Exploring Geological and Topographical Controls on Low Flows with Hydrogeological Models

Area of Science:

• Hydrology
• Hydrogeology
• Geomorphology

Background:

• Low-flow dynamics are crucial for water resource management and ecosystem health.
• Previous studies often oversimplify or neglect geological characteristics in low-flow assessments.
• Understanding catchment properties' influence on low flows is essential for accurate hydrological modeling.

Purpose of the Study:

• To systematically investigate the influence of catchment properties on low-flow dynamics using synthetic models.
• To assess the impact of bedrock and alluvial aquifer properties, hillslope, and river slope on catchment behavior.
• To develop a new index for quantifying bedrock influence on low flows.

Main Methods:

• Utilized 496 synthetic catchment models with varying geological and topographical parameters.
• Employed the physically based hydrogeological simulator HydroGeoSphere.
• Analyzed low-flow indicators such as Q95/Q50 and Q95 relative to mean net precipitation.

Main Results:

• Bedrock hydraulic conductivity (K_bedrock) was the dominant factor controlling low flows, explaining 60% of Q95/Q50 variance.
• Hillslope gradients and alluvial aquifer properties modulated low-flow dynamics for catchments with similar K_bedrock.
• The proposed dimensionless bedrock productivity index (BPI) explained 82% of the variance in Q95 relative to mean net precipitation for bedrock-only models.

Conclusions:

• Bedrock hydraulic conductivity and hillslope gradient are key determinants of catchment buffering capacity during low flows.
• Alluvial aquifers significantly influence low flows when bedrock productivity is limited.
• The study provides quantitative insights into geology-topography-low flow interrelations, challenging simplified hydrological models.