Damon Rd Drainage Systemr
Damon Road
Drainage System
Improvements
Feasibility Report
Northampton,
Massachusetts
Prepared for Massachusetts Department of Transportation
Highway Division
Boston, Massachusetts
Prepared by Vanasse Hangen Brustlin, Inc.
Watertown, Massachusetts
May 2010
LJ
L.
r
r l l
1 Executive Summary 1
2 Introduction . 2
Existing Conditions 3
Geotechnical Investigation 6
Other Geotechnical and Bridge Information 7
8
Introduction. 8
Design Assumptions 9
Design Criteria 9
Alternatives ' 11
Project Decision Matrix 14
Environmental Issues. 15.
Introduction 15
Anticipated Environmental. Impacts and Mitigation 15
Wetland Permits / Environmental Clearances 15
6 Conceptual Project Costs • 17
7 Conclusions 19
Introduction 19
Recommendations 19
Figures and Appendices
Figure 1 - Locus Map
Figure 2 - Existing Conditions Plan .
Figure 3 - Alternative #1
Figure 4 - Alternative #2
Figure 5 - Alternative #3
Figure 6 - Bank Stabilization - Typical Section
Alternatives Analysis
Appendix A
Appendix B
Appendix C
Appendix D
City of Northampton --
Damon Road
Drainage System Improvements
Feasibility Report
Table of Contents
FI
L J
Executive Summary
The Massachusetts Department of Transportation (MassDOT), acting through its
Environmental Division and the District 2 office in Northampton, is planning major
repairs to a portion of the Damon Road drainage system adjacent to the Norwottuck
Rail Trail Bridge and the Connecticut River in Northampton, Massachusetts.
For more than 10 years, the existing drainage system has been in a continual state of
failure. The existing culvert beneath Water Street (abandoned) has collapsed and the
downstream headwall has migrated down slope toward the Connecticut River.
Major bank erosion is actively occurring and is approaching the western -most pier
(Pier 9) of the Norwottuck Rail Trail Bridge.
The repair alternatives included in this feasibility report contain approaches to repair
the existing drainage system, improve the hydraulics, and reduce and repair bank
erosion. Alternatives 1 & 2 include removal of the Water Street embankment and
culvert to "daylight" the existing drainage ditch. Alternative 3 proposes hydraulic
improvements to the system, and reconstructing the Water Street culvert and
headwalls.
On March 4, 2010, VHB met with representatives from MassDOT's Environmental
Division and District 2 office, and a representative from the Department of
Conservation and Recreation (DCR) to provide an update of the project and review
the alternatives developed for the drainage system improvements. Based on input
from all parties, Alternative 2 has been selected to be advanced into final design.
VHB documented the decision - making process with the use of a Project Decision
Matrix (included in Section 4) which shows that all three Alternatives achieve the
required goals of the project. Alternative 2 was found to have more advantages,
including greater wildlife habitat improvements and less maintenance costs.
Executive Summary
•
n
J'
u
;.J
r
r7
Introduction
The study area is located on the west bank of the Connecticut River, in the City of
Northampton, Massachusetts (see Figure 1). The site is bound on the northeast by the
Connecticut River, on the southwest by Damon Road, on the south and east by the
Norwottuck Rail Trail and associated parking lot, and on the west by private
property.
The existing drainage system (see Figure 2) receives flows from a large drainage area.
The drainage area includes a portion of Damon Road, a portion of Interstate 91 and
an industrial park west of Interstate 91.
Drainage ditches at the base of the Interstate 91 embankment flow to an open
drainage ditch which enters a 40 -inch reinforced concrete pipe (RCP) culvert on the
southwest side of Damon Road. The 40 -inch RCP culvert ends in an open drainage
ditch on the northeast side of Damon Road where it collects a portion of the Damon
Road runoff. The ditch remains open for approximately 140 feet where it enters a
48 -inch RCP culvert under Water Street. Water Street is an abandoned City roadway.
Prior to failure of the system the culvert extended from a cement concrete headwall
on the southwest side of the Water Street embankment to a headwall on the
northeast side. Downstream of the 48 -inch culvert, the ditch extends approximately
100 feet where stormwater is discharged to the bank of the Connecticut River.
Additionally, a 48 -inch drainage trunk line, originating in the industrial park to the
west of Interstate 91, extends beneath the rail trail, west of Damon Road. The trunk
line travels 120 feet from Damon Road and turns left at a 62 degree angle in a 16 feet
deep drain manhole, 25 feet northwest of the rail trail bridge's west abutment. The
trunk line then extends approximately 40 feet to the Water Street culvert. The
industrial park drain line enters the Water Street culvert in a manhole at
approximately a 90 degree angle.
Two other major MassDOT projects are planned within the same area as the
Damon Road Drainage Improvements discussed in this report. These projects
include the Damon Road Transportation Improvement Project, which involves the
widening of Damon Road (with minor vertical and horizontal realignment) to
provide four foot shoulders and a sidewalk; and the Interstate 91 /Route 9
Introduction
n
J
Interchange project, which involves construction of a new north -bound entrance
ramp to I -91 from Damon Road.
Introduction
\ \Mawatr \ev\ 10829.00 \GIS\ project \NorthamptonDamonRoad\LocusMap larger.mxd
oin9A4iu+rM+e fmnrM.
T 0 250 500 Feet a Highway
Source: MassGIS 2005
Site Location
FIGURE 1
Site Location Map
Drainage Improvements
Damon Road
Northampton, MA
J
T
T
I
L
f
_J
Alternatives - Analysis..
3
Existing Conditions
In 2005, the Water Street culvert began to collapse. The system has continued to
deteriorate through a combination of factors, including continued drainage flows
within the collapsed system and flooding of the Connecticut River. In addition,
existing soil conditions and the age and condition of the system's components may
have contributed to the initial collapse and continued deterioration of the system.
The downstream headwall of the Water Street culvert has migrated down slope
toward the Connecticut River, along with a portion of the culvert, downstream of the
industrial park manhole connection. As far back as 1999, substantial bank erosion
approaching the Norwottuck Rail Trail bridge pier, has been occurring. The failure of
the culvert and downstream headwall appears to have resulted in significant
additional slope erosion. Slope erosion is actively occurring and eroding the Water
Street embankment. Slope erosion is also actively eroding the bank adjacent to the
western most pier (Pier 9) of the Norwottuck Rail Trail Bridge. Several large and
many smaller trees are being undercut and falling into the ditch.
The downstream headwall has
migrated down slope.
Alternatives Analysis
Erosion is occurring around the
industrial park trunk line
connection manhole at the
Water Street culvert.
The upstream headwall
exhibits major concrete
deterioration and extensive
siltation of the Water Street
culvert.
The embankment, adjacent to
the Norwottuck Rail Trail
Bridge pier, at the Connecticut
River, shows severe soil erosion.
The open drainage ditch,
upstream. from _ the Water
Street embankment is
experiencing moderate slope
erosion.
The downstream end of the Damon
Road culvert is in satisfactory condition.
1 This culvert will be extended
approximately twenty feet to facilitate
the widening of Damon Road.
5 Alternatives Analysis
The Water Street culvert has
collapsed causing slope erosion
and toppling vegetation into the
drainage ditch.
-
Li
ri
In addition to the existing system failures described above, the existing industrial
park trunk line may be experiencing significant energy losses due to severe bends in
the 48inch line. The existing drain manholes may be sustaining severe wear
internally due to major hydraulic impacts.
It appears that a drainage easement is in place for the existing industrial park trunk
line. No existing drainage easements have been identified for the existing open
drainage ditch between Damon Road and Water Street.
Geotechnical Investigation
A geotechnical report was prepared for VHB by Nobis Engineering Inc., dated
January 25, 2010, and is included as Appendix A. The geotechnical report was
prepared in order to assess the structural and drainage characteristics of the site soils
for supporting new headwalls, and how site soil conditions may have contributed to
the failure of the existing drainage system.
Conclusions of the Nobis Engineering Inc. report:
Based on the conclusions listed above, it is our geotechnical consultant's opinion that
the drainage structures at Damon Road failed due to the deteriorated condition of the
downstream retaining wall, combined with a lack of drainage behind the retaining
wall. The flooding that occurred_ during the flood of October 9, 2005 may have
contributed to the eventual collapse, but was not the sole cause of the collapse. The
soil laboratory analyses suggest that the soils underlying the drainage structures are
over - consolidated clays which are less susceptible to settlement in comparison to
normally consolidated clays. The evidence suggests that the downstream retaining
wall was in a progressive state of collapse for a significant period of time.
7 Existing Conditions
1. The drainage system failed in a progressive manner, it was not the result of a
single event (e.g. flood);
2. A'major flood event occurred in the area on October 9, 2005; however, there
is insufficient data to link this flood event with the drainage system failure;
3. Based on the soil investigation and site reconnaissance, it is presumed that
the existing retaining walls were backfilled with poorly drained soils,
possibly contributing to the failure;
4 Subsurface conditions revealed significant depths of clay, extending to
72 feet below the surface;
5. Clay just below the surface fill is over- consolidated and is considered
sensitive to disturbance since the natural moisture content is above the
Liquid Limit. It is possible that the clay at greater depth is normally
consolidated.
Other Geotechnical and Bridge Information
The Department of Conservation and Recreation (DCR) requested its consultant to
inspect the ground conditions at the Norwottuck Rail Trail bridge and develop a
scope of work for a full bridge inspection. A technical memorandum, prepared for
the DCR by Simpson Gumpertz & Heger Inc., dated March 8, 2010, is included as
Appendix B.
Recommendations of the report included: weekly visual monitoring of the pier;
immediate placement and monthly monitoring of survey points on the pier;
subsurface investigation to determine nature of pier footing; coordination with
drainage system repair to move the mouth of the channel further upstream of the
pier; and the addition of rip rap revetment or other stabilization . measures on the
banks at the north and east sides of the pier from the mudline to the top of the bank.
The DCR [formerly Department of Environmental Management (DEM)] requested its
consultant to perform a structural investigation of the Northampton Bikeway Bridge
(Norwottuck Rail Trail bridge). A bridge report was prepared by BETA Engineering,
Inc., titled "Connecticut River Greenway State Park, Massachusetts, Northampton
Bikeway Bridge over the Connecticut River, Structural Evaluation", dated
December, 1999, is included as Appendix C. The report indicates that erosion of the
bank, adjacent to the bridge pier had been an issue in the area since December 1999.
Recommendations of the report included stabilization of the bank adjacent to the pier
with rip rap and /or a steel sheeting bulkhead to prevent further erosion.
A subsurface investigation was performed at pier 9 of the Rail Trail Bridge, by GEI
Consultants, Inc. for Simpson Gumpertz & Heger, Inc., DCR's consultant. The report,
titled "Subsurface Exploration and Foundation Evaluation, Pier P9, Norwottuck Rail
Trail Bridge, Over the Connecticut River ", dated May 2010, is included as
Appendix D.
The investigation was performed to determine subsurface conditions and evaluate
the existing foundation of Pier 9. It was determined that the pier foundation
consisted of a stepped stone foundation, underlain by wood piles or cribbing.
Recommendations of the report include performing a scour analysis at the pier and
provide design recommendations to stop erosion at this location.
1 I
LJ
In also our geotechnical consultant's opinion that since it appears that the former
drainage structures failed due to age, - deteriorated condition, - and lack of . free _.
draining backfill in the original design, it is considered possible to re- construct the
existing structures in like kind, provided the replacement structures are engineered
to current design standards.
8 Existing Conditions
r
r
J
Introduction
The primary goal of any drainage system improvement alternative is stop erosion of
the existing Water Street embankment and the bank of the Connecticut River
downstream of the Water Street culvert, . and to reconstruct the drainage system in
this area in a manner that provides long -term stability and ease of maintenance. An
improvement to the existing hydraulic design is essential to prevent further erosion.
Methods to reduce erosive velocities of concentrated runoff include plunge pools and
drop manholes. Since any repair solution will require some degree of maintenance,
access to the area by City of Northampton DPW staff is required. Due to the site's
proximity to a popular outdoor family destination (the Norwottuck Rail Trail), safety
and. security" of the site is essential. Overall aesthetics are also considered an
important factor in selection of an alternative.
An additional goal of this project is to assist MassDOT and DCR in establishing a
plan of action for resolving the related erosion problems that are potentially
destabilizing the adjacent Norwottuck Rail Trail bridge pier (Pier 9).
Both rigid and flexible bank stabilization techniques have been explored for the
drainage system improvement alternatives. One option considered is removing the
headwalls and culvert under Water Street and opening the channel. Water Street is
an abandoned City right of way. During a site visit in the Fall of 2009, DPW staff
from the city of Northampton agreed that opening the channel was desirable.
Construction activities will greatly change the aesthetics of the area, therefore final
restoration will include a landscaping plan consisting of native vegetation such as
grasses, groundcover and /or shrubs.
All Alternatives include the extension of the existing Damon Road culvert to
accommodate roadway widening and sidewalk construction proposed in the
MassDOT Damon Road Transportation Improvement Project (MassDOT project
No. 180525)
Alternatives Analysis
Alternatives Analysis
Design Assumptions
It is assumed that the existing culvert and trunk line sizes are adequate to convey
existing flows; therefore, a full watershed analysis has not been performed as part of .
this feasibility report.
Design Criteria
Goals
Bank Stabilization
The Norwottuck Rail Trail Bridge is owned and operated by the DCR. It is assumed
that the DCR and its consultants are investigating repair alternatives in the vicinity of
the bank erosion at the bridge pier. Final design of the Damon Road drainage repairs
and bank stabilization must be closely coordinated with bridge pier bank
stabilization.
The proposed drainage improvements will be designed in accordance with the
United States Department of Agriculture (USDA), Natural Resources Conservation
Service, Engineering Field Handbook, December 1996; AASHTO Highway Drainage
Guidelines, 1999; MA Department of Environmental Protection Stormwater
Management Standards, 2008; Massachusetts Department of Transportation
(MassDOT) Project Development and Design Guide, 2006.
The major goals of this project are:
> Bank Stabilization
> Improved Hydraulics
> Improved Stormwater Management
> Safety
> Maintenance
> Aesthetics
More information on each of these design goals are provided in the following
sections. Among the repair alternatives deemed feasible, construction costs have
been compared to determine the most cost - effective repair alternative.
The primary goal of this project is to stabilize the river bank. Information on options for
bank stabilization is provided in the USDA's Engineering Field Handbook. The options
include stone or concrete revetment to the top of "stream forming flow" elevations and
vegetative plantings below and above this elevation.
0 Alternatives Analysis
r
r
Improved Hydraulics
Compliance with. Wetlands Protection Act/ Stormwater
Management Standards
The proposed drainage improvement project is within wetland resources under the
jurisdiction of the Massachusetts Wetland Protection Act. As such the project requires
review by the Northampton Conservation Commission. MassDOT must demonstrate to
the Commission that the alternative selected limits impact to wetland resources to the
greatest extent practicable, provides appropriate compensation for affected wetland
resources and comply with the DEP Stormwater Management Standards.
Safety
After consideration of site conditions, including soil types, extent of erosion and the
steepness and condition of the existing ditch, VHB is proposing Vegetated Geogrids for
the purpose of bank stabilization. This method of bank stabilization utilizes stone for the
lower portion of the bank at up to a 1.5h:1v slope. Above this course, compacted soil
wrapped in a geotextile fabric (Geogrids) is installed. This course may be at 2h:1v. slope.
The Geogrids are interspersed with live cuttings, extending into the existing bank face.
Above this middle course, the grade is sloped at 3h:lv or flatter, loamed and seeded and
planted with native vegetation.
The design of the existing drainage system is hydraulically inefficient. The existing
48 -inch drainage trunk line makes two very sharp bends within the system. The
hydraulics could be improved by removing these two bends and straightening the trunk
line. It is assumed that the industrial park drainage trunk line was designed to flow full
during the design storm. These flows would be quite substantial and require some type
of energy dissipation. This is achieved by a plunge pool at the outlet, or a drop manhole
prior to outletting.
With the abandonment of Water Street, the culvert beneath Water Street has become
obsolete. The existing culvert shows . evidence of major siltation and is an obstruction to
wildlife. The removal of the Water Street culvert and embankment would provide some
degree of improvement to wildlife habitat. This change has been incorporated in
Alternative 2 and 3.
The proposed location of the project, adjacent to a Norwottuck Rail Trail and the trail
parking area, requires that safety and security measures for the site be analyzed and
incorporated into the project design. Access . to the project area during and after
construction should be closed to the general public. The installation of fencing, to
discourage access by the public, may help in maintaining safety in the area. Outlet pipes
of 48inch may require safety bars to prevent unauthorized access.
11
Alternatives Analysis
■
Maintenance
Aesthetics
Alternatives
Alternative 1
The existing system may have. benefitted from additional inspection and maintenance. In
order for any drainage improvements to function properly over their expected lifecycle,
adequate maintenance must be performed. Each alternative includes a stabilized surface
to provide access to the drainage system components for City maintenance equipment.
Access gates within the proposed fencing are proposed.
Due to the project's location adjacent to the popular Norwottuck Rail Trail and on the
bank of the Connecticut River, aesthetics are considered an important factor in the
design of the drainage improvements. Natural materials, such as stone and
vegetation, are incorporated wherever possible and appropriate. Vegetation would
be native species such as grasses, groundcover and /or shrubs. Also, concrete liners,
designed to provide an aesthetic appeal to concrete retaining walls could be
incorporated. A landscaping plan will be developed to revegetate areas disturbed by
project.
The alternatives evaluated in this report are as follows:.
> Alternative 1 (Figure 3): Remove Water St. embankment and culvert; provide
outlet control for industrial park drainage, outlet toward ditch.
> Alternative 2 (Figure .4): Remove Water St. embankment and culvert; provide
drop manhole for industrial park drainage, outlet toward Connecticut River.
> Alternative 3 (Figure 5): Replace Water St. culvert; straighten and extend
industrial park drainage trunk line; provide single combined outlet structure.
Depending on the alternative chosen, materials proposed in this report may be
substituted with alternative materials, such as stone gabions in place of riprap. The
following is a general discussion and comparison of the alternatives in terms of
staging and aesthetics. A cost comparison for each alternative is included in the
discussion of each alternative.
Alternative 1 (Figure 3) generally involves the removal of the existing drainage
system components (headwalls and manhole) under Water Street and reconstructing
this area as an open charnel from Damon Road to the Connecticut River. The trunk
line from the industrial park would be reconstructed and straightened (removal of
the 90- degree bend within the manhole). This trunk line would discharge to a plunge
12 Alternatives Analysis
r
Alternative 2
pool with an overflow weir directing flow towards the open channel. Figure 3 shows
specific elements of Alternative 1 including:
1. Extend Damon Road 42 -inch RCP culvert in preparation for. Damon Road
widening
2. Install downstream headwall for 42 -inch Damon Road culvert
3. Remove existing 48" RCP culvert under Water Street embankment
4. Open drainage ditch through Water Street embankment
5. Create natural stream bed
6. Install slope protection at 1.5h:lv up to approximate elevation 115
7. Grade slope 2h:lv or flatter to meet existing
8. Straighten industrial park 48 -inch drainage trunk line
9. Outlet industrial park trunk line into rip rap plunge pool with overflow weir to
ditch
10. Install stabilized surface to allow access for maintenance of plunge pool
11. Install safety fencing and gate along bike path
12. Install landscaping.
These elements are identified by number on Figure 3.
Similar to Alternative 1, Alternative 2 (Figure 4) involves the removal of existing
drainage system components (headwalls and manhole) under Water Street and
reconstructing this area as an open channel from Damon Road to the Connecticut
River. The trunk line from the industrial park would be designed differently than
Alternative 1. The existing manhole would be replaced with a deeper drop manhole
to allow stormwater to exit the manhole at close to the same elevation as the
Connecticut River. This alternative does not require a plunge pool to reduce
stormwater velocity. Stormwater exits the manhole through a trunk line to an
armored ditch prior to discharging to the Connecticut River. Figure 4 shows specific
elements of Alternative 2 including:
1. Extend Damon Road 42 -inch RCP culvert in preparation for Damon Road
widening
2. Install downstream headwall for 42 -inch Damon Road culvert
3. Remove existing 48 -inch RCP culvert under Water Street embankment
4. Open drainage ditch through Water Street embankment
5. Create natural stream bed
6. Install slope protection at 1.5h:1v up to approximate elevation 115
7. Grade slope 2h:lv or flatter to meet existing
8. Replace existing industrial park drain manhole with new drop manhole
9. Straighten industrial park 48 -inch drainage trunk line
10. Outlet industrial park trunk line through bank toward Connecticut River
11. Install stabilized surface for maintenance access to drop manhole
12. Install safety fencing and gate along bike path
13. Install landscaping.
13 Alternatives - Analysis
f
Alternative 3
These elements are identified by number on Figure 4.
These elements are identified by number on Figure 5.
14 Alternatives Analysis
Alternative 3 (Figure 5) represents the reconstruction of the Water Street culvert and.
embankment. The downstream and upstream headwalls at Water Street and a new
culvert would be constructed. The industrial park trunk line manhole would be
replaced with a deeper drop manhole. An extension of the existing trunk line would
convey the stormwater to a combined - outlet headwall. Figure 5 shows specific
elements of Alternative 3 including:
1. Extend Damon Road 42 -inch RCP culvert in preparation for Damon
widening
2. Install downstream headwall for 42 -inch Damon Road culvert
3. Replace existing upstream headwall at Water Street culvert
4. Replace existing. 48 -inch RCP culvert under Water Street embankment
5. Replace existing industrial park drain manhole with new drop manhole
6. Straighten and extend industrial park 48 -inch drainage trunk line
7. Replace existing downstream headwall with combined outlet headwall
8. Install slope protection at 1.5h:1v up to approximate elevation 115
9. Install maintenance drive to headwalls
10. Install safety fencing and gate along bike path
11: Install landscaping.
Road
Improvement
Description
Advantages
Disadvantages
•
Provides Bank
Stabilization
Improves
Hydraulics
Improves
Safety
Maintenance
Costs
Improves
Aesthetics
Construction Costs
Alternatives
Do Nothing
Allow existing drainage to
continue to erode bank
•
No Cost
•
•
Unsafe, poor hydraulics,
Continued negative impact to
bridge pier
X
X
X
X
X
None
Alternative 1
Extend Damon Road
Culvert, Remove Water
•
•
Stops slope erosion
Improved hydraulics
•
Large rock plunge pool not
aesthetically pleasing
Street Embankment and
Stabilize Banks, Realign
Industrial Park. Trunk Line,
Stone Plunge Pool
•
•
Improved safety
Improved wildlife habitat along
open channel
Plunge pool provides
pretreatment of stormwater
•
Greater maintenance costs
than Alternative 2
Moderate
Alternative 2
Extend Damon Road
•
Stops slope erosion
•
Slightly higher costs than
Culvert, Remove Water
•
Improves hydraulics
Alternatives 1 & 3
Street Embankment and
•
Improves safety
•
Stabilize Banks, Realign
Industrial Park Trunk Line,
Drop Manhole
•
•
Greater landscaping
opportunities
Improved wildlife habitat along
open channel
4
J+
4
J+
.
Al+
Moderate
•
Drop Manhole reduces
stormwater velocities
•
Lower maintenance costs
than Alternatives 1 & 3
Alternative 3
Extend Damon Road
Culvert, Rebuild Water
Street Culvert and
•
•
•
Stops slope erosion
Improves hydraulics
Improves safety
•
Fewer wildlife habitat
improvements (no open
channel)
Headwalls, Realign
•
No pretreatment of stormwater
Industrial Park Trunk Line
•
Greater construction costs
associated with large headwalls
Moderate
•
Greater maintenance costs than
Alternatives 1 & 2
Project Decision Matrix
J+ = Major Positive Impact/Yes
= Positive Impact/Yes
15 Alternatives Analysis
= No Impact /Maybe
X = Negative Impact/No
//PAW /,
•. • Tiara C{;ntro/ \
p. 1 ti — Cabe 7e1
y kC an Ccnc:
1,Y 5.0 ``r' �` \ ' I� % '
9P eyo '....,'''::"V:")"..; . //�
_ \ N
Poe lath Pea.
Push Buttai
and Signal
140
135-
130-
125-
120-
115-
110-
105-
100-
I;T7 -397 \�
O NUMBERS CORRESPOND TO ALTERNATIVE
ELEMENTS LISTED IN SECTION 4
ALTERNATIVE 1
PROPOSED LOAM, SEED AND LANDSCAPING
PROPOSED STONE SLOPE PROTECTION
PROPOSED DRAINAGE DITCH BOTTOM
PROPOSED MAINTENANCE DRIVE
ter,,
pe op
? �e C
`SS �
A 4/
E: \ 10829.08 \rep orts \Rgure —Color— Aits.dwg
��� • Troffic Centre/ �\
Gobbet \
�cf a; Conc. P.F.Ci
f 33:0 ` @ \ G; °a va. /
"'-`2' 4 \/ 4i
••.1 .
//
ACufm�
O NUMBERS CORRESPOND TO ALTERNATIVE
ELEMENTS LISTED IN SECTION 4
ALTERNATIVE 2
PROPOSED LOAM, SEED AND LANDSCAPING
PROPOSED STONE SLOPE PROTECTION
PROPOSED DRAINAGE DITCH BOTTOM
E: \ 10829.08 \reporte \Rgure — Color— Alte.dwg
f
/ d oss
UP` ,3 NFIT /
�.., Rol& Centro/ `\
--Gobbet
oa Conc l.eut
Pale RV/ Pea.
Pvch Rattan
and goo/
PROPOSED LOAM, SEED AND LANDSCAPING
PROPOSED STONE SLOPE PROTECTION
PROPOSED MAINTENANCE DRIVE
E: \10829.08 \reports \Figure —Col or —AI ts. dwg
P
rI
r..
ri
1 FT
GEOGRIDS
4
125
3 FT /NATIVE PLANTINGS LOAM AND SEED
115
112
1.5 FT 109
1 FT
0
107
LOAM AND SEED
GRAVEL FILTER FABRIC
TYPICAL SECTION 104 +50
STREAMBANK STABILIZATION
NOT TO SCALE
4
SCALE IN FEET
TYPICAL OPEN CHANNEL SECTION
PLANTING NOTES FOR STREAMBANK STABILIZATION:
LOWER SLOPE — ELEVATIONS FROM 100.0 TO 112.0
THE LOWER EMBANKMENT WILL BE STABIUZED WITH RIPRAP FROM THE LOW FLOW
ELEVATION TO 3 FEET ABOVE BANKFULL ELEVATION. DOGWOOD AND WILLOW LIVE
STAKES SHALL BE A MINIMUM OF 5 FEET IN LENGTH AND PROTRUDE FROM THE
RIPRAP A MINIMUM OF 6 INCHES.
MIDDLE SLOPE — ELEVATIONS FROM 112.0 TO 115.0
THE MIDDLE EMBANKMENT SHALL BE STABILIZED WITH VEGETATED GEOGRIDS (SOIL
LIFTS WRAPPED WITH GEOTEXTILE FABRIC) WITH A BRUSH LAYER PLANTED BELOW
THE LOWER LIFT. GEOGRIDS SHALL CONSIST OF APPROXIMATELY ONE FOOT OF
COMPACTED TOPSOIL PLACED ON A GEOTEXTILE. THE GEOTEXTILE SHALL BE
WRAPPED OVER THE COMPACTED SOIL A BRUSH LAYER SHALL BE
CONSTRUCTED, COMBINING A 6 INCH BED OF LOAM BORROW WITH AN EQUAL MIX
OF 4 FOOT, 5 FOOT AND 6 FOOT DOGWOOD, WILLOW AND SPECKLED ALDER BARE
ROOT STOCK. ROOTED ENDS SHALL TOUCH THE BACK OF THE EXCAVATED SLOPE.
AND BRANCH TIPS WILL PROTRUDE APPROXIMATELY 6 INCHES OR LESS
PERPENDICULAR TO STREAM FLOW.
UPPER SLOPE — ELEVATIONS ABOVE 115.0
THE UPPER EMBANKMENT SHALL BE GRADED TO A SLOPE OF 3:1 WITH.
APPROXIMATELY 6 INCHES OF LOAM BORROW. LOAM BORROW SHALL BE
COVERED WITH EROSION CONTROL FABRIC —JUTE AND SEEDED. THE LOWER EDGE
OF EROSION CONTROL FABRIC —JUTE SHALL BE ANCHORED TO THE UPPERMOST
LAYER OF GEOTEXTILE FROM THE MIDDLE SLOPE. SHRUBS AND SAPLINGS SHALL
BE PLANTED THROUGH THE EROSION CONTROL MAT. SHRUBS AND TREES SHALL
BE MULCHED WITH HAY MULCH.
100 YEAR FLOOD ELEV = 125.00
TOP OF SLOPE ELEV = 115.00
BANK FULL ELEV = 109.00
MEAN LOW WATER ELEV = 100.00
PROP EROSION
CONTROL
FABRIC -JUTE
BURLAP
GEOTEXTILE FABRIC
ORDINARY BORROW
FIGURE 6
E: 10829.08 \reports \Rgure— Sectlon.dwg