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Home My WebLink About20220204 Ver 1_4520018 EWP Duplin County Permitting REPORT_20220131_;� � . Ate• • v �.-. - , 6l - `... ,f Prepared by: (� LDS1 Jonathan Hinkle, PE LDSI, Inc. I Kinston, NC 1308 H WY 258 N Kinston NC 28504 Phone: 910-663-4123 jhinkle@ldsi-inc.com Prepared for: DUPLIN COUNTY dupllncauntync-cam Angie B. Quinn, Soil Conservation Director ❑uplin Soil & Water Conservation 165 Agriculture Drive, Suite B. Kenansville, NC 28349 angie.quinn@duplincountync.com BACKGROUND LDSI was contracted by Duplin County to assist with 3 sites that were affected by Hurricane Florence. LDSI has previously assisted the County with the initial Damage Survey Reports (DSRs) which portions of this submittal utilizes information gleaned during that project. LDSI has conducted topographic surveys and field reconnaissance work to collect data that will be necessary to complete these projects. The sites are located throughout Duplin County, NC. Two project sites include Channel Bank Stabilization and Sediment Removal, while the third project site is just a Bank Stabilization. The purpose of this project is to restore the drainage infrastructure to a condition which existed prior to the hurricane. EXISTING CONDITIONS Figure 1: National Wetlands Inventory Wetlands map of project area Duplin County lies within the coastal plain of North Carolina and its landscape is characterized by agriculture, pineland, forested wetlands, and residential areas. Numerous streams and freshwater wetlands drain to the Northeast Cape Fear River, which runs through the county in a corridor of forested wetlands. The soils present within the project sites are primarily sandy, well -drained soils that are typical of North Carolina's Coastal Region. The damage done to the three sites within the project was caused by approximately 29.5 inches of rainfall that occurred during Hurricane Florence. This resulted in debris and sediment build up, stream bank erosion, and significant scour. The existing conditions of the specific project sites are listed below. (OLDS1 DUPLI N COUNTY Page 2 of 10 G:\2020\4520018\16-Permitting\4520018 EWP Duplin County Permitting REPORTA— 039 — Tandam Branch Project site 039 is located on prior converted farmland and contains a section of Tandam Branch that passes through a box culvert beneath NC Highway 111. This channel has experienced increased erosion and related damages as a result of Hurricane Florence. Bank failures and excessive sediment deposition along the channel bed have de -stabilized the stream and bank blowouts near the culvert pose risk to the existing roadway. Consequently, Tandam Branch is in need of rehabilitation. 040 — Dark Branch Project site 040 is located on prior converted farmland and includes an approximately 1,000 LF section of Dark Branch, starting at the outlet of two culverts passing under Dark Branch Road. This channel has experienced severe erosion and scour as a result of Hurricane Florence. The slope of the stream bed varies significantly throughout the reach and has become unstable. The left bank was blown out at the upstream end of the reach by Dark Branch Road and poses a threat to the roadway if left unaddressed. 043 — Sarecta Road The roadside bank located within project site 043 has experienced severe erosion from Hurricane Florence. Failures can be seen along the side of Sarecta Road and the eroding slope will impact the existing roadway and utilities if not addressed. No waters of the State were seen in this project area. Soils Data Descriptions of the unique soils found within the project areas are listed below. These represent the soils most likely to be encountered during these projects. BbA—Bibb sandy loam, 0 to 1 percent slopes, frequently flooded Setting • Landform: Flood plains • Landform position (two- dimensional): Toeslope • Down -slope shape: Concave • Across -slope shape: Linear • Parent material: Sandy and loamy alluvium GtA—Grifton fine sandy loam, 0 to 2 percent slopes Setting • Landform: Depressions • Down -slope shape: Concave • Across -slope shape: Linear • Parent material: Loamy fluviomarine deposits over marly sandy and clayey alluvium 4 (OLDSI DUP� COUNTY Typical profile A - 0 to 6 inches: loamy sand Cg1 - 6 to 60 inches: sandy loam Cg2 - 60 to 80 inches: loamy sand Typical profile • A - 0 to 8 inches: fine sandy loam • Eg - 8 to 11 inches: sandy loam • Btg - 11 to 50 inches: sandy clay loam • Cg - 50 to 60 inches: loamy sand • 2Cg - 60 to 80 inches: loamy sand Page 3 of 10 G:\2020\4520018\16-Permitting\4520018 EWP Duplin County Permitting REPORTA— JoA—Johns fine sandy loam, 0 to 2 percent slopes Setting • Landform: Stream terraces • Landform position (three-dimensional): Tread • Down -slope shape: Convex • Across -slope shape: Convex • Parent material: Loamy alluvium over sandy alluvium LsB—Lucy loamy sand, 0 to 6 percent slopes Typical profile • Ap - 0 to 7 inches: fine sandy loam • E - 7 to 11 inches: fine sandy loam • Bt - 11 to 37 inches: sandy clay loam • 2Cg - 37 to 80 inches: sand Setting Typical profile • Landform: Broad interstream divides on marine 0 Ap - 0 to 8 inches: loamy sand terraces, ridges on marine terraces 0 E - 8 to 24 inches: loamy sand • Landform position (two-dimensional): Summit, 0 Bt1 - 24 to 35 inches: sandy loam shoulder 0 Bt2 - 35 to 80 inches: sandy clay • Landform position (three-dimensional): Crest loam • Down -slope shape: Convex • Across -slope shape: Convex • Parent material: Loamy marine deposits McC—Marvyn and Gritney soils, 6 to 15 percent slopes Setting Typical profile • Landform: Ridges on marine terraces 0 Ap - 0 to 4 inches: loamy fine sand • Landform position (two-dimensional): Shoulder, 0 E - 4 to 12 inches: loamy fine sand backslope 0 Bt - 12 to 45 inches: sandy clay • Down -slope shape: Convex loam • Across -slope shape: Convex 0 Cg - 45 to 80 inches: sandy clay • Parent material: Loamy and clayey marine deposits loam NbB—Noboco loamy fine sand, 2 to 6 percent slopes Setting Typical profile • Landform: Broad interstream divides on marine • Ap - 0 to 10 inches: loamy sand terraces, ridges on marine terraces • E - 10 to 13 inches: loamy sand • Landform position (two-dimensional): Summit, shoulder • Bt - 13 to 80 inches: sandy clay • Landform position (three-dimensional): Crest loam • Down -slope shape: Convex • Across -slope shape: Convex • Parent material: Loamy marine deposits OLDSI DUPLIN COUNTY Page 4 of 10 G:\2020\4520018\16-Permitting\4520018 EWP Duplin County Permitting REPORT.do PROJECT GOALS The purpose of this project is to provide technical and administrative services to restore the three project sites to pre -hurricane conditions while complying with the requirements of the USDA-NRCS Emergency Watershed Protection program. This will be achieved by the following project objectives: • Removal of sediment deposits within stream reaches • Channel bank stabilization via grading and planting • Installation of in -stream structures to maintain grade over time • Backfilling large scour holes throughout the project sites (OLDS1 DUPLI N COUNTY Page 5 of 10 G:\2020\4520018\16-Permitting\4520018 EWP Duplin County Permitting REPORTA— 039 — Tandam Branch 039.A Hydrology Watershed characteristics for Tandam Branch were determined primarily through the USGS StreamStats tool along with field reconnaissance. It was found that the watershed draining into the stream is approximately 1.77 sq miles (1133 Acres) in size and has a 50-year peak flow of approximately 435 CFS (Figure 2). The project site is at minimal flood risk in Flood Zone X. 0 2500 5000 Feet PEAK FLOW STATISTICS STATISTIC VALUE UNIT 2-YEAR PEAK FLOOD 87.3 CFS 5-YEAR PEAK FLOOD 176 CFS 10-YEAR PEAK FLOOD 247 CFS 25-YEAR PEAK FLOOD 347 CFS 50-YEAR PEAK FLOOD 435 CFS Figure 2: StreamStats Watershed and Peak Flow Statistics for Tandam Branch OLDS1 DUPLIN COUNTY Page 6 of 10 G:\2020\4520018\16-Permitting\4520018 EWP Duplin County Permitting REPORT.d— 039.13 Hydraulics The dimensional parameters for the proposed stream at Tandam Branch were calculated by referencing the work of Barbara Doll. Her work statistically analyzed the dimensional characteristics of pristine streams within the coastal regions of North Carolina to determine the parameters of stable, healthy streams. PARAMETER VALUE UNIT AREA OF BANKFULL (Abkf) 20.8 SQFT FLOW AT BANKFULL (Qbkf) 24.5 CFS WIDTH OF BANKFULL (Wbkf) 13.3 FT DEPTH AT BANKFULL (Dbkf) 1.5 FT Figure 3: Dimensional Parameters of the Proposed Stream at Tandam Branch 039.0 Proposed Design The proposed stream section of Tandam Branch will utilize control structures to maintain grade, prevent unwanted erosion, and promote pool scour to increase biodiversity within the stream. These structures will include 6 Log Sills that will be installed at the start of each pool section. They will allow the stream to hold grade during high -flow storm events. The banks of the channel will be graded back at a stable slope and side slopes will be matted with fiber matting and staked with live stakes to restore bank integrity. OLDS1 DUPLIN COUNTY Page 7 of 10 G:\2020\4520018\16-Permitting\4520018 EWP Duplin County Permitting REPORTA— 040 — Dark Branch 040.A Hydrology Watershed characteristics for Dark Branch were determined primarily through the USGS StreamStats tool along with field reconnaissance. It was found that the watershed draining into the stream is approximately 2.34 sq miles (1498 Acres) in size and has a 50-year peak flow of approximately 515 CFS (Figure 4). A detailed Drainage Area and Soils Map for the Dark Branch watershed is included in Appendix A. The project site is located in Flood Zone AE with a base flood elevation of 67.4 ft. .: 3 PEAK FLOW STATISTICS STATISTIC VALUE UNIT 2-YEAR PEAK FLOOD 105 CFS 5-YEAR PEAK FLOOD 210 CFS 10-YEAR PEAK FLOOD 294 CFS 25-YEAR PEAK FLOOD 411 CFS 50-YEAR PEAK FLOOD 515 CFS Figure 4: StreamStats Watershed and Peak Flow Statistics for Dark Branch Page 8 of 10 OLDS1 DUPLIN COrUNTY G\2020\4520018\16-Permitting\4520018EWPDuplinCounty Perm ittingREPORT.d— 083.13 Hydraulics The dimensional parameters for the proposed stream at Dark Branch were calculated by referencing the work of Barbara Doll. Her work statistically analyzed the dimensional characteristics of pristine streams within the coastal regions of North Carolina to determine the parameters of stable, healthy streams. PARAMETER VALUE UNIT AREA OF BANKFULL (Abkf) 25.4 SQFT FLOW AT BANKFULL (Qbkf) 30.5 CFS WIDTH OF BANKFULL (Wbkf) 14.9 FT DEPTH AT BANKFULL (Dbkf) 1.7 FT Figure 5: Dimensional Parameters of the Proposed Stream at Dark Branch 083.0 Proposed Design The proposed section of stream at Dark Branch will implement multiple Log Sill structures as a means for maintaining the designed grade while promoting beneficial pool scour. There are 16 proposed Log Sills throughout the Dark Branch reach that will be installed at the start of each pool section. They will be especially useful in maintaining grade at the upstream end, at the outlet of the existing culverts. Culverts traditionally cause scour pools to form at both the upstream and downstream ends, and while they have desirable characteristics, they also tend to increase in size over time. The Log Sill structures will prevent the culvert scour pool from moving downstream and causing an excessively large pool area. The channel banks will be graded back to stable slopes and the side slopes will be matted with fiber matting and staked with live stakes to restore bank integrity. 043 — Sarecta Road To repair the failing bank along Sarecta Road, stabilization of the slope is necessary. Stabilization of the area will reduce sloughing and erosion of the roadside bank which is important to protect the adjacent roadway and utilities. Due to the constraints of the project area and the risk to utility services, a structural approach was favored over a natural approach. The bank will be graded back at a more stable slope and secured with flexible concrete armor. In addition to the concrete armoring, the site will be reseeded and vegetation will be able to take hold. The project site is at minimal flood risk in Flood Zone X. (OLDS1 DUPLI N COUNTY Page 9 of 10 G:\2020\4520018\16-Permitting\4520018 EWP Duplin County Permitting REPORTA— PERMITTING AND NEXT STEPS It is our intent to permit all three sites under one NWP 37. "Nationwide Permit 37 - Emergency Watershed Protection and Rehabilitation. Work done by or funded by: (a) The Natural Resources Conservation Service for a situation requiring immediate action under its emergency Watershed Protection Program (7 CFR part 624); (b) The U.S. Forest Service under its Burned -Area Emergency Rehabilitation Handbook (FSH 2509.13); (c) The Department of the Interior for wildland fire management burned area emergency stabilization and rehabilitation (DOI Manual part 620, Ch. 3); (d) The Office of Surface Mining, or states with approved programs, for abandoned mine land reclamation activities under Title IV of the Surface Mining Control and Reclamation Act (30 CFR subchapter R), where the activity does not involve coal extraction; or (e) The Farm Service Agency under its Emergency Conservation Program (7 CFR part 701). In general, the prospective permittee should wait until the district engineer issues an NWP verification or 45 calendar days have passed before proceeding with the watershed protection and rehabilitation activity. However, in cases where there is an unacceptable hazard to life or a significant loss of property or economic hardship will occur, the emergency watershed protection and rehabilitation activity may proceed immediately and the district engineer will consider the information in the pre -construction notification and any comments received as a result of agency coordination to decide whether the NWP 37 authorization should be modified, suspended, or revoked in accordance with the procedures at 33 CFR 330.5. Notification: Except in cases where there is an unacceptable hazard to life or a significant loss of property or economic hardship will occur, the permittee must submit a pre -construction notification to the district engineer prior to commencing the activity (see general condition 32). (Authorities: Sections 10 and 404)"' 1https://www.swt.usace.army.miI/Portals/41 /docs/missions/requlatory/NationwidePermits/Nationwide%20Permit%203 7%20-%20Emeraencv%20Watershed%20Protection%20and%20Rehab ilitation. Ddf?ver=201 7-03-31 -150709-317 Page 10 of 10 LDS DUPLIN COUNTY G:\2020\4520018\16-Permitting\4520018 EWP Duplin County Permitting REPORT.docx