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Report, CBCL Limited, November 2010. Because of further detailed development of the
compensation design proposal, information presented here should supersede information
previously presented in Chapter 5 of the earlier report.
1.2 Overall Compensation Project Any compensation project proposed for the study area would be subject to all regulatory conditions
set by the various levels of government reviewing the project. The compensation project includes
seven components:
a) Crown purchase and protection of 11.3 ha of wetlands and 13.7 ha of riparian buffer adjacent to
the Antigonish Wildlife Management Area;
b) Bank stabilization work by Unlimited Habitat and DFO on the West River;
c) Proposed bank stabilization by NSTIR on the Rights River (adjacent to the Antigonish Landing
Trail);
d) Restoration of approximately 10.8 ha of tidal-influenced wetland habitat;
e) Creation and enhancement of approximately 4.8 ha of wetland habitat;
f) Development of a 765 m interpretive walking trail; and
g) Invasive Alien Plant Program being conducted by the Nova Scotia Agricultural College (long-term
applied research program to determine optimal control of Japanese knotweed).
Figure A - Existing Habitat and Wetlands, presents the various habitats within the Study Area. Figure
B illustrates the concept for the proposed compensation project.
1.3 Study Area - North and South Compensation Sites The study area, for ease of discussion, has been divided into the North Site and the South. The
North Site is more tidal influenced than the South Site. The South site experiences more ice scour
during the winter than the North Site.
Nova Scotia Department ofTransportation and
Infrastructure RenewalAntigonish Wetland
Compensation Project
Ri g
h t s Ri v e
r
We s t R i v e r
Antigonish WildlifeManagement Area
Cape Breton & Central Nova Scotia Railway
N-1AML-1
N-2
S-1
S-7
S-9
S-3
S-2
S-5
S-10
S-4
S-6
S-8
S-11
0 50 10025 Meters
[
Notes:
Date Saved: 30/09/2011 3:33:29 PM
Coordinate System: NAD 1983 CSRS UTM Zone 20NProjection: Transverse MercatorDatum: North American 1983 CSRSFalse Easting: 500,000.0000False Northing: 0.0000Central Meridian: -63.0000Scale Factor: 0.9996Latitude Of Origin: 0.0000Units: Meter
Proposed Armor Stone BankStabilization, Constructed
by Others
Culvert 2Installation Done
by Others
Culvert 1Installation Done
by Others
Culvert 3Installation Done
by Others
Armor Stone BankStabilization, Constructed
by Others
0 50 10025 Meters
[Date Saved: 30/09/2011 3:37:31 PM
Coordinate System: NAD 1983 CSRS UTM Zone 20NProjection: Transverse MercatorDatum: North American 1983 CSRSFalse Easting: 500,000.0000False Northing: 0.0000Central Meridian: -63.0000Scale Factor: 0.9996Latitude Of Origin: 0.0000Units: Meter
(Culvert 2; approximately 2 m wide) and extending the existing channel to connect the two culverts
would further restore the flushing of the wetland and fish habitat. Including open water areas
(ponds) within the new channel section will restore open water habitat for wildlife. Placement of a
third culvert (Culvert 3; 1.2 m) under the Landing Trail and a connecting channel back to Culvert 2
would reconnect Wetland N-2 to Wetland N-1. Two large open-water ponds on either side of
Culvert 3 will also restore and enhance diversity in both Wetland N-2 and N-1. Overall, wetland
compensation will provide a total of 10.8 ha of restored, tidal-influenced wetland habitat. NSTIR
proposes to carry-out this work during October 2011 to March 2012 (October-November 2011 for
the three culverts with excavation work for ponds and channels during winter, frozen-ground
periods).
While NSTIR have chosen to pursue the design of the culvert installations, the attached drawings
present the design for the proposed channels, ponds and wetland fringes for the North Site. Further
discussion about the wetland design is described below. 1.4.2 AML-1 Wetland Characterization Wetland AML-1, which lies on lands owned by the Asset Management Ltd., is the western portion of the much larger wetland N-1. AML-1 comprises 2.43 ha of wetland habitat consisting of Treed Fen/ Swamp, Shrub Swamp and Wet Meadow. A significant portion of the wetland AML-1 is a mixed-wood treed fen with peat deposits in excess of 1.22 m (48”). These deposits support a mature stand of trees dominated by red maple with lesser amounts of black spruce and tamarack and a diverse shrub and herbaceous understory. The southeastern tip of AML-1 is comprised mainly of shrub swamp (dominated by speckled alder and red maple) and wet meadow (dominated by reed-canary grass with lesser amounts of cattails and various sedges), both of which extend onto the NSTIR portion of the wetland (See Figure A). In the westernmost portion of the wetland, the deep peat deposits yield to a mineral soil substrate supporting a dense growth of speckled alder. AML-1 is receiving a modest amount of inflow via a drainage corridor at the northern tip, adjacent to the large area of fill along the property’s border with Bay St. It is assumed that the wetland is receiving significant groundwater discharge from the base of Mt. Cameron, as well as surface water runoff from Mt. Cameron and the lots along both Adam and Bay Streets. A significant drainage ditch has been excavated along the southern boundary of the property, which presumably collects water from the various gravelled lots along Adam St. There is no distinct watercourse leading through the wetland, however an existing tidal-influenced channel does eventually form down-gradient on the NSTIR lands, at the toe of slope to Mt. Cameron. Sampling within the wetland showed the water table to be between 150 mm and 400 mm below surface. Surface water was observed at many locations throughout the wetland. The wetlands location at the fringe of the Rights River floodplain suggests that portions of it may occasionally be inundated with floodwaters during extreme storm or tidal events. No species of conservation concern were encountered during the survey, although no exhaustive inventory surveys for flora and fauna were conducted for the purposes of this delineation. It is known that the adjacent NSTIR portion of the wetland (N-1) is fairly biodiverse in terms of flora and fauna, and does contain the uncommon species coffee-tinkers weed (Triosteum aurantiacum). It is very likely that the downgradient portion of wetland N-1, which is tidally influenced and contains a distinct channel, is fish habitat. As such, the upgradient portions of N-1 and AML-1 may be important in maintaining water quality/quantity for this area. Overall, it is considered that wetland
AML-1 is relatively rich in terms of its habitat value, due to its structural diversity and proximity to N-1 and the Antigonish Wildlife Management Area.
1.5 The South Site – Wetland Enhancement
1.5.1 Rationale and Design
The South Site is defined by the Rights River to the north and the West River to the south. The Cape
Breton and Central Nova Scotia Railway (CBCNSR) further defines the northern boundary of the area
of enhancement for purposes of construction logistics, access and safety. The South Site is largely a
floodplain that is manicured seasonally by ice scour, caused mostly from ice coming from the Rights
River. As a result, there are very few stands of riparian trees on the floodplain. Historically, the
Rights River has been realigned and channelized to help the Town reduce the risk of flooding each
spring. Over time, the floodplain of the South Site has been largely used for agricultural purposes.
There are no current activities on site today. However, recent activities left behind remnants of haul
roads used to harvest topsoil. Topsoil harvesting occurred up until quite recently in the site’s
history. This practice created depressions within the landscape that, left alone, appear to be
groundwater charged and capable of sustaining wetland vegetation and other wetland processes.
Field work demonstrated that digging a soil pit in tight clay loam soils down to gravels (no greater
than a metre) would typically cause water to fill the pit to within a few centimetres of the surface.
A matrix of nine, small (300 square metres +/-) and isolated, freshwater wetlands were identified
south of the CBCNSR. These wetlands, together, occupy a total of 0.65 ha. Most of these are slight
impressions on the floodplain as a result of topsoil harvesting. Described as Wet Meadow wetlands,
their plant communities generally consist of Phalaris, Juncus, Scirpus and Carex species. Very little
open water exists on the South Site.
Wetland compensation on the South Site will be achieved through the enhancement of the wetland
matrix by connecting the individual wetlands together. Enhancement would involve creating
shallow, open water ponds and depressions within the floodplain adjacent to the existing wetlands,
similar to what is currently observed on site. Ponds and depressions would be carefully graded to
address critical water elevations and plant communities. The wetland compensation would provide
a total of 4.8 ha of enhanced wetland habitat. Wetland enhancement is intended to boost the
ecological integrity of the South Site and provide habitat for waterfowl, herpetiles (amphibians and
reptiles) and aquatic biota. This work is planned for Summer 2012.
1.5.2 Trail System
Project compensation also proposes developing a soft-surface interpretative walking trail on the
South Site. Approximately 765 m in length, the trail would be raised above the landscape no greater
than 200 mm to reduce any impediment to flooding. Useable excavation from the wetland
enhancement project would be used to build the shallow berm onto which the trail would be set.
Excess material would be strategically placed in and around the wetlands to create relief and
moisture gradient regimes necessary for increasing plant and animal species diversity. Figure C
provides a sketch showing the transition from existing conditions to enhanced conditions on the
South Site. NSTIR will work with NSE and NSDNR to develop appropriate educational signage for
placement along both the existing and new interpretive trails.
1.6 Detailed Design for Ponds, Channels and Wetland Vegetation The proposed compensation effort includes a total of six ponds and wetland habitat areas to be
constructed on the North Site and three more to be built on the South Site. The attached drawing
set provides the detailed design for the various wetland compensation components. The design of
the ponds is intended to maintain a central open water area, free of vegetation. The open water
area will be surrounded by different plant communities, depending on their moisture regime.
Design of gradual side slopes (20 percent) around the ponds is to allow a broad moisture gradient at
the edge that will encourage the establishment of a greater diversity of wetland plant species. Side
slopes are designed to be steeper closer to the center of the ponds. This is also designed for safe
approach purposes. As depicted in the drawing set, for both the North Site and South sites, three
planting zones within the wetland
will be established for most ponds:
fringe (water depth < 150 mm),
shallow water (water depth < 300
mm) and deep water (< 1500
mm). Open water habitat
(unplanted) will be controlled
through depth of water. In this
instance ponds will have a
maximum depth of 2,000 mm.
Berms, created using the
excavated materials will have a
maximum height of 1,500 mm
with side slopes of 33 percent and
would provide opportunity for the
establishment of upland plant
communities. Other species
identified will be best suited to
revegetating the floodplain
around the wetland matrix on the
South Site.
Table 1.4 presents a list of possible
plant species selected for
colonizing the various wetland
ponds and berms within the North
and South sites. This list is largely
developed from species observed
in the local area. Plantings are
listed as upland, wetland/ pond
fringe, shallow water and deep
water, for purposes of placement
in design. Final selection of
plantings will be based on
availability and substitutions may
be likely.
Figure C: Showing wetland enhancement on the South Site
The monitoring program for the North Site is presented in Table 1.5. This program is based on
experience gained by CBWES at seven other salt marsh monitoring sites in Nova Scotia and many
other investigators in the eastern US – Gulf of Maine area, i.e., the Global Program of Action
Coalition for the Gulf of Maine Regional Monitoring Protocols (also known as the GPAC protocols).
Table 1.5: The Antigonish Landing Tidal Marsh (North Site) Restoration monitoring program including core and additional ecological indicators, methodologies, and sampling frequency (annual application indicated by X – completed; Y – Future sampling event)
Category Parameters Sampling Method
Annual Sampling Frequency
Baseline (2010)
Post-Construction (2012-2016)
1 2 3 4 5
Hydrology
Tidal Signal Continuous (five minute intervals) water level recorders (Solinst Levelogger (Model 3001).
Minimum three week period, once per required sampling year. Baseline sampling occurred 7/9/10 to 5/10/10 & 19/10/10 to
To: Clinton Pinks CBCL Ltd. Re: Antigonish Landing North – Tidal Restriction Analysis and Flood Mapping.
Dear Mr. Pinks: Please find enclosed a copy of the tidal restriction analysis and flood mapping for the Antigonish Landing North Site as part of the NSTIR – Antigonish Wetland Compensation Project (baseline inventory report). Part I: Antigonish North Site – Tidal Restriction Analysis Part II: Antigonish North Site – Flood Map and Restoration Scenarios Sincerely,
Tony M. Bowron Director, Coastal Wetland Ecologist CBWES Inc.
Antigonish Wetland Compensation CBWES Inc.
Antigonish Landing North – Tidal Restriction Analysis and Flood Mapping 1
Part I: Antigonish North Site – Tidal Restriction Analysis
Dataloggers were installed upstream (within study site) and downstream (Rights River) of the main culvert (north end of Antigonish Landing North site) on 18 November 2010. Water level (elevation, mm) was recorded at five minute intervals between 18 November 2010 and 3 December 2010 in order to capture a spring and neap tide cycle. The maximum water level recorded during this period was ~ 1.5 m (Table 2). Water levels inside the study site were found to be, on average, 11.6 cm higher than downstream water levels. Part of this separation may be a result of survey error, however it is well within reasonable limits and not problematic in detecting a restriction. Comparison of the upstream and downstream water levels at high tide indicated both a spatial and temporal restriction of flow on recorded high tides greater than ~0.9 m (CGVD28). For this comparison the highest water level for each event (regardless of the timestamp) was selected. Not all high water levels were recorded at the same time in a given event due to a temporal delay in peak tide. Most tides exceeding ~0.9 m showed a delay in peak tide ranging from 5 to 25 minutes. The largest delay occurred on 19 November 2010, where peak tide was delayed by 25 minutes (water level within the study site continued to rise and peaked 25 minutes after the recorded peak downstream). The tide signals for the study site (upstream) and river (downstream), as well as associated statistics, are presented in Figure 1 and Table 1, respectively. The difference in tide height (upstream minus downstream tide height) is also provided in Figure 1 at each time step. The highest recorded tide (1.5 m), occurring on the 24 November 2010, and experienced a 15 minute delay in peak tide within the study site. A drop in the water level deficit on this date immediately prior to high tide and a rise immediately following, supports a delay in peak tide in the study area and a delay in ebb, with flows in the river rising and dropping more rapidly than in the study site. Peak tide was 9.7 cm higher in the study site than in the river, indicating that although there was a significant temporal delay, loss of tidal prism was probably not significant on the recorded tides. Although loss of tidal prism was not significant on the recorded tides, higher tides (greater than the recorded 1.5 m) which may be anticipated due to the Saros tidal cycle, sea level rise, and storm events (storm surges; increased freshwater input) may be significantly restricted. Best fit correlation (Figure 2) of upstream versus downstream high tide heights was used to predict the level of restriction under current crossing conditions as well as under unrestricted conditions, and is shown in Table 2. The degree of restriction was calculated up to a tide height of 2.1 m, based on the current highest recorded event plus the estimated 100 years of sea level rise at 70 cm/century, the minimum predicted rate for Nova Scotia1. It should be noted, however, that this approach is only valid to the elevation of the current trail (road) (~1.7 m). Any tidal event with a water elevation greater than 1.7 m would overtop (flood) the trail, making the culvert restriction irrelevant. A storm surge, which could add up to an additional meter in water elevation, would also lead to overtopping of the trial under both current and predicted conditions regardless of any
1 The State of Nova Scotia’s Coast: Technical Report. 1998. www.gov.ns.ca/coast/documents/report/Coastal-Tech-Report-Chapter7.pdf
Antigonish Wetland Compensation CBWES Inc.
Antigonish Landing North – Tidal Restriction Analysis and Flood Mapping 2
restoration efforts made at this site. Increasing the crossing size would, however significantly improve flushing of the system following a large flood event, thereby decreasing residency time for flood waters within the site, reduce flood risk of adjacent properties, and significantly improve fish passage and the transport of materials into and out of the restoration site. Figure 1 Tidal signal for the Antigonish Landing North Restoration (study) site and Right’s River, for the period of 18 November to 3 December 2010.
Table 1 Tidal signal statistics.
STAT DS (m) US (m) US/DS Deficit Min water level 0.06 0.06 0.003 Mean water level 0.61 0.73 0.116 Mean high tide 0.89 1.00 0.113 Max high tide 1.40 1.49 0.097 ST Dev 0.27 0.27 --
Antigonish Wetland Compensation CBWES Inc.
Antigonish Landing North – Tidal Restriction Analysis and Flood Mapping 3
Figure 2 Tide height (elevation) upstream versus downstream of the main culvert at the Antigonish Landing North Restoration Site.
Antigonish Wetland Compensation CBWES Inc.
Antigonish Landing North – Tidal Restriction Analysis and Flood Mapping 4
Table 2 Predicted tide heights within the study sites under current conditions up to 2.1 m downstream with tide height at 5 cm increments. Calculated using power function derived from correlation of recorded high tides (R2= 0.9999).
Antigonish Landing North – Tidal Restriction Analysis and Flood Mapping 5
Part II: Antigonish North Site – Flood Map and Restoration Scenarios
A flood map was produced for the Antigonish Landing North site based on the digital elevation model for the site and the recorded tides for the period of 18 November to 3 December 2010. Figure 3, Panel A shows the area flooded by the mean recorded tide (1.0 m) under current conditions (restrictive culvert). This mean tide level would be maintained even if a larger crossing was to be installed. The predicted flood pattern associated with the first restoration scenario – replacement of the north (primary) culvert with a larger crossing (minimum width of 3.5 m) in order to facilitate unrestricted tidal flow on the highest recorded tide (1.51 m) is depicted in Figure 3, Panel B. Hydrological conditions under a second restoration scenario involving unrestricted tidal flow through both the north and central (secondary) culverts (2 m opening), the creation of a tidal channel connecting the existing channel at the back of the site (base of hill) to the secondary culvert, and the excavation of two ponds on the marsh surface, is depicted in Figure 4, Panel B. Scenario two was produced using the recorded tide data and the full restoration design described in the Antigonish Wetland Compensation Proposal & Baseline Inventory Report. Restoration scenario two (Figure 4) is the preferred restoration option as it would result in the elimination of the tidal restriction; greater hydrological connectivity within the site and with the broader estuarine system; increased fish passage, habitat and access to the marsh surface; improved transport of materials, recharge and improved water quality in open water habitats within the site; and improve flushing of the site (reduced flood risk).
Antigonish Wetland Compensation CBWES Inc.
Antigonish Landing North – Tidal Restriction Analysis and Flood Mapping 6
Figure 3 Current hydrological conditions and restoration scenario one.
Antigonish Wetland Compensation CBWES Inc.
Antigonish Landing North – Tidal Restriction Analysis and Flood Mapping 7