Larson Design Group Choconut Assessment
for Choconut Creek Watershed Association
Funded by Pennsylvania Growing Greener Grant
Draft Choconut
Creek Wetland Investigation
Introduction
Choconut
Creek experiences high flow events that result in significant bank erosion and
flooding. At several points along the
mainstem, the creek currently overflows its banks and flood waters travel in
old overflow channel in the floodplain.
However, the floodplain has been altered by residential, agricultural,
commercial, and road encroachment. The
members of the watershed association have identified the flooding issue as one
of their primary concerns. One
possible solution to reducing the flood volumes is to create additional wetland
areas in the floodplain. There are
numerous wetlands throughout the watershed, some of which currently offer some
flood flow attenuation. In addition to
flood storage, wetlands enhance water quality and
provide habitat for a wide variety of organisms. The purpose of this investigation was to
document the existing major wetland areas in the watershed and identify areas
for potential wetland expansion.
Wetlands were identified with aerial photography and locations verified
with fieldwork. The wetland maps
presented in this section, were developed based on
aerial photography. The wetland
boundaries drawn on these maps do not represent a jurisdictional determination.
Rather, the boundaries indicate major
wetland areas in the study area. The
mapping includes other medium size wetlands that may not be discussed in detail
in this report. There are numerous small
spring seeps or other wetland pockets that were not sketched on the map. The primary investigation area focused on the
mainstem valley floor since this area offers the greatest potential for wetland
expansion. Most of the tributaries in
the
Potential
wetland enhancement/creation sites have been identified as part of this field
investigation. The identified sites have
been prioritized based on depth of excavation, available acreage, access,
likelihood of successful flood attenuation.
Wetland areas identified with an “A” have the highest potential, “B” wetlands have
moderate potential, and “C” wetlands may encounter the most difficulty in
construction or are smaller areas. However,
all of the sites are viable replacement areas.
Prior to
development of detailed replacement wetland designs several issues need to be
addressed. A detailed delineation of the
existing jurisdictional wetlands must be completed to accurately identify the
wetland boundary. A detailed topographic
survey must be completed to located the wetland boundary and establish accurate
elevations for development of a grading plan.
Backhoe test pits should be excavated within the chosen replacement
wetland area to determine depths of ground water for development of the wetland
creation grading plan.
Existing Wetland Descriptions
General
wetland protection notes: All wetlands
should be protected from disturbance to the greatest extend possible. If landowners are willing, wetlands should be
fenced out of pastures and not mowed to allow for development of woody
plants. Woody plants within the
floodplain provide greater soil erosion protection, increased roughness coefficient,
and improved stream shading. Some of
these benefits can also be realized from the development of riparian upland
forest buffers.
Riparian floodplain areas along the mainstem.
Main hydrology sources appear to be spring seeps, high groundwater, and
overland flow during flood events.
1.
2. Near the
3. Doolittle’s property. This wetland is located on the west side of
valley bottom along the stream. It is
comprised primarily of riparian scrub/shrub with speckled alder. The area appears to have some pasture
activity. Area C1 is active pasture.
Typical dominant plant species include:
speckled alder, willow, soft rush, sedges, reed canary grass. There are low chroma
mineral soils. The area receives
hydrology from hillside seeps to the east (across the road/behind the house),
discharge from the pond area, and an elevated water table within the
wetland. Expansion area B2 and C1 are
associated with this system. This
wetland is approximately 16.87 acres. Photos 6,7.
4. Near
the trailer park. The wetland is
east/northeast of the trailer park on east side of valley along base of
hill. There is a hayfield between the
wetland and the trailers. There is a
spring seep emerging from north side of access road and along base of hillside. The southern half of the wetland is wetter,
the northern half is dryer. PEM system dominated by sedges, cattails, sensitive fern, sweetflags, and willow. Northern half plant community is dominated by
sedges and goldenrod. A road travels
from main road to stream and bisects the wetland. There is probably a ford in stream and it
continues to house on western hillside. There is no evidence of grazing in the
area and the wetland is in good shape.
This wetland is approximately 6.06 acres. Photo 8.
5. Upstream of the school at the confluence of
the
6. Across from Rounds Propane Company. This is a mosaic of spring seeps and hummocky
topography, with emergent wetland species and old field communities throughout
a floodplain meadow. This wetland system
spans the entire valley width. It is
comprised primarily of riparian emergent plants with some shrub/scrub in the
drainage areas. The typical dominant
plant species include: soft rush,
sedges, reed canary grass, sensitive fern, and cattails, with speckled alder
and willow in the drainages. There are
low chroma mineral soils. This wetland receives hydrology from hillside
seeps that ultimately discharge into the main channel. Expansion areas A3 and B3 are associated with
this system. This wetland is
approximately 22.54 acres in overall size with numerous small upland
inclusions. A detailed delineation of
these upland inclusions may prove to be beneficial if wetland expansion work is
to occur. This may provide additional
acreage suitable for wetland creation
7. Located downstream of
8. Located in large meadow on the State
Line. It is comprised of riparian
emergent wetland species dominated by soft rush, sedges, and reed canary grass. The area contains low chroma
mineral soils. This wetland includes a
hillside seep as well as several seeps within the valley floor that discharge
into the main channel. Expansion areas
B4 and C3 are associated with this system.
This wetland is approximately 7.88 acres. Photo 16 looking northwest.
Wetland Expansion Areas
A Priorities
Top
priority areas because:
1. They are
currently considered upland areas
2. They are adjacent to existing wetlands
3. They are positioned within the floodplain
and/or there is evidence of recent flood debris
4. There is enough land to construct several
acres of wetlands
Drawbacks
1. All areas appear to be active hayfields, PC?
2. Excavated material will need to be hauled off
site
3. Landowner interest is unknown
A1 Flaharty site. This is a large hay field with the main
channel along the eastern and southern side.
There is a small tributary that has been ditched on the west side of the
field along the base of road bank. There is a seep in the north central section
of the field. There is fairly uniform
topography throughout the area. Photos 4,5.
Expansion
issues:
1. This site is at the confluence of the two
main tributaries in the upper Choconut Creek watershed. This would allow flood waters to be detained
in the upper watershed.
2. It would require shallow excavation of the
hayfield between the two channels, which could incorporate the mid-field
seep. There is good access for
construction equipment. Consider
constructing a high flow inlet downstream of the barn and discharge to the
creek by the bridge.
A2, Fields upstream of the elementary school. This area is a hayfield with a PEM wetland
finger bisecting the field, expansion areas could be
located around the existing wetland finger.
The soil profile was observed along the cut bank of the stream.
Expansion
issues:
1. This area can incorporated flood flow
2. Shallow excavation, 2-3 feet should expose
low chroma soils and high groundwater.
3. Could incorporate an upstream overflow
channel.
4. Could remove low dike along tributary so the
water has access to the floodplain at the school baseball field.
5. Access may be an issue
A3, the north end of study area, adjacent to Wetland
#6. This site is positioned between the wetland
and Choconut Creek. The site consists of
a mowed hayfield. There is a flood
overflow channel with recent debris on the western edge of the hayfield which
enters the scrub/shrub wetland finger. Photo 13.
Expansion
issues:
1. Access to remove excavated any material will likely
require wetland crossings.
2. Approx. 2 to 3 ft of excavation.
3. Could potentially yield several acres of
wetlands as an expansion of the existing large wetland system already
present.
B Priority
Criteria
1. Smaller acreage than the “A” sites
2. Will
require deeper excavation
3. There is less evidence of recent flood debris
B1,
B2, Doolittle property.
This is an active hayfield on the eastern side of the valley
bottom. There is a scrub/shrub wetland
on the northwest side and an emergent community along the ditch on the east
side of area. There is no evidence of
recent flood debris and the area may require deeper excavation. However there is good road access.
B3,
across
from Rounds Propane. Part of area near
Route 267 is staked out for a lot. This
expansion area would be immediately north of Wetland #6. There is a tributary entering from the east
just downstream of this site. The
tributary appears to have high volume during flood events as the mouth is wide
and scoured. There is a small elevated
floodplain along eastern bank of the mainstem with willows and red maple. It has evidence of flood debris. This wetland creation may not intercept
mainstem floodplain flows. However, sidehill seeps near the propane company can be intercepted
and attenuated. The northern end of this
site could be designed to intercept flow from both the tributary and
mainstem. An elevated wetland bench
could be created downstream of the tributary on the eastern side of the
channel. It is also a possibility to
expand further east into the hayfield. This section of mainstem channel near
B4,
near the
state line. This site is at the north
end of the project area. It is south and
west of a new pond built behind the tall wood sided house. This replacement area is part of a large open
field associated with wetland #8 and there is recent flood debris in the
field. This site is positioned close to
Route 267. Access for fill removal is
good. It may require deeper excavation
than other expansion areas. There may be
a stability issue as there is already evidence of flood waters flowing in this
area. There is concern that stream
channel may relocated into the newly created wetland if excavation is too deep
and occurs too close to the existing channel.
Photos 17 and 18.
C Priority
Criteria
1. Deeper excavation required
2. Even smaller acreage
3. Access issues
C1,
across
from Doolittle’s. This site is adjacent
to the streamside wetlands on western edge of field. It is an active pasture area with a newly
constructed fence. The existing wetland
forms a semi-circle on northern end of area.
There are concerns about stream stability and stream channel relocating
into an excavation area. However this
area would be an obvious expansion of the PSS and it had lots of recent flood
debris.
C2,
Large
hayfield downstream of school. There is
a small section of dike along the field on downstream side of bridge. There is excellent access at this site. There is an old overflow channel within field
but no recent debris. This area is
higher than the other sites and would require deeper excavation. The western edge
of site along corn field is higher in elevation. The expansion could be concentrated along the
old channel (not as much excavation needed).
There is a newer upslope diversion ditch west of the cornfield that has
cut off upslope runoff to floodplain. The streambanks are
2 to 3 ft. high at the lower end of the field, providing access for flood flow
into the potential wetland. Photo 11.
C3,
near the
state line. This area
in at the north end of study area, behind the tall wood-sided house. The site is part of a large mowed field,
associated with wetland system #8 and near expansion area B4. This expansion area is at the western end of
the field near creek. The concern in
this area is the stability of stream channel and the possible relocation into
newly excavated wetland. Photo 17.
Headwater ponds – There are several small seeps
noted higher in the watershed. Consider
“gully plugs” to create wet bottom ponds with large storage capacity to
attenuate floodwaters. Discuss in land
use section.
