Geology Lecture Outline

   Running Water – (Ch 16)

 

 

I. Lecture Content

       The Hydrologic Cycle

       Nature of Running Water

       Running Water & Erosion

       Running Water & Sediment Transport

       Running Water & Deposition

       River Flooding

       Flood Control

       River Dynamics and Evolution

       Surface Waters - a Natural Resource

       Water Pollution and Conservation            

 

II. Introduction

       A. Running Water and Earth's Changing Surface

1. Critical part of the hydrologic cycle

 

2. Major influence shaping the Earth's surface

 

3. Leading surface erosion, transport and deposition agent

 

        B. Running Water and Human Civilization

              1. Lifeblood of most societies

 

                2. One of the most devastating natural hazard

 

                3. Major religious significance to many cultures

 

                4. Economic, political, and environmental issues

 

III. The Hydrologic Cycle

        A. Continuous Recycling of Water between the Ocean,

            Atmosphere and Land

                1. The Hydrologic cycle is Solar-powered

 

                2. Connected to global climate fluctuations and cycles

 

                3. Streams, rivers and lakes are part of this cycle

 

4. See Figure 15.6

 

B. Components of the Hydrologic Cycle

                1. Ocean evaporation and plant transpiration

 

                2. Cloud condensation

 

                3. Precipitation

 

                4. Surface and subsurface storage and runoff

 

IV. The Nature of Running Water

       A. Precipitation on the Land - Aspects of Runoff

               1. Amount of runoff depends on surface conditions

·       Regional climate (amount of precipitation)

·       Infiltration capacity = ground "soakability" factor

·       Melting snowpack

 

2. Two Styles of surface runoff

·       Sheet flow

·       Channel flow

 

B. Anatomy of a River - Terminology

1.  River and streams- Defined

·       Channelized runoff  - flow along surface channels

 

·       Increasing channel size scale:

Ø   Rivulets, creeks, streams, and rivers

 

       2. Upstream versus downstream

 

        3. Stream gradient

·       Stream profile

 

·       Base levels

Ø    Defined: lower limit to which a stream can erode

Ø    Ultimate BL: Ocean (sea level)

Ø    Other BL's: lakes and reservoirs (above sea level)

 

4. Stream banks and natural levees

 

        5. Stream bed (bottom)

 

        6. Meander and Oxbow lake

 

        7. Headwaters

 

        8. Main branch and its Tributaries

 

9. Floodplain

 

10. Delta

 

11. Alluvial fan

 

12. Drainage basin

 

13. Stream divide

 

V. Stream Erosion, Transport and Deposition

A. Aspects of Channel Flow - Water and Sediment

 

      1. Stream Recharge

 

·        Recharge = Rate at which a given amount of water

                       is added to the stream’s surface water system

 

·        Sources of recharge

ü    Snowpack melt

ü    Rain runoff

ü    Groundwater and Springs

 

 

·        Recharge will be affected by

ü    Seasons

ü    Climate changes

ü    Pumping and Irrigation

 

      2. Stream Velocity

 

·       Measure of the downstream rate of water flow

 

·       Varies in respect to:

Ø    Stream gradient

ü    Vertical drop over horizontal distance

 

Ø    Shape of the channel

ü    Channel width and height

 

Ø    Location in the channel

ü    Top, bottom, side, center, inside/outside bend

 

Ø    Channel roughness (surface friction)

ü    Smooth versus rough

 

Ø    Sediment load

ü    High versus low load capacity

 

        3. Stream Discharge

 

·        Discharge = Rate at which a given amount of water

                       flows past a specific point along the stream

 

·        Measured using stream gauges and a hydrograph

 

·        Calculated by multiplying the stream's channel area (that is filled by water) by the stream velocity

 

·        Usually measured in cubic feet per second (CFS)

 

·        Typical discharges for various size streams and rivers

 

·        Ultimate destinations of discharge

ü    Groundwater

ü    Lakes and Internally draining basins

ü    Ocean or Sea

 

B. Nature of Stream Erosion

     1. Hydrologic power (kinetic energy + mass) of running water

           has the capacity to do work, i.e. erode rock and sediment

 

·        Ability to Erode (remove) and Transport (move)

      massive amounts of material across great distances

 

·        Powerful shaper of landforms

 

·        One of most destructive natural hazards

 

2. Three major means of erosion by running water

·        Hydraulic action

 

·        Abrasion

 

·       Dissolution

 

3. Stream erosion occurs when the sediment load of the

       stream is less than its load carrying capacity.

 

·       This may vary across a single channel profile

depending on what part of the channel

 

4. Typically the greater the stream gradient, the greater the

         erosional ability of a stream

 

5. Majority of river erosion occurs in the headwaters region

 

6. In a meandering stream, erosion typically occurs along

    the outside curve of a meander where the stream

    velocity is greatest

 

 

C. Nature of Stream Transport

 

        1. Stream Load

v   The sediment and dissolved material carried by a stream or river

 

Ø    Bed load - sediment moving on the stream bed

ü    Larger-sized material from sand to boulders

 

Ø    Suspension load - sediment carried in water column

ü    Includes very fine solid particles (clay and silt)

 

Ø    Dissolved load

ü   Dissolved minerals and chemicals

 

        2. Load Capacity

·        Maximum amount of sediment a river with a given

                   size discharge can carry

       

3. Methods of sediment transport

·        Saltation

ü    Moving by bouncing/skipping along bottom

 

·        Suspension

ü    Moving while suspended in the water column

 

4. Typical Loads for various size streams and rivers

 

D. Nature of Stream Deposition

 

               1. Deposition occurs in a stream or river when its sediment

                       load exceeds its load capacity

·       Conditions where this occurs

Ø    Slowing down of stream velocity

ü           Decrease in stream gradient

ü           Widening & shallowing of stream channel

 

Ø    Increase in surface infiltration (percolation)

 

·       A braided stream is typical of this condition

 

                2. Formation of point bars along inside bends of meanders

 

                3. Deposition of stream sediment on floodplains

·        Occurs during floodstage of a stream or river

 

·        Lateral and vertical accretion of silt/sand deposits

 

·        Building up of stream terraces

 

4. Formation of a delta

·  Defined: Sediment pile deposited at a river mouth

 

·        Deltas form at river mouths at either the edge of

           a lake or ocean shoreline where stream velocity

           slows down drastically

 

·        Type of delta formation depends hydraulic factors

Ø    Stream-dominated

Ø    Wave-dominated

Ø    Tide-dominated

 

                5. Formation of alluvial fans

·        Alluvial fans form at the base of mountain fronts

           in arid and semi-arid localities.

 

·       Braided streams are common on alluvial fans

 

E. Graded Streams

1. Defined: A stream system where erosion and deposition

           are in a dynamic balance

 

2. Factors: gradient, velocity, discharge, channel & load

 

VI. Flooding

       A. Conditions for Flooding

               1. Defined: Discharge exceeds channel capacity

·       River overflows its banks and natural levees

 

·       Sediment-laden flood waters flow out onto the floodplain

 

                2. The condition for a flooding river is termed floodstage

               

3. Normally as broad, shallow, slow-moving waters

·       Typical in broad, low-gradient floodplains

 

                4. Sometimes as treacherous, fast moving torrents

·       Called "flash floods"

 

·       Typical in narrow floodplains and canyons

 

        B. Flood Control Measures

               1. Artificial levees

 

                2. Dams and Catch basins

 

                3. Floodway diversions

 

                4. Artificial cement "channelizing" of river channels

 

C. Effects of Damming a River

               1. Positive Effects

§       Flood control

 

§       Hydroelectricity

 

§       Irrigation

 

§       Residential and industrial uses

 

§       Recreation

 

§       Aquatic wildlife habitat

 

                2. Negative Effects

§       Results of dam failure to everything downstream

 

§       Loss of land habitat

 

§       Barrier to wild fish migration

 

§       Effect wild river ecosystems

 

§       Loss of valuable nutrient-laden flood waters

 

§       Less water for everything downstream

 

 

VII. River Drainage Basins and Patterns

       A. Drainage Basins and Divides

              1. Drainage basin

·       Defined: Regional area of all runoff surfaces that make

               up an interconnected system of streams which

   end up draining out through a single exit point (stream)

 

·       Drainage basins have wide range of sizes and shapes

 

·       Drainage basins change in size and shape over time

 

                2. Drainage divides

·       Defined: Topographic highs surrounding a drainage basin

                   that separate adjacent drainage basins.

 

·       Regional divides control where river systems empty into in

         terms of oceans, seas, or continental interiors

 

       B. Drainage Basin Patterns

                1. Typically controlled by underlying rock structures

 

·       River and stream placement typically along regional

        zones of rock weakness  

 

·       Examples:

ü    Folding and faulting patterns

 

ü    Regional joint patterns

 

ü    Contacts between rock bodies

 

ü    Mountains and volcanoes

 

                2. Sometimes drainage pattern is controlled by previously

                      eroded structures that are no longer present

 

                3. Types of drainage patterns

ü    Dendritic

ü    Radial

ü    Trellis

ü    Rectangular

ü    Deranged

4. See Figure 15.28 for illustration of drainage patterns

 

C. Drainage Basin Development

 

1. Two types of basin stream erosion

·       Lateral erosion

 

·       Headward erosion

 

2. Other erosional and deposition processes occurring

·       Stream piracy

 

·       Stream terracing

 

·       Reduction (flattening) of stream gradient

 

VIII. Evolution of a River and Its Associated Landforms

A.  Begins with Major Uplift Event = Orogeny

 

        1. Tectonism

 

2. Creation of topographic highlands

 

B.  Followed by Long History of Erosion and Deposition

1. Wearing down of the highlands

 

2. Lengthening and broadening of stream/river valleys

 

3. Flattening of stream gradient

 

4. Gradual filling in of the lowlands with alluvium

 

C. Sequence of River Evolution Stages over Time

§        Youth

 

§        Adolescent

 

§        Mature

 

§        Old Age

 

       D. Renewed Uplift of a Matured Drainage Basin

§       Steepening of the stream gradient

 

§       Accelerated down-cutting of stream channels

 

§       Rejuvenation

 

IX. Surface Fresh Water - A Natural Resource

       A. Water Needs for a Thirsty World

               1. Acquiring, storing, transporting, and distributing

                    adequate supplies of clean fresh water is a problematic 

                    endeavor for most societies

 

·        Economics - Very costly

 

·        Politics - Who gets how much? From where to where?

 

·        Environmental - Impacts of major water projects

 

·        Limited resource - Ongoing "Water Wars"

 

·        Demographics - More people = less water per person

 

                2. Modern day fresh water supplies in many parts of the

world are becoming increasingly inadequate

 

·       Rapid increases in human population

·       Widespread droughts

 

       B. California's Water Problem

                1. Major discrepancy between where most of the state's

                     people live, and where the most of the water occurs

 

·        Most people live in semiarid Southern California

 

·        Most of the water is found in wet Northern California

     and the Colorado River

 

·        The need to import freshwater from distant sources

    requires the construction & maintenance of a vast,

    statewide system of aqueducts

 

                2. California's population continues to increase while it's

                        freshwater resources remain relatively constant

 

                3. Neighboring states' populations are also increasing and

                      they want their fair share (e.g. from Colorado River)

 

                4. Water quality is an increasing concern for some regions

·        Colorado River water

·        Suspect groundwater sources

 

       5. California has its own "Water Wars" going on, both within

            the state and with its neighboring states and Mexico

·        Northern versus Southern California

 

·        California versus Oregon, Arizona, Nevada, and Baja

 

C. San Diego's Water Supply

        1. San Diego is a major water importer

 

2. San Diego's water supply comes from several sources

·        Local runoff stored in the county's reservoirs

 

·        Local groundwater

 

·        Colorado River

 

·        Owen's Valley - Mono Lake

 

·        Central and Northern California

 

·        Future sources?

 

                              2.  San Diego's water supply is stored and distributed within

                     an interconnected water-works system

·       Aqueducts

 

·       Reservoirs

 

·       Water treatment facilities

 

·       Underground water pipe network

 

3. San Diego uses water in many different ways

·       Residential

 

·       Commercial and Industrial

 

·       Parks and Golf courses

 

·       Farming and Ranching

 

·       Other uses?

 

X. River and Lake Pollution

       A. Several Types of Water Contaminants

1.  Sewage

 

2. Garbage

 

3. Chemicals and Toxins

 

4. Thermal

 

5. Sediment

 

        B. Numerous Sources where Contaminants Originate

1. Sewage treatment plants

 

2. Landfills and garbage dumps

 

3. Industrial plants and factories

 

3. Residential and urban dumping and runoff

 

4. Farms and ranches

       

5. Mining and drilling operations

 

XI. River and Lake Remediation and Conservation

B. Remediation and Conservation

        1. Cleanup and prevention measures and practices

·        Stop the pollution at its source

 

·        Fine/punish the polluters

 

·        Remove pollutant from water body

ü    Natural flushing, dilution & filtration means

 

·        Environmental monitoring systems

 

·        Tough pollution laws

 

·       Public awareness

 

·        Other potential measures and solutions

 

        2. Conservation measures

·       Conservation, Restrictions, and Reclamation

 

XII. Vocabulary - Rivers and Streams - Ch 15

Abrasion

Alluvial fan

Alluvium

Base load

Bed load

Braided stream

Dam

Delta

Dissolved load

Drainage basin

Drainage divides

Drainage patterns

Floodplain

Hydraulic action

Hydrologic cycle

Infiltration capacity

Levee (natural and artificial)

Load (carrying) capacity

Meanders

Oxbow lake

Point bar

River mouth

Runoff

Stream

Stream discharge

Stream gradient

Suspended load

Stream velocity