Rice farming in the Lower Colorado River basin of Texas, US, is a major economic engine and a major water consumer. The Lower Colorado River Authority (LCRA) and the San Antonio Water System (SAWS) sponsored a joint project from 2004 through 2009 to study the feasibility of developing and conserving water to provide sufficient water to farmers in the Lower Colorado River basin, while allowing transfer of water to the city of San Antonio. A major focus of the project was the development of a web-based rice water conservation analyzer (RiceWCA) to evaluate field- and regional-level costs, water savings, and yield benefit associated with implementing on-farm conservation measures, including precision leveling, multiple inlets, conservation tillage, lateral improvement, tailwater recovery, and a production system based on growing high-yielding water efficient cultivars. This paper describes the development and evaluation of the crop development and water balance components of RiceWCA. RiceWCA uses a phenology model to time water management events, including flushing and flush drainage for the main crop, and permanent flood, flood maintenance, and drainage before harvest for the main and ratoon crops. RiceWCA simulates daily water balance for each rice field within the Lower Colorado River basin, as affected by the degree of implementing different conservation measures. The water balance model includes site-specific estimation of soil saturation deficit, evapotranspiration, percolation, seepage, rainfall, irrigation, and tailwater. The water balance model was calibrated and verified using 2000 and 2002 weekly irrigation records for the Lakeside and Gulf Coast irrigation districts, and validated using 2001, 2003, and 2004 weekly irrigation records. Tailwater recovery offers the largest water saving, followed by adoption of high-yielding cultivars, multiple inlet systems, precision leveling, and conservation tillage. Water saving from lateral improvement varies depending on the extent of existing laterals.
