FLOOD04722

• County: Las Animas
• Basin: Arkansas
• Title: Storm and Flood of July2-3, 1981 Frijole Creek Basin
• Date: 9/1/1982
• Prepared For: Colorado and Southern Railway
• Prepared By: Bishop Associates, Inc.
• Floodplain - Doc Type: Flood Documentation Report

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survey dats. For the firat two hours, one resident measured an inten-

sity of 6 inches per hour using a 6-inch raingage, but did not continue

observations throughout the storm. Another observed a 6-inch raingage

for the first hour only. Two buckets, one 12 and one 13 inches deep

were reportedly filled and overflowing.

Rainfall measurements up to 13 inches are fairly reliable and based

on observation of rain gage data for the first 2 hours of the storm and

reports of buckets overtopping. Rainfall beyond 13 inches is estimated

based on observations of the residents comparing rainfall intensity with

the first two hours of the atorm. The only container observed which was

deeper than 13 inches had a hole in the bottom and the owner reported an

unknown amount of water leaked out before a measurement was taken.

The total rainfall for July 2-3, 1981, is shown on the isohyetal

map (Plate 1). The analysis was based on the minimum estimates given by

observers. Observations of residents in the area, as given in personal

interviews on July 7, 1981, are detailed in Appendix A.

Total rainfall probably exceeded 16 inches in some locations, and

averaged in excess of 11.8 inches over the Frijole Creek basin. The

isohyetal diagram (Plate 1) was drawn based on the point estimates of

total rainfall described in Appendix A, the probable storm shape based

on satellite photos, radar data, and local topographic features. The

storm shown in Plate 1 is based on relatively few data points, and

probably represents a conservative estimate of the July 2-3 event; it is

likely that cumulative precipitation was much higher than shown in the

higher elevations southwest of the indicated storm center, possibly

totaling 20 to 24 inches in some areas.

100-Year Precipitation

Based on information published by The National Oceanic and Atmos-

pheric Administration (NOAA), the 100-year, 4-hour storm in the Frijole

Creek basin would result in 3.1 inches of precipitation. A 100-year

storm is a storm of such magnitude that, over the long term, it would be

expected to occur an average of once every 100 years. The storm on July

2-3 was almost four times as large as the 100-year, 4-hour event.

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