# Model Development

The “MODFLOW 6” software released in 2017 allows simulation of both regional and local hydrologic systems simultaneously, as illustrated for the large-scale and inset model domains.

The USGS is at the forefront of devising new techniques and computer software to solve practical problems in the study of water resources. Predictive models are needed to make informed decisions in many emerging areas related to the effects of water resources development. New models and methods enhance all USGS water programs. State and local governments as well as scientists and engineers in the private sector regularly use USGS models as an integral part of their work.

Numerical simulation software is critical to the water resource studies of the USGS Water Availability and Use Science Program (WAUSP). Software developed and maintained by the USGS such as the Precipitation Runoff Modeling System (PRMS), Water Balance Model (WBM), the International River Interface Cooperative (iRIC) software, Soil-Water Balance (SWB), MODFLOW, GSFLOW, PEST++, and Groundwater Toolbox are integral to WAUSP studies and are required to effectively forecast future conditions. Moreover, this software is used in studies across the USGS.

WAUSP supports modeling software development to:

• simulate groundwater and surface-water flow with computer codes such as PRMS, MODFLOW, GSFLOW, and iRIC;
• allow the creation and viewing of groundwater and surface-water models with graphical user interfaces such as ModelMuse and web applications such as GWWebFlow;
• automate the fine-tuning (calibration) of models to real-world data with PEST++, pyEMU, and Luca;
• separate the primary components of streamflow into runoff from the land surface and groundwater discharge from adjoining aquifers with the Groundwater Toolbox;
• store and retrieve subsurface information with the GeoLog Locator web service;
• estimate groundwater recharge with the Soil-Water Balance (SWB) model;
• analyze temperature, flowmeter, and geophysical data.

In 2018, support for model development totaled approximately $2.3M, of which$1.095M was designated as groundwater model development, maintenance, and sustainability research and development to advance water science.

Recent highlights:

• In 2017, the USGS released the newest version of its flagship hydrologic simulation code MODFLOW. Named “MODFLOW 6,” the code has been redesigned to provide greater flexibility to simulate regional- and local-scale groundwater systems simultaneously and for improved integration with other types of watershed, chemical-transport, and water-operations models. During 2019, MODFLOW 6 will be expanded to include simulation of land subsidence and compaction and simulation of dissolved constituents in groundwater systems.

• In 2018, the USGS released the Surface-Water Toolbox, which is a graphical and mapping interface for analysis of hydrologic data developed in collaboration with the US Environmental Protection Agency. The software directly accesses streamflow data from the USGS National Water Information System and provides many tools for statistical analysis of the data. During 2019, the Surface-Water and Groundwater Toolboxes will be integrated to provide a single, uniform platform for groundwater and surface-water analyses.

• During 2018, WAUSP funded the development of a spatial framework to support regional and national-scale modeling across the continental United States. The uniform grid of 1-kilometer square cells is already being used in ongoing regional studies of the Nation’s groundwater resources funded through WAUSP and will support collaboration with other Federal agencies working on national-domain water models.

• During 2019, work will continue to make USGS data more accessible to water-resource managers, scientists, and the public through web applications to support viewing of groundwater-modeling results (GWWebFlow) and retrieval of borehole geophysical logs (USGS GeoLog Locator).

• A number of updates to the PRMS  model code have been made including modules for dynamic parameters, water use, improved stream and lake flow routing, and updates to surface-depression storage simulation.