2016 NGWA Groundwater Summit

Testing the Ideas of Walter White: An Estimation of Riparian Evapotranspiration Using Groundwater Upwelling

Tuesday, April 26, 2016: 2:50 p.m.
Platte River Room (The Westin Denver Downtown)
Jacob Kollen , Oregon State University, Corvallis, OR
John Selker, Ph.D. , Oregon State University, Corvallis, OR
Chad Higgins, Ph.D. , Oregon State University, Corvallis, OR

In arid and semi-arid systems the riparian zone boarding a stream has high evapotranspiration rates compared to uplands. Evapotranspiration (ET) is difficult to estimate, but accounts for much of the water loss from landscapes. Walter White (1932) introduced a method using the diurnal fluctuation of groundwater depth to estimate ET. With the advent of accurate data logging pressure sensors, the White method has recently reemerged as an important strategy. A persistent challenge of the White method is knowledge of how much water is released per unit fall in the water table (the “specific yield”). Specific yield is highly variable, and there exists no validated method for its measurement. Our experiment will indirectly measure this term using two methods. The first method utilizes soil moisture probes, spaced 3cm apart along the vertical axis of a soil column to measure the volumetric change in water content accompanying changes in water table. Soil moisture and tension data will be used in conjunction with the Hydrus 1-D numerical model to estimate evapotranspiration. The second method is performing classical pump tests to estimate the in situ specific yield, and using this estimated specific yield term in the Walter White equation to estimate evapotranspiration. We will compare these groundwater based estimations of evapotranspiration against two micrometeorological data based estimations of evapotranspiration. The micrometeorological based methods are the ‘eddy covariance’ method as well as the ‘Penman-Monteith’ method. The deliverable by the end of this project will be a simple method to install and calibrate a groundwater table depth observation well to produce an accurate estimation of evapotranspiration and groundwater upwelling in areas with shallow water tables such as riparian areas.

Jacob Kollen, Oregon State University, Corvallis, OR
Jacob Kollen has worked as tradesman in forestry, construction, and mechanics before pursuing a Masters in Water Resources Engineering. His areas of interest include field soil description, soil mapping, hydrologic budgeting, groundwater hydraulics, vadose zone processes and irrigation systems.

John Selker, Ph.D., Oregon State University, Corvallis, OR
Dr. Selker, TAHMO co-Director, has worked as a consulting engineer in the USA, Kenya, Somalia, Sri Lanka, Canada, and England. Additionally he has carried out scientific research in Chile, Ghana, Senegal, Israel, China, and 10 European countries. His areas of expertise include electronic design (e.g., lead engineer on the Sun Microsystems optical mouse project), irrigation and water systems, and development projects. Since completing his doctoral studies Dr. Selker has been a professor in the department of Biological and Ecological Engineering at Oregon State University for 23 years focused on Water Resources Engineering.

Chad Higgins, Ph.D., Oregon State University, Corvallis, OR
Dr. Higgins interests include environmental fluid mechanics with special interest in applications to atmospheric flows and hydrology, measuring and modelling of fluxes through the soil-plant-atmosphere continuum, optimum water management in agriculture, spatial variability of the land surface and its effect on transport, large eddy simulations, Raman Lidar of atmospheric water vapor, and the development of novel measurement techniques for atmospheric fluxes.