Andrew P. Brooks, Timothy Howell, Tim B. Abbe, Angela H. Arthington -
Confronting hysteresis: wood based river rehabilitation in highly altered
riverine landscapes of south-eastern Australia
David R. Butler - Human-induced changes in animal populations and distributions, and their subsequent effects on fluvial systems
Anne Chin - Urban transformation of river landscapes in a global context
Andrew S. Goudie (Keynote) - Global warming and fluvial geomorphology
William L. Graf - Downstream hydrologic and geomorphic effects of large dams on American rivers
Kenneth J. Gregory - The human role in changing river channels
Carol P. Harden - Human impacts on headwater fluvial systems in the northern and central Andes
Janet M. Hooke - Human impacts on fluvial systems in the Mediterranean Region
L. Allan James and W. Andrew Marcus - Research on the human role in changing fluvial systems: Retrospect, inventory and prospect
Ranbir S. Kang and Richard A. Marston - Geomorphic effects of rural-to-urban land use conversion on three streams in the central Redbed Plains of Oklahoma
James C. Knox - Floodplain sedimentation in the Upper Mississippi Valley: Natural versus human accelerated
Mark G. Macklin, P. A. Brewer, K. A. Hudson-Edwards, G. Bird, T. J. Coulthard, I. A. Dennis, P. J. Lechler, J. R. Miller, J. N. Turner - A geomorphological approach to the management of rivers contaminated by metal mining
Patricia F. McDowell - Grazing in riparian zones in the western U.S.: Impacts, management and scientific progress. Article not included in book volume.
N. LeRoy Poff, Brian P. Bledsoe, Christopher O. Cuhaciyan - Hydrologic variation with land use across the contiguous United States: geomorphic and ecological consequences for stream ecosystems
Andrew Simon and Massimo Rinaldi - Channelized and other incised streams: Experiences with excess flow energy and stream power in compressed time scales
Des E. Walling - Scales and Locales of Impact: Human impact on land-ocean sediment transfer by the world’s rivers
Ellen Wohl - Human Impacts to Mountain Streams
M. G. (Reds) Wolman (TBA) - Reflections on the changing geomorphic landscape. Article not included in book volume.
Confronting hysteresis: wood based river rehabilitation in highly altered
riverine landscapes of south-eastern Australia -
Andrew P. Brooks1, Timothy Howell1,
2, Tim B. Abbe3 and Angela H. Arthington1
1Centre for Riverine Landscapes, Griffith University, Nathan Qld
4111 Australia. E-mail:
andrew.brooks@griffith.edu.au
2New South Wales Department of Primary Industries, Locked Bag 1,
Nelson Bay 2315, Australia.
3Herrera Environmental Consultants Inc., 2200 Sixth Ave., Suite
1100, Seattle Washington, 98121 USA
Abstract: This study evaluates
an experiment in river rehabilitation which uses large wood to stimulate and
emulate natural system processes in an effort to reverse channel degradation,
excess sediment transport and habitat simplification that has resulted from
two centuries of human induced disturbances, particularly desnagging. The
experiment involved the reintroduction of 436 logs (350 t) within 20
engineered log jams (ELJs) over an 1100 m reach. Commencing in 1999, the
experiment was set up as a standard BACI design, with a control reach 3 km
upstream. In the five years since implementing the rehabilitation strategy,
the study reach has experienced five floods greater than the mean annual, and
a further five events capable of mobilising the gravel bed. Five surveys of
channel terrain have been completed since treatment implementation, and the
changes to net sediment storage and morphologic diversity assessed in
comparison to the control reach. Seven surveys of the fish population in the
reach have also been undertaken during the project to measure the ecological
response to the introduced wood. The experiment has demonstrated the
effectiveness of ELJ technology in achieving engineering and geomorphic goals.
To date, the treatment has halted further degradation of the river and
increased sediment storage, with the test reach now storing, on average, 40 m3/1000
m2 more sediment than in the control. These values, it would
appear, represent a new reach-scale dynamic equilibrium storage level over
decadal timescales. Additional sediment storage amounts to 3.5 m3
per m3 of wood added. At the reach scale this additional
storage represents a reduction of just 2% or less of the post-European
expansion in channel capacity, suggesting far greater efforts are required
than those employed here to reverse the cumulative effects of 180 years of
channel erosion and simplification.
Pool and bar area in the test reach increased by around 5% and 3.5%,
respectively, while the corresponding values in the control were around 1.5%
and 1%, respectively. Two indices of morphologic diversity were measured for
each bed survey: the standard deviation of 3D residuals of change compared
with the baseline survey (SDiΔ3D); and the standard deviation of thalweg
residuals from the line of best fit (SDiTR). The SDiΔ3D index shows both
reaches increased in complexity through the study, with the treatment
increasing more than the control (0.37 and 0.29, respectively). The SDiTR
index does not detect clear changes because of the low signal to noise ratio,
however, it does suggest the test reach was more complex than the control at
the outset. The observed increase in fish abundance after the first 12 months
of monitoring, reported previously, is now far less distinct four years on – a
pattern seemingly reflecting the relatively minor increases in critical pool
habitat and habitat diversity over the same period. Although no significant
differences were detectable in fish species richness or total abundance from
the reach aggregate data after 4 years, analysis of individual structures show
them to be high quality habitat for native fish compared to the rest of the
reach and the upstream control.
These results highlight the challenges river managers face in achieving
measurable improvements in the health of aquatic ecosystems in highly altered
rivers. Managers must confront hysteresis in a biophysical and institutional
sense when attempting to reverse the degradation of rivers. The scale of
treatment implemented in this experiment was at the upper end of the spectrum
of rehabilitation efforts currently being undertaken in Australia, suggesting
that far greater resources and longer timescales are required to achieve the
levels of improvement in the diversity of stream habitat expected by the
community. The study also highlights problems with the strategy of attempting
to meet multiple objectives within a reach scale rehabilitation project.
While this treatment successfully met some geomorphic study objectives,
maximising the benefits for fish habitat would require a strategy focused
primarily on the creation of complex woody habitat within deeper pools,
particularly pools immediately below riffles.
Key Words: river rehabilitation; large woody debris; geomorphic recovery; complex response, meso-habitat; micro-habitat, freshwater fish
Human-induced changes in animal populations and distributions, and the subsequent effects on fluvial systems - David R. Butler
Department of Geography, Texas State University-San Marcos, San Marcos, TX 78666-4616, USA
Abstract: Humans have profoundly altered hydrological pathways and fluvial systems through their near-extirpation of native populations of animal species that strongly influenced hydrology and removal of surface sediment, and through the introduction of now-feral populations of animals that bring to bear a suite of different geomorphic effects on the fluvial system. In the category of effects of extirpation, examples are offered through an examination of the geomorphic effects and former spatial extent of beavers, bison, prairie dogs, and grizzly bears. Beavers entrapped hundreds of billions of cubic meters of sediment in North American stream systems prior to European contact. Individual bison wallows, that numbered in the range of 100 million wallows, each displaced up to 23 m3 of sediment. Burrowing by prairie dogs displaced more than 5000kg and possibly up to 67,500 kg of sediment per hectare. In the category of feral populations, the roles of feral rabbits, burros and horses, and pigs are highlighted. Much work remains to adequately quantify the geomorphic effects animals have on fluvial systems, but the influence is undeniable.
Key Words: zoogeomorphology, geomorphology and animal impacts, fluvial systems, bison and prairie dogs, feral animals
Urban transformation of river landscapes in a global context - Anne Chin
Department of Geography, Texas A&M University, College Station, TX 77843, USA
E-mail: chin@tamu.edu
Abstract: Over the past 50 years considerable progress has been made in understanding the impacts of urban development on river processes and forms. Such advances have occurred as urban population growth has accelerated around the world. Using a compilation of research results from more than 100 studies conducted in a range of areas (58 addressing morphological change), this paper describes how urbanization has transformed river landscapes across Earth’s surface, emphasizing the distribution of impacts in a global comparative context. Urban development induces an initial phase of sediment mobilization, characterized by increased sediment production on the order of 2-10 times, followed by eventual decline that couples with erosion from increased runoff to enlarge channels. Channels generally enlarge to 2-3 times and as much as 15 times the original size. Whereas research has emphasized temperate environments, data from recent studies of tropical areas indicate a tendency for channel reduction, characterized by strong sediment erosion and deposition responses because of intense precipitation and highly weathered soils. Embryonic research in arid environments further suggests variable river responses to urbanization that are characterized by rapid morphological change over short distances. Regardless of location, the persistence of the sediment production phase varies from months to several years, whereas several decades are likely needed for enlarging channels to stabilize and potentially reach a new equilibrium. Urbanizing streams pose particular challenges for management given an inherent changing nature. Successful management requires a clear understanding of the temporal and spatial variations in adjustment processes.
Keywords: urbanization, channel adjustments; stream equilibrium; river management
Global
warming and fluvial geomorphology - Andrew S.Goudie
St. Cross College and Oxford University Centre for the Environment, St Cross
College, Oxford, OX1 3LZ, Oxford, UK
E-mail:
andrew.goudie@stx.ox.ac.uk
Abstract: Future global warming has a number of implications for fluvial
geomorphology because of changes in such phenomena as rates of
evapotranspiration, precipitation characteristics, plant distributions, plant
stomatal closure, sea levels, glacier and permafrost melting, and human
responses. Potential changes in rivers are outlined in this review in the
context of changes in the intensity of rainfall, the activity of tropical
cyclones, runoff response (including that of Europe, dry lands and high
latitude environments), and geomorphological reactions, including rates of
soil erosion. In general, however, much work remains to be done to establish
the full range of geomorphological responses that may take place in fluvial
systems.
Keywords: global warming, fluvial geomorphology, runoff, snow pack,
deltas
Downstream Hydrologic and Geomorphic Effects of Large Dams on American Rivers - William L. Graf
Department of Geography, University of South Carolina, Columbia, SC, 29208, USA
E-mail: graf@sc.edu
Abstract:
The hydrology and geomorphology of large rivers in America reflect the
pervasive influence of an extensive water control infrastructure including
more than 75,000 dams. One hundred thirty-seven of the very large dams, each
storing 1.2 km3 (106 acre feet) of water or more, alter
the flows of every large river in the country. The hydrologic effects of
these very large dams emerge from an analysis of the stream gage records of
72 river reaches organized into 36 pairs. One member of each pair is an
unregulated reach above a dam, whereas the other is a regulated reach
downstream from the same structure. Comparison of the regulated and
unregulated reaches shows that very large dams, on average, reduce annual peak
discharges 67 percent (in some individual cases up to 90 percent), decrease
the ratio of annual maximum/mean flow 60 percent, decrease the range of daily
discharges 64 percent, increase the number of reversals in discharge by 34
percent, and reduce the daily rates of ramping as much as 60 percent. Dams
alter the timing of high and low flows and change the timing of the yearly
maximum and minimum flows, in some cases by as much as half a year. Regional
variation in rivers, dams, and responses are substantial: rivers in the Great
Plains and Ozark/Ouachita regions have annual maximum/mean flow ratios that
are 7 times greater than ratios for rivers in the Pacific Northwest. At the
same time, the ratio of storage capacity/mean annual water yield for dams is
greatest for Interior Western, Ozark/Ouachita and Great Plains rivers and
least for Pacific Northwest streams. Thus, in many cases those rivers with
the highest annual variability have the greatest potential impact from dams
because structures can exert substantial control over downstream hydrology.
The hydrologic changes by dams have fostered dramatic geomorphic differences
between regulated and unregulated reaches. When compared to similar
unregulated reaches, regulated reaches have 32 percent larger low flow
channels, 50 percent smaller high flow channels, 79 percent less active flood
plain area, and 3.6 times more inactive flood plain area. Dams also affect
the area of active areas, the functional surfaces that are functionally
connected to the present regime of the river. Regulated reaches have active
areas that are 72 smaller than the active areas of similar unregulated
reaches. The geomorphic complexity (number of separate functional surfaces
per unit of channel length) is 37 percent less in regulated reaches.
Reductions in the size of hydrologically active functional surfaces are
greatest in rivers in the Great Plains and least in Eastern streams. The
largest differences in geomorphic complexity are in interior western rivers.
The shrunken, simplified geomorphology of regulated large rivers has had
direct effects on riparian ecology, producing spatially smaller, less diverse
riparian ecosystems compared to the larger, more complex ecosystems along
unregulated reaches of rivers.
Keywords: dams, rivers, hydrology, fluvial geomorphology, aquatic and riparian habitats
The human role in changing river channels - Kenneth J. Gregory
Department of Geography, University of Southampton, Southampton, S017 1BJ, UK
E-mail address: k.j.gregory@ntlworld.com
Abstract:
Direct
consequences of the human role, where human activity affects river
channels through engineering works including channelization, dam construction,
diversion and culverting, have been long recognized (Marsh, 1864; Thomas Jr.,
1956). The less obvious indirect effects of point and reach changes occurring
downstream and throughout the basin, however, are much more recently
appreciated, dating from key contributions by Strahler (1956), Wolman (1967),
Schumm (1969), and Graf (1977). These are complemented by effects of
alterations of land use, such as deforestation, intensive agriculture and
incidence of fire, with the most extreme effects produced by building
activity and urbanization.
Changing river channels are most evident in the channel cross-section where changes of size, shape and composition are now well-established, with up to tenfold increases or decreases illustrated by results from more than 200 world studies. In addition the overall channel planform, the network and the ecology have changed. Specific terms have become associated with changing river channels including enlargement, shrinkage and metamorphosis. Although the scope of adjustment has been established, it has not always been possible to predict what will happen in a particular location, because of complex response and contingency. The ways in which changes in cross-section relate to reach and network changes are less clear, despite investigations showing the distribution of changes along segmented channels.
When considering the human role in relation to changing river channels, at least five challenges persist. First, because prediction of the nature and amount of likely change at a particular location is not certain, and because the contrasting responses of humid and arid systems needs to be considered, modelling is required to reduce uncertainty, as was first emphasised by Burkham (1981). Second, feedback effects incorporated within the relationship between changes at channel, reach and network scales can have considerable implications, especially because changes now evident may have occurred, or have been initiated, under different environmental conditions. Third, consideration of global climate change is imperative when considering channel sensitivity and responses to threshold conditions. Fourth, channel design involving geomorphology should now be an integral part of restoration procedures. This requires, fifthly, greater awareness of different cultures as a basis for understanding constraints imposed by legislative frameworks. Better understanding of the ways in which the perception of the human role in changing river channels varies with culture as well as varying over time should enhance application of design for river channel landscapes (Table 6).
Key words: river channel changes, river channel management, human impact
Human impacts on headwater fluvial systems in the northern and
central Andes - Carol P. Harden
Department of Geography 304 Burchfiel Geography
Building, University of Tennessee, Knoxville, TN37996-0925, USA
E-mail address:
charden@utk.edu
Abstract: South America delivers more freshwater runoff to the ocean per km2 land
area than any other continent, and much of that water enters the fluvial
system from headwaters in the Andes Mountains. This paper reviews ways in
which human occupation of high mountain landscapes in the Andes have affected
the delivery of water and sediment to headwater river channels at local to
regional scales for millennia, and provides special focus on the vulnerability
of páramo soils to human impact. People have intentionally altered the
fluvial system by damming rivers at a few strategic locations, and more widely
by withdrawing surface water, primarily for irrigation. Unintended changes
brought about by human activities are even more widespread and include forest
clearance, agriculture, grazing, road construction, and urbanization, which
increase rates of rainfall runoff and accelerate processes of water erosion.
Some excavations deliver more sediment to river channels by destabilizing
slopes and triggering processes of mass-movement.
The northern and central Andes are more affected by human activity than
most high mountain regions. The wetter northern Andes are also unusual for the
very high water retention characteristics of páramo (high elevation grass and
shrub) soils, which cover most of the land above 3000 m. Páramo soils are
important regulators of headwater hydrology, but human activities that promote
vegetation loss and drying cause them to lose water storage capacity. New data
from a case study in southern Ecuador show very low bulk densities (median
0.26 g cm-3), high organic matter contents (median 43%), and high
water-holding capacities (12% to 86% volumetrically). These data document
wetter soils under grass than under tree cover. Effects of human activity on
the fluvial system are evident at local scales, but difficult to discern at
broader scales in the regional context of geomorphic adjustment to tectonic
and volcanic processes.
Key words: human impact, soil erosion, fluvial
geomorphology, soil moisture, Andes
Human impacts on fluvial systems in the Mediterranean Region
- Janet M. Hooke
Department of Geography, University of Portsmouth. Buckingham Building, Lion
Terrace, Portsmouth, UK PO1 3HE
E-mail:
janet.hooke@port.ac.uk
Abstract: The long history of substantial human impacts on the landscape of the
Mediterranean region, and their effects on fluvial systems, is documented.
These effects have included impacts of deforestation and other land use
changes, agricultural terracing on a wide scale, water transfers, and
irrigation schemes. During the 20th Century, major changes were made directly
to channels through channelisation, construction of dams of various sizes, and
extraction of gravel, and indirectly by reforestation. These changes have
caused a major phase of incision on some rivers. Runoff and soil erosion have
been affected by types of crops and agricultural practices as well as by the
varying extent of cultivation and grazing. Some recent agricultural practices
involve whole scale relandscaping of the topography and alteration of surface
properties of material. The importance of analysing the connectivity within
different land units and of the spatial position of human activity within a
catchment is illustrated. The analysis of connectivity is the key to
understanding the variability of impact and the extent of propagation of
effects.
Key words: soil erosion, land degradation, Mediterrean,
rivers, connectivity, land management, river management
Research on the human role in changing fluvial systems: Retrospect, inventory
and prospect - L. Allan James1 and W. Andrew Marcus2
1Department of Geography, University of South Carolina, Columbia,
SC 29208, U.S.A.
E-mail:
AJames@sc.edu
Phone: 803-777-6117
2Department of Geography, University of Oregon, Eugene, OR
97403-1251 U.S.A.
E-mail:
marcus@uoregon.edu
Phone: 541-346-5709
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, 1956a). 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 gemorphologists. The 2006 Binghamton Geomorphology Symposium
compliments 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.
Keywords: human impacts; gluvial geomorphology;
watersheds; hydrology
Geomorphic effects of rural-to-urban land use conversion on three streams in
the
central Redbed Plains of Oklahoma - Ranbir S. Kanga and
Richard A. Marstonb*
a Department
of Geography, Oklahoma State University, Stillwater, OK 74078-4073, USA
b Department
of Geography, 118 Seaton Hall, Kansas State University, Manhattan, KS
66506-2904, USA
*Corresponding author E-mail: rmarston@ksu.edu .
Abstract: This research evaluates the impact of rural-to-urban land use conversion on
channel morphology and riparian vegetation for three streams in the central Redbed Plains geomorphic province (central Great Plains ecoregion) of
Oklahoma. The Deep Fork Creek watershed is largely urbanized; the Skeleton
Creek watershed is largely rural; and the Stillwater Creek watershed is
experiencing a rapid transition from rural to urban land cover. Each channel
was divided into reaches based on tributary junctions, sinuosity, and slope.
Field surveys were conducted at transects in a total of 90 reaches, including
measurements of channel units, channel cross-section at bankfull stage, and
riparian vegetation. Historical aerial photographs were available for only
Stillwater Creek watershed, which were used to document land cover in this
watershed, especially changes in the extent of urban areas (impervious
cover).
The three streams have very low gradients (< 0.001), width-to-depth ratios
< 10, and cohesive channel banks, but have incised into red Permian shales and
sandstone. The riparian vegetation is dominated by cottonwoods, ash, and elm
trees that provide a dense root mat on stream banks where the riparian
vegetation is intact. Channels increased in width and depth in the downstream
direction as is normally expected, but the substrate materials and channel
units remained unchanged. Statistical analyses demonstrated that
urbanization did not explain spatial patterns of changes in any variables.
These three channels in the central Redbed Plains are responding as flumes
during peak flows, funneling runoff and the wash-load sediment downstream in
major runoff events without any effect on channel dimensions. Therefore, local
geological conditions (similar bed rock, cohesive substrates and similar
riparian vegetation) are mitigating the effects of urbanization.
Keywords: channel morphology, watershed, riparian vegetation,
channelization, urban, urbanization
Floodplain Sedimentation in the Upper Mississippi Valley:
Natural versus Human Accelerated - James C. Knox
Department of Geography, University of Wisconsin, Madison, Wisconsin
53706-1491 USA
E-mail:
knox@geography.wisc.edu
Abstract: Floodplains represent one of the more important components of watershed
systems because they not only affect downstream storage and delivery of overbank flood waters, but they also serve as sources and temporary sinks for
sediments and toxic substances delivered by river systems. Here, I examine a
reach of the upper Mississippi River and adjacent tributaries in southwestern
Wisconsin and northwestern Illinois to show how rates of overbank floodplain
vertical accretion changed when the adjacent landscape was converted from a
late Holocene mosaic of prairie and forest to a landscape dominated by
cropland and pastureland associated with Euro-American settlement.
Numerous radiocarbon ages for organic material contained in floodplain
alluvium indicate that the average long-term natural rates of vertical
accretion were about 0.02 cm yr-1 in tributary watersheds smaller than about
700 km2 and about 0.09 cm yr-1 on the floodplain of the upper Mississippi
River where the contributing watershed area increases to about 170,000 km2.
Hydrologic effects of mining and agricultural settlement started by the 1820s,
but by the mid-19th century much of the study area was significantly
influenced by agricultural land use. Rates of historical vertical accretion
on tributary floodplains have averaged between 0.2 and 2 cm yr-1, with short
episodes of even higher rates during times of particularly poor land
conservation practices.
Resistant, armored, late Wisconsin age gravels have restricted tributary
channels to lateral movement and prevented incision during Holocene and
historical times. Overbank flooding, accelerated by agriculture, led to
extensive overbank vertical accretion and an eventual near doubling of bank
heights. Subsequently, deep, high-energy flows eroded channel margins and
produced a historical meander belt that confined flood waters which previously
flowed onto the wide valley floors. The meander belt serves as a “flume-like”
channel to transmit water and sediment to floodplains of downstream
tributaries reaches where the meander belt is poorly developed or absent and
to the floodplain of the upper Mississippi River. Consequently, downstream
floodplains experience overbank sedimentation rates that are higher than what
might be expected given improved land cover and land conservation since about
1950, and this effect is expected to persist for many decades in the future.
High resolution dating of floodplain vertical accretion deposits shows
that large floods have been responsible for a significant fraction of the overbank deposition for both tributaries and the main valley upper Mississippi
River. Global atmospheric circulation models indicate that the upper
Mississippi River valley will be associated with an increased incidence of
extreme hydrologic events. Both instrument and stratigraphic records suggest
that a shift to more frequent large floods has occurred since 1950 on the
upper Mississippi River, and these floods have been associated with high
magnitudes of floodplain sedimentation.
Keywords: floodplain, floods, vertical accretion, sedimentation
rates, Driftless Area, Mississippi River
A geomorphological approach to the management of rivers contaminated by metal mining - Mark G. Macklin a*, P.A. Brewer a, K.A. Hudson-Edwards b, G. Bird a, T.J. Coulthard c, I.A. Dennis a, P.J. Lechler d, J.R. Miller e, J.N. Turner f
a River Basin Dynamics and
Hydrology Research Group, Institute of Geography and Earth Sciences,
University of Wales Aberystwyth, Ceredigion, SY23 3DB, UK.
*Corresponding author e-mail address: mvm@aber.ac.
uk
b Research School
of Earth Sciences at UCL-Birkbeck, University of London, Malet Street, London,
WC1E 7HX, UK.
c Department of Geography, The University of Hull, Cottingham Road, Hull, HU6 7RU, UK.
d Nevada Bureau of Mines and Geology, University of Nevada, Reno, NV 89557, USA.
e Department of Geoscience and Natural Resources Management, Western Carolina University, Cullowhee, NC 28723, USA.
f School of Geography, Planning and Environmental Policy, John Henry Newman Building, University College Dublin, Belfield, Dublin 4, Eire.
Abstract: As the result of current and historical metal mining, river channels and floodplains in many parts of the world have become contaminated by metal-rich waste in concentrations that may pose a hazard to human livelihoods and sustainable development. Environmental and human health impacts commonly arise because of the prolonged residence time of heavy metals in river sediments and alluvial soils and their bioaccumulatory nature in plants and animals. This paper considers how an understanding of the processes of sediment-associated metal dispersion in rivers, and the space and timescales over which they operate, can be used in a practical way to help river basin managers more effectively control and remediate catchments affected by current and historical metal mining. A geomorphological approach to the management of rivers contaminated by metals is outlined and four emerging research themes are highlighted and critically reviewed. These are: (1) response and recovery of river systems following the failures of major tailings dams; (2) effects of flooding on river contamination and the sustainable use of floodplains; (3) new developments in isotopic fingerprinting, remote sensing and numerical modelling for identifying the sources of contaminant metals and for mapping the spatial distribution of contaminants in river channels and floodplains; and (4) current approaches to the remediation of river basins affected by mining, appraised in light of the European Union’s Water Framework Directive (2000/60/EC). Future opportunities for geomorphologically-based assessments of mining-affected catchments are also identified.
Keywords: mining-affected rivers; heavy metal contamination; integrated river basin management; geomorphology; hydrology
Grazing in riparian zones in the western U.S.: Impacts, management and scientific progress -Patricia F. McDowell
Department of Geography, University of Oregon, Eugene, OR 97403-1251 U.S.A.
E-mail: pmcd@uoregon.edu
Abstract: Concentrated grazing by domesticated animals is one of the most ancient and widespread of human impacts on landscapes. While uplands are affected through vegetation modification and soil erosion, grazing impacts are most intensive in riparian zones and stream channels. Geomorphic effects including bank destabilization, channel incision and/or widening, and siltation of gravel beds have been widely observed and measured. Related ecological effects include loss of pools, cover, spawning areas, and other habitat elements essential for fish; degraded water quality; water table decline under riparian zones resulting from channel incision; and loss of woody vegetation in the riparian zone. In the western U.S., negative effects from cattle grazing have been recognized for well over a century. Land management policies to reduce grazing impacts were initiated by the 1890s, but progress in improving riparian zones and fluvial systems was slow, and degraded riparian areas are still common. The debate continues on how to restore riparian zones to ecological health in landscapes where grazing is the dominant land use, with complete removal of cattle and intense management of cattle in riparian zones being the two most polar views. Studies of grazing impacts by rangeland scientists, fisheries scientists, aquatic ecologists, and geomorphologists have used different approaches, and communication among these disciplines has been insubstantial until recently. Research from the different disciplines has been used in support of both sides of the debate. The research has documented numerous direct and indirect impacts, but an integrated model of physical and biotic effects and pathways of recovery has not yet emerged. Recent and future research on topics such as hydraulic effects of bank vegetation, and processes of channel recovery from incision or enlargement will provide support for a more integrated conceptual model to inform policy on riparian grazing.
Hydrologic variation with land use across the contiguous United States: geomorphic and ecological consequences for stream ecosystems - N. LeRoy Poffa*, Brian P. Bledsoeb, Christopher O. Cuhaciyanb
aDepartment of Biology, Colorado State University, Fort Collins CO 80523 U.S.A
*Corresponding author, email: poff@lamar.colostate.edu
bDepartment of Civil Engineering, Colorado State University, Fort Collins CO 80523 U.S.A.
Abstract: Using daily discharge data from the USGS, we analyzed how hydrologic regimes vary with land use in four large hydrologic regions that span a gradient of natural land cover and precipitation across the continental United States. In each region we identified small streams (contributing area < 282 km2) that have continuous daily streamflow data. Using a national database, we characterized the composition of land cover of the watersheds in terms of aggregate measures of agriculture, urbanization, and least disturbed (“natural”). We calculated hydrologic alteration using 10 ecologically-relevant hydrologic metrics that describe magnitude, frequency, and duration of flow for 158 watersheds within the Southeast (SE), Central (CE), Pacific Northwest (NW), and Southwest (SW) hydrologic regions of the United States. Within each watershed, we calculated percent cover for agriculture, urbanized land, and less disturbed land to elucidate how components of the natural flow regime inherent to a hydrologic region is modified by different types and proportions of land cover. We also evaluated how dams in these regions altered the hydrologic regimes of the 43 streams that have pre- and post-dam daily streamflow data. In an analysis of flow alteration along gradients of increasing proportion of the three land cover types, we found many regional differences in hydrologic responses. In response to increasing urban land cover, peak flows increased (SE and CE), minimum flows increased (CE) or decreased (NW), duration of near-bankfull flows declined (SE, NW) and flow variability increased (SE, CE, and NW). Responses to increasing agricultural land cover were less pronounced, as minimum flows decreased (CE), near-bankfull flow durations increased (SE and SW), flow variability declined (CE). In a second analysis, for three of the regions, we compared the difference between least disturbed watersheds and those having either >15% urban and >25% agricultural land cover. Relative to natural land cover in each region, urbanization either increased (SE and NW) or decreased (SW) peak flows, decreased minimum flows (SE, NW, and SW), decreased near-bankfull flows (SE, NW, and SW), and increased flow variability (SE, NW, and SW). Agriculture had similar effects except in the SE, where near-bankfull flow durations increased. Overall, urbanization appeared to induce greater hydrologic responses than similar proportions of agricultural land cover in watersheds. Finally, the effects of dams on hydrologic variation were largely consistent across regions, with a decrease in peak flows, and increase in minimum flows, an increase in near-bankfull flow durations, and a decreased in flow variability. We use this analysis to evaluate the relative degree to which land use has altered flow regimes across regions in the US with naturally varying climate and natural land cover, and we discuss the geomorphic and ecological implications of such flow modification. We end with a consideration of what elements will ultimately be required to conduct a more comprehensive national assessment of the hydrologic responses of streams to land cover types and dams. These include improved tools for modeling hydrologic metrics in ungauged watersheds, incorporation of high-resolution geospatial data to map geomorphic and hydrologic drivers of stream response to different types of land cover, and analysis of scale dependence in the distribution of land-use impacts, including mixed land uses. Finally, ecological and geomorphic responses to human alteration of land cover will have to be calibrated to the regional hydroclimatological, geologic, and historical context in which the streams occur, in order to determine the degree to which stream responses are region-specific versus geographically independent and broadly transferable.
Keywords: Stream ecosystem, hydroecology, fluvial geomorphology, hydrologic alteration, land use, dams
Disturbance, stream incision, and channel evolution: The roles of excess transport capacity and boundary materials in controlling channel response -Andrew Simona and Massimo Rinaldib
a USDA – Agricultural Research Service, National Sedimentation Laboratory, P.O. Box 1157, Oxford, MS 38655, USA
E-mail: asimon@ars.usda.gov
bDipartimento di Ingeneria di Civile, Universita degli Studi di Firenze, 50121, Firenze, Italia
Abstract Channel incision is part of denudation, drainage-network development, and landscape evolution. Rejuvenation of fluvial networks by channel incision often leads to further network development and an increase in drainage density as gullies migrate into previously non-incised surfaces. Large, anthropogenic disturbances, similar to large or catastrophic “natural” events, greatly compress time scales for incision and related processes by creating enormous imbalances between upstream sediment delivery and available transporting power. Field examples of channel responses to antrhopogenic and “natural” disturbances are presented for fluvial systems in the mid continent and Pacific Northwest, USA, and central Italy. Responses to different types of disturbances are shown to result in similar spatial and temporal trends of incision for vastly different fluvial systems. Similar disturbances are shown to result in varying relative magnitudes of vertical and lateral (widening) processes, and different channel morphologies as a function of the type of boundary sediments comprising the bed and banks. This apparent contradiction is explained through an analysis of temporal adjustments to flow energy, shear stress, and stream power with time. Numerical simulations of sand-bed channels of varying bank resistance and disturbed by reducing the upstream sediment supply by half, show identical adjustments in flow energy and the rate of energy dissipation. The processes that dominate adjustment and the ultimate stable geometries, however, are vastly different, depending on the cohesion of the channel banks and the supply of hydraulically-controlled sediment (sand) provided by bank erosion.
The non-linear asymptotic nature of fluvial adjustment to incision caused by channelization or other causes is borne out in similar temporal trends of sediment loads from disturbed systems. The sediments emanating from incised channels can represent a large proportion of the total sediment yield from a landscape, with erosion from the channel banks generally the dominant source. Disturbances that effect available force, stream power or flow energy, or change erosional resistance such that an excess of flow energy occurs can result in incision. Channel incision, therefore, can be considered a quintessential feature of dis-equilibrated fluvial systems.
Human
impact on land-ocean sediment transfer by the world’s rivers
- D.E. Walling
Department of Geography, University of Exeter, EXETER, EX4 4RJ, UK
E-mail:
d.e.walling@exeter.ac.uk
Abstract: Land-ocean transfer of sediment by rivers is a key pathway for material
transfer on Earth. Contemporary data on the sediment loads of rivers provide
clear evidence of significant recent changes in the sediment fluxes of several
rivers in response to human impact. The key drivers of increased sediment
loads include land clearance for agriculture and other facets of land surface
disturbance, including logging activity and mining. Although, programmes for
soil conservation and sediment control can result in reduced sediment loads,
the trapping of sediment by dams represents the dominant cause of reduced
loads. This influence is currently assuming increasing importance at the
global scale. Any attempt to link these drivers to changes in the global
land-ocean sediment flux must take account of the aggregation and buffering
effects that operate in larger basins, which can cause damping and even
removal of signals of increasing flux within the upstream basin, and
complicate the link between upstream and downstream response to human impact.
Further work is required to provide a precise quantitative assessment of the
human impact on global land-ocean sediment fluxes and the net effect of
increasing and decreasing fluxes. Particular attention must be paid to the
temporal perspective and the variation of impact trajectories in different
areas of the globe and for river basins of different sizes.
Key words: Suspended sediment loads, global land-ocean sediment
flux, human impact, land disturbance, dams, sediment trapping, buffering
effects, impact trajectories.
Human
Impacts to Mountain Streams - Ellen Wohl
Department of Geosciences, Colorado State University, Ft. Collins, Colorado
80523 USA
E-mail:
ellenw@cnr.colostate.edu
Abstract: Mountain streams are here defined as channel networks within mountainous
regions of the world. This definition encompasses tremendous diversity of
physical and biological conditions, as well as history of land use. Human
effects on mountain streams may result from activities undertaken within the
stream channel that directly alter channel geometry, the dynamics of water and
sediment movement, contaminants in the stream, or aquatic and riparian
communities. Examples include channelization, construction of grade-control
structures or check dams, removal of beavers, and placer mining. Human effects
can also result from activities within the watershed that indirectly affect
streams by altering the movement of water, sediment, and contaminants into the
channel. Deforestation, cropping, grazing, land drainage, and urbanization are
among the land uses that indirectly alter stream processes. An overview of the
relative intensity of human impacts to mountain streams is provided by a table
summarizing human effects on each of the world’s major mountainous regions
with respect to five categories: flow regulation, biotic integrity, water
pollution, channel alteration, and land use. This table indicates that very
few mountains have streams not at least moderately affected by land use. The
least affected mountainous regions are those at very high or very low
latitudes, although our scientific ignorance of conditions in low-latitude
mountains in particular means that streams in these mountains might be more
altered than is widely recognized. Four case studies from northern Sweden
(arctic region), Colorado Front Range (semiarid temperate region), Swiss Alps
(humid temperate region), and Papua New Guinea (humid tropics) are also used
to explore in detail the history and effects on rivers of human activities in
mountainous regions. The overview and case studies indicate that mountain
streams must be managed with particular attention to upstream/downstream
connections, hillslope/channel connections, process domains, physical and
ecological roles of disturbance, and stream resilience.
Keywords: mountain streams, human impacts, Colorado, Switzerland,
Papua New Guinea, Sweden
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