Agenda - Council - 03/22/1994 - Laserfiche WebLink

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12. ~v [te Pl~un Development Permit will require a maintenance guarantee to ensure thc ~1 of the plantinss for a 2 year Period. The plan proposed convca'fing 1.05 am'cs of thc 1.15 acre sim to an impermeable T~c n:~jofity of the ~it~ da'a~ge is !m-opos, c,d to be ~ to the west ~r'bline of .Ebony Strict via three paved flumes. The storm sewer m Ebony Street in turn conveys the runoff, to the Mississipi Pdvcr. The westernmost 32 feet of pavement is directed to drain westbound toward the property hnc of. the City park. Draim ge is a major concm"n on this site plan from two separate criteria; water quality stunt2 ~is set by the local warn- munagement orguni~-ation and thc capacity of thc existing storm ~,ater system to handle thc volume of runoff generated. The l~,ower Rum River Water Management Organization (LRRWMO) requires . ime[nmrion prior to discharge into a Class A warm-body which is the classification of the sSisgppi River. In addition to the drainage requirements of the WMO, the adeqnasy of the existing storm sewer ~ervicing the propc:rty must be considcre& The commercial area served by the ,storm sewer ~o which thc proposed development would discharge includes approximatel) 9.25 am-es. ?his includes the land uses south of I-:t/ghway #10 between Fekispm- and Dolomite Street.[ The proposed development covers an area of 1.15 acres or 12% of the total drainage arcs. The capaciD, of the exit. ring storm sewer is 14 cfs. If approved in the raann~ propose& the expanded self-sm-race storage fa~I/ry would have a tot. al knpervious m o~3.5 am-es. ~his would generate enough runoff to equal the capacity of the existing storm~ar~r.pipe for.2 year ~ ,, .~,;.,~-, ,....~:~.. .__, -j;~ ...... ::,v,~. ' ..... ; ..... .;4.'~:~.~'~J- . ._-._' -~'='-~. '--,.~..'::.':: 7 If the ¢ apmty of the storm sewer were to be allommd based upon ~ the d/schar~e fi'om the proposed development should be !~mit. ed to 1.? cfs, As proposed, thc runoff/a-om this facility!from s 2 ye. ar storm would be 3.8 ¢fs. However, since theranofffl-om the existing self stl .ra~e facility already exceeds its proportionate share of the capacit3,, I would recom~ ~end that the aforementioned discharge l~mitafion be allowed on the condition that the exJ ~ring self storage be reduced through thc installation of detention volume when conc-m .. curb is/nstalled to meet the 1997 fasility reqmnts. Tlae u~ount of volume needed to a¢hieve a discharge of 1.7 cl~ could be a¢hieved by cons ~m~g a two foot deep ve¢ sump m along the eastm'n property line. Such a sump could ~ mude mowable by ut~li75ng a mum side slope of 4:1 und would occupy a width Of approximately 20 feet. .. ~,... A revi.,~,d drainage plan datext February 23, 1994 was Teceived which shows one-half of the run,~ff generamd to be diver'md to the west into the':Ciry. Park. There is a berm in close proxin~,~ty to the sites western boundary in thc City park which carries a paved park wail, beyond~which is a L2a'aded depression covered by a drainage easement. A culvert would need to}be plac~ through the berm to ~-e. aeh this easement. Ln ~cldqfion, the capacity of the detention arm of the drainage easement was paid for by thc developers of the R.ivenwiek