ITEM 4.1 PowerpointItem 4.1
Public Hearing
Comprehensive Watershed Map
History
2014 to today
Overall watershed of 2014 vs today
increased 2.4 acres or 0.3% - goal was
to maintain water to same watershed
wherever possible
Additional 9.7 acre was routed through
86-7W due to a downstream draintile not
functioning causing stormwater issues
along 70t" St
History — 2014 to today
n), Runoff that ultimately drained to 86-8P
will still get to 86-8P
86-7W History
Has overtopped twice in last 40 years
causing issues with homes, garages,
septic systems and wells
2. Latest overtopping occurred in 2014
(pre -70t" StProject)
National Wetland Inventory
L Legend
Parcel
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Year
Annual Precip
%
Notable
2012
29.59
93%
2013
32.77
103%
2014
35.44
111%
May, June and July accounted for 22.19" or 11,9" above average for those three months - 86-7W overtopped (pre 70th St project)
2015
36.14
113%
July 7,28" or 3.28" above normal during construciton of 70th St)
2016
40,32
126%
2nd half of year- every month much above average - constituted 26,9" or 10.17" above average going into freeze up
9/1/16 to 8/31/17
46.8
147%
1st half of continued very wet cycle- running year almost 50% more than normal
Avg Year 31.89
Summary - working on 5th straight year above average precipitation
Reason for Project
Minimize flooding potential of residential
homes and property adjacent to 86-7W
and shorten time of elevated water
elevation at 86-7W to provide storage
potential for next large runoff event
Reason for Project
Currently 86-7W recedes to NWL below
overflow elevation only by evaporation
and infiltration and is extremely
dependent on temperature, humidity,
wind, and additional precipitation
Design Criteria by City and DNR
Water quality of 86-302 maintained by
directing 86-7W to 86-8P
Set outlet of 86-7W @ 926.7 to preserve
existing wetland (slightly above OHWL)
Outlet must have fish barrier design to
keep undesirable fish out of 86-7W
Design Criteria by City and DNR
Size outlet pipe to reduce high water
elevations and lessen drain down time of
86-7W without negatively affecting
downstream
Lower risk of any house being flooded
Minimize number of properties affected
by construction
� Complete in time of year that minimize
affects to property (late fall)
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