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United States Department of Agriculture

Agricultural Research Service

Title: Etrs Arrays: a Boundary Layer to Water Table Total Flux Measurement System

Authors
item Marks, Daniel
item Duffy, Christopher - PENN STATE UNIV
item Seyfried, Mark

Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: September 5, 2004
Publication Date: September 5, 2004
Citation: Marks, D., Duffy, C.J., and Seyfried, M., 2004. ETRS Arrays: A boundary layer to water table total flux measurement system, EOS Transactions of the American Geophysical Union, Vol 85 (47): F801 (CD-ROM abstract)

Technical Abstract: Developing an observing system that will close the water and energy balance over a specified region (site, hill slope, catchment) in complex terrain is a difficult problem. In this research we propose to integrate three independent flux measurement systems for evapotranspiration, snowmelt, and infiltration/recharge, into a single coherent measurement platform. We refer to the measurement system as an ETRS Array (Evaporation, Transpiration, Recharge, Snowmelt). The goal of the ETRS measurement system is to close the vertical and horizontal energy and moisture flux in a finite volume of soil, snow, and atmosphere extending from the water table to the atmospheric boundary layer. The concept has recently been proposed to measure ET from shallow water tables at riparian sites in the Rio Grande in New Mexico. Here we extend the concept to include snowmelt processes. Eddy covariance (EC) systems with complete meteorological observations are used to monitor both above and below canopy fluxes of heat and moisture. Snowcover energy, mass balance and melt for the site volume are computed from above and below canopy precipitation, and canopy corrected radiation, temperature, humidity and wind. Validation of the snow energy and mass state is derived from continuously monitored snow depth, temperature and water equivalent (SWE) and is augmented with bi-weekly snow pits and courses, and a series of detailed snow surveys conducted during mid-winter, at peak accumulation, and during ablation. Concurrent soil temperature and moisture arrays and water table measurements are use to monitor the below ground portion of the volume. The experimental design requires sensor arrays to be deployed at the centroid and boundaries of the soil volume such that the net vertical flux (E, T, and R) through the soil column and lateral flow advected through the below ground portion of the volume can be formed along with the snowcover energy and mass balance and the EC data into a complete water and energy balance of the soil-snow-atmosphere volume. For the subsurface, a local, dynamic water balance is formed by direct integration of Richards' equation using a Finite Volume (FV) formulation of unsaturated-saturated moisture storage. The resulting dynamical system is continuous in time, discrete in space. Using field estimates of soil characteristic curves, the dynamical equations are solved numerically. An example design will presented for a field site in a small headwater catchment within the Reynolds Creek Experimental Watershed in Idaho. This research will show how the theory can be used for optimal sensor design given soil conditions and approximate depth to water table.

Last Modified: 11/22/2014
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