Modeling ground water flow in alluvial mountainous catchments on a watershed scale

Area of Science:

• Hydrogeology
• Environmental Modeling
• Water Resources Management

Background:

• Shallow unconfined alluvial aquifers are crucial for subsurface runoff in mountainous catchments but pose challenges for large-scale groundwater flow models.
• River basin scale models are essential for integrated water resources management and assessing climate change impacts on groundwater.
• Coarse model discretization in regional studies can conflict with natural aquifer geometries, impacting model accuracy.

Purpose of the Study:

• To develop and test an approach for adapting aquifer geometry to coarse model discretization in large mountainous catchments.
• To ensure numerical requirements of groundwater flow models align with natural system properties.
• To enhance the applicability of physically based groundwater models for river basin scale assessments.

Main Methods:

• Developed a modified concept from hydrological catchment drainage analysis to adapt aquifer geometry.
• Utilized MODFLOW to create a coarse groundwater flow model for the German-Austrian Upper Danube catchment.
• Tested the method by comparing a coarse model with a finely discretized model of the Ammer subcatchment.

Main Results:

• The developed approach successfully adapted the aquifer geometry to meet the numerical requirements of coarse model discretization.
• The adapted geometry respected cell width, thickness, gradients, and connectivity.
• Comparison with a finely discretized model demonstrated the applicability and efficiency of the new method.

Conclusions:

• The new approach effectively overcomes discrepancies between model discretization and natural aquifer geometry in large catchments.
• This method facilitates the use of physically based groundwater models at the river basin scale.
• The findings contribute to improved integrated water resources management and climate change impact studies.