2005-12-29 Culvert Replacement Study
Jan 04 2006 7:31AM
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[.32Dl 392-S2Cl7
(EIXJ) 5I!:2-B982
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5Z75 EcIr'a In:I. Blvd.
MpIs.. MN 55439
(952) 835-4646
[BOO] 450-7047
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. CDncr.~. PrDduct. Campany. Inc.
c.w.an FIIIIII PIIInt
2C2O Ca.nty Rd. 251
CI!nr'D'l FBIIs. MN S5[J]9
(5IJ7) 263-3935
[8lJIJJ 1542-4435
CGl.Wtlllnd PIImt.
Dl Fa..rtt1 Street
Ccu-t:Iand. MN 56021
[5D7J 354-2615
[8OD) 4SIJ.26J5
December 29, 2005
Mr. John H. Brennan
Attorney at Law
11200 West 78th Street
.Suite 300.
Eden Prairie, MN 55344
RE: Albertville Culvert
Dear Mr. Brerman:
I am writing this letter in response to your letter dated December 23, 2005 regarding the
culvert replacement study I prepared for a culvert located near the Prairie Run plat.
As you know, I prepared a culvert replacement study for the culvert on County State Aid
Highway 1810cated in Section 1 of Township 120 Nonil, Range 24 West, in Wright
. County Minnesota. The primary pmpose of the study was to determine an appropriate
size culvert to replace the existing s1IUcture at this location. The study was conducted in
accordance with standard practice for bridge and culvert replacement projects as outlined
in the Minnesota Department of Transportation's Drainage Manual, and. to the best of .
my knowledge, is consistent with Minnesota Department of Natural Resources rules and
regulations and Minnesota Ditch Laws.
One of the requirements for a study of~s type is to compare the hydraulic
characteriS1ics of the exi.Wng structure with the proposed structure at the occurrence of
the lOO-year flood event. The reason for this is to make sure that the proposed structure
(culvert) does Dot materially increase the risk of flood damage. In order to make this
comparison, it is first necessary to estimate the lOO-year flow rate and flood stage. But it
should be pointed out that the pmpose of the 100-year flood estimate is to assist in the
selection of the proper culvert size. not to establish 1 DO-year flood levels for zoning
purposes.
The degree of BCCU11I'?Y in determination of the lOO-year flood stage. for culvert sizing is
typically not sufficient for flood plain zoning purposes. A Well designed culvert crossing
needs to function properly for floods ranging from say a 2-year event aD the way up to a
SOO-year event. Hthe lOO-year estimate is off slightly. it will not significantly affect the
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www.hancockconcrete.com
EXHIBIT
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Jan 04 2006 7:31AM
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JOHN H. BRENNAN
9529424740
p.3
Mr. Brennan, Attorney at Law
December 29, 200S
Page 2
perfoIDlance of the culvert. Therefore, the additional expense to prepare a more detailed
study to more accurately dctennine the lOO-year flood stage is generally not warranted.
When a predicted loo-year flood stage is used for flood plain zoning, the accuracy of the
prediction is significantly more important. For example: If the flood stage is under
estimated and a development is bunt within the flood plain, the potential loss due to
flooding can be significant; Likewise, if the flood stage is over estimated and
development restricted, the loss of property value can also be significant. Therefore, a
much higher degree of accuracy is necessary when deten:nining loo-year flood stages for
. .-.flood.plain zoDing, andthe a1d~tio!!al cost for a more detailed studY. cm be justified.
For the above stated reasons, 100.-year flood stages determined for bridge and culvert
replacements should generally not be utilized for flood plain zoning pwposes.
Hopefully the above explanation will shed more light on the situation and answer your
questions. If you still have questions, please feel free to contact me at the Minneapolis
Sales Office.
Sincerely,
Hancock Concrete Products Co., Inc.
d~ .~~/J L~~
Brian D. Walter, P.E.
Director of Engineering