New Instrumentation for Water Budget Evaluation

The Delaware Environmental Observation System (DEOS) and the Delaware Geological Survey have recently acquired new instrumentation to measure evapotranspiration (ET). The purchase of an eddy covariance instrument, partially supported by the Department of Natural Resources and Environmental Control, will improve the ability to quantify ET during agricultural and water supply drought periods and improve water availability estimates for resource managers. The project is being conducted by DEOS’s Kevin Brinson and DGS’s Scott Andres and Changming He.

Key to evaluation of the sustainability of surface and groundwater resources is an accurate accounting of the water budget in which precipitation input is balanced by runoff and ET. Precipitation and runoff are fairly well monitored. Evapotranspiration (ET), however, which accounts for approximately two-thirds of the annual average water budget, is not directly measured in Delaware. Instead ET is estimated, and estimates are difficult to quantitatively validate and are highly generalized over spatial and temporal scales. Quantitative assessment of ET will improve our ability to manage water resources during agricultural and water supply drought periods.

Eddy covariance instruments and methods are available to provide direct measurement and assessment of evapotranspiration at multiple time and spatial scales. Coupled with automated high-frequency groundwater level, precipitation, and soil moisture observations that are already being collected, eddy covariance measurements of ET can be used to rapidly and more accurately quantify the amounts of water available for groundwater recharge from storms that have passed. Future efforts are envisioned that will build tools to predict the amount of potential recharge that would be expected from storms that are forecast.

The new instrument will be installed at an existing DEOS weather station located near Fairmount, Delaware at the University’s Warrington Farm Agricultural Experimental Station. Research will be done over the next year to compare direct ET measurements from the sensor to ET estimates derived by traditional methods. In the future, the relationships between time variant ET and groundwater recharge will be gradually incorporated into water conditions assessments.

For questions and information, contact DGS at, 302-831-2833