ANNUAL REPORT FOR 2007
Southwest Creek Mitigation Site
Lenoir County
TIP No. R-2001B
Prepared By:
Natural Environment Unit & Roadside Environmental Unit
North Carolina Department of Transportation
January 2007
TABLE OF CONTENTS
SUMMARY...................................................................................................................... 1
1.0 INTRODUCTION.................................................................................................. 2
1.1 Project Description..................................................................................... 2
1.2 Purpose ..................................................................................................... 2
1.3 Project History ........................................................................................... 2
2.0 HYDROLOGY....................................................................................................... 4
2.1 Success Criteria......................................................................................... 4
2.2 Hydrologic Description............................................................................... 4
2.3 Results of Hydrologic Monitoring ............................................................... 6
2.3.1 Site Data ......................................................................................... 6
2.3.2 Climatic Data................................................................................... 6
2.4 Conclusions ............................................................................................... 6
3.0 VEGETATION .................................................................................................... 10
3.1 Success Criteria....................................................................................... 10
3.2 Description of Species ............................................................................. 10
3.3 Results of Vegetation Monitoring ............................................................. 10
3.4 Conclusions ............................................................................................. 11
4.0 OVERALL CONCLUSIONS/RECOMMENDATIONS.......................................... 11
LIST OF FIGURES
Figure 1. Site Location Map ........................................................................................... 3
Figure 2. Gauge Location Map....................................................................................... 5
Figure 3. 2006 Hydrologic Monitoring Gauge Results................................................... 8
Figure 4. 30-70 Percentile Graph ................................................................................... 9
LIST OF TABLES
Table 1. Hydrologic Monitoring Results.......................................................................... 6
Table 2. Hydrologic Monitoring Results (2003-2007) ...................................................... 6
Table 3. Vegetation Monitoring Statistics ..................................................................... 10
APPENDICES
APPENDIX A GAUGE DATA GRAPHS
APPENDIX B SITE PHOTOGRAPHS, PHOTO & PLOT LOCATIONS
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SUMMARY
The following report summarizes the monitoring activities that have occurred in the past
year for the Southwest Creek mitigation site. Monitoring activities in 2007 represent the
fifth year of monitoring for the site. The site must demonstrate both hydrologic and
vegetation success for a minimum of five years or until the site is deemed successful.
On May 15, 2003, two groundwater gauges, two surface water gauges, and one rain
gauge were installed to monitor the site for hydrologic success. One groundwater
gauge of the two in the forested wetland met the requirement for jurisdictional wetland
hydrology (12.5% of the growing season). Gauge GW-1 recorded hydrology for 17.6%,
while GW-2 recorded hydrology for 3.7% of the growing season. However, due to the
drought conditions that occurred in 2007, the site recorded below average rainfall. The
restored marsh gauge (SG-1) was comparable with the flooding patterns and inundation
periods from the reference marsh gauge (SG-2).
There were two vegetation monitoring plots established throughout the 2.9 acre planting
area. The 2007 vegetation monitoring of the site revealed an average tree density of
680 trees per acre. This average is well above the minimum success criteria of 240
trees per acre.
Base on five years of successful monitoring results, NCDOT recommends discontinuing
hydrologic and vegetation monitoring at the Southwest Creek mitigation site.
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1.0 INTRODUCTION
1.1 Project Description
The Southwest Creek mitigation site consists of two areas that serve as onsite
mitigation for the NC 11 Deep Run Bypass (Figure 1). The Southwest Creek site
includes approximately 43.1 acres of wetland preservation and approximately 3.61
acres of wetland restoration. The site consists of the former NC 11 road bed that has
been graded to meet the elevations of surrounding wetlands.
1.2 Purpose
In order to demonstrate successful mitigation, the site must be monitored for a minimum
of five years or until success criteria are achieved. Success criteria are based on
federal guidelines for wetland mitigation and are stipulated in the approved mitigation
plan and in relevant environmental permits. Criteria for both hydrologic conditions and
vegetation survival are included in these documents. Included in this report are
analyses of both hydrologic and vegetative monitoring results, as well as local climate
conditions throughout the growing season.
1.3 Project History
April 2003 Site Planted
May 2003 Monitoring Gauges Installed
May-November 2003 Hydrologic Monitoring (Year 1)
July 2003 Vegetation Monitoring (Year 1)
May-November 2004 Hydrologic Monitoring (Year 2)
September 2004 Vegetation Monitoring (Year 2)
March-November 2005 Hydrologic Monitoring (Year 3)
September 2005 Vegetation Monitoring (Year 3)
March-November 2006 Hydrologic Monitoring (Year 4)
August 2006 Vegetation Monitoring (Year 4)
March-November 2007 Hydrologic Monitoring (Year 5)
June 2007 Vegetation Monitoring (Year 5)
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Figure1. Site Location Map
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2.0 HYDROLOGY
2.1 Success Criteria
The Southwest Creek site has different success criteria to account for both marsh and
swamp areas. In accordance with federal guidelines for wetland mitigation, the success
criteria for hydrology state that the area must be inundated or saturated (within 12
inches of the surface) by surface or groundwater for at least a consecutive 12.5% of the
growing season during years of normal rainfall. Hydrologic success criteria for the
swamp area are consistent with federal guidelines. As was stated in the March 2000
mitigation plan, the success of the restored marsh will be determined by comparing the
hydrologic data (by demonstrating patterns of flooding or inundation) to that recorded
within the reference marsh system adjacent to the site.
According to the Soil Conservation Service, the growing season in Lenoir County
extends from March 17 to November 15, approximately 244 days. Thirty-one
consecutive days would equal 12.5% of the growing season for Southwest Creek.
Local climate must represent average conditions for the area in order for the hydrologic
data to be valid. Average conditions are determined through an analysis of monthly
rainfall totals recorded at the nearest official weather station.
2.2 Hydrologic Description
Two groundwater gauges are being used to measure groundwater levels within the
forested wetland portions. Two additional surface gauges are located within the marsh
area. One surface gauge is in the restored area and another gauge serves as a
reference within the existing marsh (reference marsh) adjacent to the site. The data
from the two surface gauges are compared to determine the success of the marsh
portion. A rain gauge is also located within the swamp area in order to obtain accurate
site rainfall measurements. The site rainfall data is used to analyze the site’s
(specifically, the swamp portion) response to rainfall events. Figure 2 is a map showing
the location of all of the site gauges.
Appendix A contains a plot of the water depth for each of the groundwater and surface
water monitoring gauges. Precipitation events, measured by the onsite rain gauge, are
included on each groundwater gauge graph as bars.
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2.3 Results of Hydrologic Monitoring
2.3.1 Site Data
The total number of consecutive days that the groundwater was within twelve
inches of the surface was determined at each groundwater monitoring gauge
location. This number was converted into a percentage of the total growing
season. Table 1 presents the hydrologic results for 2007. Figure 3 is a graphical
representation of the hydrologic monitoring results for 2007.
Table 1. Hydrologic Monitoring Results
Monitoring
Gauge < 5% 5-8% 8-12.5% >12.5% Actual % Dates of Success
SW-GW1 r 17.6 March 17-Apr 28
SW-GW2 r 3.7
Table 2. Hydrologic Monitoring Results (2003-2007)
Monitoring
Gauge 2003 Results 2004 Results 2005 Results 2006 Results 2007 Results
SW-GW1 75.4 38.9 36.9 46.3 17.6
SW-GW2 75.4 35.6 76.6 31.1 3.7
Average
Rainfall
Average
Rainfall
Average
Rainfall
Average
Rainfall
Below
Average
2.3.2 Climatic Data
Figure 4 is a comparison of monthly rainfall for the period of January through
November 2006 to historical precipitation (collected between 1975 and 2006) for
Kinston, North Carolina. This comparison gives an indication of how 2007
relates to historical data in terms of climate conditions. The NC State Climate
Office provided all local rainfall information.
For the 2007-year, the month of May experienced above average rainfall. The
months of January, April, June, July, and October recorded average rainfall for
the site. February, March, August, September, and November experienced
below average rainfall. Overall, 2007 experienced a below average rainfall year.
2.4 Conclusions
The 2007-year represents the fifth full growing season for which the hydrologic
data has been examined. One groundwater gauge of the two in the forested
wetland met the requirement for jurisdictional wetland hydrology (12.5% of the
growing season). Gauge GW-1 recorded hydrology for 17.6%, while GW-2
recorded hydrology for 3.7% of the growing season. The restored marsh gauge
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(SG-1) was comparable with the flooding patterns and inundation periods from
the reference marsh gauge (SG-2).
NCDOT recommends discontinuing hydrologic monitoring at the Southwest
Creek mitigation site.
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Figure 4. 30-70 Percentile Graph
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3.0 VEGETATION: SOUTHWEST CREEK MITIGATION SITE
(YEAR 5 MONITORING)
3.1 Success Criteria
The success criteria state that at least 320 stems per acre must survive after the
completion of the third growing season and 240 stems per acre after the fifth growing
season. If desired vegetation has not been established, NCDOT will notify the
appropriate agencies and will implement corrective measures.
3.2 Description of Species
The following tree species were planted in the Wetland Restoration Area:
Fraxinus pennsylvanica, Green Ash
Taxodium distichum, Bald cypress
Quercus lyrata, Overcup Oak
Nyssa aquatica, Water Tupelo
3.3 Results of Vegetation Monitoring
Table 3. Vegetative Monitoring Statistics
Site Notes: Overcup oak and water tupelo were noted living outside of plots even
though very few were noted in the stem counts. Other species noted: cattail, Juncus sp.,
Scirpus sp., black willow, broomsedge, woolgrass, fennel, goldenrod, trumpet creeper,
sedge, water grass, smart weed, laurel oak, tulip poplar, Baccharis sp., indian grass,
wax myrtle, red maple, sweetgum, and various grasses. Plot #
Green Ash
Baldcypress
Overcup Oak
Water Tupelo
Total (5 year)
Total (at planting)
Density (Trees/Acre)
1 14 21 1 1 37 37 680
2 15 21 3 1 40 40 680
6 8 0
A v e r a g e
D e n s i ty
( T re e s /A c re )
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3.4 Conclusions
There were 2 vegetation monitoring plots established throughout the 2.9 acre planting
area. The 2007 vegetation monitoring of the site revealed an average tree density of
680 trees per acre. This average is well above the minimum success criteria of 240
trees per acre for Year 5.
NCDOT recommends discontinuing vegetation monitoring at Southwest Creek
mitigation site.
4.0 OVERALL CONCLUSIONS/RECOMMENDATIONS
The following report summarizes the monitoring activities that have occurred in the past
year for the Southwest Creek mitigation site. Monitoring activities in 2007 represent the
fifth year of monitoring for the site. The site must demonstrate both hydrologic and
vegetation success for a minimum of five years or until the site is deemed successful.
The fifth year of monitoring indicated marginal hydrologic success, with one of the two
groundwater gauges in the forested wetland area meeting the success criteria (within
12” of the surface for 12.5% of the growing season). The groundwater gauges revealed
saturation levels of 17.6% and 3.7% of the growing season. However, due to the
drought conditions that occurred in 2007, the site recorded below average rainfall. In
accordance with the mitigation plan, the restored marsh gauge (SG-1) was comparable
with the flooding patterns and inundation periods of the reference marsh gauge (SG-2).
There were two vegetation monitoring plots established throughout the 2.9 acre planting
area. The 2007 vegetation monitoring of the site revealed an average tree density of
680 trees per acre. This average is well above the minimum success criteria of 240
trees per acre.
Based on five years of successful monitoring results, NCDOT recommends
discontinuing hydrologic and vegetation monitoring at the Southwest Creek mitigation
site.
APPENDIX A
GAUGE DATA GRAPHS
APPENDIX B
SITE PHOTOGRAPHS, PHOTO & PLOT LOCATIONS
SOUTHWEST CREEK
Photo 1 Photo 2
June 2006
APPENDIX A
GAUGE DATA GRAPHS
GROUNDWATER GAUGES
SURFACE WATER GAUGES