Subsurface Water: Storage, Movement, and Management

Subsurface Water: Introduction and Soil Properties

• Recap of Water Cycle: The previous lecture covered the water cycle, starting with the atmosphere (evapotranspiration) and moving to the surface. This lecture focuses on the subsurface.

• Significance of Subsurface Water: Subsurface water accounts for approximately $25\%$ of excess water globally. Understanding its storage and movement is crucial.

Soil and Water Storage Capabilities

• Soil as the First Contact: As water permeates downward into the Earth, soil is the first material it encounters.

• Soil Analogy: Soil can be thought of as a sponge for holding water. It contains empty spaces, or 'nooks and crannies,' which can be filled with either water or air.

Key Terms for Water Storage Capacity

1. Porosity:

   • Definition: The volume of void spaces (empty spaces) within a soil or rock sample relative to its total volume.

   • Formula: $\text{Porosity} = \frac{\text{Volume of Voids}}{\text{Total Volume}}$

   • Implication: High porosity means a large amount of empty space, allowing the soil to hold a significant volume of water. Low porosity indicates less empty space, thus less water storage capacity.

   • Analogy: Controls the