fluid flow in rocks modelling

• Groundwater is the water retained in the pore space of rocks below the water table. 
• Water table is the surface separating unsaturated rock from saturated rock below. 
• Aquifers are bodies of porous and permeable rock capable of sorting lots of water. 
• Groundwater comes from rainwater, infiltrating soil and percolating downwards through pore spaces. 
• The water table follows the topography but with less relief and intersects ground surfaces (lakes, rivers and springs). The level may fluctuate due to seasons. 
• Aquicludes are beds that water cannot move through easily due to impermeability (clay and shale). 
• Aquitards are aquicludes that slowly transmit water. 
• Recharge zones are the areas that are open to the atmosphere to allow replenishment of water. 
• Unconfined - open to the atmosphere and recharged by rainwater, water would need to be pumped out of the aquifer. 
• Confined - surrounded by permeable rocks, groundwater held by hydrostatic pressure. Water is replenished via recharge zones. 
• Perched - sit above regional water table and are underlain by impermeable rock. 
• Potentiometric surface - imaginary surface where the groundwater rises under hydrostatic pressure. Highest point of water table in a confined aquifer. 
• Artesian well - hold water under hydrostatic pressure which rises up to potentiometric surface when pressure releases. If well is below this surface no pumps are needed. 
• Artesian basin - large synclinal confined aquifers. 
• Water in aquifers flows as a result of hydrostatic pressure. 
• Fluid motion is due to pressure differences - high to low or down hydraulic gradients. 
• Hydraulic gradient = difference in hydrostatic pressure / distance between points. 
• As pressure is dependent on hydrostatic head or height of water column gradient can be calculated by:

  • Hydraulic gradient = difference in height / distance 
• Darcy's law = 

  • Q = rate of flow 
  • K = hydraulic conductivity 
  • A = cross sectional area 
  • (ha-hb)/L = hydraulic gradient 
• Darcy's law is used to calculate flow rate, time of travel and arrival of pollution.