CR 97-225 Order Plans - Nince Mile Creek~ t ~ o
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December 11, 1997 ° a KEN Council Report No. 97-225
ORDER PLANS AND SPECIFICATIONS
NINE MILE CREEK MAINTENANCE
ProUOSed Action.
Staff recommends adoption of the following motion: Move that
Council authorize RCM Associates to draw up plans and
specifications concernina a Nine Mile Creek bank stabilization
and sediment removal project.
Overview.
Subsequent to last summer's heavy rainfall and flooding episodes,
staff noted occurrences of serious bank erosion and sediment
build-up at various locations along Nine Mile Creek. Staff
viewed these problems as maintenance issues, but ordered a study
of conditions before proceeding with any improvements. The aim
of the study was to determine the magnitude of the problems and
identify the required permitting process with the watershed
district and the DNR. That study, along with recommendations, is
before Council for the purpose of ordering a project.
Primary Issues to Consider.
Existing conditions
o Improvements
Costs
Recommendations
SunnortincT Information.
RCM report
J s Gessele
Engineering Superintendent
Council Report 97-225
December 11, 1997
Page 2
Analvsis
Existing conditions
The City and its consultant have identified four sites
along Nine Mile Creek where significant bank erosion and
sediment deposition have occurred: 11th Avenue crossing,
7th Street crossing, creek channel adjacent to Westbrooke
Way, drainage ditch along T.H. 169. (See attached map)
The 11th Avenue crossing is in need of sediment removal at
the entrance to the northerly box culvert. There is some
creek flow restriction because of the sediment deposits.
The 7th Street crossing also suffers sediment deposits at
the upstream entrance to the box culverts. Of more
serious nature is the bank erosion resulting from the
creek realigning itself around the sediment delta.
Continued bank erosion could adversely affect a
residential garage on the Dusoski property.
The creek bed immediately east of Westbrooke Way suffers
erosion over a 500-foot distance. Although there is no
imminent threat to the adjacent street and bituminous
trail, left unchecked their structural integrity could be
compromised.
The drainage ditch along T.H. 169 at the very south end of
the City is completely filled in. As the report
indicates, this site was cleaned out in 1994/95. A
tributary ditch beginning at the end of 2nd Avenue South
is also substantially silted shut and has thus increased
the potential for flooding near the Nine Mile Cove
development. The ditch along T.H. 169 is also plagued
with an issue of how to maintain access across it when
heavy storm flows tend to wash out the pipe culvert
crossing.
o Improvements
The consultant has made the following proposals:
Site 1 - 11th Avenue crossing
Remove and dispose of approximately 5 cubic yards of
sediment deposits.
Council Report 97-225
December 11, 1997
Page 3
Site 2 - 7th Street Crossing
Remove 125 cubic yards of sediment, regrade the channel,
and place riprap along the creek's east bank.
Site 3 - Creek Adiacent to Westbrooke Wav
Bank slopes are too steep to be treated with ordinary
riprap procedures. Three options are noted:
1. Relocate the creek bed away from the street about 25
feet easterly into Valley Park.
2. Leave creek channel in place and line the west bank
with gabions, wire baskets filled with rock.
3. Use bioengineering techniques incorporating
establishment of vegetation to limit bank erosion.
Site 4 - Drainage Ditch Along T.H, 169
Remove approximately 700 cubic yards of sediment along a
1100-foot segment of the ditch upstream from its
confluence with Nine Mile Creek. Remove as much as 400
cubic yards of material from a tributary ditch draining
the Nine Mile Cove development. Possibly replace an
access culvert crossing.
Costs
Construction Cost Summary Table
Site 1 $ 1,250
Site 2 $ 6,500
Site 3 $30,000 - $60,000
Site 4 $35,500 - $65,500
Engineering Costs
Site 1 and 2 $1,500
Site 3 No costs identified,
further study
recommended
Site 4 $5,500 (design & bidding)
$8,500 (permitting &
construction)
Funding for a project can be accomplished in part from a
storm sewer maintenance line item in the City's budget. A
major source would need to be the storm sewer utility.
Another funding source is maintenance grants from Nine
Mile Creek Watershed District. A modest funding
Council Report 97-225
December 11, 1997
Page 4
participation could be anticipated.
o Recommendation
Staff concurs with the consultant's assessment that the
City proceed with design, permitting and construction
improvements at sites 1,2, and 4. Staff also concurs that
site 3 needs further study to provide a remedy that is
engineering sound yet meets the aesthetic needs of the
neighborhood. Staff recommends that the City enter into
an agreement with RCM for services at a cost not to exceed
the quoted amount.
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FEASIBILITY REPORT
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NINE MILE CREEK
BANK STABILIZATION/SEDIMENT REMOVAL
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HOPKINS, MINNESOTA
DECEMBER 1997
RIEKE CARROLL HULLER ASSOCIATES, INC.
~: RCM PROJECT NO.10418.01
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I hereby certify that this plan, specification, or report was prepazed by me or under my direct supervision
and that I am a duly Registered Professional Engineer under the laws of the State of Minnesota.
Date: _/2//097 1 ~o~P/t~'~ ~~er~.~
L Robert L. Moberg, P.E. ,Reg. No. 23334
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Introduction
Figure 1
Existing Conditions
1 Proposed Improvements
• Permits
Project Cost Summary
Conclusions and Recommendations
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TABLE OF CONTENTS
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This feasibility report has been prepazed and is submitted in accordance with an agreement dated August 22,
1997 between the City of Hopkins and Rieke Carroll Muller Associates, Inc. (RCM). The purpose of this report
~~ is to identify the scope of improvements recommended to mitigate streambank erosion and sediment deposition
1~ at four specific locations along the North Fork of Nine Mile Creek. Locations aze shown on tha following map.
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NINE MILE CREEK REVISIONS SHEET N0.
BANK STABILIZATION AND SEDIMENT 7
REMOVAL AREAS
HOPKINS, MINNESOTA onTE FlLE N0.
NOV.1997 10418.01
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EXISTING CONDTfIONS
The North Fork of Nine Mile Creek is primarily a riparian stream interspersed with several culvert crossings
`" throughout the City of Hopkins. Several of the culvert crossings have been upgraded in recent years to reduce
flooding potential in azeas adjacent to the creek. Reconnaissance along the creek and its tributaries during the
summer of 1997 revealed four sites where significant amounts of streambaok erosion and/or streambed sediment
deposition have occurred. These four sites and the conditions associated with them aze described below.
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~ ` 1. Site 1-Eleventh Avenue Crossing
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~~ Approximately 5 cubic yards of sediment material has been deposited in the creek immediately upstream
of the culvert crossing at Eleventh Avenue South. The existing crossing consists of one 10 foot-wide by
5 foot-high RC box and one 12 foot-wide by S foot-high RC box. The two box culverts are spaced 17
feet apart, center to center. The sediment material has been deposited at the entrance to the most
northerly box culvert. The presence of this material is restricting the low-flow capacity of the box
culverts.
~' 2. Site 2 -Seventh Street Crossing
The existing crossing at Seventh Street South consists of two 10 foot-wide by 6 foot-high RC box
culverts, spaced 25 feet apart, center to center. As is the case at Site 1, sediment material has been
deposited at the upstream entrance to the box culverts. Approximately 1500 sq. ft. of streambed has been
_ covered with sedunent deposits at this location. In addition, approximately 30 feet of the east bank of
the creek has experienced significant erosion. The erosion is a direct result of the creek realigning itself
to flow around the 12 to 36 inch-deep sediment deposits left at the box culvert entrance. Left unchecked,
continuation of this bank erosion will eventually affect the structural integrity of a residential garage
building on the Dusoski property adjacent to the creek.
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3. . itP 3 - Cha^nel Adiac~*_st to Westbrooke Wav
~ Nine Mile Creels parallels Westbrooke Way between Ninth Avenue South and a point approximately 400
feet north of Old Settler's Trail. Erosion of the west bank has occurred innumerous places along this
length ofchannel (approximately 500 feet). Bank slopes of 2:1 and steeper are found in this area and are
susceptible to further erosion during periods of high streamflow. Bank erosion has occurred to within
3-5 feet of an existing bituminous trail on the east side of Westbrooke Way. Further erosion will likely
undermine the trail and may in time impact the structural integrity of the street.
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4. Site 4 -Drainage Ditch Along_TH 169
The drainage ditch along the west side of Tnmk Highway 169 is a tributary of Nine Mile Creek and
~ ' conveys stonmwater from an 84-inch diameter C5P storm sewer. This area was cleaned out during
the winter of 1994/95 and a sedimentation basin was excavated in the upper 350 feet of the channel
~} at that time. The sedimentation basin is now completely filled in. This ditch was observed to have
substantial amounts of sediment deposits along its entire length of approximately 1100 feet, with the
[ i upper 750 feet particularly congested. Cattails were found to be growing in the channel at several
~ ~ points. Ditch banks were found to be in good condition.
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' In conjunction with the ditch cleanout project of 1994/95, the City of Hopkins placed a 36-inch RCP
~ in the ditch to allow for utility access across the chamrel. This pipe culvert is undersized and was
destroyed by heavy storm flows this summer. The destruction of this culvert contributed to the heavy
level of sediment deposition in the reach of ditch upstream from the culverk
Jurisdictional responsibility for this &tch is ambiguous. The ditch lies within MnDOT right-of-way
obtained from Hennepin County when TH 169 was constructed. MnDOT personnel are not aware
~" of any maintenance agreements which require the City of Hopkins to maintain the ditch. It does not
appear that roadway drainage from the TH 169 has a significant impact of sediment loading for the
ditch.
A tributary ditch which flows easterly from the southerly terminus of Second Avenue South into the
ditch which parallels TH 169 is in need of cleaning. This ditch segment is approximately 500 feet
in length and is overgrown with vegetation, resulting in a reduction of flow-carrying capacity. This
reduction in capacity has increased the potential for flooding upstream, particularly in the Nine Mile
Cove developmenk
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` PROPOSED IMPROVEMENTS
f The proposed plan for improvements includes removal and disposal of sediment deposits, placement of riprap
°1 or other bank stabilization material, channel realignment, and placement of appropriate temporary erosion
control devices to mitigate corutmction impacts. Site construction activities will be performed during the
} winter low-flow period, to m;n;m;~P impacts. Specific improvements are outlined below.
1. Site 1 -Eleventh Avenue Crossin
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Approximately 5 cubic yards of sediment material deposited at the northerly box culvert entrance will
' be removed and disposed of. The channel bottom will be regraded to direct streamflow toward the
two culvert entrances. A siltation check dam will be placed at the downstream end of the culverts,
~ in order to contain material washed downstream during wnstcuction activities.
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2. Site 2 -Seventh Street Crossing
Approximately 125 cubic yards of material will be removed from the upstream entrance to the box
~' culverts. The channel will be regraded to direct streamflow towazd both entrances. Approximately
(. , 60 cubic yards of riprap and filter blanket will be placed along the east bank of the creek. Some bank
excavation may be required to accommodate placement of riprap. A temporary construction easement
will be obtained to allow for constnuKion of bank improvements. A siltation check dam will be
placed as indicated for Site 1.
3. Site 3 - Channel Adiacent to Westbrooke Wav
Bank slopes in this area are too steep to be stabilized with riprap. Other means of bank protection will
be required to *~;n;m;~P erosion. Three possible alternatives are outlined below.
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~ Relocation of approximately 400 linear feet may be done to eliminate the steep banks in this area
- without impacting existing street improvements on Westbrooke Way. The channel could be moved
approximately 25 feet easterly into Valley Park Approximately 1600 cubic yazds of material would
~ be excavated for the new channel. This material, if found to be suitable for fill, may be stored on site
and eventually placed is the old streambed. Riprap would need to be placed to protect the abutments
~ ` for an existing pedestrian bridge over the creek Approximately 300 lineaz feet of an 8-foot wide
aggregate-surfaced trail would need to be moved to accommodate channel relocation.
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The west bank of the creek could be lined with gabions, which are wire baskets filled with rock. The
k' baskets are tied together and anchored to the bank slope. This application can be used with bank slopes
e- as steep a 1.5:1.
Option 3
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The creek banks could be stabilized using bioengineering techniques. This option would incorporate the
~ establishment of vegetation on the slope that limits bank erosion through development of an extensive
toot structure. Planting of Willow roots and branches aze an example of this approach.
~ 4. Site 4 - Draina fe Ditch Alone TH 169
Sediment needs to be removed along the entire 1100-foot segment of the ditch upstream of its confluence
with Rine Mile Creek. As much as 500 cubic yards of material may need to be removed. Reestablishment
of the channel sedimentation basin requires removal of an additiona1200 cubic yazds of material As
~ much as 400 cubic yazds of material may need to be removed along the 500-foot segment of tributary
E ° ditch. Some clearing of brush and trees is also needed along the tributary ditch.
~• Replacement of the undersized 36-inch diameter RCP culvert will require 13 barrels of identical-size
pipe to meet the capacity (385 cfs fora 10-year frequency) of the 84-inch pipe outtetting into the ditch.
Hydraulically, two barrels of 72-inch diameter pipe can be used to convey the same flow. ff a box culvert
were to be used in place of a pipe, a 5-foot high by 12-feet wide box will be sufficient. Because the ditch
is only 4 feet deep, both a pipe option and a box option will require significant amounts of fill to provide
adequate cover. Placement of additional fill will have an undesirable impact on the surrounding
floodplam. It is also anticipated that if a concrete structure is used, a pile foundation will be required,
1' ` due to the probability of unstable soils in the area. Use of CSP material may allow the City to avoid the
need for a pile foundation, if some pipe settlement is acceptable.
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f ' ~ PERMITS
Project coordination andJor permitting will be required with the following agencies:
Army Corps of Engineers (COE)
Nine Mile Creek Watershed District
Minnesota Depamnent of Natural Resources (DNR)
Minnesota Department of Transportation (MnDOT}
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The permit from COE is likely to be a Nationwide Permit, as the total surface area disturbed by construction
is less than 1 acre. During their permit review process, COE will determine whether U.S. Fish and Wildlife
Service involvement is needed.
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Nine Mile Creek Watershed District has obtained a general permit from DNR which allows for placement
of riprap at isolated locations along the waterway. The purpose of this general permit is to allow the
Watershed District to issue individual permits as an ageat for DNR, thereby eliminating the need for separate
permits. According to DNR stag the scope of work identified for Sites I and 2 meets the conditions indicated
in the general permit issued to the Watershed District. Proposed improvements for Site 3 and 4 will likely
requve a separate DNR permit.
If the City decides not to pursue the scope of work identified for Site 4, a MnDOT permit is not needed for
work at the other sites.
PROJECT COST SUMMARY
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A-: Estimated construction costs for each site are identified below (temporary erosion control is included):
s Location Activity Estimate d Construction Cost
Site 1 1. SedimentRemovai $1,250
Site 2 1. Sediment Removal $2,250
i' ` ~ 2. Bank Stabilization 250
r' Total Sites 1 and 2 $7,750
Site4 1. Sediment Removal $35,500
r' 2. Corrugated Steel Culvert Crossing 30 000
Total Site 4 $65,500
Although a specific option for Site 3 has not been recommended, estimated construction costs for the site aze
expected to be in the range of $30,000-$60,000.
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~-~ Estimated engineering consultant costs associated with Sites 1 and 2 is $1,500. This estimate includes all work
provided through permit acquisition. Hiring a contractor and administration of a contract are assumed to be the
responsibility of City staff.
}"" Project engineering vests for work at Site 3 have not been identified, as further study of possible alternatives is
[- needed.
Estimated engineering and administration costs associated with Site 4 are as follows:
F ' Design and Bidding Phase $5,500
Construction Phase 8 5 0
f.# Total $14,000
lti Nine Mile Creek Watershed District has discretionary funds available to use for maintenance activities. The
{ ~ extent to which the Watershed District is willing to participate in the project will be determined during the
~~ pernutting process.
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~~ CONCLUSIONS AND RECOMMENDATIONS
~ Removal of sedunent deposits at Site 1 and Srte 2 will improve streamflow characteristics and will reduce the
1"` potential for bank erosion in these meas. Placement of riprap along the east bank at Site 2 will provide additional
protection from bank erosion and erosion of the adjacent property. A temporary construction easement or right
of entry permit needs to be acquired from the adjacent property owner at Site 2.
Further study of Site 3 is necessary to determine an optimal solution for providing stream bank protection along
1' ~ Westbrooke Way. Three possible solutions are identified on page 5 of this report.
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Removal of sediment deposits at Site 4 is recommended, as additional flood protection for areas upstream of the
ditches can be realized. Recent history indicates that the main ditch will need to be cleaned every 3-4 yeazs,
unless sediment loading is reduced further upstream.
The City of Hopkins does not have an obligation to provide utility access across the ditch at Site 4. Placement
of a permanent culvert to accommodate a uliliry crossing is cost-pmlubitive. Placement of a culvert which is lazge
enough to convey high-frequency flows in the ditch will have a negative impact on the surrounding floodplain.
g RCM's recommendation is for the City to procced with design, permitting, and construction of improvements at
1'~ Sites 1, 2 and 4. If the permitting process associated with improvements proposed for Site 4 becomes time-
t`~ consuming, this work can be isolated as a separate projeck Work at Sites 1 and 2 can be performed without going
f~ through a public bidding process, if the City so chooses. Design and construction of improvements at Site 3
should be deferred until an optimal solution can be identified
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