Accuracy of annual volume from current-meter-based stage discharges

Many water users have been strongly encouraged to reduce the amount of their diversions through improved water management practices. However, the impact of improved practices can be lost in the uncertainty of measured water volumes. A firm understanding of the accuracy of flow measurements and accumulated volumes is important for identifying opportunities for improvement. Stage-discharge relationships are often used to estimate discharge over time from near-continuous measurements of stage. The stage-discharge relationship is usually determined from periodic current-meter discharge measurements. Random errors in current-meter discharge measurements and changes in the true stage-discharge relationship as the channel properties change with erosion, sedimentation, vegetation growth, etc., all compromise our ability to infer discharge over time from stage measurements. Some water users adjust the stage-discharge relationship with each current-meter discharge measurement. In this paper, we present procedures to estimate the accuracy of various methods for inferring total annual water volume based on near-continuous measurement of stage and various methods for determining the stage-discharge relationship. These uncertainty estimates can then be used to obtain insight into water users' flow measurement strategies as well as suggestions on improving these strategies.