Compost filter sock traps
(See Chapter 3)
CHAPTER 8
Sediment Traps
(CHANGES HIGHLIGHTED IN YELLOW)
Design Criteria
Design Criteria
Max drainage area = 5.0 acres
Access to be provided in accordance with
standards in Chapter 3
Accesses to be maintained for life of trap
When no longer
g needed,, accesses to be regraded
g
& stabilized as per Chapter 11(Stabilization
Methods and Standards)
Min storage volume = 2,000 cuft for each
acre of contributing drainage area
(disturbed & undisturbed)
Greater surface area increases trapping efficiency
Traps located in fine
fine--textured soils (sandy clay,
silty clay, silty clay loam, clay loam, & clay), min
surface area ((sqft
sqft)) = 5300 times number of
contributory drainage acres
Example, a trap with 5 acre drainage area needs
26,500 sqft of surface area (trap with storage
volume surface area of about 115
115 X 230)
230 )
If not possible, consider using of soil stabilizer
and/or sediment forebay
Traps which will be converted into infiltration basins
to be constructed as per Pa Stormwater BMP Manual
700 cuft/ac
cuft/ac for sediment storage
1300 cuft/ac
cuft/ac for dewatering zone
Supporting calcs to be provided for irregularly
shaped traps (Standard Worksheet #14
recommended)
Design Criteria
Minimum flow length:width ratio =
4L:1W for all traps located in Special
Protection Watersheds (HQ or EV)
Min ratio = 2:1 for all other traps
Min Length (L) of Flow through trap =
10 ft unless trap constructed around
inlet structure
Baffles may be required to achieve
flow length:width ratio, see Fig. 7.5 in
Chapter 7
Design Criteria
Max Constructed Embankment Height
= 5.0 unless berm constructed as
permanent stormwater management
basin with corresponding increased
top width
Any trap that will be converted to
permanent stormwater facility might
need key trench
Min embankment top width = 5.0
Max Embankment Side Slopes =
2H:1V
Min Freeboard above Maximum
Design Water Level = 12
Embankment Trap
Not an ABACT
Can be ABACT for HQ by adding 6
compost layer on inside face of
spillway & anchoring with suitable
netting
May ABACT for EV by replacing filter
cloth with 24 dia compost socks
staked across inside face of spillway
Embankment Trap
Embankment Trap
Min spillway width (ft
(ft)) = 2 X number of
acres of contributing drainage area
If not discharging directly into
waterway, min width ((ft
ft)) = 6 X the
number acres
Min spillway crest elevation = the
elevation at which required 2,000
cuft/acre
cuft
/acre storage capacity provided.
Max spillway side slope = 2H:1V
Min rock size for spillway = RR-3
R-4 or larger rock recommended for
drainage areas > 3.0 acres
Entire spillway should be constructed
with rock (above clean out elevation,
see SCD # 88-1)
Inside face of spillway to be covered
with 6
6 (min) thick layer of filter stone
(max size = AASHTO #57)
Filter fabric to be securely staked on
top of filter stone up to top of spillway
Excess fabric to be staked to bottom of
trap
Standard Construction
Detail # 8
8--1 Embankment
Sediment Trap
SCD# 8
8--1 Notes (Embankment Type)
Embankment outlet composed entirely
of rock above clean out elevation (COE)
Main body RR-3 or larger (R
(R--4 or larger rock
recommended for drainage areas greater
than 3.0 acres)
Inside face AASHTO # 57 stone or smaller
6 thick layer of compost, compost sock, or
clean sand to be installed on top of AASHTO
#57 stone & securely anchored in HQ
Watersheds.
24 diameter Compost Sock(s) in lieu of filter
fabric & AASHTO #57 Stone in EV
Watersheds
SCD# 8
8--1 Notes (Embankment Type)
Check embankments, spillways, & outlets
for erosion, piping & settlement
Clogged or damaged spillways and/or
embankments to be immediately restored
to design specs
Remove accumulated sediment & stabilize
disturbed areas inside trap before
conversion to stormwater management
facility
SCD# 8
8--1 Notes (Embankment Type)
Fill material for embankments to be free of roots, or other
woody vegetation, organic material, large stones, & other
objectionable materials
Embankment to be compacted in layered lifts of < 6 to 9
Max rock size < 2/3 lift thickness
Upon completion, embankment to be seeded & mulched
or otherwise stabilized as per specs of E&S Plan
Inspect all traps at least weekly & after each runoff event
Provide access for sediment removal & other required
maintenance
Clean out stake to be placed near center of each trap
Dispose of materials removed from trap as per E&S Plan
8-2 Barrel/Riser Sediment Trap
This device has MODERATE sediment
removal efficiency and is an ABACT
BMP for HQ watersheds but not for EV
watersheds The efficiency can be
watersheds.
raised to HIGH (ABACT for HQ and EV
watersheds) by substituting a skimmer
dewatering device for the perforated
riser (See Chapter 7 for skimmer
design).
Trap with Riser
Riser--Moderate Efficiency
Barrel/Riser Trap
Crest of riser to be set at elevation at which
2,000 cuft
cuft/acre
/acre storage capacity provided
Riser & outlet barrel to provide 1.5 cfs
cfs/acre
/acre
(min) discharge capacity
Recommended min Barrel & Riser
diameters in Table 8.1
Supporting calcs to be provided
Embankment to provide > 12 Freeboard
above max design water elevation
(elevation at which 1.5 cfs/acre
cfs/acre discharge
capacity provided)
Perforations in riser to dewater the trap
limited to one 1 dia. hole per vertical ft of
riser
Trap with SkimmerSkimmer-High Efficiency
Table 8.1 Recommended
Minimum Pipe Sizes for
Barrel/Riser Sediment Traps
Standard Construction
Detail # 8
8--2 Barrel/Riser
Sediment Trap
SCD# 8
8--2 Notes (Barrel/Riser Type)
Check embankments, spillways, &
outlets for erosion, piping &
settlement
SCD# 8
8--2 Notes (Barrel/Riser Type)
Fill material for embankments to be free of roots, or other
woody vegetation, organic material, large stones, & other
objectionable materials
Embankment to be compacted in layered lifts of < 6 to 9
Max rock size < 2/3 lift thickness
Upon completion, embankment to be seeded & mulched or
otherwise stabilized as per specs of E&S Plan
Inspect all traps at least weekly & after each runoff event
Provide access for sediment removal & other required
maintenance
Clean out stake to be placed near center of each trap
Accumulated sediment to be removed when at clean out
elevation on stake & trap restored to original dimensions
Dispose of materials removed from trap as per E&S Plan
Standard Construction Detail # 883 Sediment Trap Temporary Riser
Clogged or damaged spillways and/or
embankments to be immediately restored
to design specs
Replace displaced riprap within outlet
protection immediately
Remove accumulated sediment &
stabilize disturbed areas inside trap
before conversion to stormwater
management facility
SCD# 8
8--3 Notes (Temp. Riser)
Standard Construction Detail
#8
8--4 Dry Barrel/Riser
Sediment Trap
Repair clogged or damaged spillways immediately
Remove trash & other debris from trap & riser
Minimum 2 #8 rebars placed at right angles and
projecting through sides of riser to anchor it to
concrete base. Rebars shall project a minimum of
riser diameter beyond outside of riser.
Concrete base shall be poured in such a manner as
to insure that concrete fills bottom of riser to invert
of the outlet pipe to prevent riser from breaking
away from the base. Minimum base width equals 2
X riser diameter.
Embedded section of aluminum or aluminized pipe
shall be painted with zinc chromate or equivalent
SCD# 8
8--4 Notes
In Special Protection (HQ) Watersheds, add 6 layer of
compost on top of stone or in (EV) Watersheds, replace stone
with suitable compost filter sock
Fill material for embankments to be free of roots, or other
woody vegetation, organic material, large stones, & other
objectionable materials
Embankment to be compacted in layered lifts of < 6 to 9
Max rock size < 2/3 lift thickness
Upon completion, embankment to be seeded & mulched or
otherwise
th
i stabilized
t bili d as per specs off E&S Plan
Pl
Inspect all traps at least weekly & after each runoff event
Provide access for sediment removal & other required
maintenance
Clean out stake to be placed near center of each trap
Accumulated sediment to be removed when at clean out
elevation on stake & trap restored to original dimensions
Dispose of materials removed from trap as per E&S Plan
Total Trap Dewatering
Filter cloth wrapped around riser not
acceptable alternative due to potential for
clogging
Outlet Protection
Standard Construction Detail
#8
8--5 Dry Sediment Trap
Temporary Riser
At a min, outlet protection to consist
of Rock Outlet Basin with dimensions
conforming to Figure 88-6
Acceptable alternative is riprap apron
designed according to dimensions
from Figure 9.2 or Figure 9.3
For excessive discharge velocity,
consider using drop inlet structure or
other velocity reduction device prior
to outletting to basin or apron
Standard Construction
Detail # 8
8--6 Sediment Trap
Outlet Basin Detail
SCD# 8
8--6 Notes (Outlet
Basin)
Inspect all trap outlet basins weekly &
after each runoff event
Replace displaced riprap within outlet
basin immediately
Side slopes not to exceed 1.5H:1V
Standard Construction
Detail # 8
8--7 Type M Inlet
Sediment Trap
Standard
Construction
Detail # 8
8--7
Type M Inlet
Sediment
Trap (cont.)
Standard Construction
Detail # 8
8--8 Concrete Riser
with Temporary Dewatering
Holes
Standard Construction
Detail # 8
8--8 Concrete Riser
with Temporary Dewatering
Holes (cont.)
QUESTIONS?
MarkLonergan
Mark
Lonergan
PADEP ReadingDistrictOffice
(610)9160100
10
