This document discusses different types of gutters and inlets used for drainage. It describes the key components of HEC-22 type inlets including gutter cross slope, cross slope, and local depression. It also summarizes different types of inlets like grate inlets, curb openings, combination inlets, and slotted drains. Slotted inlets and trench drains are discussed in more detail regarding their use cases and equations for calculating capacity. The document concludes by mentioning specific inlet types used for drainage in New Jersey.

1. GUTTERS
AND
INLETS
ER. MANDEEP SINGH
(ASSISTANT PROFESSOR)
DEPARTMENT OF CIVIL ENGINEERING
BGIET, SANGRUR

5. Among other data, each inlet has a gutter cross section that consists of a
width, cross-slope, compound gutter cross slopes, Sw and Sx, and an
optional local depression, a. HEC-22 -type inlets can be very confusing
and hopefully this article will help to simplify.

6. Section at the upstream end of inlet. The dotted line is the gutter slope at
the inlet face. Depression, a, plus Throat Height equals the total
opening.
Sx: -Sx is the cross-slope of the pavement section between the center of
the pavement and the edge of the gutter. Common value is 2% or 0.02
feet per feet.
Sw: - Sw refers to the cross-slope of the gutter section just upstream of
the inlet opening. This is not necessarily the cross-slope of the gutter
section at the face of the inlet. See Local Depression below. Common
values of Sw hover around 5% or 0.05 feet per feet.

7. Local Depression, a: -The local depression describes the gutter slope at
the face of the inlet. But instead of describing it as a slope, it is
described as the vertical distance between a projection of Sx and the
invert of the inlet opening. Note the heavy dotted line in the sketch
above. Typical values range from 1 to 3 inches.
If Sw > Sx, then HEC-22 considers it to be a depressed inlet. Depressed
inlets will have smaller spreads at the face of the inlet but the depression
has no affect on the computed spreads upstream in the gutter section.

12. 1

16. W = ZY
3=33.33 Y
Y= 0.09

18. Figure 4.2 depicts four commonly used types of inlets, namely
grate inlet, curb opening inlet, combination inlet, and slotted
drain inlet. It is to be noted that curb openings and combination
inlets are not common in some countries. Photos 4.1 and 4.2
show an inlet along a curb in Budapest, Hungary, and an inlet at
a parking lot median, in a roadside service center in Austria,
respectively. The latter photograph also shows a basket under an
inlet grate to intercept floatables and debris.

20. To avoid bottles and cans from entering a curb opening, a new type of
curb piece designated as Eco-curb piece is being used in new inlets in
New Jersey. The New Jersey Department of Environmental Protection
(NJDEP) has also mandated that all existing curb pieces be replaced
with the new curb pieces having openings less than 2 in. wide. Figure
4.3 shows a sketch of these curb pieces. Environmental Retrofit
Solutions (ERS), a company in Hawthorne, NJ, used to manufacture
curb pieces made of Core-Ten high strength/low alloy weathering steel
which can be readily mounted over the existing curb inlets (see Figure
4.4). These curb pieces are now available through Campbell Foundry in
New Jersey, which also does business as Campbell-ERS since 2009.
Photo 4.3a and b shows a new curb piece and a traditional curb piece,
respectively.

22. A modified type of slotted drain is the trench drain. This type of drain
commonly consists of a rectangular flume and a continuous grate. A
variety of trench drains are commercially available. ACO Drain is one
such trench drain which comes in 0.5 and 1m long sections (see
Figure 4.5a).ACO has recently begun manufacturing Highway Drains.
These drains, which are made of polymer concrete, come in as one piece
trench and grate 4 ft long, 8 in. inside width with 1/16 in. per
ft (0.16%) internal longitudinal slope (refer to Figure 4.5b). ACO
Highway Drain provides significantly larger capacity than original ACO
drains. ACO Highway Drain is also nearly four times less
expensive than the older models, and as such, is highly suitable for
roads of small longitudinal slope.

23. To provide access for maintenance, ACO Highway Drain is also
available with ductile iron grate bolted at the four corners. ACO also
manufactures flume outlets for connection into collector lines or catch
basins. These are available in 8 or 12 in. schedule 40 vertical or
horizontal outlets with iron access grates. Figure 4.5c shows an ACO
access drain and outlet channel. Following the author’s
recommendation, ACO Highway Drain was installed in State Route 30
in Magnolia, Camden County, under a New Jersey DOT roadway
improvement project.
A number of foundries, including Neenah and Campbell, manufacture
various sizes of grates for trench drains. Figure 4.6 exemplifies grates
manufactured by Campbell Foundry in Harrison and
Kearny, New Jersey (2005). This foundry makes 6–48in. wide grates

25. Slotted Inlets: -Slotted inlets offer little interference to traffic and can be used in
curbed or uncurbed sections.
They are particularly effective in airport runways, parking lots, garage entries at
downhill driveways, docks and ports, and roads with small longitudinal slope
where the runoff would impound on the gutter. For slotted inlets in sag locations,
the inlet capacity may be calculated using the weir flow equation for a depth of up
to 0.2 ft (5 cm) and the orifice flow equation for depths larger than 0.4 ft (0.12m).
Within these depths, the flow is in a transient condition. The inlet capacity for
the weir flow condition can be calculated using the same equation as the curb
opening (Equation 4.13). In that equation, the depth at curb measured from the
normal cross slope is substituted for depth of water, d, and the weir coefficient
“Cw” varies with flow depth and slot length with a typical value of

26. Cw = 2 5. CU
Cw = 1 4. SI
The orifice flow condition follows the equation
Q= 0.8LW (2gd)^0.5 = …………………………(4.18)
where
L is the length of slot, ft (m)
W is the width of slot, ft (m)
g is the acceleration of gravity, 32.2 ft/s2 (9.81m/s2)
d is the depth of water at slot inlet, ft (m)
This equation is valid when the depth of water is greater than
the opening which results in inundation of the slot. For smaller
flow depths, the weir flow equation should be used

27. As previously indicated, a number of trench drains are commercially
available. One such drain is the ACO drain which comes in sections 0.5
and 1m long and 9 mm (3.75in.) and upward widths and various depths.
Capacity and technical information on this and other trench drains can
be obtained from the manufacturers’ specifications.
Combination Inlets: -Combination inlets are used to intercept debris in
addition to runoff in order to avoid clogging of the grates. The
interception capacity of a combination inlet consists of the sum of the
capacities of the grate and curb opening. However, this capacity is not
considerably greater than the capacity of the grate alone. This is
particularly the case for new curb pieces which provide small openings.
Therefore, in practice, the interception capacity of combination inlets
may be calculated neglecting the curb pieces.

28. New Jersey Inlets:-Many states have specific inlet grates. In New
Jersey, for example, four types of inlets are commonly used for streets,
roads, and parking areas. These are grate inlet types “A” and “E” having
2′×4′ and 4′×4′ grates and combination inlets type “B” and “D” having
2′×4′ grates plus curb pieces. The only difference between type “B” and
type “D” inlets is that the former inlet has larger inside dimensions than
the latter. These inlets are depicted in Figure 4.11. Also available are
2′×2′and smaller inlets for lawn and gardens.
The New Jersey Department of Transportation (NJDOT) has developed
the following equation for the interception capacity of grate inlets at
gutters (Drainage Design Manual, August 2006):