Loading...
HomeMy WebLinkAboutWPO201300037 Assessment - Environmental 2013-05-30 EROSION & SEDIMENT CONTROL NARRATIVE WILLOW GLEN PHASE 2 ALBEMARLE COUNTY, VIRGINIA 20 May 2013 Prepared by: Alan Franklin PE, LLC 427 Cranberry Lane Crozet, Virginia 22932 (434) 531-5544 Project Description Sugaray Two, LLC proposes to establish a new residential neighborhood composed of single-family homes, duplexes, townhomes, and condominiums along with a variety of recreation and amenities within significant open space. The nearly 22-acre parcel lies north of the City of Charlottesville, in Albemarle County. The property is located on the east side of Dickerson Road, roughly 1/2 mile south of the intersection with Airport Road. The airport property is directly across the street on the west side of Dickerson Road. To the east are Deerwood Village, a SFD residential community, and a residential section of Hollymead Town Center that is just now developing. The neighboring property to the north is rural-residential in nature, and to the south is a vacant, wooded parcel that is zoned for medium density residential. While the main entry into the new community will ultimately be from Dickerson Road and a majority of the density will occur on the north side of a perennial stream that bisects the property, the developer would like to pursue as the first phase of development, the secondary entrance connection to Town Center Drive and the approved improvements to the property on the south side of the perennial stream that bisects the property. The future phase areas on the north side of the stream will be used as a borrow area. It is the intent of the developer to quickly tie Willow Glen into the fabric of Hollymead Town Center and to build equity in the project to assist with future phase improvements such as the bridge over the perennial stream. Existing Site Conditions Several modest houses that currently occupy the property are scheduled to be demolished. The property is a mix of open fields, overgrown thicket, and woodland. A gentle ridge runs in an easterly direction down the center of the property. Consequently, the property's topography slopes to the north, south, and east. Two dry stormwater management basins exist adjacent to Dickerson Road on the Airport property. These facilities appear to have been installed to handle runoff from the airport property. To some degree their presence detains airport runoff prior to allowing it to travel off-site and under Dickerson Road. The outfall from these two basins ends up being conveyed within natural channels that initially delineate the northern and southern boundary limits of Willow Glen. Eventually their courses transect the Willow Glen tract. The northern swale intersects what can best be described as a creek that flows from north to south along the eastern boundary limits. A little further south of there the second swale intersects this same creek. During dry periods these swales are dry or nearly dry, indicating that they are predominantly spring-fed. Albemarle County considers slopes that are 4:1 or steeper as critical slopes, and these are protected by code. Critical slopes are not much of an issue on this site, but a critical slope waiver has been granted for limited disturbance. Many of the critical slopes that do exist are manmade from the construction of Dickerson Road. Soils on site consist largely of the Louisburg and Wedowee series. Wetlands are present in small pockets along the course of the creek which runs north to south along the eastern boundary. WILLOW GLEN PHASE 2 May 20,2013 Erosion Control Narrative Adjacent Property The property lies within the Hollymead growth area and is included in the Places29 Master Plan for that community. Residential subdivisions exist to the east, rural- residential parcels to the north, the airport to the west, and an undeveloped residential tract to the south. The proposed development is consistent with, and complimentary to, the existing and planned development for this area. Off-Site Areas The area surrounding the development is evolving into a community in-and-of itself, with light industrial, retail, office, and service uses complimenting the wide variety of residential units. Years ago utility infrastructure and stormwater management facilities were put in place to support both existing development and a certain amount of future growth. Road improvements have been, or are in the process of being, implemented within the precinct. Connectivity between parcels has been encouraged, therefore some degree of off-site road and sidewalk improvements are in the offing. Water and sanitary sewer service are available, but there may eventually be a capacity issue with the sanitary sewer as the Hollymead community nears build-out. No regional stormwater management facilities are present, so this development will have to create their own installation on- site. Soils The soils on the property have been classified as Louisburg and Wedowee series, with the Wedowee soils occupying the gently sloping ridges and the Louisburg underlying the lower areas along the swales and creek bottom. The Louisburg soil is not very deep and is somewhat excessively drained, while the Wedowee soils are much deeper. Both are sandy loams and formed from decomposed granite. Below are additional characteristics of each soil found on-site. Name Code Erodibility Permeability Depth Shrink/Swell Strength Louisburg 47C Severe Rapid 48" + Very Low High Wedowee 94B Moderate Moderate 60"+ Moderate Low Wedowee 94C Severe Moderate 60"+ Moderate Low One will note that the Wedowee soils listed have low strength, which leads one to surmise that, in their native state they would have limitations as road fill and other fill uses. However, given proper moisture content, placement, and compaction, those shortcomings may be overcome. When grading in or moving the Louisburg soils additional care should be taken to prevent erosion of exposed grades. Deep excavations in this soil, such as is proposed around the stormwater management basin, should be expected to encounter rock. Due to the permeability of the soil, importation of clay or use of Bentonite or a pond liner may be necessary. In certain areas retaining walls have been specified. The material to be placed behind these wall installations is expected to include a considerable amount of select backfill and possibly drainage fill consisting of stone, WILLOW GLEN PHASE 2 May 20,2013 Erosion Control Narrative strategically placed and compacted. Therefore there is little concern of the native soils compromising proposed buildings and parking areas below. Critical Erosion Areas Critical erosion-prone areas on site are rather minimal and limited to the certain small areas adjacent to the creek along the eastern boundary and as a result of any grading to occur adjacent to Dickerson Road. The main body of the property does not contain critical slopes. The Louisburg soils on site are highly erodable, but much of this area will be left undisturbed or will drain toward one or more of the stormwater management facilities proposed. Because Dickerson Road is a significant collector road, it is critical that the roadway be kept clean and safe. It is expected that the earthwork on this site will balance so soil import or export will not take place. However, Willow Glen is a considerable undertaking and its construction will occur over a number of years and involve a variety of trades repeatedly entering and exiting the site on a daily basis. The community will likely be developed in phases, with some degree of earthwork being associated with each phase. Staying on top of the erosion control program and responding to the dynamics of the construction program will be a challenge. A single plan that covers all of the externalities and details of a project of this magnitude would be nearly impossible to devise. To make the proposal more manageable and understandable the Owner and Engineer have approached the development of this erosion control plan as a series of construction stages. Initially, there would be activities associated with establishing a construction entrance into the site, providing wash-down and equipment staging areas, and preparing for limited clearing of the property near the entrance to ensure safe sight distance. The property was thereafter divided into three main zones, A, B, and C, with A being the first to experience land disturbance. A general program for development and associated erosion control measures have been developed for each of the three zones. These activities would result in a rough graded site condition with all utility mains, stormwater management facilities, and roadways in place and the individual building pads ready for building construction. Within each building pad, additional erosion control measures may need to be employed to relegate sedimentation to that particular work area. Each builder will be held responsible for implementation of erosion control measures at that final level of construction. Erosion & Sediment Control Measures As referenced above, an attempt has been made to describe the sequencing of construction and the erosion control measures that should be associated with each step. The proposed program is outlined on the following pages, as well as on the plan sheet(s). The program includes initial, overall erosion control measures to be employed at the advent of the construction effort, zone treatments associated with the mass clearing and grading of portions of the property, and a third level of detail that is associated with general construction of infrastructure within subsections of Willow Glen. Notes outlining the chronological steps recommended for construction and the erosion control program are included. Of course, weather and other events or constraints may necessitate minor deviation from this plan. For that reason, the contractor shall take extra care to check, WILLOW GLEN PHASE 2 May 20,2013 Erosion Control Narrative maintain, alter, and repair all erosion control measures on a daily basis. They are also to report any concerns or problems to the Engineer and County Agent. Erosion Control Sequencing An attempt has been made to describe the sequencing of construction and the erosion control measures that should be associated with the development of Willow Glen. The program includes initial, overall erosion control measures to be employed at the advent of the construction effort, zone treatments associated with the mass clearing and grading of the property and installation of primary infrastructure. Notes outlining the chronological steps recommended for construction and the erosion control program have been included. Prior to Construction Before commencement of work: • Call MISS UTILITY and request marking of all utilities. • Contact and coordinate with utility companies to ensure proper and complete disconnection of all services to existing homes and the proper methodology of removing or relocating any and all utility features as shown on the plans. • Contact and coordinate with VDOT to secure all necessary entrance permits and agree upon needed traffic control measures and construction entrance configuration specifics. • Field stake limits of any areas to be protected from construction activity and install markers and/or other prescribed measures of protection. Zone A - Stage 1 1. Continue use of established construction entrance at Dickerson Road from previous phase of construction. 2. Establish contractor parking and staging area. 3. Utilize construction roads from previous phase of construction and existing dirt roads through Zone 'A' to install perimeter measures and construct sediment basin and sediment trap #4. 4. Complete any demolition of structures to be removed. 5. Install perimeter silt fencing with wire support. 6. Install safety fence around TMP 32-49B. 7. Construct temporary sediment basin and sediment trap #4 along with any diversion dikes directing runoff to these measures. 8. Install class 1 rip rap spillways on the two receiving legs of the sediment basin. 9. Install safety fence with signs around perimeters of sediment basin and sediment Trap. 10.Install diversion dike just upstream of sediment basin to protect sediment basin foreslope and direct majority of site runoff to the rip rap spillways on the two receiving legs of the sediment basin. 11.0nce perimeter measures are installed, decommission any erosion measures from a previous phase of construction. 12.Establish stockpile area in location shown on the plan. WILLOW GLEN PHASE 2 May 20,2013 Erosion Control Narrative 13.Strip topsoil of land to be disturbed and store in stockpile area. Install temporary seeding and silt fence to the stockpile as needed. 14.Begin clearing, grubbing and mass grading of Zone 'A' ensuring that all disturbed areas drain to either the sediment trap or basin. 15.Make off-site sanitary sewer connection and install aerial sanitary sewer/stream crossing without disturbance of the stream. No stream disturbance is permitted during this phase of construction. 16.Continue installation of sanitary sewer pipe and sanitary sewer structures ZA1, ZA2, ZA3, ZA4, ZC1, ZB1, ZB2, ZB3, and ZB4 prior to completing foreslope of sediment basin to Stage 2 grades. 17.After installation of sanitary sewer as indicated above proceed to Stage 2 plan. Zone A-Stage Two 1. Continue grading to establish rough final grades indicated on the Stage 2 plan. 2. Maintain perimeter silt fencing with wire support. Adjust location as necessary. 3. Install and adjust diversion dikes, diversions, fill diversions, and slope drains to direct all zone a runoff to the sediment basin and sediment trap #4 which are to be maintained throughout Stage 2 construction. 4. Utilize area draining to sediment trap #4 for earthen borrow or waste operations as this area is a part of a future phase of construction. 5. Continue installation of sanitary sewer and install waterline and storm drainage facilities as depicted on the Stage 2 plan. The limits and location of proposed sanitary sewer, waterline, and storm drainage facilities are to based on the approved site plans. 6. Install inlet protection on all grate, curb, and drop inlets and outlet protection on all pipe outlets as necessary. 7. As Phase 2 (Zone 'A') roadway grades are finalized install roadway base materials and concrete curbing adjusting inlet protection as necessary. 8. Contractor to coordinate with home builder to establish building pad grades. 9. As Phase 2 (Zone 'A') building pad grades are finalized, perform surface roughening on slopes and prepare zone a disturbed areas for permanent stabilization. 10.Apply topsoil, permanent seeding, straw mulch, and matting as required to all disturbed areas that are to be vegetated. 11.0nce all Zone 'A' road base materials and curbing are installed, all permanent vegetation is established on turfed areas , and the Zone 'A' site is deemed stabilized by the county erosion control inspector, convert facilities to bmp, remove all other erosion & sediment control measures, dispose of silt/debris/trash in an approved manner, and install all required stormwater BM P's. Vegetative Practices After the majority of the grading program has been executed and, in particular, once the cut and fill slopes outside the building envelopes have been established, they should be redressed with an ample depth of topsoil from the stockpiles and surface roughened. WILLOW GLEN PHASE 2 May 20,2013 Erosion Control Narrative Thereafter, all matting, seeding, plantings, and mulch should be applied. If for some reason, building construction on certain pad sites does not commence soon after the mass grading of the site is complete, exposed areas are to be treated with temporary seeding and mulch until such time as construction begins. Management Strategies 1. Construction will be sequenced so that grading operations can begin and end as quickly as possible. 2. Areas which are outside the construction limits and not to be disturbed shall be clearly marked with safety fence or tree protection. 3. Tree protection shall be installed before any grading activities commence and before equipment and material storage areas are established. 4. Sediment trapping measures shall be installed as a first step in grading and will be seeded and mulched immediately following installation. 5. Matting and seeding, whether temporary or permanent, will follow immediately after grading. 6. The site contractor shall be responsible for the installation and maintenance of all erosion and sediment control practices. 7. After achieving adequate stabilization, the temporary erosion and sediment controls will be cleaned up and removed and final grades established according to the grading plan for the project. Permanent Stabilization As mentioned above, permanent seeding is to be applied to all areas not proposed for hardscape or building improvements within 10 days of final grading in that area. Stormwater Management All stormwater management is to be accomplished via two bio-filters (one in Phase 2 and one in a future phase), a bio-detention basin (in Phase 1), and a stormwater management/amenity pond (Phase 2) which provide water quality treatment per state and County requirements as well as detention and attenuation of the 2-yr and 10-yr design storms to pre-development runoff rates. The stormwater management strategy and calculations are depicted on the attached plans. Minimum Standard 19 is addressed through detention, attenuation, and discharge of stormwater from the 2-yr and 10-yr storms to existing adequate receiving channels (as determined through on-site inspection, at the pre-development rates. Maintenance In general, all erosion and sediment control measures will be checked daily and after each significant rainfall. The following items will be checked in particular: 1. The sediment traps will be checked every 3 weeks and after each significant rainfall for sediment cleanout. WILLOW GLEN PHASE 2 May 20,2013 Erosion Control Narrative 2. The gravel outlets will be checked every 3 weeks and after each significant rainfall for sediment buildup which would prevent drainage. If the gravel is clogged by sediment, it shall be removed and cleaned or replaced. 3. The silt fence barrier will be checked every 3 weeks and after each significant rainfall for undermining or 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 seeded areas will be checked every 3 weeks and after each significant rainfall to ensure that a good stand is maintained. Areas shall be fertilized and reseeded as determined necessary by the county agent. State Minimum Standards An erosion and sediment control program adopted by a district or locality must be consistent with the following criteria, techniques and methods: 1. 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 WILLOW GLEN PHASE 2 May 20,2013 Erosion Control Narrative of drainage area. The outfall system shall, at a minimum, maintain the structural integrity of the basin during a twenty-five 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. 9. Whenever water seeps from a slope face, adequate drainage or other protection shall be provided. 10.A11 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. Non-erodible material shall be used for the construction of causeways and cofferdams. Earthen fill may be used for these structures if armored by non-erodible 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 non- erodible material shall be provided. 14.A11 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. WILLOW GLEN PHASE 2 May 20,2013 Erosion Control Narrative c. Effluent from dewatering operations shall be filtered or passed through 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 of each 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 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: (1) 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; and (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. WILLOW GLEN PHASE 2 May 20,2013 Erosion Control Narrative c. If existing natural receiving channels or previously constructed man-made channels or pipes are not adequate, the applicant shall: (1) Improve the channel 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. 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 dissipaters 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 runoff 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. 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. WILLOW GLEN PHASE 2 May 20,2013 Erosion Control Narrative SEDIMENT BASIN/TRAP CALCULATIONS WILLOW GLEN PHASE 2 May 20,2013 Erosion Control Narrative Table 16:Sediment Trap design (spec 3.13) SEDIMENT TRAP DESIGN#4 Drainage Area(acres)(<3) 2.89 Ac. (=1 .:1 Trap Volumes: euO°'r"".e MVP'a smolt VIM l _ Elevation(ft) Area(sf) Volume(cy) " 546 2936 0 nc.: i=.i?"w, tO 548 3958 255 •:•��"�' 550 5080 590 c��t^ �!^`i �.�wr. n+ar cult. a�w. a+ec o Wet Storage: .*X ft.113-∎ rtnrec wwac.,s`• cuss:MM. Wet Storage Required(cy)(67'DA) 193.6 Bottom of stone weir(ft) 547.6 Wet Storage Provided at this Eelevation(cy) 200.0 Slope of Wet Storage Sides 2:1 Weir Length(ft)(6XDA) 17.3 Dry Storage: Bottom of Trap Elevation(ft) 546 Dry Storage Required(cy)(67'DA) 193.6 Bottom Trap Dimensions: 37x102' Crest of Stone Weir 548.9 Top of Dam Elevation(ft) 550 Dry Storage Provided at this Elevation(cy) 200.0 Top Width of Dam(ft) 4 Slope of Dry Storage Sides 2:1 Top Trap Dimensions 51'x118' for reference: w 6_ SEDIMENT TRAP#4 DESIGN ___________ i.5 0.5 20 2.0 1,] 2.0 2.5 1.5 2.5 3.0 2.] 2.5 ... s'.7. 3.5 2.5 3.0 o A.0 3.2 3.0 4.5 3.5 l.0 60p 11.11-0° 5.0 1.0 4.5 IGII�11 ....., __ pw ocrm =u° 500 K 1 0 400 .::E__ ...a_...;. ,.,....,.-,...',., w 300 ,;= _. 200 ,.$..w^•_ 100 . .R_,_ . Irmo �. 545 546 547 548 549 550 551 ELEVATION(FT) Table 15:Sediment Basin design(spec 3.14) SEDIMENT I:ASIN DESIGN Drainage Area(acres) 14.41 , ,,,, ,, Basin Volumes:(using 2'contour intervals) 2...1j UT W" �E"`" Elevation(ft) Contour Area(sf) Volume(cy) DESIGN NIGH WATER .L (xs- slaw ELlV.) 524 13011 0 illiWilitz:526 17447 1128 IN------— 528 22320 2601 ,u-s• asr 530 27615 4450 DRY sroacE 532 33322 6707 "'� 42 .cr Wet Storage: Wet Storage Required(cy)(67*DA) 965.5 Dewatering Orifice Elevation(ft) 526.0 Design High Water 529.0 T. Wet Storage Provided at this Elevation(cy) 1128.0 Top of Dam(ft) 532.0 Available Volume Before Cleanout(cy)(33*DA) 475.5 Top Width of Dam(ft) 10.0 Cleanout Elevation(ft) 525.0 Bottom of Basin(ft) 526.0 Distance from Cleanout to Orifice(ft)(>1') 1.0 Approx.Bottom Dimensions: 100'x200' Upstream Face Slope: 3:1 Dry Storage: Downstream Face Slope: 3:1 Dry Storage Required(cy)(67*DA) 965.5 Principle Spillway Crest(ft) 527.2 Baffles: no Dry Storage Provided at this Elevation(cy) 1000.0 Length of Flow,L(ft) 100 Diameter of Dewatering Orifice(in) 8.0 Effective Width,We(ft) 174.47 Diameter of Flexible Tubing(in)(orifice+2") 10.0 L/We (baffles required if>2) 0.6 Runoff: Collars: n/a c(use 0.45 for bare earth) 0.45 Depth of Water at Spillway Crest(ft) n/a tc(min) 12.46 Slope of Upstream Face(Z:1) n/a i 2yr 3.8 0 2yr 24.6 Slope of Barrel(Sb) n/a i 25yr 4.9 0 25yr 31.8 Length of Barrel in Saturated Zone(Ls) n/a i 100yr 6.4 0 100yr 41.5 Number Collars Required n/a Dimension of Collars n/a Principle Spillway: Available Head(ft) 1.8 Emergency Spillway: n/a Diameter Riser(in) 42 Required Capacity(025-Op)(cfs) n/a Spillway Capacity,Op(cfs) 60.0 Bottom Width(ft) n/a Diameter Trash Rack(in) 60 Slope of Exit Channel(fUft) n/a Barrel Length(ft) 95 Minimun Length of Exit Channel(ft) n/a Head on Barrel through Embankment(ft) 11.0 Crest of Spillway(ft) 532 Diameter of Barrel(in) 24 SEDIMENT BASIN DESIGN v 5000 4000 3000 U 2000 1000 o 523 524 525 526 527 528 529 530 531 532 533 ELEVATION(FT) .. A 9P S M/Amenity Pond 2S Post-Amenity Subcat Reacta 'OCie Link Drainage Diagram for WILLOWGLEN-FINAL-Phase2-rat ,,, ly Prepared by Terra Concepts, PC, Printed 5/19/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC WILLOWGLEN-FINAL-Pha VA-Albemarle-ATLAS14 2-Year Duration=33 min, Inten=2.22 in/hr Prepared by Terra Concepts, PC Printed 5/19/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 2 Summary for Subcatchment 2S: Post-Amenity Runoff = 26.50 cfs @ 0.20 hrs, Volume= 61,847 cf, Depth= 0.97" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-8.00 hrs, dt= 0.01 hrs VA-Albemarle-ATLAS14 2-Year Duration=33 min, Inten=2.22 in/hr Area (ac) C Description 8.950 0.90 Paving/Roof 1.000 0.30 Undeveloped Land 7.150 0.40 Developed Open Space 0.550 1.00 Pond 17.650 0.67 Weighted Average 17.100 Pervious Area 0.550 Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 9.3 150 0.1000 0.27 Sheet Flow, Grass: Dense n= 0.240 P2= 4.00" 0.5 88 0.0350 3.01 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 2.0 995 0.0200 8.41 14.86 Circular Channel (pipe), Diam= 18.0" Area= 1.8 sf Perim= 4.7' r= 0.38' n= 0.013 11.8 1,233 Total Subcatchment 2S: Post-Amenity Hydrograph LEI Runoff 26.50 cfs 26; r otio I VA-Albemarle-ATLASI4 2-Year 24- Duration=33 min 22- ' Inten=2.22 in/hr 20- _ Runoff Area=17.650 ac , Runoff Volume=61,847 cf 1st Runoff Depth=0.97" 0 14 Flow Length=1,233' 12= Tc=11.8 min 10_ C=0.67 8� 6. 040 4 filrol 2 01 0 Allit WOf/17/7/eo°2 707/i ..//`/~ef.�7a55.0fe��fsii'ri. Fi#97 `729.0�ii*ir�.I�/rlir 4:17 0 1 2 3 4 5 6 7 8 Time (hours) WILLOWGLEN-FINAL-Pha VA-Albemarle-ATLAS14 2-Year Duration=33 min, Inten=2.22 in/hr Prepared by Terra Concepts, PC Printed 5/19/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 3 Hydrograph for Subcatchment 2S: Post-Amenity Time Runoff Time Runoff Time Runoff Time Runoff (hours) (cfs) (hours) (cfs) (hours) (cfs) (hours) (cfs) 0.00 0.00 2.65 0.00 5.30 0.00 7.95 0.00 0.05 6.74 2.70 0.00 5.35 0.00 8.00 0.00 0.10 13.47 2.75 0.00 5.40 0.00 0.15 20.21 2.80 0.00 5.45 0.00 0.20 26.50 2.85 0.00 5.50 0.00 0.25 26.50 2.90 0.00 5.55 0.00 0.30 26.50 2.95 0.00 5.60 0.00 0.35 26.50 3.00 0.00 5.65 0.00 0.40 26.50 3.05 0.00 5.70 0.00 0.45 26.50 3.10 0.00 5.75 0.00 0.50 26.50 3.15 0.00 5.80 0.00 0.55 26.50 3.20 0.00 5.85 0.00 0.60 23.13 3.25 0.00 5.90 0.00 0.65 19.76 3.30 0.00 5.95 0.00 0.70 16.39 3.35 0.00 6.00 0.00 0.75 13.03 3.40 0.00 6.05 0.00 0.80 9.66 3.45 0.00 6.10 0.00 0.85 6.29 3.50 0.00 6.15 0.00 0.90 2.92 3.55 0.00 6.20 0.00 0.95 0.00 3.60 0.00 6.25 0.00 1.00 0.00 3.65 0.00 6.30 0.00 1.05 0.00 3.70 0.00 6.35 0.00 1.10 0.00 3.75 0.00 6.40 0.00 1.15 0.00 3.80 0.00 6.45 0.00 1.20 0.00 3.85 0.00 6.50 0.00 1.25 0.00 3.90 0.00 6.55 0.00 1.30 0.00 3.95 0.00 6.60 0.00 1.35 0.00 4.00 0.00 6.65 0.00 1.40 0.00 4.05 0.00 6.70 0.00 1.45 0.00 4.10 0.00 6.75 0.00 1.50 0.00 4.15 0.00 6.80 0.00 1.55 0.00 4.20 0.00 6.85 0.00 1.60 0.00 4.25 0.00 6.90 0.00 1.65 0.00 4.30 0.00 6.95 0.00 1.70 0.00 4.35 0.00 7.00 0.00 1.75 0.00 4.40 0.00 7.05 0.00 1.80 0.00 4.45 0.00 7.10 0.00 1.85 0.00 4.50 0.00 7.15 0.00 1.90 0.00 4.55 0.00 7.20 0.00 1.95 0.00 4.60 0.00 7.25 0.00 2.00 0.00 4.65 0.00 7.30 0.00 2.05 0.00 4.70 0.00 7.35 0.00 2.10 0.00 4.75 0.00 7.40 0.00 2.15 0.00 4.80 0.00 7.45 0.00 2.20 0.00 4.85 0.00 7.50 0.00 2.25 0.00 4.90 0.00 7.55 0.00 2.30 0.00 4.95 0.00 7.60 0.00 2.35 0.00 5.00 0.00 7.65 0.00 2.40 0.00 5.05 0.00 7.70 0.00 2.45 0.00 5.10 0.00 7.75 0.00 2.50 0.00 5.15 0.00 7.80 0.00 2.55 0.00 5.20 0.00 7.85 0.00 2.60 0.00 5.25 0.00 7.90 0.00 WILLOWGLEN-FINAL-Pha VA-Albemarle-ATLAS14 2-Year Duration=33 min, Inten=2.22 in/hr Prepared by Terra Concepts, PC Printed 5/19/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 4 Summary for Pond 9P: SWM/Amenity Pond Inflow Area = 768,834 sf, 3.12% Impervious, Inflow Depth = 0.97" for 2-Year event Inflow = 26.50 cfs @ 0.20 hrs, Volume= 61,847 cf Outflow = 12.04 cfs @ 0.77 hrs, Volume= 61,487 cf, Atten= 55%, Lag= 34.2 min Primary = 12.04 cfs @ 0.77 hrs, Volume= 61,487 cf Routing by Sim-Route method, Time Span= 0.00-8.00 hrs, dt= 0.01 hrs Starting Elev= 527.00' Surf.Area= 22,322 sf Storage= 101,194 cf Peak Elev= 528.74' @ 0.77 hrs Surf.Area= 22,322 sf Storage= 139,979 cf (38,785 cf above start) Plug-Flow detention time= (not calculated: initial storage excedes outflow) Center-of-Mass det. time= 49.4 min ( 75.2 - 25.8 ) Volume Invert Avail.Storage Storage Description #1 518.00' 229,196 cf Custom Stage Data (Irregular)Listed below (Recalc) Elevation Surf.Area Perim. Inc.Store Cum.Store Wet.Area (feet) (sq-ft) (feet) (cubic-feet) (cubic-feet) (sq-ft) 518.00 4,692 303.0 0 0 4,692 520.00 8,011 458.0 12,556 12,556 14,109 522.00 10,162 509.0 18,130 30,686 18,151 524.00 12,429 551.0 22,553 53,239 21,849 526.00 15,109 608.0 27,494 80,734 27,233 526.50 22,322 717.0 9,299 90,033 38,730 527.00 22,322 717.0 11,161 101,194 39,089 530.50 22,322 717.0 78,127 179,321 41,598 531.00 34,190 1,106.0 14,023 193,344 98,032 532.00 37,540 1,153.0 35,852 229,196 106,556 Device Routing Invert Outlet Devices #1 Primary 518.50' 24.0" x 60.0' long Culvert RCP, square edge headwall, Ke= 0.500 Outlet Invert= 518.00' S= 0.0083 '/' Cc= 0.900 n= 0.013 #2 Device 1 527.00' 1.00' W x 0.50' H Vert. Orifice/Grate X 4.00 C= 0.600 #3 Device 1 528.65' 0.92' W x 0.50' H Vert. Orifice/Grate X 4.00 C= 0.600 #4 Device 1 529.65' 6.00' x 6.00' Horiz. RISER-WSE Limited to weir flow C= 0.600 Primary OutFlow Max=12.04 cfs @ 0.77 hrs HW=528.74' TW=0.00' (Dynamic Tailwater) L=Culvert (Passes 12.04 cfs of 45.97 cfs potential flow) -2=Orifice/Grate (Orifice Controls 11.73 cfs @ 5.87 fps) -3=Orifice/Grate (Orifice Controls 0.31 cfs @ 0.95 fps) -4=RISER-WSE ( Controls 0.00 cfs) WILLOWGLEN-FINAL-Pha VA-Albemarle-ATLAS14 2-Year Duration=33 min, Inten=2.22 in/hr Prepared by Terra Concepts, PC Printed 5/19/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 5 Pond 9P: SWM/Amenity Pond Hydrograph 2 0 cfs __ ❑Inflow 281 i ❑Primary _ Inflow Area=768,834 sf 26- 0 24 I Peak Elev=528.74' � I _ I I 22 Storage=139,979 cf 20. 1s: - o 16= I 0 14_ 12.04 cfs rz 12-; e4. 10 l� i / / ��z: 1/ %1/4ee° 74r/f7;f -4/01/1//�'11/1//.W''ZZ 0- 0 1 2 3 4 5 6 7 8 Time (hours) Pond 9P: SWM/Amenity Pond Stage-Discharge 532 I 1 `` Primary 531 i 530 A�,e RISER-WSE 529 /, /ems Orifice/Grate, 7 528 1 Orifice/Grate 527 526 /` .. I I I 0 525 l R w 523 522 j 521 %' 520 "2„. I I 519 / Culvert 518 f. . . . . . . . . . . . . . . . . . . . . . . . , . , . r . . . , , . . r 0 5 10 15 20 25 30 35 40 45 50 Discharge (cfs) WILLOWGLEN-FINAL-Pha VA-Albemarle-ATLAS14 2-Year Duration=33 min, Inten=2.22 in/hr Prepared by Terra Concepts, PC Printed 5/19/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 6 Pond 9P: SWM/Amenity Pond Stage-Area-Storage Surface/Horizontal/wetted Area(sq-ft) 0 5,000 10,000 15,000 20,000 25,000 30,000 35,000 0 Surface I D Storage 532 `� 53115. ..,E. 530 // 5294. �%�!� /� 528 , 527 Starting Elevation ; 2 526 w 0 525 d 524i. w = 523=-, 522 521= ,' : Custom Stage Data 0 50,000 100,000 150,000 200,000 Storage(cubic-feet) WILLOWGLEN-FINAL-Pha VA-Albemarle-ATLAS14 2-Year Duration=33 min, Inten=2.22 in/hr Prepared by Terra Concepts, PC Printed 5/19/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 7 Hydrograph for Pond 9P: SWM/Amenity Pond Time Inflow Storage Elevation Primary (hours) (cfs) (cubic-feet) (feet) (cfs) 0.00 0.00 101,194 527.00 0.00 0.20 26.50 109,901 527.39 3.13 0.40 26.50 124,473 528.04 8.54 0.60 23.13 136,227 528.57 11.05 0.80 9.66 139,869 528.73 11.99 1.00 0.00 134,317 528.48 10.68 1.20 0.00 127,144 528.16 9.17 1.40 0.00 121,059 527.89 7.65 1.60 0.00 116,073 527.67 6.11 1.80 0.00 112,219 527.49 4.46 2.00 0.00 109,573 527.38 2.95 2.20 0.00 107,779 527.30 2.06 2.40 0.00 106,506 527.24 1.49 2.60 0.00 105,570 527.20 1.11 2.80 0.00 104,862 527.16 0.86 3.00 0.00 104,313 527.14 0.67 3.20 0.00 103,879 527.12 0.54 3.40 0.00 103,529 527.10 0.43 3.60 0.00 103,244 527.09 0.36 3.80 0.00 103,008 527.08 0.30 4.00 0.00 102,811 527.07 0.25 4.20 0.00 102,644 527.06 0.21 4.40 0.00 102,502 527.06 0.18 4.60 0.00 102,379 527.05 0.16 4.80 0.00 102,274 527.05 0.14 5.00 0.00 102,181 527.04 0.12 5.20 0.00 102,100 527.04 0.11 5.40 0.00 102,029 527.04 0.09 5.60 0.00 101,966 527.03 0.08 5.80 0.00 101,909 527.03 0.07 6.00 0.00 101,859 527.03 0.07 6.20 0.00 101,814 527.03 0.06 6.40 0.00 101,773 527.03 0.05 6.60 0.00 101,736 527.02 0.05 6.80 0.00 101,703 527.02 0.04 7.00 0.00 101,672 527.02 0.04 7.20 0.00 101,645 527.02 0.04 7.40 0.00 101,619 527.02 0.03 7.60 0.00 101,596 527.02 0.03 7.80 0.00 101,574 527.02 0.03 8.00 0.00 101,555 527.02 0.03 • WILLOWGLEN-FINAL-Ph VA-Albemarle-ATLAS14 10-Year Duration=40 min, Inten=2.72 in/hr Prepared by Terra Concepts, PC Printed 5/19/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 1 Summary for Subcatchment 2S: Post-Amenity Runoff = 32.41 cfs @ 0.20 hrs, Volume= 89,247 cf, Depth= 1.39" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-8.00 hrs, dt= 0.01 hrs VA-Albemarle-ATLAS14 10-Year Duration=40 min, Inten=2.72 in/hr Area (ac) C Description 8.950 0.90 Paving/Roof 1.000 0.30 Undeveloped Land 7.150 0.40 Developed Open Space 0.550 1.00 Pond 17.650 0.67 Weighted Average 17.100 Pervious Area 0.550 Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 9.3 150 0.1000 0.27 Sheet Flow, Grass: Dense n= 0.240 P2= 4.00" 0.5 88 0.0350 3.01 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 2.0 995 0.0200 8.41 14.86 Circular Channel (pipe), Diam= 18.0" Area= 1.8 sf Perim= 4.7' r= 0.38' n= 0.013 11.8 1,233 Total Subcatchment 2S: Post-Amenity Hydrograph 36 p Runoff 32.41 cfs Sri®s® 32 r VA-Albemarle-ATLAS14 10-Year 30 Duration=40 min,00 28 Inten=2.72 in/hr 26 / Runoff Area=17.650 ac 24 0 zz Runoff Volume=89,247 cf 28 Runoff Depth=1.39" 18 0 Flow Length=1,233' LL 16 Tc=11.8 min- 14 12 C=0.67 10 0 8 6I rot 0 1 2 3 4 5 6 7 8 Time (hours) WILLOWGLEN-FINAL-Ph VA-Albemarle-ATLAS14 10-Year Duration=40 min, Inten=2.72 in/hr Prepared by Terra Concepts, PC Printed 5/19/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 2 Hydrograph for Subcatchment 2S: Post-Amenity Time Runoff Time Runoff Time Runoff Time Runoff (hours) (cfs) (hours) (cfs) (hours) (cfs) (hours) (cfs) 0.00 0.00 2.65 0.00 5.30 0.00 7.95 0.00 0.05 8.24 2.70 0.00 5.35 0.00 8.00 0.00 0.10 16.48 2.75 0.00 5.40 0.00 0.15 24.72 2.80 0.00 5.45 0.00 0.20 32.41 2.85 0.00 5.50 0.00 0.25 32.41 2.90 0.00 5.55 0.00 0.30 32.41 2.95 0.00 5.60 0.00 0.35 32.41 3.00 0.00 5.65 0.00 0.40 32.41 3.05 0.00 5.70 0.00 0.45 32.41 3.10 0.00 5.75 0.00 0.50 32.41 3.15 0.00 5.80 0.00 0.55 32.41 3.20 0.00 5.85 0.00 0.60 32.41 3.25 0.00 5.90 0.00 0.65 32.41 3.30 0.00 5.95 0.00 0.70 29.66 3.35 0.00 6.00 0.00 0.75 25.54 3.40 0.00 6.05 0.00 0.80 21.42 3.45 0.00 6.10 0.00 0.85 17.30 3.50 0.00 6.15 0.00 0.90 13.18 3.55 0.00 6.20 0.00 0.95 9.06 3.60 0.00 6.25 0.00 1.00 4.94 3.65 0.00 6.30 0.00 1.05 0.82 3.70 0.00 6.35 0.00 1.10 0.00 3.75 0.00 6.40 0.00 1.15 0.00 3.80 0.00 6.45 0.00 1.20 0.00 3.85 0.00 6.50 0.00 1.25 0.00 3.90 0.00 6.55 0.00 1.30 0.00 3.95 0.00 6.60 0.00 1.35 0.00 4.00 0.00 6.65 0.00 1.40 0.00 4.05 0.00 6.70 0.00 1.45 0.00 4.10 0.00 6.75 0.00 1.50 0.00 4.15 0.00 6.80 0.00 1.55 0.00 4.20 0.00 6.85 0.00 1.60 0.00 4.25 0.00 6.90 0.00 1.65 0.00 4.30 0.00 6.95 0.00 1.70 0.00 4.35 0.00 7.00 0.00 1.75 0.00 4.40 0.00 7.05 0.00 1.80 0.00 4.45 0.00 7.10 0.00 1.85 0.00 4.50 0.00 7.15 0.00 1.90 0.00 4.55 0.00 7.20 0.00 1.95 0.00 4.60 0.00 7.25 0.00 2.00 0.00 4.65 0.00 7.30 0.00 2.05 0.00 4.70 0.00 7.35 0.00 2.10 0.00 4.75 0.00 7.40 0.00 2.15 0.00 4.80 0.00 7.45 0.00 2.20 0.00 4.85 0.00 7.50 0.00 2.25 0.00 4.90 0.00 7.55 0.00 2.30 0.00 4.95 0.00 7.60 0.00 2.35 0.00 5.00 0.00 7.65 0.00 2.40 0.00 5.05 0.00 7.70 0.00 2.45 0.00 5.10 0.00 7.75 0.00 2.50 0.00 5.15 0.00 7.80 0.00 2.55 0.00 5.20 0.00 7.85 0.00 2.60 0.00 5.25 0.00 7.90 0.00 WILLOWGLEN-FINAL-Ph VA-Albemarle-ATLAS14 10-Year Duration=40 min, Inten=2.72 in/hr Prepared by Terra Concepts, PC Printed 5/19/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 3 Summary for Pond 9P: SWM/Amenity Pond Inflow Area = 768,834 sf, 3.12% Impervious, Inflow Depth = 1.39" for 10-Year event Inflow = 32.41 cfs @ 0.20 hrs, Volume= 89,247 cf Outflow = 19.57 cfs @ 0.83 hrs, Volume= 88,854 cf, Atten= 40%, Lag= 37.7 min Primary = 19.57 cfs @ 0.83 hrs, Volume= 88,854 cf Routing by Sim-Route method, Time Span= 0.00-8.00 hrs, dt= 0.01 hrs Starting Elev= 527.00' Surf.Area= 22,322 sf Storage= 101,194 cf Peak Elev= 529.33' @ 0.83 hrs Surf.Area= 22,322 sf Storage= 153,137 cf (51,943 cf above start) Plug-Flow detention time= (not calculated: initial storage excedes outflow) Center-of-Mass det. time= 47.7 min ( 76.9 - 29.2 ) Volume Invert Avail.Storage Storage Description #1 518.00' 229,196 cf Custom Stage Data (Irregular)Listed below (Recalc) Elevation Surf.Area Perim. Inc.Store Cum.Store Wet.Area (feet) (sq-ft) (feet) (cubic-feet) (cubic-feet) (sq-ft) 518.00 4,692 303.0 0 0 4,692 520.00 8,011 458.0 12,556 12,556 14,109 522.00 10,162 509.0 18,130 30,686 18,151 524.00 12,429 551.0 22,553 53,239 21,849 526.00 15,109 608.0 27,494 80,734 27,233 526.50 22,322 717.0 9,299 90,033 38,730 527.00 22,322 717.0 11,161 101,194 39,089 530.50 22,322 717.0 78,127 179,321 41,598 531.00 34,190 1,106.0 14,023 193,344 98,032 532.00 37,540 1,153.0 35,852 229,196 106,556 Device Routing Invert Outlet Devices #1 Primary 518.50' 24.0" x 60.0' long Culvert RCP, square edge headwall, Ke= 0.500 Outlet Invert= 518.00' S= 0.0083 '/' Cc= 0.900 n= 0.013 #2 Device 1 527.00' 1.00'W x 0.50' H Vert. Orifice/Grate X 4.00 C= 0.600 #3 Device 1 528.65' 0.92' W x 0.50' H Vert. Orifice/Grate X 4.00 C= 0.600 #4 Device 1 529.65' 6.00' x 6.00' Horiz. RISER-WSE Limited to weir flow C= 0.600 Primary OutFlow Max=19.57 cfs @ 0.83 hrs HW=529.33' TW=0.00' (Dynamic Tailwater) t =Culvert (Passes 19.57 cfs of 47.42 cfs potential flow) 2=Orifice/Grate (Orifice Controls 13.87 cfs @ 6.93 fps) 3=Orifice/Grate (Orifice Controls 5.70 cfs @ 3.10 fps) =RISER-WSE ( Controls 0.00 cfs) WILLOWGLEN-FINAL-Ph VA-Albemarle-ATLASI4 10-Year Duration=40 min, Inten=2.72 in/hr Prepared by Terra Concepts, PC Printed 5/19/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 4 Pond 9P: SWM/Amenity Pond Hydrograph 3 32.41 cfs 0 Primary 34" zfr.��- ` D Inflow 32 Inflow Area=768,834 sf 30-% Peak_EJev=529,33_ 26 SI'torage=153,137 cf 24 , 22; 19.57 cfs 3 18� / / o 14-% 84 ���// 0 1 2 3 4 5 6 7 8 Time (hours) Pond 9P: SWM/Amenity Pond Stage-Discharge 532 531 1 o Primary` 530 RISER-WSE 529 //®/+` Orifice/Grate 528 7 .rAlfir Orifice/Grate ^ 527 A 526 f - 525 I. 524 uw f 523 522 % 521 r 520 f519 'Culvert 518 T 0 5 10 15 20 25 30 35 40 45 50 Discharge (cfs) WILLOWGLEN-FINAL-Ph VA-Albemarle-ATLAS14 10-Year Duration=40 min, Inten=2.72 in/hr Prepared by Terra Concepts, PC Printed 5/19/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 5 Pond 9P: SWM/Amenity Pond Stage-Area-Storage Surface/Horizontal/wetted Area(sq-ft) 0 5,000 10,000 15,000 20,000 25,000 30,000 35,000 0 Surface 0 Storage II 532_ .�'" 531_ 530: e7:7�,� 529 528_ 527J Starting Elevation -- 526=' 0 525 d 524 W 523 522 521 4 520=" i 519 m" ` ` Custom Stage D Cu Data . , . / f 0 50,000 100,000 150,000 200,000 Storage(cubic-feet) WILLOWGLEN-FINAL-Ph VA-Albemarle-ATLASI4 10-Year Duration=40 min, Inten=2.72 in/hr Prepared by Terra Concepts, PC Printed 5/19/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 6 Hydrograph for Pond 9P: SWM/Amenity Pond Time Inflow Storage Elevation Primary (hours) (cfs) (cubic-feet) (feet) (cfs) 0.00 0.00 101,194 527.00 0.00 0.20 32.41 111,780 527.47 4.19 0.40 32.41 129,814 528.28 9.76 0.60 32.41 144,836 528.96 14.55 0.80 21.42 153,022 529.32 19.52 1.00 4.94 149,117 529.15 17.39 1.20 0.00 139,363 528.71 11.79 1.40 0.00 131,500 528.36 10.11 1.60 0.00 124,735 528.05 8.60 1.80 0.00 119,061 527.80 7.08 2.00 0.00 114,491 527.60 5.52 2.20 0.00 111,096 527.44 3.79 2.40 0.00 108,823 527.34 2.57 2.60 0.00 107,253 527.27 1.82 2.80 0.00 106,123 527.22 1.33 3.00 0.00 105,282 527.18 1.01 3.20 0.00 104,640 527.15 0.78 3.40 0.00 104,139 527.13 0.62 3.60 0.00 103,739 527.11 0.49 3.80 0.00 103,416 527.10 0.40 4.00 0.00 103,151 527.09 0.33 4.20 0.00 102,930 527.08 0.28 4.40 0.00 102,745 527.07 0.24 4.60 0.00 102,588 527.06 0.20 4.80 0.00 102,454 527.06 0.17 5.00 0.00 102,338 527.05 0.15 5.20 0.00 102,238 527.05 0.13 5.40 0.00 102,150 527.04 0.11 5.60 0.00 102,073 527.04 0.10 5.80 0.00 102,004 527.04 0.09 6.00 0.00 101,944 527.03 0.08 6.20 0.00 101,890 527.03 0.07 6.40 0.00 101,842 527.03 0.06 6.60 0.00 101,798 527.03 0.06 6.80 0.00 101,759 527.03 0.05 7.00 0.00 101,723 527.02 0.05 7.20 0.00 101,691 527.02 0.04 7.40 0.00 101,662 527.02 0.04 7.60 0.00 101,635 527.02 0.04 7.80 0.00 101,610 527.02 0.03 8.00 0.00 101,588 527.02 0.03 A 9P S M/Amenity Pond 2S Post-Amenity SubCat Reacts °on•. Li{i( Drainage Diagram for WILLOWGLEN-FINAL-Phase2-rat f Prepared by Terra Concepts, PC, Printed 5/22/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC WILLOWGLEN-FINAL-P VA-Albemarle-ATLASI4 100-Year Duration=43 min, Inten=3.70 in/hr Prepared by Terra Concepts, PC Printed 5/22/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 2 Summary for Subcatchment 2S: Post-Amenity Runoff = 44.09 cfs @ 0.20 hrs, Volume= 129,353 cf, Depth= 2.02" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-8.00 hrs, dt= 0.01 hrs VA-Albemarle-ATLAS14 100-Year Duration=43 min, Inten=3.70 in/hr Area (ac) C Description 8.950 0.90 Paving/Roof 1.000 0.30 Undeveloped Land 7.150 0.40 Developed Open Space 0.550 1.00 Pond 17.650 0.67 Weighted Average 17.100 Pervious Area 0.550 Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 9.3 150 0.1000 0.27 Sheet Flow, Grass: Dense n= 0.240 P2= 4.00" 0.5 88 0.0350 3.01 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 2.0 995 0.0200 8.41 14.86 Circular Channel (pipe), Diam= 18.0" Area= 1.8 sf Perim= 4.7' r= 0.38' n= 0.013 11.8 1,233 Total Subcatchment 2S: Post-Amenity Hydrograph 4 Lo Runoff` 44.09 cfs 4a VA-Albemarle-ATLAS14100-Year- 42f, , _ ao� ,Duration=43 min, 38: d0 400 lnten=3:70 in/hr 36 3a e� Runoff Area=17.650 ac 324. 30 Runoff Volume=129,353 cf F. 28, Runoff Depth=2:02"._ 2" 24-:2a° Flow Length=1,233' LL z2 Tc=11.8 min 20 184), C=0.67- . 16 14 12: rot 10 8= 6 rdfd 4= r 0 trZZA fir/✓e/Aa�s.f*52Yi. .41"74 °��(°/.f/e�/",7; /.f✓CIA/ ./eii//// ece• //ire 0 1 2 3 4 5 6 7 8 Time (hours) WILLOWGLEN-FINAL-P VA-Albemarle-ATLAS14 100-Year Duration=43 min, Inten=3.70 in/hr Prepared by Terra Concepts, PC Printed 5/22/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 3 Hydrograph for Subcatchment 2S: Post-Amenity Time Runoff Time Runoff Time Runoff Time Runoff (hours) (cfs) (hours) (cfs) (hours) (cfs) (hours) (cfs) 0.00 0.00 2.65 0.00 5.30 0.00 7.95 0.00 0.05 11.21 2.70 0.00 5.35 0.00 8.00 0.00 0.10 22.42 2.75 0.00 5.40 0.00 0.15 33.63 2.80 0.00 5.45 0.00 0.20 44.09 2.85 0.00 5.50 0.00 0.25 44.09 2.90 0.00 5.55 0.00 0.30 44.09 2.95 0.00 5.60 0.00 0.35 44.09 3.00 0.00 5.65 0.00 0.40 44.09 3.05 0.00 5.70 0.00 0.45 44.09 3.10 0.00 5.75 0.00 0.50 44.09 3.15 0.00 5.80 0.00 0.55 44.09 3.20 0.00 5.85 0.00 0.60 44.09 3.25 0.00 5.90 0.00 0.65 44.09 3.30 0.00 5.95 0.00 0.70 44.09 3.35 0.00 6.00 0.00 0.75 40.36 3.40 0.00 6.05 0.00 0.80 34.75 3.45 0.00 6.10 0.00 0.85 29.15 3.50 0.00 6.15 0.00 0.90 23.54 3.55 0.00 6.20 0.00 0.95 17.94 3.60 0.00 6.25 0.00 1.00 12.33 3.65 0.00 6.30 0.00 1.05 6.73 3.70 0.00 6.35 0.00 1.10 1.12 3.75 0.00 6.40 0.00 1.15 0.00 3.80 0.00 6.45 0.00 1.20 0.00 3.85 0.00 6.50 0.00 1.25 0.00 3.90 0.00 6.55 0.00 1.30 0.00 3.95 0.00 6.60 0.00 1.35 0.00 4.00 0.00 6.65 0.00 1.40 0.00 4.05 0.00 6.70 0.00 1.45 0.00 4.10 0.00 6.75 0.00 1.50 0.00 4.15 0.00 6.80 0.00 1.55 0.00 4.20 0.00 6.85 0.00 1.60 0.00 4.25 0.00 6.90 0.00 1.65 0.00 4.30 0.00 6.95 0.00 1.70 0.00 4.35 0.00 7.00 0.00 1.75 0.00 4.40 0.00 7.05 0.00 1.80 0.00 4.45 0.00 7.10 0.00 1.85 0.00 4.50 0.00 7.15 0.00 1.90 0.00 4.55 0.00 7.20 0.00 1.95 0.00 4.60 0.00 7.25 0.00 2.00 0.00 4.65 0.00 7.30 0.00 2.05 0.00 4.70 0.00 7.35 0.00 2.10 0.00 4.75 0.00 7.40 0.00 2.15 0.00 4.80 0.00 7.45 0.00 2.20 0.00 4.85 0.00 7.50 0.00 2.25 0.00 4.90 0.00 7.55 0.00 2.30 0.00 4.95 0.00 7.60 0.00 2.35 0.00 5.00 0.00 7.65 0.00 2.40 0.00 5.05 0.00 7.70 0.00 2.45 0.00 5.10 0.00 7.75 0.00 2.50 0.00 5.15 0.00 7.80 0.00 2.55 0.00 5.20 0.00 7.85 0.00 2.60 0.00 5.25 0.00 7.90 0.00 • WILLOWGLEN-FINAL-P VA-Albemarle-ATLAS14 100-Year Duration=43 min, Inten=3.70 in/hr Prepared by Terra Concepts, PC Printed 5/22/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 4 Summary for Pond 9P: SWM/Amenity Pond Inflow Area = 768,834 sf, 3.12% Impervious, Inflow Depth = 2.02" for 100-Year event Inflow = 44.09 cfs @ 0.20 hrs, Volume= 129,353 cf Outflow = 38.38 cfs @ 0.77 hrs, Volume= 128,939 cf, Atten= 13%, Lag= 34.4 min Primary = 38.38 cfs @ 0.77 hrs, Volume= 128,939 cf Routing by Sim-Route method, Time Span= 0.00-8.00 hrs, dt= 0.01 hrs Starting Elev= 527.00' Surf.Area= 22,322 sf Storage= 101,194 cf Peak Elev= 529.96' @ 0.77 hrs Surf.Area= 22,322 sf Storage= 167,231 cf (66,037 cf above start) Plug-Flow detention time= 135.0 min calculated for 27,711 cf(21% of inflow) Center-of-Mass det. time= 42.3 min ( 73.0 - 30.7 ) Volume Invert Avail.Storage Storage Description #1 518.00' 229,196 cf Custom Stage Data (Irregular)Listed below (Recalc) Elevation Surf.Area Perim. Inc.Store Cum.Store Wet.Area (feet) (sq-ft) (feet) (cubic-feet) (cubic-feet) (sq-ft) 518.00 4,692 303.0 0 0 4,692 520.00 8,011 458.0 12,556 12,556 14,109 522.00 10,162 509.0 18,130 30,686 18,151 524.00 12,429 551.0 22,553 53,239 21,849 526.00 15,109 608.0 27,494 80,734 27,233 526.50 22,322 717.0 9,299 90,033 38,730 527.00 22,322 717.0 11,161 101,194 39,089 530.50 22,322 717.0 78,127 179,321 41,598 531.00 34,190 1,106.0 14,023 193,344 98,032 532.00 37,540 1,153.0 35,852 229,196 106,556 Device Routing Invert Outlet Devices #1 Primary 518.50' 24.0" x 60.0' long Culvert RCP, square edge headwall, Ke= 0.500 Outlet Invert= 518.00' S= 0.0083 '/' Cc= 0.900 n= 0.013 #2 Device 1 527.00' 1.00' W x 0.50' H Vert. Orifice/Grate X 4.00 C= 0.600 #3 Device 1 528.65' 0.92'W x 0.50' H Vert. Orifice/Grate X 4.00 C= 0.600 #4 Device 1 529.65' 6.00' x 6.00' Horiz. RISER-WSE Limited to weir flow C= 0.600 Primary OutFlow Max=38.36 cfs @ 0.77 hrs HW=529.96' TW=0.00' (Dynamic Tailwater) t.=Culvert (Passes 38.36 cfs of 48.92 cfs potential flow) -2=Orifice/Grate (Orifice Controls 15.84 cfs © 7.92 fps) -3=Orifice/Grate (Orifice Controls 9.09 cfs @ 4.94 fps) -4=RISER-WSE (Weir Controls 13.43 cfs @ 1.82 fps) WILLOWGLEN-FINAL-P VA-Albemarle-ATLAS14 100-Year Duration=43 min, Inten=3.70 in/hr Prepared by Terra Concepts, PC Printed 5/22/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 5 Pond 9P: SWM/Amenity Pond Hydrograph o Inflow 4 44.09 cfs r 46 ❑Primary Inflow Area=768,834 sf 44 40>; 38.38 cfs Peak EIev=5 9.96` 381 +�/ 34 Storage=167,231 cf 32 X11 30' w 284 ® , 26: P Ad O• 22 + a 20� : 14 ' 12, �� 10i 2 o�.�Is !�'���.e��////°r��fif/l���i►rP�i.r�1.1�'. //s�.F�«i���l/i �f//� 1 2 3 4 5 6 7 8 Time (hours) Pond 9P: SWM/Amenity Pond Stage-Discharge 532 {`, 0 Primary) 531 530 i2tSER WSE ANWIr �� 529 Orifice/Grate 528 .-- Arrfri Orifice/Grate 527 A 526 ... 525 d 524 523 7� %� 522 521 %� 520 519 C;ulverf, r i; 0 5 10 15 20 25 30 35 40 45 50 Discharge (cfs) WILLOWGLEN-FINAL-P VA-Albemarle-ATLAS14 100-Year Duration=43 min, Inten=3.70 in/hr Prepared by Terra Concepts, PC Printed 5/22/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 6 Pond 9P: SWM/Amenity Pond Stage-Area-Storage Surface/Horizontal/Wetted Area(sq-ft) 0 5,000 10,000 15,000 20,000 25,000 30,000 35,000 ®Surface Storage /�e�`� ` `� 530_ �r/`// 529= 77� /���/� Starting Elevation'_ 527= //7".7; U ... 526:.: 0 525 524 w 523 522; 521= .. _ 52OEr - Custom Stage Data. 0 50,000 100,000 150,000 200,000 Storage(cubic-feet) WILLOWGLEN-FINAL-P VA-Albemarle ATLASI4 100-Year Duration=43 min, Inten=3.70 in/hr Prepared by Terra Concepts, PC Printed 5/22/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 7 Hydrograph for Pond 9P: SWM/Amenity Pond Time Inflow Storage Elevation Primary (hours) (cfs) (cubic-feet) (feet) (cfs) 0.00 0.00 101,194 527.00 0.00 0.20 44.09 115,463 527.64 5.90 0.40 44.09 140,615 528.77 12.31 0.60 44.09 159,598 529.62 22.27 0.80 34.75 167,088 529.95 37.91 1.00 12.33 161,547 529.70 23.97 1.20 0.00 149,181 529.15 17.44 1.40 0.00 138,964 528.69 11.65 1.60 0.00 131,159 528.34 10.04 1.80 0.00 124,444 528.04 8.53 2.00 0.00 118,821 527.79 7.01 2.20 0.00 114,305 527.59 5.45 2.40 0.00 110,968 527.44 3.72 2.60 0.00 108,737 527.34 2.52 2.80 0.00 107,192 527.27 1.79 3.00 0.00 106,078 527.22 1.31 3.20 0.00 105,248 527.18 0.99 3.40 0.00 104,614 527.15 0.77 3.60 0.00 104,118 527.13 0.61 3.80 0.00 103,722 527.11 0.49 4.00 0.00 103,402 527.10 0.40 4.20 0.00 103,139 527.09 0.33 4.40 0.00 102,921 527.08 0.28 4.60 0.00 102,737 527.07 0.23 4.80 0.00 102,581 527.06 0.20 5.00 0.00 102,448 527.06 0.17 5.20 0.00 102,333 527.05 0.15 5.40 0.00 102,233 527.05 0.13 5.60 0.00 102,146 527.04 0.11 5.80 0.00 102,069 527.04 0.10 6.00 0.00 102,001 527.04 0.09 6.20 0.00 101,941 527.03 0.08 6.40 0.00 101,888 527.03 0.07 6.60 0.00 101,839 527.03 0.06 6.80 0.00 101,796 527.03 0.06 7.00 0.00 101,757 527.03 0.05 7.20 0.00 101,722 527.02 0.05 7.40 0.00 101,690 527.02 0.04 7.60 0.00 101,660 527.02 0.04 7.80 0.00 101,634 527.02 0.04 8.00 0.00 101,609 527.02 0.03