FLOOD02473

• County: Weld
• County: Logan
• Basin: South Platte
• Title: A Post Evaluation of Rainfall Reports Associated with Pawnee Creek Flood of July 29-30, 1997 in Eastern Weld and Western Logan Countie in Northeastern Colorado
• Date: 8/1/1998
• Prepared For: Weld County/Logan County
• Prepared By: CSU
• Floodplain - Doc Type: Flood Documentation Report

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2) Site visits and interviews with residents near the primary core of the stonn,

The 1997 storm survey was conducted as well and as quickly as possible after the Pawnee
Creek flood. However, the survey was not conducted by meteorologists or experts on
rainfall measurement procedures and gauge exposure. Since the event occurred, many
questions have been raised concerning the accuracy and representativeness of rainfall
reports. The purpose of these site visits and interviews was to independently evaluate the
original rainfall reports and assign levels of confidence to the reports that were assembled
after the storm. We feared that this would be quite difficult due to how much time has
elapsed since the storm. However, with the cooperation of the local residents, many
questions could still be answered.

The following is a rather thorough summary of each site visit and/or phone interview
followed by conclusions about data accuracy and confidence. A simple rating system was
developed to assign confidence to each observation. "A" represents complete confidence.
"B" means reasonable confidence but with some unanswered or unanswerable questions.
"c' means the data are uncertainty but contain some useful information. "D" represents
almost no confidence, In each case, an explanation is given,

Roger and Peggy Blake (and family)
75144 WCR 110, Stoneham

T 9N R 56W' Sec. 3 extreme north edge
Original rainfall report: 15. 1 inches from rain
gauge accumulations.

Evaluation:
This was one of a handful of reports used to define the core of maximum rainfall for the
storm. At the time of the 1997 storm survey, this report was given high confidence
because it was the only excessive precipitation total (greater than 6 inches) that was based
solely on rain gauge accumulation, Family members checked and emptied the small
conical gauge (capacity of just over 6 inches) approximately every two hours during the
storm and were thus able to report an accumulated storm total.

In interviewing the family, they showed me the 1997 calendar on which a daily rainfall
total of 15" had been written, Based on their memories and notes (mother and daughter,
Christy, had both helped read the gauge and agreed with each other), rainfall amounts and
times of observation were approximately as follows:

12 midnight
2 AM MDT 7/30/98
approx 7 AM 7/30/98
TOTAL

5.5"
2"
1.5"
15"

They had just gotten home from Ft. Collins.
Gauge nearly but not quite full to the top - still
raining hard.
Still raining hard.
Rain letting up so family went to bed at 2:30 AM
They weren't quite sure how they had come up
with the 15.1" total reported previously.

7:30 PM MDT 7/29/98
10 PM MDT

Rain Began
6"

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