HomeMy WebLinkAboutmemo re site visit t
Memorandum �Bonestroo
2335 Highway 36 W
To: Lyle Oman Project: 2690 Fox Street Dace: 11-14-07 st.Paui,MN 55113
From: Lance Hoff Client: City of Orono Tel 651-636-4600
Fax 651-636-1311
Re: 11-12-07 Slte Vislt File No: 139Gen �W,bonestroo.com
Plat#139-A11097
Background:
I met with Steve Moore at his site on Monday the 12`h at his request. He had previously walked
the watershed and spoken with neighbors and felt that the SWMP and associated modeling
may have overestimated the amount of area/runoff routed through his property. He felt this
may have also led to an over-design of the proposed pipe and berm design on his property. I
walked the area with him and he pointed out what he has observed and we discussed his prior
conversations he has had with his neighbors. The list below summarizes the main points from
that site visit:
1. The existing 8" draintile that appears to convey the majority of the upstream base
flows has been routed around the house using 8" PVC and connected to the existing
on-site structure. Base flow discharging from the new 8" PVC draintile was observed
in the existing on-site structure during the site visit.
2. The upstream watershed routed to the site is restricted by the small(�12") existing
and partially clogged CMP running under Old Chrystal Bay road. This culvert is
located approximately 200' north of the Old Chrystal Bay Road and Fox Street
intersection.
3. Neighbor observations indicate that a limited amount of flow typically discharges
overland to the Moore property. Steve mentioned that even with the large amount of
rainfall the region received in October, the draintile appeared to convey most of the
flow with very little runoff conveyed overland across his property.
4. The 24" RCP culvert crossing under Old Chrystal Bay Road located approximately
1,200' north of the Old Chrystal Bay Road and Fox Street intersection drains around
the site and does not contribute runoff to the site.
5. There is an existing 5" clay tile line located in the NE corner of the property at the low
point that does not appear to be conveying flows.
Comments:
The following comments correspond to the main points listed above.
1. The 8" PVC tile connection from the existing 8" tile line to the existing structure
appears to have been properly constructed and is conveying upstream flows
adequately. The upstream low area that the draintile services also appeared to be
sufficiently drained.
2. I double checked the watershed areas and routing shown in the City's LSWMP using
2' contour maps. The drainage areas and routing are shown correctly in the LSWMP.
The difference between the contour maps and the LSWMP is that the LSWMP assumes
ultimate conditions and infrastructure to accommodate stormwater flows associated
with ultimate conditions. In this case,the existing �12" CMP culvert under Old
Chrystal Bay Road is proposed to be increase to a 24" RCP. Increased flow from
upstream is then proposed to be attenuated using the proposed 18" pipe at the
Moore property and corresponding upstream storage. Therefore, it is recommended
that the 18" pipe shown in the SWMP be installed at the Moore property at this time,
as shown in the City's LSWMP.
3. The observations from October reflect the current watershed's response to multiple
small storm events. The largest daily rainfall amount in the area in October was
approximately 2.5". This storm depth is approximately equivalent to a 1-yr storm
event. The LSWMP storm drainage system is designed to convey flows generated
during a 100-yr storm and ultimate conditions. For these reasons, and the reasons
stated in#2 above, we recommend installation of the 18" pipe shown in the City's
LSWMP.
4. It is accurate that flow from the existing 24" culvert crossing does not contribute flow
to the Moore property. This was correctly reflected in the stormwater model and the
proposed design for the 18" pipe and berm.
5. As discussed with Steve Moore, we recommend that the existing 5" clay tile line be
discharged to a structure that drains to the proposed 18" pipe as a precautionary
measure.
Please don't hesitate to call me directly at(651)604-4755 if you have any questions!
Page1 of1
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