FLOOD00812

• County: Larimer
• Community: Fort Collins
• Stream Name: McClellands and Mail Creek
• Title: Major Drainageway Planning
• Date: 12/1/1980
• Prepared For: Fort Collins
• Prepared By: CWCB
• Contract/PO #: &&
• Floodplain - Doc Type: Floodplain Report/Masterplan

Within a 24-hour periOd on September 20-2l, 1902, 6.B4-inches of rainfall
was recorded. Flooding of streets up to one-foot deep and cel1ars was reported
in the Fort Collins area. Also, there were reports of some agricultural crop
damage in the Bellvue area. However, no particular damage was reported in McClel-
lands and Mail Creek Basins.

TABLE 1II-1
PRECIPITATION INTENSITY (injhr)
Time 2 5 10 15 50 100 Percent
Interval (min) Year Year Year Year Year Year of Total
0
5 0.36 0.51 0.61 0.73 0.84 0.95 2.7
10 0.42 0.59 0.70 0.84 0.97 1.09 3.1
15 0.51 0.72 0.86 1.03 1.19 1.34 3.8
20 0.87 1.23 1.47 1.76 2.03 2.29 5.5
25 1.46 2.07 2.47 2.94 3.40 3.83 10.9
30 3.48 4.91 5.87 6.99 8.08 9.11 25.9
35 1.92 2.7l 3.24 3.86 4.46 5.03 14.3
4Q 0.91 1.29 1.54 1.84 2.l2 2.39 6.8
45 0.87 1.23 1.47 1.76 2.03 2.29 6.5
50 0.46 0.64 0.77 0.92 1.06 1.20 3.4
55 0.42 0.59 0.70 0.84 0.97 1.09 3.1
60 0.36 0.51 0.61 0.73 0.84 0.95 2.7
65 0.19 0.27 0.32 0.38 0.44 0.49 1.4
70 0.16 0.23 0.27 0.32 0.37 0.42 1.2
75 0.16 0.23 0.27 0.32 C.37 0..12 :.2
80 Q.13 0.l9 0.23 0.27 0.31 0.35 1.0
85 0.13 0.19 0.23 0.27 0.31 0.35 1.0
SO 0.11 0.15 0.18 0.22 0.25 0.28 0.8
95 0.11 0.15 0.18 0.22 0.25 0.28 0.8
100 0.11 0.15 0.18 0.22 0.25 0.28 0.8
105 0.09 D.l3 0.16 0.19 0.22 0.25 0.7
110 0.09 0.13 0.16 0.19 0.22 0.2b 0./
115 0.09 0.l3 0.16 0.19 0.22 0.25 0.7
120 0 0 0 0 0 0 0
Total Precipitation
(in) 1.12 1.58 1.89 2.25 2.60 2.93
riotes: I. Information was obtained from the NOAA ~,tlas lsoplwvial Maps foe
precipitation values.
2. Tables II and 12 of the NOAA atlas were wsed todetermlne n-minute
pr'ecipitation valu€s.
3. Nearea adjustw.ents were made from Figure 14 of the NOAA Atlas due
to the size of basin.

The flooding on May 2, 1904 was a result of 3.0-inches of rain falling in
the Fort Collins area within a 24-hour period. A 7.year.old boy drowned 6-miles
east of fort Collins as a result of a bank failure in the Larimer and Weld Canal.
Also, substantial damag€ was caused by excessive rainfall in the upper Boxelder
area. Again, no particular damage was reported in the basin study area.
On September 4, 1938, 3.s-inches of rain fell ~ithin a 24-hour period,
causing flooding and damage in scattered areas around Fort Collins. An additional
l.5-inch€s of rain fell in the following 39-hour period. Most of the damage
occurred in the Bellvue area northwest of Fort Collins. Damage to roadways and
bridges was substantial in the Spring Canyon area. No noted reports of damage
were found for the Mail Creek and McClellands Basins.

A total of 6.1-inches of rain fell on the Fort Collins area on August 3
and 4, 1951, causing flooding deemed responsible for the death of seven (7) people.
A 24-hour precipitation of 2.95~inches followed by another 24-hour precipitation
of 3.11.inches created flooding in several areas of the City. Oamagetothecounty
hospital, post office and numerous basements ~as reported. However, no particular
damage was reported in the area of this study.
During a 4-day period from July 13-17, 1965, heavy rainfall was reported
with a maximum of 2.5.inches within a 24-hour period. The great amount of rain-
fall coupled with high flows in the irrigation ditches which flow into Mail Creek
caused extensive damage to the pond spillway and drop structure in the Fairway
Estates subdivision. The spillway at that time consisted of a low water bridge
and grouted rip-rap chute apprexi~ate1y 200 feet west of the present structures.
This spillway was replaced with a double box culvert and concrete chute with
energy dissipator blOCks in the fall of 1965 for approximately $12,Ooo.OO.The da-
maged drop structure was rebuilt in the spring of 1966 for approximately $3,000.00.
It was the opinion of the owner of Fairway Estates that the damage to the struc-
tures could have been minimal had it not been for the substantial contri~ting
flows from the New Mercer Canal; all of which routed through Mail Creek instead
of into Mail Creek Ditch.

On August 15, 1975, nearly 4-in,hes of rain fell on the central western
area of Fort Collins. Miner flash flooding was r€~orted and ~any basem~nts W~~~
flooded requiring assistance from the local fire department.
The headline, "Can It RainHere"-YouSet It Can" was seen in the Fort
Collins Coloradoan on July 25, 1977, as rainfall from 2.5 to 5.1 inches fell on
Fort COll1nS wlthln a 24-hourperiod. In the area south of Horsetooth Reservoir,
S.l-inches fell, causing widespread flooding of basements and crawl spaces, re-
quiring assistance from the fire Department. Harmony Road between Shields Street
and U.S. 287 was hard-hit by this ~orm and was closed due to poor conditions_ As
reported by the New Mercer Ditch Company, close to 4-feet of water was flowing
OUEr the drop structure at the Mail Creek ditch headgate. No significant damage
was reported elsewhere in the basin study area.

1I1-3

III.4