New Instrumentation for Water Budget Evaluation

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The Delaware Environmental Observation System (DEOS) and the Delaware Geological Survey have acquired and installed new instrumentation to measure evapotranspiration (ET). The eddy covariance (EC) instrument system (Table 1 and Figure), purchased with support from 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 DS’s Scott Andres and Changming He.

Table 1. Instrumentation Package

Eddy Covariance Array
Soil heat flux sensor
Volumetric soil water sensor
Soil temperature sensor
Controller software and data logger
Power supply
Tower and mounting hardware

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.

EC 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, EC 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. EC measurements of ET are also used to evaluate crop water demands and assist with irrigation scheduling.

The new instrument is operating 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 (Thornthwaite and Penman-Monteith) and by an Atmometer, a low-tech instrument. In the future, the relationships between time variant ET and groundwater recharge will be gradually incorporated into water conditions assessments. Data collected by the new instrumentation will also be useful to research by the College of Agriculture and Natural Resources into water demands by crops and development of more efficient irrigation practices.

August 2015