Hydraulic Performance of Curb and Gutter Inlets

Report No.
K-TRAN: KU-99-1
Final Report
HYDRAULIC PERFORMANCE OF CURB AND GUTTER
INLETS
Bruce M. McEnroe
Reuben P. Wade
Andrew K. Smith
University of Kansas
Lawrence, Kansas
September 1999
K-TRAN
A COOPERATIVE TRANSPORTATION RESEARCH PROGRAM BETWEEN:
KANSAS DEPARTMENT OF TRANSPORTATION
THE KANSAS STATE UNIVERSITY
THE UNIVERSITY OF KANSAS
1. Report No.
K-TRAN: KU-99-1
2. Government Accession No. 3. Recipient Catalog No.
5 Report Date
September 1999
4 Title and Subtitle
HYDRAULIC PERFORMANCE OF CURB AND GUTTER
INLETS
6 Performing Organization
Code
7. Author(s)
Bruce M. McEnroe, Reuben P. Wade and Andrew K. Smith
8 Performing Organization
Report No.
10 Work Unit No. (TRAIS)

9 Performing Organization Name and Address
School of Engineering
Lawrence, Kansas 66045
11 Contract or Grant No.
C-1077
13 Type of Report and Period
Covered
Final Report
May 1998 to September 1999
12 Sponsoring Agency Name and Address
Kansas Department of Transportation
Docking State Office Bldg.
Topeka, Kansas 66612
14 Sponsoring Agency Code
106-RE-0176-01
15 Supplementary Notes
For more information write to address in block 9.
16 Abstract
The performance characteristics of KDOTs standard curb and gutter inlets have been determined from
hydraulic model tests and theoretical calculations. The standard inlets are the concrete gutter inlet, the
Type B gutter inlet, the Type 12 combination inlet, and Type 22 curb inlets with lengths of 1.5 m, 3.0 m and
4.5 m. Model tests of these inlets on grade provided the relationships between captured discharge and total
discharge for grades from 0.5% to 5.0% and cross-slopes of 1.6% and 3.1%. The model tests were
performed in the hydraulics laboratory at the University of Kansas. The inlets, curbs and gutters were
modeled at one-quarter scale. The model roadway was 15 m long with adjustable grade and cross-slope.
The three inlets with gutter openings (the concrete gutter inlet, Type B gutter inlet and Type 12 combination
inlets) exhibited similar performance characteristics under all conditions tested. The grade of the roadway
does not have a significant effect on performance of these inlets. The Type 22 curb inlets perform better on
mild grades than on steep grades. All of the inlets perform slightly better on the steeper cross-slope. The
depth-discharge relationships for the inlets in sag locations were computed from fundamental hydraulic
principals of orifice flow and weir flow. Relationships for the spread of water on streets with the standard
gutter and the Type I combination curb and gutter were also developed from standard hydraulic formulas.
The design aids in this report provide a sound basis for the selection and sizing of curb and gutter inlets.
17 Key Words
Curb, Grade, Gutter, Hydraulic Model Tests,
Inlets
18 Distribution Statement
No restrictions. This document is
available to the public through the
National Technical Information Service,
Springfield, Virginia 22161
19 Security
Classification (of
this report)
Unclassified
Security
Classification (of
this page)
Unclassified
20 No. of pages
60
21 Price
Form DOT F 1700.7 (8-72)
Final Report
K-TRAN Research Project KU-99-1
Hydraulic Performance of Curb and Gutter Inlets
by
Bruce M. McEnroe
Reuben P. Wade
Andrew K. Smith
Department of Civil and Environmental Engineering
for
Kansas Department of Transportation
September 1999
PREFACE
This research project was funded by the Kansas Department of Transportation K-TRAN
research program. The Kansas Transportation Research and New-Developments (K-TRAN)
Research Program is an ongoing, cooperative and comprehensive research program
addressing transportation needs of the State of Kansas utilizing academic and research
resources from the Kansas Department of Transportation, Kansas State University and the
University of Kansas. The projects included in the research program are jointly developed
by transportation professionals in KDOT and the universities.
NOTICE
The authors and the State of Kansas do not endorse products or manufacturers. Trade
and manufacturers names appear herein solely because they are considered essential to the
object of this report.
This information is available in alternative accessible formats. To obtain an alternative
format, contact the Kansas Department of Transportation, Office of Public Information, 7th
Floor, Docking State Office Building, Topeka, Kansas, 66612-1568 or phone (785)296-3585
(Voice) (TDD).
DISCLAIMER
The contents of this report reflect the views of the authors who are responsible for the
facts and accuracy of the data presented herein. The contents do not necessarily reflect the
views or the policies of the State of Kansas. This report does not constitute a standard,
specification or regulation.
i
ABSTRACT
The performance characteristics of KDOTs standard curb and gutter inlets have been determined
from hydraulic model tests and theoretical calculations. The standard inlets are the concrete gutter
inlet, the Type B gutter inlet, the Type 12 combination inlet, and Type 22 curb inlets with lengths of
1.5 m, 3.0 m and 4.5 m. Model tests of these inlets on grade provided the relationships between
captured discharge and total discharge for grades from 0.5% to 5.0% and cross-slopes of 1.6% and
3.1%. The model tests were performed in the hydraulics laboratory at the University of Kansas. The
inlets, curbs and gutters were modeled at one-quarter scale. The model roadway was 15 m long with
adjustable grade and cross-slope. The three inlets with gutter openings (the concrete gutter inlet, Type
B gutter inlet and Type 12 combination inlets) exhibited similar performance characteristics under all
conditions tested. The grade of the roadway does not have a significant effect on performance of these
inlets. The Type 22 curb inlets perform better on mild grades than on steep grades. All of the inlets
perform slightly better on the steeper cross-slope. The depth-discharge relationships for the inlets in
sag locations were computed from fundamental hydraulic principals of orifice flow and weir flow.
Relationships for the spread of water on streets with the standard gutter and the Type I combination
curb and gutter were also developed from standard hydraulic formulas. The design aids in this report
provide a sound basis for the selection and sizing of curb and gutter inlets.
ii
ACKNOWLEDGMENT
This project was supported by the Kansas Department of Transportation (KDOT) through the K-
TRAN Cooperative Transportation Research Program. The authors sincerely appreciate this support.
Mr. James Richardson. P. E., of KDOT deserves special thanks for his contributions as project
monitor.
iii
TABLE OF CONTENTS
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2. KDOT Curb and Gutter Inlets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
3. Hydraulic Performance of Inlets on Grade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1 Experimental Set-Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2 Test Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3 Model-Prototype Relations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.4 Calibration of the Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.5 Analysis of Experimental Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.6 Comparisons of Inlet Performance on Grade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4. Hydraulic Performance of Inlets in Sag Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1 General Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.2 Concrete Gutter Inlet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.3 Type B Gutter Inlet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.4 Type 12 Combination Inlet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.5 Type 22 Curb Inlets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5. Spread of Water on Pavement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Appendix A. Graphs for Experimental Results for Inlets on Grade . . . . . . . . . . . . . . . . . . . . . . . 22
Appendix B. Design Charts for Inlets on Grade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Appendix C. Design Charts for Spread of Water on Pavement . . . . . . . . . . . . . . . . . . . . . . . . . . 44
iv
LIST OF TABLES
1. Design Curves for Inlet Performance on Grade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2. Discharges Captured by Inlets in Sag Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
LIST OF FIGURES
1. Standard Gutter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Type I Combined Curb and Gutter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Concrete Gutter Inlet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Type B Gutter Inlet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Type 12 Combination Inlet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
6. Type 22 Curb Inlet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
A.1 Concrete Gutter Inlet on Pavement with 1.6% Cross-Slope . . . . . . . . . . . . . . . . . . . . . . . . 23
A.2 Concrete Gutter Inlet on Pavement with 3.1% Cross-Slope . . . . . . . . . . . . . . . . . . . . . . . . 24
A.3 Type B Gutter Inlet on Pavement with 1.6% Cross-Slope . . . . . . . . . . . . . . . . . . . . . . . . . . 25
A.4 Type B Gutter Inlet on Pavement with 3.1% Cross-Slope . . . . . . . . . . . . . . . . . . . . . . . . . . 26
A.5 Type 12 Combination Inlet on Pavement with 1.6% Cross-Slope . . . . . . . . . . . . . . . . . . . . 27
A.6 Type 12 Combination Inlet on Pavement with 3.1% Cross-Slope . . . . . . . . . . . . . . . . . . . . 28
A.7 Type 22 Curb Inlet, 1.5 m, on Pavement with 1.6% Cross-Slope . . . . . . . . . . . . . . . . . . . . 29
A.12 Type 22 Curb Inlet with, 4.5 m, on Pavement with 3.1% Cross-Slope . . . . . . . . . . . . . . . . 34
B.1 Gutter and Combination Inlets on Pavement with 1.6% Cross-Slope . . . . . . . . . . . . . . . . . 36
B.2 Gutter and Combination Inlets on Pavements with 3.1% Cross-Slope . . . . . . . . . . . . . . . . . 37
B.3 Type 22 Curb Inlet, 1.5 m, on Pavement with 1.6% Cross-Slope . . . . . . . . . . . . . . . . . . . . 38
v
C.1 Spread on Pavement with 1.6% Cross-Slope and Type I Combined Curb and Gutter . . . . . 45
C.2 Spread on Pavement with 1.6% Cross-Slope and Standard Gutter . . . . . . . . . . . . . . . . . . . 46
C.3 Spread on Pavement with 3.1% Cross-Slope and Type I Combined Curb and Gutter . . . . . 47
C.4 Spread on Pavement with 3.1% Cross-Slope and Standard Gutter . . . . . . . . . . . . . . . . . . . 48
C.5 Depth of Flow in Type I Combined Curb and Gutter, 1.6% Cross-Slope . . . . . . . . . . . . . . 49
C.6 Depth of Flow in Standard Gutter, 1.6% Cross-Slope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
C.7 Depth of Flow in Type I Combined Curb and Gutter, 3.1% Cross-Slope . . . . . . . . . . . . . . 51
C.8 Depth of Flow in Standard Gutter, 3.1% Cross-Slope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
1
1. INTRODUCTION
Proper drainage of the roadway is essential to highway safety. Drainage systems for roadways
with curb and gutters are designed to limit spread of water on the pavement. Excess water must be
captured by curb and gutter inlets. To locate and size these inlets properly, designers need reliable
information on their hydraulic performance.
This report provides complete information on the hydraulic performance characteristics of
KDOTs standard curb and gutter inlets on grade and in sag locations. It also provides design charts
for the spread of water on roadways with curbs and gutters. The design charts for inlets on grade
were developed from hydraulic model tests. The capacities of inlets in sag locations were computed
from fundamental hydraulic principles.
2. KDOT CURB AND GUTTER INLETS
KDOT has four standard designs for curb and gutter inlets: the concrete gutter inlet, the Type B
gutter inlet, the Type 12 combination inlet, and the Type 22 curb inlet. Figures 2.3 through 2.6 show
the design features that are relevant to hydraulic performance. KDOT standard drawings show the
complete designs of these inlets. The concrete gutter inlet is used on pavements with the KDOT
standard gutter (Figure 2.1). The standard gutter is a 850-mm-wide shallow gutter with a flowline 40
mm below the edge of the pavement and an outer edge 40 mm above the edge of the pavement. The
other three KDOT inlets are normally used on roadways with a Type I combined curb and gutter
(Figure 2.2). The Type I curb and gutter is 750 mm wide. The flowline is 45 mm below the edge of
the pavement and the top of the curb is 105 mm above the edge of the pavement.
The concrete gutter inlet (Figure 2.3) has a grated gutter opening 750 mm long (parallel to the
edge of the pavement) and 700 mm wide. The opening is not depressed. The principal (top) bars of
the grate are oriented longitudinally. The rectangular bars are 16 mm wide, and the clear openings
between the bars are 48 mm wide.
The Type B gutter inlet (Figure 2.4) has a grated gutter opening 750 mm long and 450 mm wide.
The opening is aligned with the gutter (not recessed) and is only slightly depressed (25 mm below the
gutter). The principal bars of the grate are oriented longitudinally. The rectangular bars are 16 mm
wide, and the clear openings between the bars are 32 mm wide.
The Type 12 combination inlet (Figure 2.5) has a grated gutter opening and a curb opening.
2
Fig. 1. Standard Gutter
Fig. 2. Type I Combined Curb and Gutter
3
(a) Elevation
(b) Plan of Grate
Fig. 3. Concrete Gutter Inlet
4
(a) Plan
(b) Elevation (Section A-A)
Fig. 4. Type B Gutter Inlet
5
(a) Plan
Fig. 5. Type 12 Combination Inlet
6
(a) Plan
Fig. 6. Type 22 Curb Inlet
7
These openings are depressed and recessed slightly. The gutter opening is 750 mm long and 475 mm
wide. The principal bars of the grate are oriented longitudinally. The rectangular bars are 16 mm
wide, and the clear openings between the bars are 54 mm wide. The curb opening is 750 mm long.
The Type 22 curb inlet (Figure 2.6) has a curb opening that is depressed and recessed slightly
and no gutter opening. The three standard lengths of Type 22 inlets are 1.5 m, 3.0 m and 4.5 m. These
dimensions are the lengths of concrete box structures. The corresponding lengths of the curb openings
are 1.2 m, 2.7 m and 4.3 m.
3. HYDRAULIC PERFORMANCE OF INLETS ON GRADE
3.1 Experimental Set-Up
The hydraulic model studies of the KDOT standard inlets were conducted in the hydraulics
laboratory at the University of Kansas. One-quarter-scale models of the inlets were constructed and
tested on a 15-m-long model of a section of roadway. This apparatus was built in 1997 to test the
Overland Park set-back inlets in K-TRAN Project KU-98-3 (McEnroe and Wade, 1998). New one-
quarter-scale curbs and gutters were constructed and installed on the model roadway. The KDOT
standard gutter was installed one side, and a Type I combined curb and gutter on the other side. The
model curbs, gutters, inlets and transitions were constructed of wood and plaster. The grade and
cross-slope of the model roadway are adjustable. The downstream end of the supporting box beam
is hinged to the floor of the laboratory. The grade of the roadway is adjusted by raising or lowering
the upstream end of the beam with a chain hoist. The roadway can be tilted toward either curb at any
desired cross-slope. The distance from the upper end of the roadway to the start of the inlet transition
is 9 m. High-density polyurethane foam panels form the roadway surface. All surfaces are painted.
A commercial non-skid product was mixed into the paint to increase the roughness of the surfaces.
Water is supplied by the recirculating system that serves the two large flumes in the hydraulics
laboratory. A 64-mm flexible conduit delivers water to a stilling basin attached to the upstream end
of the roadway. This line is fed from a constant-head tank on the roof of the laboratory. The
discharge is controlled with a ball valve. The water spills out of the stilling basin into the gutter and
roadway. The water captured by the inlet is directed to a wooden box with a 90 V-notch weir at the
downstream end. The water that bypasses the inlet is directed to an identical weir box at the
downstream end of the roadway. The captured and bypassed discharges are measured with these
weirs. The water level in the each weir box is measured in a stilling well with a point gage. The
8
corresponding discharge is computed from the well established head-discharge relationship for a 90
V-notch weir (Bos, 1989). Each weir box contain baffles that distribute the flow uniformly and
minimize surface waves. Discharges at heads below 0.03 m (0.1 ft) are determined volumetrically
with a graduated cylinder and a stopwatch. The outflows from the weir boxes are directed to a sump
pit. Water is pumped continuously from the sump pit to the constant-head tank.
3.2 Test Program
We tested each inlet at all combinations of five grades and two cross-slopes. The five grades
were 0.5%, 1%, 2%, 3% and 5%. The two cross-slopes were 1.6% (3/16 inch per foot) and 3.1%
(3/8 inch per foot). At each setup, the objective was to determine the relationship between the
captured discharge and the total discharge (the sum of the captured and bypassed discharges).
Initially, flow was established at a discharge that was captured entirely. This discharge was measured
at the weir box. The flow was then increased slightly. When the water levels in the weir boxes
stabilized, the captured discharge and the bypassed discharge (if any) were measured. This process
was repeated until the flow overtopped the curb upstream of the inlet.
3.3 Model-Prototype Relations
The flow pattern in the vicinity of an inlet is determined primarily by two factors: gravity and
inertia. The turning of the flow into the inlet is driven by gravity and resisted by inertia. The Froude
number is the dimensionless number that indicates the relative importance of gravity and inertia.
Within the inlet itself, frictional resistance is relatively insignificant. At normal grades, the flow in
the gutter and roadway is supercritical. Supercritical flow is controlled from upstream. Therefore,
the flow pattern in the vicinity of the inlet depends on the velocity and depth in the gutter and roadway
upstream of the inlet. Under normal conditions, the upstream flow in the gutter and roadway is
approximately uniform, meaning that the gravitational driving force and the frictional resistance are
approximately in balance.
Model-prototype relations for geometrically similar inlets can be developed from a dimensional
analysis. The discharge captured by a model of a particular design depends primarily on the size of
the model, the depth and velocity of the flow upstream of the inlet, and the density and specific weight
of the fluid. This relationship can be expressed as
9
(1)
Q f L, y V
c o o
( , , , )
in which Q
c
is the captured discharge, L is a characteristic length dimension, y
o
and V
o
are the depth
and velocity of uniform flow in the gutter and roadway upstream of the inlet, and and are the
density and specific weight of the fluid. Dimensional analysis leads to the relationship
(2)
Q
gL
f
y
L
V
gL
c o o
5

_
,
,
Geometric similarity requires equal values of y
o
/L in the model and prototype. If the Froude
numbers of the uniform flows are also equal, then the captured discharges are related as follows:
(3)
Q
Q
L
L
c m
c p
m
p
,
,
_
,
5/2
(Henderson, 1966) in which the subscripts m and p indicate model and prototype. This scaling law,
which follows from Eq. 2, also applies to the total discharge, Q
t
(the sum of the captured and bypassed
discharges), provided that the same conditions are satisfied:
(4)
Q
Q
L
L
t m
t p
m
p
,
,
_
,
5/2
In our tests, the length ratio L
m
/L
p
was 1/4, and the discharge ratios Q
c,m
/Q
c,p
and Q
t,m
/Q
t,p
were 1/32.
3.4. Calibration of the Model
The model was calibrated by adjusting the roughness of the surface. The objective was to
10
achieve equal Froude numbers in the model and prototype for uniform flows at geometrically scaled
depths, so that discharges could be scaled with Eqs. 2 and 3. This condition is met when the Manning
friction factors for the model and prototype, n
m
and n
p
, are related as follows (Henderson, 1966):
(5)
n
n
L
L
m
p
m
p
_
,
1 6 /
For a one-quarter-scale model, Eq. 5 requires that n
m
= 0.79 n
p
. For full-scale gutters and roadways,
Manning friction factors typically range from 0.013 to 0.016, depending on condition (Chow, 1959;
FHWA, 1996). In the model calibration tests, a constant discharge was established and measured, and
the cross-section of the flow (depth versus distance from edge of pavement) was measured at a
location where the flow was approximately uniform. The Manning n for the model was computed
from the measured quantities. In repeated tests, the Manning n value of the model was found to be
0.010, which corresponds to a prototype Manning n of 0.013. This equivalent prototype roughness
is at the smooth end of the normal range. For inlet tests, a roadway roughness at the smooth end of the
normal range is appropriately conservative. The smoother the surface, the higher the velocity in the
gutter and roadway. For most inlets, a higher velocity in the gutter and roadway results in a smaller
captured discharge.
3.5 Analysis of Experimental Data
The graphs in Appendix A show the relationships between the captured discharge and the total
discharge from all of the tests. The plotted discharges are equivalent prototype discharges. These
graphs show both the experimental data and the fitted design curves for each combination of inlet
type, cross-slope and grade.
We found that relationship between captured discharge and total discharge for each set-up can
be approximated satisfactorily by a two-parameter equation. For certain combinations of conditions,
the data are fitted well by the equation
11
(6) Q
Q for Q Q
Q Q Q
Q Q
Q Q
for Q Q
c
t t o
o a o
t o
a o
t o
_
,
1
]
1
'
>
'
( ) exp 1
with parameters Q
o
and Q
a
. For other combinations of conditions, the data are fitted well by the
equation
(7)
Q
Q for Q Q
Q Q Q for Q Q
c
t t o
t t o
k
t o
>
'
( )
with parameters Q
o
and k. In both equations, the parameter Q
o
represents the largest discharge that
is captured completely. In Eq. 6, the parameter Q
a
represents the upper limit on the captured
discharge, which is approached asymptotically with increasing total discharge.
We used Eqs. 6 and 7 to fit the design curves to the experimental results. In some cases, the
design curve approximates the minimum performance of the inlet at any grade. In other cases, a
separate design curve applies to each grade. The design curves are plotted without the experimental
results in Appendix B. Table 1 shows the form of the equation and the values of the parameters for
each design curve.
3.6 Comparisons of Inlet Performance on Grade
Comparisons of the experimental results for the various set-ups lead to the following
observations:
1. The grade of the roadway has little effect on the performance of the three inlets with gutter
openings (concrete gutter inlet, Type B gutter inlet and Type 12 combination inlet). The effect
of grade is also insignificant for the 4.5-m Type 22 curb inlet. All of these inlets perform as well
(or slightly better) on steep grades (up to 5%) as on mild grades (down to 0.5%).
2. The grade of the roadway does have a significant effect on performance of the 1.5-m Type 22
12
curb inlet. The effect of grade is also significant for the 3.0-m Type 22 inlet at the steeper cross-
slope. These inlets perform better on mild grades than on steep grades.
3. On a grade of 0.5%, the 1.5-m Type 22 curb inlet performs as well as the Type 12 combination
inlet and the Type B gutter inlet. On steeper grades, the Type 12 and Type B inlets perform better
than the Type 22 inlet.
4. All of the inlets perform slightly better on the steeper cross-slope.
5. The performance characteristics of the concrete gutter inlet and the Type B gutter inlet are similar
for all test conditions.
6. The Type 12 combination inlet performs slightly better than the Type B gutter inlet on the milder
cross-slope. On the steeper cross-slope, their performance characteristics are similar.
4. HYDRAULIC PERFORMANCE OF INLETS IN SAG LOCATIONS
4.1 General Principles
The depth-discharge relationship for an inlet in a sag location can be computed from fundamental
hydraulic principles of orifice flow and weir flow. The application of these principles to inlets in sag
locations is explained in the FHWAs Hydraulic Engineering Circular No. 12, Drainage of Highway
Pavements (FHWA, 1984). The discharge into the inlet can be limited by weir flow (critical flow)
around the perimeter of the opening or depressed area or by orifice flow (full flow) through the inlet
opening.
The starting point for the analysis of weir flow into an inlet is the formula for the unit discharge
(discharge per unit width normal to the direction of flow), q, in a critical-flow section,
(8) q g d 0385 2
3/2
.
in which d is the specific energy (depth plus velocity head) at the critical-flow section. The specific
energy at the critical-flow section is the ponded depth, referenced to the bottom level at the critical-
flow section. Water enters the inlet from the front (the street side) and from the gutters on each side.
On the street side, the critical-flow section is horizontal, so the frontal discharge, Q
f
, is given by the
formula
13
(9) Q L g d
f
0 385 2
3/2
.
in which L is the length of the critical-flow section. On the gutter sides, the bottom has a significant
cross-slope, so d varies across the critical-flow section. For a bottom with a constant cross-slope,
the formula for the side discharge, Q
s
, is
(10) ( ) Q L g
m
d d
s
0385 2
1
1
5/2
2
5/2
.
where m is the cross-slope of the critical-flow section, d
1
is specific energy at the lowest point in the
cross-section and d
2
is specific energy at the highest point in the cross-section. This formula is
obtained by integration of Eq. 8 over the cross-section. For a critical-flow section with two different
cross-slopes (e.g., the cross-slope of the gutter and the cross-slope of the curb face), m
1
and m
2
, the
weir-flow formula is
(11) ( ) ( ) Q L g
m
d d
m
d d
s
+
1
]
1
0385 2
2
5
1 1
1
1
5/2
2
5/2
2
2
5/2
3
5/2
.
in which d
1
is the specific energy at the outer edge of segment 1, d
2
is the specific energy at the
intersection of segments 1 and 2, and , and d
3
is specific energy at the outer edge of segment 2.
14
TABLE 1. Design Curves for Inlet Performance on Grade
Inlet type
S
x
(%)
S
o
(%) Eq. #
Qo
m
3
/s
Qa
(m
3
/s) k
Concrete gutter inlet 1.6 0.5 5.0 7 0.01 -- 1.29
3.1 0.5 5.0 6 0 0.12 --
Type B gutter inlet 1.6 0.5 5.0 7 0 -- 1.385
3.1 0.5 5.0 7 0 -- 1.57
Type 12 combination inlet 1.6 0.5 5.0 7 0.01 -- 1.41
3.1 0.5 5.0 7 0.02 -- 1.43
Type 22 curb inlet, 1.5 m 1.6 0.5 6 0.01 0.114 --
1.0 6 0.01 0.087 --
2.0 6 0.01 0.068 --
3.0 6 0.01 0.060 --
5.0 6 0.01 0.050 --
3.1 0.5 6 0.01 0.122 --
1.0 6 0.01 0.092 --
2.0 6 0.01 0.068 --
3.0 6 0.01 0.060 --
5.0 6 0.01 0.045
Type 22 curb inlet, 3.0 m 1.6 0.5 5.0 6 0 0.195 --
3.1 0.5 6 0.02 0.270 --
1.0 6 0.02 0.240 --
2.0 6 0.02 0.195 --
3.0 6 0.02 0.175 --
5.0 6 0.02 0.155 --
Type 22 curb inlet, 4.5 m 1.6 0.5 5.0 7 0.03 -- 1.64
3.1 0.5 5.0 7 0.06 -- 1.70
15
In applying the weir-flow formulas, the key issue is the location of the critical-flow section. The
location of critical-flow section depends on the geometry of the area around the inlet opening. Critical
flow does not necessarily occur at the perimeter of the inlet opening. In some cases, the exact location
of critical flow is uncertain and must be estimated. The location of critical flow can vary with the
depth of ponding.
The general formula for the discharge into an inlet under orifice-flow conditions is
(12) Q C A g h
c o o
2
in which C
c
is the contraction coefficient, A
o
is area of the opening, and h
o
is the depth of the ponded
water measured from the centroid of the opening.
4.2 Concrete Gutter Inlet
The front edge of the concrete gutter inlet structure is depressed 13 mm below the edge of the
pavement. The critical-flow section for the frontal flow would most likely be located at the edge of
the pavement rather than the edge of the inlet opening. In computing the frontal discharge, critical flow
is assumed to occur at the edge of the pavement. This assumption is conservative. If critical flow
actually occurred at the edge of the inlet opening, the specific energy would be higher and the
discharge would be larger. The length of the weir crest for the frontal flow would be approximately
1.00 m, the total length of the inlet structure. The flow from the sides would pass through critical
approximately where the gutter section terminates at the inlet structure. The standard gutter is 850 mm
wide with the outer edge 40 mm above the edge of the pavement. The flowline of the gutter is 600 mm
from the edge of the pavement and approximately 40 mm below the edge of the pavement. The formula
for the total discharge into the concrete gutter inlet by weir flow is
(13)
Q
d d d d
_
,
+
+
_
,

_
,
_
,
+
+
_
,
1
]
1
1
'
1705 100
1000
2
2
5
600
40
40
1000 1000
250
40
40
1000
3/ 2 5/ 2 5/ 2 5/ 2
. .
in which d is the depth of the ponded water in mm, measured from the edge of the pavement, and Q
16
is in m
3
/s. Table 2 shows computed discharges for ponded depths up to 40 mm (the top of the gutter
). The discharge into the concrete gutter inlet is controlled by the weir-flow condition over the entire
range of possible depths.
4.3 Type B Gutter Inlet
The Type B gutter inlet is depressed slightly below the gutter of the Type I combined curb and
gutter. The front edge of the Type B inlet structure slopes steeply (17% slope) toward the grated
opening. The critical-flow section for the frontal flow would most likely be located at the edge of the
pavement rather than the edge of the inlet opening. The length of the weir crest for the frontal flow
would be approximately 0.91 m, the total length of the inlet structure. The flow from the sides is
assumed to pass through critical at the side edges of the inlet structure. Based on these assumptions
and the dimensions and geometry of the inlet structure, the formula for the total discharge into the Type
B gutter inlet by weir flow is
Q
d d d d d
_
,
+
+
_
,

+
_
,
_
,
+
+
_
,

_
,
_
,
1
]
1
1
'
1705 0 91
1000
2
2
5
450
35
60
1000
25
1000
150
25
25
1000 1000
3/2 5/2 5/ 2 5/ 2 5/2
. .
(14)
is in m
3
/s. Table 2 shows computed discharges for ponded depths up to 105 mm (the top of the curb).
The discharge into the Type B gutter inlet is controlled by the weir-flow condition over the entire
range of possible depths.
17
TABLE 2. Discharges Captured by Inlets in Sag Locations
Depth at
edge of
pavement
(mm)
Captured discharge (m
3
/s)
Concrete
gutter inlet Type B Type 12
Type 22,
1.5 m
Type 22,
3.0 m
Type 22,
4.5 m
0 0.008 0.015 0.035 0.035 0.035 0.035
5 0.011 0.018 0.039 0.040 0.041 0.042
10 0.015 0.022 0.044 0.046 0.048 0.051
15 0.020 0.027 0.049 0.052 0.057 0.061
20 0.025 0.032 0.055 0.059 0.066 0.073
25 0.031 0.037 0.061 0.066 0.076 0.087
30 0.038 0.043 0.067 0.074 0.087 0.101
35 0.045 0.049 0.074 0.082 0.099 0.116
40 0.052 0.055 0.081 0.091 0.111 0.132
45 0.062 0.089 0.100 0.124 0.149
50 0.069 0.096 0.109 0.138 0.166
55 0.076 0.104 0.119 0.152 0.185
60 0.083 0.112 0.129 0.167 0.204
65 0.091 0.120 0.139 0.182 0.224
70 0.099 0.129 0.150 0.197 .0245
75 0.107 0.138 0.161 0.213 0.266
80 0.116 0.147 0.172 0.23 0.288
85 0.124 0.156 0.184 0.247 0.310
90 0.133 0.165 0.188 0.264 0.334
95 0.142 0.175 0.191 0.282 0.357
100 0.151 0.185 0.193 0.301 0.382
105 0.161 0.195 0.196 0.319 0.406
18
4.4 Type 12 Combination Inlet
The Type 12 combination inlet is depressed below the gutter of the Type I combined curb and
gutter. The transition from the normal gutter to the inlet structure is 760 mm long. The flowline of the
gutter falls 80 mm within the transition. The front edge of the Type 12 inlet structure slopes steeply
(20% slope) toward the grated opening. The critical-flow section for the frontal flow would most
likely be located at the edge of the pavement rather than the edge of the inlet opening. The length of
the weir crest for the frontal flow would be at least 0.91 m, the total length of the inlet structure. The
flow from the sides is assumed to pass through critical at the side edges of the inlet opening. The flow
from the sides might actually pass through critical at the start of the transition from the normal gutter.
This would result in less flow from the sides, but it would increase the effective length of the weir
crest for frontal flow, and result in a larger overall discharge. Therefore, the assumption of critical
flow at the side edges of the inlet opening is conservative. Based on these assumptions and the
dimensions and geometry of the inlet structure, the formula for the total discharge into the Type 12
combination inlet by weir flow is
(15) Q
d d d
_
,
+
+
_
,

_
,
1
]
1
1
'
1705 0 91
1000
2
2
5
610
120
120
1000 1000
3/ 2 5/2 5/2
. .
is in m
3
/s. Table 2 shows computed discharges for ponded depths up to 105 mm (the top of the curb).
The discharge into the Type 12 combination inlet is controlled by the weir-flow condition over the
entire range of possible depths.
4.5 Type 22 Curb Inlet
The Type 22 curb inlets are depressed below the gutter of the Type I combined curb and gutter.
The transition from the normal gutter to the inlet structure is 760 mm long. The flowline of the gutter
falls 80 mm within the transition. The concrete surface in front of the Type 22 inlet slopes steeply
(19% slope) toward the grated opening. The critical-flow section for the frontal flow would most
likely be located at the edge of the pavement rather than the edge of the inlet opening. The length of
the weir crest for the frontal flow would equal or exceed total length of the inlet structure (1.5, 3.0 or
19
4.5 m). The flow from the sides is assumed to pass through critical at the side edges of the inlet
opening (a conservative assumption). Based on these assumptions and the dimensions and geometry
of the inlet structure, the formula for the total discharge into a Type 22 curb inlet by weir flow is
(16) Q L
d d d
_
,
+
+
_
,

_
,
1
]
1
1
'
1705
1000
2
2
5
625
120
120
1000 1000
3/2 5/2 5/2
.
in which L is the total length of the inlet structure in meters, d is the depth of the ponded water in mm,
measured from the edge of the pavement, and Q is in m
3
/s.
The Type 22 inlet must also be analyzed for orifice-flow control. The effective cross-sectional
area of the inlet opening in m
2
is 0.101 (L-0.300), where L is the total length of the inlet structure.
This quantity is the area of the opening at the brink of the overfall into the inlet box, measured
perpendicular to the sloping top of the opening. The centroid of this area is 91 mm below the edge
of the pavement. Directly upstream of the brink, the planes of the top and bottom concrete surfaces
converge at an angle of 24.4. This situation is similar to flow under a partially raised radial gate.
The contraction coefficient, C
c
, for a radial gate varies with the angle of convergence, , according
to the formula C
c
= 1 - 0.75 + 0.36
2
(Henderson, 1966). The contraction coefficient for =
24.4 is 0.823. The lateral contraction of the inflow would be negligible because the sides of the
entrance are well rounded (125-mm radius of curvature). Based on these assumptions and the
dimensions and geometry of the inlet structure, the formula for the discharge into a Type 22 curb inlet
by orifice flow is
(17) Q L d + 0823 0101 0 300 19 62 0 091 . ( . ) ( . ) . ( . )
in which L is the total length of the inlet structure in meters, d is the depth of the ponded water in mm,
measured from the edge of the pavement, and Q is in m
3
/s.
Table 2 shows computed discharges for ponded depths up to 105 mm (the top of the curb). The
discharge into the 1.5-m Type 22 inlet is controlled by the orifice-flow condition for depths of
ponding over 80 mm, and by the weir-flow condition for shallower depths. The discharges into the
20
3.0-m and 4.5-m Type 22 inlets are controlled by the weir-flow condition over the entire range of
possible depths.
5. SPREAD OF WATER ON ROADWAYS
The spread of water on a roadway depends on many factors. The principal factors are the
discharge, the dimensions of the curb and gutter, the grade and cross-slope of the roadway, and the
roughness of the gutter and pavement. Although the discharge increases in the direction of flow, the
principles of uniform flow govern the local depth-discharge relationship. The Manning equation
cannot be applied directly to the entire cross-section of the flow due to the extreme variation in depth
across the section. However, the depth-averaged velocity at any location within the cross-section can
be obtained from the Manning equation with the hydraulic radius replaced by the local depth.
Integration of the product of this local velocity and the local depth leads to the Izzard formula for
discharge. Manning friction factors (n values) for gutters and streets typically range from 0.013 to
0.016, depending on condition (Chow, 1959; FHWA, 1996).
The spread on a street with a standard gutter or a Type I combination curb and gutter can be
estimated with the design charts in Appendix C. These charts were developed by Izzards method
using a Manning n value of 0.016. Because they are based on a rougher-than-average condition, these
charts should provide reasonably conservative estimates of spread.
6. CONCLUSIONS
The performance characteristics of KDOTs standard curb and gutter inlets have been determined
from hydraulic model tests and theoretical calculations. Model tests of inlets on grade provided the
relationships between captured discharge and total discharge for grades from 0.5% to 5.0% and cross-
slopes of 1.6% and 3.1%. The three inlets with gutter openings (the concrete gutter inlet, Type B
gutter inlet and Type 12 combination inlets) perform similarly under all conditions tested. The grade
of the roadway does not have a significant effect on performance of these inlets. The Type 22 curb
inlets perform better on mild grades than on steep grades. All of the inlets perform slightly better on
the steeper cross-slope. The design charts in Appendix B are based on the minimum performance
characteristics from the model tests.
The depth-discharge relationships for the inlets in sag locations, shown in Table 2, were
computed from fundamental hydraulic principals of orifice flow and weir flow. The concrete gutter
21
inlet has a much smaller capacity than the other inlets in sag locations due to the low profile of the
standard gutter. The spread of water on a street with a standard gutter or a Type I combination curb
and gutter can be estimated with the design charts in Appendix C.
The design aids in this report provide a sound basis for the selection and sizing of curb and gutter
inlets. More accurate sizing of inlets could improve roadway safety and reduce drainage costs.
REFERENCES
Bos, M. G. (1989). Discharge Measurement Structures, p. 161-169.
Chow, V. T. (1959). Open-Channel Hydraulics, McGraw-Hill Co., p. 111.
Federal Highway Administration (1996). Drainage of Highway Pavements, Highway Engineering
Circular No. 12.
Federal Highway Administration (1996). Urban Drainage Design Manual, Highway Engineering
Circular No. 22, p. 4-9.
Henderson, F. M. (1966). Open Channel Flow, Macmillan Co.
Izzard, C. F. (1946). Hydraulics of Runoff from Developed Surfaces, Proceedings of Highway
Research Board, Vol. 26, p. 129-150.
McEnroe, B. M., and R. P. Wade (1998). Hydraulic Performance of Set-Back Curb Inlets, Report
No. K-TRAN: KU-98-3, Kansas Department of Transportation.
22
Appendix A
Graphs of Experimental Results
for Inlets on Grade
Fig. A.1. Concrete Gutter Inlet on Pavement with 1.6% Cross-Slope
0.00
0.05
0.10
0.15
0.20
0.25
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
Total discharge, m
3
/s
C
a
p
t
u
r
e
d

d
i
s
c
h
a
r
g
e
,

m
3
/
s
So=0.5%
So=1%
So=2%
So=3%
So=5%
Design
Fig. A.2. Concrete Gutter Inlet on Pavement with 3.1% Cross-Slope
0.00
0.05
0.10
0.15
0.20
0.25
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
Total discharge, m
3
/s
C
a
p
t
u
r
e
d

d
i
s
c
h
a
r
g
e
,

m
3
/
s
So=0.5%
So=1%
So=2%
So=3%
So=5%
Design
Fig. A.3. Type B Gutter Inlet on Pavement with 1.6% Cross-Slope
0.00
0.05
0.10
0.15
0.20
0.25
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
Total discharge, m
3
/s
C
a
p
t
u
r
e
d

d
i
s
c
h
a
r
g
e
,

m
3
/
s
So=0.5%
So=1%
So=2%
So=3%
So=5%
Design
Fig. A.4. Type B Gutter Inlet on Pavement with 3.1% Cross-Slope
0.00
0.05
0.10
0.15
0.20
0.25
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
Total discharge, m
3
/s
C
a
p
t
u
r
e
d

d
i
s
c
h
a
r
g
e
,

m
3
/
s
So=0.5%
So=1%
So=2%
So=3%
So=5%
Design
Fig. A.5. Type 12 Combination Inlet on Pavement with 1.6% Cross-Slope
0.00
0.05
0.10
0.15
0.20
0.25
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
Total discharge, m
3
/s
C
a
p
t
u
r
e
d

d
i
s
c
h
a
r
g
e
,

m
3
/
s
So=0.5%
So=1%
So=2%
So=3%
So=5%
Design
Fig. A.6. Type 12 Combination Inlet on Pavement with 3.1% Cross-Slope
0.00
0.05
0.10
0.15
0.20
0.25
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
Total discharge, m
3
/s
C
a
p
t
u
r
e
d

d
i
s
c
h
a
r
g
e
,

m
3
/
s
So=0.5%
So=1%
So=2%
So=3%
So=5%
Design
Fig. A.7. Type 22 Curb Inlet, 1.5 m, on Pavement with 1.6% Cross-Slope
0.00
0.05
0.10
0.15
0.20
0.25
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
Total discharge, m
3
/s
C
a
p
t
u
r
e
d

d
i
s
c
h
a
r
g
e
,

m
3
/
s
So=0.5%
So=1%
So=2%
So=3%
So=5%
So=0.5%
So=1%
So=2%
So=3%
So=5%
0.00
0.05
0.10
0.15
0.20
0.25
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
Total discharge, m
3
/s
C
a
p
t
u
r
e
d

d
i
s
c
h
a
r
g
e
,

m
3
/
s
So=0.5%
So=1%
So=2%
So=3%
So=5%
So=0.5%
So=1%
So=2%
So=3%
So=5%
0.00
0.05
0.10
0.15
0.20
0.25
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
Total discharge, m
3
/s
C
a
p
t
u
r
e
d

d
i
s
c
h
a
r
g
e
,

m
3
/
s
So=0.5%
So=1%
So=2%
So=3%
So=5%
Design
0.00
0.05
0.10
0.15
0.20
0.25
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
Total discharge, m
3
/s
C
a
p
t
u
r
e
d

d
i
s
c
h
a
r
g
e
,

m
3
/
s
So=0.5%
So=1%
So=2%
So=3%
So=5%
So=0.5%
So=1%
So=2%
So=3%
So=5%
0.00
0.05
0.10
0.15
0.20
0.25
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
Total discharge, m
3
/s
C
a
p
t
u
r
e
d

d
i
s
c
h
a
r
g
e
,

m
3
/
s
So=0.5%
So=1%
So=2%
So=3%
So=5%
Design
0.00
0.05
0.10
0.15
0.20
0.25
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
Total discharge, m
3
/s
C
a
p
t
u
r
e
d

d
i
s
c
h
a
r
g
e
,

m
3
/
s
So=0.5%
So=1%
So=2%
So=3%
So=5%
Design
35
Appendix B
Design Charts for Inlets on Grade
Fig. B.1. Gutter and Combination Inlets on Pavements with 1.6% Cross-Slopes
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20
Total discharge, m
3
/s
C
a
p
t
u
r
e
d

d
i
s
c
h
a
r
g
e
,

m
3
/
s
Type 12 combination inlet
Type B gutter inlet
Concrete gutter inlet
Fig. B.2. Gutter and Combination Inlets on Pavement with 3.1% Cross-Slope
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20
Total discharge, m
3
/s
C
a
p
t
u
r
e
d

d
i
s
c
h
a
r
g
e
,

m
3
/
s
Type 12 combination inlet
Type B gutter inlet
Concrete gutter inlet
Fig. B.3. Type 22 Curb Inlet, 1.5 m, on Pavement with 1.6% Cross-Slope
0.00
0.02
0.04
0.06
0.08
0.10
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20
Total discharge, m
3
/s
C
a
p
t
u
r
e
d

d
i
s
c
h
a
r
g
e
,

m
3
/
s
So=0.5%
So=1%
So=2%
So=3%
So=5%
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20
Total discharge, m
3
/s
C
a
p
t
u
r
e
d

d
i
s
c
h
a
r
g
e
,

m
3
/
s
So=0.5%
So=1%
So=2%
So=3%
So=5%
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 0.22 0.24 0.26
Total discharge, m
3
/s
C
a
p
t
u
r
e
d

d
i
s
c
h
a
r
g
e
,

m
3
/
s
0.00
0.04
0.08
0.12
0.16
0.20
0.00 0.04 0.08 0.12 0.16 0.20 0.24 0.28 0.32
Total discharge, m
3
/s
C
a
p
t
u
r
e
d

d
i
s
c
h
a
r
g
e
,

m
3
/
s
So=0.5%
So=1%
So=2%
So=3%
So=5%
0.00
0.04
0.08
0.12
0.16
0.20
0.00 0.04 0.08 0.12 0.16 0.20 0.24 0.28 0.32
Total discharge, m
3
/s
C
a
p
t
u
r
e
d

d
i
s
c
h
a
r
g
e
,

m
3
/
s
0.00
0.04
0.08
0.12
0.16
0.20
0.24
0.00 0.04 0.08 0.12 0.16 0.20 0.24 0.28 0.32
Total discharge, m
3
/s
C
a
p
t
u
r
e
d

d
i
s
c
h
a
r
g
e
,

m
3
/
s
44
Appendix C
Design Charts for Spread of Water on Pavement
Fig. C.1. Spread on Pavement with 1.6% Cross-Slope and Type I Combined Curb and Gutter
0
1
2
3
4
5
6
7
8
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
Discharge, m
3
/s
S
p
r
e
a
d
,

m
Grade = 0.5% 1.0% 2.0% 3.0% 5.0%
Fig. C.2. Spread on Pavement with 1.6% Cross-Slope and Standard Gutter
0.0
1.0
2.0
3.0
4.0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Discharge, m
3
/s
S
p
r
e
a
d
,

m
Grade = 0.5% 1.0% 2.0% 3.0% 5.0%
Fig. C.3. Spread on Pavement with 3.1% Cross-Slope and Type I Combined Curb and Gutter
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18
Discharge, m
3
/s
S
p
r
e
a
d
,

m
Grade = 0.5% 1.0% 2.0% 3.0% 5.0%
Fig. C.4. Spread on Pavement with 3.1% Cross-Slope and Standard Gutter
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14
Discharge, m
3
/s
S
p
r
e
a
d
,

m
Grade = 0.5% 1.0% 2.0% 3.0% 5.0%
Fig. C.5. Depth of Flow in Type I Combined Curb and Gutter, for Pavement with 1.6% Cross-Slope
40
60
80
100
120
140
160
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
Discharge, m
3
/s
D
e
p
t
h
,

m
m
Grade = 0.5% 1.0% 2.0% 3.0% 5.0%
Fig. C.6. Depth of Flow in Standard Gutter, for Pavement with 1.6% Cross-Slope
40.0
60.0
80.0
100.0
120.0
140.0
160.0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Discharge, m
3
/s
D
e
p
t
h
,

m
m
Grade = 0.5% 1.0% 2.0% 3.0% 5.0%
Fig. C.7. Depth of Flow in Type I Combined Curb and Gutter, for Pavement with 3.1% Cross-Slope
40.0
50.0
60.0
70.0
80.0
90.0
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18
Discharge, m
3
/s
D
e
p
t
h
,

m
m
Grade = 0.5% 1.0% 2.0% 3.0% 5.0%
Fig. C.8. Depth of Flow in Standard Gutter, for Pavement with 3.1% Cross-Slope
40.0
50.0
60.0
70.0
80.0
90.0
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14
Discharge, m
3
/s
D
e
p
t
h
,

m
m
Grade = 0.5% 1.0% 2.0% 3.0% 5.0%

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