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Home My WebLink AboutWPO201800051 Other 2021-08-05MIN FA VA DEQ STORMWATER DESIGN SPECIFICATION NO.2 SHEET FLOW TO FILTER OR OPEN SPACE VA DEQ STORMWATER DESIGN SPECIFICATION NO. 14 WET POND SECTION 9. MAINTENANCE SECTION 9: MAINTENANCE 9.1. Maintenance Agreements 9.1. Maintenance Agreements Section 4 VAC 50-60-124 of the regulations specifies the circumstances under which a Section 4 VAC 50-60-124 of the regulations specifies the circumstances under which a maintenance agreement must be executed between the owner and the local program. This section maintenance agreement must be executed between the owner and the local program. This section sets forth inspection requirements, compliance procedures if maintenance is neglected, sets forth inspection requirements, compliance procedures if maintenance is neglected, notification of the local program upon transfer of ownership, and fight -of -entry for local program notification of the local program upon transfer of ownership, and right -of -entry for local program personnel. personnel. Access to wet ponds should be covered by a drainage easement to allow inspection and maintenance. All Vegetated Filter Strips must be covered by a drainage easement to allow inspection and maintenance. If the filter area is a natural Conserved Open Space, it must be protected by a It is also recommended that the maintenance agreement include a list of qualified contractors that perpetual easement or deed restriction that assigns the responsible party to ensure that no future can perform inspection or maintenance services, as well as contact information for owners to get development, disturbance or clearing may occur within the area, except as stipulated in the local or state assistance to solve common nuisance problems, such as mosquito control, geese, vegetation maintenance plan. invasive plants, vegetative management, and beaver removal. The CWP Pond and Weiland Maintenance Guidebook (2004) provides some excellent templates of how to respond to these If the Vegetated Filter Strip is located on a residential private lot, the existence and purpose of problems. the Filter Strip shall be noted on the deed of record. Homeowners will need to be provided a simple document that explains the purpose of the Filter Strip and routine maintenance needs. A 9.2. First Year Maintenance Operations deed restriction or other mechanism enforceable by the qualifying local program must be in place to help ensure that Filter Strips are maintained and Conserved Open Space Areas are not Successful establishment of wet ponds requires that the following tasks be undertaken during the converted or disturbed. The mechanism should, if possible, grant authority for local agencies to first year following construction. access the property for inspection or corrective action. Initial inspections. For the first six months following construction, the site should be inspected 9.2. Maintenance Inspections at least twice after storm events that exceed a 1/2-inch of rainfall. Annual inspections are used to trigger maintenance operations such as sediment removal, spot re- planting of Aquatic Benches. The aquatic benches should be planted with emergent wetland vegetation and level spreader repair, ideally, inspections should be conducted in the non -growing species, following the planting recommendations contained in Stormwater Design Specification season when it easier to see the flow path. Example maintenance inspection checklists for Sheet No. 13 (Constructed Wetlands). Flow to a Filter Strip or Conserved Open Space areas can be accessed in Appendix C of Chapter 9 of the Virginia Stormwater Management Handbook or at the Center for Watershed Protection's Spot Reseeding. Inspectors should look for bare or eroding areas in the contributing drainage website at: area or around the pond buffer, and make sure they are immediately stabilized with grass cover. httD://www.cwo.ora/Resource Library/Controllina Runoff and Discharoes/sm.htm Watering. Trees planted in the pond buffer need to be watered during the first growing season. In (scroll to Tool6: Plan Review, BMP Construction, and Maintenance Checklists) general, consider watering every 3 days for first month, and then weekly during the remainder of the first growing season (April - October), depending on rainfall. Inspectors should check to ensure that: 9.3. Inspections and Ongoing Maintenance Tasks • Flows through the Filter Strip do not short-circuit the overflow control section; • Debris and sediment does not build up at the top of the Filter Strip; Maintenance of a wet pond is driven by annual inspections that evaluate the condition and • Foot or vehicular traffic does not compromise the gravel diaphragm; performance of the pond, including the following: • Scour and erosion do not occur within the Filter Strip; • Sediments are cleaned out of Level Spreader forebays and flow splitters; and • Measure sediment accumulation levels in the forebay. • Vegetative density exceeds a 900% cover in the boundary zone or grass filter. • Monitor the growth of wetland plants, trees and shrubs planted. Record the species and their 9.3. Ongoing Maintenance approximate coverage, and note the presence of any invasive plant species. Once established, Vegetated Filter Strips have minimal maintenance needs outside of the spring clean up, regular mowing, repair of check dams and other measures to maintain the hydraulic efficiency of the strip and a dense, healthy grass cover. Vegetated Filter Strips that consist of grass/turf cover should be mowed at least twice a year to prevent woody growth. • Inspect the condition of stormwater inlets to the pond for material damage, erosion or Table 14.6. Typical Wet Pond Maintenance Tasks and Frequency undercutting. • Inspect the banks of upstream and downstream channels for evidence of sloughing, animal borrows, boggy areas, woody growth, or gully erosion that may undermine embankment integrity. • Inspect the pond outfall channel for erosion, undercutting, rip -rap displacement, woody growth, etc. • Inspect the condition of the principal spillway and riser for evidence of spalling, joint failure, leakage, corrosion, etc. • Inspect the condition of all trash racks, reverse -sloped pipes, or flashboard risers for evidence ofclo 'n leakage, debris accumulation etc. clogging, g • • Inspect maintenance access to ensure it is free of wood elation and check to see whether P Y vegetation, valves manholes and locks can be opened and operated. erated. • P Inspect internal and external side slopes of the pond for evidence of sparse vegetative cover, P P Po P g erosion, or slumping, and make needed repairs immediately. B 1 t' It f t k it] b t' red E I ' t Maintenance Items Frequency • Mowing - twice a year Quarterly or after major storms • Remove debris and blockages (>1 inch of rainfall) • Repair undercut, eroded, and bare soil areas • Mowing Twice a year Y • Shoreline cleanup to remove trash, debris and flcatables • A Tull maintenance inspection Annually Y • Open u the riser to access and test the valves P P • Repair broken mechanical components, if needed • Pond buffer and aquatic bench reinforcement plantings One time -duringthe second year followingconstruction • Foreba Sediment Removal Every 5 to 7 years • Repair es the riser andspillway,as needed From 5 to 25 years as on mspec ion resu s, sped is ma m enance [as s wt a in . xamp a man enance inspection checklists for Wet Ponds can be accessed in Appendix C of Chapter 9 of the Virginia Stormwater Management Handbook (2010) or at the CWP website at: 9.4. Sediment Removal IhltD7//www.cwD.ora/ResourceLibrary/Controllina Runoff and Dischara Frequent sediment removal from the forebay is essential to maintain the function and (scroll to Tool6: Plan Review, BMP Construction, and Maintenance Checklists) performance of a wet pond. Maintenance plans should schedule cleanouts approximately every 5 to 7 years, or when inspections indicate that 50% of fombay sediment storage capacity has been For a more detailed maintenance inspection checklist, see Appendix B in CWP Stormwater Pond filled. The designer should also check to see whether removed sediments can be spoiled on -site and Wetland Maintenance Guidebook (2004). or must be hauled away. Sediments excavated from wet ponds are not usually considered toxic or hazardous. They can be safely disposed of by either land application or land filling. Sediment Maintenance is needed so stormwater ponds continue to operate as designed on a long-term testing may be needed prior to sediment disposal if the retrofit serves a hotspot land use. basis. Wet ponds normally have fewer routine maintenance requirements than other stormwater control measures. Stormwater pond maintenance activities vary regarding the level of effort and SECTION 10: COMMUNITY & ENVIRONMENTAL CONCERNS expertise required to perform them. Routine stormwater pond maintenance, such as mowing and removing debris and trash, is needed several times each year (See Table 14.6). More significant Wet ponds can generate the following community and environmental concerns that need to be maintenance (e.g., removing accumulated sediment) is needed less frequently but requires more addressed during design. skilled labor and special equipment. Inspection and repair of critical structural features (e.g., embankments and risers) needs to be performed by a qualified professional (e.g., a structural Aesthetic Issues. Many residents feel that wet ponds are an attractive landscape feature, promote engineer) who has experience in the construction, inspection, and repair of these features. a greater sense of community and are an attractive habitat for fisb and wildlife. Designers should note that these benefits are often diminished where wet ponds are under -sized or have small The maintenance plan should clearly outline how vegetation in the pond and its buffer will be contributing drainage areas. managed or harvested in the future. Periodic mowing of the stormwater buffer is only required along maintenance rights -of -way and the embankment. The remaining buffer can be managed as Existing Wettands. A wet pond should never be constructed within an existing natural wetland. a meadow (mowing every other year) or forest. The maintenance plan should schedule a Discharges from a wet pond into an existing natural wetland should be minimized to prevent shoreline cleanup at least once a year to remove trash and floatables. pollution damage and changes to its hydroperiod. Existing Forests. Construction of a wet pond may involve extensive clearing of existing forest cover. Designers can expect a great deal of neighborhood opposition if they do not make a concerted effort to save mature trees during pond design and construction. V `. , , I IN, IN -, IN PROPOSE GREENWAY/OPEN , SPACE BUFFER-= I I ' 1 1 I 1 1 1 11 I1 1 1 11 1 I 1 I1 1 1 1 I 1 I I 1 I I1 1 I 1 1 I 1 1 1 I I I I 1 1 1 I I 1 I I I I I I I I I I I I I , I I 1 I I I I I 1 I I I 1 I I i 1 I I I ; 3'x5' Rip Rap , i i I I 1 I I I , I I I I I IN - I ITI v ' I 1 � I I ' 1 I Ii I I I I ,-- I I I I I 1 I 1 I 1 1 I , 1 1 1 I I 1 I 1 I I I 1 I 1 1 1 , 1 I 1 , 1 I , I 1 1 , I 1\ , 1 , I 1 ` 1 ` I 1 1 1 , I I I 1 I 1 1 1 , I I , I I , , 1 , , I , I I I , G 446.'. l , , , , , , , , 43,28 \\1 y ',/ (/ // // Z //. 3 - ��G-_=-=---1,_�� Under drain to /I daylight here, / I / approximately I - at a 438.5 invert out I elevation 797 add 25 If of 4" rROsolid pipe P. MULTIFAMILY f' proposed bend and cleanout IaUILUINU ITrt U) FF = 458.50 442.20 ,I BF=447.84 I G' 1.70 I s' I ;J Ensure bottom of Swale is set 8" G44 .20 r below lip of the level spreader. At bottom of Swale cut out a 2' wide by I 20" deep area, and place 4" of 57 4. stone followed by 120 of 4 perforated pipe wrapped in filter fabric, and cap it with 1' of 57 stone I laid on top. � i I G 41.70 G 44 .00 12.20 ; L - / T 1 l I ' � I I ,F-!J 4AT 4 NG - 443i 9 t i +` G 4as.sa 11 1 l I 1 l , 1 , 1 \ 1` , l 1 , , l , l , l 1 Level Spreader Design Table Level Spreader ID LS-413 Comments Downstream Outfall Undisturbed Native Outfall Condition Vegetation Grassed area with 90% land Land Cover coverage or better Slope (%) 2.22% Length (ft) 35' Design Criteria 1-yr Inflow (cfs) 2.05 Flow Spreader Length (ft) 116.9 13 LF min 130 LF max NOTE: 1. Minimum Flow Spreader length shall be 40LF per 1 CFS of inflow when outfalling to a Forested or Re -forested area, and 13LF per 1 CFS of inflow 0 when outfallin to a grassed area with 90%land coverage or better. g g g 2. The first 10 of filter past the levels Y p reader must b 2% slope or flatter. p p 3. SEE SITE PLAN SDP2018-00050 FOR LEVEL SPREADER DITCH CALCULATIONS. LEVEL SPREADER DETAIL EXISTING 2:1 MAX SLOPE LEVEL SPREADER RIGID LIPS r-8" DEEP V-DITCH PROP 4" PERFORATED PIPE INSTALLED IN I -MIN. TWIDE LAYER OF #57 STONE 3" THICK 57 STONE, WRAPPED IN FILTER FABRIC W/FILTER FABRIC NOTES: AMILY 1. FILTER FABRIC MUST BE PERMEABLE AND MEET THE G 445.84 NITS REQUIREMENTS FOUND IN STD. &SPEC. 3.191N THE VESCH. 4 STORY 60' MAX 2. THE RIGID LIP LEVEL SPREADER SHALL BE STANDARD WEIGHT PROP. HEIGHT 3000 PSI CONCRETE. (BUILDING TYPE -C-) 3. LEVEL SPREADER LENGTH SHALL BE DETERMINED BASED FF=456.50 BF = 445.84 UPON THE LEVEL SPREADER DESIGN CALCULATIONS INCLUDED IN THIS PLAN. 4. CONTRACTOR TO ENSURE THAT THE RIGID LIP REMAINS AT A CONSTANT ELEVATION FOR THE ENTIRE LENGTH. ` - I CS 1 G 445.84 , ` I , , g � I \ rIN - J n G445.0 I I G 445.84 1 - I I ` - I G 445.56 \ `` `` G 44a.s \� I Gaas.ea `. 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NOT APPROVED FOR CONSTRUCTION PROJECT NO.: V152000 DRAWN BY: EEN CHECKED BY: RTY DATE: 4/8/2019 SCALE: NA CAD I.D.: Sw1 PROJECT: VIRGINIA STORMWATER MANAGEMENT PLAN FOR BROOKHILL BLOCKS 4A AND 4B APARTMENTS- AMENDMENT1 LOCATION OF SITE ROUTE 29 SEMINOLE TRAIL RD AND STATE ROUTE 643 POLO GROUNDS ROAD CHARLOTTESVILLE ALBEMARLE COUNTY, VA R N G 28 BLACKWELL PARK LANE, SUITE 201 WARRENTON, VIRGINIA 20186 Phone: (540) 349-4500 Fax: (540)349-0321 VA@BohlerEng.com Lic. No. 0402056625 A 6/19/19 4 SHEET TITLE: LEVEL SPREADER LS-413 DETAIL SHEET NUMBER: C-907 -FINK SREPLAMN BLOOKMMD4B BUILTPW V15lOW$WI.O PRIWEDBY:ABEOIR 7.2021®4:WPM r $AV DBY:ABEDIR TYPICAL LEVEL SPREADER DETAIL