|Wahlin, Brian - DAVEY-CAIRO, TEMPE, AZ|
Submitted to: Journal Hydrologic Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 22, 2005
Publication Date: August 1, 2006
Citation: Clemmens, A.J., Wahlin, B.T. 2006. Accuracy of annual volume from current-meter based stage-discharges. Journal Hydrologic Engineering. 132(5):489-501. Interpretive Summary: Water supplies in the Western United States are limited and often over allocated. Accurate knowledge of water delivered and used is important to proper distribution of available supplies. However, the measurement of water quantities is never perfect, opening up the possibility of water disputes and making it difficult to quantify the impact of water conservation measures. Knowledge of water measurement accuracy is important for determining whether existing methods are sufficient or further investment in improved technology is warranted. This paper presents a methodology for determining the accuracy of water volume for rivers, streams and canals whose water levels are monitored continuously and discharge is based on a relationship between water level and discharge based on current meter discharge measurements. This information should be of interest to the U.S. Geological Survey, the U.S. Bureau of Reclamation, irrigation districts, consultants and water resources professionals.
Technical Abstract: 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. Where a fixed measurement structure is not available, 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.