Floodflow characteristics of Illinois River tributary near Siloam Springs, Arkansas

The peak discharge of the Illinois River tributary for the flood of June 8, 1974, is well above that of the 100-year flood. Reconstruction of State Highway 59 caused an increase in water-surface elevation of 5.1 ft (feet) or 1.5 m (metres) for the 25-year flood, 5.5 ft (1.68 m) for the 50-year flood, and 10.8 ft (3.29 m) for the flood of June 8, 1974, at the approach section to the new culvert, as shown by flood profiles.

Discharge for the 25-year flood is 640 ft³/s (cubic feet per second) or 18.11 m³/s (cubic metres per second), for the 50-year flood is 770 ft³/s (21.79 m³/s), and the peak discharge for the flood of June 8, 1974, was 1,470 ft³/s (41.60 m³/s).