Modified DRAINMOD for random and irregular networks (MODRAIN)

Randomly spaced tile drainage systems are the norm rather than the exception in Central Illinois and many parts of the Midwest. However, the drainage equations used in most models are based on the assumption of parallel drainage systems. These models are used with random systems by replacing the spacing parameter by the effective region of influence of a single tile. This paper describes another approach to modeling random systems, in which equations that are based on the assumption of parallel tiles are replaced by equations that have been specifically developed for randomly spaced subsurface drainage systems. These equations were incorporated as a random system option into an old (1985) version of DRAINMOD. A simulation study using the revised model with 4 to 6 years of weather data from Urbana, IL, and 4 to 6 years of flow data from Little Vermilion River Watershed sites, determined the applicability of the new option. The modified model has the potential to explain drainage patterns more precisely when there is random tile spacing without affecting the performance of the model with parallel tile systems.