HomeMy WebLinkAboutRe: culvert , � .
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� � May 3, 1995
Lyle Oman
City of Orono
PO Box 66
Crystal Bay, MN 55323-0066
Re: 1650 North Farm Road
Dear Mr. Oman:
At Terry Dahlstrom's request I have reviewed Barr Engineering's study, dated July 10, 1995, of the small
pond on this property. Mr. Dahlstrom has asked for alternatives to raising the proposed house to an
elevation 3" above the low point of Long Lake Road or constructing an emergency overflow swale through
the wooded site to the south. Both of these alternative would have negative impacts on the aesthetics of the
home site.
The issue appears to be two fold: what happens if the culvert under Long Lake Road becomes plugged and
secondly, what happens if there is an event in excess of the 100 year event. It is my belief that both
concerns can be addressed by the installation of a second culvert under Long Lake Road. The culvert
should be set 4 inches higher than the existing culvert. This will help prevent sediment from collecting in
the second pipe, since under typical situations it will remain dry. The culvert should be 18" in diameter to
minimize the potential for clogging. The pipe material should be double wall corrugated polyethylene
(MNDOT 3247), which provides a smooth inner wall, again to minimize clogging. Polyethylene pipe
should be bed in sand to prevent deforming the pipe. A bedding detail is attached.
As an added precaution I recommend that the house be raised six inches. This will allow storage for a
second 100 year rainfall event, in the event that both culverts are blocked. As a reference point a visable
permanent marker (i.e. a boulder, fence post, etc.) should be placed near the proposed home by Mr.
Dahlstrom's surveyor at the outlet elevation of the pond (986.7). Standing water above the marker could
alert the homeowner to a blocked culvert. Within a day of most rainfall events the water level should
return to the outlet elevation
If you have any questions feel free to contact me.
Sincerely,
LANDFORM ENGINEERING COMPANY
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Step n M. Jo ston,P.E.
/sMJ
Landform Engineering Company,905 Twelve Oaks Center,I5500 Wayzata Blvd.,Wayzata,Minnesota 55391,(612)475-3272,Fax/Data(612)475-3159
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GRANULAR FOUNDATION
CLASS B
CLASS B BEDDING THE PIPE IS BEDDED IN
COMPACTED GRANULAR MATERIAL PLACED UP TO A
HEIGHT EQUAL TO ONE—HALF THE OUTSIDE DIAMETER OF
THE PIPE. THE DEPTH OF THE GRANULAR BEDDING
BELOW THE PIPE IS A MINIMUM OF 3" FOR 27'�
DIAMETER AND SMALLER PIPE, 6" FOR 66" DIAMETER
AND LARGER PIPE, AND 4" FOR INTERMEDIATE SIZES.
THE INITIAL FILL MATERIAL SHOULD BE DENSELY COM—
PACTED UP TO A HEIGHT OF 12�� OVER THE TOP OF THE
PIPE.
CLASS B BEDDING