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City Council Regular Meeting Minutes October 11, 2011 Page 2 1 IV. PUBLIC HEARING 2 3 None. 4 5 V. REPORTS FROM COMMISSION AND STAFF. 6 7 None. 8 9 VI. GENERAL BUSINESS OF COUNCIL. 10 11 A. July 16, 2011 Flood Information presentation 'Todd Hubmer, City Engineer,.presenting. 12 13 City Engineer Hubmer presented an update regarding the July 16, 2011, flood event and stated 14 that the report is being prepared in collaboration with New Brighton City staff. He explained 15 that there are three Ramsey County ditches being reviewed, including Ditch No. 5, Ditch No. 3 16 which goes down Silver Lane and enters Ditch No. 5 at which point it turns into Ditch No. 2 17 which drains into Pike Lake on the north side of 694. Ile presented photographs taken of the 18 July 16°i flooding in both St. Anthony and New Brighton and provided an update on activities to 19 date, including completion of the Mirror Lake pond survey and televising of the storm sewers. 20 He stated they are currently working on rainfall analysis and modeling efforts and added that 21 they now have a detailed survey of the outlet structure. He indicated they are aware that Mirror 22 Lake spilled over the berm and found some settlement but nothing significant. He advised that 23 on the south end of the City, they have completed televising in the industrial park which includes 24 two drainage systems that drain to the back of the industrial park with most of the flooding 25 occurring in one particular building. He noted that this storm sewer was found to be clean and 26 functioning as intended, but the system that goes to the south is full of debris and they are in the 27 process of cleaning it out. Ile advised that they are looking at a hydraulic analysis for additional 28 storage to provide additional protection to the buildings between the cemetery and industrial 29 buildings. He discussed the televising done in the Mirror Lake area where it attaches to Silver 30 Lane and is the beginning of Ditch No. 3 and this was found to be clear of debris and in proper 31 working order. He provided information regarding the rainfall analysis for a 24 hour, 100 year 32 storm event, which showed that St. Anthony received a one hour equivalent of 3.3" and a 2.5 33 hour event was 3.9". He stated that the Fridley weather station reported 4.18" in 2.35 hours and 34 an additional 1.25" for a total of 4.53". He noted that another site in Fridley recorded 5.88" and 35 New Brighton recorded 3.75" in a 2.5 hour period. He indicated that because rainfall can be 36 variable, they are reviewing radar images over a 36 hour period showing the intensity of the rain 37 event and this data will be input into a model that will show actual performance of the system 38 over the entire watershed during the time of the storm. He advised that once modeling is 39 complete, they will begin to review next steps, complete the rainfall analysis, and evaluate the 40 performance of the system to see if there are any locations where the system did not perform as 41 designed. He stated they believe that one pipe in New Brighton may not have been in the best 42 condition and they intend to develop alternatives to improve flood protection levels to elevate 43 and increase protection. He added that their findings will be reviewed with the City and its 44 residents and they anticipate completion of the report sometime this winter. 45