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DR9303-AG 920714Disc~sion of possible ~ainage solutions related to B~b~a A~tin prop~ty. Cit~ Engine~ S~dy L~e ~b~a Au~n Prope~). ~e problem, ~ ~ 199~ ]euer to ~e Mayor, Ci~ Co~cil ~d S~, w~ ~ ~e ~o~t of w~er ~m~ng on~ h~ ~rope~, since developmem of prope~ ~ ~e ~u~ of her, h~ w~hed ou~ her d~vew~ ~d k~lled sever~ I~ge o~ ~e~. p~pe headed no~w~d from S~dy Lake in ~e M~re Ro~ ~ of way ex~ng concrete ch~el on ~e west side of M~re Ro~. Du~ng a m~ng ~ ~e Co~il area ~d ~e existing gro~d on ~e e~t s~de of M~re Ro~ h~ no~d from ~ ~e, from S~dy L~e p~lel ~ M~re Ro~ ~d have ~t ouff~l imo ~e ~ng ~nel. ~e only way to ouff~I imo ~he existing ch~nel would be to con~c~ a ~on of ~e pro~ ~ncr~ ouff~l ~nm ~at pipe. SEE ~XT PAGE (CO~D) B~ BARBARA AUSTIN DRAINAGE (CONTINUED) PAGE 2 There is approximately 81 acres of drainage area going through the Austin property. Based on the development south of her, this is approximately 400 CFS of drainage. To construct an open barrow' ditch that would handle that much drainage would necessitate cutting a ditch with 3:1 side slopes that would range from 4 to almost 12 foot deep. This equates to a maximum top width of about 71 feet. Because of the large oak trees in this area, it is not feasible to construct a channel of this magnitude on a tempora~ basis. I then looked at alternative solutions. In trying to maintain a 3:1 side slope and only pick-up the increase in drainage caused by the development of the property to the south of the Austin property, I looked at the drainage area coming onto the Austin property that has developed recently, i.e., the elementary school, the fire station, and the residential development at the southeast comer of Moore and Sandy Lake Road. In a developed condition, that area contributes about 270 CFS of water to the drainage basin. I then looked at what that area would contribute in its undeveloped condition. If it were still undeveloped, it would probably contribute about 150 CFS to the drainage basin. I then looked at a channel parallel to Moore Road that would accommodate the increase in the runoff, i.e. about 120 CFS. To construct a channel with the typical 3:1 side slopes would necessitate cutting a channel that ranges from 3.2 feet deep to 4.4 feet deep. The slope on the channel would be flat until it approached the reinforced concrete pipe and then it would drop approximately 6 feet into the pipe. The maximum top width of the channel with 3:1 side slopes would be about 26 foot. I then looked at a channel section with 2:1 side slopes. The steeper side slopes are not real maintainable, however, on an interim basis, they might be acceptable so as to not create such a wide ditch that several large oak trees would have to be eliminated. The ditch section would range from 3.1 feet deep to 4.8 feet deep. The maximum top width of the channel would be about 19 feet. It also would drop approximately 6 foot into the reinforced concrete pipe. The construction items associated with the interium solution would necessitate the excavation of the channel, removal and replacement of the concrete paving across Moore Road to install the concrete pipe and approximately 250 linear foot of 66" RCP coming out of the concrete channel in a southeasterly direction across Moore Road to the location of where the earthen channel would begin. The estimated cost of this solution would be approximately $70,000.00. This solution does not include the cost for right of way. Obviously, the City cannot expend funds on private property. If this solution is considered for further evaluation, my recommendation would be that we attempt to get Ms. Austin to dedicate all necessary right of way along Moore Road prior to the construction of any drainage improvements in that area. There is also a structure in the general area of where the future street would be and where the proposal channel would be. This structure would have to be eliminated. I do not know if it is currently being used. If it is, then that could pose a problem. Attached to this is a sketch showing the proposed location and alternatives discussed. I will be available to answer any questions at the council meeting.