Question

The hydrologic cycle is governed by which of the following equation?

• A. Bernoulli
• B. Dalton
• C. Continuity
• D. Darcy

Hint:

The heart of hydrology is the water balance equation: \( I - O = \Delta S \). This is simply the continuity equation applied to water. It's the fundamental accounting principle for the entire hydrologic cycle.

Answer 1

The Correct Option is C

Step 1: Define the Hydrologic Cycle. The hydrologic cycle describes the continuous movement of water on, above, and below the surface of the Earth. At any scale (from a small watershed to the entire globe), it can be viewed as a system with inputs, outputs, and changes in storage.
Step 2: Analyze the given equations/principles.
- Bernoulli's equation: Relates pressure, velocity, and elevation for a moving fluid; an energy conservation principle.
- Dalton's Law: Relates to partial pressures in a mixture of gases, relevant to evaporation.
- Continuity Equation: A mass balance equation. In hydrology, it is often called the water balance equation and is stated as: Inflow - Outflow = Change in Storage (\( I - O = \Delta S \)). This is the fundamental principle that governs the entire hydrologic cycle.
- Darcy's Law: Describes the flow of a fluid through a porous medium, relevant to groundwater flow.
Step 3: Identify the governing equation. While laws by Dalton and Darcy describe specific processes within the cycle, the overall cycle is governed by the principle of mass conservation, which is expressed by the Continuity Equation.