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:

   Rivulets, creeks, streams, and rivers


2. Upstream versus downstream


3. Stream gradient

       Stream profile


       Base levels

    Defined: lower limit to which a stream can erode

    Ultimate BL: Ocean (sea level)

    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 streams surface water system


        Sources of recharge

    Snowpack melt

    Rain runoff

    Groundwater and Springs



        Recharge will be affected by


    Climate changes

    Pumping and Irrigation


2. Stream Velocity


       Measure of the downstream rate of water flow


       Varies in respect to:

    Stream gradient

    Vertical drop over horizontal distance


    Shape of the channel

    Channel width and height


    Location in the channel

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


    Channel roughness (surface friction)

    Smooth versus rough


    Sediment load

    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


    Lakes and Internally draining basins

    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






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


    Bed load - sediment moving on the stream bed

    Larger-sized material from sand to boulders


    Suspension load - sediment carried in water column

    Includes very fine solid particles (clay and silt)

    Dissolved load

   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


    Moving by bouncing/skipping along bottom



    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

    Slowing down of stream velocity

           Decrease in stream gradient

           Widening & shallowing of stream channel


    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





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






       Residential and industrial uses




       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



    Folding and faulting patterns


    Regional joint patterns


    Contacts between rock bodies


    Mountains and volcanoes


2. Sometimes drainage pattern is controlled by previously

eroded structures that are no longer present


3. Types of drainage patterns






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







        Old Age


D. Renewed Uplift of a Matured Drainage Basin

       Steepening of the stream gradient


       Accelerated down-cutting of stream channels




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





       Water treatment facilities


       Underground water pipe network


3. San Diego uses water in many different ways



       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

    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


Alluvial fan


Base load

Bed load

Braided stream



Dissolved load

Drainage basin

Drainage divides

Drainage patterns


Hydraulic action

Hydrologic cycle

Infiltration capacity

Levee (natural and artificial)

Load (carrying) capacity


Oxbow lake

Point bar

River mouth



Stream discharge

Stream gradient

Suspended load

Stream velocity