BOARD02102

• Board Meeting Date: 1/12/1998
• Description: Flood Section - Post-Flood Activities for the 1997 Flood Events
• Board Meetings - Doc Type: Memo

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Colorado Water Conservation Board
Department of Natural Resources
721 Centennial Building
1 31 3 Sherman Street
Denver, Colorado 80203
Phone: [phone]
FAX: [phone]

STATE OF COLORI\DO

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Roy Romer
Governor

MEMORANDUM

J.lmes S. Lochhead
Executive Director, DNR

Darie$ C.Ule, P.E.
Director. CWCB

TO:

Colorado Water Conservation Board Members

FROM: Larry Lang

DATE: January 19, 1998

SUBJECT: Agenda Item 20.a., January 28-29, 1998 Board Meeting-
Post-Flood Activities For The 1997 Flood Events

Description of the Events
During the summer months, the Front Range and eastern high plains of Colorado are subject to
convective thunderstorms that produce large amounts of rainfall in short time periods. In late
July 1997, a large high pressure system stalled over the central high plains of the United States.
The system's clockwise rotation began pumping moisture into Colorado from the Gulf of
Mexico. At the same time, a stronger-than-normal and earlier-than-normal monsoonal system
was occurring due to a static low pressure system situated over the California! Arizona border.
This system pumped large amounts of moisture further north than usual. As a result, a collision
of moisture-laden air from both sources began occurring along Colorado's Front Range from
Trinidad north to the Wyoming/Colorado border.

In the 3-4 dayspreceding, July 28, 1997, the City of Fort Collins and portions of northeastern
Colorado received soaking and/or drenching rains from the moist air. The result of these rains
was to increase soil moisture while at the same time decrease the storage capacity of subsequent
rainfall in the general soil environment.

On the evening of Monday, July 28,1997, intense rains began around 6:30 p.m. in the foothills
west of Fort Collins. Meanwhile, a weak stationary front was located east of the area in Weld
County. This front prevented thunderstorms from moving eastward, as they typically do. This
stalling effect caused large amounts of rainfall to be deposited in the headwaters areas of Spring
Creek, the Fairbrooke Channel, the Clearview Channel and the Plum Channel, the last two of
which are tributary to the Colorado State University Drainage Basin. A point rainfall amount of
8.31 inches in 4 It, hours was measured near the centroid of the storm located over the upper
Spring Creek basin. Over 6 inches of rainfall, during the same time period, was recorded on the
CSU Main Campus. Weather observers at several locations on the western side of Fort Collins
measured similar amounts of rainfall.