The URL can be used to link to this page

Home My WebLink AboutWPO202000051 Checklist 2020-11-05 (2)Albemarle 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 (1cfs 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 stnds 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)