A Model for Simulating Soil-Zone Processes at the Regional Scale

The soil zone has been described as the upper most region of the vadose zone where plant and soil processes enhance storage and permeability, providing a fast pathway for water and solutes to streams. The soil zone connects the land surface to the deeper unsaturated and saturated zones. Modeling of soil-zone processes has been used to gain understanding of watershed hydrologic processes. Currently MODFLOW does not simulate dynamic near-surface hydrologic processes such as, infiltration, hortonian runoff, dunnian runoff, and return flow. The Soil-Zone Flow Package (SZF) for MODFLOW is being developed to address these near-surface components for simulating watershed processes in the context of basin-scale groundwater-flow modeling. especially those processes that partition rainfall into evapotranspiration, runoff, and deep percolation. In a series of test simulations, Richards' equation (RE) was compared with MODFLOW-SZF. Across a range of hydraulic conductivities and applied precipitation rates, MODFLOW-SZF achieved a good infiltration and interflow solution (0.014-0.052 RMSE) with only 6 grid cells and 0.11 seconds computation time compared to the 6250 grid cells and 40 seconds of computation time required for a stable solution to RE. MODFLOW-SZF solutions had negligible errors due to grid effects (<0.01 RMSE) however, RE solutions were sensitive to grid resolution (up to 0.12 RMSE). Errors associated with using the groundwater flow equation to represent soil-zone flow instead of RE were much lower (<0.052 RMSE) than the errors caused by grid effects in RE (0.12 RMSE, 0.5 m cell). This research suggests that the SZF Package will be an effective tool for efficiently representing soil-zone processes at the basin scale.

Level thesis:degree_level

Master's Degree

Year dc:date.issued

2011

Author dc:creator

• Henson, Wesley R.

Advisor dc:contributor.advisor

• Niswonger, Richard G.

Committee members dc:contributor.committeemember

• Prudic, David E.
• Pohll, Greg

• Infiltration
• Interflow
• MODFLOW
• Recharge
• Soil-Zone
• Stormflow

Statement dc:rights

• In Copyright(All Rights Reserved)

Handle dc:identifier.uri

http://hdl.handle.net/11714/3847

OAI identifier oai:identifier

oai:scholarwolf.unr.edu:11714/3847