The letters following each Review Question refer to the corresponding Learning Objective from the Chapter Opener. What is a water table, and what factors affect its level? What factors affect the flow direction of the water below the water table? (C)

A water table is the upper surface of the zone of saturation in the ground, where the pores and fractures in soil, sediment, and rock are soaked with water. It separates the zone of aeration above, which contains air and water, and the zone of saturation below, where groundwater is found.

There are several factors that influence the water table level: 1. Precipitation: Higher precipitation levels can raise the water table, while lower precipitation levels can lower it. 2. Evapotranspiration: Evapotranspiration is the combined process of evaporation (water turning into vapor) and transpiration (water released by plants). Higher evapotranspiration can lower the water table, while lower evapotranspiration can raise it. 3. Human activities: Groundwater withdrawals for agriculture, industry, and domestic purposes can also affect the water table level. Excessive groundwater extraction can cause the water table to drop. 4. Geology and topography: The type of soil and rock in an area can determine how water moves through the ground and affect the water table level. Steeper slopes can cause water to flow faster and lead to lower water tables.

The flow direction of water below the water table can be influenced by the following factors: 1. Topography: The land surface directly influences the subsurface flow of water. Water will generally flow from higher elevations to lower elevations. 2. Geology and soil type: Permeable materials, such as sand and gravel, allow water to flow easily, while less permeable materials, such as clay, can hinder movement. The presence of fractures in bedrock also affects flow direction. 3. Hydraulic gradient: The difference in groundwater elevation between two points divided by the distance between the points determines the hydraulic gradient. Steeper gradients result in faster flow rates. 4. Human activities: Pumping of groundwater for various purposes can create artificial gradients, altering the natural flow direction of water below the water table.