FLOOD08495

• County: Statewide
• Community: Statewide
• Basin: Statewide
• Title: Methodology for Evaluation of Feasibility: Multijurisdictional Urban Drainage and Flood Control Projects
• Date: 2/1/1977
• Prepared By: UDFCD
• Floodplain - Doc Type: Educational/Technical/Reference Information

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25

1, Natural type channel (soft channel)

2. Lined channel (hard channel)

3. New Condu it

4. No Change
Each of the alternatives (except No.4) can be installed for

any design frequency. The lowest cost system for the range of
desired design frequencies can be identified by the following

analysis.
Soft channel, hard channel or conduit designs increase in cost

with design frequency, The variation in annual cost, including

maintenance, might be as shown in Figure 11-5.

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<(
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200

\
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"-. ~
"-'.:
~. CONDUIT
I -:::::::-'-.-HARD
I -- - SOFT

400

.....
-

300

100

o
o 0.1 0.2 0.3 0.4 0.5 0.6

EXCEEDANCE PROBABILITY

Figure II - 5

This shows that the soft channel affords lowest annual cost*

protection below a 0,27 exceedance probability whereas hard channel

is lowest for all other cases.

*Oetermining annual cost involved applying the appropriate discount
factor to the present cost of the improvements, See any engineering
economics text for details.