RESOURCES: WATER, SOIL, MINERAL & ROCK, AND ENERGY

• Resources necessary to human life and civilization

  • Water
  • Soil
  • Mineral & Rock
  • Energy
• Most of the fresh water is locked up as ice, mainly in the large polar ice caps. Even the ground water beneath continental surfaces is not all fresh.
• The need for restraint in our use of fresh water is a must.
• Geologically, water is a renewable resource, but local supplies may be inadequate in the short term.
• Porosity


  The proportion of void space in the material (holes or cracks), unfilled by solid material, within or between individual mineral grains and is a measure of how much fluid the material can store
• Permeability


  A measure of how readily fluids pass through the material. It is related to the extent to which pores or cracks are interconnected, and to their size
• Porosity and permeability of geologic materials are both influenced by the shapes of mineral grains or rock fragments in the material, the range of grain sizes present, and the way in which the grains fit together.

  
• Saturated zone or phreatic zone


  A volume of rock or soil above the impermeable material that is water-saturated, in which water fills all the accessible pore space. Groundwater is the water in the saturated zone.

  
• Unsaturated zone or vadose zone

  Rock or soil above the saturated zone in which the pore spaces are filled partly with water, partly with air. The water in unsaturated soil is soil moisture, and is often an important factor in agricultural productivity.

  
• Subsurface water

  All of the water occupying pore space below the ground surface this includes ground water, soil moisture, and water in unsaturated rocks.

  
• Water table

  The top surface of the saturated zone, where the saturated zone is not confined by overlying impermeable rocks. The water table is not always below the ground surface.

  
• Recharge


  The processes of infiltration and migration or percolation by which ground water is replaced.

  
• Groundwater discharge

  Where ground water flows into a stream, escapes at the surface in a spring, or otherwise exits the aquifer.

  
• Aquifer


  A rock that holds enough water and transmits it rapidly enough to be useful as a source of water.

  
• Aquitard


  A rock that may store a considerable quantity of water, but in which water flow is slowed, or retarded; that is, its permeability is low, regardless of its porosity.

  
• Unconfined aquifer


  When the aquifer is directly overlain only by permeable rocks and soil. An unconfined aquifer may be recharged by infiltration over the whole area underlain by that aquifer.

  
• Confined aquifer


  Bounded above and below by low permeability rocks (aquitards). Water in a confined aquifer may be under considerable pressure from the adjacent rocks, or as a consequence of lateral differences in elevation within the aquifer.

  
• When ground water is pumped out from an aquifer

  The rate at which water flows in from surrounding rock to replace the extracted water is generally slower than the rate at which water is taken out.

  
• Cone of depression


  A circular lowering of the water table immediately around the well in an unconfined aquifer.

  
• When there are many closely spaced wells

  The cones of depression of adjacent wells may overlap, further lowering the water table between wells.

  
• If over a period of time, groundwater withdrawal rates consistently exceed recharge rates, the regional water table may drop.

  
• Groundwater flow rates are highly variable, but in many aquifers, they are of the order of only meters or tens of meters per year.

  
• Recharge of significant amounts of ground water, especially to confined aquifers with limited recharge areas, can thus require decades or centuries.

  
• Mining ground water

  The idea is not necessarily that the water will never be recharged but that the rate is so slow on the human timescale as to be insignificant.

  
• If the aquifer rocks are no longer saturated with water


  They may become compacted from the weight of overlying rocks, decreasing their porosity and permeability.

  
• As the rocks below compact and settle

  The ground surface itself may subside (collapse).
• In low-elevation coastal regions, the subsidence may lead to extensive flooding, as well as to increased rates of coastal erosion.

  
• In areas were surface had subsided , simple solutions such as pumping water back underground are unlikely to work. The rocks may have been permanently compacted.

  
• Salt water intrusion


  Another problem arising from groundwater use in coastal regions.
• If consumption of fresh ground water is more rapid

  The freshwater lens thins and the denser saline ground water laden with dissolved sodium chloride moves up to fill in pores emptied by removal of fresh water.

  
• Once a section of an aquifer becomes tainted with salt, it cannot readily be "made fresh" again.
• As urbanization modifies surface runoff and the ratio of runoff to infiltration

  It also influences groundwater hydrology.
• If impermeable cover is built over the recharge area of a confined aquifer

  Recharge can be considerably reduced, thus aggravating the water-supply situation.

  
• Filling in wetlands is a common way to provide more land for construction


  This practice can interfere with recharge, especially if surface runoff is rapid elsewhere in the area.
• In steeply sloping areas or those with low-permeability soils, well-planned construction that includes artificial recharge basins can aid in increasing groundwater recharge.

  
• Recharge basins are a partial solution to the problem of areas where groundwater use exceeds natural recharge rate, but they are effective only where there is surface runoff to catch, and they rely on precipitation.

  
• Karst

  Rock types such as carbonate rocks or beds of rock salt or gypsum, chemical sediments deposited in shallow seas, can develop sinkholes and other karst features due to dissolution by groundwater.

  
• Artificial Recharge Basins

  1. Catch surface runoff during high-runoff events

  2. Slow surface runoff

  
• Recharge basins are a partial solution to the problem of areas where groundwater use exceeds natural recharge rate, but they are effective only where there is surface runoff to catch, and they rely on precipitation

  
• Artificial recharge also involves diverting streams