The hydrologic cycle, commonly referred to as the water cycle, is closely related to the interrelationship of the biotic and physical environment. Man can not survive without water nor would we have lakes, ponds or streams. The water cycle is continuous movement of water from the atmosphere to the earth and from the earth back to the atmosphere. The water that moves from the atmosphere to the earth is called precipitation. However, the water will return to the atmosphere through evaporation.
During a rain storm, some of the rainwater evaporates as it falls to the ground. But most of the rainwater runs along the surface of the ground and travels to the rivers, streams and ponds. The water running along the surface is known as runoff water. Large amounts of precipitation also enter the soil to become ground water. This water can reach a pond, lake or ocean through springs or underground streams; or it may move upward through the soil during dry periods and pass again into the atmosphere as water vapor. The warm air that rises through the atmosphere contains tiny droplets of water. This water cools as it climbs higher into the atmosphere causing the water vapor to condense into droplets of water which forms clouds. The droplets collect to form drops that eventually fall from the clouds as rain. If the water vapor condenses at a temperature below the freezing point of water, then snow is formed.
Ground water is also a part of the water cycle. The ground holds and receives water from precipitation. However, some of the water moves downward into subsoil and fills the spaces around the rock particles. The upper level of the soil where it is saturated with water is known as the water table. If the soil is over saturated with water, the water will run off the surface instead of penetrating into the soil. The depth of the water table depends on the amount of precipitation, the nature of the rock layer under the soil, the proximity of large bodies of water, and the condition of the soil surface for receiving water.
