HomeMy WebLinkAbout20140193 Ver 1_MP_2015_REVISED PAGES ONLY_20151028
Henry Fork Mitigation Site
Final Mitigation Plan Page 23
each model was run for a 65‐year period from January 1949 through December 2013 using temperature
and precipitation data collected from the stations outlined above.
5.3.1.4 Modeling Results and Conclusions
DrainMod was used to determine the effect of proposed practices on site hydrology for wetland areas 1
and 2 (Figure 9). Groundwater gages 1 and 2 were used to analyze hydrology within Wetland 1 and
groundwater gages 4, 5, and 6 were used to analyze hydrology within Wetland 2. For the purpose of
establishing a preliminary model‐based attainment standard, an 80% success rate was identified as an
appropriate break point for the proposed wetland areas. In other words, the preliminary attainment
standard was chosen at the point at which on average all gages would meet the standard a minimum of
80% of the model years (52 out of the 65 years simulated). Model simulations were run starting at a 5%
consecutive standard. The consecutive standard was then increased by approximately ½ percent
increments in subsequent model runs to determine at what attainment standard the proposed wetland
areas would meet the minimum success rate (80% of modeled years). This approach suggests that a
7.2% hydroperiod would be appropriate attainment standard based on modeled input. During project
review, a higher project performance standard of 8.5% was agreed to with the understanding that this
standard would be a trend exhibited by most gages in most years, and not a uniform standard applied to
all gages in all years. The higher standard is expected to be achievable based on the influence of surface
flow which is not adequately accounted for in model behavior. While other models were investigated,
DrainMod was deemed the most applicable. The modeling analysis and predicted well performance
based on DrainMod is described below.
The model‐based wetland attainment standard used to evaluate site hydrology was that the water table
must be within 12 inches of the ground surface at each gage for a minimum of 7.2% (17 consecutive
days) of the 236‐day growing season (March 20 through November 11). The growing season was
determined from the long‐term records from the National Weather Service provided in the WETS table
for the Hickory Regional Airport. Each gage location was evaluated to determine success rates for the
established performance standard. Table 10 presents model results and depicts the number of years out
of the 65‐year monitoring period that each gage is expected to meet the model‐based target
hydroperiod.
Gages 4, 5, and 6 all have modeled hydroperiod attainment rates at or below 15% of modeled years,
based on the existing site conditions. After the incorporation of the proposed site changes including
raising stream bed elevations, re‐aligning stream channels, and grading to lower ground surface, all
three gage attainment rates increase to over 90% of the modeled period.
The existing conditions modeling results show that gages 1 and 2 currently only meet the attainment
standard approximately 37% of the modeled period. These results align with site observations. The
areas near gages 1 and 2 are rarely ponded, show borderline hydric formations within overburden
material, and are adjacent to some areas which are currently jurisdictional. By incorporating proposed
site changes to the model, the modeled hydroperiod attainment rates for gages 1 and 2 increase by 25%
and 49% of modeled years, respectively. While the 80% minimum is not met for Gage 1, this is
attributed to its location along the boundary of the re‐establishment area. In addition, Gages 2, 4, 5, and
6 greatly exceeded the performance standard success rate of 80%.
Based on these model results it is anticipated that the proposed site changes will increase water table
elevations and inundation periods within wetland areas 1 and 2. The associated hydrologic uplift will
result in the re‐establishment of wetland function and development of hydric soils.
Henry Fork Mitigation Site
Final Mitigation Plan Page 35
originally proposed as part of the proposal, subsequent investigations have yielded a substantial acreage
of existing wetlands, most of which are biologically affected by prior deforestation and maintenance of
golf course vegetation. Planting these wetlands is a valuable activity to enhance habitat and water
quality through establishment of a forested canopy. This intervention is warranted given their current
condition, and should be credited at an enhancement level. Wetlands that are already forested have not
been included for enhancement and will be preserved to the extent that they lie within the easement
area.
A credit ratio of 1:1 is proposed for the re‐establishment work on site due to the significant
improvement to wetland functions proposed related to hydrology, soils, and vegetation. Fills soils will be
removed to near the level of the buried topsoil and hydric horizons. A detailed soil boring grid was used
to identify areas of non‐hydric overburden that will be removed to uncover wetland soils. Due to history
of the site as a golf course, is it recognized that floodplain manipulation was drastic on the site and
wetlands were filled and drained to create associated infrastructure for the golf course. In addition to
adding drainage ditches to remove water from wetland areas, large amounts of fill material were added
to fairways, greens, and tee boxes in an effort to dry out wetland areas for use as a golf course.
Hydrology will be restored to wetland areas by plugging ditches and raising adjacent stream channels
that currently have a draining effect on the area. Restored streams will have appropriate cross section
dimension and bank height to allow for frequent overbank flooding of riparian wetland areas. Invasive
species will be removed and a riparian wetland vegetation community will be established. This
vegetation community will support habitat and will also provide shade for cooling of surface water and
groundwater recharge sources. The proposed re‐establishment work will address the floodplain
manipulation and will result in a gain of aquatic resources in both area and function.
A credit ratio of 1.5:1 is proposed for the rehabilitation work on site due to significant improvement to
wetland functions as a result of positive improvements to site hydrology, soils, and vegetation. Fill soils
will be removed and the original hydric soils reestablished as the hydric horizon. Wetland hydrology will
be enhanced and restored to wetland areas by raising adjacent stream channels that currently have a
draining effect on jurisdictional wetlands, and by reducing the elevation of the wetlands by removing
overburden. The stream channels will be restored to an appropriate cross section dimension to allow for
frequent overbank flooding of riparian wetland areas creating a stream‐wetland interaction that is not
present under current conditions. Invasive species will be removed and a riparian wetland vegetation
community will be established. This vegetation community will support habitat and will also provide
shade for cooling of surface water and groundwater recharge sources.
A credit ratio of 2:1 is proposed for wetland enhancement work on site to recognize the restoration of
native vegetation and a forest canopy, as well as treatment of invasive species. This vegetation
community will support habitat and will also provide shade for cooling of surface water and
groundwater recharge sources.
DMS reserves the right to request additional wetland credits created by the project. If applicable,
potential wetland credit generating areas will be identified early in the monitoring process, and gaged to
record data in order to be able to demonstrate that performance standards are met over the remainder
of the monitoring period.
Henry Fork Mitigation Site
Final Mitigation Plan Page 58
12.1.5 Bankfull Events and Intermittent Stream Hydrology
Two bankfull flow events must be documented on the restoration and enhancement reaches, within the
seven‐year monitoring period. The two bankfull events must occur in separate years. Stream monitoring
will continue until success criteria in the form of two bankfull events in separate years have been
documented.
Adequate hydrology for intermittent streams must be documented. Direct measurements of
continuous interval stream flow data will be made with a gage. The flow regime should indicate
sufficient flow to maintain an Ordinary High Water Mark (OHWM), specifically a minimum of 30
consecutive days of flow during periods of normal rainfall. Photographic evidence of streamflow
coupled with rainfall gage data from the project site will be used to help support this assessment.
12.2 Vegetation
The final vegetative success criteria will be the survival of 210 planted stems per acre in the planted
riparian and wetland areas at the end of the required monitoring period (year seven). The interim
measure of vegetative success for the site will be the survival of at least 320 planted stems per acre at
the end of the third monitoring year and at least 260 stems per acre at the end of the fifth year of
monitoring. Planted vegetation must average 10 feet in height in each plot at the end of the seventh
year of monitoring. If this performance standard is met by year five and stem density is trending
towards success (i.e., no less than 260 five year old stems/acre), monitoring of vegetation on the site
may be terminated provided written approval is provided by the USACE in consultation with the NC IRT.
It is anticipated that Chinese privet from the adjacent areas to the west could migrate onto the site; this
will be closely monitored. Invasive species treatment will be conducted in the mitigation area during the
7‐year monitoring period as needed to ensure the hydrologic and ecologic success of the project.
12.3 Wetlands
The preliminary wetland performance standard used to evaluate site hydrology is that the water table
must be within 12 inches of the ground surface at each gage for a minimum of 20 consecutive days
(8.5%) of the 236 day growing season (March 20 through November 11) for Catawba County. The
process used to model and assess wetland performance is outlined in Section 5.3.1.4 of this report. The
growing season was determined from the long‐term records from the National Weather Service
provided in the WETS table for the Hickory Regional Airport and may be evaluated at the project site
during the monitoring period using soil temperature loggers in order to base growing season on the
measured data.
12.4 Visual Assessments
Visual assessments should support the specific performance standards for each metric as described
above.
13.0 Monitoring Plan
Using the DMS Baseline Monitoring Plan Template (version 2.0, 10/14/10), a baseline monitoring
document and as‐built record drawings of the project will be developed within 60 days of the planting
completion and monitoring installation on the restored site. Annual monitoring data will be reported
using the DMS Monitoring Report template (version 1.5, 6/8/12). The monitoring report shall provide a
project data chronology that will facilitate an understanding of project status and trends, population of
DMS databases for analysis, research purposes, and assist in decision making regarding close‐out. The
monitoring period will extend seven years beyond completion of construction or until performance
Henry Fork Mitigation Site
Final Mitigation Plan Page 59
criteria have been met per the criteria stated in the DMS Monitoring Requirements and Performance
Standards for Stream and/or Wetland Mitigation (11/7/2011). All survey will be tied to grid.
13.1 Site Specific Monitoring
Project monitoring requirements are listed in more detail in Table 22. Approximate locations of the
proposed vegetation plots and groundwater gage monitoring components are illustrated in Figure 11.
Table 22: Monitoring Requirements ‐ Henry Fork Mitigation Site
Parameter Monitoring Feature
Quantity/ Length by Reach
Frequency Notes
UT1 UT1A UT1B UT2 Wetlands
1 & 2
Dimension
Riffle Cross Sections 3 1 1 2 N/A Year 1, 2, 3,
5 and 7
Pool Cross Section 3 1 1 2 N/A
Pattern Pattern N/A N/A N/A N/A N/A N/A
1 Profile Longitudinal Profile N/A N/A N/A N/A N/A N/A
Substrate Reach wide (RW), Riffle
(RF) 100 pebble count
RW‐2,
RF‐2 N/A RW‐1,
RF‐1 N/A N/A N/A 2
Stream
Hydrology Crest Gage/ Transducer 1 1 1 1 N/A N/A 3
Wetland
Hydrology Groundwater Gages n/a n/a n/a n/a 7 Quarterly
Vegetation CVS Level 2 15 Year 1, 2, 3,
5 and 7 4
Exotic and
nuisance
vegetation
Annual 5
Project
Boundary
Annual 6
Reference
Photos Photographs 29 Annual
Notes:
1. Pattern and profile will be assessed visually during semi‐annual site visits. Longitudinal profile will be collected during as‐built
baseline monitoring survey only, unless observations indicate lack of stability and profile survey is warranted in additional years.
2. Riffle pebble counts will be conducted on UT1 Reach 1 upper and lower cross sections only, but not on UT1 Reach 2.
3. Crest gages and/or transducers will be inspected quarterly or semi‐annually, evidence of bankfull events will be documented with
a photo when possible. Transducers will be set to record stage once every hour or more frequently if deemed necessary. Device
will be inspected and downloaded semi‐annually. Transducers will be used on intermittent streams to evaluate flow regime.
4. 13 plots were required based on the 14.9 acres to be planted within required project stream buffers and wetlands. An additional
2 vegetation plots have been added within the 100‐foot planting buffer on Henry Fork.
5. Locations of exotic and nuisance vegetation within the conservation easement area will be mapped. Chinese privet or other exotic
invasive vegetation migrating into the project area will be treated as needed with cut and treat or other suitable methods.
6. Locations of vegetation damage, boundary encroachments, etc. will be mapped.
Henry Fork Mitigation Site
Final Mitigation Plan Page 62
reference wetlands to assess whether atypical weather conditions occurred during the monitoring
period.
13.4 Visual Assessments
Visual assessments will be performed along all stream and wetland areas on a semi‐annual basis during
the seven year monitoring period. Problem areas will be noted, such as channel instability (i.e. lateral
and/or vertical instability, in‐stream structure failure/instability and/or piping, headcuts), vegetated
health (i.e. low stem density, vegetation mortality, invasive species or encroachment), beaver activity, or
livestock access. Areas of concern will be mapped and photographed, accompanied by a written
description in the annual report. Problem areas will be re‐evaluated during each subsequent visual
assessment. Should remedial actions be required, recommendations will be provided in the annual
monitoring report. Invasive species occurrences, including Chinese privet migrating into the site, will be
documented and treated with cut and treat, or other adequate removal methods.
14.0 Long‐Term Management Plan
The site will be transferred to the NCDENR Division of Natural Resource Planning and Conservation’s
Stewardship Program. This party shall be responsible for periodic inspection of the site to ensure that
restrictions required in the conservation easement or the deed restriction document(s) are upheld.
Endowment funds required to uphold easement and deed restrictions shall be negotiated prior to site
transfer to the responsible party.
The NCDENR Division of Natural Resource Planning and Conservation’s Stewardship Program currently
houses DMS stewardship endowments within the non‐reverting, interest‐bearing Conservation Lands
Stewardship Endowment Account. The use of funds from the Endowment Account is governed by North
Carolina General Statue GS 113A‐232(d)(3). Interest gained by the endowment fund may be used only
for the purpose of stewardship, monitoring, stewardship administration, and land transaction costs, if
applicable. The NCDENR Stewardship Program intends to manage the account as a non‐wasting
endowment. Only interest generated from the endowment funds will be used to steward the
compensatory mitigation sites. Interest funds not used for those purposes will be re‐invested in the
Endowment Account to offset losses due to inflation.
The Stewardship Program will periodically install signage as needed to identify boundary
markings. There are no livestock, or associated fencing, to maintain. There are no permanent crossings
or other site features that will warrant long‐term maintenance.
15.0 Adaptive Management Plan
Upon completion of site construction, DMS will implement the post‐construction monitoring protocols
previously defined in this document. Project maintenance will be performed, as described previously in
this document. If, during the course of annual monitoring, it is determined the site’s ability to achieve
site performance standards are jeopardized, DMS will notify the USACE of the need to develop a Plan of
Corrective Action. The Plan of Corrective Action may be prepared using in‐house technical staff or may
require engineering and consulting services. Once the Corrective Action Plan is prepared and finalized
DMS will:
Notify the USACE as required by the Nationwide 27 permit general conditions;