Groundwater Groundwater • • Groundwater ---> water stored in open spaces Groundwater ---> water stored in open spaces within underground rocks and sediments. within underground rocks and sediments. • • More than 65% of the groundwater used in the More than 65% of the groundwater used in the U.S. is attributable to agricultural needs. U.S. is attributable to agricultural needs. • • Demand has depleted the supply of groundwater in many places. in many places. > > New sources must be found; New sources must be found; > > Existing resources must be protected. Existing resources must be protected. > > A non-renewable resource in most places A non-renewable resource in most places • • Capable of shaping the landscape ( Capable of shaping the landscape ( Karst ) > > erosion and deposition of silt, clay, and dissolved materials erosion and deposition of silt, clay, and dissolved materials caves, sinkholes, and speleothems caves, sinkholes, and speleothems > > forms forms

Porosity & Permeability Porosity & Permeability • • Porosity Porosity > > that portion of the material's volume which is that portion of the material's volume which is pore spaces. pore spaces. > > i.e. i.e. the amount of empty space in rock or sediments • • Permeability Permeability > > the ability of a material to transmit fluids. the ability of a material to transmit fluids. > i.e. the degree of interconnectedness of the degree of interconnectedness of > i.e. the empty space the empty space

Porosity affected by particle size, particle shape, sorting of particles, amount of material cementing the grains together, fractures in materials, and internal arrangement of particles

Typical Porosity values

Permeability Permeability • • Materials must have both Porosity & Permeability Permeability to allow water to move to allow water to move through it! through it! • • Styrofoam has high porosity Styrofoam has high porosity > > this makes it a good insulator this makes it a good insulator - - keeps things hot or cold keeps things hot or cold • • Styrofoam has low permeability Styrofoam has low permeability > > allows you to keep liquids in it. allows you to keep liquids in it. > > clay has high porosity, but low clay has high porosity, but low permeability-> little water movement permeability-> little water movement through clay through clay

Materials with high porosity AND high permeability Unlithified (sediment) Sand Gravel Lithified (rock) Sandstone fractured limestone fractured granites

Aquifers and Aquicludes Aquifers and Aquicludes • • Aquifer Aquifer > > a a porous porous & & permeable permeable layer capable of layer capable of transmitting groundwater. transmitting groundwater. - - well rounded, well sorted, sand & gravel. well rounded, well sorted, sand & gravel. • • Aquiclude Aquiclude (or (or Aquitard Aquitard ) ) > > an an impermeable impermeable layer preventing layer preventing movement of groundwater. movement of groundwater. - - Shales, unfractured Ign & Mm Rxs. Shales, unfractured Ign & Mm rock, crystalline limestone.

Water Table the boundary between saturated (filled) vs unsaturated (unfilled) pore spaces In unconfined aquifer systems only

Confined systems Groundwater is confined between impermeable layers ( layers ( Aquicludes Aquicludes or or Aquitards Aquitards ) and builds up ) and builds up hydrostatic pressure. hydrostatic pressure. Water rises to that pressure surface once a well is Water rises to that pressure surface once a well is drilled. drilled. Many rural communities utilize this principle with Many rural communities utilize this principle with water towers as the municipal water supply. water towers as the municipal water supply.

Modifications & Effects on Modifications & Effects on Groundwater Currently ~20-30% of the water used in the U.S. is • • groundwater. Much higher in some places • • Modifications will.... Modifications will.... > > 1) lower the water table; 1) lower the water table; > > 2) decrease hydrostatic pressure; 2) decrease hydrostatic pressure; > > 3) allow saltwater encroachment; 3) allow saltwater encroachment; > > 4) cause subsidence; 4) cause subsidence; > > 5) allow contamination of the groundwater. 5) allow contamination of the groundwater.

Salt Water Intrusion

Ground water related subsidence ground levels have decreased in elevation due to water withdrawal from aquifers

Contamination issues-1: Septic tanks

Contamination issues-2: landfills

Wetlands and groundwater Many wetland areas are tied to water by location e.g., riverine, downslope, lake/sea margins, etc. Most wetlands are fed in part by groundwater and surface water e.g., fens, marshes, swamps Thus groundwater serves to stabilize water levels over longer term, feeding water to the system over extended dry periods, and providing mineralogical nutrients to the biological and geological systems. Bogs are a unique case, as they are not typically influenced by groundwater outside the perimeter of the wetland area, yet still have groundwater within them.

Types of Wetlands Marshes – areas of land that are frequently to constantly inundated and are characterized by soft stemmed emergent vegetation Swamps -areas of land that are frequently to constantly inundated and are characterized by woody emergent vegetation Bogs – a wetland fed almost exclusively by precipitation characterized by excessive peat deposits, acidic conditions, are somewhat nutrient poor, and have a sphagnum moss surface carpet. Fens – Peat forming wetlands fed by many sources of water/nutrients. Nutrient rich, less acidic, and generally more diverse than Bogs

Swamp

Marsh

Bog

Bog- note the boardwalk

Fen

Hot groundwater-geysers and hot springs

Karst landscapes Created by groundwater and streams dissolving limestone pseudokarst involves dissolving non-carbonate rock Enlarges fractures and pore spaces as rock dissolves Increases flow of water through the system Triggers more dissolution of limestone.