Section 5 - Hydrology, Mass Movement, Weathering

Section 5
  1. Hydrology
  2. Groundwater
  3. Mass Movement

Hydrology - Lecture Notes

"All the rivers run into the sea, yet the sea is not full; unto the place from whence the rivers come, thither they return again."  Ecclesiastes, Ch. 1

The movement of water is called hydrology.  Water doesn't just appear.  It moves around in a "cycle".  In this cycle it can take the form of solid (ice), liquid, gas (water vapor).

Historically, people weren't sure where the water originated.  They did not know what kept supplying rivers and springs with water even during dry spells.  Many postulated the existence of complex underground channels that enable ocean water to flow inland to springs.  This is not found to be the case.
   Pierre Perrault (1674) was the first to measure precipitation and drainage from the Seine River basin.
   Edme' Mariotte (1684) demonstrated that much of the rainfall infiltrates into the ground.
   Edmund Halley (1693) investigated evaporation of the Mediterranean Sea.  He found that more than enough water was being evaporated to feed the rivers flowing into this Sea.

    Water falling to the ground from the atmosphere is precipitation.  (9x1013 m3/yr falls onto land, 37x1013 m3/yr falls into the ocean)  A large amount of H2O is taken back into the atmosphere by evaporation and plant transpiration.  These two processes are usually grouped together as evapo-transpiration. (40x1013 m3/yr  from the ocean, 6x1013 m3/yr from the soil and surface water)
   For the precipitation that falls onto the ground, some goes into runoff (rivers and surface water), another soaks into the ground by a process of infiltration.  Water that sinks into the ground is called groundwater.
   The drainage basin of a river is the entire area from which a stream and its tributaries receive their water.

The water cycle can be summed up schematically by
Water Cycle

Where is all the water on the earth? 
97.2% oceans, 2.15% ice caps and glaciers, 0.65% lakes, streams, groundwater, and atmosphere
Where is all the freshwater on the earth?
85% ice caps and glaciers, 14% groundwater, 0.5% lakes and reserviors, 0.3% soil moisture, 0.05% water vapor, 0.004% rivers

Stream Dynamics

The flow of water in a stream is usually characterized as being laminar (usually low velocity, mature streams) and turbulent (usually high velocity, young streams).  Discharge is an important quantity when describing a stream's flow.

Discharge has units of volume per unit of time (such as m3/min, ft3/min, etc.).  It is a measure of the volume of water that passes a particular point along a river (or cross-sectional area) in a given amount of time.

(Discharge) = (cross-sectional area) x (average velocity)

The measure of discharge as a function of time is called a hydrograph (shown below). 

Standard hydrograph. 

It is quite important to ascertain the threat of flooding in a proposed construction area.  How can this be done? 

I. Examine the general topology.  Does it look like a potential floodplain of a river?
II.  Talk to the "indigenous" people.  Ask them if a particular area floods and how often.
III.  Examine historical records of flood levels and the number of occurrences.
IV.  Sometimes flood waters will leave marks on buildings and trees.  This will indicate some of the highest flood levels.
V.  The soil may contain evidence of sedimentation from a floodplain.

Potential for flooding is a probability.  Let P equal the probability in any given year that a flood of a given stage will occur.  Then


This is a close approximation to a true statistical analysis.  It should be noted that artificial structures built in or around rivers may change the probabilities over time.

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This animation is not a theoretical model.  It is just an illustration of the basic principles in stream dynamics.  (Such that, some details are not to scale)

Basic Principles (Assuming the same precipitation onto the rivers drainage basin):
1.  Urbanization (pavement, residential housing, etc.) of a rivers drainage basin will cause the peak discharge to increase and the time lag to decrease.  Less infiltration and more runoff that moves into the river more quickly.
2.  Dam construction allows the downstream discharge to be regulated.  This usually reduces the peak discharge and increases the time lag.
3.  Constricting a rivers floodplain with flood walls, dikes, and/or levees causes the peak discharge to increase and time lag to decrease in spots downstream.  When a river is allowed to spread out into the surrounding floodplains, the water slows down and it "stretches" out with respect to a downstream hydrograph.

As a general rule, artificial structures placed into a river or a river's floodplain will usually change the dynamics of that river with regards to flooding.

The "ultimate floodplain management?":

"After ordering tens of thousands of residents to abandon their homes, engineers dynamited levees along a stretch of the swollen Yangtze (river in China) on Sunday to ease floodwaters menacing cities in central China...engineers blew up secondary dikes in Jianli County, about 90 miles upriver from Wuhan, a tri-city industrial area with a population of 7 million...Engineers hope the diversion of up to 28 billion cubic feet of water into miles of farmland behind the dike will lower the raging Yangtze's water level by as much as 10 inches."   (Pioneer Press article, St. Paul, MN, China Dynamites Levees to Spare Cities, 8/8/98)

Flooding and Construction Fact Sheet

Erosion and Deposition

Most stream erosion occurs by lifting loose unconsolidated particles and by abrasion.  In general, the stronger the water current - the more the erosion.

Sediments in the stream travel as a bed load, suspended load, or dissolved load.  When a river overflows its banks, it will drop much of its load because of the water slowing down.  This is why you'll find a lot of silt and sand within floodplains.

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Beaver Creek in the Beaver Creek Reserve near Eau Claire, WI.

This stream meanders and erodes the banks on the outside of the river bends where the water is moving fast.  On the inside turns the water is moving more slowly creating deposition sand bars.  This pictures shows a tree fallen across the river from the bank being eroded.

(Click on the picture to enlarge.)


River deposition pattern where Gilbert Creek empties into the Red Cedar just South of Riverside Park in Menomonie, WI.
(Click on the picture to enlarge.)

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Gilbert Creek, a small tributary of the Red Cedar river just South of Riverside Park.

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Riverside park looking South along the Red Cedar river.  The picture was taken August 24, 2003, during a period of low discharge.  The ripples in the surface of the water show the subsurface area where deposition is happening and a sandbar exists.  The girl in the background is standing at the edge of the sandbar.

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A closer look at the edge of the sandbar.  The water gets deep very quickly on the left side of the picture

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Another view of the sandbar.  To the right is upstream in the Red Cedar river.  To the left is where the sediment laden Gilbert Creek empties into the Red Cedar.  The water slows down and deposits it's suspended load. 

Water drainage flows downhill and can be affected by local geology (more or less resistance rock layers).  There are generally 4 types of drainage patterns Dendritic, Radial, Trellis, and Rectangular.

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Characteristics of Young and Old River Valleys

Immature (young) River Valleys

Steep gradient
"V" shaped valley (steep sides)
Turbulent flow
No meandering
small floodplain

Mature (old) River Valleys

Gentle gradient
Very few waterfalls
Wide "U" shaped valley
Laminar flow
large floodplain

Snake River valley 
© 2002, Alan J. Scott
Snake River valley in Hell's Canyon National Recreational Area in Idaho. Snake River is a young river valley.

Mississippi River Valley
© 2002, Alan J. Scott
Mississippi River Valley
Barn Bluff, Redwing, Minnesota
Mississippi is an old river valley.


Drainage Concerns For Residential Construction

"In the space of one hundred and seventy-six years the Mississippi has shortened itself two hundred and forty-two miles. Therefore ... in the Old Silurian Period the Mississippi River was upward of one million three hundred thousand miles long ... seven hundred and forty-two years from now the Mississippi will be only a mile and three-quarters long. ... There is something fascinating about science. One gets such wholesome returns of conjecture out of such a trifling investment of fact."
                    -- Mark Twain  


Groundwater is 66 times the amount of water in streams and freshwater lakes.  Precipitation that infiltrates into the ground is called groundwater.

The zone of aeration is the region of soil closest to the surface.  It contains some moisture but is not 100% saturated with water.  As one digs deeper, the zone of saturation is encountered.  This zone is 100% saturated.  The boundary between these zones is called the water table

The water table does reflect variations in the ground surface (such that, has a topology), the irregularities in the water table are less pronounced.

The ability of water to flow (or be transmitted) underground is termed permeability.  For something to be permeable it needs to have a material that is porous and has some interconnections between the openings.
A permeable material that actually carries underground water is called an aquifer.
Low permeable material (i.e. solid rock) is called aquicludes.
When the water table intersects the surface, a spring, swamp, river, and/or lake may appear.

How fast water travels through an aquifer follows Darcy's Law:

Darcy's Law.

The velocity of the water is proportional to k (which is related to the permeability) and is proportional to the hydraulic gradient, h/l (which is the slope of the water table).  The volume of water flow per unit of time follows the equation Q=A . v where A is an area and is related to the geometry of a well.

What happens to the water table when a well is drilled and water is pumped?  A cone of depression is formed in the water table. 

Cone of depression
Sometimes the use of underground water needs to be regulated.  Suppose a farmer is irrigating their crops by pumping water from well A.  If another farmer comes along with a bigger irrigation system requiring a deeper well and higher pump rate at B, you can see what happens to well A.  Underground pumping can also cause land subsidence.

More on Water Permeability and Dewatering

An artesian well requires a specific underground geologic structure to exist.  It requires an inclined aquifer bounded on the top with an aquiclude.  Wells drilled through the aquiclude into the aquifer may have water freely flowing out without any pumping necessary.  (see fig. 11.14 in Tarbucks and Lutgens)

State Revokes Well-Driller's License, Dunn County News Article, December 5, 1999
After a Department of Natural Resources investigation, a well driller (from Eau Claire) had his license revoked for violating several Wisconsin well drilling codes.  A State Administrative Law Judge found that the person had violated 23 separate codes on 340 occasions.
"...license revoked for violations of Wisconsin well drilling codes that are designed to protect a pure water supply and assure private wells produce clean water....(the) violations included use of improper well construction methods, failure to report information about well construction and water testing, and construction of wells too close to possible pollutant sources."
"...he did not collect many bacteriological water samples within 30 days of well completion...installed wells within restricted distances of solid waste or hazardous waste facilities without required variances...used unapproved drilling methods and unapproved well casing."

Karst Topograph are geographical regions that have been significantly shaped by water partially dissolving an underground rock strata (usually limestone).  This topography has a large number of sinkholes on the surface.


If you are lucky enough (or un-lucky depending on the pay rate) to get a construction job in a cold region such as Alaska and a good portion of Canada, permafrost is going to be a big concern.  Permafrost regions have soil that is frozen at some depth year round (see pg 210 in Tarbucks and Lutgens).  This type of soil can be divided into two regions.  An active region near the surface that experiences thawing/freezing and the permanently frozen ground underneath the active region.

THE PROBLEM - Thawed soil in the active zone is usually weak and compressible.  Furthermore, it usually contains trapped water making it "muck-like".  Two important rules need to be followed when building sturdy structures in regions of permafrost:
1.  Base of the foundations should be placed into the permanently frozen ground.  If the active region reaches below the base of the foundation, the foundation will lose its ability to support loads.
2.  The foundation needs to be thermally insulated from the rest of the structure.  One doesn't want heat from the building to melt the permanently frozen ground.

The Alaskan Highway project during WWII and the Alaskan Pipeline are two prime examples of building in permafrost regions.  (A pictorial history of building the Alaskan Highway.)


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Red Cedar River
Aerial view with pictures of landforms and river dynamics.  Click on the picture for a larger version.  (~6 Mb)

Here is a picture of myself (Dr. Scott) during a river dive down the Rainbow River in Florida.

Several years ago I had the opportunity to scuba dive in the Rainbow River in Florida.  The water is a magnificently clear.  The river begins at a large pond area which is being fed water through several springs in the bottom of the pond.  These springs feed the stream with 500 million gallons of water per day.  (I've also got a picture diving with Manitee's.)

Hydrology - Related Web Links

USGS Geology Water Cycle *New*
International Erosion Control Association, Photogallery pictures
Water Quality Help Guide
at Wilkes University - Excellent resource about "hard water", bacteria, contaminants, etc.
Class tour of the Menomonie Hydroelectric Power Dam
FEMA Fact Sheet on Floods and Flash Floods 
Resources from the Dept. of Geology and Geophysics, UW-Madison (by Philip E. Brown) Water and Soil
Dr. Andy Frank's Physical Geology - Groundwater
Dr. Pamela Gore's lecture notes on hydrology
Dr. Susan DeBari's lecture notes on Rivers and Running Water
Geology 41 at Duke University - Groundwater (Part I and Part II), Streams (Part I and Part II)
Meteorology Education Links On-line Tutorial and Decision Aid
Protecting Groundwater: A Guide for the Pesticide User
Groundwater: Nature's Hidden Treasure
USGS Real-time flow data for the Red Cedar River (station just downstream from the dam), USGS Water Resources and Publication Data for Wisconsin, USGS national water data
St. Francis Dam Failure by Kelita Stephens
Construction of the Hoover Dam
Google - Search for Hydrology
Google - Search for River Pictures
Google - Search for River Dynamics
Google - Search for Groundwater

Mass Movement - Lecture Notes

Earth material moving downhill in a solid or somewhat viscous form are called mass movements.  This movement is analagous to a block on a inclined plane.  When the downhill force of gravity exceeds the internal frictional forces resisting motion, the material will move.  In other words, a slope will remain stable until the externally exerted stresses cause it to reach its threshold.  This is the point to which the passive, internal frictional forces are exceeded.

These mass movements have been characterized as a slide, fall, flow, and heave (note: these are not mutually exclusive categories)
Slide is when the material maintains continuous contact with the surface.  It can preserve its form or be extensively deformed.
Fall  refers to the free fall of material (looses contact with the surface).
Flow involves continuous movement with the material behaving in a plastic to liquid manner.  Individual particles get rearranged.
Heave is a slow movement where the particles are pushed up perpendicular to the sloping surface then "let down" in the direction of gravity.

Speed and Type of Movements

Slow Movements (1mm/yr - 1mm/day)
   Slow movement downward of surface material is called creep.  Signs that creep is happening include posts tilting, soil profile, roots, trees tilting, etc.
   Frost heaving can occur when water gets behind or underneath an object and freezes.  Upon freezing water expands and can apply large forces on objects.
   Solifluction refers to the downslope movement of debris under saturated conditions.  This movement is common in regions of permafrost.

Moderate Movements (1 cm/day - 1 cm/sec)
  Slump is the downward and outward movement of earth traveling as a unit or as a series of units.  Occurs many times after a hillsides slope has been changed.  Commonly occurs when soil has been graded to steeply at a work site. 
  Earthflows are slow but perceptible movements.  These are usually helped by excessive moisture.  If sufficient moisture is added it will become a mudflow.
  Debris slide involves the movement of comparatively dry unconsolidated material.  It is usually coarser material than an earthflow.

Rapid Movements (can go quite fast - free fall)
Rockfall is the free fall of earth material.  It creates a build up of rocks at the base of cliffs called talus.


Factors that increase the chances of a slope failure:

External Influences
  Removal of Lateral Support - too steeply grading hillside, erosion, etc.
  Removal of Underlying Support - dissolving rock layer beneath the surface, bearing capacity failure, mining
  Addition of Mass (assuming a cohesive soil) - adding weight to the hillside
  Addition of Lateral Pressure - expanding clay soils, water freezing
  Vibrations - earthquakes, blasting, heavy traffic, sonic booms, etc.
Internal Influences
  Weathering - mechanical and chemical weathering can reduce the macroscopic bonding of particles within the soil.
  Pore Water - decreases the effective stress pushing the soil particles together.
  Organic Activity - removal of vegetative roots, burrowing animals, prying by plant roots

An Introduction To Slope Stability Theory


Slide show (with audio) of this slope failure in Menomonie, WI

s5-17 Lake Bank Reconstruction Project - Summer 1999, Lake Menomin, Menomonie, WI (PowerPoint presentation)
[Some text and audio still need added to this slide show, but I wanted to make it available to you for previewing.]

Mass Movement - Related Web Links

Images of how Mass Movements have affected buildings or structures
Slump in a new road cut
Broken Pavement
Displaced Curb, Another Displace Curb

Dr. Andy Frank's Physical Geology Landslides
FEMA Fact Sheet on Landslides and Mudflows (Adobe Acrobat format)
Geology 41 at Duke University - Mass Movement (Part I and Part II)
Landslide Mitigation Techniques by J. David Rogers (mitigation using subdrainage)
Homeowner's Landslide Guide For Hillside Flooding, Debris Flows, Erosion, and Landslide Control
published by the Oregon Emergency Management (FEMA)
A huge landslide on Mars
Mass Wasting - Prof. Stephen A. Nelson -Tulane University
Mass Movement pictures from Washington State University
Google - Search for Mass Movement
Google - Search for Landslides

Weathering - Lecture Notes

Geographical regions with high average rainfall and temperatures have the most weathering of natural materials.  This usually implies that these regions also have the deepest soils (in particular, residual soils).

Weathering can be broken down into mechanical and chemical.

Mechanical weathering (or physical weathering, or disintegration) involves a reduction in the size of the rock and mineral particles but no change in the composition.
  Frost Action - water expands upon freezing and can exert tremendous pressures.
  Exfoliation - Rock that is formed deep underground is in equilibrium with high pressures.  When these high pressures are removed (i.e. erosion), the stresses within the rock cause it to fracture into sheets or leaves that are parallel to the ground surface.
  Thermal expansion and contraction - almost all materials expand upon heating and contract upon cooling.  This can cause internal stresses to build up and break down the rock.  Different minerals expand and contract differently which results in stress along mineral boundaries.
  Abrasion - constant rubbing between surfaces.
  Animals (including humans) can mechanically break down rock.

Chemical weathering (or decomposition) involves a change in the composition of the material weathered.  (Usually involves H2O, CO2, O2, and acidic water)
  Dissolution - happens when solid material dissolves in water (i.e. it all becomes a solution).
  Oxidation - minerals can react with oxygen.  A common example is "rusting" with iron-bearing silicate minerals.  (olivine, pyroxene)  Colors can include red, orange, and brown.  (Carbonatization involves carbon dioxide as an chemical reactant.)
  Hydration involves the structural addition of water to a solid to form a hydrated solid product.  Silicate minerals weather by hydration to form clay.  An example:

2KAlSi3O8 (potassium feldspar) + H2O + 2H+ --> 2K+ + Al2Si2O5(OH)4 (clay) + 4SiO2

  Feldspar - stable at high temperature and pressure
   Clay - stable under conditions at the surface

The Rate of Weathering (in particular, chemical weathering) is proportional to the surface area of the material.  Such that, a single rock with a volume of 100 cm3 will weather much faster if it is broken into 10 rocks each having a volume of 10 cm3.  In fact, if we assume spherically shaped rocks

(total surface area of the 10 smaller rocks)/(total surface area of the single rock) = 2.17

Thus, the 10 smaller rocks will weather 2.17 times faster than the big rock.

The Rate of Weathering also depends on the composition of the rock or mineral.  As a general "rule-of-thumb", minerals which crystallize at high temperatures and pressures are least stable and weather most quickly.  Minerals that crystallize at lower temperatures and pressures are most stable to weathering at the surface.  One can think this in the following way - minerals that are furthest from their "zone of stability" (or conditions in which they were formed), weather the fastest. 

Soils from a Geological Perspective

Soil is generally defined as the unconsolidated material that consists of sand, clay, and decayed plant material (called humus) and exists near the surface.

Important note for the construction industry:  The abundance and widespread presence of soil makes it an important topic to examine in the construction industry.  Unless placed on rock, most structures must be founded on soil.  Soil displays considerable variability in its characteristics and properties due to a variety of geological and biological factors.

Residual soils have developed in place on the bedrock from which they are derived.  Other soils have been transported from elsewhere.

What governs the type of soil that will develop?
1.  Parent Bedrock
2.  Climate
3.  Topology of the land
4.  Time
5.  Vegetation

There can be certain generalizations made about the "macroscopic" structure of soil (in particular, residual soils)

  • The composition and particle sizes vary with depth.
  • There are visually recognizable zones (or horizons).

Soil Profile (starting at the surface and going deeper):
(Horizon O - Contains humus on the ground surface, a large amount of organic matter, sometimes considered part of the A horizon)
Horizon A - Considered the top soil, rich in organic matter, typically darker in color, also called the zone of leaching.  The smaller soil particles migrate out of this horizon and into the deeper horizons in a process called eluviation.    
(Horizon E -  very little clay particles and very little humus)
Horizon B - Considered the subsoil, also known as the zone of accumulation, usually contains soluble minerals (particularly in arid regions)
Horizon C - Weathered bedrock or disintegrating bedrock
(Horizon R - bedrock, this is usually not classified as an horizon but simply rock)

Soil Profile Images

(Geologist have also broken down different soil profiles into soil orders.)

Water passing downward through soil can wash out and dissolve soil components.  Eluviation is when smaller particles are washed out of the top part of the soil and moved into the lower part.  When soluble minerals are dissolved in the top part of the soil and precipitated out in the lower parts, it is called leaching.

An immature soil lacks any clearly developed horizons and resembles the parent material.  Mature soils have fully developed horizons and is built-up.

A general classification of soils can be done based mainly upon the climate that has created the soil.
Pedalfer - is a soil rich in aluminum and iron, they usually form in humid climates (Southeastern U.S.). Most of the residual soil in Wisconsin is a pedalfer.
Pedocal - rich in calcium, usually form in arid climates (Southwestern U.S.), these soils often contain caliche.  Caliche is a cemented layer of soil (quite hard). 
Laterite - derived from heavy weathering, depleted of almost all elements except aluminum and iron oxides, usually form in the tropics.  Soils that form in the tropics are not rich in nutrients.  Most of the nutrients come from the humus.  If deforestation occurs and the soil dries out, it becomes hard and does not support plant growth well.
Bauxite - (an extreme case of laterites)

Basic information on plant growth and soils
(Large earthwork contracts sometime specify what characteristics the top layer of soil must have because it will be used for plant growth.  The highway construction project just East of Menomonie on highway 29/12 kept the top soil separate from the rest of the soil that was moved.  This top soil was layed down last on the re-graded slopes along the highway.)

County Extension office can perform a soil analysis for plant growth.  This is a service (with a fee) that is mainly provided for the farmers. 
Soil Acidity (%H+ or PH level) has a strong effect on plant growth.  If your soil is acidic you'll have to add lime.  Soil may also be basic (base, OH).
Plants require certain nutrients in the soil or their growth may be stunted.  (P, K, Ca, Mg, B, Mn, Zn, etc.)
Fertilizers usually provide nitrogen, phosphorous, and potassium.  Listed as weight percents, such as:
5-10-5 or 10-10-10, respectively.

A glance at how a geologist, soil scientists, and soil engineers view soil:


UW-Stout library has a VHS tape on soils.
   From Rock To Sand To Muck: All The Dirt On Soils, Blue Sky Associates video
   Call Number: S591 .F76x 1996

Weathering - Related Web Links

Dr. Andy Frank's Physical Geology Weathering
Dr. Pamela Gore's lecture notes on weathering
Dr. Pamela Gore's lecture notes on soils
Geology 41 at Duke University - Weathering (Part I and Part II)
Richard Terry's Agronomy and Horticulture lecture notes on soils, slide show on soil horizons
National Soil Survey Center (lots of good pictures) soil profiles, landscapes, land use
National Soil Survey Center, Soil Science Education Website
Huge list of web links and information on soils (WWW Virtual Library on Soils and Substrates)
Iowa State Soil Judging Team
Google - Search for Weathering
Google - Search for Soils, Geology

Review Quizzes
Section 5

Review Quiz Section 5
Tarbuck and Lutgens, Essentials of Geology, Self-Quiz (Select Chapter Running Water, Groundwater, Mass Wasting, Weathering and Soils)
- Dr. Andy Frank's Practice Exam
Mass Movement
- Dr. Andy Frank's Practice Exam
- Dr. Andy Frank's Practice Exam
Streams - North Dakota State University Self-Test, Geology 120
Underground Water - North Dakota State University Self-Test, Geology 120
Mass Wasting - North Dakota State University Self-Test, Geology 120
Weathering - North Dakota State University Self-Test, Geology 120
Soils - North Dakota State University Self-Test, Geology 120