Hydrology & ClimatologyHydrology & Climatology (including Geohydrology)(including Geohydrology)

Louisiana Department of Environmental QualityLouisiana Department of Environmental Quality

2010 Envirothon Training2010 Envirothon Training

The Hydrologic CycleThe Hydrologic Cycle

Consists of inflows, outflows, and storage

What is Groundwater?What is Groundwater?Any water beneath the ground surface.

Groundwater is stored in aquifers.

What is an Aquifer?What is an Aquifer? A water-bearing stratum (or layer) of A water-bearing stratum (or layer) of sand and/or gravel that yields significant sand and/or gravel that yields significant

quantities of water to wells.quantities of water to wells.

Groundwater 101Groundwater 101

Vadose Zone – water partially fills pore spacesSaturated Zone - all pores are filled; water table is upper boundary

Porosity & PermeabilityPorosity is the percentage of a material occupied by void space or “pores.”

Permeability is a measure of the interconnectedness of the pore space allowing the material to transmit water.

The rate at which a material transmits water depends on its total porosity and the size of the interconnections between voids (permeability).

Aquifers – gravel, sandAquitards (impede flow) - clay

Aquifers

Surface Extent of Louisiana’s Aquifers and Aquifer Systems

**Aquifers in Southeastern Louisiana collectively called Southern Hills Aquifer System

**

Cross Section Example

-Identify recharge areas-Where are the aquifers confined and unconfined?

Drawdown

Understanding drawdown/cone of depression is important to:•Ensure continuous supply of water (avoid “dry wells”)•Management of overlying land area (vulnerability)•Identify source of ground water (water once discharging to a stream may now be pulled into well)

Impact of Pumping on Natural Ground Water Flow

•Strategic Placement of wells•Design of appropriate pumping rates & frequencies•Manipulate ground water flow

Groundwater - Surface Water Interaction

Gaining Stream - Altitude of water table higher than altitude of stream-water surface -- groundwater discharges to stream

Losing Stream - Altitude of water table lower than altitude of stream-water surface -- surface water recharges groundwater

Groundwater Recharge & Discharge

Recharge– - Infiltration– - Losing Streams– - Artificial

Discharge– - Springs– - Gaining Streams– - Pumping wells– - Flowing artesian wells

Effects of Groundwater Withdrawal on Surface Water

Groundwater discharges to stream under natural conditions

Pumping well at rate of Q1 intercepts some of groundwater that would have discharged to stream

Pumping well at rate of Q2 intercepts additional water and draws water from stream (Q2 > Q1)**Stream quality affects groundwater quality

Impacts of Global WarmingChanges in groundwater recharge resulting

from changes in precipitation and temperatureMore severe and longer lasting droughts

which could lead to overdraft and saltwater intrusion

Possible increased demandSurficial aquifers most sensitiveAffects energy use and production