Site Summary Flint Creek near West Siloam Springs, Oklahoma

October 17, 2000; The team now based out of Siloam Springs, Arkansas ventured out to the gage station on Flint Creek near West Siloam Springs, just a few miles from the Oklahoma/Arkansas border and approximately (~)800 feet downstream from a Delaware County Bridge. Flint Creek also originates in NW Arkansas, Flint Creek's watershed receives a little less than 43 inches of precipitation annually, mostly in the form of rain. Annual runoff averages just over 11 inches.

A Pebble Count was taken, 35 times in the first cross section, 171 feet downstream from the gage and 43 times in the pool below. The median size of the particle’s secondary axis is 16 mm. The median size compares well with the prediction that 17 mm particles are the minimum size transported during bankfull flows.

The bankfull discharge is predicted to be 638 cubic feet per second (cfs). This rating was obtained by projecting the average reach slope of 0.0022 ft/ft through the bankfull indicators of the reach back to the gage at station 100. The recurrence interval, based upon the Weibull Extreme Value plotting positions of 20 peak annual discharges, is 1.43 years. This can also be expressed by saying that the stream has a 69% chance of exceeding 638 cfs within a consecutive 12-month period. The bankfull discharge of 638 cfs appears small for a watershed of 59.8 square miles in this area, but reasonable considering the length of flow record. Waters may also be diverted to other basins via solution channels commonly found in limestone formations.

Bankfull Stage at gage is 6.0 feet; gage datum is 958 feet above mean sea level. The bankfull stage in the first cross section at station 271 is 5.6 feet gage height, 6.5 feet above the bed. Water is flowing at a mean velocity of 2.4 feet per second through this cross section. Manning’s roughness is 0.056, according to all of the assumptions of steady uniform flow. The bankfull stage in the second cross section at station 643 is 4.8 feet gage height, 5 feet above the bed. Water is now moving at a mean velocity of 3.5 feet per second. The cross sectional flow area is down to 184 square feet, bankfull top width is 69 feet, and the mean or hydraulic depth is 2.7 feet through this cross section, Manning’s roughness is reduced to 0.037.

According to Rosgen’s criteria for stream classification, Flint Creek near West Siloam Springs, OK below the gage is a C4. It is mildly entrenched, (Entrenchment Ratio =5.8) as it expands to widths greater than 400 feet as the depth doubles. The right hand floodplain is inundated at the 3.2-year return interval. Sinuosity is ~1.35 and the width to depth ratio is 26.

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