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HomeMy WebLinkAbout12-11 Comments Erosion Control Hayfield SubstationFrederick Count] Engineering Manual For SVEC - Mayfield Substation Erosion Control & Drainage Calcs April 5, 2011 �pLTH pF O Gt U�ATHAN W. CKWEL a o� Lie. No.045075 y/0 ��SSIONAL E'G� Blackwell EnLygneeriny PLC 566 East Market Street Harrisonburg, VA 22801 Ph. (540) 432 -9555 Fax (540) 434 -7604 Blackwellengineering.com 4/5/2011 BE # 2200 9 0 Table of Contents SVEC — Hayfield Substation Project #2200 Description page ESC Narrative 01 -09 Erosion & Sediment Control Bond Estimate 10 Runoff Calculations Existing 11 -12 Proposed 13 -14 Drainage Map Attached BE 2200 SVEC - Hayfield Substation 0 Erosion and Sediment Control Narrative Project Description The purpose of this project is to expand the existing substation on site, including the construction of a 192 square foot controls building. The site is located in Frederick County, Virginia on S. Hayfield Road. The site is currently used as a Shenandoah Valley Electric Cooperative substation. A total of 0.35 acres are to be disturbed during the project. Existing Site Conditions The portion of site being considered for construction is currently grass covered and existing gravel. The site consists of low and generally flat terrain; the land slopes gently toward the northeast at approximately 24%. Adjacent Property One rural residence with agricultural property surrounds the site to the south, west and north. S. Hayfield Road borders the site to the east of the property. Offsite Area Any off-site area needed for borrow or spoils will utilize a site with an approved E &SC plan. SO /LS (See Soil Map) (10) Craigsville cobbly sandy loam, 0 to 5 percent slopes, subject to flooding. Soil is very deep, nearly level to gently sloping and well drained. It is on flood plains and first bottoms. Areas of the soil are commonly elongated and follow the course of the adjacent stream. Typically the surface layer of the Craigsville is dark brown cobbly sandy loam about 5 inches thick. The subsoil extends to a depth of 32 inches and is reddish brown very cobbly sandy loam. The substratum is reddish brown extremely cobbly sandy loam and extends to a depth of 60 inches or more. K value for Craigsville soils is 0.17. 30B — Monongahela gravelly loam, 2 to 7 percent slopes. This soil is deep, gently sloping, and moderately well drained. Typically the surface layer is brown gravelly loam about 7 inches thick. The subsoil extends to a depth of about 43 inches thick. Permeability in this soil is moderate above the fragipan and moderately slow or slow in the fragipan. It has low available water capacity and low shrink swell potential. This soil is droughty during the growing season. The seasonal high water table, permeability in the fragipan, and depth to bedrock are the main limitations to use of this soil for community development. The land is Blackwell Engineering, PLC 566 East Market St. arrisonburg, VA 22801 BE 2200 SVEC - Hayfield Substation capability classification is IIe. Erodibility index "K" factor is 0.37 for depths of 0 -7 inches and 31 -43 inches, and 0.43 for depths of 7 -31 inches. Critical Erosion Areas Disturbed Slopes greater the 2:1 are to be matted or otherwise seeded to insure proper vegetation. Proper maintenance of the Construction Entrance will ensure that sediment is not tracked onto the pavement and public roads by construction traffic. Erosion and Sediment Control Measures Unless otherwise indicated, all vegetative and structural erosion and sediment control practices shall be constructed and maintained according to the minimum standards and specifications of the Virginia Erosion and Sediment Control Regulations, latest edition. The minimum standards of the handbook shall be adhered to unless otherwise waived or approved by a variance. Structural Practices 1. Temporary Construction Entrance — 3.02 A temporary construction entrance shall be installed as shown on the plans. During muddy conditions, drivers of construction vehicles shall be required to clean off their wheels before entering the highway. Runoff created during this procedure shall pass through an approved sediment removing process. 2. Construction Road Stabilization — 3.03 The temporary stabilization of access roads, subdivision roads, parking areas, and other on- site vehicle transportation routes shall be implemented with stone immediately after grading 3. Silt Fence— 3.05 A temporary sediment barrier constructed of posts, filter fabric and, in some cases, a wire support fence, shall be installed where shown on the plans to intercept and filter sediment and decrease flow velocities from drainage areas of limited size. 4. Diversion Dike — 3.09 To divert storm runoff from upslope drainage areas away from unprotected disturbed areas and slopes to a stabilized outlet. 5. Rock Check Dam — 3.20 Small temporary stone dams constructed across a Swale or drainage ditch shall be constructed as shown on the plans. Blackwell Engineering, PLC 566 East Market St. arrisonburg, VA 22801 2 BE 2200 SVEC - Hayfield Substation 6. Permanent Seeding= 3_32 Permanent seeding shall be applied to denuded areas within seven days after final grade is reached on any portion of the site 7. Other practices shall be provided if determined by the Engineer or County E &SC Administrator. Vegetative Practices 1. Top soiling (stockpile) Topsoil shall be stripped from the area to be graded and stockpiled for later use and shall be stabilized by seeding with seed mix appropriate for the time of year. 2. Permanent Seeding Permanent seeding shall be applied (appropriate to the time of year) to areas that have been brought to final grade. Management Strategies 1. Perimeter sediment trapping measures to be installed prior to any excavation on site. 2. Construction shall be conducted so that existing cover will not be disturbed anymore than necessary. 3. Construction shall be sequenced so that grading operations can begin and end as quickly as possible. 4. Permanent seeding and other stabilization shall follow immediately after grading. 5. Areas that will be disturbed shall be clearly marked by flags, signs, etc. 6. Thejob superintendent shall be responsible for the installation and maintenance of all erosion and sediment control practices. 7. After achieving adequate stabilization to the satisfaction of the E &SC Administrator, the temporary E &S controls shall be removed. Blackwell Engineering, PLC 566 East Market St. arrisonburg, VA 22801 3 BE 2200 SVEC - Hayfield Substation • Permanent Stabilization All areas disturbed by construction and not otherwise stabilized, shall be stabilized with permanent seeding within 7 days following finish grading. Seeding shall be done according to standard & specification 3.32, PERMANENT SEEDING, of the handbook Seeding shall be applied depending on time of the year according to E &SC handbook specifications. In all seeding operations, seed, fertilizer, and lime shall be applied prior to mulching. Erosion control blankets shall be installed over fill slopes which have been brought to final grade and have been seeded to protect the slopes from rill and gully erosion and to allow seed to germinate properly. Mulch (straw or fiber) shall be used on relatively flat areas. In all seeding operations, seed, fertilizer, and lime shall be applied prior to mulching. Storm Water Management/ Existing Downstream Channel The substation area (existing and proposed) of 0.60 acres consists of 0.50 acres of impervious area. Total proposed impervious area is 0.20 acres. The stormwater exits the site two ways. One way is into the VDOT ditch along S. Hayfield Road and the second is offsite to the north by way of sheet flow. The increase in flow from the pre development to post development runoff to the VDOT ditch is minimal, only 0.3 and 0.5 cfs for the 10 and 100 year storms respectively. The increase in flow from the pre development to post development runoff to the north property line by way of sheet flow is also minimal, only 0.2 and 0.3 cfs for the 10 and 100 year storms respectively. Due to the trivial increase in flow in both situations, no additional stormwater management controls are being provided for the substation expansion project. Disturbed area is less than one acre, therefore no water quality is proposed. Maintenance In general, all erosion and sediment control measures shall be checked daily and after each significant rainfall. The following items shall be checked in particular: 1. The seeded area shall be checked regularly to ensure that a good stand is maintained. Areas shall be fertilized and reseeded as needed. 2. The gravel Construction Entrance shall be maintained in a condition which will prevent tracking or flow of mud onto public right -of -ways. Periodic top dressing with additional stone or the washing and reworking of existing stone shall be required when the stone is covered or has been pushed into the soil. It shall be returned to its original depth of 6" (min.). toBlackwell Engineering, PLC 566 East Market St. glarrisonbUrg, VA 22801 4 BE 2200 SVEC - Hayfield Substation 3. The Silt Fence barrier if used shall be checked regularly for undermining of deterioration of the fabric. Sediment shall be removed when the level of sediment deposition reaches half way to the top of the barrier. 4. The outlet protection shall be checked regularly for sediment buildup that will prevent drainage. If the stone is clogged by sediment, it shall be removed and cleaned or replaced. Riprap shall be inspected periodically to determine if high flows have caused scour beneath the riprap or filter fabric and dislodged any of the stone. Care must be taken to properly control sediment -laden construction runoff, which may drain to the point of the new installation. 5. The inlet protection structure shall be inspected after each rain and repairs made as needed. Sediment shall be removed and the trap restored to its original dimensions when the sediment has accumulated to one half the design depth of the trap. 6. Maintenance of the Sediment Trap shall include mowing and repair of the detention trap berms, spillways, and grass areas; cleaning out sediment buildup; clearing of debris and trash from the outlet pipe system. As well as the removing of sediment when it reaches the cleanout level. • 7. The temporary diversion dike shall be inspected after every storm and repairs made if necessary. Once every two weeks whether a storm has occurred or not, the measure shall be inspected and repairs made if needed. Damages made by construction traffic or other activity must be repaired before the end of the working day. 8. The inlet and outlet protection filter system shall be checked regularly for sediment buildup which will prevent drainage. If the stone filter is clogged by sediment, it shall be removed and cleaned or replaced. Blackwell Engineering, PLC 566 East Market St. Harrisonburg, VA 22801 9 BE 2200 SVEC - Hayfield Substation 4VAC50- 30 -40. MINIMUM STANDARDS An erosion and sediment control program adopted by a district or locality must be consistent with the following criteria, techniques and methods: I. Permanent or temporary soil stabilization shall be applied to denuded areas within seven days after final grade is reached on any portion of the site. Temporary soil stabilization shall be applied within seven days to denuded areas that may not be at final grade but will remain dormant for longer than 30 days. Permanent stabilization shall be applied to areas that are to be left dormant for more than one year. 2. During construction of the project, soil stockpiles and borrow areas shall be stabilized or protected with sediment trapping measures. The applicant is responsible for the temporary protection and permanent stabilization of all soil stockpiles on site as well as borrow areas and soil intentionally transported from the project site. 3. A permanent vegetative cover shall be established on denuded areas not otherwise permanently stabilized. Permanent vegetation shall not be considered established until a ground cover is achieved that is uniform, mature enough to survive and will inhibit erosion. 4. Sediment basins and traps; perimeter dikes, sediment barriers and other measures intended to trap sediment shall be constructed as a first step in any land- disturbing activity and shall be made functional before upslope land disturbance takes place. 5. Stabilization measures shall be applied to earthen structures such as dams, dikes and diversions immediately after installation. 6. Sediment traps and sediment basins shall be designed and constructed based upon the total drainage area to be served by the trap or basin. a. The minimum storage capacity of a sediment trap shall be 134 cubic yards per acre of drainage area and the trap shall only control drainage areas less than three acres. b. Surface runoff from disturbed areas that is comprised of flow from drainage areas greater than or equal to three acres shall be controlled by a sediment basin. The minimum storage capacity of a sediment basin shall be 134 cubic yards per acre of drainage area. The outfall system shall, at a minimum, maintain the structural integrity of the basin during a 25 -year storm of 24 -hour duration. Runoff coefficients used in runoff calculations shall correspond to a bare earth condition or those conditions expected to exist while the sediment basin is utilized. 7. Cut and fill slopes shall be designed and constructed in a manner that will minimize erosion. Slopes that are found to be eroding excessively within one year of permanent stabilization shall be provided with additional slope stabilizing measures until the problem is corrected. 8. Concentrated runoff shall not flow down cut or fill slopes unless contained within an adequate temporary or permanent channel, flume or slope drain structure. Blackwell Engineering, PLC 566 East Market St. arrisonburg, VA 22801 BE 2200 SVEC - Hayfield Substation 9. Whenever water seeps from a slope face, adequate drainage or other protection shall be provided. 10. All storm sewer inlets that are made operable during construction shall be protected so that sediment -laden water cannot enter the conveyance system without first being filtered or otherwise treated to remove sediment. 11. Before newly constructed stormwater conveyance channels or pipes are made operational, adequate outlet protection and any required temporary or permanent channel lining shall be installed in both the conveyance channel and receiving channel. 12. When work in a live watercourse is performed, precautions shall be taken to minimize encroachment, control sediment transport and stabilize the work area to the greatest extent possible during construction. Nonerodible material shall be used for the construction of causeways and cofferdams. Earthen fill may be used for these structures if armored by nonerodible cover materials. 13. When a live watercourse must be crossed by construction vehicles more than twice in any six - month period, a temporary vehicular stream crossing constructed of nonerodible material shall be provided. 14. All applicable federal, state and local regulations pertaining to working in or crossing live watercourses shall be met. 15. The bed and banks of a watercourse shall be stabilized immediately after work in the watercourse is completed. 16. Underground utility lines shall be installed in accordance with the following standards in addition to other applicable criteria: a. No more than 500 linear feet of trench may be opened at one time. b. Excavated material shall be placed on the uphill side of trenches. c. Effluent from dewatering operations shall be filtered or passed through an approved sediment trapping device, or both, and discharged in a manner that does not adversely affect flowing streams or off -site property. d. Material used for backfilling trenches shall be properly compacted in order to minimize erosion and promote stabilization. e. Restabilization shall be accomplished in accordance with these regulations. f. Applicable safety regulations shall be complied with. 17. Where construction vehicle access routes intersect paved or public roads, provisions shall be made to minimize the transport of sediment by vehicular tracking onto the paved surface. Where sediment is transported onto a paved or public road surface, the road surface shall be cleaned thoroughly at the end ofeach day. Sediment shall be removed from the roads by shoveling or sweeping and transported to a sediment control disposal area. Street washing shall be allowed only Blackwell Engineering, PLC P�arrisonburg, 66 East Market St. VA 22801 BE 2200 SVEC - Hayfield Substation after sediment is removed in this manner. This provision shall apply to individual development lots as well as to larger land- disturbing activities. 18. All temporary erosion and sediment control measures shall be removed within 30 days after final site stabilization or after the temporary measures are no longer needed, unless otherwise authorized by the local program authority. Trapped sediment and the disturbed soil areas resulting from the disposition of temporary measures shall be permanently stabilized to prevent further erosion and sedimentation. 19. Properties and waterways downstream from development sites shall be protected from sediment deposition, erosion and damage due to increases in volume, velocity and peak flow rate of stormwater runoff for the stated frequency storm of 24 -hour duration in accordance with the following standards and criteria: a. Concentrated stormwater runoff leaving a development site shall be discharged directly into an adequate natural or man -made receiving channel, pipe or storm sewer system. For those sites where runoff is discharged into a pipe or pipe system, downstream stability analyses at the outfall of the pipe or pipe system shall be performed. b. Adequacy of all channels and pipes shall be verified in the following manner: (I ) The applicant shall demonstrate that the total drainage area to the point of analysis within the channel is one hundred times greater than the contributing drainage area of the project in question; or (2) (a) Natural channels shall be analyzed by the use of a two -year storm to verify that stormwater will not overtop channel banks nor cause erosion of channel bed or banks. (b) All previously constructed man -made channels shall be analyzed by the use of a ten -year storm to verify that stormwater will not overtop its banks and by the use of a two -year storm to demonstrate that stormwater will not cause erosion of channel bed or banks; and (c) Pipes and storm sewer systems shall be analyzed by the use of a ten -year storm to verify that stormwater will be contained within the pipe or system. c. If existing natural receiving channels or previously constructed man -made channels or pipes are not adequate, the applicant shall: (I ) Improve the channels to a condition where a ten -year storm will not overtop the banks and a two -year storm will not cause erosion to the channel bed or banks; or (2) Improve the pipe or pipe system to a condition where the ten -year storm is contained within the appurtenances; or (3) Develop a site design that will not cause the pre - development peak runoff rate from a two -year storm to increase when runoff outfalls into a natural channel or will not cause the pre - development peak runoff rate from a ten -year storm to increase when runoff outfalls into a man -made channel; or (4) Provide a combination of channel improvement, stormwater detention or other measures which is satisfactory to the plan - approving authority to prevent downstream erosion. d. The applicant shall provide evidence of permission to make the improvements. PZi Blackwell Engineering, PLC 566 Fast Market St. arrisonburg, VA 22801 BE 2200 SVEC - Hayfield Substation e. All hydrologic analyses shall be based on the existing watershed characteristics and the ultimate development of the subject project. f. If the applicant chooses an option that includes stormwater detention, he shall obtain approval from the locality of a plan for maintenance of the detention facilities. The plan shall set forth the maintenance requirements of the facility and the person responsible for performing the maintenance. g. Outfall from a detention facility shall be discharged to a receiving channel, and energy dissipators shall be placed at the outfall of all detention facilities as necessary to provide a stabilized transition from the facility to the receiving channel. h. All on -site channels must be verified to be adequate. i. Increased volumes of sheet Flows that may cause erosion or sedimentation on adjacent property shall be diverted to a stable outlet, adequate channel, pipe or pipe system, or to a detention facility. j. In applying these stormwater management criteria, individual lots or parcels in a residential, commercial or industrial development shall not be considered to be separate development projects. Instead, the development, as a whole, shall be considered to be a single development project. Hydrologic parameters that reflect the ultimate development condition shall be used in all engineering calculations. r k. All measures used to protect properties and waterways shall be employed in a manner which minimizes impacts on the physical, chemical and biological integrity of rivers, streams and other waters of the state. Blackwell Engineering, PLC 566 East Market St. arrisonbura, VA 22801 U 0 0 SVEC - Hayfield Substation Erosion & Sediment Control Cost Estimate MIN. STD. Item 3.01 Safety Fence 3.02 Construction Entrance 3.05 Reinforced Silt Fence 3.07 Curb Inlet Protection 3.08 Culvert Inlet Protection 3.09 Diversion Berm 3.10 Fill Diversion 3.12 Diversion 3.13 Sediment Trap - 1 acre 300.00 Sediment Trap - 2 acre Subtotal Sediment Trap - 3 acre 3.14 Sediment / Stormwater Basin 3.16 Paved Flume 3.17 Stormwater Conveyance Channel Seeded Sodded Temporary Matting Perminant Matting Riprap 3.18 Outlet Protection Riprap Grouted Riprap Concrete 3.20 Rock Check Dam 3.21 Level Spreader 3.22 Temporary Seeding /Mulch 3.23 Perminant Seeding /Mulch Units LF 1 Each 270 LF Each Each 270 LF LF LF Each Each Each Each sq /yd sq /yd sq /yd sq /yd sq /yd sq /yd Price 4.00 1,500.00 5.00 150.00 200.00 5.00 2.00 12.00 2,000.00 2,500.00 3,000.00 4,000.00 35.00 10.00 20.00 30.00 40.00 60.00 Total 1,500.00 1.350.00 1,350.00 sq /yd 60.00 sq /yd 50.00 sq /yd 40.00 - 2 sq /yd 30.00 60.00 sq /yd 12.00 - acre 2,500.00 - 0.1 acre 3,000.00 300.00 Subtotal 4,560.00 25% Contingency 1,140.00 Total = 5,700.00 Blackwell Engineering, PLC Attn: Nathan Blackwell (540) 432 -9555 2200 - FREDERICK County -E &SC Bond Estimate.xls m File: 2200 TC CALCS.As 2.68 iph 125 = Printed: 41512011 iph 110 = Runoff Calculations - Rational Method iph 1100 = 5.03 DA Existing #1 5.) Proposed Flows: Q = ACI 1.) Area = 3.45 ac Project Name: Q2 = SVEC - Hayfield Substation cfs Q25 = Project # : cfs 2200 4.5 2.) C = 0.36 0.33 ac @ 0.90 Impervious 0.00 ac @ 0.45 Cultivated Rows 3.12 ac @ 0.30 Pasture /Grass 3.) Time of Concentration Slope a. Overland: (200' max) L = 200 ft. Height = 4 ft. 2.0% VDOT Drainage Manual Appendix 6D -1: Tc = 12.1 min. b. Shallow: (1000' max) L= 0 ft. Height = 0 ft. Average velocity = 0.0 fps (paved) VDOT Drainage Manual Appendix 6D -6: Tc = 0.0 min. L = 286 ft. Height = 10 ft. 3.5% Average velocity = 3.0 fps (unpaved) VDOT Drainage Manual Appendix 6D -6: T, = 1.6 min. T, = L /60V Subtotal Tc = 1.6 min. c. Channel: L = 0 ft. Height = 0 ft.(paved) VDOT Drainage Manual Appendix 6D -5: Tc = 0.0 min. L = 342 ft. Height = 16 ft.(unpaved; 4.7% VDOT Drainage Manual Appendix 6D -5: T, = 2.4 min. Subtotal Tc = 2.4 min. d. Total T.: Tc = 16.1 min. 4.) Rainfall Intensities For Tc = 16 min. 12 = 2.68 iph 125 = 4.25 iph 110 = 3.64 iph 1100 = 5.03 iph 5.) Proposed Flows: Q = ACI Q2 = 3.3 cfs Q25 = 5.2 cfs Q10 = 4.5 cfs Q100 = 6.2 cfs @ 2005 Jonathan Brumfield, T. Basil Finnegan, Aaron Showalter Blackwell Engineering, PLC 566 East Market Street Harrisonburg, VA 22801 • C� File: 2200 TC CALCS.xls Punted: 4/5/2011 Runoff Calculations - Rational Method DA Existing #2 1.) Area = 0.87 ac Project Name: SVEC - Hayfield Substation Project # : 2200 2.) C = 0.39 0.13 ac @ 0.90 Impervious 0.00 ac @ 0.45 Cultivated Rows 0.74 ac @ 0.30 Pasture /Grass 3.) Time of Concentration a. Overland: (200' max) L = 200 ft. Height = 6 ft. VDOT Drainage Manual Appendix 6D -1: Tc = 10.9 min. b. Shallow: (1000' max) L = 0 ft. Height = Average velocity = VDOT Drainage Manual Appendix 6D -6: T, = L = 180 ft. Height = Average velocity = VDOT Drainage Manual Appendix 6D -6: T, = T, = L /60V Subtotal T, = c. Channel: L = 0 ft. Height = VDOT Drainage Manual Appendix 6D -5: T, = L = 0 ft. Height = VDOT Drainage Manual Appendix 6D -5: T, = Subtotal T, = d. Total T.: T, = 11.5 min. 4.) Rainfall Intensities: 0 ft. 0.0 fps (paved) 0.0 min. 16 ft. 4.8 fps (unpaved) 0.6 min. 0.6 min. 0 ft.(paved) 0.0 min. 0 ft.(unpaved 0.0 min. 0.0 min. For T,= 12 min. 12 = 3.06 iph 125 = 4.83 iph 110 = 4.14 iph lion = 5.68 iph 5.) Proposed Flows: Q = ACI Q2 = 1.0 cfs Q25 = 1.6 cfs Q10 = 1.4 cfs Q100 = 1.9 cfs @ 2005 Jonathan Brumfield, T. Basil Finnegan, Aaron Showalter Blackwell Engineering, PLC 566 East Market Street Harrisonburg, VA 22801 Slope 3.0% 8.9% 12 0 File: 2200 TC CALCS.xls Printed: 4/5/2011 Runoff Calculations - Rational Method DA Proposed #1 1.) Area = 3.44 ac Project Name: SVEC - Hayfield Substation Project # : 2200 2.) C = 0.39 0.49 ac @ 0.90 Impervious 0.00 ac @ 0.45 Cultivated Rows 2.95 ac @ 0.30 Pasture /Grass 3.) Time of Concentration a. Overland: (200' max) L = 200 ft. Height = 4 ft. VDOT Drainage Manual Appendix 6D -1: T� = 11.6 min. b. Shallow: (1000' max) L = 0 ft. Height = Average velocity = VDOT Drainage Manual Appendix 6D -6: Tc = L = 250 ft. Height = Average velocity = VDOT Drainage Manual Appendix 6D -6: T, = Tc = L /60V Subtotal T, = 0 ft. 0.0 fps (paved) 0.0 min. 7 ft. 2.7 fps (unpaved) 1.6 min. 1.6 min. Slope 2.0% 2.8% c. Channel: L = 0 ft. Height = 0 ft.(paved) VDOT Drainage Manual Appendix 6D -5: Tc = 0.0 min. L = 373 ft. Height = 18 ft.(unpaved; 4.8% VDOT Drainage Manual Appendix 6D -5: T� = 2.5 min. Subtotal Tc = 2.5 min. d. Total T,: T, = 15.7 min. 4.) Rainfall Intensities: For Tc= 16 min. IZ = 2.68 iph 125 = 4.25 iph Ile = 3.64 iph /too = 5.03 iph 5.) Proposed Flows: Q = ACI Q2 = 3.6 cfs Q25 = 5.6 cfs Q10 = 4.8 cfs Q100 = 6.7 cfs @ 2005 Jonathan Brumfield, T. Basil Finnegan, Aaron Showalter Blackwell Engineering, PLC 566 East Market Street Harrisonburg, VA 22801 13 J • r1 LJ File: 2200 TC CAM As Pnnted: 41512011 Runoff Calculations - Rational Method DA Proposed #2 1.) Area = 0.88 ac Project Name: SVEC - Hayfield Substation Project # : 2200 2.) C = 0.42 0.17 ac @ 0.90 Impervious 0.00 ac @ 0.45 Cultivated Rows 0.71 ac @ 0.30 Pasture /Grass 3.) Time of Concentration a. Overland: (200' max) L = 200 ft. Height = 6 ft. VDOT Drainage Manual Appendix 6D -1: T, = 10.4 min. b. Shallow: (1000' max) L= 0 ft. Height = Average velocity = VDOT Drainage Manual Appendix 6D -6: Tc = L = 180 ft. Height = Average velocity = VDOT Drainage Manual Appendix 6D -6: T, = T, = L /60V Subtotal T, = 0 ft. 0.0 fps (paved) 0.0 min. 16 ft. 4.8 fps (unpaved) 0.6 min. 0.6 min. c. Channel: L = 0 ft. Height = 0 ft.(paved) VDOT Drainage Manual Appendix 6D -5: T� = 0.0 min. L = 0 ft. Height = 0 ft.(unpaved; VDOT Drainage Manual Appendix 6D -5: T� = 0.0 min. Subtotal T, = 0.0 min. d. Total T,: 4.) Rainfall Intensities: For T,= 11 5.) Proposed Flows: T, = 11.0 min. min. 12 = 3.18 iph 125 = 5.01 iph 110 = 4.29 iph 1100 = 5.89 iph Q =ACI Q2 = 1.2 cfs Q25 = 1.8 cfs Q10 = 1.6 cfs Q100 = 2.2 cfs © 2005 Jonathan Brumfield, T. Basil Finnegan, Aaron Showalter Blackwell Engineering, PLC 566 East Market Street Harrisonburg, VA 22801 Slope 3.0% 8.9% 14