EASC 325: Hydrogeology and Hydrology Overview

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Questions and Answers

What is the primary focus of hydrology?

The occurrence and movement of water on Earth's surface (correct)

The interaction between geological materials and water underground

The study of underground water quality

The engineering aspects of groundwater flow

Which statement accurately describes hydrogeology?

It focuses only on surface water bodies.

It examines atmospheric water movements.

It is solely concerned with the engineering of water systems.

It studies the occurrence and quality of water beneath the Earth's surface. (correct)

What percentage of Earth's water is found in the oceans?

About 60%

About 97.2% (correct)

About 75%

About 50%

What is the approximate percentage of usable freshwater that groundwater constitutes on Earth?

95% Signup and view all the answers

Which component accounts for the smallest percentage of Earth's freshwater distribution?

Soil moisture Signup and view all the answers

What is the primary measure of the hydrologic cycle's components?

All of the above Signup and view all the answers

Geohydrology specifically focuses on which aspect of groundwater?

The hydraulics and engineering aspects of groundwater flow Signup and view all the answers

Which of the following is NOT a component of the hydrologic cycle?

Photosynthesis Signup and view all the answers

What primary process describes the movement of water from the ocean into the atmosphere?

Evaporation Signup and view all the answers

Which of the following reservoirs contains the least amount of Earth's water?

Atmosphere Signup and view all the answers

What is the term for the combined loss of water from transpiration and evaporation?

Evapotranspiration Signup and view all the answers

Which factor primarily influences actual evapotranspiration in arid environments?

Low precipitation levels Signup and view all the answers

What process occurs when water vapor changes to liquid water, leading to cloud formation?

Condensation Signup and view all the answers

Which method allows water to move from the surface into the soil, contributing to groundwater recharge?

Infiltration Signup and view all the answers

What captures the totality of water loss due to both transpiration from plants and evaporation under field conditions?

Actual Evapotranspiration Signup and view all the answers

What are phreatophytes primarily specialized for in relation to the water cycle?

Transpiring groundwater Signup and view all the answers

What happens to the infiltration capacity of soil as the moisture content increases?

It reduces exponentially. Signup and view all the answers

Which conditions favor a high infiltration rate?

Coarse soils and low soil moisture. Signup and view all the answers

What does the hydrologic equation express?

The relationship between inflow, outflow, and storage. Signup and view all the answers

Which of the following is NOT a component of runoff?

Soil infiltration Signup and view all the answers

In the groundwater system equation, what does RN represent?

Groundwater recharge from precipitation. Signup and view all the answers

What method is used to measure precipitation?

Rain gauge Signup and view all the answers

What best describes the hydrologic cycle?

A continuous movement of water through various phases. Signup and view all the answers

Which factor does NOT contribute to change in storage in the hydrologic equation?

Soil texture Signup and view all the answers

What is the primary use of a rain gauge?

To measure rainfall Signup and view all the answers

In Ghana, how is rainfall quantification typically expressed?

Millimeters per day, month, or year Signup and view all the answers

What factors influence the accuracy of rainfall measurements from a rain gauge?

Wind intensity and positioning of the gauge Signup and view all the answers

What method can be used to estimate missing rainfall data from a rain gauge station?

Using measurements from three surrounding stations and averaging Signup and view all the answers

Isohyetal maps are useful for estimating precipitation at which locations?

At ungauged locations Signup and view all the answers

What is a defining feature of the Thiessen method for estimating precipitation?

It connects gauged stations with lines to form polygons. Signup and view all the answers

What does the weighting factor in the Thiessen method depend on?

The area of the basin closest to the gauged station Signup and view all the answers

What is typically computed using various methods at the end of a specified time period?

The average rainfall in a basin Signup and view all the answers

What is the primary function of the Thiessen method in precipitation measurement?

To determine the effective uniform depth of precipitation Signup and view all the answers

Which of the following factors can lead to errors when using the Thiessen method?

Variation of rainfall amounts over short distances Signup and view all the answers

What geometric approach is used when employing the Thiessen method?

Creating polygons by connecting bisectors Signup and view all the answers

Which method is NOT mentioned as a way to estimate the effective uniform depth (EUD)?

Thompson method Signup and view all the answers

What is the weighted average dependent on in the Thiessen method?

The size and precipitation of each polygon Signup and view all the answers

The area of each polygon created in the Thiessen method is essential for which calculation?

Calculating the fraction of total precipitation Signup and view all the answers

In mountainous regions, what is essential to consider when using the Thiessen method?

The impact of varying elevations on rainfall Signup and view all the answers

What is typically created by drawing lines between closest stations in the Thiessen method?

Bisectors and polygons Signup and view all the answers

How is the effective uniform depth (EUD) of precipitation calculated using the Thiessen method?

By multiplying the precipitation by its respective polygon area and summing the results Signup and view all the answers

What role do fractional areas play in the Thiessen method?

They provide a basis for calculating weighted averages Signup and view all the answers

Study Notes

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.

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Description

Test your understanding of hydrogeology and hydrology with this quiz focused on the Earth's water distribution, the hydrologic cycle, and key concepts distinguishing the two fields. Understand how water behaves in various contexts and the importance of the hydrogeologic equation.