Location: Hydrology and Remote Sensing Laboratory
Project Number: 8042-13610-030-099-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Sep 15, 2025
End Date: Aug 19, 2027
Objective:
Design a watershed modeling approach to quantify groundwater residence time and nitrate-N (NO3-N) travel times from croplands to streams. The SWAT+ watershed modeling code will be used as the base model, due to its extensive use in the Conservation Effects Assessment Project (CEAP). A groundwater flow module (gwflow) for SWAT+ was recently created to simulate the storage and movement of groundwater in a physically-based, spatially-distributed manner, in connection with land surface features (soil, stream channels, reservoirs, wetlands, canals, irrigation, wetlands, floodplains). This module will be amended utilizing data collected in the watershed lag time project and various landscape data streams.
Approach:
The gwflow module will be amended to include the mass storage and transport of nitrate (NO3-N) in the aquifer system, using groundwater volumes and flow rates from the gwflow routines. The module will account for major spatial and temporal groundwater sources and sinks of NO3-N throughout the watershed, and loadings to/from land surface features such as soils, channels, reservoirs, and wetlands. The N transport routines will also include an algorithm that tracks N mass through the aquifer system and calculates total travel times from croplands (source) to stream (destination). The modified SWAT+ model code will then be applied to several watersheds with watershed lag time project data, where MESA is used as a temporal marker to indicate the age of water and elucidate dominant transport pathways. The water age estimates from the field data will be used to test the simulated transit times and water ages provided by the model. These comparisons will likely lead to additional changes in the gwflow N routines and will assist in providing targets for model calibration.