Biological assessment
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- DIRECT IMPACTS-APPALACHIAN ELKTOE
- Stream Fill (Substrate (Habitat) Disturbance/Loss)
- Tributaries-Cane River
- South Toe River
- Tributaries- South Toe River
- Tributaries-North Toe River
- Alteration of Flows/Channel Stability
- Cane River and South Toe River
- Roadway Runoff
determination of effectsThe determination of effects was made after analyzing the likelihood of the identified potential project-related impacts (Section 4.0) resulting in adverse as well as beneficial effects to the Appalachian elktoe and its Critical Habitat. DIRECT IMPACTS-APPALACHIAN ELKTOEAlthough the Proposed Avoidance/Minimization Measures discussed above will reduce some potential impacts to the Appalachian elktoe and Designated Critical Habitat, project construction will result in various unavoidable direct impacts to the species and its critical habitat. Stream Fill (Substrate (Habitat) Disturbance/Loss)The construction of the project will result in a permanent loss of 50 ft2 (4.6 square meters) and a temporary loss of 700 ft2 (65 square meters) of potentially occupied habitat at the Cane River crossing, and a temporary loss of 9,600 ft2 (892 square meters) of occupied habitat at the South Toe River crossing. The temporary loss of habitat may have long-lived effects on the Appalachian elktoe’s re-colonization of the habitat. The combined permanent and temporary loss of habitat, as well as the construction activities taking place in the river may result in the loss of individual Appalachian elktoe mussels. NCDOT is proposing to relocate as many individuals from the impact area as possible to help to offset these impacts (See Conservation Measures and Proposed Measures to Offset Impacts Section 7.0). Cane RiverThe existing bridge on US 19E over the Cane River (Bridge No. 9) will be widened during project construction. The two-lane bridge was constructed in 1984, and will not require demolition for the US 19/US 19 E improvement project. Bridge No. 9 is a 3-span structure that consists of a reinforced concrete floor on pre-stressed concrete girders. An August 2003 Bridge Inspection Report rates the condition of the bridge as “good” with no structural scour problems identified. The end bents and interior bents are composed of concrete with reinforcing steel. The overall length of the structure is 204 feet (62.2 meters). Presently, the bridge has an inventory rating of HS-31 and an operating rating of HS-53. The posted speed limit over the bridge is 55 miles per hour. Bridge maintenance records show the only recorded problems with the structure have been the approach slabs. Widening the bridge will consist of constructing an adjacent structure to the north (downstream) of the existing bridge. In order to connect the two bridge decks, the existing concrete guardrail along the northern edge of the deck will be removed. Best Management Practices for Bridge Demolition and Removal will be implemented to remove the existing concrete guardrail. Every precaution will be taken to ensure that the guardrail does not enter the river. The existing deck will not be removed; however, it will be connected, with side to side dowel rods, to a new adjacent deck to the north (downstream). The existing deck is crowned and will be milled to match the adjacent new deck. The existing and new deck will be wide enough to support five-lanes of traffic. The deck drains on the existing bridge will be closed off; storm water runoff will not be directly discharged in the river. Hazardous spill catch basins will be constructed near the northeast and southwest quadrants of the bridge to further protect the river. The basins will be positioned such that any potential spill runoff will be directed through the facility (basin) and temporarily stored to prevent the material from entering the adjacent water. NCDOT will monitor the stream before and after the construction to see if there are any changes to the stream cross section because of construction. If there is a change in the stream related to the new bridge, NCDOT will take appropriate steps to protect the mussel populations near the bridge. This may include placing other structures in the water to redirect the flow. The need for any in-stream structures will be determined through monitoring but may include cross vanes or other appropriate devices. The Hydraulics Unit of NCDOT recommends the piers for the new bridge line up with the existing piers to reduce scour around the piers from accumulated debris. The east interior bent is currently on the bank. For bent construction, a stone work pad would be necessary but would not be installed in the river. The west interior bent is approximately 10 feet (3.05 meters) out in the river. The distance between the bank and the new west interior bent becomes smaller downstream of the existing bridge. A small causeway will be needed to construct the west interior bent. Temporary impacts to the stream bed for this causeway are approximately 500 square feet (46.5 square meters). A total of four drilled piers with 4-foot (1.2 meters) diameter shafts would be needed for the new adjacent structure. The total direct impact to the stream bed is 50 square feet (4.6 square meters) for the four shafts. All girders may possibly be set from the bank. If the girders cannot be set from the bank, a work bridge will be necessary. The stream bed impacts from a work bridge would be temporary. Work bridge construction may include pre-cast concrete footings lifted in place by a crane to rest on the stream bed. Conservative estimate of stream bed impact would be 5 feet by 20 feet or 100 square feet (ft2) per foundation. Two foundations would be needed for the work bridge. Total stream bed impacts for work bridge foundations would be 200 square feet. The proposed structure will result in 50 ft2 of permanent impacts to the stream bed as a result of bent placement in the river. Additionally, 500 ft2 of stream bed will be impacted by a causeway needed to construct the west interior bent and 200 ft2 of stream bed will be impacted by work bridge foundations. Tributaries-Cane RiverThere are 42 stream impact sites within the Cane River subbasin (Table 13). Bald Creek is the major tributary west of the project crossing of the Cane River, and Pine Swamp Branch is the major tributary on the east side of the project crossing of the river. The roadway corridor follows the valley formed by these two streams, and cross the streams multiple times, as well as 20 tributaries to Bald Creek and 3 tributaries to Pine Swamp Branch. Price Creek, Phipps Creek and an unnamed tributary to the Cane River are also crossed. Table 13. Impacts to Cane River (CR) Tributaries from west to east.
* Stream Names from EA (NCDOT 2001), or developed during 9-11-2003 Jurisdictional Field meeting, or provided by NCDOT ** RCBC, RCP, CSP, CSPA and CSP denote Reinforced Concrete Box Culvert, Reinforced Concrete Pipe, Corrugated Steel Pipe, Corrugated Steel Pipe Arch and Corrugated Steel Pipe, respectively. South Toe RiverThe Merger 01 Team has concurred with the location of the R-2519B Best Fit alignment. The existing US 19E bridge over the South Toe River (Bridge No. 43) is proposed to be replaced with a new dual structure on similar alignment 40 feet south of the existing structure. The existing bridge will carry traffic while the new structure is built. Traffic will be shifted to the new structure once complete, and the old bridge will be removed. The US 19E South Toe Bridge preliminary design for R-2519B is proposed to span the river with a simple span plate girder bridge with a main span of approximately 170 feet proposed. Based on current information, a total of five causeways are proposed for construction of the South Toe River Bridge. Two 40-foot by 60-foot causeways will be needed for placing the temporary bents in the water. Two 30-foot by 50-foot causeways are recommended for placing the girders. One 30-foot by 60-foot causeway will be needed for removing the existing bent. The total temporary impacts would be 9,600 ft2, which is a worst case scenario. Further details regarding the removal of existing Bridge No. 43 will need to be developed in coordination with the USFWS, NCWRC, DWQ and the US Army Corps of Engineers. It is assumed in this impact analysis that the bridge will be removed in a manner that does not result in any debris from the bridge entering the river.
Tributaries- South Toe RiverThere are 24 impact sites in the R-2519A Section of the proposed action that occur within the South Toe River subbasin (Table 14). Little Crabtree Creek is the major tributary to the South Toe River, arising approximately 7.5 miles west of the South Toe River in Burnsville. Table 14. Impacts to South Toe River (STR) Tributaries in Section R-2519A from west to east.
*Stream Names from EA (NCDOT 2001), or developed during September 11, 2003, Jurisdictional Field meeting or were provided by NCDOT. ** RCBC, RCP, CSP, CSPA and CSP denote Reinforced Concrete Box Culvert, Reinforced Concrete Pipe, Corrugated Steel Pipe, Corrugated Steel Pipe Arch and Corrugated Steel Pipe, respectively. *** Distances were estimated via GIS, not calculated by NCDOT There are 24 impact sites in the R-2519B Section of the proposed action that occur within the South Toe River subbasin (Table 15). Major streams include Little Crabtree Creek (LCC) and Long Branch. Design information on this section of the project is preliminary, and impacts may change. Table 15. Streams in South Toe River in R-2519B Segment from West to East.
* Assigned field names are based on Stream Name, if known, or Stream ID, if names not available ** NA denotes information not available at this time Tributaries-North Toe RiverThe North Toe River is not crossed by the proposed action; however; a total of 18 stream segments within the North Toe River subbasin will be impacted based on the preliminary design plans preferred alternative for this section. The stream names are identified in the NRTR for this project (NCDOT 2004). The streams identified in Table 16 are the ones most likely to be impacted by the proposed action. Table 16. Streams in North Toe River from West to East (R-2519B).
* Assigned field names are based on Stream Name, if known, or Stream ID, if names not available ** NA denotes information not available at this time Erosion/Sedimentation from Construction Sites Adverse impacts to the Appalachian elktoe and its habitat resulting from project-related sedimentation/erosion are expected to be minimal; erosion control standards will be strictly enforced by NCDOT. Enforcement will involve various levels of quality control above and beyond what is implemented on standard NCDOT projects (Section 5.0). To eliminate/minimize the potential for sedimentation, the NCDOT has developed specific erosion control measures for this project designed to protect this species. Sedimentation and erosion control measures that adhere to the Design Standards in Sensitive Watersheds [15A NCAC 04B .0124 (b) – (e)] will be implemented within the entire portion of the project found within the Nolichucky River Basin (Cane River, South Toe River and North Toe River Watersheds). Additionally, the areas around the South Toe River and Cane River crossings will be designated as environmentally sensitive. There are no practical erosion control measures that can totally eliminate the chance for sedimentation from a project site; however, if the Erosion Control Plans are properly incorporated into project construction and strictly adhered to, the potential for project-related adverse impacts of erosion and sedimentation to aquatic habitat of the Cane, South Toe and North Toe rivers should be greatly reduced. Alteration of Flows/Channel StabilityThe temporary causeways proposed at both bridge sites may result in small-scale localized changes in flow patterns at the respective sites. The potential for this type of impact is greatest at the South Toe River crossing. These changes will be temporary, during the life of the respective causeways, and are not expected to result in significant impacts to the Appalachian elktoe and its habitat. Cane River and South Toe RiverThe designs of the bridge crossings of the Cane River and South Toe River were developed to minimize the amount of in-stream piers. With the presence of the rock line near the bed surface at the two crossings, scour potential is limited at these sites. Temporary construction/demolition causeways will be used at both bridge construction sites. The temporary construction/demolition causeways used for these projects were designed to result in the least amount of fill into the river as is practical. Given the relatively small size of the causeway needed at the Cane River crossing, 500 ft2 (47 m2), the potential for it to cause significant channel instability and upstream pooling is low. The potential for this type of impact is much greater at the South Toe River crossing as five causeways totaling 9,600 ft2 (892 m2) in size are proposed at this site. The causeways will incorporate full pipes into the design to achieve linear stream flow and minimize upstream pooling. These full pipes will direct water through the causeways, resulting in no diversion of flow outside the main channel. Any pooling that occurs will be temporary and will revert to normal water levels and conditions once the causeways are removed. The placement of causeways in the river will also constrict flows, thus creating higher velocities downstream. The use of full pipes in the causeway will help to maintain linear flow. Causeway construction will be phased at both bridge replacement sites. The phasing of the causeway construction will limit the amount of causeway in the river at any one time and at no time will the causeway extend the entire width of the river. The predominance of bedrock at or near the surface at both sites limits the potential for significant scour of the riverbed to occur. The effects of increased velocities on channel stability are expected to be minimal and temporary; reverting to normal conditions once the causeways are removed. Stream bottom and stream bank stability will be monitored before, during, and after construction (See Conservation Measures-Proposed Measures to Offset Impacts) at the Cane River and South Toe River crossings. If any problems with regards to stream stability are detected during the monitoring, NCDOT will take immediate actions to correct the problems. TributariesWith the exception of proposed bridges at Price Creek (Sta.# 192+18 –L-) and Bald Creek (Sta.# 175+60 –L-) all the tributaries draining to either the Cane River or South Toe River will be crossed with some type of culvert or pipe structure (Tables 9-12). Many of these crossings will be extensions of existing structures. The design and installation of the various culvert and pipe crossings will attempt to minimize the potential for channel instability, which will minimize the potential of affecting occupied habitat in the Cane, South Toe, or North Toe rivers downstream of these crossings. Traditionally, culverts and pipe crossings were designed to convey water flow, with little considerations for impacts to the affected aquatic resources. Improperly designed culverts can initiate channel erosion when the outlet end is above the streambed (perched culvert) creating a waterfall that can lead to bed scouring and bank erosion, as well as act as a barrier to fish migration. The use of open-bottom arch structures or the burial of inverts of closed structures like box culverts and pipes lessens the potential for these types of impacts to occur. The potential for these types of impacts was taken into consideration when designing the appropriate structure at each crossing. NCDOT believes that, with proper installation, the proposed crossing structures will not result in significant degradation of the stream channels. NCDOT will review the hydraulic designs and best management practices with all involved resource agencies at the Merger 01 4B and 4C concurrence points for each section of the project. Best management practices will be employed to the maximum extent practicable. A stormwater management plan will be developed for each section of the project that identifies the best management practices used. Finley and Young (1993) found grassy swales to be an effective means of pollutant removal for storm water. The existing bridges over the Cane River and South Toe River discharge roadway water directly into the respective rivers via scuppers (weep holes). This direct discharge will be eliminated at these sites following construction. The elimination of drop inlets at the two new bridges will reduce roadway runoff into the Cane River and South Toe River respectively. The elimination/reduction of runoff to the rivers will result in a decrease of daily pollutant loads in the receiving water. This may result in localized improvements to water quality, and thus have a beneficial effect on the Appalachian elktoe, or a reduction of the likely adverse effects. Thus, despite the increase in impervious surface area associated with the widening of the roadway, upon the completion of the combined projects, there will be a reduction in the amount of roadway runoff directly entering the Cane River and South Toe River at these respective crossings as a result of stormwater management and elimination of direct discharge. 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