Groundwater level

• groundwater: water below groundwater table

  • positive pressure
• soil moisture: water above groundwater table

  • negative pressure
• groundwater level tubes used to measure groundwater levels

  • results show groundwater level with respect to reference level
• hydraulic head (H): water column height

  elevation head (z): elevation of water droplet compared to certain reference level

  • reference level is sea level (elevation head is 0 at sea level)

  pressure head (h): local pressure measured with pressure meter

  • reference level is atmospheric pressure (pressure head is 0 at atmospheric pressure)
• hydraulic head: H = h + z

  • water flows from high H to low H
  • the larger the H difference, the faster the flow velocity
  • water continues to move along gradient until H1 = H2
• unsaturated zone = combination of water, soil and air (gradual decrease in air further underground)
• saturated zone = pores between soil are entirely filled with water due to capillary rise
• differences in hydraulic heads cause groundwater flow
• groundwater class is combination of AHG and ALG

  • AHG: average of HG3 (mean of 3 highest groundwater levels in hydrological year) for a period of > 8 years
  • ALG: average of LG3 (mean of 3 lowest groundwater levels in hydrological year) for period of > 8 years
  • traditionally groundwater levels measured every two weeks but recently groundwater level tubes are equipped with electronic pressure meters which allow continuous measurement
• groundwater level distance below soil surface is important for interaction with vegetation (root water uptake) and surface water
• main force of groundwater flow is solar energy

  • leads to evaporation of water at one location while precipitation is formed and falls at different location