White Oak Stream Restoration
and
Greenway Project
Design Alternatives Report
December 2006
Prepared
for:
|
Town of Cary
|
Town of Apex
|
|
|
|
Prepared by:
__________________________________________
Steve Bevington
Project Manager
Buck Engineering, a unit of Michael Baker Corporation, is
performing a study to assess the potential design alternatives for stream
restoration, enhancement, and preservation along a proposed greenway
corridor. The study area is in the White
Oak Creek watershed between Wimberly and Green Level West Roads, within a historically
rural area of the Town of Apex. It includes White Oak Creek, Clark Branch,
and six unnamed tributaries to White Oak Creek.
The watershed draining to the study area includes land under the
jurisdiction of both the Town of Apex
and the Town of Cary. While most of the study area is forested, the
larger watershed contains multiple land uses.
The initial phase of the project involved
the collection of watershed and geographic information system (GIS) data. Field assessments focused on classifying
stream reaches within the project boundary, identifying bank erosion on project
reaches, as well as classifying natural communities and developing a farmland/land
use GIS database for the study area. Identification
of the greenway corridor alternatives was preformed by Haden Stanziale and
focused on potential trail routings based upon view-sheds, educational points
of interest, potential stream and wetland crossings, and potential easement
requirements. This report summarizes the
findings of the study and evaluates stream restoration and greenway
alternatives. In addition, the report evaluates
the limited potential cumulative and secondary impacts within the project
watershed and provides recommendations for stream, wetland, and buffer
preservation, as well as stormwater best management practices (BMPs).
Approximately 3.4 miles of
streams were assessed within the study area, with drainage areas ranging from
0.07 to 11.93 square miles. The majority
of the evaluated stream reaches were relatively stable, with most maintaining
natural access to their floodplains.
However, Clark Branch and Unnamed Tributary 1 (UT1) were more incised
and had moderate to high bank height ratios that correspond to a higher threat
of bank erosion during moderate floods. These
two incised stream reaches are possible candidates for stream restoration.
While some effort could be
made to restore the most actively eroding stream reaches in the study area,
which comprise a small percentage of total stream length, it is the general
conclusion of this report that the primary management focus for the watershed should
be ensuring the careful implementation of existing rules and policies to
preserve the high quality riparian environment.
Further, because such good habitat is becoming increasingly rare in the
developing Triangle area, it is recommended that the watershed continue to be
monitored in the future so that the value of the existing land use rules and
policies currently in place can be directly linked to the maintenance of high
quality watersheds in an urbanizing region.
Table of Contents
Executive Summary. ii
1 Introduction. 1
1.1 Project
Objective. 1
1.2 Methodologies. 1
2 Watershed
Overview.. 3
2.1 Soil
Survey. 3
2.2 Geology. 4
2.3 National
Wetland Inventory. 4
2.4 Land Use. 4
2.5 Watershed
Management 5
2.6 Threatened
and Endangered Species. 6
2.7 Farmland
Assessment 9
3 Stream
and Natural Communities Assessment 11
3.1 Stream
Classification. 11
3.2 Bank
Erosion Hazard Index (BEHI) 14
3.3 Wetland
Communities. 14
3.4 Terrestrial
Communities. 15
4 Secondary
and Cumulative Impacts. 16
4.1 Potential
Impacts. 16
4.2 Expected
Development 16
4.3 Town of
Cary and Town of Apex Master Mitigation Plans. 17
4.4 Conclusion. 17
5 Recommendations
and Alternatives Analysis. 18
5.1 Stream
and Wetland Restoration and Preservation Alternatives. 18
5.2 Greenway
Alternatives. 21
5.3 Best
Management Practice Recommendations. 24
5.4 Farmland
and Open Space Preservation Opportunities. 26
6 References. 28
Buck Engineering, a unit of Michael Baker Corporation, performed a
study to assess the potential stream design alternatives for White Oak Creek,
Clark Branch, and six unnamed tributaries to White Oak Creek in Apex, North
Carolina (see Exhibit 1 – Project Vicinity Map). The assessment focused primarily on White Oak
Creek, Clark Branch, and the larger tributaries between Green Level West and
Wimberly Roads, which exhibit greater vulnerability to disturbance than other
small streams in the study area.
The objective of the study was to identify stream, wetland, and riparian
buffer restoration and preservation opportunities within the study area in
combination with proposed greenway alternatives. The study also identifies potential farmland
and upland areas suitable for open space preservation. The project is part of a larger effort to
reduce non-point source pollution entering Jordan
Lake.
This report summarizes the findings of the study and provides
recommendations for stream restoration and enhancement, stream and wetland
preservation, and farmland/upland preservation within the study area. The report also gives some general
recommendations for best management practices (BMPs) that could be implemented
within the watershed. The alternatives
presented in the report include construction costs and priority ratings. The Towns of Cary and Apex will choose which
alternatives to implement based on the information provided. The selected alternatives will be used to
complete the final design phase of the project.
The study involved the collection of field data (stream channel cross-sections,
bank erosion assessments, community types, and wetland assessments), geographic
information system (GIS) data, endangered species occurrence listings, and
other information to evaluate the stream, wetland, and riparian buffer restoration
and preservation potential within the study area. GIS data were used to produce site feature
maps, including parcel boundaries, aerial photography, soils, roads and
transportation, National Wetland Inventory (NWI), topography, hydrography, and
land use (existing and planned) (see exhibits for GIS maps). These maps were used to develop greenway
alignment options and identify stream and wetland restoration and preservation
alternatives.
Buck Engineering performed on-site assessments of streams in the
study area to evaluate restoration potential.
Field data and site features were collected from March to May 2006. Topographic maps and GIS data were used to
delineate the watersheds for streams within the study area (Exhibit 2). The streams were divided into approximately 1,000-foot
reaches for analysis. Channel dimensions
were evaluated by surveying one riffle cross-section on each reach. Data from the surveys are provided in Appendix
1. Photographs, taken at the beginning
and end of each reach and at cross-sections, are provided in Appendix 2. Bank erosion assessments were conducted on the
streams using the Bank Erosion Hazard Index (BEHI) methodology (Rosgen,
2001). A graph summarizing bank erosion on
the larger tributaries is provided in Appendix 3. Vegetation and wetland characteristics in the
study area were noted during the site assessments.
Other data used to assess project alternatives were collect