The URL can be used to link to this page

Home My WebLink AboutWPO202100046 Checklist 2021-08-12Albemarle County Engineering Drainage Plan checklist for plan reviewers Updated 1 Dec 2014 A drainage plans is typically a component of a road plan, site plan, or stormwater management plan. It consists of the channel, ditch, culvert, and stormsewer design drawings, drainage maps, and computations for hydrology and hydraulics. Reference key; [Square Brackets] are County Code references, {Curved Brackets} are policy references, and (regular parenthesis) are explanatory. Links to reference documents are provided where possible. A professional seal should be provided for any computation packages where are separate from sealed plans. Drainage: [18-32.6.2d, 14-305, 311] drainage area maps (This is a basic element, and without this there is no review) drainage computations (usually in the form of tables from the VDOT Drainage Manual App. 9B-1 LD-2014, App.7B-1 LD-268, App., App. 8B-1 LD-269, etc. -computations are a basic element, and without them there is no review) all proposed and existing storm sewer must be shown in plan view for residential development, principle access free of flooding during the 25yr storm [ 14- 410] site runoff and entrances do not drain into streets (from VDOT Drainage Manual 9.4.5.2, 9.4.6.2) concentrated runoff (lcfs or greater) does not run across travelways/streets (as above following VDOT design) drainage does not run across, through, or backwater in dumpster areas [ 18-4.12.19] overland relief is provided for any drainage structure or inlet in case of clogging. The failure of any system will not cause structures, streets or yards to flood. (Policy) direction of flow change (or deflection angle) in each drainage structure is 90 degrees or greater (flow should not have to reverse direction) (from guide of VDOT Drainage Manual 9.4.9.3.2.3) labels on all drainage structures provided (and should match the drainage computations and profiles) provisions and easements for drainage across 3 or more lots. Dense development where fencing, decking, sheds, patios, etc. are expected should provide yard inlets and pipes in easements, rather than ditches {Policy) Drainage profiles: (applicable to site plans, road and drainage plans) [14-311, 18-32] drainage profiles for each pipe, structure or channel must contain: existing ground proposed ground any channel linings all utility crossings a VDOT designation (MH-1, DI-3B, etc.) for each structure throat length for each drop inlet grate type for each grate inlet a label on each structure to correspond with the computations Albemarle County Engineering Drainage Plan Checklist Page 2 of 2 material and strength class or gage of each pipe manhole access every 300' for 15"42" or 800' for 48" or greater pipe slopes at 0.5% min. to 16% max. (per VDOT studs for anchors over 16%) concrete inlet shaping (IS-1) specified on any structure with a 4' or greater drop safety slabs (SL-1) in any structure taller than 12'. top or rim elevation for each structure all invert elevations for each structure (with positive flow drop between inverts). end sections (ES-1) or endwalls (EW-1) on all pipe outlets. Endwalls for culverts 48" or taller scour outlet protection at all outlets, corresponding to computations (Green Brook, OP) Drainage computations: (applicable to any plan proposing pipes, channels, etc.) Pipe computations for all pipes All proposed systems are designed within open channel flow capacities. (HGL computations are not necessary, and should not be relied upon unless the entire system is to be watertight.) For systems within drainage easements, all proposed pipes are a minimum 15" in diameter _ There are no excessive outlet velocities (> 15fps) Curb inlet computations for any curb inlets on grade All spreads are less than 10' carryover is accounted for 100% capture at entrances so no flow runs out entrances into travel lanes 100% capture, or overland flow of capacity storm, to stormwater management facilities. Typically stormwater management is designed to the 10year storm, and inlets on grade often cannot capture this. Inlets in sumps should be used. Curb inlet computations for any curb inlets in sump conditions All flow depths are below 6" in the capacity table All spreads are less than 10' _ 100% capture to stormwater management facilities Ditch computations for any ditches ditch linings specified per plans meet velocity requirements Culvert computations for any culverts headwaters < 1.5 x culvert height, and 18" below shoulder elevation of streets. Outlet protection computations for all outlets dimensions and stone sizes for all outfalls Proposed pipe and inlet drainage area map limits of all areas and sub -areas draining to proposed structures, and existing structures or channels which will be impacted acreage of each drainage area as used in computations hydrologic coefficient for each drainage area as used in the computations time of concentration for each drainage area as used in the computations destination structure labeled for each drainage area (if not obvious)