Hydrogeology vs Hydrology: Understanding the Difference

Hydrogeology vs. Hydrology

• Hydrogeology is the branch of geology that deals with the occurrence, distribution, and effect of groundwater.
• Hydrology is the science of water occurrence, movement, and transport.

Hydrologic Cycle

• The hydrologic cycle is the natural process of recycling water from the atmosphere to the earth and back to the atmosphere again.
• It begins with evaporation, where water rises into the sky from open bodies of water and near-surface soil.
• Water in the sky eventually falls to the earth as precipitation (sleet, hail, snow, rain, dew).
• Precipitation that falls onto land becomes the source of all surface water.
• A significant portion of surface water soaks into the ground, recharging groundwater.

Processes in Hydrologic Cycle

• Evaporation: water rises into the sky from open bodies of water and near-surface soil.
• Condensation: water vapor in the atmosphere cools and turns into liquid or ice.
• Precipitation: any form of solid or liquid water that falls from the atmosphere to the earth's surface.
• Transpiration (Biological Processes): plants draw water out of the ground through their roots.
• Interflow: water infiltrated but not below the water table.
• Groundwater flow: water infiltrated and below the water table.
• Baseflow: groundwater flow that reaches a stream.
• Overland flow: water on the surface.

Precipitation

• Precipitation is the single strongest variable driving hydrologic processes.
• It is formed by water vapor in the atmosphere.
• Causes of precipitation include:
• Frontal precipitation: occurs when warm or light air mass meets a cold or heavy air mass.
• Convective precipitation: air expands when heated by solar energy and becomes lighter than the air around it.
• Orographic precipitation: air currents force air masses to rise over hills and mountains.

Hillslope Hydrology

• Runoff processes include:
• Horton overland flow
• Subsurface stormflow
• Return flow
• Groundwater flow
• Many processes occur simultaneously, and shifts can occur between processes in space and time.
• Antecedent wetness conditions are important, and watershed characteristics play a central role.

Runoff Generation

• Horton overland flow occurs when rainfall intensity exceeds infiltration capacity.
• It was once thought to be the only mechanism of runoff generation.
• Subsequent work showed the role of partial source area, where saturation overland flow is produced.

Subsurface Stormflow

• Lateral flow through soil above conductivity contrast.
• Consists of both slower matrix flow and faster macropore flow.

Saturation Overland Flow

• Direct rainfall onto saturated areas.
• Return flow from saturated soils in topographic lows and along valley.