HomeMy WebLinkAboutSUB202100115 Checklist 2021-10-22Albemarle County Engineering
Drainage Plan checklist for plan reviewers
18 Feb 2014 (Use the latest checklist from the Team Services engineering forms site)
A drainage plans is typically a component of a road plan, site plan, or stormwater management plan. It
consists of the channel, ditch, culvert, or 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
n/a 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 (1 cfs 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)
n/a provisions and easements for drainage across 3 or more lots. Dense development where
fencing, decking, etc is 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
n/a 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%)
n/a concrete inlet shaping (IS-1) specified on any structure with a 4' or greater drop
n/a 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 cannot capture this.
✓ 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
n/a Ditch computations for any ditches
n/a ditch linings specified per plans meet velocity requirements
n/a Culvert computations for any culverts
n/a 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)