FLOOD07908

• Designation Number: 260
• County: Jefferson
• Community: Unincorporated Jefferson County
• Basin: South Platte
• Title: Major Drainageway Planning - Sanderson Gulch/Weir Gulch Volume I
• Date: 8/1/1972
• Designation Date: 12/1/1987
• Floodplain - Doc Type: Floodplain Report/Masterplan

Sum", of the alternatives ",,;n, ><uY'Y'.ested fur r..vi.e... in the cOn-
tract and others were added as the study progressed as they appeared
to be logical and justifiable alternatives.

alternative is shown to have an estimated cost of $740,000.00
'"hile providing bcnefits on the order of $600,000.00. This gives
a benefit/cost ratio of 0.8l.

In each case, where applicable, preliminary alternatives were
reviewed with the attorney for a legal opinion on the alternative.
In addition, an independent planner provided input on each
alternative concerning the cnvironmental and aesthetic impact
of the alternative.

Table VI-~ shows the economic comparison of the alternatives
on Sanderson Gulch in Lakewood. In this area thc recommended
alternative is based on a 10 year design frequency. The re-
commended alternative rcprescnts a cost of $)~),OOO.OO,
providing $280,000.00 in benefits. The benefit/cost ratio
for this total reach is 0.87.

Using the approach of review of preliminary plans on an engineering,
planning and legal basis permitted the elimination of some alter-
native approaches. Other alternatives, particularly the major
underground conduits, which appeared impractical and uneconomical
in most reaches were, however, considered as plausible alternatives
in the alternative summary sheets.

Figure VI-) gives the alternative comparison for No. Sanderson
Gulch. Included in this comparison were variations in reservoir
improvements in Green Gables Park, referred to on the chart
as Robbins Dasher Lake. The recommended approach for No.
Sanderson represented an estimated cost of $324,000.00 for a
realization of $73,000.00 in benefits. The benefit/cost ratio
is 0.22. The unfavorable benefit/cost ratio is characteristic
of improvements in upper areas of a drainage basin where flood
damage potential is low.
~igure VI-4 shows the comparison of alternatives considered for
Weir Gulch through Denver. The first reach from the So. Platte
River to Federal waS analy~ed for two conditions, with and with-
out improvements provided at Barnum Lake. A compa~ison of
the benefits to be derived from improvements at Barnum Lake
certainly justify the work. Above Federal Blvd. and between
Hooker and First the recommended alternative is not the lowest
co~t ~ince an effort waR made to continue the strip park through
these areas as desired by the Parks Department. It is felt
that the acquisition of real estate to make room for the channel
<Ictually made the alternative more expensive. The cost of land
acquisition used in the estimate was based on typical land
valu~~ f0r the ar~a and did not reflect th~ actual lo~~tion of
the property being in the flood plain. At the bottom of the
sheet the recommended alternative for Weir Gulch in Dcnvcr
indicated an estimated cost of ~1,530,000.OO. The tradeoff
in benefits was set at Sl,896,000.00. The benefit/cost ratio
is 1.24.

ALTERNATIVE SUMMARY SHEETS

TO assist in the selection of the desired alternative for drainage-
way improvements, alternativc summary sheets wcre prepared. Thcsc
sheets broke the channel into representative design reaches and
for each design frequency presented the average discharge, approxi-
mate reduction in flood damage, estimated cost for alternatives
considered and the recommended approach for total channel improve-
ment.

The approximatc reduction in flood damage columns represent the
benefit to be derived by designing the facility to accommodate
the particular storm frequency indicated. In all cases, the 100
year reduction in flood damage is equal to the total damage poten-
tial in the reach being considered. The difference between the
100 year reduction in flood damage and the reduction in flood
damage for the frequency being considered represents the remaining
flood damage potential in the reach after completion of the im-
provemcnts.

Table VI-l is the s~~ary sheet for Sanderson Gulch through Denver.
In this partic~lar suwmary sheet, the two righthand columns
indicate the estimated cost and approximate benefits derived from
the recommended improvements. The recommended approach was
slightly different from the specific alternative tabulated. The
10 year frequency was not tightly adhered to so that more existing
culverts could be utilized. It was felt the minimal damaqes to
roads during overtopping was ~cceptable, thus the benefits for the
recommended alternative are slightly less than those for a com-
plete 10 year design. At the bottom of the shcet, the recommended

Weir Gulch In L<;lkewood, Figure VI-S, is not as complex. The
only point to be made is that the reach from Agricultural Ditch
to Main Reservoir had only one practical solution at the time.
~h~~ W~~ ~o cx~c~c ~ 10 yc~r cc~ign ~tor~ ~cwcr fro~ ~hc ditch
to the reservoir. Thus only one cost estimate was considered
for the reach. The recolMlendation for this portion of the gulch
had an estin..ted cost of $420,000.00 with recognizable benefits
set at $305,000.00. The benefit/cost ratio is 0.73.

-69-

-,"-