Comparison of computed flow through manually operated water control structures in Florida using theoretical versus calibrated coefficients

Abstract

The U.S. Geological Survey (USGS) calculated discharge at 13 water control structures in Florida using theoretical equations and uncalibrated coefficients gathered from previous studies and typical textbook values for selected flow regimes and structure types. These discharges were compared to the real-time discharges calculated and published by the USGS from October 1, 2007, to September 30, 2019, using traditional methods and coefficients verified by direct discharge measurements. The theoretical and USGS-calculated daily mean discharges were compared at each structure for different flow regimes covering the entire range of discharges that occurred over the study period except those less than 10 cubic feet per second to avoid large percentage errors for small actual differences in discharge. The discharges were also not compared if (1) any alterations were made to the USGS discharge to account for factors such as debris or construction, (2) any values were missing throughout the day, (3) the flow regime changed during the day, or (4) the USGS discharge was estimated. The structures compared include a mixture of vertical lift and radial gates with free and submerged conditions for orifice and weir flow. The study totals showed that the average absolute difference for all structures was 18.7 percent. Average percent differences ranged from −26.5 to 28.6 percent, and 4 of the 13 structures had average differences within 10 percent.