Understanding how water moves and is stored within the landscape is among the most pervasive themes of hydrological research, but important aspects of the water cycle remain poorly known. The proposed research project will address current limitations in characterizing the water cycle and is motivated by two related hypotheses: 1. Hydrologically important changes in water content are sufficient to cause measurable changes in the in situ state of stress. 2. Transient changes of in situ stress can be used to estimate hydrologic fluxes and changes in storage over multiple scales. This investigation will develop conceptual and numerical methods for analyzing hydrologic processes associated with changes of in situ stress as well as instruments and field techniques for measuring these changes. New field instrumentation will be developed to measure total and effective stress changes with a target resolution of 1 Pa. A proof-of-concept field test near Clemson, SC will compare high resolution stress measurements to transient changes in water content and other processes. A more rigorous field test will take place in Kansas, where the method will be used to estimate changes in mass resulting from evapotranspiration and other effects in a riparian zone along the Arkansas River. Theoretical analyses of poroelasticity in the vadose and saturated zones will be used to evaluate how stresses are affected by changes in water content, as well as a variety of other potentially competing effects including barometric pressure change, subsurface geology, earth tides, ground water extraction, regional horizontal flows, surface impoundments, traffic, wind, temperature, etc. New field approaches are catalysts for discovery in hydrologic sciences, and the intellectual merit of the proposed investigation is that it has the potential to be such a catalyst for discovery. The investigation will provide the scientific basis for new field techniques, theoretical analyses and instrumentation that will advance the ability to characterize key aspects of the hydrological cycle (ET, change in soil moisture, recharge, stormflow, etc.) over scales from less than 1 m to greater than 100 m. The techniques developed for this project will have broad impacts by providing multi-scale data that can be used to improve: validation and calibration of remote sensing instruments and algorithms; estimates of melting or accumulation of snow pack or glaciers; assessment of rates of erosion or sediment deposition; reduction of noise and resolution of tectonic strain; assessment of rates of carbon storage; methods for scheduling irrigation; understanding mass changes resulting from forest fires, and related.
