FLOOD07967

• Designation Number: 181
• County: Larimer
• Community: Loveland
• Stream Name: Big Thompson River
• Basin: South Platte
• Title: Floodplain Information Report - Big Thompson River, Loveland
• Date: 10/1/1981
• Designation Date: 12/1/1981
• Floodplain - Doc Type: Floodplain Report/Masterplan

The creSs s~ctions for the study ~ere otiginally obtained by photo-
grammetric and/or field survey methods in August 1976. This survey infonna-
tion and base maps were then updated by the Same methods to reflect May
1981 conditions. These cross sections, whose alignments are shown On the
mapping, were used in the hydraulic calculations by using the Army Corps of
Engineers HEC-2 program to determine the ~ater-surface profiles sho~~ in
thi~ report. A total of 62 digitized cross sections and i7 field cross
sections ~ere used in the hydraulic computations.

All bridges and other significant structures that might divert Ot
restrict flows significantly ~ere field surveyed. Additionally, because
the digitized cross sections indicate vater-surface elevations, the cross
sections were corrected by field meaSurements to reflect streambed eleva-
tions.

Should you desire any additional information concerning these maps and
surveys, it can be obtained from the City of Loveland, Larimer County, the
Colorado Water Conservation Board, or by pet~ission fro~ one of the above

agencies through the contractor.

Related Flood Studies

A flOOd-plain information report that included the Big Thompson River
w,,~ 1>T"pa~.._d hy th.. Corp" of Engineers in \971 (R,,{ _ 1). In that r"port
the water-surface profile for the Big Thompson River for the lOO-year flood
thro,,~h the City of Loveland waS somewhat different than the lOO-year
fleod water~surface profile used in the present study. Review of cross-
section data used by the Corpa of EnEine~rs verif1.ed that the earlier
water-surface profile was based on 1971 flood-plain ~ond1tio~s and i~ now
Obsolete. S1nce the water-surface profile in the present study reflects
existing conditions (1981), it supersedes the water-surface profile in the
previous Corps of Engineers report.

FlOOd inaurance stuJies ~ere completed by the Federal Insurance
Adminietrat10n in 1978 (Ref. 6 and Ref. 7). Sinc" the~e studies "',,re
~om?leted, there have been signifIcant changes in the flood-plain a~eas
vhi~h necessitate the revision of these do~uments. Therefore, since the

5

RE:\OURCE: CON\UlT~NT\ INC

I
t

water-surfa~e profile in the present study reflects existing conditions, it
supersedes the ~ater-surface profile in the previous FIA reports for the
Big Thompson River bet~een Stations 123,700 and 165,300.

Another related study of flood plains in the area was completed by the
Corps of Engineers in 1977 (Ref. 2) which studied the reach of the Big
Thompson River between Weld County and the lower limit of this study reach.

I,
"
!
,
I
,
,
,
I

I

,
I;

,

RE:\OURCE: CON\ULT~NT\ INC