Site Summary Flint Creek at Springtown, Arkansas

On the afternoon of October 17, the team went upstream into Arkansas to where Flint Creek has a drainage area of 14.2 square miles, Approximately (~)1 mile downstream from Springtown, AR. Mean annual precipitation is a little less than 43 inches, but the annual runoff from this smaller watershed averages just over 14.5 inches.

A Pebble Count was taken, 45 times in the riffle section just upstream from the surveyed cross section, 171 feet downstream from the gage. The median size of the particle’s secondary axis is 18 mm. The median size in the bed compares well with the prediction that 21 mm particles are the minimum size transported during bankfull flows.

The bankfull discharge is predicted to be 416 cubic feet per second (cfs). This rating was obtained by projecting the average bankfull slope of 0.0027 ft/ft from the bankfull indicators at 5.49 ft gage height in the cross section at station 291 back to the gage at station 120. The recurrence interval, based upon the Weibull Extreme Value plotting positions of 40 peak annual discharges, is 1.46 years. This can also be expressed by saying that the stream has a 69% chance of exceeding 416 cfs within a consecutive 12-month period. Bankfull discharges on Flint Creek have been noted, the bankfull discharge of 416 cfs appears more reasonable for a 14 square mile drainage than the 638 cfs bankfull discharge for 60 square miles near West Siloam Springs.

Bankfull Stage at gage is 5.96 feet; gage datum is 1,173.47 feet above mean sea level. The bankfull stage in the first cross section at station 291 is ~5.5 feet gage height, ~2.3 feet above the bed. Water is flowing at a mean velocity of 4.3 feet per second through the riffle and cross section. Manning’s roughness is 0.033, according to all of the assumptions of steady uniform flow. The cross sectional flow area is 97 square feet, bankfull top width is 39 feet, and the mean or hydraulic depth is 2.5 feet through this cross section.

According to Rosgen’s criteria for stream classification, Flint Creek At Springtown, AR below the gage is a transitional B4C reach. The median bed size of 18 mm is coarse gravel, It is moderately entrenched, (Entrenchment Ratio =1.6) as it only expands to a width of 60 feet as the depth doubles. The width to depth ratio is a moderate 15, and sinuosity is 1.26.

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