Ground Water and Runoff
I hope you have viewed the hydrologic cycle page first because groundwater and runoff were explained as being a natural part of the recycling process for water. The groundwater, also known as filtration, and the runoff both play significant roles in the hydrologic cycle. Some areas can produce more runoff even in smaller storms just due to the soil and other factors that could cause a flood. So, just to warn you storms are not always the major cause of floods. Note the geography around you. You may decide that you have not chosen the wisest place to live.
Water will infiltrate the ground and the soil will absorbed the water. Gravity will pull it down until the soil has reached it's saturation point. The level of water that has collected is called the water table. The level of this water table differs and will change depending on various factors. Periods of high precipitation and periods of low precipitation can affect the level at which the table is at. The area above the water level is called the unsaturated zone, while the area below is labeled the saturated zone and also called groundwater.
Image taken from: ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hyd/home.rxml
Groundwater in the unsaturated zone is contained in aquifers. Defining the water table in an aquifer depends on if the aquifer is enclosed or not. If it is not enclosed it is defined by the top of the aquifer, otherwise it is defined by the beginning of the bounding soil. Water is under pressure if it is in an enclosed area and this pressure may cause it to rise above the water table. When or if the water reaches the surface it is defined as a flowing artesian well. Water is refereed to as being discharged if it moves from an aquifer and enters a lake or stream. Likewise, if water entered an aquifer it would be referred to as recharge. Infiltration is common in recharging an aquifer while other types include receiving it from its source and an overlying aquifer.
Image taken from: ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hyd/home.rxml
When water does not infiltrate the ground and flows over the surface to a body of water it is designated surface runoff. This runoff usually flows downhill to lower elevations reaching above ground water sources such as rivers or streams. Any water, not matter from what direction, that reaches the same designation, like a pond or lake, is considered to be the same watershed. This runoff my have influencing factors before it reaches its destination. The runoff my pick up many contaminants, man made is one possibility, that contribute to its quality. After the destination is reached or if it is infiltrated into the soil its location remains key due to its quality. The understanding of the factors and the location determine were the quality water is located and how the contaminants are dispersed.
