Site Summary Baron Fork at Eldon, Oklahoma

October 16, 2000; The team met up in Northeast Oklahoma, under State Highway 51 bridge over the Baron Fork near Eldon. The Baron Fork originates in northwestern Arkansas and is within the southwestern portion of the Springfield Plateau Physiographic Province. The topography is characterized by gently rolling hills, local relief in the area is around two hundred feet from ridgeline to adjacent valley floor. Runoff is flashy. The Baron Fork watershed receives ~44 inches of precipitation annually, most in the form of rain. Runoff from the watershed averages just under 15 inches. Geologically, the Baron Fork is underlain by fine- to coarse-grained limestones and cherty limestones of the Mississippian age Boone Formation. The stream has historically been mined for gravel.

A Pebble Count was taken, 57 times in the first cross section, 1,485 feet downstream (DS) from the DS bridge piers and 29 times in the pool above. The median size of the particle’s secondary axis is just under 24 mm. This median size compares well with the prediction that 22 mm particles are the minimum size transported during bankfull flows.

The bankfull discharge is predicted to be 9,620 cubic feet per second (cfs). This rating was obtained by projecting the average reach slope of 0.00147 ft/ft by the bankfull indicators in the two cross sections back to the gage at station 23 feet. The recurrence interval, based upon the Weibull Extreme Value plotting positions of 52 peak annual discharges is 1.45 years. This can also be expressed by saying that the stream has a 69% chance of exceeding 9,620 cfs within any consecutive 12-month period.

Bankfull Stage at the gage is 13.75 feet. Gage datum is 701.14 feet above mean sea level. The bankfull stage 1,485 feet downstream from the gage (cross section #1) is 11.6 feet gage height, which is 9.4 feet above the bed. At bankfull stage water is flowing at a mean velocity of 5.2 feet per second through this cross section, Manning’s roughness is 0.035, according to all of the assumptions of steady uniform flow. The bankfull stage 2,017 feet downstream from the gage (cross section #2), is 10.8 feet gage height, which is 8.8 feet above the bed. Water is now moving at a mean velocity of 6.7 feet per second. The cross sectional flow area is down to 1,443 square feet, bankfull top width is 300 feet, and the mean or hydraulic depth is 4.8 feet through cross section #2. Manning’s roughness is reduced to 0.024; this lowered resistance indicates that the stream bed material is now semi-mobile.

According to Rosgen’s criteria for stream classification, the Baron Fork at Eldon, below the gage is a C4. It is slightly entrenched, as it expands to widths greater than 700 feet as the depth doubles. Sinuosity is ~1.28 and the width to depth ratio is 62.

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