HomeMy WebLinkAboutWPO202200011 Checklist 2022-03-21Albemarle 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.
idA 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)
iddrainage 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)
_jd_ all proposed and existing storm sewer must be shown in plan view
Id for residential development, principle access free of flooding during the 25yr storm [ 14-
410]
Id site runoff and entrances do not drain into streets (from VDOT Drainage Manual 9.4.5.2,
9.4.6.2)
Id concentrated runoff (lcfs or greater) does not run across travelways/streets (as above
following VDOT design)
id drainage does not run across, through, or backwater in dumpster areas [ 18-4.12.19]
id 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)
Id 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)
Id labels on all drainage structures provided (and should match the drainage computations
and profiles)
id 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:
Id existing ground
Id proposed ground
NA any channel linings
idall utility crossings
id a VDOT designation (MH-1, DI-3B, etc.) for each structure
id throat length for each drop inlet
grate type for each grate inlet
id a label on each structure to correspond with the computations
Albemarle County
Engineering Drainage Plan Checklist
Page 2 of 2
m material and strength class or gage of each pipe
m manhole access every 300' for 15"42" or 800' for 48" or greater
0 pipe slopes at 0.5% min. to 16% max. (per VDOT studs for anchors over 16%)
0 concrete inlet shaping (IS-1) specified on any structure with a 4' or greater drop
m safety slabs (SL-1) in any structure taller than 12'.
B top or rim elevation for each structure
Id 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
Id scour outlet protection at all outlets, corresponding to computations (Green Brook, OP)
Drainage computations: (applicable to any plan proposing pipes, channels, etc.)
Id Pipe computations for all pipes
Id 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)
Id Curb inlet computations for any curb inlets on grade
Id All spreads are less than 10'
Id carryover is accounted for
Id 100% capture at entrances so no flow runs out entrances into travel lanes
Id 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.
id Curb inlet computations for any curb inlets in sump conditions
Id All flow depths are below 6" in the capacity table
Id All spreads are less than 10'
Id 100% capture to stormwater management facilities
NA Ditch computations for any ditches
ditch linings specified per plans meet velocity requirements
NA Culvert computations for any culverts
headwaters < 1.5 x culvert height, and 18" below shoulder elevation of streets.
Id Outlet protection computations for all outlets
id dimensions and stone sizes for all outfalls
Id Proposed pipe and inlet drainage area map
Id 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
Id time of concentration for each drainage area as used in the computations
Id destination structure labeled for each drainage area (if not obvious)