Introduction

• Hydrology is defined as the discipline dealing with the properties, occurrence, distribution and movement of water on and beneath the surface of the land.
• Domains of hydrology include hydrometeorology, surface hydrology, hydrogeology, drainage basin management and water quality, where water plays the central role.

Hydrologic cycle/ Water cycle

• The central theme of hydrology is that water moves through the Earth through different pathways and at different rates.
• The most vivid image of this is in the evaporation of water from the ocean, which forms clouds.
• These clouds drift over the land and produce rain.
• The rainwater flows into lakes, rivers, or aquifers.
• The water in lakes, rivers, and aquifers then either evaporates back to the atmosphere or eventually flows back to the ocean, completing a cycle.

Components of Hydrologic cycle

1) Precipitation- rain: droplets > 0.5 mm diameter, drizzle <0.5 mm diameter, dew

2) Evapotranspiration: Evapotranspiration is the sum of evaporation from the land surface plus transpiration from plants

3) Runoff: Runoff can be described as the part of the water cycle that flows over land as surface water instead of being absorbed into groundwater or evaporating

4) Percolation: The soil percolation rate indicates how quickly water moves through soil and helps evaluate the ability of the soil to absorb and treat effluent

5) Infiltration: Infiltration is the process by which water on the ground surface enters the soil.