FLOOD10390

• County: Boulder
• Community: Boulder
• Stream Name: Fourmile Canyon
• Basin: South Platte
• Title: Fourmile Canyon Creek - Major Drainageway Planning - Phase A Report - Alternatives Analysis
• Date: 6/1/2000
• Prepared For: UDFCD, Boulder
• Prepared By: Love & Associates
• Floodplain - Doc Type: Flood Mitigation/Flood Warning/Watershed Restoration

Table 8-5
Average Annual Flood Damages
Alternate 2 - tOO-year Channel Improvements

The ROW/property acquisition cost estimates include ROW costs along the 9th Street Extension.
These ROW costs were developed by City of Boulder staff and were included in this cost estimate
without additional markups.

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Present Value, $ 'Ie

Average Annual Flood
Dama2es! $IY ear

Reach

101000
$0

$

$400
$0

$ 167,000
$ 21,000
$ 203,000
$ 255,000
$ 154,000
$ 149,000
$ 62,000

$ 6,500
$ 800

$ 7,900
$ 9,900
$ 6,000
$ 5,800
$ 2,400

1
2a
2b
3
4
5
6a
6b
6c

All construction and ROW/property acquisition costs are in year 2000 dollars. No financing costs or
monetary impacts of phased construction or property acquisition are included in these cost estimates.

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FLOOD DAMAGE REDUCTION WITH IMPLEMENTATION OF AL TERNA TES

Each of the alternates will still incur an expected damage during flood events. Examples of these
damages would include isolated bank erosion spots in the constructed "natural" channel alternate or
wide spread damage in the maintaining of the existing floodplain configuration alternate. The level
of damages incurred will also be dependent on the design frequency of the alternate. For example, if
the "natural" channel is designed to handle the 50-year frequency flood, then damages will occur
during a greater than 50-year frequency event, which would overflow the top of banks.

8.7

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$ 1,021,000
$ .347,000

Present Value (PV) based on a 50-year penod and a discount rate of3%,
(6% interest minus 3% inflation).
Includes split flow damages

$ 39,700
$ 13,500

Total **
Split Flow

*

**

Future damages with Alternates 1 and 2 in place were estimated and are summarized in Tables 8-4
and 8-5. Future damages for Alternate 3 were estimated as part of Damage Analysis Chapter of this
report, see Chapter 5 and Table 5-2. It isUimportant to note the flood damages presented in this report
do not include flood damages that will be experienced in the Wonderland Creek floodplain as a result
of the spill flows from Fourmile Canyon Creek.

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Table 8-4
Average Annual Flood Damages
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In general the

BENEFIT/COST ANALYSIS

One method commonly used to compare alternatives is the benefit/cost (B/C) ratio
higher the B/C ratio the more cost effective an alternative is

8.8

In this study the benefit/cost ratio compares the total cost to implement a flood control
with the benefits that would be realized if that flood control alternative were implemented
cost to implement a flood control alternative was calculated as the sum of the construction costs,
property acquisition costs and O&M costs required to implement an alternative, as discussed in
paragraph 8.6. The benefit that would be realized if the flood control alternative is implemented was
calculated as the difference between flood damages under existing conditions minus flood damages
that would be incurred after implementation of the alternative.

alternative
The total

in Place

with Alternative

- LFuture Flood Damages
Implement Alternative

Flood Damages
Cost to

Ratio = [Existin

Benefit/Cost

... --..-- .--..- ... -- - - ----
Reach Average Annual Flood Present Value, $ 'Ie
Damages, $IY ear
1 $ 800 $ 21,000
2a $ 100 $ 3,000
2b $ 68,800 $ 1,770,000
3 $ 300 $ 8,000
4 $ 8,400 $ 216,000
5 $ 25,800 $ 664.000
6a $ 13,000 $ 334 000
6b $ 7,300 $ 188.000
6c $ 2,400 $ 62.000
Total * * $ 226,900 $ 3,266,000
Split Flow $ 14,600 $ 376,000

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* Present Value (PV) based on a 50-year penod and a discount rate of3%,
(6% interest minus 3% inflation).
** Includes split flow damages

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7

8-1

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