A methodology to reduce uncertainties in the high-flow portion of the rating curve for Goodwater Creek Watershed

Authors: Baffaut, Claire; Sadler, Edward

Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 6/22/2012
Publication Date: 7/29/2012
Citation: Baffaut, C., Sadler, E.J. 2012. A methodology to reduce uncertainties in the high-flow portion of the rating curve for Goodwater Creek Watershed. ASABE Annual International Meeting, 07/29-08/01/2012, Dallas, Texas. Paper No. 121337015.

Interpretive Summary: Continuous measurement of flow in a stream is done by measuring water stage. The stage is then converted into a flow rate using a rating curve that describes the relationship between stage and flow. This curve is developed from actual flow measurements at various stages. During out-of-bank flow conditions, measurement errors increase because of safety concerns and difficulties in measuring flow velocity in the flood plain. With increasing frequency of large rain events associated with climate change, it becomes critical to have an accurate rating curve for out-of-bank flows. We propose a methodology based on physical and mathematical principles to test and develop a rating curve that is accurate for high flows. The methodology was tested using flow data from the Goodwater Experimental Watershed, a 72-km2 watershed in Northeast Missouri. Preliminary results indicate that flow values that correspond to out-of-bank stage were overestimated by 40 percent in the original rating curve. This method provides additional and innovative means to verify the accuracy of the high limb of a rating curve. It is of value to hydrologists and flow data users for any site where the rating curve is in question.

Technical Abstract: Flow monitoring at watershed scale relies on the establishment of a rating curve that describes the relationship between stage and flow and is developed from actual flow measurements at various stages. Measurement errors increase with out-of-bank flow conditions because of safety concerns and difficulties in measuring flow velocity in the flood plain. With increasing frequency of large rain events associated with climate change, it becomes critical to have an accurate rating curve for out-of-bank flows. We propose a methodology based on the Manning formula on one hand and physical and mathematical principles that govern the hydrograph and the rating curve on the other hand to test and develop the high flow limb of a rating curve. The methodology was developed and tested using flow data from the Goodwater Experimental Watershed, a 72-km2 watershed in Northeast Missouri. A final water balance on flow events was performed using measured precipitation, and evapotranspiration and soil water estimated from a SWAT model. Preliminary results indicate that flow values that correspond to out-of-bank stage were overestimated by 40 percent in the original rating curve. This method provides additional and innovative means to verify the accuracy of the high limb of a rating curve.