HomeMy WebLinkAbout20100315 - VIII-A-1MEMO
To: Honorable Mayor and City Council
From: Tom Montgomery
Date: March 8, 2oio
Re: Flood Forecast and Recommended City Response
Flood Forecast & Flood Stage References
The National Weather Service is predicting a 50 % to go % chance of the
Mississippi River exceeding flood stage (i5 ft.) this spring. At flood stage, the lst
Street railroad underpass begins to flood -little else is affected.
The National Weather Service is also predicting a io % to 50 % chance of moderate
to major flooding on the Mississippi River in early April (see enclosed prediction
table and flood elevation information). At the moderate flood stage of i~ ft.,
water is over the riprap at Levee Park. At the major flood stage of i8 ft., water is
over the riprap at Jaycee Park and inay start to impact the basements of up to 8
homes on east lst Street.
If flood waters rise above a i9 ft. flood stage, the Lock and Dam Road and lst
Street on either side of Franklin Street may become flooded.
Recommended City Response
As flood levels rise, Public Worlcs, Parks, Police and Fire will coordinate efforts
and close roadways, trails and parks as appropriate. We will monitor river levels
and flood forecasts. Aside from some park structures in Lake Rebecca Park, no
City structures are expected to be impacted by flooding.
In the past two floods, the City has assisted four to six homes on East lst Street by
providing empty sand bags, sand, and poly sheeting and using Public Works
operators and skid loaders to move pallets of filled sandbags to around homes
where they are needed. Volunteers were utilized to fill and place sandbags and
local civic organizations were contacted to solicit and schedule volunteer labor.
City workers were not used to fill and place sandbags.
With the current flood forecast, there is less than a 50/5o chance that the major
flood stage of i8 feet will be exceeded. However, if the flood stage reaches i6.5
feet and the flood forecast at that time is predicting flood levels to exceed i8 feet,
staff recommends utilizing a maximum of $io,ooo in funding from the Critical
Incident ERF (current balance is $~o,ooo) to purchase sandbags and other
materials needed to protect the four to six East lst Street homes and to fund
overtime for the City workers operating skid loaders to move pallets of sandbags
for volunteers. City workers would not fill sandbags, only provide and move
them. City workers also would not go onto private property to remove sandbags.
COUNCIL ACTION REQUESTED
Council is requested to authorize the use of up to $io,ooo from the Critical
Incident ERF to purchase materials and fund overtime for flood fighting activities
for the homes on East 15t Street if flood forecasts are predicting flood levels to
exceed i8 feet.
1 Week Chances of Exceeding River Levels on the MISSISSIPPI RIVER a# HRSTINGS, NN
La#itude: 44.9 Longgi#ude: 98.@
Forecas# for the period 8~8f2@1@ - Sf31f2@10
This is a conditional simulation based on the current condi#ions as of 3f1~2@1@
21.70
19.$0 ~
17.90 hod i rig
I oc~d i r-ig
16.00
Flood
14.1@
lJeek I y
Naximum 12.2@
Stage
CFT7 1@.3@
8.40
6.50
4.60
2.70
~/$ ~f]
12:00 E
Important Elevations:
STAGE ELEVATION DESCRIPTION
14.41 685.06 Low Point - 1st St/RR Bridge Underpass
15.35 686 Low Point - Mississippi River Trail by Levee Pk steps
15.35 686 Top of Riprap -Levee Pk
17.35 688 Top of Riprap -Jaycee Pk
18.43 689.08 Low Point - L/D Road
18.85 689.5 Low Beam - E 41h St. Bridge
19.35 690 Low Point - 1st St & Franklin
19.35 690 Boat Ramp Parking Lot
19.85 690.5 Front Deck Hydropower Plant
22.35 693 Top of Deck - E 41h St. Bridge
23.45 694.1 Top of Lock Wall - Hydro Access
Historical Crests
(1) 25.90 ft on 04/17/1965
(2) 24.30 ft on 04/16/1969
(3) 22.00 ft on 04/29/2001
(4) 21.60 ft on 04/17/2001
(5) 21.30 ft on 04/13/1997
(6) 20.90 ft on 04/16/1952
(7) 18.90 ft on 06/28/1993
(7) 18.90 ft on 04/18/1951
(9) 17.10 ft on 05/04/1975
(10) 16.90 ft on 04/07/1986
Exceedance
Probability
^ 10 - 507.
. 50 - 907.
^ >= 90~
Exceedance Probablility
Flood Level 15.0 {Feet?