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Site Summary Spavinaw Creek near Sycamore, Oklahoma

On the afternoon of October 18, the team headed north to Spavinaw Creek near Sycamore, Oklahoma. Spavinaw Creek also originates in northwest Arkansas up on the Springfield Plateau. The 133 square mile watershed near Sycamore averages just under 43 inches of precipitation annually, mostly in the form of rain. The annual runoff is just under 12 inches.

A Pebble Count was taken; 46 times in a riffle section near station 334, 364 feet downstream from the surveyed cross section (station 698), and 43 times in a riffle section near station 844, 146 feet upstream from the surveyed cross section. The median size of the particle� secondary axis is 21 mm. The median size of bed material is approximately (~)30% larger than the predicted minimum particle size transported (16 mm particles) during bankfull flows. All predictions are based upon the critical shear stress equation t = gRS.

The bankfull discharge is predicted to be 1,813 cubic feet per second (cfs). This rating was obtained by projecting the average reach slope of 0.0017 ft/ft through the highest bankfull indicators measured along the profile, through the cross section and back to the gage at station 0. The recurrence interval, based upon the Weibull Extreme Value plotting positions of 40 peak annual discharges, is 1.45 years. This can also be expressed by saying that the stream has a 69% chance of exceeding 1,813 cfs within a consecutive 12-month period.

Bankfull Stage at gage is 7.9 feet; gage datum is 875 feet above mean sea level. The bankfull stage in the cross section at station 698 is 9.1 feet gage height, 5 feet above the bed. Water is flowing at a mean velocity of 4.7 feet per second through the riffle section. Manning� roughness is 0.027, according to all of the assumptions of steady uniform flow. The cross sectional flow area is 389 square feet, bankfull top width is 129 feet, and the mean or hydraulic depth is 3 feet.

According to Rosgen� criteria for stream classification, Spavinaw Creek near Sycamore, OK above the gage is a C4 reach. It is slightly entrenched, (Entrenchment Ratio =2.3) as it expands to a width of 300 feet as the depth doubles. Sinuosity is ~1.28 and the width to depth ratio is 42. This stream's classification is in agreement with Russ Dutnell's work, although he found a reach section 27 feet narrower, the bankfull cross sectional areas are within 6 square feet of each other.

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