A vadose zone field study: Subsurface tile drainage, hydrology, and variablity

Vadose zone hydrology is a complex and challenging field of study. Quantification of a highly variable dynamic system demands extensive monitoring of many variables. This field project consisted of multiple studies employing experimental field equipment designed to maximize the number of spatial and temporal measurement locations with minimal cost. The equipment maintenance and subsequent data handling proved to be a large time commitment. Furthermore, this project demonstrated and highlighted areas where further instrument development is required to properly support the pursuit of science in the vadose zone.;The construction and application of vadose zone monitoring equipment is reported herein, as well as supporting studies investigating the hydrology and soil behavior of four replicate (27m x 30m) field plots. A chemical tracer study was also performed during the same period. The hydrology at the field site is dominated by tile drainage, thus the supporting studies revolve around this specialized drainage condition.;Results include an analysis of the water balance components over periods bounded with similar satiated moisture storage conditions. The field site was found to have an excess storage during most periods which is partially explained by the atmospheric ET models underpredicting evaporation during energy limiting periods. A winter flow period was marked with a large loss of water to tile flow possibly the result of off site regional groundwater contributions. The piezometer analysis showed the difference in water table behavior between undrained and drained conditions. Cluster analysis showed more variability for the drained than the undrained condition, and the water table fell more rapidly after a rainfall event for the drained condition. Piezometer measurements and tile flow were found to be highly correlated despite the tile flow variability between the replicate plots. The results of the tracer experiments showed that tracer was not recovered at detectible levels. This indicated that for this soil and variable natural rainfall, higher concentrations of tracer need to be applied to find the tracers in a diffuse tile flow effluent.