What is the Hydrologic Cycle Definition
The classic hydrologic cycle shows the relationship between surface and groundwater and the constant movement of water in the environment. Moisture on the earthâs surface evaporates to form clouds, which deposit precipitation on land in the form of rain, snow, or hail. That moisture is absorbed by the soil and percolates into the ground.When the precipitation rate exceeds infiltration, overland flow occurs and streams, rivers and reservoirs receive the runoff. Water from surface sources will reach its final destination in the ocean, where the hydrologic cycle begins again with the evaporation process. The hydrologic cycle is affected by land features and ocean currents that determine changing weather patterns and deliver precipitation unevenly, with some areas getting ample rainfall and others getting little.
Sources of water contamination occur throughout the hydrologic cycle. Contaminants can be diluted, concentrated, or transported through the cycle and affect drinking water.The objective of source water quality management is to minimize (or eliminate, if possible) contaminant input within a watershed basin, the geographic area that drains to the source water intake. Water sources can be affected by both chronic and acute water quality impacts. Chronic impacts may be subtle and persist over an extended period of time, resulting in a gradual deterioration of the source water. An example of a chronic impact is increased human activity within a watershed, producing increased nutrient levels in a lake or reservoir and accelerated eutrophication. An acute impact occurs as an incident, like an oil spill, which can be remedied quickly. The water quality manager needs to appreciate all source-water impacts in order to respond at the plant or on the watershed to minimize the impact on drinking water quality. The protection of water quality may require taking a treatment plant out of service for a time or installing additional treatments to meet the changing quality in the source water.
The geology within a watershed basin influences source quality, as do seasonal flow variations and climate. Microbiological activity in lakes and reservoirs can affect water quality. A variety of human activities can introduce pathogens and increase nutrient levels contributing to eutrophication of lakes and reservoirs.