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

    Seasons

    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

    Groundwater

    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

 

        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

 

    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

        Saltation

    Moving by bouncing/skipping along bottom

 

        Suspension

    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

    Stream-dominated

    Wave-dominated

    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:

    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

    Dendritic

    Radial

    Trellis

    Rectangular

    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

    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