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Storm Drainage Systems 11.9-1
October 2000
ConnDOT Drainage Manual
11.9 Gutter Flow Calculations
11.9.1 Introduction
Gutter flow calculations are necessary in order to relate the quantity of flow (Q) in the curbed
channel to the spread of water on the shoulder, parking lane, or pavement section. The nomograph
on Figure 11-1 can be utilized to solve uniform cross slope channels, composite gutter sections and
V shape gutter sections. Figure 11-3 is also very useful in solving composite gutter section
problems. Computer programs such as the FHWA HEC 12 program is also very useful for this
computation as well as inlet capacity. Example problems for each gutter section are shown in the
following sections.
11.9.2 Manning's n For Pavements
Table 11-3 Manning’s n For Streets and Pavement Gutters
11.9.3 Uniform Cross Slope Procedure
The nomograph in Figure 11-1 is used with the following procedures to find gutter capacity for
uniform cross slopes:
CONDITION 1: Find spread (T), given gutter flow (Q).
Step 1
Determine input parameters, including longitudinal slope (S), cross slope (S
x
), gutter flow
(Q) and Manning's n.
Step 2
Draw a line between the S and S
x
scales and note where it intersects the turning line.
Type of Gutter or Pavement
Manning's n
Concrete gutter, troweled finish
0.012
Asphalt Pavement:
Smooth texture
Rough texture
0.013
0.016
Concrete gutter-asphalt pavement
Smooth
Rough
0.013
0.015
Concrete pavement
Float finish
Broom finish
0.014
0.016
For gutters with small slope, where
sediment may accumulate, increase
above n values by:
0.002
Reference: USDOT, FHWA, HDS-3 (1961)