Lecture 14 Flashcards
What is groundwater, and why is it important?
Water found in soil pores/bedrock fractures, largest reservoir of water available to humans. Dissolves limestone, creating sinkholes.
What is the belt of soil moisture?
Water held near surface by molecular attraction to soil particles
What is the zone of saturation, and what is its significance?
Where all open spaces are fully filled with water. Groundwater resides.
Define the water table and its relation to the zone of saturation.
Upper limit of zone of saturation and helps predict well productivity.
What is the capillary fringe?
Place where groundwater is held by surface tension in tiny spaces between sediment grains.
Describe the zone of aeration.
- (vadose zone)
- above water table
- includes capillary fringe and belt of soil moisture.
- Water here cannot be pumped by wells.
How does the shape of the water table typically appear?
Subdued replica of the surface topography, varying in depth seasonally and with rainfall.
What factors influence groundwater storage and movement?
- Porosity
- Permeability
- Specific yield/retention
What is an aquitard versus an aquifer?
- Aquitard : hinders water movement (clay),
- Aquifer : permeable layer (sand or gravel) that transmits groundwater freely.
Explain Darcy’s Law in groundwater movement.
Groundwater velocity increases as the slope of the water table increases, assuming uniform permeability.
What determines the movement of groundwater?
- Gravity : permeability of materials
- Hydraulic gradient : slope of the water table
What is hydraulic head?
Vertical diff. between recharge and discharge points in groundwater.
What is a spring, and how does it form?
Groundwater flowing naturally where the water table meets Earth’s surface (blocked by aquitard)
What causes hot springs?
Water is heated at depth by Earth’s temperature or igneous rock, making it 6–9°C warmer than the local air temperature.
What are geysers, and how do they erupt?
Intermittent fountains of hot water and steam, caused by groundwater heated in chambers until it expands and erupts.
What is the impact of pumping wells on the water table?
Causes drawdown = cone of depression (can dry nearby wells)
What are artesian wells?
- Wells where water rises above the aquifer due to pressure.
- Flowing (above ground level) and non-flowing (below ground).
Why is groundwater considered non-renewable in some areas?
Recharge rates are slower than rate of withdrawal = depletion.
What causes land subsidence from groundwater use?
Over-pumping reduces water pressure = land is sinking (especially in sediment-rich areas)
What are common sources of groundwater contamination?
- Sewage
- highway salt
- fertilizers
- pesticides
- industrial chemicals
- landfill leachate.
Define the permeability ? (IMPORTANT)
Ability of a material to transmit a fluid
What are the two categories of groundwater ? (IMPORTANT)
- Specific yield : Portion that will drain with gravity
- Specific retention : Portion retained as film on rock surfaces
What is porosity ? (IMPORTANT)
The percentage of total volume of rock or sediment that consists of pore spaces.
It determines how much water can be stored
On what pore space depends on ? (IMPORTANT)
- Size and shape of grains
- How grains are packed together
- Degree of sorting
- Amount of cementing material
