The human role in changing fluvial systems:
Retrospect, inventory and prospect
L. Allan James a,⁎, W. Andrew Marcus b,1
a
Department of Geography, University of South Carolina, Columbia, SC 29208, United States
b
Department of Geography, University of Oregon, Eugene, OR 97403-1251, United States
Received 23 August 2005; received in revised form 15 June 2006; accepted 15 June 2006
Available online 17 August 2006
Abstract
Historical and modern scientific contexts are provided for the 2006 Binghamton Geomorphology Symposium on the Human Role
in Changing Fluvial Systems. The 2006 symposium provides a synthesis of research concerned with human impacts on fluvial
systems — including hydrologic and geomorphic changes to watersheds — while also commemorating the 50th anniversary of the
1955 Man's Role in Changing the Face of the Earth Symposium [Thomas, Jr., W. L. (Ed.), 1956a. Man's Role in Changing the Face of
the Earth. Univ. Chicago Press, Chicago. 1193 pp]. This paper examines the 1955 symposium from the perspective of human impacts
on rivers, reviews current inquiry on anthropogenic interactions in fluvial systems, and anticipates future directions in this field.
Although the 1955 symposium did not have an explicit geomorphic focus, it set the stage for many subsequent anthropogeomorphic
studies. The 1955 conference provided guidance to geomorphologists by recommending and practicing interdisciplinary scholarship,
through the use of diverse methodologies applied at extensive temporal and geographical scales, and through its insistence on an
integrated understanding of human interactions with nature. Since 1956, research on human impacts to fluvial systems has been
influenced by fundamental changes in why the research is done, what is studied, how river studies are conducted, and who does the
research. Rationales for river research are now driven to a greater degree by institutional needs, environmental regulations, and aquatic
restoration. New techniques include a host of dating, spatial imaging, and ground measurement methods that can be coupled with
analytical functions and digital models. These new methods have led to a greater understanding of channel change, variations across
multiple temporal and spatial scales, and integrated watershed perspectives; all changes that are reflected by the papers in this volume.
These new methods also bring a set of technical demands for the training of geomorphologists. The 2006 Binghamton Geomorphology
Symposium complements the 1956 symposium by providing a more specific and updated view of river systems coupled with human
interactions. The symposium focuses on linkages between human land use, structures, and channel modification with geomorphology,
hydrology, and ecology. The emergence of sustainability as a central policy guideline in environmental management should generate
greater interest in geomorphic perspectives, especially as they pertain to human activities. The lack of theories of anthropogeomorphic
change, however, presents a challenge for the next generation of geomorphologists in this rapidly growing subfield.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Human impacts; Fluvial geomorphology; Watersheds; Hydrology; Rivers
1. Introduction
The 2006 Binghamton Geomorphology Symposium
has two purposes. The first purpose is to provide a synthesis
of research on human impacts on river morphology. The
Geomorphology 79 (2006) 152–171
www.elsevier.com/locate/geomorph
⁎ Corresponding author. Tel.: +1 803 777 6117; fax: +1 803 777 4972.
E-mail addresses: AJames@sc.edu (L.A. James),
marcus@uoregon.edu (W.A. Marcus).
1
Tel.: +1 541 346 5709.
0169-555X/$ - see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.geomorph.2006.06.017
majority of papers in this volume, therefore, focus on
specific causes of change in rivers or look at cumulative
human impacts on rivers at regional to global scales. A
second purpose of the symposium is to commemorate the
50th anniversary of the 1955 Man's Role in Changing the
Face of the Earth conference and its 1956 proceedings
volume (Thomas, 1956a), henceforth referred to collectively
as Changing the Earth. Through the examination of
human impacts on fluvial geomorphology, the research
papers in this volume carry on the tradition of the 1955
symposium and honor the work of our scholarly predecessors.
In addition, several articles explicitly identify some of
the links between the 1955 symposium and this 2006
Binghamton conference.
This paper provides historical and conceptual context
for the 1955 and 2006 symposiums by summarizing
some of the major changes since 1955 and outlining the
challenges and opportunities for research concerned with
human impacts on fluvial systems as exemplified by
papers in this volume. The purpose is not to provide a
comprehensive historical review of human impact
studies in fluvial geomorphology. This paper does not
address the full scope of human impact studies in fluvial
systems, especially as they have occurred outside Europe
and English-speaking countries. Nor does it attempt to
survey the vast literature on human-nature relations and
human impact studies. Rather, the purpose of this paper
is threefold: (A) to set the stage for later articles in this
volume with a retrospective review of the 1956 Changing
the Earth proceedings and some of its links to the
2006 Binghamton Symposium, (B) to review changes in
the research process since 1956 with a focus on why,
what, and how human impacts are studied, and (C) to
identify prospective directions in this field. This perspective
is intended to provide a broad context for many
of the key issues raised by papers in this volume.
2. Retrospect: The 1956 Changing the Earth
proceedings
The 1956 proceedings, Changing the Earth (Thomas,
1956a), presented many examples and explanations of
human-caused environmental changes, especially in
Europe and North America. This novel synthesis of
previously disparate findings from many different fields
and locations helped motivate and inform two generations
of scholars through its recognition of the long-term
historical roots and the spatial extent of human impacts to
the face of Earth. As important as those proceedings were,
however, they did not arise from a vacuum. Substantial
work on human impacts preceded the Changing the Earth
Symposium. This review begins with a brief synopsis of
the origins of concern about anthropogenic change in
colonial North America, although such concepts can be
traced elsewhere to antiquity (Glacken, 1967).
2.1. Precursors to the Changing the Earth Symposium
Precursors to the Changing the Earth Symposium in
North America can be traced to concerns about
destruction of natural resources seen in the writings and
paintings of 19th century artists, poets, and scholars such
as John James Audubon (1831–39), Susan Fenimore
Cooper (1850), Henry David Thoreau (1854), and S.H.
Hammond (1857), to name a few of the prominent voices
(James, in press). After the Civil War in the United States,
concerns over global-scale anthropogenic changes were
greatly influenced by Man and Nature, George Perkins
Marsh's (1864) classic work that documented the breadth
of human impacts on natural systems. As the son of a
U.S. Congressional Representative and as a paleontologist,
diplomat to Turkey and Italy, an architect of the
Washington Monument, and scholar of languages, Marsh
(Fig. 1) moved in high intellectual and political circles
Fig. 1. George P. Marsh, photographed by Mathew B. Brady between
1855 and 1865. Brady-Handy Collection (Library of Congress). [call
number: BH8201-4981; reproduction number: LC-BH8201-4981
DLC (b&w film copy neg.)].
153L.A. James, W.A. Marcus / Geomorphology 79 (2006) 152–171
(Lowenthal, 1965). His stature increased the effectiveness
and dissemination of his ideas, ensuring that Man and
Nature was widely read and acknowledged as an
important work in physical geography. Moreover,
Marsh's thesis that humans were causing serious
destruction that endangered nature as well as society,
resonated with contemporary public sentiment. Marsh's
book was the first to integrate the ideas that humans are
part of nature but also rely heavily on nature, that the
magnitude of human impacts could exceed the ability of
nature to recover, and that nature was frail in the face of
human exploitation. Prior to Marsh, the common view
was that Earth molded human nature and that global
resources were abundant. After Marsh, an alternative
awareness emerged that humans change a natural world
that is composed of finite resources (Lowenthal, 1990).
Marsh's work was critical in changing the perception of
nature from a fear of the wrath of God to a fear of the wrath
of nature (Pisani, 1996). Man and Nature has been
described as “the fountainhead of the conservation
movement” (Mumford, 1931, in Lowenthal, 1965). His
writings on natural processes were widely influential on
geomorphologists of the late 19th century through the
work of explorers such as Hayden, Newberry, Wheeler,
and Powell (Vitek and Ritter, 1993).
An extensive review of early 20th century writing on
human transformations is given in the original Changing
the Earth proceedings (Thomas, 1956b). A few key
individuals and works, as noted by Thomas, deserve
special mention for works that have direct bearing on
geomorphic systems discussed in this volume. For
example, the Russian, German, and French writings of
Alexander Ivanovich Woeikof of Saint Petersburg were
widely read in Europe. His writings focused on humaninduced
soil erosion and sedimentation through the
modification of vegetation by grazing, fire, and
urbanization (Woeikof, 1901). Neither Marsh nor
Woeikof addressed population growth as a cause of
change or human impacts outside of the northern and
western hemispheres. Nathaniel Southgate Shaler, a
Harvard geology professor, took up Marsh's conservation
mantle but went further by identifying the link
between rapid population growth and resource depletion
and damage to pristine natural systems (Shaler, 1905).
As a geologist, Shaler was interested also in soil erosion
and agricultural practices.
In the late 19th and early 20th centuries in the United
States, rapid landscape development and degradation led to
a greater recognition of the need for conservation.
Strengthening of the conservation movement was characterized
by scientific land-management policies brought
from Europe by Gifford Pinchot. These policies sought to
conserve resources and maintain federal land ownership, in
contrast to earlier policies aimed at distributing government
lands to private owners (Hays, 1959). Continued population
growth and resource consumption coupled with
growing alienation of preservationists, however, limited
the effectiveness of the conservation movement in
curtailing erosive land use, river fragmentation, and other
landscape alterations (Fox, 1985). The inability of
conservation policies to stop environmental degradation
and the ability of humans to alter geomorphology at
landscapes scales was made clear by the 1930s Dust Bowl
disaster, and the massive dam-building efforts initiated
under Roosevelt's New Deal. The shocking potential for
humans to radically and almost instantaneously disrupt
environmental and geomorphic systems was suddenly
demonstrated by the 1945 Hiroshima nuclear bomb, and
sustained by subsequent attempts of Project Plowshare to
harness nuclear explosions for excavating mines, canals,
aqueducts, roadways, and harbors during the 1940s and
1950s (Kiersch, 1998; Neal, 1998). Post-World War II
public action and scholarly research on human impacts to
the Earth thus proceeded during a period of fundamentally
changed perceptions of the effectiveness of humans as
agents of change.
2.2. The Changing the Earth Symposium and its
geomorphic legacy
The combination of rapid environmental degradation,
increasing technical potential, and evolving
political philosophies created a fertile ground for a
symposium on human impacts to Earth. Yet, it still took
the efforts of William L. Thomas, Jr., Assistant Director
of research at the Wenner–Gren Foundation, to bring the
Changing the Earth conference to life. The active lead
of Thomas and the Wenner–Gren Foundation, which
was dedicated to the advancement of anthropology
(Fejos, 1956, p. vii), encouraged many of the studies in
the proceedings to address the origins of human culture
and how cultural history relates to landscape changes
over time periods spanning the Holocene. The Changing
the Earth Symposium, however, was not only
about anthropological findings. Thomas asked Carl
Sauer to chair the conference and help in its organization,
and together they took a broadly geographical
approach to its content (Thomas, 1956b). Participants
came from diverse origins and eclectic professional
backgrounds; the perspectives they brought were
equally broad. While the Changing the Earth proceedings
did not have an explicit geomorphic focus, they
provided perspectives that remain relevant to human
impact studies in geomorphology to this day.
154 L.A. James, W.A. Marcus / Geomorphology 79 (2006) 152–171
2.2.1. Geomorphology in the Changing the Earth
proceedings
Despite its breadth, the emphasis of the Changing the
Earth Symposium on human alterations, and its extensive
discussion of geomorphically important variables such as
climate, land use, vegetation, mining, urbanization and
agriculture, surprisingly little direct attention was paid to
landform change. Geomorphic issues continually emerged
in various guises throughout the proceedings, but only
rarely were they the primary focus. The term “geomorphology”
is only cited twice in the index for a 1193-page
text; once when it is used by Carl Sauer (1956, p. 61) in a
list of topics one must know to understand changes in
habitability, the other time by Arthur Strahler (1956, p. 621)
in explaining how his perspective differs from that of an
engineer examining soil erosion and aggradation. “Geomorphogeny”
is used as a heading in a critical discussion of
Davisian geomorphology (Russell, 1956).
Early concepts of humans as geomorphic agents may
have underestimated the geomorphic effectiveness of
cultural activities. By the 1920s, however, awareness was
sufficient to generate a call from Seuss for the addition of
the noösphere (bGreek noös=mind) to the realms of
Earth in addition to the lithosphere, hydrosphere,
biosphere, and atmosphere (de Chardin, 1956; Fig. 2).
By the year 2000, increasing realization of the geomorphic
effectiveness of humans was driving the emergence
of a new human-impacts sub-field in geomorphology
(e.g., Haff, 2001). It also led to calls for distinguishing the
modern period — following the late 1700s — as a new
geologic epoch known as the Anthropocene, characterized
by distinct evidence of human activities preserved in the
geologic record (Crutzen and Stoermer, 2000; Crutzen,
2002).
The limited attention in the Changing the Earth
proceedings given to human impacts on river habitats
warrants attention because of the key role that rivers
play in cultural activities. When rivers were discussed,
most of the emphasis was on built structures, such as
canals and irrigation works (Klimm, 1956; Sears, 1956;
Wittfogel, 1956), on water quantity (Thomas, 1956c), or
on factors that affect water quality such as sediment
yield (Leopold, 1956) and human waste (Wolman,
1956). The physical habitat and geomorphology of
rivers were generally ignored except for brief mention of
natural factors such as river capture or changes in
channel course that alter river flows and human
habitability (Huzayyin, 1956; Russell, 1956). References
to human-induced changes in river morphology
are mostly in relation to river mouths and deltas (Davis,
1956; Klimm, 1956). Two papers directly addressed
surface runoff, sediment, and fluvial changes. Strahler
(1956) focused on drainage density and upland river
variables by introducing Horton's quantitative hydrology
concepts in the context of human impacts. Leopold
(1956) focused on the relation between sediment yield
and land use, although he could not resist talking about
stream channels, making the prescient comment that:
…man's work directly on river channels has been and
probably will continue to be a far more important
determinant of future channel conditions than the
natural operation of river mechanics in response to
man's changes on the watershed. It is probable that
long before the effects of the latter can occur, river
conditions will have been so altered by dams that
[dams] will be the primary factor in controlling riverchannel
characteristics (Leopold, 1956, p. 646).
The relative importance of watershed-wide land-use
impacts and dam impacts on channel morphology can be
debated, but Leopold's comment foreshadowed the
modern research emphasis on effects of dams on rivers
(e.g., Beyer, 2005; Graf, 2006-this volume; Poff et al.,
2006-this volume).
Fluvial geomorphology was not completely missing
from the Changing the Earth Symposium, but it was not
an explicit focus of the articles. Many of the chapters
referred to the effects of agriculture, forest clearing, urbanization,
fire, and other human activities on runoff and
Fig. 2. Pierre Teilhard de Chardin at the Princeton Symposium in 1956.
Source: Wenner Gren Foundation. Printed with permission.
155L.A. James, W.A. Marcus / Geomorphology 79 (2006) 152–171
soil erosion. The emphasis was usually on the socioeconomic
and cultural changes that led to these impacts,
however, rather than on downstream implications of the
impacts. The emphasis on upland changes rather than
riparian impacts reflected a pervasive contemporary bias
of the soil-conservation movement towards on-site issues
while disregarding off-site effects. Soil conservationists in
the United States during the 1930s and 1940s provided
numerous examples of soil stewardship, but few instances
of concern for downstream impacts (James, in press). This
may have reflected a widespread lack of perception of the
value of aquatic systems to public and environmental
health or of the pervasive nature of riparian and wetland
destruction (see Happ, 1944 for an exception). Concern
for offsite losses began to build in the 1950s and was a
keystone of the environmental movement in the 1960s.
The lack of geomorphology or concern for fluvial
systems in the Changing the Earth proceedings can be
explained, in part, by the tremendous breadth of
environmental impacts covered in the symposium.
Few areas in the litany of topics addressed in Changing
the Earth are undeserving of coverage. To the
contrary, the list of relevant human impacts is so large
that river impacts are subsumed within the vast panoply
of human impacts.
If the Changing the Earth Symposium did not
address geomorphology per se, however, why hold a
geomorphology symposium that commemorates the
Changing the Earth contributions? The answer is that
the documentation and guidance provided by the
Changing the Earth conference has been a major
impetus to subsequent in-depth environmental scholarship
— research that includes studies of human impacts
in fluvial geomorphology, the focus of the 2006
Binghamton Symposium. In particular, the Changing
the Earth proceedings provided an excellent prototype
of the broad-scale mixing of natural and societal
perspectives needed to develop a compelling synthesis
of anthropogenic changes to fluvial systems.
2.2.2. Broad scale approaches and the melding of
nature and culture
The Changing the Earth Symposium contributed to
modern thinking, in part, through its advocacy and
demonstration of certain approaches in studying human
impacts — methodological perspectives that in some ways
needed to be rediscovered in geomorphology. These
methods employed broad scales of time and space. By
taking the long view (the anthropological view) of human
history and impact, the conference foreshadowed modern
human-impact approaches in geomorphology, where
historical process and contingency play key roles in
explaining landscape characteristics, and geomorphic
explanation requires more than static equations based on
Newtonian physics. Ironically, at the very time of the
conference, geomorphology was undergoing a sweeping
change in its methodologies by abandoning the historical
Davisian approaches in favor of more reductionist
approaches that quantified relations between process and
form, and examined the role of humans by using these new
physical science-based approaches (Goudie, 1995, 2000).
These quantitative process studies, however, tended to
operate at moderately small scales of time and space to
avoid the data needs and non-linearities of longer-term,
broader scales (Fig. 3). Moreover, even at local scales, these
quantitative studies of processes often sought to eliminate
or control for the effects of human agency that could
obscure mechanistic process–response relationships.
The Changing the Earth Symposium also maintained
a broad spatial perspective and emphasized the landscape
scale. From a geomorphic viewpoint, the emphasis
on landscape scale is most notable in Strahler's (1956)
article where he explicitly explains the rationale for the
landscape process approach, in part to counter the plotspecific
work that process-based scientists with engineering
backgrounds had emphasized. The Changing
the Earth volume also emphasized change through time
in specific regions, landscapes, or ‘faces’ as they were
later referred (Turner et al., 1990). This landscape scale
of analysis now dominates much of the human impact
work in fluvial geomorphology and is being encouraged
by integrated watershed approaches described later.
Fig. 3. Four domains of fluvial geomorphic theory postulated by
Church (1996) as functions of time and space. The two lines depict
approximate rates of water flow (1 m s−1
) and sediment transport (100
m year−1
). The five fields represent a scale dependency of theoretical
causality or explanation that is important to considerations of human
agency in geomorphic processes. Adapted from Church (1996).
156 L.A. James, W.A. Marcus / Geomorphology 79 (2006) 152–171
In its documentation of human impacts in many
regions of the Earth over several millennia, Changing
the Earth presaged the modern recognition that finding a
truly “natural” fluvial system may be difficult (Graf,
1996), and that humans and nature are inextricably
intertwined within the fluvial landscape. This, in turn,
reinforced the contingent nature of geomorphology and
human agency, where river systems in similar natural
environments can vary greatly between different cultural
landscapes. Such systems cannot be completely modeled
using linear equations of force and resistance to simulate
the natural elements in isolation, but are best characterized
with an understanding of idiosyncrasies of cultural
traits and histories. Glacken (1956, p. 87) describes this
modern scientific challenge by emphasizing the importance
of considering humans as part of nature:
If human activities, however, are considered — or
defined — as interferences with this balance [of
nature], we assume the existence of a nature which is
an abstraction, and we neglect the effects of prehistoric
and historic cultures on the natural environment. These
effects are historical events, and, if not regarded as
such, the study of human cultures, with their mass of
customs and traditions, and the study of physical
environments will go their separate ways, and the gap
between the two will be bridged with metaphors.
In a fluvial context, this means that the history of humanriver
interactions must be known to fully understand
consequences to rivers and to humans. Fifty years later, in
these proceedings, Gregory (2006-this volume) echoes
this same call to contemplate a “cultural geomorphology:”
It is therefore not possible to prescribe a universal
approach to managing rivers, but only one which
reflects the influence of the particular cultural overlay.
Therefore it is now timely for geomorphologists to
raise awareness of such cultural distinctions and to
consider these when constructing recommendations.
2.2.3. Scholarly purpose
The 1955 conference foreshadowed current trends in
geomorphology, such as historically contingent
approaches, the intertwining of culture and nature, and
analysis at landscape scales. Providing methodological
exemplars was not the primary purpose of the proceedings,
however, and Thomas (1956b, p. xxii) was very
clear in stating that the primary objective was publication
of a permanent record accessible to a large audience and
available to future scholars. The conference succeeded in
this regard, providing expansive and, at times, overwhelming
documentation of human transformation of
Earth. At a simple inventory level, the conference provided
the baseline documentation that was needed to justify
making research on human impacts a major priority. The
scholarly influence of the symposium, however, went
beyond simple inventory. Through its comprehensive
documentation and explanation of the true breadth of
human impacts on Earth, Changing the Earth provided a
gathering point; that is, a unified vision of the many and
varied types of environmental degradation resulting from
population growth, accelerating rates of consumption of
resources, and the lack of societal awareness about the
consequences of cultural habits. These visions were from
many different perspectives and were integrated over
broad temporal and spatial scales. Although the volume
has been criticized for taking “a tad indifferent” tone that
did not push the public to action (Wilson, 2005), this
opinion seems unduly harsh. The proceedings were
written so that articles could be read by the educated
public, but the primary audience was clearly a scholarly
one. Its explicit goal was to generate an objective, new
scientific synthesis. To criticize it for lacking the rhetorical
and emotional appeal of Rachel Carson's (1962) Silent
Spring is to misconstrue its central purpose.
More than any particular article or new concept, the
sense of scientific exploration within the proceedings of
Changing the Earth has influenced scholars over several
generations. Within academia the conference provided
an enduring model for the multidisciplinary study of
environmental degradation. Global change research and
the current branch of geography often referred to as
“Nature and Society” were encouraged and influenced
by Changing the Earth (Kates et al., 1990; p.4). Just as
earth science was moving more and more towards
specialization with a narrowing focus of professional
expertise in individual fields, Changing the Earth
provided a much-needed synthesis in the opposite
direction. By inviting experts from a great diversity of
fields, new interdisciplinary ties were forged and a new
generation of scholars emerged in the 1960s and 1970s
with new perspectives. The work of these scholars and
the students they trained ultimately led to this 2006
Binghamton Geomorphology Symposium on The
Human Role in Changing Fluvial Systems.
3. Changes in research since the Changing the Earth
Symposium
Much has transpired in human impact studies in fluvial
systems since the scholarly environmental perspectives of
1956. More is now known about the history, locations,
sequence, and agents of change in fluvial systems.
Technologies, methods, theoretical constructs, and the
157L.A. James, W.A. Marcus / Geomorphology 79 (2006) 152–171
social setting of human impact studies are remarkably
different than they were two generations ago. Rather than
attempting an encyclopedic review, an overview is
provided here of some major changes in geomorphic
research since 1956, particularly as they relate to the 2006
Binghamton proceedings (see Walker and Grabau (1993)
for a more comprehensive summary of the historical
evolution of geomorphic research in the late 20th
century). These changes are described in terms of why
scholars study human impacts in rivers, what is being
studied over various time periods, how data have been
collected and analyzed, and who has carried out the
studies.
3.1. Why study human impacts on fluvial systems?
Many motivations for studying anthropogenic
impacts to fluvial systems are similar to the reasons
given in 1956 for studying broader environmental
impacts. These include documentation, inventory, and
explanation of change, as well as a desire to ameliorate
the destructive influences of humans on nature. Since
that time, however, some new rationales have emerged
and some existing ones have evolved and taken on
greater import. To a much greater degree than in 1956,
rationales for studying human impacts on rivers are now
driven by institutional needs, concerns over future
environmental change, and a growing desire to restore
natural functionality to streams.
3.1.1. Institutional needs and environmental
regulations
Discussion of regulation or policy-driven research
topics is nearly absent from the 1956 proceedings,
although Abel Wolman's (1956) paper addresses the
needs of water quality in this context. Other contemporary
fluvial research outside the 1956 proceedings was also
largely devoid of applied environmental topics, with the
exception of flood control, soil erosion, and water quality;
topics that were mostly treated from the perspective of
protecting human safety and economic well being. Since
1956, however, establishment of a wide array of
environmental regulations and a growing awareness of
environmental change and degradation have motivated
support for a growing amount of environmental monitoring
and research. Environmental legislation affecting
rivers in the USA range from the National Environmental
Policy Act and the Endangered Species Act to the Clean
Water Act; similar laws exist in other developed nations.
These laws have promoted environmental research and
the development of research protocols. They have improved
understanding of hydrogeomorphic topics ranging
from the establishment of sediment quality standards
(Marcus, 1989, 1991), to recommendations for developing
geomorphic indicators of stream health (Graf, 2001),
to guidelines for stream restoration (Rosgen, 1996).
Because government agencies and funding institutions
support much of the modern scholarship on rivers,
much of the rationale for modern studies of impact in
rivers is related to activities that agencies manage or
attempt to influence. These activities are largely in
response to accelerating pressures from development, a
growing awareness of health effects and environmental
degradation, and environmental regulations intended to
preserve, conserve, or restore natural systems. In the
United States, institutional initiatives for watershed or
river studies take the form of requests for proposals
(RFPs) from funding agencies, which typically focus on
understanding the history and processes of change and
predicting future change under different development
and mitigation scenarios. Motives for these studies
include development of viable strategies to protect and
enhance water quality, public health, aquatic ecosystems,
individual species, flood-conveyance systems, and water
resources. RFP-driven rationales may seek explanation,
but are often more concerned with applications of
existing knowledge to develop rational river policies,
management tools, or engineering solutions to specific
problems. In this context, the reasons for studying rivers
often take on a more pragmatic, applied perspective than
was demonstrated in the 1956 proceedings.
Growing institutional concerns about global to
regional change also provide greater incentives for
research on environmental impacts than in the past. An
increasing number of studies focus on how rivers have
responded or are expected to respond to deforestation,
agriculture, urbanization, or climate change. The rationale
for these studies is typically expressed in terms of trying to
understand and predict future response of rivers in order to
stabilize and maintain present river environments, or to
develop adaptive policies in response to those changes.
3.1.2. Aquatic restoration
Growing awareness of the magnitude of fluvial change
has led to an increasing emphasis on understanding ways
in which altered fluvial systems can be restored.
Recognition of the extreme changes that many fluvial
systems have undergone and the consequences of these
changes — positive and negative — is a first step in
ensuring that policies are implemented based on informed
criteria. For example, stream ‘restoration’ has become
emblematic to many river management programs and is
being widely practiced (e.g., Brooks et al., 2006-this
volume, provide Australian examples). The general
158 L.A. James, W.A. Marcus / Geomorphology 79 (2006) 152–171
rationale for restoration projects and related research is
readily apparent from any inventory of advancing
population growth, resource depletion, environmental
degradation, and esthetic disfigurement of natural systems.
The specific motivations behind “restoration”
projects vary dramatically, however, with land ownership,
funding agency, and cultural setting. The definition of
restoration thus ranges from attempts to return streams to a
pre-disturbance state to stabilization projects with structural
armoring that may disrupt natural processes and
reduce habitat diversity. A common definition of
restoration requires that stream channels be returned to a
previous condition (NRC, 1992). This criterion calls for
explicit historical reconstructions of changes to the fluvial
system, a practice that requires geomorphic expertise.
To restore a river on a sustainable basis often requires
that the processes controlling channel adjustments be
understood at a scale extending well upstream of a
specific stream reach and over multi-generational time
periods. An understanding is needed, therefore, of the
water and sediment loads integrated over the watershed,
which has led to a growth in integrated watershed assessment
as a tool in river restoration. Integrated approaches,
described later, require geomorphic expertise in
river processes and should include an assessment of the
key contemporary and historic physical, ecological, and
social controls on river change. These needs call for
geomorphic studies to go beyond physical processes to
examine also social aspects of river systems such as
economic pressures, land-use policies, and historical
development. Strong ties between ecologists and
geomorphologists are now emerging (e.g., Malanson,
1993), as exemplified by the 1995 Binghamton
Symposium devoted to Geomorphology and Ecosystems
(Hupp et al., 1995).
3.2. What is studied and when
As with all research disciplines, certain conventional
topics in fluvial geomorphology have received close
attention while other potential areas of study have gone
largely unattended. The Changing the Earth proceedings
emphasized change through time at specific regions and
landscapes, or ‘faces’ as they have been referred to. A
subsequent conference known as the Earth Transformed
Symposium (Kates et al., 1990) placed additional
emphasis on fluxes of energy and mass, thus framing
many of the physical questions raised by the study of
anthropogenic changes in terms compatible with mainstream
physical science. This section identifies some
ways in which the focus of research concerned with
human impacts on fluvial systems has changed since the
1950s in response to research on channel changes, scales
of observation, integrated watershed analysis, and
climate change. This list is by no means comprehensive
in terms of factors that have changed since 1956; rather,
it highlights notable changes addressed by papers in this
volume.
3.2.1. Channel changes
Channel hydraulics and morphology were addressed
peripherally in Changing the Earth, and largely from a
different perspective than that taken by contemporary
scholars — although some familiar refrains can be
heard. For example, an awareness of human impacts on
rivers clearly existed, but many of the implications of
these changes were not brought out. Klimm (1956)
notes, for instance, that the Grand Canal and other
projects on the China plain are of such antiquity that
distinguishing between canals and natural channel
systems is often impossible, but he does not describe
how modified systems differ from natural ones. In
contrast, the Leopold (1956) comment noted in Section
2.2.1 presaged the modern documentation of river
disruption by dams and indicated an appreciation for
the implications of fragmentation. Most radical perhaps
was Wittfogel's (1956) advocacy for a theory of hydraulic
civilizations, which postulated that civilization
springs not from urbanization, but from the development
and maintenance of irrigation agriculture. The
geomorphic implication of Witfogelian theory is that
river regulation is not simply a side effect of human
occupation, but represents an inherent and prerequisite
condition of civilization.
The central role that channel hydraulics and
morphology now play in the studies of human impacts
on rivers is represented by the 2006 Binghamton
Symposium (this volume), which contains an overview
of the topic (Gregory, 2006-this volume) as well as
articles on impacts of channelization and leveeing
(Simon and Rinaldi, 2006-this volume), dams (Graf,
2006-this volume; Poff et al., this volume), agricultural
land clearance in the upper Midwest, USA (Knox, 2006this
volume), mining (Macklin et al., 2006-this volume),
urbanization (Chin, 2006-this volume; Kang and
Marston, 2006-this volume), and alterations of animal
populations (Butler, this volume). This list does not
include additional potential impacts such as logging,
roads, gravel extraction, and a host of other types of
resource uses in and around rivers. The discussions of
the morphologic changes of channels in most of the
articles in this volume reflect the central role that
channel change has taken in modern studies of human
impacts on rivers.
159L.A. James, W.A. Marcus / Geomorphology 79 (2006) 152–171
3.2.2. Scales of observations — time and space
Identifying scales of data and research focus is critical
to developing a proper interpretation of anthropogeomorphic
impacts. For example, broad landscape-scale
changes that have accumulated over a long period of the
Holocene and recent local effects of urbanization are both
exhibited in the same riverscape. Allocating how much
variability is driven by each impact is difficult at best and
sometimes impossible, as is exemplified by the controversy
over anthropogenic versus climatic drivers of arroyo
cutting in the southwestern USA (Cooke and Reeves,
1976). Although time was explicitly addressed in the
1950s human impacts literature, from a theoretical basis
and from a practical methodological basis, considerable
difficulty was encountered in separating anthropogenic
from natural causes and effects across multiple scales.
From a theoretical perspective, Schumm and Lichty's
(1965) simple but widely influential paper provided a basis
for distinguishing between independent and dependent
variables and helped to structure many geomorphic
arguments around concepts of space and time. McDowell
et al. (1990) refined these arguments and provided an
explicit physical basis for scales at which process–
response systems operate, ranging from weather-related
events such as thunderstorms at small scales of space and
time up through tectonic forcing of glacial epochs at large
scales. Most of the human-induced changes described in
this volume occur within the second and third classes of
this model; that is, short period variations and neoglacial
events. The fourth class of orbital forcing, however, is of
importance to long-term anthropogeomorphic studies,
because the transition from late glacial climatic regimes
was a period of great cultural development and prefaced
the massive agricultural developments that sprang from
the Neolithic. Recognition of multiple drivers and
responses operating at various spatial and temporal scales
is now well established, and attempts to work across those
scales should be a goal of future studies.
From a practical perspective, discussions about multiscalar
analysiswereseverelylimitedin1956bymethodsthat
could not adequately characterize the full spectrum of local
to macro scales in space, or temporal changes ranging from
hours to millennia. As discussed later, new dating, measurement,
data storage, data dissemination, and analysis
techniques now facilitate analysis at multiple scales.
Not all the theoretical and practical difficulties in
separating processes and responses across scales have
been resolved (Phillips, 2004). Although the accuracy of
measurements has advanced and theory has provided
guidance, major obstacles to these analyses remain. For
example, distinguishing and understanding changes
driven by natural vs. human processes is essential to
understanding the relative role of anthropogenic influence.
Unfortunately, isolating human influences on
fluvial changes is difficult, because of the absence of
monitoring in most areas and the difficulty in applying
proxy records over large areas or over relatively short
time scales at which human-driven change can occur
(e.g., Simon and Rinaldi, 2006-this volume). To this day,
processes are not monitored in many parts of the world,
particularly in remote or developing nations (Marcus et
al., 2004; Wohl, 2006-this volume). Difficulties from
non-uniformities in global data sets are addressed by
Walling (2006-this volume) in analyzing suspended
sediment loads at global scales.
Process–response links can also be hard to isolate
because of factors such as inheritance of form,
polygenetic causalities and equifinality, lagged timing,
and threshold responses (McDowell et al., 1990).
Geomorphic responses to human activities such as
forest clearance may, therefore, be quite different in the
same location when considered under different conditions
or over different time scales. Moreover, recent
work suggests that geomorphic systems are often nonlinear
(Phillips, 1999). In this case, it may not be
possible to reconstruct which variable drove which
response. This situation suggests a need for techniques
to identify non-linearity and scale dependency in river
systems (e.g., Phillips, 2006), so that researchers and
managers can determine where and over what periods
monitoring is useful for identifying drivers of change
and predicting future change. Understanding long- to
short-term effects across multiple spatial scales thus
remains one of the major challenges to research of
human impacts in rivers.
3.2.3. Integrated watershed perspectives
The post-1950s quantitative revolution in geomorphology,
coupled with a turn towards using physics to
understand river process and response, led to the study
of many rivers as objects not tied to the surrounding
systems within the watersheds. This detailed study of
individual fluvial components in isolation — so important
to scientific understanding of causality — can
lead to a hydraulic myopia that fails to explain how rivers
respond as complex non-linear systems interacting with
human activities. Contemporary research on human
impacts in fluvial settings thus often needs to step outside
of this reductionist box and cross over the traditional
boundaries between fluvial geomorphology, aquatic and
riparian ecology, river engineering, planning, economics,
and related fields. An important development in this
regard is the move towards integrated studies of
watersheds.
160 L.A. James, W.A. Marcus / Geomorphology 79 (2006) 152–171
Integrated perspectives have taken hold in key
national and international arenas. In North America,
holistic river-management is often referred to as an integrated
watershed approach where ‘watershed’ is used
synonymously with catchment or drainage basin (as
opposed to its European use as a drainage divide). At the
national level, institutional structures and funding
mechanisms have changed dramatically in response to
the need for integration, and this has created new research
agendas and management policies that emphasize
watershed-scale approaches (USEPA, 1993; Naiman
and Bilby, 1998; NRC, 1999; Finlayson and Brizga,
2000; Lal, 2000; Downs and Gregory, 2004). The international
support for integrating multiple systems to
manage global fresh water supplies is displayed in
Agenda 21 of the United Nations Earth Summit in Rio de
Janeiro:
The complex interconnectedness of freshwater systems
demands that freshwater management be holistic
(taking a catchment management approach) and based
on a balanced consideration of the needs of people and
the environment. The Mar del Plata Action Plan has
already recognised the intrinsic linkage between water
resource development projects and their significant
physical, chemical, biological, health and socioeconomic
repercussions (UN, 1992; Section 18.36).
Multi-disciplinary approaches to the study and
management of fluvial systems acknowledge the interdependencies
between channel morphology, aquatic and
riparian ecology, climate, water resources, and numerous
other systems that govern the magnitude, frequency, and
quality of deliveries of water and sediment. Integrated
approaches should also consider changes to upland landuses
that drive the hydrologic and fluvial systems. An
important value of the Changing the Earth Symposium
was its broad coverage of many Earth surface systems. A
primary goal of this Binghamton Symposium is to
examine human impacts on fluvial systems within this
broad context of catchment dynamics.
Many studies in the 1956 proceedings address basinscale
changes that are relevant to hydrologic and fluvial
adjustments, including impacts of fire (Sauer, 1956;
Stewart, 1956) and technology (Darby, 1956; Heichelheim,
1956; Pfeiffer, 1956). Although these changes in
land cover clearly effected fluvial systems, rarely were
these changes or watershed processes explicitly linked to
river responses in the papers, or even to the runoff and
erosion so critical to rivers. In contrast, Strahler (1956)
made the watershed approach a central theme of his article.
In the modern context, it is now ill-advised to consider
major river changes without also considering the basinwide
context. The 2006 Binghamton Proceedings (this
volume) merely touches the surface of a vast literature on
topics of watershed changes and the linkages to channel
change. The effects of urbanization on fluvial systems are
addressed by Chin (2006-this volume) and Kang and
Marston (2006-this volume). A modern view of historical
changes and of current erosion conditions in the
Mediterranean region is provided by Hooke (2006-this
volume), landcover changesin North America are covered
by Knox (2006-this volume) and Poff et al. (2006-this
volume), and agricultural impacts on South American
rivers are examined by Harden (2006-this volume).
3.2.4. Global change and climate change
Although global climate change has long been an
important theme in studies of anthropogenic change, it
has only emerged recently as a major topic in the context
of human impacts on rivers. The Changing the Earth
proceedings clearly indicate the scientific perception of
climate change in the mid-1950s. The symposium
revealed a growing awareness of substantial changes in
temperature and precipitation regimes and sea level
changes in the recent past, and some papers discussed
implications of climate change to ecosystems, water
resources, and hydrology. At that time, however, the
importance of global-scale changes in atmospheric
chemistry, such as greenhouse gases, was not understood,
so the dimension of global anthropogenic climate change
was completely missing. Thus, while Quaternary climate
change was a recurrent theme at the Changing the Earth
Symposium, it was viewed as an independent variable
helping to explain human adjustments (Huzayyin, 1956;
Sauer, 1956). To the limited degree that human-induced
changes in climate were considered, they were relegated
to local surface changes to the water budget and resultant
radiation balance (Thornthwaite, 1956), and to urban
effects such as the urban heat island (Landsberg, 1956).
Ironically, the realization that human-induced CO2
warming could be significant was first raised in the
same year that the Changing the Earth proceedings were
published (Plass, 1956) and greatly advanced by one of
the participants (Landsberg, 1970). Clearly, one of the
most fundamental changes over the past fifty years in the
understanding of human impacts on rivers is the
realization that global scale climate changes can be
driven by humans and can be effective agents of change
within modern river systems (Goudie, 2006-this volume).
3.3. How research can be conducted
Modern technological innovations have simultaneously
complicated and improved the methods by which
161L.A. James, W.A. Marcus / Geomorphology 79 (2006) 152–171
human impacts on river systems can be studied. Major
changes in data collection, analysis, and delivery techniques
facilitate anthropogeomorphic research into the
multi-scalar, integrated watershed perspectives discussed
previously. These changes include advances in dating
techniques, mapping techniques, digital simulation, and
analytic methods. In addition, advances in the internet —
as found throughout the Earth sciences — have greatly
expanded the ability of researchers and the public to
access data and research results, to collaborate, and to get
involved in the development of research agenda, river
management, and policy.
Traditional approaches to collection of field data —
ranging from coring to erosion pins — have been enhanced
by numerous new data collection technologies
for field, laboratory, remote sensing, and analytical
methods. In the temporal domain, river scholars now
have access to dating technologies not even imagined in
the 1950s, when dating methods were largely restricted
to relative dating derived from stratigraphy or absolute
dates derived from dendrochronology, varves, or longterm
written records. Although Libby had begun in the
late 1940s to experiment with radiocarbon as a means of
dating carbon compounds, the reliability of this method
was still being tested in 1956. Since the 1950s, however,
14
C and a battery of additional isotopes have become
extremely important tools for dating late Quaternary
stratigraphy, identifying sources of water and sediment,
and constraining environmental changes. For example,
cosmogenic radionuclides allow dating of erosional
surfaces and alluvium over Quaternary time periods
(36
Cl, 26
Al, or 10
Be) down to a period of months (7
Be).
Other isotopes such as 210
Pb or 137
Cs allow fingerprinting
and dating of sedimentary deposits on intermediate
historical time scales (Aalto et al., 2003). Additional
dating tools, such as thermoluminescence and optically
stimulated luminescence (OSL), have expanded the
range of dates and applications. A broad suite of modern
techniques now enable specification of numerical ages
across a wide range of time scales with quantitative
measures of uncertainty.
A similar revolution occurred in spatial data
collection and processing techniques. Geographic
coordinates of field locations can now be quickly
measured to sub-meter resolutions, and mapping
surveys can easily collect large amounts of data and
register them with remote sensing imagery and a variety
of feature attributes. A striking feature of Changing the
Earth was the series of oblique aerial photographs of
cultural landscapes in the opening chapter (Gutkind,
2006). To contemporary readers, the vantage provided
by oblique aerial views was presumably novel and
provided an impressive new synthesis of patterns of
human development. In contrast, global and landscape
views are now commonplace as remote sensing imagery
and visualization tools have proliferated, clarifying the
relationship between landforms and cultural features.
These capabilities are of particular interest in anthropogenic
studies because the scale of human impacts is
often too small to be measurable — if detectable — on
standard topographic maps.
The advent of computer and spatial data in digital form
has powered the development of geographic information
systems (GIS) and the proliferation of digital elevation
models (DEMs) and digital maps of soils, vegetation,
rivers, roads, as well as other information for much of the
developed world. These advances have stimulated the
development of sophisticated spatially distributed numerical
models and automated simulations of physical systems.
Entire research initiatives and companies are now
devoted to developing algorithms to handle these data sets
and digital tools. In rivers, measurements of key hydraulic
parameters and habitat characterization can now be
acquired with multispectral (Fonstad and Marcus, 2005;
Carbonneau et al., in press) and hyperspectral optical
imaging devices (Marcus et al., 2003), ground penetrating
radar (Costa et al., 2000), and acoustic doppler current
profilers (Morlock et al., 2002). Detailed mapping of
topography with radar and lidar (Baltsavias, 1999; Cobby
et al., 2001), and of land cover with a variety of remote
sensing devices that operate across the electromagnetic
spectrum (Jensen, 2000) has become standard. Even advances
in microscale to subatomic measurements (Tsong,
2006) are gaining attention as geochemical interactions
with geomorphic, hydrologic, and biotic processes are
increasingly incorporated into the studies of human
impacts on rivers (e.g., Macklin et al., 2006-this volume).
Having praised the capabilities of modern spatial
technologies, caution should be urged about some
consequences. The power of the resultant spatially distributed
models and the persuasive nature of visualizations
of the output can lead users to believe that the models
are real, causing them to bypass the field calibration and
validation steps that are essential (Wilson and Gallant,
2000a). In recent years, a substantial effort has been
devoted to identifying error propagation in models and
digital data sets and how model performances vary in
different settings (Choudhry et al., 1998; Wilson and
Gallant, 2000b).
Much information is readily available over the internet,
where data repositories, online journals, list servers, and
email have greatly sped up and facilitated access to data
and expertise. Obtaining data, mapping the nature and
extent of human and natural features at various scales, and
162 L.A. James, W.A. Marcus / Geomorphology 79 (2006) 152–171
disseminating the results has never been so easy. For
example, improvements in the accessibility of global
spatial data recently accelerated with the advent of Google
Earth™ and other open sources of geographic data. These
new techniques hearken a renewed interest in subcontinental-scale
geomorphology that has not been in favor
since the physiographic studies of the early twentieth
century. New emphases on global change, coupled with
the need for integrated watershed-scale analyses and the
availability of data from other regions, will be likely to
stimulate these studies.
3.4. Who does the research — the changing social
context
Studies of human impact in fluvial geomorphology
have evolved greatly over the last fifty years, partly in
response to changes in the social context of the research.
These changes apply to human impact studies and also
more broadly to Earth sciences. This discussion focuses
on institutional changes that have affected how geomorphology
is practiced, primarily in the English speaking
world. The demographic profile of geomorphologists
and the institutional setting of geomorphology outside of
the English language settings is beyond the scope of this
paper. Interested readers are referred to Walker and
Grabau (1993) and Sack (2004) for discussions of these
topics.
Most investigators of human impacts in 1956 came
from universities, museums, or government agencies
focused primarily on monitoring (e.g., the U.S.
Geological Survey). These institutions remain crucial
to geomorphology as sources of data, funding, expert
personnel, and other resources. They have been joined
by other groups, however — including additional
government agencies, non-governmental organizations,
the private sector, and individuals — who now play
major roles in driving studies of human impacts on
rivers and watersheds. Integrated research approaches
have encouraged many of these new institutional players
and promoted a substantial broadening of the types of
scientists and managers now studying rivers.
Pervasive institutional changes that have arisen from
environmental regulations probably are the greatest
causes of change in who is doing human impact studies.
Two Acts of the U.S. Congress serve as diverse examples
of environmental legislation that have substantially
changed how fluvial systems are studied and managed
in the United States. The 1969 National Environmental
Policy Act (NEPA, 1969) required all federal agencies to
assess the environmental impact of federally funded
projects. It also introduced to the decision making
process the requirement for public participation in
environmental planning (James, in press). As a result,
studies of human impacts in rivers in the United States
often involve research scientists, environmental consultants,
multiple government agencies, and the public.
Despite the diversity of inputs from different sectors,
these studies must conform to strictly codified guidelines,
and have generated few new concepts of river form
and function. They have created, however, an entire
employment sector for river scientists and, by promoting
interest and employment in human impact analysis, they
have provided students for universities and generated
further research on anthropogenic changes.
The Clean Water Act (CWA) is another example of a
key set of environmental laws that has affected the study
and management of human impacts in rivers in the United
States. In the preamble to this lengthy Act, the stated
objectives are “…to restore and maintain the chemical,
physical, and biological integrity of the Nation's waters”
(CWA, Title I; 33 UCS 1251) (Arbuckle, 1993). These
goals have not been met in most water bodies and are
arguably unattainable in many, but the laws and regulatory
procedures that the CWA established are pervasive and
deeply intertwined with environmental management practices.
Unfortunately, regulatory efforts have focused largely
on restoring the chemical integrity of water bodies with
little or no attention to the physical condition (Adler et al.,
1993). Fluvial geomorphologists and hydrologists have
played an important role, however, in recommending
physically-based criteria (Marcus, 1989, 1991; Graf, 2001).
Furthermore, the CWA has spurred funding initiatives by
federal and state agencies to support basic and applied
research in river systems. Similar environmental regulatory
structures and pressures have emerged in many parts of the
world. Collectively, environmental legislation and awareness
have stimulated interest in geomorphic studies,
broadened the cast of participants in fluvial studies, and
increased funding and employment opportunities.
Changes in methodologies have also altered the
social context of anthropogeomorphic research. The
new methods usually require more resources in the form
of sophisticated laboratory facilities, field equipment,
imagery, computer resources, and a host of other
substantial expenditures. The opportunity for creative
projects that can be done on low budgets remains for the
truly innovative and resourceful scientist, but, in most
cases, a rod and level survey will no longer suffice. An
increasing amount of river research is being conducted
by teams that include specialists, such as geochemists,
hydrologists, pedologists, sedimentologists, surveyors,
numerical modelers, and geographic information scientists.
Furthermore, this list should be broadened for
163L.A. James, W.A. Marcus / Geomorphology 79 (2006) 152–171
research teams needed in studies that incorporate
cultural and socioeconomic elements.
The need to include the social elements of landscape
processes and watershed management in river studies will
call for a greater diversity of participants. Otherwise,
geomorphologists in the field risk being viewed as
outsiders without “standing” in the local cultural contexts
of the rivers that are to be preserved or enhanced.
Researchers should be cognizant of management and
restoration policy and of integrated watershed conditions.
Moreover, the modern era of anthropogenic fluvial
geomorphology will likely generate research opportunities
at a wide range of scales; from local to global spatial
scales and over Quaternary to contemporary time frames.
Fragmentation and overspecialization in geomorphic
training should be avoided and greater emphasis placed
on broad integrated training.
The explosion of new data sets, new analytical
techniques, and the greater need for specialists has
created challenges for non-specialists and those without
computer resources (Marcus et al., 2004). Thus, at a
time when the emphasis in environmental science and
management is often on increased public involvement,
and data delivery makes this involvement increasingly
possible, the disparities between rich and poor, literate
and illiterate, digitally and non-digitally proficient, and
specialist and non-specialist have grown. These disparities
pose a major obstacle that could undermine many
of the positive advances being made (Clark, 1996;
Rango and Shalaby, 1998). How geomorphic research is
conducted and explained can determine its relevance or
threaten its effectiveness for one of the major audiences
that should be reached — those who use and live along
rivers. For this reason, Marcus et al. (2004) argue that it
is increasingly important for geomorphologists and
hydrologists to plan educational and outreach components
for their research projects, particularly in areas
where people are less familiar with scientific approaches
and rationales.
4. Prospect: A sustainable future and theories of
human impacts
The road ahead holds an increasing need for a deeper
understanding of anthropogenic change in fluvial systems.
Rates of fluvial change are accelerating in many
river basins, public and institutional awareness of the
changes has grown, and the need to manage the changes
or adapt to them is growing more acute. Studies of human
impacts on rivers are rapidly evolving and many changes
in research directions may be projected into the future.
Rather than trying to catalog these potential incremental
changes, the focus here is on two topics of substantive
change. The first topic, sustainability, reflects a clear
mandate from the global community and many national
governments to adjust planning criteria to address longer
periods of resource depletion, human needs, and
maintenance of habitat. The second topic notes the need
for theories that integrate cultural and physical components
of river systems to provide a more holistic
understanding of the river–human interface.
4.1. Sustainability science
Sustainability refers to the use of resources in ways
that can be maintained over multiple generations while
minimizing damage to environmental and social
systems. The concept was initially introduced in the
social sciences, but was later adopted and advanced in
the physical sciences and in river science (Kates et al.,
2001; Clark and Dickson, 2003). Adoption of sustainability
as a policy constraint is generating new research
initiatives in human impacts and a reconsideration of the
role of government in general. The continued expansion
of sustainability as a policy guideline will create a
growing demand for geomorphic expertise, because it
encourages consideration of long-term environmental
changes over a period of centuries. This view is in
harmony with concepts of geomorphic time and
geomorphic perceptions of landscape change. Moreover,
sustainability science provides an important
incentive for geomorphologists and social scientists to
work together while adopting the integrative, long-term
perspectives required by integrated watershed and river
basin management.
Although the concept of sustainability is invoked
repeatedly in modern environmental research, it is by no
means a new concept. Indeed, many participants of the
1955 Changing the Earth Symposium recognized the
pitfalls of equating human domination over nature with
progress (Glacken, 1956) and calls for projecting an
environmental ethic into the future were lucid (Sears,
1956). Carl Sauer clearly expressed the need for an
environmental ethic of sustainability when he asked:
Are our newly found powers to transform the world,
so successful in the short run of the last years, proper
and wise beyond the tenure of those now living? To
what end are we committing the world to increasing
momentum of change? (Carl Sauer, 1956; p.66).
Sauer goes on to proclaim:
For the present, living beyond one's means has
become civic virtue, increase of ‘output’ the goal of
164 L.A. James, W.A. Marcus / Geomorphology 79 (2006) 152–171
society. The prophets of a new world by material
progress may be stopped by economic limits of
physical matter… The high moments of history have
come not when man was most concerned with the
comforts and displays of the flesh but when his spirit
was moved to grow in grace. What we need more
perhaps is an ethic and aesthetic under which man,
practicing the qualities of prudence and moderation,
may indeed pass on to posterity a good Earth (Carl
Sauer, 1956; p.67).
Sauer (Fig. 4) was a principal in the Changing the
Earth leadership.
In the lexicon of modern environmentalism these
concerns for sustainability could be phrased in terms of
a social responsibility to maintain intergenerational
equity, one of the central tenets of sustainable resource
use. Although much modern environmental research is
steered towards this end, the failure to alter the overall
course of environmental degradation is striking. A new
set of motivating questions and rationales are needed
that cannot come from the engineering and technical
sectors alone, because values are not scientifically
testable. These questions will require collaborations
between natural scientists, social scientists, philosophers,
and ethicists. They will call for new perspectives
on natural process–response systems that include
changes brought about by human agency. Herein lies a
growing challenge to studies of human impacts and to
the next generation of geomorphologists who address
questions of anthropogenic change.
4.2. Where is theory?
Major progress has been made since 1956 in
understanding the location, magnitude, and persistence
of human impacts; and these findings have substantially
advanced an understanding of the geomorphic human
imprint. On the other hand, as a discipline, little effort
has been made to tie these studies together into broader
overarching statements about what can be known — and
equally important what cannot be known — about
cause, effect, and prediction in rivers altered by humans.
To the degree that theories of river change and stability
exist, they are largely based on physical studies that
control for, eliminate, or ignore anthropogenic changes,
or they may simply treat human influence as another
physical or biological process.
To reach the next level of understanding and
predictive capability, theories are needed that specifically
apply to anthropogenic change. A number of
questions can be raised to demonstrate some of the areas
of concern (Table 1.1). This list could be extended
indefinitely, but the point is that general principles of
causality are lacking for this emerging field of
anthropogeomorphology and that conceptual models
are needed to explain change and provide important
Fig. 4. Carl O. Sauer at Princeton conference in 1956. Source: Wenner
Gren Foundation. Printed with permission.
Table 1.1
Questions revealing the need for anthropogeomorphic theories
Scale:
*) Are there spatial or temporal scales at which responses to human
pressures change fundamentally?
— If so, at what scales do anthropogenic processes become non-linear,
chaotic, or contingent and do these scales differ from natural
processes? The importance of time and space to broad theoretical
realms implies that fundamental changes to theoretical constructs
occur at different scales of time and space (Fig. 3; Church, 1996).
Hydrologic response:
*) Is there a critical proportion of impermeable area of a basin before
human impacts on runoff generation generate downstream changes in
channel morphology (Kang and Marston, 2006-this volume)? If so,
why? Do these thresholds change with climate, topography, or soils?
*) Do anthropogenic increases in runoff, due to agricultural or urban
land use, effect extreme flood magnitudes (e.g., ≥50-year
recurrence intervals), or do natural soils become so saturated
during those events that human changes are ineffective?
Geomorphic responses:
*) Are sediment waves induced by human activities–such as
deforestation, agricultural clearance, or mining–inherently
different in their character and behavior than those generated
naturally by landslides, climate change, or tectonics?
— How does this apply to sediment budgets or to Knox's (1972)
biogeomorphic response model?
*) To what extent is channel morphology affected by changes in
riparian ecosystems due to vegetation removal or invasion by alien
species?
165L.A. James, W.A. Marcus / Geomorphology 79 (2006) 152–171
predictive capabilities. The Binghamton 2006 symposium
was convened in large part to initiate a dialogue
and to spur efforts to identify some incipient theories of
anthropogeomorphology, and to point the way to fruitful
avenues of theoretical development (e.g., Gregory,
2006-this volume).
4.2.1. Obstacles to theory development
The general lack of theory in anthropogeomorphology
reflects, in part, its early stage of development as a distinct
field of study. Many studies of human impacts on fluvial
systems have been driven by immediate, applied needs
and have not focused on identifying theory. Studies
concerned with aquatic restoration, stream stabilization,
or flood hydrology, for example, have been largely
applied and have not often resulted in the development
and testing of theories of the human element of systems.
The lack of integrative theory also reflects the
emphasis on physical science methods in fluvial geomorphology
and hydrology. Only recently has a substantial
effort been made to integrate studies of the biological
and physical systems. Integrating cultural phenomena
into a holistic understanding of river response will be
even more difficult. Some barriers arise because scholars
in cultural studies often use language that is alien to Earth
scientists, engage in protracted social critiques that are
not perceived to be germane to natural science concerns,
and construct qualitative models that can be seemingly
incompatible with quantitative models of natural systems.
Individuals who can elucidate both cultures are
needed to bridge these differences. This will require
institutional support that enables individuals from one
field to engage in starting up in another. Whether the
resource-constrained research community has the will to
take such steps is an important question. It is easy to say
“interdisciplinary,” but making it happen is another
matter, particularly when some aspects of disciplines are
so different as to seem antithetical. A concerted effort is
needed to overcome differences in methodology, research
goals, and conceptual frameworks.
Even within geomorphology and hydrology substantial
cultural barriers exist and the nature of discourse often
obstructs the development of theory. Some empiricists
argue that established theories are detrimental to the
operation of science because they can bias methods and
observations (Brown, 1996). When studies attempt to
extend findings beyond a specific type of impact or
outside of the watersheds for which empirical data are
available, they often receive harsh criticisms from
reviewers who resist making generalizations about
systems where local history and context are important.
The difficulties faced by authors in making generalizations
about anthropogenic impact and river response
are real and pervasive. The potential criticism from
reviewers can be swift and hard. Yet, theoretical discourse
is essential to science and should be encouraged.
Finally, the complexity of geomorphic systems and
tremendous local variability can make it hard to identify
and define causal relationships and generalizable
geomorphic principles, causing scholars to shy away
from making overarching statements (Rhoads and
Thorn, 1996). This becomes even more of a problem
where nonlinear dynamics introduce chaotic response
and uncertainty in the trajectories of change (Phillips,
1996). When human activities are included in geomorphic
systems, the complexity of the system is often
greatly multiplied. Many researchers, therefore, focus
on one human cause of change in one watershed or
region; e.g., post-agricultural dispersion of sediments
throughout a basin. Because scholars often lack the
resources needed to extend findings further, inquiry
stops. Clearly, a shift in priorities is needed to expand
studies to the broader range of multiple human changes
and interactions between them.
4.2.2. Use of existing physically-based theories
Despite the obstacles, notable attempts are being
made to progress beyond explanations that apply only to
local settings. Two avenues have commonly been
followed to develop more general theoretical constructs.
One approach has been to adopt existing fluvial theories
to human-impacted systems. Several theories of runoff
and sediment generation, fluvial channel processes, and
other landform processes are often applied to understanding
human impacts on fluvial systems (e.g.,
Schumm, 1977). This has been the dominant approach
to understanding human impacts to fluvial systems.
Although few existing fluvial and hydrologic theories
were intended for direct use in studies of human impact,
they often may be applied to these changes. For
example, the variable source area, complex response,
and biogeomorphic response models, as well as the
concept of grade and non-linear dynamics are compelling
theories that may improve interpretations of fluvial
responses to watershed alterations. The question is how
to adapt them to incorporate the effects of highly
variable human activities.
Another approach to developing anthropogenic
theory has been to focus on one component of human
impact and develop theory around that particular
feature, thus allowing characterization of the impact in
physical terms. For example, Graf (2006-this volume)
provides a general model for the nature and range of
dam impacts by examining stream segments above and
166 L.A. James, W.A. Marcus / Geomorphology 79 (2006) 152–171
below dams in relatively undisturbed settings. In this
way, a general theory of dam impacts is developed
because the human component can be treated as a
change in flow regime.
The direct transfer of physical models to broader
conceptualizations of human impact theory is often
justifiable, especially where human impacts can be
characterized in physical terms. In many settings,
however, the human presence is so intertwined in the
history and in the landscape, that separation of human
impacts from natural changes is impossible. Much of
Graf's effort in the example above went toward locating
relatively undisturbed river reaches above major dams.
Moreover, human activities may result in system response
that cannot be subsumed by conventional fluvial theory
based on physical science (Urban, 2002; Gregory, 2006this
volume). Research is needed on the extent to which
existing theories may be applicable to situations where
human impacts are a central factor. This need calls for an
examination of elements of anthropogenic fluvial change
that are unique and defy categorization by traditional
physics, chemistry, or biological parameters.
4.2.3. Anthropogeomorphic theory
For theories of anthropogeomorphology to advance, a
change in attitude within geomorphology and hydrology
may be needed about the use of terms such as scientific
“theories” and “laws.” These terms are often held up as
paragons of scientific accomplishment, that can only be
claimed when the universality of application can match the
legendary status of theories by Newton, Einstein, or Bohr.
Lofty notions of what theory generation should be may
inhibit a scholar's willingness to make generalizations.
Whereas such strict and high standards may prevent the
trivial from being elevated to the status of the grand, they
also promote the promulgation of studies confined to
empirical findings and local case studies loaded with
idiosyncrasies. Empirical articles making local claims of
explanation are far more likely to be published, so the
tendency for empiricism is reinforced. In some ways, this
can be a good thing, as it encourages research to produce
data that can be used to test and develop theories. In
actuality, however, few theories have been forthcoming
from the data, and greater efforts are needed to extract
general principles from applied case studies.
Cultural phenomena need to be explicity addressed by
theory. Spatial and historical variations in livelihood
strategies, local culture, and politics may tell us more
about contemporary floodplain form (e.g., Bravard,
2006), than a model that is based on flood recurrence
intervals. The potential for development of theories of
fluvial anthropogeomorphology, however, is problematic;
it is more easily stated than practiced. The development of
such theories should be given a high priority for future
work because anticipating future human impacts requires
knowledge of how humans interact with natural systems.
One obvious statement that can be made in this regard is
that geomorphologists should seek collaborations with
social scientists, planners, humanist scholars, local
residents, and policy makers to establish a broader
understanding of the role of humans in these systems.
Collaboration alone, however, is not enough. All players
must move outside their intellectual comfort zones and
willingly adapt their methods, research designs, and
vocabulary to accommodate diverse perspectives on what
constitutes valid knowledge, understanding, and prediction.
If only physically-based findings are produced, only
physically-based predictability will be achieved. Anthropogeomorphology
calls for new methods of discourse that
truly allow culture and nature to be included in theories of
human impacts and environmental change in river
systems. Thomas (1956b, p. xxxvii) clearly understood
this when he stated:
“The dichotomy of man and nature is thus seen as an
intellectual device and as such should not be
confused with reality; no longer can man's physical–biological
environment be treated, except in
theory, as ‘natural’.”
5. Summary
Studies of the impact of humans on rivers have
progressed far since the 1956 Man's Role proceedings.
The works of pioneers such as Luna Leopold (e.g., 1953,
1956) and Arthur Strahler (e.g., 1952, 1956) were just
beginning to guide the growth of a new quantitative,
process-oriented approach to river studies. The contrast
between research in 1956 and 2006 is thus remarkable in
many ways. Human impact studies are now driven to a
much greater extent by environmental regulations,
institutional needs, and restoration goals, which in turn
have led to increased involvement of government
regulators, nongovernmental organizations, and consultants
in river studies. Methods now include a remarkable
array of dating techniques, spatial data acquisition at local
to global scales, and computer-based quantitative analysis,
mapping and modeling. The evolving social drivers of
research and new methods have led to shifts in topics that
are studied, with increasing emphasis on channel changes,
human agency across multiple scales, and development of
approaches to sustainability and integrated management
throughout watersheds. Paradigms used to characterize
river responses to the impacts of humans are often
167L.A. James, W.A. Marcus / Geomorphology 79 (2006) 152–171
different, commonly including concepts of nonlinearity,
complexity, and thresholds.
Yet at another level, much about human impact
research in rivers remains the same. The 1956 Changing
the Earth proceedings highlighted the need to look at the
big picture –to assess human impacts at landscape scales
and over century-to-millennial time periods so as to grasp
the true scope of human influences on Earth. In
articulating this need, the scholars of 1956 made it clear
that landscapes are contingent; that they evolve differently
under different natural and cultural influences. These
themes are echoed in the watershed perspectives, the
complex response paradigms, and the historical reconstructions
conducted by modern-day river scientists and
reflected by articles in this volume. Similarly, the scholars
of the Changing the Earth Symposium clearly articulated
the need for models that bridge the cultural studies–
physical science divide. River scholars continue to
grapple with this issue, suggesting it may be time to
adopt Rhoad's (2004, p. 752) recommendation “…to
forget about conceptualizing how an integrative geography
should work and get on with the business of trying to
make it work.”
A common sense of purpose also permeates the
literature of 1956 and 2006, although that purpose is
often muted in the dry prose of modern scientific writing.
Whether it be through explanation of human impacts,
calls for new regulatory measures, discussions of new
research approaches, or arguments for greater involvement
of river scientists in decision making, a clear and
deep sense of caring for rivers pervades the articles in this
volume and the larger literature on human impacts in
rivers. Thus, while many of the particulars of scholarship
on human impacts in rivers have changed, the underlying
intent remains the same: to enrich our understanding of
how humans alter rivers, and to protect and enhance the
rivers that we study.
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