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Home My WebLink About20190210 Ver 2_Site 5 design information_Existing_ProposedConditions_Writeup_02.01.19_20201113A-0011C Stream Relocation Hyatt Mill Creek, Clay County, NC February 1, 2019 Page 1 of 3 A-0011C Stream Relocation Project – Hyatt Mill Creek Existing Conditions Summary The existing Hyatt Mill Creek project reach begins at an existing 60” CMP and flows approximately 600 ft to the confluence with Coleman Creek. An existing 60” RCP is located at a driveway crossing near the middle of the existing project reach. Hyatt Mill Creek is classified as a perennial stream within the channel relocation reach. The drainage area for the project site is 0.35 square miles (224 acres). Average reach slope along the existing channel is 1.7%. Methodology for classifying stream type followed Technical Supplement E in Part 654 of the National Engineering Handbook. The project reach is slightly entrenched (entrenchment ratio of 2.4 to 3.3), has a low width/depth ratio (5.5 to 10.6), and sinuosity of 1.04. Considering that width/depth ratios can vary by 2.0 units and sinuosity can vary by 0.2 units, the existing Hyatt Mill Creek project reach is classified as a C4 stream. Rosgen C-type channels are described as low-gradient, meandering alluvial channels with point bars, riffle-pool morphology, and broad, well-defined floodplains. The channel bed consists primarily of medium and coarse gravel. Bank height ranges from 2.0 to 3.1 ft. Bank material throughout the project reach was observed as primarily loam. Minor areas of erosion and undercutting was observed along the right bank. Stream banks and floodplains along much of the project reach are densely vegetated with tall grass, small trees, and shrubs. The existing planform appears to be stable with minimal likelihood of lateral channel migration at rates outside of natural conditions. Proposed Conditions Summary The proposed design includes a mixture of channel relocation, bed stabilization, and bank grading and stabilization along approximately 633 ft of Hyatt Mill Creek. Proposed work begins at a 60” CMP and continues approximately 633 ft to the confluence with Coleman Creek. The existing driveway currently located approximately 350 ft downstream of the start of proposed work, is proposed to be relocated approximately 50 ft downstream from the currently location. The proposed driveway will have a 95” x 67” steel pipe arch culvert compared to the existing 60” RCP. The proposed reach slope is 1.6%. Local slope along the proposed vertical alignment varies depending on the location of proposed riffle and pool features. Riffle slopes vary between 2.6% and 3.5% and slope along proposed pool features varies from 0% to 0.6%. Maximum pool depth was set to be 1 foot deeper than maximum riffle depth. Proposed bankfull width is 10 feet. Cross section geometry along pool sections were set to be 10% wider than the riffle sections. Channel banks will be graded to a 2:1 (H:V) slope, seeded, stabilized with coir fiber matting, and planted with live stakes along the channel banks and trees and shrubs along the top-of-bank area. Riffle grade control and wood drop riffle structures are proposed along the project reach in order to provide grade control and habitat along the cross-over (riffle) areas along the proposed alignment and immediately downstream of culverts along the proposed channel. Toe boulder protection is proposed in areas of high shear stress and/or velocity and where the proposed alignment results in tight and/or long bend geometry. A rock cross vane is proposed along Coleman Creek upstream of the confluence with Hyatt Mill Creek to decrease shear stress and velocity to protect the banks by diverting the energy to the center of the channel as it approaches the culvert extension. The proposed rock mix that matches the calculated grain size consist of 70% Class 2, 15% Class 1, and 15% Class B. Proposed vane rock dimensions are 1.5 ft x 2.5 ft x 3.5 ft. A-0011C Stream Relocation Hyatt Mill Creek, Clay County, NC February 1, 2019 Page 2 of 3 Proposed planting along the Hyatt Mill Creek stream relocation project consists of Type 1 Streambank Reforestation (Live Stakes), Type 2 Streambank Reforestation (Trees and Shrubs), Type 2 Streambank Reforestation (Embankment Shrubs), and native grass seed mixture. Shrubs will be planted along the roadway embankment to extend the buffer zone on the eastern size of the proposed channel. The proposed plantings were chosen based on their native and wetland indicator status. Proposed species are listed in Table 1. See Table 2 for the native grass seed mix species from the NCDOT standard specification. Live stakes (Type I) will be planted at 2-ft on center spacing, trees and shrubs (Type II) will be planted at 6 ft 10 ft (average of 8 ft) on-center spacing. See Table 2 for the native grass seed mix rates of application. Average buffer width (measured from the bankfull channel limit) that will be replanted along the stream is 40 feet with widths ranging from 20 to 65 feet. There is an area on the left bank at approximate station 10+10 that has a buffer width of approximately 25 feet due to an existing pond that the R/W and buffer zone were brought in to avoid. In addition, two areas located at approximate stations 10+70 and 12+62 along the right bank have a buffer width ranging from 22 to 24 feet due to the stream alignment being generated to have an appropriate belt width based on the locations of the upstream pipe and the proposed driveway pipe arch. Table 1. Proposed Trees, Shrubs, and Live Stakes Botanical Name Common Name Wetland Indicator Status* Live Stakes Salix nigra Black Willow FACW Cornus amomum Silky Dogwood OBL Trees and Shrubs Pinus virginiana Virginia Pine UPL Robinia pseudoacacia Black Locust FACU Platanus occidentalis Sycamore FACW Acer rubrum Red Maple FAC Cornus amomum Silky Dogwood FACW Viburnum dentatum Spicebush FAC Lindera benzoin Southern Arrowwood FAC Corylus americana American Hazlenut FACU Embankment Shrubs Cornus racemosa Gray Dogwood FAC Hamamelis virginiana American Witchhazel FACU Viburnum dentatum Southern Arrowwood FAC Sambucus racemosa Red Elderberry FACU *UPL – Upland; FACU – Facultative upland; FAC – Facultative; FACW – Facultative Upland; OBL – Obligate Wetland A-0011C Stream Relocation Hyatt Mill Creek, Clay County, NC February 1, 2019 Page 3 of 3 Table 2. Proposed Native Grass Seed Mixture Rate of Application (lbs/acre) Species August 1 – June 1* 18 Creeping Red Fescue 8 Big Bluestem 6 Indiangrass 4 Switchgrass 35 Rye Grain May 1 – September 1* 18 Creeping Red Fescue 8 Big Bluestem 6 Indiangrass 4 Switchgrass 25 German or Browntop Millet *During periods of overlapping dates, the kind of seed to be used shall be determined.