EASC 325: Hydrogeology and Hydrology Overview

Course: EASC 325: Fundamentals of Hydrogeology and Hydrology

• Course focuses on hydrogeology and hydrology
• Earth is a watery planet with water covering three-fourths of its surface.
• Water is stored as ice in high mountains and Earth's poles.
• Water forms clouds in Earth's atmosphere.
• 97.2% of Earth's water is in the oceans, which are salty.

Introduction

• Differentiate hydrology and hydrogeology
• Outline water distribution on Earth
• Discuss components of the hydrologic cycle
• Explain the hydrogeologic equation

Objectives

• Differentiate between hydrology and hydrogeology
• Understand water distribution on Earth
• Define and describe the elements of the hydrologic cycle
• Explain measurement methods of water cycle elements
• Write a hydrogeologic cycle equation

Hydrology vs. Hydrogeology

• Hydrology: The study of water occurrence, movement, and transport on Earth's surface.
• Hydrogeology: The branch of geology focusing on the occurrence, movement, and quality of water beneath the Earth's surface (groundwater).
• Geohydrology: The hydraulics or engineering aspects of groundwater flow.
• Hydrogeology examines the relationships between geologic materials and flowing water underground.

Distribution of Water on Earth

• Oceans: 97.2% of Earth's water, salty.
• Groundwater: 0.62% of Earth's water but 95% of usable freshwater.
• Glaciers: 2.15% of Earth's water.
• Lakes, swamps, rivers, and streams: 3.5% of Earth's water.
• Soil Moisture: 1.5% of Earth's water.
• Atmosphere: 0.001% of Earth's water.

Hydrologic Cycle

• Describes continuous water circulation on, over, and within Earth.
• Tracks water movement between reservoirs.

Reservoirs of the Hydrologic Cycle

• Oceans
• Ice caps
• Groundwater
• Lakes/Rivers
• Atmosphere

Processes in the Hydrologic Cycle

• Evaporation, Sublimation, and Transpiration (liquid to gas)
• Condensation (gas to liquid, forming clouds)
• Precipitation
• Infiltration
• Runoff (includes overland flow, interflow, and baseflow)

Evapotranspiration

• The combined water loss through transpiration from plants and evaporation.
• The two processes are inseparable in the field.
• Phreatophytes are plants with long roots that tap groundwater to transpire large water quantities, especially during their growth periods.
• Potential evapotranspiration: the amount of water potentially lost to the atmosphere if water is always available.
• Actual evapotranspiration: the actual amount of water lost to the atmosphere under prevailing conditions.

Measuring Precipitation

• Measured using rain gauges, radar, and satellites. (Rain gauges are most common type.)
• Different rain gauge types exist, with some measuring automatically and others manually.
• Results in precipitation measurements depend on wind intensity and rain gauge positioning.

Thiessen Method

• Used to estimate precipitation depths at ungauged locations or areas where data is missing.
• Thiessen polygons are created by connecting closely positioned measuring stations with lines.
• Perpendicular bisectors are drawn at the midpoints of these lines.
• Polygons are created by connecting the bisectors.
• The area of each polygon determines the weighted factor for estimating precipitation amounts at ungauged stations.
• Used in mountainous areas (important to consider elevation differences in these areas for accurate data).

Hydrologic Equation

• Inflow = Outflow ± Storage

• Inflow = precipitation, surface inflow, subsurface inflow, overland flow, groundwater discharge.

• Outflow = evaporation, transpiration, surface outflow, soil evaporation

• Storage = increase or decrease in subsurface or surface storage.

• For the groundwater system: RN + Qi – ET – Qo = ΔS.

• RN = Groundwater recharge from precipitation.

• Qi = Groundwater inputs from streams/other surface water reservoirs.

• ET = Evapotranspiration.

• Qo = Groundwater output into streams.

• ΔS = Change in groundwater storage.

Quantifying Evaporation

• Various methods are used to measure evaporation.
• Evaporation meters, analytical methods, and empirical equations are used.

Reading Assignment

• Read Chapter 2 of Applied Hydrogeology by C.W. Fetter, 4th Edition, 2001, Prentice Hall.