HomeMy WebLinkAbout020_Confluence HOA Pond Report
Prepared for:
Cattail Creek Community Association
Attn: Jaymie Larsen
PO Box 11842
Bozeman, MT 59719
Submitted By:
Cattail Creek Community Association
Confluence Consulting, Inc.
PO Box 1133
Bozeman, Montana 59771
(406) 585-9500
Cattail Creek Stormwater Detention Ponds #1-3 and
#5-7 60% Design
October 21, 2020
DESIGN REPORT
Cattail Creek Stormwater Detention Ponds #1-3 & 5-7 60% Design
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Table of Contents
1. INTRODUCTION ................................................................................................................ 3
Background ............................................................................................................................ 3
2. INFORMATION COLLECTION / SITE ASSESSMENT / SURVEY ..................................... 4
2.1. Topographical Survey / Site Evaluation ........................................................................ 5
2.2. Stormwater Pond Capacity Analysis ............................................................................ 5
Pond Volume Required ....................................................................................................... 6
As-Built Pond Volume ......................................................................................................... 7
Current Pond Capacity ........................................................................................................ 7
Groundwater Level .............................................................................................................. 8
2.3. Soils Analysis ..............................................................................................................12
3. POND ISSUES AND RECOMMENDATIONS ....................................................................13
Pond 1: ..................................................................................................................................13
Problems............................................................................................................................13
Recommendations .............................................................................................................13
Pond 2: ..................................................................................................................................14
Problems............................................................................................................................14
Solutions ............................................................................................................................14
Pond 3: ..................................................................................................................................15
Problems............................................................................................................................15
Recommendations .............................................................................................................15
Pond 5: ..................................................................................................................................16
Problems............................................................................................................................16
Recommendations .............................................................................................................16
Pond 6: ..................................................................................................................................17
Problems............................................................................................................................17
Recommendations .............................................................................................................18
Pond 7: ..................................................................................................................................18
Problems............................................................................................................................18
Recommendations .............................................................................................................18
Pond 6 and 7 Alternatives: .....................................................................................................18
Alternative 1 – Groundwater sump pump / interceptor drains .............................................19
Alternative 2 – Construct berm at outlet of ponds to increase pond capacity ......................19
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Common Treatments .............................................................................................................20
1. Sediment Trap ............................................................................................................20
2. Install Staff Gages.......................................................................................................20
3. Vegetation Maintenance .............................................................................................20
4. COST ESTIMATES ...........................................................................................................20
5. PERMITTING .....................................................................................................................23
Ponds 1,2,3, and 5 .............................................................................................................23
Ponds 6 and 7 ....................................................................................................................23
6. CONCLUSIONS ................................................................................................................23
APPENDIX A ............................................................................................................................25
Photolog ................................................................................................................................25
APPENDIX B ............................................................................................................................26
Conceptual Design Site Plans and Details .............................................................................26
APPENDIX C ............................................................................................................................27
City of Bozeman Stormwater Basin Maintenance Program – Cattail Creek Homeowners
Association Stormwater Basin Inventory 6/22/2016 ...............................................................27
City of Bozeman Stormwater Basin Maintenance Guide ........................................................27
APPENDIX D ............................................................................................................................28
As-Built Plans for Pond “1-7” TD&H (6/12/02) ........................................................................28
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1. INTRODUCTION
Confluence Consulting, Inc. (Confluence) was contracted by the Cattail Creek Homeowner’s
Association for design services to evaluate and develop a 60% design to restore several
stormwater detention ponds identified as Stormwater Basin ID #’s 1-3 and 5-7 located on the
south side of Catamount Street and the North side of Cattail St, between Warbler Way and
Blackbird Drive.
Confluence has collected survey and field data, conducted volume analysis of the pond, and
provided recommendations and a preliminary design for treatments to maintain compliance with
the City of Bozeman Stormwater Basin Maintenance Program, and to improve upon the function
of the pond, with the goal of reducing future pond maintenance costs. The results are provided in
this report.
Background
Stormwater basins #1-7 were designed and constructed to collect and treat stormwater runoff as
part of the Cattail Creek Subdivision Phases 1-3, which were constructed in the early 2000’s. The
City of Bozeman has identified potential problems and maintenance concerns related to the
stormwater ponds in Cattail Creek Subdivision and has provided an outline of the issues in the
Stormwater Basin Maintenance Program Inventory for Cattail Creek Subdivision dated June 22,
2016. A copy of this document is provided in Appendix B. In this document, the City identified
the following issues and recommendations with Stormwater Basins #1-3 & 5-7. A summary of the
COB’s recommendation for each basin is found below in table 1. It should be noted that while
the City refers to each pond, by its Basin ID number, Ponds are identified by letters “A-F” in the
Cattail Creek Subdivision Phases 1-3 Record Plans prepared by TD&H Engineering.
Table 1: Summary of Basin Maintenance Inventory for Ponds 1-3 & 5-7
Basin ID # Current Issues Recommended HOA Maintenance
1 (C)
Inlet and outlet pipes are
obstructed
Storage capacity has been
reduced because of buildup of
decayed vegetation and the
growth of trees/shrubs
Remove vegetation and debris
built up around inlet and outlet
pipes
Remove trees and shrubs
Maintain moving forward per
attached Stormwater Basin
Maintenance Guide
2 (D)
Inlet and outlet pipes are
obstructed
Storage capacity has been
reduced because of buildup of
decayed vegetation and the
growth of trees/shrubs
Remove vegetation and debris
built up around inlet and outlet
pipes
Remove trees and shrubs
Dredge and contour the basin as
drawn on the Engineering Plans
for Cattail Creek
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A channel has developed
allowing flow through to
occur
Subdivision.
Maintain moving forward per
attached Stormwater Basin
Maintenance Guide
3 (B)
Inlet and outlet pipes are
obstructed
Storage capacity has been
reduced because of buildup of
decayed vegetation
The basin is not discharging
properly because of an
elevated berm adjacent to the
receiving waterway
Remove vegetation and debris
built up around inlet and outlet
pipes
Dredge and contour the basin as
drawn on the Engineering Plans
for Cattail Creek Subdivision
Maintain moving forward per
attached Stormwater Basin
Maintenance Guide
5 (E)
Inlet and outlet pipes are
obstructed
Storage capacity has been
reduced because of buildup of
decayed vegetation and the
growth of trees/shrubs
Remove vegetation and debris
built up around inlet and outlet
pipes
Remove trees and shrubs
Maintain moving forward per
attached Stormwater Basin
Maintenance Guide
6 (F)
Inlet and outlet pipes are
obstructed
Storage capacity has been
reduced because of buildup of
decayed vegetation and the
growth of trees/shrubs
Remove vegetation and debris
built up around inlet and outlet
pipes
Remove trees and shrubs
Maintain moving forward per
attached Stormwater Basin
Maintenance Guide
7 (G)
Inlet and outlet pipes are
obstructed
Storage capacity has been
reduced because of buildup of
decayed vegetation and the
growth of trees/shrubs
Remove vegetation and debris
built up around inlet and outlet
pipes
Remove trees and shrubs
Maintain moving forward per
attached Stormwater Basin
Maintenance Guide
2. INFORMATION COLLECTION / SITE ASSESSMENT / SURVEY
Confluence has obtained and reviewed the Cattail Creek Phase 1-3 construction as-builts, design
report and City of Bozeman Stormwater Basin Program Inventory Report to aid in understanding
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Cattail Creek Stormwater Detention Ponds #1-3 & 5-7 60% Design
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the intended function of each pond and to develop treatments to improve the function of each
pond.
2.1. Topographical Survey / Site Evaluation
Confluence visited the site on April 14, 2020 to conduct the site evaluation and topographic
survey. Ponds 2 and 3 were primarily vegetated with the same species of upland grasses found
in the surrounding open space and park. All other ponds were densely vegetated with wetland
vegetation, primarily cattails and willows. Documentation of specific vegetation can be found in
Table 2.
Table 2: Summary of Vegetation present in Ponds 1-3 & 5-7
Basin ID # Vegetation Communities
1 (C) Predominantly cattail and willow, some sedge present
2 (D) Predominantly grass with some rushes present
3 (B) Upland grass
5 (E) Predominantly willow, with some cattail and sedge present
6 (F) Predominantly cattail (mowed), with some sedge
7 (G) Cattail in open water
Each basin was found to vary in volume, vegetation composition and sediment accumulation.
Detailed discussion of each basin is provided in Section 3. To view basin specific overviews and
images, see the attached photolog and the attached site plan in the Appendix A and B
respectively.
Sites were surveyed using RTK GPS survey equipment and the elevations were adjusted to the
City of Bozeman vertical datum based on established benchmarks at fire hydrants within the
subdivision. The survey is based on the NAD83 Montana State Plane Coordinate System
(International Feet). Topographical survey of the ponds and associated infrastructure was
conducted and included; the pond, immediate topography around the pond edge, existing
trees/shrubs, inlet and outlet pipe inverts, and topography of flow path between outlet pipe and
creek. Topography of the sites is provided on the site plans in Appendix B.
In addition to topographic survey, structure inverts were surveyed to assess functionality. Several
of the culvert structures surveyed displayed the ground elevation around the inlet and outlet pipes
to be higher than the invert of the pipes, indicating that either the ponds have likely accumulated
sediment from runoff or detritus from decayed wetland vegetation or the ponds were constructed
or designed improperly, reducing the ability of the site to function properly to store and treat
stormwater. For an example, see Photo 3B in Appendix A Photolog, for an example of a concrete
inlet displaying sediment accumulation.
2.2. Stormwater Pond Capacity Analysis
Primary analysis of the ponds, consisted of investigating stormwater capacity with supplemental
groundwater analysis, with the aim of evaluating the ponds’ capacity and to determine if the
existing pond volumes meet the original design required by the City of Bozeman during its
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approval process. This was achieved by comparing as-built pond volumes, with required and
current pond volumes. Results comparing the as-built, required and current volume for each pond
can be found in Table 3.
Analysis first began with review of design documents. The design report and as-built record
drawings for all phases of pond construction were obtained from the City of Bozeman’s website
to compare existing conditions with the as-built ponds and to review the pond design and
requirements.
The record as-built drawings for Cattail Creek Subdivision Phase 1 were created by TD&H
Engineering and dated 06/07/2002. The record as-built drawings for Cattail Creek Subdivision
Phase 2 were created by TD&H Engineering and dated December 2002. The record as-built
drawings for Cattail Creek Subdivision Phase 3 were created by TD&H Engineering and dated
01/03/2005 and can be found in Appendix D. The stormwater design report for the subdivision,
titled “Stormwater Master Plan Cattail Creek Subdivision” was also created by TD&H and was
reviewed in part as it relates to the subject pond.
Pond Volume Required
A cursory review of the calculations for the ponds was conducted, though a detailed review was
not performed as the Master Plan did not include delineated drainage areas, making a detailed
check of the exact calculations impossible. The following provides an outline to the methodology
used by TD&H to design the stormwater pond. Based on our review, the methods used appear
to be in accordance with the City of Bozeman Design Standards.
According to the Stormwater Master Plan, ponds in the subdivision were designed to detain the
post development runoff to a rate that does not exceed the predevelopment peak runoff rate. In
order to size ponds, each pond was “routed” using a mass balance spreadsheet. The
spreadsheet utilized the modified rational method for calculating the pond inflow (post-
construction runoff) and the pond outflow (pre-construction runoff) to determine the required
volume based on the maximum pond volume at a given time-step in the routing spreadsheet.
The modified rational method was used to calculate pre-construction and post-construction
conditions. The pre-construction runoff was calculated based on the local drainage area for each
pond, a rainfall intensity for the 10-year discharge, and pre-construction runoff discharge
coefficient ranging from 0.19-0.30. The post-construction runoff was calculated based on the local
post-construction drainage area, a discharge coefficient ranging from 0.39-0.55, as well as the
rainfall intensity for a 10-year discharge. The rainfall intensity was calculated as a function of the
time of concentration which was determined using a combination of overland flow, gutter flow,
and storm drain conveyance.
Table 3 displays a summary of the variables used to calculate the max required volume for each
pond.
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Cattail Creek Stormwater Detention Ponds #1-3 & 5-7 60% Design
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Table 3: Pond Drainage Summary for Basins 1-3 and 5-7, By TD&H
Pre-Construction Post Construction
Pond
Number Drainage
Area (Acre)
Discharge
Coefficient
(C)
Runoff (CFS)
Discharge
Coefficient
(C)
Required
Pond Volume1
(ft³)
1 (C) 12.1 0.30 3.15 0.52 6,900
2 (D) 15.4 0.29 2.70 0.56 10,700
3 (B) 14.0 0.30 5.16 0.39 6,000
5 (E) 23.5 0.19 3.6 0.49 14,500
6 (F) 23.7 0.20 3.29 0.55 24,900
7 (G) 19.2 0.20 2.63 0.55 19,900
Based on the TD&H Design and Design Reports for Phase 1-3, found in Appendix D
As-Built Pond Volume
Where listed on the as-built documentation, the volume provided was used. Where volumes were
not provided in the as-built documentation, the as-built site plans for each pond was used to create
a surface in Autocad Civil 3D. A volume surface was developed comparing the design top of
pond elevation, to the design pond surface to calculate the as-built pond volume. This exercise
indicates that in general ponds were constructed with a volume significantly higher than the
required volumes. However, based upon field observation and topographic survey of the
constructed pond shape and the design shape, it appears that ponds were not constructed exactly
to the dimensions and elevations shown on the as-built plans. Thus, the actual constructed pond
volumes may have been slightly more or less than what was calculated. As built volumes for all
ponds can be found in Table 4.
Current Pond Capacity
Current pond volumes were estimated using the same process described with the as-built pond
volumes, except that the water surface elevation used for developing volumes was determined
by identifying the lowest point along the top of pond based on the topographic survey. This is the
elevation where the pond is overtopped. The water surface elevation was compared to the current
surveyed pond topography. Where groundwater does not affect the capacity of the pond, a
volume surface was developed to determine the pond’s capacity without consideration of
vegetation. This volume can be found in Table 4 below. Where groundwater was present at the
time of the survey or was determined to be present based on groundwater monitoring, the pond
capacity was determined assuming the pond is partially filled with water, reducing the amount of
capacity available for stormwater runoff. The water surface elevation used as the “bottom” of the
pond was based on either the measured peak groundwater elevation based on groundwater
monitoring or an assumed depth above the outlet pipe invert elevation of 0.2 feet.
The comparison of as-built pond volumes to current pond volumes, indicates varying reduction in
pond capacity, with a reduction for ponds 2,3,6 and 7 ranging from 7-24%. Ponds 1 and 5 current
capacities are larger than the documented as-built capacities.
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However, because actual volume is likely less than topographic survey due to vegetated cover, a
volume including vegetation was established. Firstly, an estimate of the volume of vegetation
within each site was made based on observation and best engineering judgement. Then given
each percentage of vegetation, the volume of the pond being composed of above ground
vegetation (composed of stems and leaves of wetland grasses, shrubs, and trees) was calculated.
Percentage of vegetation varied from 5%, where cattails and sedge dominated, to 1% which was
reflective of short grasses. Results for vegetated pond volume further reduced the difference
between required and current pond volumes. Based on a comparison of the current pond volumes
accounting for vegetation and groundwater to the required pond volumes, ponds 2, 6, and 7
currently do not meet the COB requirements for capacity.
Table 4: Pond Volumes for Basins, 1-3 & 5-7
Groundwater Level
Four groundwater monitoring wells with continuous groundwater monitoring devices were
installed at locations throughout the subdivision. The groundwater monitoring wells were installed
to allow for more accurate evaluation of groundwater at the other stormwater pond locations in
the subdivision. The monitoring devices were installed on October 31st and November 1st, 2018
and surveyed with RTK GPS to tie in the groundwater elevations with the design/as-built
elevation. The continuous groundwater monitoring devices were installed in PVC wells to a depth
of 3-4’ below ground and provided daily water surface elevation data throughout the spring, 2019
(10/30/19-1/25/20) season, to document the maximum groundwater elevation through the
season. Figure 1 displays the well location with respect to pond locations.
The presence of extensive wetland vegetation, especially cattails, indicates high groundwater in
ponds 1, 5, 6, and 7. As anticipated groundwater was found to rise during the spring and early
summer. Early fall also displayed a groundwater rise.
1 (C) 6,848 7,821 8,910 5% 8,465 693 7,772 -49 924 YES
2 (D) 10,688 12,067 9,422 1% 9,328 0 9,328 -2,739 -1,360 NO
3 (B) 5,990 8,219 6,268 1% 6,205 40 6,165 -2,054 175 YES
5 (E) 14,515 16,611 17,373 2% 17,026 1 17,025 414 2,510 YES
6 (F) 24,881 26,182 21,501 5% 20,426 3,483 16,943 -9,239 -7,938 NO
7 (G) 19,878 20,939 17,437 5% 16,565 12,960 3,605 -17,333 -16,273 NO
1.) Based on TD&H Design and Design Report
2.) Based on As-Built Drawings - Actual constructed volume was not provided with plans or design report
3.) Based on approximate top of pond before overtopping
Required
Pond
Volume1
(ft³)
As-Built
Pond
Volume2
(ft³)
Current
Pond
Volume
(Without
Vegetation)3
Percentage
of
Vegetation
(ft³)
Current
Pond
Volume With
Vegetation
(ft³)
Volume
Difference
from As-
Built
Pond (ft³)
Volume
Difference
from
Required
Capacity
(ft³)
Meets City of
Bozeman
Requirement
Pond
Number
Current Pond
Volume with
Vegetation
and
Groundwater
(ft³)
Volume of
Groundwater
in Pond (ft³)
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Hydrographs were created for each well and compared with pond elevations to assess capacity
limitations and excavation limits. For instance, if current pond elevations are below the
groundwater peak, it can be assumed that functionality of the ponds may be reduced due to the
high water, with the potential for flooding. Hydrographs corresponding to each well can be found
in Figure 2.
In general, peak elevations occurred on 4/9/2019 except for well F/G, which peaked on 9/21/2019.
Groundwater peak elevations varied for each pond, where water level peaked by as little as 0.5
ft below the pond surface and much as 2ft above pond surface. Profiles displaying the existing
pond ground with the peak groundwater elevation for each site are provided on the site plan in
Appendix B.
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Figure 2: Groundwater Elevations from 10/30/2018-1/25/2020
2.3. Soils Analysis
A soil investigation was conducted at each pond site in order to evaluate the suitability of the soil
for the proposed treatments and to aid in determination of sedimentation in the ponds. The soil
investigation was conducted by Confluence staff on October 20, 2020. Soil pits were excavated
in the center of each pond until contact was made with the underlying gravel, cobble, and sand
layer. Table 5 provides general descriptions of the soil pits excavated for each pond. Soil pit
depths provided in Table 5 indicate the depth to this layer except for Pond 3, which was only
excavated two inches below the surface of, a very hard, very gravelly layer which was highly
restrictive.
Table 5: General soil descriptions for stormwater ponds 1,2,3,5, 6, and 7
Pond
Number
Depth to Water
Table (inches)
Soil Pit Depth
(Inches) General Soil Description
1 (C) Inundated 18 6 inches of silt loam with high organic content (top 2 inches were
mixed with undecomposed material) over 12 inches of silty clay
2 (D) NA 18 2 inches of silt clay over 16 inches of fine sandy clay loam
3 (B) NA 14 2 inches of silty clay loam over 12 inches of clay, clay layer became
very hard at a depth of 6 inches, and very gravelly at 11 inches
5 (E) 13 14 4 inches of silt loam with ahigh organic content over 10 inches of silty
clay
6 (F) 4 6 0.5-1 inch of undecomposed organic material over 6 inches of silt
loam with high organic content
7 (G) Inundated 16 2 inches of undecomposed organic material over 4-14 inches of
mucky peat mixed with silt, over 1-2 inches of clay
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3. POND ISSUES AND RECOMMENDATIONS
The following provides site specific descriptions of the ponds along with a discussion of issues
related at the capacity and function of the ponds to treat stormwater. In addition, recommended
actions are described and discussed in this section.
Pond 1:
Pond Description / Plumbing
Pond 1 is a detention pond which treats stormwater runoff from the south side of the subdivision.
The runoff enters the pond through a concrete inlet pipe from a curb inlet on Cattail Street. At the
time of the site visit, approximately 7 inches of standing water was observed in the inlet basin and
at the outlet of the inlet culvert (Photo 1B). A small amount of water was observed flowing in the
outlet pipe (Photo 1C). This is caused by a combination of issues. The inlet pipe was installed
0.5 feet lower than designed, approximately 0.6 feet lower than the bottom of the pond.
Pond Capacity
The pond has seen only a slight reduction in capacity. The existing pond exceeds the design
capacity by almost 1,000 cubic feet, thus excavation for capacity is not necessary.
Vegetation and Groundwater
The pond is densely vegetated with cattails indicating prolonged high groundwater at this site.
Mature willows are present along the south edge of the pond (Photo 1A). Groundwater
monitoring at this pond indicates the peak groundwater elevation occurs above the bottom of the
pond which is consistent with the vegetation composition. Standing water was observed
throughout the pond site.
Problems
1. The inlet pipe from street was installed 0.5’ lower than designed resulting in sedimentation
in storm pipe and reducing the capacity of the pipe. The configuration and elevations of
the pipes prevent an obvious solution to prevent sedimentation in the pipes. The
groundwater is backwatering into the inlet basin in Cattail Street; thus, the inlet and
upstream pipes would need to be raised to prevent this from occurring.
2. High groundwater persists at the site, resulting in dense wetland vegetation, primarily
cattails. The storage capacity has not been reduced significantly at this site, but the
ongoing annual accumulation of dead cattails will eventually result in reduced capacity in
the pond.
Recommendations
1. Install Sediment Trap
2. Lower outlet pipe – Lowering the outlet pipe by 0.5 feet will allow the groundwater in the
pond to drain out of the pond, increase pond capacity and reduce sedimentation and
backwatering in the inlet pipe.
3. Vegetation Maintenance - Remove Willows at inlet pipe, and clip and remove cattails.
4. Install staff gauges to monitor sediment accumulation.
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Cattail Creek Stormwater Detention Ponds #1-3 & 5-7 60% Design
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Pond 2:
Pond Description / Plumbing
Pond 2 is a detention pond which treats stormwater runoff conveyed by a concrete inlet pipe which
enters the pond in the southwest corner. At the time of the site visit, the inlet pipe was clear with
some debris / leaves at the outlet (Photo 2B). A small channel has been excavated which conveys
runoff through the pond into a 10” pvc outlet pipe. Though it appears that this channel was part of
the original design, the channel acts to convey stormwater directly through the pond, minimizing
the ability of the detention pond to treat stormwater. The outlet pipe serves as detention control
limiting the flow of water out of the pond during peak events.
Pond Capacity
This capacity of the pond has been reduced from the as-built capacity by approximately 2,700
cubic feet as a result of sedimentation.
Vegetation and Groundwater
The vegetation in the primarily park grasses with some rushes. The rushes are a wetland grass
which indicates high groundwater. Groundwater monitoring at this pond indicates the peak
groundwater elevation was coincident with the bottom of the pond at the outlet, thus has not
impacted the capacity of the pond during this monitoring period.
There is very little woody vegetation in the pond and the existing vegetation does not appear to
reduce the capacity of the pond (Photo 2A).
Problems
1. It appears that the pond was either not built according to the plans or sediment has
accumulated in the upper end of the pond reducing the capacity of the pond. There is no
obvious sign of accumulated sediment. In addition, the site is relatively dry with minimal
vegetation which has resulted in minimal detritus; thus, it is our opinion that the pond was
not built in accordance with the as-built documentation.
Solutions
1. Excavation of the bottom of the pond to the design elevations will restore the pond to the
as-built capacity. Where excavation is proposed, 6”-9” of vegetated topsoil will be stripped
and stockpiled, then the subsoil will be excavated to the subgrade elevation. Excavated
material will be hauled off site and topsoil will be placed on top of subgrade to ensure
finished grade matches the design elevations.
2. Install staff gauges to monitor sediment accumulation.
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Cattail Creek Stormwater Detention Ponds #1-3 & 5-7 60% Design
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Pond 3:
Pond Description / Plumbing
Pond 3 is a detention pond which treats stormwater runoff from the east side of the subdivision.
Runoff is conveyed by a concrete inlet pipe from a manhole in Warbler Way which enters the west
edge side of the pond. At the time of the site visit, the inlet pipe was obstructed with 9 inches of
sediment (Photo 3B). The inlet pipe invert was designed and installed 0.5 feet lower than the
bottom of the pond. This configuration is likely the primary cause of sedimentation in the inlet pipe
and will require long-term maintenance to keep clear.
A 12” outlet pipe serves as detention control, limiting the flow of water out of the pond during peak
events. The design shows the outlet being conveyed to Cattail Creek immediately west of the
pond. However, there is a North/South oriented ridge west of the pond preventing the stormwater
to enter Cattail Creek as designed. The stormwater is directed through a swale to the north
approximately 130 feet before entering Cattail Creek. It is unclear why this was constructed this
way, though the longer flow path provides increased duration of contact with vegetation and is
likely a better solution for treatment of stormwater, thus no modification to the outlet swale is
recommended.
Pond Capacity
The survey indicates a substantial reduction in pond volume from the as-built records. However,
there is no obvious sign of accumulated sediment. The bottom of pond elevation on the south
side of the pond is up to 1 foot higher than the as-built records indicate. It is possible that this is
a result of sedimentation. However, it is likely the pond was not constructed in accordance with
the as-built documentation. In addition, the existing pond exceeds the design capacity, thus not
requiring additional excavation to maintain compliance with the COB.
Vegetation and Groundwater
The vegetation appears to be well maintained and consists primarily of upland grass consistent
with the surrounding park / open space. Groundwater monitoring at this pond indicates the peak
groundwater elevation occurs near the top of the pond. Though there is no wetland vegetation
present which would indicate prolonged wetting of the pond, the sedimentation in the inlet pipe
may be a partially caused by prolonged standing water. It is also possible that the groundwater
well used for estimating groundwater in this pond does not reflect the actual groundwater at the
pond. There is no woody vegetation in the pond and the existing vegetation does not appear to
reduce the capacity of the pond (Photo 3A).
Problems
1. The pond inlet pipe was installed 0.5’ lower than the bottom of pond resulting in
sedimentation in the outlet of the inlet pipe and reducing the capacity of the pipe.
2. Pond capacity is reduced from the as-built documentation.
Recommendations
1. Clearing of the inlet pipe and excavation of sediment around the outlet of the inlet pipe.
Install sediment trap.
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Cattail Creek Stormwater Detention Ponds #1-3 & 5-7 60% Design
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2. Additional excavation of the pond may be considered to increase capacity as the pond’s
current capacity exceeds design capacity by 175 cubic feet.
3. Install staff gauges to monitor sediment accumulation.
Pond 5:
Pond Description / Plumbing
Pond 5 is a detention pond which treats stormwater runoff from the west side of the subdivision.
Runoff is conveyed by a concrete inlet pipe from a manhole at the intersection of Catron Street
and Blackbird Drive into the southwest corner of the pond. At the time of the site visit, the inlet
pipe was obstructed with 9 inches of sediment (Photo 5B). The manhole lid for the inlet pipe was
removed and approximately 8 inches of standing water was observed in the pipe.
A 6” outlet pipe serves as detention control, limiting the flow of water out of the pond during peak
events. The stormwater is directed through the outlet pipe into Cattail Creek to the northeast of
the pond.
Pond Capacity
This pond appears to have accumulated some sediment, especially at the south end of the pond,
reducing the available capacity of the pond. However, the inlet culvert’s outlet elevation is
approximately 0.5 feet lower than the bottom of the pond indicated on the as-builts. The bottom
of pond elevation on the south side of the site is slightly higher than the as-built elevation, but it
appears that the primary cause of backwatering is because the pipe is set too low. Also, the
pond’s existing capacity exceeds the design and as-built capacity, thus additional excavation is
not needed to meet the COB requirements.
Vegetation and Groundwater
The pond is densely vegetated with wetland grasses and young willows indicating high
groundwater at this site. Mature willows and trees are present at the southwest corner near the
inlet. Groundwater monitoring at this pond indicates the peak groundwater elevation occurs near
the bottom of the pond which is consistent with the vegetation composition.
Problems
1. The combination of the inlet pipe being set too low and sedimentation in the south end of
the pond have resulting in backwatering/sedimentation of inlet pipe.
2. The vegetation in the pond, primarily young willow shoots, has proliferated in the last
couple of years. The vegetation is not currently limiting the capacity of the pond, but if
allowed to grow unfettered, the willows may reduce the capacity of the pond in the future.
Recommendations
1. Excavate a swale from inlet pipe to an area in the north end of the pond. The swale will
provide positive drainage from the inlet pipe into the pond reducing the backwater and
sedimentation in the pipe and allowing the storm pipes and pond to treat runoff more
DESIGN REPORT
Cattail Creek Stormwater Detention Ponds #1-3 & 5-7 60% Design
17
effectively. The swale will be excavated with a bottom width of approximately 2’ and
sloped at a 3:1 on the side slopes.
2. Cut and remove willow shoots from the pond. Clear willows at the outlet of the inlet culvert
to reduce the potential for woody debris from obstructing flow path.
3. Install staff gauges to monitor sediment accumulation.
Pond 6:
Pond Description / Plumbing
Pond 6 is a detention pond which treats stormwater runoff from the west side of the subdivision.
Runoff is conveyed to the pond by two concrete inlet pipes. One pipe enters the west side of the
pond from a cub inlet on Blackbird Drive and the other enters the pond from the north form a
storm sewer manhole on Catamount Street. At the time of the site visit, both culverts were
obstructed with sediment and exhibit standing water. The Blackbird drive culvert was almost
completely submerged at the outlet (Photo 6C). Approximately 10 inches of sediment was
obstructing the Blackbird inlet pipe at the outlet in the pond. Approximately 16 inches of standing
water was observed above the pipe invert in the curb inlet (Photo 6F). The Catamount Street
inlet pipe was obstructed with approximately 7 inches of sediment throughout the length of the
pipe (Photos 6B and 6E).
A 10-inch pvc outlet pipe serves as detention control, limiting the flow of water out of the pond
during peak events. The stormwater is directed through the outlet pipe into Cattail Creek to the
east of the pond. At the time of our site visit, approximately 4 inches of standing water was
observed at the outlet pipe (Photo 6D and 8C). Large culverts under Catamount Street convey
Cattail Creek to the north.
Pond Capacity
The pond has significantly less capacity than what was designed. The bottom of the pond
elevation is roughly 1 foot higher than the design bottom of pond elevation, resulting in reduced
capacity. It is unclear if this is a result of sedimentation or if the pond was not built to the design
elevation because of high groundwater.
Vegetation and Groundwater
The pond is densely vegetated with cattails indicating prolonged high groundwater at this site.
Mature willows and trees are present along the west edge of the pond (Photo 6A). Groundwater
monitoring at this pond indicates the peak groundwater elevation occurs above the bottom of the
pond which is consistent with the vegetation composition. Standing water was observed
throughout the pond site.
Problems
1. Reduced pond capacity as a result of sedimentation or high groundwater
backwatering/sedimentation of inlet pipes.
DESIGN REPORT
Cattail Creek Stormwater Detention Ponds #1-3 & 5-7 60% Design
18
Recommendations
1. See Section “Pond 6 and 7 Alternatives” below.
Pond 7:
Pond Description / Plumbing
Pond 7 is a detention pond which treats stormwater runoff from the east side of the subdivision.
Runoff is conveyed to the pond by a concrete pipe from a manhole in Catamount Street. The
pipe enters from the north side of the pond from a manhole in Catamount Street. At the time of
the site visit, the culvert was obstructed with approximately 4 inches of sediment (Photo 7B).
A 10-inch pvc outlet pipe serves as detention control, limiting the flow of water out of the pond
during peak events. The stormwater is directed through the outlet pipe into Cattail Creek to the
west of the pond. At the time of our site visit, the outlet pipe was flowing with approximately 1
inch of standing water in the pipe (Photo 7C).
Pond Capacity
Like pond 6, pond 7 has significantly less capacity than what was designed. The bottom of the
pond has accumulated sediment resulting in reduced capacity.
Vegetation and Groundwater
The pond is densely vegetated with cattails indicating prolonged high groundwater at this site.
Mature willows and trees are present along the west edge of the pond (Photo 7A). Groundwater
monitoring at this pond indicates the peak groundwater elevation occurs above the bottom of the
pond which is consistent with the vegetation composition. Standing water was observed
throughout the pond site.
Problems
1. Reduced pond capacity as a result of sedimentation or high groundwater
backwatering/sedimentation of inlet pipes.
Recommendations
1. See Section “Pond 6 and 7 Alternatives” below.
Pond 6 and 7 Alternatives:
Ponds 6 and 7 are located adjacent to each other and are affected similarly with high groundwater.
As shown in Table 4, the high groundwater reduces the capacity of the pond significantly,
approximately 17,000 cf for Pond 6 and 3,600 cf for Pond 7, greatly reducing the function of these
ponds. Lowering the elevation of these ponds and removing cattails will potentially help reduce
the sedimentation by allowing the water in the pond to drain with less obstruction. However, the,
additional storage capacity will not be gained by lowering the pond bottom as the water surface
will remain the same. Additional capacity may be gained by excavating on the south side of the
ponds and expanding the pond in this area. However, either solution will not prevent the inlet
pipes from filling with sediment.
DESIGN REPORT
Cattail Creek Stormwater Detention Ponds #1-3 & 5-7 60% Design
19
Two alternatives are proposed for consideration to address the reduced capacity in ponds 6 and
7. The following provides a description of the proposed alternatives.
Alternative 1 – Groundwater sump pump / interceptor drains
In order for ponds 6 and 7 to function properly, the groundwater must be lowered in conjunction
with excavating the bottom of the ponds. In order to dewater the sites, a groundwater sump pump
is proposed. A description of the proposed system is included below.
1. A groundwater sump pump may be installed in a concrete sump / vault located on the
north end of the site between ponds 6 and 7. Interceptor drains consisting of buried
perforated pipe surrounded by washed rock will be installed under each pond and will
drain into the pump vault. An electric submersible pump will be activated when the water
reaches the elevation of the bottom of the pond. The pump will turn off when the
groundwater elevation is approximately 6” below the bottom of the pond.
2. Excavation of the ponds to the design elevations will restore the ponds to the as-built
capacity. Where excavation is proposed, 6”-9” of vegetated topsoil will be stripped and
stockpiled, then the subsoil will be excavated to the subgrade elevation. Excavated
material will be hauled off site and topsoil will be placed on top of subgrade to ensure
finished grade matches the design elevations. Approximately 4,300 and 3,200 cubic feet
of soil from ponds 6 and 7 respectively will be removed and hauled offsite to restore the
pond to as-built condition.
3. Install staff gauges to monitor sediment accumulation.
Alternative 2 – Construct berm at outlet of ponds to increase pond capacity
If the groundwater elevation is not reduced at these pond sites, additional excavation from the
bottoms of the ponds will not increase capacity. Additional capacity could be gained by increasing
the berm height at the outlets of the ponds. Each pond has the potential for substantially more
capacity if the pond berms near the outlets are raised. Increasing the berm height would provide
the capacity required but would not prevent the inlet pipes from backwatering and accumulating
sediment. In addition, the COB requires ponds to have a maximum depth of 1.5 feet. This option
would exceed the maximum depth; thus, a variance would need to be obtained by the COB if this
option were selected.
1. Construct berm at pond outlets – The berms along the northeast and northwest sides of
ponds 6 and 7 respectively would be raised approximately 1 foot to provide additional
pond capacity. The berms would extend south until they tie into the existing grade where
the ground native ground is higher, and to the north where they intercept the road berm.
Areas where fill is proposed, topsoil would be stripped and stockpiled. Structural fill would
be imported to increase the berm elevation, and the topsoil would be placed back on top
of the berm.
2. Clearing of the inlet pipes and excavation of sediment around the outlet of the inlet pipes.
Install sediment traps at outlet of inlet pipes.
DESIGN REPORT
Cattail Creek Stormwater Detention Ponds #1-3 & 5-7 60% Design
20
3. Install staff gauges to monitor sediment accumulation.
Common Treatments
The following includes descriptions of proposed treatments included in multiple ponds.
1. Sediment Trap
We suggest the installation of a sediment trap at the outfall of the inlet pipe. Though we don’t feel
a sediment trap will be required to be in compliance with the COB’s maintenance program, it will
allow the detention pond / storm drains to function better and will likely reduce maintenance
impacts and costs in the future. A sediment trap will provide the following functions.
Reduces backwatering and sediment accumulation into the inlet pipe and storm drain
system
Provides a sump for temporary accumulation of debris / sediment, reducing accumulation
in the rest of the pond. This will result in longer lifespan of pond before requiring
excavation of the entire pond.
Located such that an excavator can easily access and remove sediment periodically with
minimal impact to vegetation / open space.
The proposed sediment trap will be excavated to a depth of approximately 2 feet deep and extend
10 feet into the pond. It is anticipated that this feature will be inundated at all times at most pond
sites, as the groundwater is very close to the surface.
2. Install Staff Gages
We recommend installing staff gages within the pond to facilitate monitoring of the capacity of the
pond. Staff gages with 1/100th increment marks will be installed in two locations in the pond to
allow the HOA and the City to monitor sediment deposition in the pond and determine when
excavation is needed to remove the deposition and restore the pond capacity. The gages will
allow the HOA to avoid additional survey in the future.
3. Vegetation Maintenance
We recommend maintaining the ponds in accordance with the City of Bozeman’s Stormwater
Basin Maintenance Guide. We do not feel the removal of trees and shrubs is necessary or
advisable to maintain the capacity of the pond. In addition, the trees and shrubs provide wildlife
habitat and are an aesthetic benefit to the open space in the subdivision.
However, it is important to mow or cut the grasses and plants within the pond annually. Cutting
should occur in the fall once the vegetation is dormant. It is important that the clippings are
removed from the pond immediately to prevent the pipes from being blocked by debris and to
prolong the life and function of the pond.
4. COST ESTIMATES
Cost estimates for the proposed actions are provided in the tables below. The costs have been
separated into two phases with the first phase of work occurring in ponds 1-5 and the second
phase for ponds 6 and 7.
DESIGN REPORT
Cattail Creek Stormwater Detention Ponds #1-3 & 5-7 60% Design
21
Table 6: Construction cost estimate for Ponds 1,2,3, and 5
Task Qty Unit Unit Cost Total
Mobilization 1 LS $1,100.00 $1,100
Pond 1
Install Sediment Trap 1 LS $1,650.00 $1,650
Remove Willows at inlet 1 LS $110.00 $110
Reset outlet culvert 1 LS $330.00 $330
Remove cattails 1 LS $110.00 $110
Install staff gauges 2 EA $330.00 $660
Subtotal:$2,860
Pond 2
Strip, stockpile and place topsoil 242 CY $5.50 $1,331
Excavate and haul off soil 80 CY $15.40 $1,232
Install staff gauges 2 EA $330.00 $660
Subtotal:$3,223
Pond 3
Install Sediment Trap 1 LS $1,650.00 $1,650
Strip, stockpile and place topsoil 56 CY $5.50 $308
Excavate and haul off soil 74 CY $15.40 $1,140
Install staff gauges 2 EA $330.00 $660
Subtotal:$3,758
Pond 5
Construct Swale 110 LF $9.00 $990
Remove willow shoots 1 LS $660.00 $660
Clear willows at inlet pipe 1 LS $330.00 $330
Install staff gauges 2 EA $330.00 $660
Subtotal:$2,640
Construction Administration / Oversight 30 HR $120.00 $3,600
Subtotal:$17,181
20% Contingency $3,440
Total (Ponds 1-3,5)$20,621
DESIGN REPORT
Cattail Creek Stormwater Detention Ponds #1-3 & 5-7 60% Design
22
Table 7: Construction cost estimate for Ponds 6 and 7 - Alternative 1
Task Qty Unit Unit Cost Total
Mobilization 1 LS $1,100.00 $1,100
Pond 6 - Alternative 1
Strip, stockpile and place topsoil 112 CY $11.00 $1,232
Excavate and haul off soil 160 CY $22.00 $3,520
Install staff gauges 2 EA $330.00 $660
Subtotal:$5,412
Pond 7 - Alternative 1
Strip, stockpile and place topsoil 84 CY $11.00 $924
Excavate and haul off soil 119 CY $22.00 $2,618
Install staff gauges 2 EA $330.00 $660
Subtotal:$4,202
Ponds 6 & 7 Dewatering - Alternative 1 Sump Pump
Design 1 LS $5,000.00 $5,000
Permitting 1 LS $10,000.00 $10,000
Install Power Service 1 LS $2,750.00 $2,750
Sump/Pump Vault 1 LS $8,800.00 $8,800
Interceptor Drain 200 LF $23.10 $4,620
Subtotal:$26,170
Construction Administration / Oversight 30 HR $120.00 $3,600
Subotal:$40,484
20% Contingency $8,100
Total (Ponds 6 & 7 Alternative 1)$48,584
DESIGN REPORT
Cattail Creek Stormwater Detention Ponds #1-3 & 5-7 60% Design
23
Table 8: Construction cost estimate for Ponds 6 and 7 - Alternative 2
5. PERMITTING
Ponds 1,2,3, and 5
It is not anticipated that permits will be required to complete the work proposed. The Army Corps
of Engineers regulates fill within jurisdictional wetlands. It is anticipated that this project will not
require a 404 permit with the Army Crops as long as the purpose of the project is to restore the
stormwater pond to design capacities. This is covered under the Nationwide Permits #43 covering
Stormwater Management Facilities.
Ponds 6 and 7
The alternatives proposed for ponds 6 and 7 may require permitting by the U.S. Army Corps as
the project will be a modification or expansion of the existing design. In addition, a 310 permit will
be required from the Gallatin Conservation District for the installation of a pipe underneath Cattail
Creek. In addition, the COB site plan review process will likely be required for work proposed at
ponds 6 and 7.
6. CONCLUSIONS
The analysis conducted for the ponds indicates that ponds 2, 6, and 7 do not currently meet
storage capacity required by the City of Bozeman and will require excavation to restore the ponds
to compliance. Confluence has identified additional work in ponds 1 and 3 that may be performed
in order to allow these ponds to work more effectively and reduce maintenance needs. Ponds 6
and 7 will require a decision by the HOA and the COB to determine which alternative is desired.
Ponds 6 & 7 Alternative 2
Task Qty Unit Unit Cost Total
Mobilization 1 LS $1,650.00 $1,650
Pond 6 - Alternative 2
Install Sediment Trap 2 EA $1,650.00 $3,300
Construct berm at outlet 1 LS $1,650.00 $1,650
Install staff gauges 2 EA $330.00 $660
Subtotal:$5,610
Pond 7 - Alternative 2
Install Sediment Trap 1 EA $1,650.00 $1,650
Construct berm at outlet 1 EA $1,210.00 $1,210
Install staff gauges 2 EA $330.00 $660
Subtotal:$3,520
Construction Administration / Oversight 20 HR $120.00 $2,400
Subtotal:$13,180
20% Contingency $2,640
Total (Ponds 6 & 7 Alternative 2)$15,820
DESIGN REPORT
Cattail Creek Stormwater Detention Ponds #1-3 & 5-7 60% Design
24
Additional design and permitting will likely be necessary for ponds 6 and 7. We recommend
submitting this report to the COB to obtain their input on the conceptual designs and alternatives.
DESIGN REPORT
Cattail Creek Stormwater Detention Ponds #1-3 & 5-7 60% Design
APPENDIX A
Photolog
Cattail Creek Photo Log – 04/14/2020
1
BASIN #1 / POND C
1A: Full view of Basin 1, facing South West
1B: Concrete inlet for Basin 1, facing North East 1C: Concrete outlet for Basin 1, facing South East
Cattail Creek Photo Log – 04/14/2020
2
BASIN #2 / POND D
2A: Full view of Basin 2, facing North East
2B: Concrete inlet for Basin 2, facing South West 2C: PVC outlet for Basin 2, Facing North East
Cattail Creek Photo Log – 04/14/2020
3
BASIN #3 / POND B
3A: Full view of Basin 3, facing South 3B: Concrete inlet for Basin 3, facing East
3C: Concrete outlet for Basin 3, Facing West 3D: Basin 3 concrete outlet, discharging into swale, facing East
Cattail Creek Photo Log – 04/14/2020
4
BASIN #5 / POND E
5A: Full view of Basin 5, facing South East
5B: Concrete inlet for Basin 5, facing South East 5C: PVC outlet for Basin 5, facing North East
Cattail Creek Photo Log – 04/14/2020
5
BASIN #6 / POND F
6A: Full view of Basin 6, facing northwest
6B: Outlet of Catamount St. inlet pipe for Basin 6, facing north 6C: Outlet of Blackbird Dr. inlet pipe for Basin 6, facing northwest
Cattail Creek Photo Log – 04/14/2020
6
BASIN #6 / POND F
6D: PVC outlet pipe for Basin 6, facing North East
6E: Storm Drain for Catamount St. inlet pipe, facing south 6F: Storm drain for Blackbird Dr. inlet pipe, facing South East
Cattail Creek Photo Log – 04/14/2020
7
POND G / BASIN #7
7A: Full view of Basin 7, facing North West
7B: Concrete inlet for Basin 7, facing North West 7C: PVC outlet for Basin 7, facing North East
Cattail Creek Photo Log – 04/14/2020
8
CATTAIL CREEK- CATAMOUNT ST CROSSING
8A: Full view of Cattail Crk crossing at Catamount St, facing North East
8B: Concrete outlets for Cattail Crk, facing North 8C: Basin 6 PVC outlet discharging into Cattail Crk, facing North East
DESIGN REPORT
Cattail Creek Stormwater Detention Ponds #1-3 & 5-7 60% Design
APPENDIX B
Conceptual Design Site Plans and Details
4" OF SEDIMENTACCUMULATION IN INLETINLET CULVERT18" RCP25' LENGTHOUTLET CULVERT12" RCP22' LENGTH0+001+001+604667466646644
6
6
3 46624664466346664664CATTAILSCATTAIL ST244134660466546704660466546700+000+501+001+501+60PEAK W.S.E. 4662.8012" RCP OUTLET CULVERTINVERT ELEV: 4662.41OUTLET CULVERTINVERT ELEV: 4662.3818" RCP INLET CULVERTINVERT ELEV: 4661.87EXISTINGPOND BOTTOMINVERT CULVERTINVERT ELEV: 4662.05WSE DAY OFSURVEYCURB INLETINSTALLSEDIMENTTRAPLOWER OUTLETPIPE BY 0.5'BASIN 1: CONCEPTUALDESIGN SITEAND DETAILS1SHEET:CATTAIL CREEK
STORMWATER POND ASSESMENT
BOZEMAN, MT
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------SCALE IN FEET2001010POND VOLUME TABLEREQUIRED PONDVOLUME (FT3)AS-BUILT POND VOLUME(FT3)CURRENT POND VOLUME(VEGETATION ANDGROUNDWATER)6,8507,8207,772LEGENDEXISTING CONTOUR MAJOR (5')EXISTING LOT BOUNDARYEXISTING WOODY VEGETATIONPOND BOTTOM OF BANKPOND TOP OF BANKEXISTING CONTOUR MINOR (1')EXISTING TREE/SHRUBSTORMWATER POND 1 PROFILE11VERTICAL SCALE: 1" = 4'HORIZONTAL SCALE: 1" = 40'EXISTING CATTAIL AREAPROPOSED ACTIONS1.INSTALL SEDIMENT TRAP - EXCAVATE SEDIMENT TRAP AT OUTLET OF INLET CULVERTFROM CATTAIL STREET.2.LOWER OUTLET PIPE BY 0.5' TO ENSURE DRAINAGE3.VEGETATION MAINTENANCE - REMOVE WILLOWS AT INLET PIPE AND CLIP ANDREMOVE CATTAILS4.INSTALL TWO STAFF GAGES IN THE POND TO ALLOW CATTAIL CREEK HOA TOVISUALLY MONITOR SEDIMENT DEPOSITION IN POND.PROPOSED STAFF GAGE
INLET CULVERT18" RCP250' LENGTHOUTLET CULVERT12" RCP22' LENGTH2+48 1+002+00 46574656465846574656
4
6
5
9
4658
TRAILCATTAIL CREEKDRAINAGE SWALETO CATTAIL CREEK231346
5
6 465646564650465546604650465546600+000+501+001+502+002+4812" OULET RPC CULVERTINVERT ELEV: 4655.70OUTLET CULVERTINVERT ELEV: 4655.6718" INLET RPC CULVERTINVERT ELEV: 4655.34EXISTING POND BOTTOMPEAK W.S.E. 4657.19PIPE EXTENDS TO MANHOLEON WARBLER WAYCATTAIL CREEKTHALWEGINSTALLSEDIMENTTRAPBASIN 3:CONCEPTUALDESIGN SITEAND DETAILS3SHEET:CATTAIL CREEK
STORMWATER POND ASSESMENT
BOZEMAN, MT
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------SCALE IN FEET2001010STORMWATER POND 3 PROFILE31VERTICAL SCALE: 1" = 3'HORIZONTAL SCALE: 1" = 30'POND VOLUME TABLEREQUIRED PONDVOLUME (FT3)AS-BUILT POND VOLUME(FT3)CURRENT POND VOLUME(VEGETATION ANDGROUNDWATER)5,9908,2196,165PROPOSED ACTIONS1.CLEAR THE INLET PIPE AND EXCAVATION OF SEDIMENT AROUND THE OUTLET OF THEINLET PIPE. INSTALL SEDIMENT TRAP.2.ADDITIONAL EXCAVATION OF 520 CF OF THE POND MAY BE CONSIDERED TO INCREASECAPACITY AS THE POND'S CURRENT CAPACITY EXCEEDS DESIGN CAPACITY BY 175CUBIC FEET.3.INSTALL TWO STAFF GAGES IN THE POND TO ALLOW CATTAIL CREEK HOA TOVISUALLY MONITOR SEDIMENT DEPOSITION IN POND.LEGENDEXISTING CONTOUR MAJOR (5')EXISTING LOT BOUNDARYEXISTING WOODY VEGETATIONPOND BOTTOM OF BANKPOND TOP OF BANKEXISTING CONTOUR MINOR (1')EXISTING TREE/SHRUBPROPOSED CONTOUR MAJOR (5')PROPOSED CONTOUR MINOR (1')PROPOSED GRADING EXTENT
CONCRETE RIP RAP PADINLET CULVERT24" RCP55' LENGTH0+000+501+001+502+002+502+584661 SWALETRAIL4660465946594661466246604662
4661STORM SEWERMANHOLE2214659OUTLET CULVERT10" PVC68' LENGTH46584655466046654655466046650+000+501+001+502+002+5010" PVC OUTLET CULVERTINVERT ELEV: 4657.29INVERT ELEV: 4656.75EXISTINGPOND BOTTOM24" RPC INLET CULVERTINVERT ELEV: 5658.52INVERT ELEV:5658.52PEAK W.S.E. 4657.20STORM SEWER MANHOLEPROPOSEDPOND BOTTOMBASIN 2:CONCEPTUALDESIGN SITEAND DETAILS2SHEET:CATTAIL CREEK
STORMWATER POND ASSESMENT
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------SCALE IN FEET2001010LEGENDEXISTING CONTOUR MAJOR (5')EXISTING LOT BOUNDARYEXISTING WOODY VEGETATIONPOND BOTTOM OF BANKPOND TOP OF BANKEXISTING CONTOUR MINOR (1')EXISTING TREE/SHRUBSTORMWATER POND 2 PROFILE21VERTICAL SCALE: 1" = 5'HORIZONTAL SCALE: 1" = 50'POND VOLUME TABLEREQUIRED PONDVOLUME (FT3)AS-BUILT POND VOLUME(FT3)CURRENT POND VOLUME(VEGETATION ANDGROUNDWATER)10,68812,0679,328PROPOSED ACTIONS1.EXCAVATE APPROXIMATELY 2700 CF FROM THE BOTTOM OF THE POND TO THEDESIGN ELEVATIONS TO RESTORE THE POND TO THE AS-BUILT CAPACITY. WHEREEXCAVATION IS PROPOSED 6"-9" OF VEGETATED TOPSOIL WILL BE STRIPPED ANDSTOCKPILED, THEN THE SUBSOIL WILL BE EXCAVATED TO THE SUBGRADE ELEVATION.EXCAVATED MATERIAL WILL BE HAULED OFF SITE AND TOPSOIL WILL BE PLACED ONTOP OF SUBGRADE TO ENSURE FINISHED GRADE MATCHES THE DESIGN ELEVATIONS.2.INSTALL TWO STAFF GAGES IN THE POND TO ALLOW CATTAIL CREEK HOA TOVISUALLY MONITOR SEDIMENT DEPOSITION IN POND.PROPOSED CONTOUR MAJOR (5')PROPOSED CONTOUR MINOR (1')PROPOSED GRADING EXTENT
OUTLET CULVERT6" PVC53' LENGTHINLET CULVERT24" RCP74' LENGTH465046494648 4652465346544653CATRON STCATTAIL CREEKSTORM SEWERMANHOLE23130+00
1+002+002+594645465046554645465046550+000+501+001+502+002+502+596" RPC OUTLET CULVERTINVERT ELEV: 4647.51EXISTING PONDGROUNDINVERT ELEV:4647.11324" RPC OUTLET CULVERTINVERT ELEV: 4648.38PEAK W.S.E. 4648.20EXTENDS TOSTORM SEWERMANHOLEPROPOSED BOTTOMOF SWALEBASIN 5:CONCEPTUALDESIGN SITEAND DETAILS4SHEET:CATTAIL CREEK
STORMWATER POND ASSESMENT
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------SCALE IN FEET3001515LEGENDEXISTING CONTOUR MAJOR (5')EXISTING LOT BOUNDARYEXISTING WOODY VEGETATIONPOND BOTTOM OF BANKPOND TOP OF BANKEXISTING CONTOUR MINOR (1')EXISTING TREE/SHRUBSTORMWATER POND 5 PROFILE41VERTICAL SCALE: 1" = 5'HORIZONTAL SCALE: 1" = 50'POND VOLUME TABLEREQUIRED PONDVOLUME (FT3)AS-BUILT POND VOLUME(FT3)CURRENT POND VOLUME(VEGETATION ANDGROUNDWATER)14,51516,61117,025PROPOSED ACTIONS1.EXCAVATE A SWALE FROM INLET PIPE TO AN AREA IN THE NORTH END OF THE POND.THE SWALE WILL PROVIDE POSITIVE DRAINAGE FROM THE INLET PIPE INTO THE PONDREDUCING THE BACKWATER AND SEDIMENTATION IN THE PIPE AND ALLOWING THESTORM PIPES AND POND TO TREAT RUNOFF MORE EFFECTIVELY. THE SWALE WILL BEEXCAVATED WITH A BOTTOM WIDTH OF APPROXIMATELY 2', WITH 3:1 SIDE SLOPES.2.CUT AND REMOVE WILLOW SHOOTS FROM THE POND. CLEAR WILLOWS AR THEOUTLET OF THE INLET CULVERT TO REDUCE THE POTENTIAL FOR WOODY DEBRISFROM OBSTRUCTING FLOW PATH3.INSTALL TWO STAFF GAGES IN THE POND TO ALLOW CATTAIL CREEK HOA TOVISUALLY MONITOR SEDIMENT DEPOSITION IN POND.PROPOSED SWALE BOTTOM OF BANK
INLET CULVERT15" RCPINLET CULVERT22 12" x 36 14" RCPA65' LENGTH31 516" x 51 18" RCPA136' LENGTHINVERT ELEV: 4638.06 42" RCP, 136' LENGTHINVERT ELV: 4636.820+000+001+001+580+001+002+00 2+31 46394641464246394641
46
4
1
464146414642464346424643
464346424641463946384639
46
3
9
46
4
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46394640
OUTLET CULVERT10" PVC41' LENGTHOUTLET CULVERT10" PVC39 LENGTHBLACKBIRD DRCURBINLETCATTAIL C
R
E
E
K EXTENDS TOSTORM SEWERMANHOLECATAMOUNT ST2214638 46393
4635464046454635464046450+000+501+001+501+58PEAK W.S.E. 4638.9022 12" x 36 14" RCPA INLET CULVERTINVERT ELEV: 4637.7110" PVC OUTLET CULVERTINVERT ELEV: 4638.07BERMEXISTING POND BOTTOMINVERTELEV: 4637.97EXTENDS TO STORM SEWERMANHOLE ON CATAMOUNT STWSE DAY OF SURVEY4635464046454635464046450+000+501+001+502+002+3110" PVC OUTLET CULVERTINVERT ELEV: 4638.07INVERTELEV: 4637.9715" RCP INLET CULVERTINVERT ELEV: 4637.89PEAK W.S.E. 4638.90EXTENDS TO STORM SEWERMANHOLE ON BLACKBIRD DRWSE DAY OF SURVEYEXISTING PONDBOTTOMPROPOSED PONDBOTTOMBASIN 6:CONCEPTUALDESIGN SITEAND DETAILSALTERNATIVE15SHEET:CATTAIL CREEK
STORMWATER POND ASSESMENT
BOZEMAN, MT
DRAWN BY:
DESIGNED BY:
REV.DATE DESCRIPTION BY APP'D
CCI JOB NO.:
FILE NAME:X:\Project\CattailCk\CAD\CATTAILCRK-PROPOSED.dwgCHECKED BY:
1
2
DATE:SW
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CAT.001
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------SCALE IN FEET3001515STORMWATER POND 6 PROFILE BLACKBIRD DR. INLET52VERTICAL SCALE: 1" = 4'HORIZONTAL SCALE: 1" = 40'STORMWATER POND 6 PROFILE CATAMOUNT ST. INLET 51VERTICAL SCALE: 1" = 3'HORIZONTAL SCALE: 1" = 30'POND VOLUME TABLEREQUIREDPONDVOLUME (FT3)AS-BUILT PONDVOLUME (FT3)CURRENT PONDVOLUME(VEGETATION ANDGROUNDWATER)24,88126,18220,400LEGENDEXISTING CONTOUR MAJOR (5')EXISTING LOT BOUNDARYEXISTING WOODY VEGETATIONPOND BOTTOM OF BANKPOND TOP OF BANKEXISTING CONTOUR MINOR (1')EXISTING TREE/SHRUBPROPOSED CONTOUR MAJOR (5')PROPOSED CONTOUR MINOR (1')PROPOSED GRADING EXTENTPROPOSED ACTIONS1.EXCAVATION OF THE POND TO THE DESIGNELEVATIONS WILL RESTORE THE POND TOTHE AS-BUILT CAPACITY. WHEREEXCAVATION IS PROPOSED, 6"-9" OFVEGETATED TOPSOIL WILL BE STRIPPEDAND STOCKPILED, THEN THE SUBSOIL WILLBE EXCAVATED TO THE SUBGRADEELEVATION. EXCAVATED MATERIAL WILL BEHAULED OFF SITE AND TOPSOIL WILL BEPLACED ON TOP OF SUBGRADE TO ENSUREFINISHED GRADE MATCHES THE DESIGNELEVATIONS. APPROXIMATELY 4,300 CUBICFEET OF SOIL WILL BE REMOVED ANDHAULED OFFSITE TO RESTORE THE PONDTO AS-BUILT CONDITION.2.INSTALL TWO STAFF GAGES IN THE PONDTO ALLOW CATTAIL CREEK HOA TOVISUALLY MONITOR SEDIMENT DEPOSITIONIN POND.3.CLEAR THE INLET PIPE AND EXCAVATIONOF SEDIMENT AROUND THE OUTLET OF THEINLET PIPE.4.
0+001+00 1+790+000+0046414643464346424641463946384639463946404640 4641463946444644 OUTLET CULVERT10" PVC41' LENGTHINLET CULVERT26 58" x 43 34" RCPA98' LENGTHOUTLET CULVERT10" PVC39 LENGTHCATTAIL CREEK 31 516" x 51 18" RCPA136' LENGTHINVERT ELV: 4638.35221463846354640463546400+000+501+001+501+7910" PVC OUTLET CULVERTINVERT ELEV: 4637.69INVERTELEV: 4637.4826 58" X 43 34" RCPA INLET CULVERTINVERT ELEV: 4637.59INVERTELEV: 4637.62BERMPROPOSED PONDBOTTOMPEAK W.S.E. 4638.89WSE DAYOF SURVEYCATTAILCREEKEXTENDS TO STORM SEWERMANHOLE ON CATAMOUNT STEXISTING PONDBOTTOMBASIN 7:CONCEPTUALDESIGN SITEAND DETAILSALTERNATIVE16SHEET:CATTAIL CREEK
STORMWATER POND ASSESMENT
BOZEMAN, MT
DRAWN BY:
DESIGNED BY:
REV.DATE DESCRIPTION BY APP'D
CCI JOB NO.:
FILE NAME:X:\Project\CattailCk\CAD\CATTAILCRK-PROPOSED.dwgCHECKED BY:
1
2
DATE:SW
TT
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10/19/20
CAT.001
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------SCALE IN FEET3001515STORMWATER POND 7 PROFILE61VERTICAL SCALE: 1" = 3'HORIZONTAL SCALE: 1" = 30'POND VOLUME TABLEREQUIRED PONDVOLUME (FT3)AS-BUILT POND VOLUME(FT3)CURRENT POND VOLUME(VEGETATION ANDGROUNDWATER)19,87820,93915,862LEGENDEXISTING CONTOUR MAJOR (5')EXISTING LOT BOUNDARYEXISTING WOODY VEGETATIONPOND BOTTOM OF BANKPOND TOP OF BANKEXISTING CONTOUR MINOR (1')EXISTING TREE/SHRUBPROPOSED CONTOUR MAJOR (5')PROPOSED CONTOUR MINOR (1')PROPOSED GRADING EXTENTPROPOSED ACTIONS1.EXCAVATION OF THE POND TO THE DESIGN ELEVATIONS WILL RESTORE THE POND TOTHE AS-BUILT CAPACITY. WHERE EXCAVATION IS PROPOSED, 6"-9" OF VEGETATEDTOPSOIL WILL BE STRIPPED AND STOCKPILED, THEN THE SUBSOIL WILL BEEXCAVATED TO THE SUBGRADE ELEVATION. EXCAVATED MATERIAL WILL BE HAULEDOFF SITE AND TOPSOIL WILL BE PLACED ON TOP OF SUBGRADE TO ENSURE FINISHEDGRADE MATCHES THE DESIGN ELEVATIONS. APPROXIMATELY 4,000 CUBIC FEET OFSOIL WILL BE REMOVED AND HAULED OFFSITE TO RESTORE THE POND TO AS-BUILTCONDITION.2.INSTALL TWO STAFF GAGES IN THE POND TO ALLOW CATTAIL CREEK HOA TOVISUALLY MONITOR SEDIMENT DEPOSITION IN POND.
INLET CULVERT22 12" x 36 14" RCPA65' LENGTH0+001+00
1+790+001+001+580+001+002+00 2+31 4639464146424639464146414641464146424643464246434643464246414639
46384639 46
3
9
46394640464046394640
4641463946444644
INLET CULVERT26 58" x 43 34" RCPA98' LENGTHBLACKBIRD DRCATTAIL CREEK CATAMOUNT STSUMP PUMP VAULTINTERCEPTOR DRAINPUMP TO CATTAIL CREEK12222ELEC INSTALL ELECTRICAL SERVICE TO PUMPBASIN 6&7:CONCEPTUALALTERNATIVE17SHEET:CATTAIL CREEK
STORMWATER POND ASSESMENT
BOZEMAN, MT
DRAWN BY:
DESIGNED BY:
REV.DATE DESCRIPTION BY APP'D
CCI JOB NO.:
FILE NAME:X:\Project\CattailCk\CAD\CATTAILCRK-PROPOSED.dwgCHECKED BY:
1
2
DATE:SW
TT
---
10/19/20
CAT.001
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------SCALE IN FEET4002020LEGENDEXISTING CONTOUR MAJOR (5')EXISTING LOT BOUNDARYEXISTING WOODY VEGETATIONPOND BOTTOM OF BANKPOND TOP OF BANKEXISTING CONTOUR MINOR (1')EXISTING TREE/SHRUBPROPOSED PIPEPROPOSED PERFORATED PIPEPROPOSED ACTIONS1.INSTALL SUMP AND INTERCEPTOR DRAINS TO INCREASE DRAINAGE AND CAPACITY.PUMP WILL DRAIN TO CATTAIL CREEK JUST ABOVE POND 6 OUTLET.2.INSTALL TWO STAFF GAGES IN THE POND TO ALLOW CATTAIL CREEK HOA TOVISUALLY MONITOR SEDIMENT DEPOSITION IN POND.PROPOSED ELECTRICAL LINEELECELEC
INLET CULVERT22 12" x 36 14" RCPA65' LENGTH0+001+00
1+790+001+001+580+001+002+00 2+31 463946414642463946414641464146414642464346424643464346424641463946384639 4639
46394640464046394640
4641463946444644
INLET CULVERT26 58" x 43 34" RCPA98' LENGTHBLACKBIRD DRCATTAIL CREEK CATAMOUNT ST33331122246354640463546400+000+501+001+501+7910" PVC OUTLET CULVERTINVERT ELEV: 4637.69INVERTELEV: 4637.4826 58" X 43 34" RCPA INLET CULVERTINVERT ELEV: 4637.59INVERTELEV: 4637.62BERMPROPOSED PONDBOTTOMWSE DAYOF SURVEYCATTAILCREEKEXTENDS TO STORM SEWERMANHOLE ON CATAMOUNT STEXISTING PONDBOTTOMPEAK W.S.E. 4638.90RAISE BERMBY 1 FTINSTALLSEDIMENT TRAP4635464046454635464046450+000+501+001+501+58PEAK W.S.E. 4638.9022 12" x 36 14" RCPA INLET CULVERTINVERT ELEV: 4637.7110" PVC OUTLET CULVERTINVERT ELEV: 4638.07BERMEXISTING POND BOTTOMINVERTELEV: 4637.97EXTENDS TO STORM SEWERMANHOLE ON CATAMOUNT STWSE DAY OF SURVEYRAISE BERMBY 1FTINSTALLSEDIMENT TRAPBASIN 6&7:CONCEPTUALALTERNATIVE28SHEET:CATTAIL CREEK
STORMWATER POND ASSESMENT
BOZEMAN, MT
DRAWN BY:
DESIGNED BY:
REV.DATE DESCRIPTION BY APP'D
CCI JOB NO.:
FILE NAME:X:\Project\CattailCk\CAD\CATTAILCRK-PROPOSED.dwgCHECKED BY:
1
2
DATE:SW
TT
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10/19/20
CAT.001
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------SCALE IN FEET4002020LEGENDEXISTING CONTOUR MAJOR (5')EXISTING LOT BOUNDARYEXISTING WOODY VEGETATIONPOND BOTTOM OF BANKPOND TOP OF BANKEXISTING CONTOUR MINOR (1')EXISTING TREE/SHRUBPROPOSED CONTOUR MAJOR (5')PROPOSED CONTOUR MINOR (1')PROPOSED GRADING EXTENTPROPOSED ACTIONS1.CONSTRUCT BERM AT POND OUTLETS. THEBERMS ALONG THE NORTHEAST ANDNORTHWEST SIDES OF PONDS 6 AND 7RESPECTIVELY WOULD BE RAISEDAPPROXIMATELY 1 FT TO PROVIDEADDITIONAL POND CAPACITY. THE BERMSWOULD EXTEND SOUTH UNTIL THEY TIE INTOTHE EXISTING GRADE WHERE THE NATIVEGROUND IS HIGHER, AND TO THE NORTHWHERE THEY INTERCEPT THE ROAD BERM.AREAS WHERE FILL IS PROPOSED, TOPSOILWOULD BE STRIPPED AND STOCKEDPILED.STRUCTURAL FILL WOULD BE IMPORTED TOINCREASE THE BERM ELEVATION, AND THETOPSOIL WOULD BE PLACED BACK ON TOP OFTHE BERM.2.CLEARING OF THE INLET PIPES ANDEXCAVATION OF SEDIMENT AROUND THEOUTLET OF THE INLET PIPES. INSTALLSEDIMENT TRAPS AT THE OUTLET OF INLETPIPES.3.INSTALL TWO STAFF GAGES IN THE POND TOALLOW CATTAIL CREEK HOA TO VISUALLYMONITOR SEDIMENT DEPOSITION IN POND.STORMWATER POND 7 PROFILE81VERTICAL SCALE: 1" = 3'HORIZONTAL SCALE: 1" = 30'STORMWATER POND 6 PROFILE CATAMOUNT ST. INLET 82VERTICAL SCALE: 1" = 3'HORIZONTAL SCALE: 1" = 30'PROPOSED BERM ADJUSTMENT
DESIGN REPORT
Cattail Creek Stormwater Detention Ponds #1-3 & 5-7 60% Design
APPENDIX C
City of Bozeman Stormwater Basin Maintenance Program – Cattail Creek
Homeowners Association Stormwater Basin Inventory 6/22/2016
City of Bozeman Stormwater Basin Maintenance Guide
Stormwater Basin Maintenance Program
Cattail Creek Home Owners Association Stormwater Basin Inventory
6/22/2016
Stormwater Basins: 7
Active Stormwater Accounts: 177 (as of 12/30/2015)
Stormwater Utility Credit: 45% per account
Image 1 – Cattail Creek Subdivision’s stormwater infrastructure network.
Cattail Creek Stormwater
Basin ID: 1
City Stormwater Basin ID:
DP.J00.00011
Current Issues
Inlet and outlet pipes are
obstructed.
Storage capacity has been
reduced because of a
buildup of decayed
vegetation and the growth
of trees/shrubs.
Recommended HOA
Maintenance
Remove vegetation and
debris built up around the
inlet and outlet pipes.
Remove trees and shrubs.
Maintain moving forward
per the attached
Stormwater Basin Maintenance Guide.
City Maintenance Responsibility
The City is responsible for maintaining the underground infrastructure below Cattail St.
and the pipe that drains into the south side of the basin.
Image 3– Obstructed inlet pipe (SW Basin 1) Image 4 – Stormwater Basin 1 (east view)
Image 2 – Location of Stormwater Basin 1
Cattail Creek Stormwater
Basin ID: 2
City Stormwater Basin ID:
DP.J00.00012
Current Issues
Inlet and outlet pipes are
obstructed.
Storage capacity has been
reduced because of a
buildup of decayed
vegetation and the growth
of trees/shrubs.
A channel has developed
allowing flow through to
occur.
Recommended HOA
Maintenance
Remove vegetation and debris built up around the inlet and outlet pipes.
Remove trees and shrubs.
Dredge and contour the basin as drawn on the Engineering Plans for Cattail Creek
Subdivision.
Maintain moving forward per the attached Stormwater Basin Maintenance Guide.
City Maintenance Responsibility
The City is responsible for maintaining the underground infrastructure located below
Blackbird Dr. and the pipe that drains into the south side of the stormwater basin.
Image 5 – Location of Stormwater Basin 2
Image 6 – Eroded channel (SW Basin 2) Image 7 – Stormwater Basin 2 (north view)
Cattail Creek Stormwater Basin
ID: 3
City Stormwater Basin ID:
DP.J00.00013
Current Issues
Inlet and outlet pipes are
obstructed.
Storage capacity has been
reduced because of a
buildup of decayed
vegetation.
The basin is not discharging
properly because of an
elevated berm adjacent to
the receiving waterway.
Recommended HOA
Maintenance
Remove vegetation and debris built up around the inlet and outlet pipes.
Dredge and contour the outlet channel as drawn on the Engineering Plans for Cattail
Creek Subdivision.
Maintain moving forward per the attached Stormwater Basin Maintenance Guide.
City Maintenance Responsibility
The City is responsible for maintaining the underground infrastructure located below
Warbler Way and the pipe that drains into the east side of the stormwater basin.
Image 8 – Location of Stormwater Basin 3
Image 9 – Stormwater Basin 3 (north view) Image 10 – Elevated outlet channel (SW Basin 3)
Cattail Creek Stormwater
Basin ID: 4
City Stormwater Basin ID:
DP.J00.00014
Current Issues
Inlet and outlet pipes are
obstructed.
Storage capacity has been
reduced because of a
buildup of decayed
vegetation and the growth
of trees/shrubs.
Recommended HOA
Maintenance
Remove vegetation and
debris built up around the
inlet and outlet pipes.
Remove trees and shrubs.
Maintain moving forward per the attached Stormwater Basin Maintenance Guide.
City Maintenance Responsibility
The City is responsible for maintaining the underground infrastructure located below
Catron St. and the pipe that drains into the south side of the stormwater basin.
Image 12 – Stormwater Basin 4 (north view) Figure 13 – Obstructed inlet pipe (SW Basin 4)
Image 11 – Location of Stormwater Basin 4
Cattail Creek Stormwater
Basin ID: 5
City Stormwater Basin ID:
DP.J00.00015
Current Issues
Inlet and outlet pipes are
obstructed.
Storage capacity has been
reduced because of a
buildup of decayed
vegetation and the growth
of trees/shrubs.
Recommended HOA
Maintenance
Remove vegetation and
debris built up around the
inlet and outlet pipes.
Remove trees and shrubs.
Maintain moving forward
per the attached
Stormwater Basin
Maintenance Guide.
City Maintenance Responsibility
The City is responsible for maintaining the underground infrastructure located below
Catron St. and the pipe that drains into the south side of the stormwater basin.
Image 15 – Stormwater Basin 5 (north view) Image 16 – Obstructed inlet pipe (SW Basin 5)
Image 14 – Location of Stormwater Basin 5
Cattail Creek Stormwater Basin ID: 6
City Stormwater Basin ID: DP.J00.00017
Current Issues
Inlet and outlet pipes are obstructed.
Storage capacity has been reduced
because of a buildup of decayed
vegetation and the growth of
trees/shrubs.
Recommended HOA Maintenance
Remove vegetation and debris built
up around the inlet and outlet pipes.
Remove trees and shrubs.
Maintain moving forward per the
attached Stormwater Basin
Maintenance Guide.
City Maintenance Responsibility
The City is responsible for maintaining
the underground infrastructure located
below Blackbird Dr., Catamount St., and
the pipes that drain into the south and
east sides of the stormwater basin.
Image 18– Stormwater Basin 6 (south view) Image 19 – Obstructed inlet pipe (SW Basin 6)
Image 17 – Location of Stormwater Basin 6
Cattail Creek Stormwater Basin
ID: 7
City Stormwater Basin ID:
DP.J00.00016
Current Issues
Inlet and outlet pipes are
obstructed.
Storage capacity has been
reduced because of a buildup of
decayed vegetation and the
growth of trees/shrubs.
Recommended HOA Maintenance
Remove vegetation and debris
built up around the inlet and
outlet pipes.
Remove trees and shrubs.
Maintain moving forward per
the attached Stormwater
Basin Maintenance Guide.
City Maintenance Responsibility
The City is responsible for
maintaining the underground
infrastructure located below
Warbler Way, Catamount St., and the pipe that drains into the north side of the
stormwater basin.
Image 20 – Map displaying stormwater basin location
Image 21 – Stormwater Basin 7 (south view) Image 22 – Obstructed inlet pipe (SW Basin 7)
Image 20 – Location of Stormwater Basin 7
1 - Version 1 Created on October 13th, 2015
Stormwater Basin Maintenance Guide
What are Stormwater Basins?
Stormwater basins are constructed depressions designed to
capture, clean, and infiltrate polluted stormwater flowing
from roads, parking lots, driveways, and rooftops.
Maintenance of stormwater basins is necessary to ensure they
function properly reducing stormwater’s impact on local
waterways.
Benefits of Stormwater Basins
Some of the benefits of a properly functioning and well maintained stormwater basin include:
Reduction in stormwater runoff flowing into streams, decreasing downstream bank erosion.
Capture of pollutants including fertilizers, pet waste, soaps, paints, and oils/greases,
protecting public health and wildlife habitat.
Removal of sediment that otherwise would clog local streams severely harming aquatic life.
Holds accumulated stormwater and controls outflow reducing the risk of flooding.
Maintenance Responsibility
HOAs are responsible for maintaining the stormwater basins in their subdivision. A plan for
stormwater basin maintenance should be formulated that includes an inspection schedule,
maintenance procedures, and a record-keeping system. Three key points to consider include:
1. Basin capacity - Vegetation and sediment buildup, if not properly managed, significantly
reduce stormwater storage space and the basins ability to contain large flows of water
2. Soil drainage - Compaction and silts limit infiltration time resulting in stagnant standing water
3. Vegetation height - 6” or higher reduces flow velocity and provides increased water treatment
Determining the Condition of Your Stormwater Basins
An inventory is the first step to identify which stormwater basins your HOA is responsible for
maintaining. This information can be found by contacting Stormwater Division staff or by
reviewing subdivision plans and maintenance agreements on file with individual HOA boards.
Once an inventory is complete, the second step is to determine the condition of each stormwater
basin. Typical symptoms that a stormwater basin requires maintenance include:
Stormwater Basin
1. Overgrown vegetation 2. Erosion causing channelized flow
Continued on back…
2 - Version 1 Created on October 13th, 2015
If any of the issues above are identified, or the pond is deemed to be non-functioning for any other
reason, a maintenance strategy must be formulated and implemented. The following section
outlines the Stormwater Division’s recommended approach.
Recommended Maintenance Strategy
Routine inspections and maintenance are necessary to reduce
downstream pollution, unpleasant odors, nuisance insects,
algae blooms, unsightly areas, and large costly repairs. The
City recommends the following maintenance strategy:
1. Routine Maintenance Activities (1-3 Months)
Designate “No-Mow” zones in the bottom of basins.
Mowing causes a buildup up debris taking away pond
capacity and compacts the soil.
Remove trash, leaves, grass clippings, pet waste, and debris
Establish a chemical free zone within and around the basin
Inspect for uniform ponding, and water disappears in 3 days
2. Annual Maintenance Activities (Annually)
Cut “No-Mow” zone to 6”, remove clippings every fall
Re-establish vegetation on eroded and barren areas
Remove excess sediment build-up in basin
Update maintenance plan and inspection log
3. Long-Term Maintenance Activities (5-10 Years)
Hire a contractor to inspect and return basin condition to
initial design found on subdivision engineering plans
Dredge basin if sediment buildup is greater than 6”
Additional Information
It is important to maintain your stormwater basin to ensure Bozeman continues to be “The Most
Livable Place”. The Stormwater Division has a responsibility to conduct audits and enforcement
action may be taken when stormwater basins are not being properly maintained. Please contact the
Stormwater Division for more information and/or to schedule a voluntary inspection.
Kyle Mehrens Frank Greenhill
Stormwater Program Coordinator Stormwater Program Technician
406-582-2270 406-582-2917
kmehrens@bozeman.net fgreenhill@bozeman.net
Annual Maintenance
Have a civil engineer compare and return
basin condition to as-built plans
Dredge basin if sediment accumulation is
greater than 6 inches
3. Obstructed inlet / outlet structures 4. Standing water remaining after 3 days
“No-Mow” zone in stormwater basin
Annual Maintenance
Have a civil engineer compare and return
basin condition to as-built plans
Dredge basin if sediment accumulation is
greater than 6 inches
Dredging of stormwater basin
Fall cutting of “No-Mow” zone to 6”
DESIGN REPORT
Cattail Creek Stormwater Detention Ponds #1-3 & 5-7 60% Design
APPENDIX D
As-Built Plans for Pond “1-7” TD&H (6/12/02)