The crop/land use package, referred to, as DYNAG was developed to handle agricultural activities and their impact on saturated groundwater flow. In many groundwater basins with extensive agricultural activity accurate groundwater pumping records are not available making model development and calibration difficult. To address this issue DYNAG was developed. The principal feature of DYNAG is the ability to compute groundwater pumping based on irrigation requirements of crops/land use patterns. The package uses some of the routines all ready available in the unsaturated DYNSOIL program.
DYNAG handles three types of land uses agricultural, urban and natural. The user may specify agricultural and urban land use by element. Additional information that is required is the evapotranspiration rates for the crops represented in the agricultural areas, and the irrigation efficiency. The model then calculates the net water demand of the element based on the percent of the element that is agricultural, the evapotranspiration rate and irrigation efficiency. The groundwater pumping required to meet this demand is then calculated as the net of the agricultural water demand, recharge due to precipitation, and applied irrigation (for example from surface water sources). DYNAG can be linked with the DYNRIVER package so river diversions can be linked with irrigation activities.