FLOOD00281

• County: Larimer
• Community: Greeley
• Title: Design Criteria and Construction Specifications volume 2 of 5 Storm Drainage Criteria
• Date: 10/1/1997
• Prepared For: Greeley
• Prepared By: Department of Public Works
• Floodplain - Doc Type: Educational/Technical/Reference Information

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continue past the inlet area (called "inlet carryover"). The
amount of carryover must be included in the drainage facility
evaluation as well as in the design of the inlet.

DESIGN OF TYPE R CURB OPENING INLETS (INITIAL STORM)

GIVEN: Street type = Arterial, 6 lane; S = 1.0 percent
Maximum flow depth = 0.5 feet (refer to section 8)
Maximum allowable gutter capacity = 11.0 cfs
starting gutter flow (Qt) = 8.0 cfs

FIND: Interception and carryover amounts for the inlets and
flow conditions illustrated on Figure 7-9.

SOLUTION: From Figure 7-9 we can see that inlets 1 and 2 are in a
continuous grade condition and inlet 3 is in a sump
condition. The first step is to calculate the
interception ratio R, for the continuous grade inlets.
This ratio is then applied to the actual gutter flow
(local runoff plus carryover flow) to determine amount
intercepted by the inlet and the carryover flow. The
final step is to calculate the size of the inlet required
for the sump condition, as discussed in the following
section.

STEP 1: From Figure 7-6 for an allowable depth of 0.50 feet and
a 15-foot inlet, read the value 8.6 cfs. Note that even
though the gutter flow is less than maximum allowable,
the maximum depth is used for Figure 7-6. The effect of
the lower depth on the inlet capacity shall be accounted
for in the following steps.

STEP 2: Compute the interception ratio R

R = Allowable inlet caoacity =
Allowable street capacity

11&
11.0

R = 0.78

STEP 3:

Compute the interception amount Q1

Q1 = R x Q street
= 0.78 x 8.0
= 6.2 cfs intercepted by inlet

STEP 4:

Compute the carryover amount Qeo

Qeo = Q street - Q1
= 8.0 - 6.2
= 1.8 cfs

7-3