Surface + Groundwater

• Surface water


  Water above Earth's surface, such as streams, rivers, and lakes
• Groundwater


  Water that drains through the soil and collects underground in rock and sediment
• Most drinking water comes from groundwater supplies in the water table
• How water moves on Earth's surface

  1. Precipitation

  2. Runoff - water flowing down slope along Earth's surface
• Factors that affect runoff

  • Vegetation
  • Rate of precipitation
  • Soil composition
  • Slope
• Tributary


  A smaller stream that feeds into a river and eventually a river system
• River system


  A network of streams and rivers that drains an area of its runoff
• Watershed


  The area of land where all of the water that is under it or drains off of it goes into the same location
• How watersheds are separated

  • By a ridge or an area of higher ground called a divide
• Precipitation that falls on one side of a divide enters one watershed, not the other
• Natural events and human activity can affect watersheds
• Gradient


  A measure of the change in elevation over a certain distance (slope)
• The higher the gradient, the faster the water moves and the more energy it has to erode rock and soil
• Stream load


  Materials carried by a stream
• Streams with high flow carry a larger stream load
• Porosity


  The percentage of rock or sediment that consists of voids or openings
• Permeability


  The capacity of a rock to transmit fluid through pores and fractures
• Groundwater movement through pores and fractures is relatively slow compared to flow of water in surface streams
• Aquifer


  A body of porous rocks that allows water to saturate and easily flow through
• Unconfined aquifer


  • Has a water table, and is only partly filled with water
  • Rapidly recharged by precipitation infiltrating down to the saturated zone
• Confined aquifer


  • Completely filled with water under pressure
  • Separated from surface by impermeable confining layer
  • Very slowly recharged
• Spring


  A place where water flows naturally from rock or sediment onto the ground surface
• The rate of groundwater flow is very slow compared to surface water
• In a typical home, about 50% of all water used is for washing clothes, bathing, washing dishes, and flushing toilets. About 33% is used to water lawns and gardens. Only the rest is used for drinking, cooking and washing hands
• Gaining streams


  Receive water from the saturated zone
• Losing streams


  Lose water to the saturated zone
• Threats to water supply

  • Overuse
  • Subsidence
  • Pollution
• By 2025, three billion people will likely lack access to clean water
• The Ogallala Aquifer, which irrigates the Great Plains, is being depleted much faster than it can recharge
• Groundwater and surface water are inextricably related through the hydrologic (or water) cycle. Extracting groundwater can impact surface water resources and vice versa