peak discharges at the design point of each subbasin for the 5, 10, 50, and 100-year recurrence intervals for storms. future dAvelopment conditions. Along the Dakota Avenue Tributary, flooded basements were not reported. Residents on Eaton Street observed that "once in awhile" flow overtops the roadway, Ponding was observed east of Depew Street, but no specific dates could be remembered. At Sheridan Boulevard and east of Sheridan Boulevard, it was Rainfall Data The rainfall intensity was assumed to be the same over the entire drainage basin for a three-hour duration, The values listed below for rainfall depth are taken from project "REUSE" for Jefferson County, T4S" R69W, and were used for both drainage basins. observed that water flowing down Alaska Place would run across Yates Street through the yards down to Xavier Street. A recent storm (June 6, 1977) provided evidence of flood problems in the area. Residents reported 30 to 60 minutes of heavy rain, and an inspection was made on the afternoon of June 7, 1977, Following are excerpts from the inspection memorandum2 which illustrates typical flood problems. TABLE 1 RAINFALL DATA Depth (Inches) Frequency 1 hour 6 hours 2- Year .68 L12 10-Year L50 2,50 50-Year 1.83 3,16 100-Year 2.00 3.50 Losses Based on the recommendations given in the "Urban Storm Drainage Criteria ~1anual", the following criteria for losses were applied to calculate the run- 2File memorandum by Jon Sorenson, L. Rice Consulting Water Engineers, dated June 8,1977, Job No. 41,01.