Real-time Open-water/Wetted-sands Evaporation Quantification for Water Operations
* What is the actual real-time water evaporation quantity per unit area per time unit that occurs in river systems from open channel water surfaces and wetted sands?
* What instrumentation, instrumentation spatial distribution, ambient paramenters, and calculations are necessary to monitor and report these depletion rates?
Need and Benefit
For water operations occurring in arid/semi-arid climates, evaporative losses from the water channel surface and associated wetted soil surfaces can account for significant depletions to daily water budgets. These depletions need to be quantified so that they can be accurately accounted for when making daily water releases to deliver contracted water, while meeting other court ordered deliveries/targets and satisfying riparian demands, while conserving remaining stored supplies.
This Science and Technology (S&T) Program research project both measure and develop a model of open-water and wetted-sands evaporation for the middle Rio Grande for utilization by the Evapo-Transpiration (ET) Toolbox, the URGWOM model, and other modeling applications. This model will be verified by field measurements over open-water and wetted-sands from state-of-the-art instrumentation, and this model could be applied in other settings and decision support systems as needed. These instruments will directly measure the evaporation in time and space by eddy covariance, Light Detection and Ranging (LiDAR) and airborne thermal, infrared, and visible scanners. The field data will be used as a reference truth-set to compare traditional simple models for open-water and wetted-sands evaporation to physics-based formulations. Once the models are developed, they will be evaluated against performance metrics, and the best model will be supplied to the ET toolbox for real-time monitoring and Reclamation water operations management-decision-making processes.
The fundamental tool for Rio Grande ET calculations is the ET Toolbox () which presently uses a modified Penman equation for open-water/wetted-sands estimates but has a new reservoir evaporation model developed from ongoing research. It is well documented and understood by all parties concerned that this parameterization is completely inadequate and must be replaced with a more technically sound model.
This Science and Technology (S&T) Program research project measures the evaporation on selected sites within the Middle Rio Grande using state-of-the-art eddy covariance, LiDAR, and airborne remote sensing systems to quantify the spatial and temporal properties of the open-water/wetted-sands evaporation. These evaporation estimates will be used as a truth-set for constructing and testing an evaporation model based upon a modified Penman-Monteith approach considering energy balance and atmospheric advection (or one based on Monin-Obukov methods). The tested and validated model for wetted sands will be designed to use basic meteorological data so that it can be used with the relatively low cost field station data supporting the ET Toolbox for water management purposes.
Performance measures for this program will be as follows: The existing open-water/wetted-sands evaporation estimates within the ET Toolbox will be compared with the direct measurements from the eddy covariance and remote sensing systems. Further, the newly developed model will also estimate the evaporation. Statistical evaluations of the existing model against the truth-set and the improved models will be made. Confidence limits will be set at 95 percent, and rejection criteria developed by analysis of variance (ANOVA) data reduction.
The best model will then be selected for inclusion in the ET Toolbox and be made available for other applications.
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