MODFLOW-NWT and MT3D-USGS models for appraising parameter sensitivity and other controlling factors in a synthetic watershed accounting for variably-saturated flow processes

A 3-dimensional (3D) synthetic model, using MODFLOW-NWT and MT3D-USGS, explores the new unsaturated zone heat transport capabilities in MT3D-USGS. Model simulations were used to explore various parameter sensitivities and unsaturated zone thicknesses and their impact on heat transport as water enters the subsurface as infiltration, flows through the unsaturated zone to the water table, and eventually exits the groundwater system as discharge to surface-water bodies. The 3D-model is patterned after a real-world watershed located in a region with a temperate, humid climate. Twenty-seven model simulations are included in this data release with the primary distinction between them the thickness of the unsaturated zone. Most model simulations either have a moderately think unsaturated zone or thick unsaturated zone. A small subset of model simulations do not simulate the downward movement of infiltration through the unsaturated zone but apply infiltration directly to the water table using the recharge (RCH) package. Twelve sensitivity run are included in the data release to help illuminate which parameters are important when engaged in heat transport simulation. This investigation begins to explore the impacts of a warming climate on groundwater temperature and ultimately on the temperature of groundwater discharge back to surface-water bodies. The synthetic model evaluated is a necessary first step to real-world applications that are more complicated by nature's heterogeneity. Temperatures simulated by MT3D-USGS were previously verified by comparing output from detailed 1-dimensional models to VS2DH output (https://doi.org/10.1111/gwat.13256). This USGS data release contains the input and output data files for the model simulations described in the associated journal article (https://doi.org/10.3390/w14233883). Model input files were developed from published information; no new datasets were collected as part of the modeling study associated with this data release. Details on data input sources and on processing of input and output files are documented in the associated journal article.