The importance of understanding the linkage between surface water and groundwater has increased over the last two decades. However, the hydrological connectivity between infiltration and redistribution processes in the vadose zone and the recharge of the aquifer still is not well understood. The body of the different chapters in this dissertation come together to provide important information on the mechanisms of water transport through the vadose zone and the effect that deep percolation from current irrigation practices in traditionally-irrigated valleys of northern New Mexico have on the recharge of the local aquifer. A combined field data and modeling approach was taken to investigate the mechanisms of water transport through the vadose zone and irrigation contributions to soil and aquifer recharge in a floodplain irrigated valley of northern New Mexico.

Water transport through the vadose zone and water table fluctuations were evaluated at the experimental plot and crop field scales. Expected aquifer recharge in response to irrigation percolation and canal seepage inputs was evaluated at the valley scale.

At the experimental plot scale, results showed low to moderate infiltration rates, relatively low levels of propagation of the wetting front, water flux, and shallow groundwater response in Fruitland sandy loam and Werlog clay loam soils as compared to Abiquiu-Peralta soil.

At the crop field scale, field measurement-based deep percolation below the root zone ranged from 2% to 89% of the total water applied, depending on antecedent soil water content and amount of irrigation. In general, deep percolation simulations by the RZWQM were in good agreement with field-measurement based deep percolation values in alfalfa but not in oat-wheatgrass crop fields. Water level rise in response to deep percolation was variable across fields and irrigations, ranging from 0.01 m to 0.8 m.

At the valley scale, aquifer recharge was estimated for a three-year period (2007 through 2009) and it remained at about 700 mm yr^-1. A seasonal water table rise was observed in response to canal seepage and irrigation percolation during all three years. Time of water table response varied across well locations, wells located near the river generally responded first, then near-canal and irrigated land wells, followed by dryland location wells.

Study results show that current irrigation practices in a traditionally-irrigated valley of northern New Mexico are directly related to the recharge of the shallow aquifer through deep percolation from irrigation and seepage from the main irrigation canal.