SPAW

The SPAW model is a daily hydrologic budget model for agricultural fields. It also includes a second routine for daily water budgets of inundated ponds and wetlands, which utilizes the field hydrology as the watershed. A hydrologic budget such as being simulated for either an agricultural field or pond requires the definition of a hydrologic system and associated processes. The field budget utilizes a one-dimensional vertical system beginning above the plant canopy and proceeding downward into the soil profile a sufficient depth to represent the complete root penetration and subsurface hydrologic processes (lateral soil water flow is not included). The pond hydrologic system is for a water holding depression with external inputs from a watershed and other water sources and outflow by spillways, pumps or seepage. The following schematics describe the field and pond hydrologic systems and each major hydrologic process impacting water movement across the system boundaries and within the systems. These are the systems and processes represented mathematically in the field and pond hydrologic simulation model and become the basis for analytical hydrologic budgets.