Evaluation of Seasonal and Annual Variations of Water Flow in Arid Soils Using Weighing Lysimeters.

The recently constructed weighing lysimeter facility in Boulder City, NV provides an excellent opportunity to study water infiltration into arid soils at the intermediate (meter) scale under well defined conditions. Three lysimeters are weighed on separate balances, each with a live mass of approximately 28,000 kg with a resolution of roughly 100 g or 0.025 mm of water. Each lysimeter contains 12 m³ of repacked homogenized and layered desert soil (dimensions: 2.258 m diameter and 3 m deep) and is instrumented with 13 different sensor technologies to measure state variables including water content, matric potential, and thermal properties at 15 depth planes. Horizontal rhizotron tubes installed at three depths from 0.60 to 1.50 m, and a vertical rhizotron tube installed throughout the lysimeter depth, images the movement of wetting front and a green/blue dye (applied at 60 cm) during precipitation events. From November 2008 to March 2010, there were 9 precipitation events registering over 10 mm of precipitation and the greatest precipitation event was on January 18, 2010 with 50 mm. By March 2010, there was nearly 100 mm of total precipitation and the wetting front reached 75 cm. This lysimeter facility closes a critical gap in vadose zone hydrology of arid environments since it allows to directly observe water infiltration, storage, and evaporation as well as to determine moisture distribution in three meter deep soil profile under well defined initial and boundary conditions to evaluate and improve infiltration models. This presentation will describe results from precipitation events from the past four years which were analyzed according to changes in total soil mass to determine the amount of water infiltration, storage, and evaporation; alterations in soil moisture profiles determined by TDR, HDU, and DHP sensors; and wetting front movement as seen by the rhizotron tubes.