2012 Annual Report 1a.Objectives (from AD-416): Objective 1. Assessment and improvement of existing modeling technologies for simulating regional scale hydrogeology, including land surface processes associated with agricultural water management; modeling assessments of the impacts of existing and changing agricultural water and land management practices on water quality for regions of interest. Objective 2. Development of new technologies for simulating agricultural practices at the regional scale by measuring or modeling mechanistic processes controlling contaminant loading rates (salinity, nutrients, and other contaminants of concern) from fields under varying environmental conditions and agricultural management practices used in arid and semi-arid regions. Objective 2.1 Development of new technologies for improved soil parameter estimates for regional hydrogeologic simulations. Objective 2.2 Development of new technologies for improved modeling of coupled overland and subsurface flow and transport. 1b.Approach (from AD-416): Water availability for irrigated agriculture is decreasing in arid and semi-arid regions, forcing a greater reliance on recycled or otherwise degraded waters. Sustainable use of low quality waters requires soil, water, and crop management practices that optimize crop production while minimizing the degradation of groundwater resources by agricultural contaminants such as salts and nutrients. Advanced computer simulation models and decision-support tools are needed to evaluate the long term impacts of irrigation and land management practices on regional groundwater quality. The project is organized around short term and long term objectives. Looking to the near term (Objective 1), we will evaluate and adapt existing modeling strategies for incorporating vadose zone processes into regional simulations, identify parsimonious modeling techniques, assess uncertainties associated with differing modeling approaches, and make calculations illustrating uncertainties associated with modeling various management scenarios. In the longer term, we anticipate that increased computing power and improved sensing technologies and land use data will eventually permit significantly higher resolution simulations than is currently possible. Toward that end (Objective 2), we will investigate the use of remote sensing and other data to estimate soil properties at a higher resolution, and will develop improved models for coupled overland and subsurface transport which will be able take advantage of high resolution topographic data. The project should lead to recommendations for developing modeling components of basin-scale salinity, nutrient management plans, and to improve capabilities for predicting the long-term effects of management decisions on soil and groundwater quality. 3.Progress Report: This report documents progress for Project 5310-61000-015-00D, which started in February 2012 and continues research from terminated Project 5310-61000-014-00D, which was entitled “Improved Knowledge and Modeling of Water Flow and Chemical Transport Processes in Irrigated Soils”. Work on Objective 1 and Objective 2.2 began in February 2012. Under Objective 1, a system is being developed which will, for a specified geolocation, provide parameter probability distributions for soil parameters that are used in hydrologic model calculations. The system works by retrieving for the specified location USDA-NRCS soil survey data (SSURGO) and processing the data to obtain the required parameter distributions. By focusing on parameter distributions (rather than single parameter values), it will be possible to evaluate uncertainty in model predictions. Data to be used in these evaluations are described in the accomplishment statement of the final annual report for the terminated project 5310-61000-014-00D. Under Objective 2.2, work has begun on a coupled surface and subsurface flow and transport model. A system of model equations has been developed and it is being solved and evaluated using a multi-physics programming environment. A critical SY vacancy has delayed initiation of work on Objective 2.1.