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Preface to historic and paleoflood analyses: New perspectives on climate, extreme flood risk, and the geomorphic effects of large floods
Accepted Manuscript Preface to historic and paleoflood analyses: New perspectives on climate, extreme flood risk, and the geomorphic effects of large floods
Lisa Davis, Tessa M. Harden, Samuel E. Munoz, Jeanne Godaire, Jim E. O'Connor PII: DOI: Reference:
S0169-555X(18)30435-5 https://doi.org/10.1016/j.geomorph.2018.10.021 GEOMOR 6559
To appear in:
Geomorphology
Received date: Revised date: Accepted date:
12 October 2018 24 October 2018 24 October 2018
Please cite this article as: Lisa Davis, Tessa M. Harden, Samuel E. Munoz, Jeanne Godaire, Jim E. O'Connor , Preface to historic and paleoflood analyses: New perspectives on climate, extreme flood risk, and the geomorphic effects of large floods. Geomor (2018), https://doi.org/10.1016/j.geomorph.2018.10.021
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Editorial Preface to Historic and paleoflood analyses: New perspectives on climate, extreme flood risk, and the geomorphic effects of large floods
Abstract
T
Paleofloods are flood events that occurred prior to instrumented records that are discerned from
IP
sedimentary evidence. Historic floods are flood events that predate the instrumented record that have been
CR
reconstructed based on evidence provided by historical sources. This special issue presents papers on historic and paleoflood analyses that stemmed from the 5th International Paleoflood Symposium held in
US
2016 and a technical paper session convened during the 2016 Annual Meeting of the Geological Society
AN
of America (GSA) in Denver, Colorado, titled ‘Paleofloods and Related Fluvial Processes during the Late Quaternary: Reconstructions and Causes.’ The papers included in this special issue address a wide variety
M
of flood science questions, including hydrologic hazard and risk assessments, the examination of
ED
prehistoric human migration patterns, understanding relationships between large floods and climate, and the investigation of cataclysmic flood processes.
1. Introduction
CE
PT
Keywords: paleofloods; paleoflood hydrology; floods
AC
Paleoflood hydrology is the study of undocumented floods, or paleofloods, based on underlying principles drawn from the disciplines of geology, biology, hydrology, geomorphology, and engineering. Once a drawing room pastime for debating the origin of boulder erratics and inexplicable sand deposits, paleoflood hydrology has grown to be a highly quantitative and technologically sophisticated field capable of providing new insights into flood processes on Earth, as well as on other planets. Paleoflood analyses produce centennial- and millennial-scale flood data, and these longer flood records have been used to explain how 1
ACCEPTED MANUSCRIPT climate affects flood frequency (Gregory et al., 2006; Benito et al., 2008; Harden et al., 2015), including the identification of specific synoptic climatological mechanisms responsible for flood clustering (North Atlantic Oscillation, for example) (Benito et al., 2008), and how human activities change flood frequency (Johnstone et al., 2006; Macklin et al., 2006). These insights
T
required a long-term perspective that shorter, systematic flood records alone cannot provide.
IP
Furthermore, paleoflood hydrology has become an important resource for managing flood risk,
CR
particularly with regard to quantifying the frequency of extreme floods. As a case in point, newly revised guidelines developed by the U.S. federal government for flood frequency analysis
US
include new methods for incorporating paleoflood data to improve estimates of extreme flood
AN
risk (see England et al., 2018). Thus, what began as an effort focused on geological curiosities in
science and risk analyses worldwide.
M
the nineteenth century is now a mature, quantitative science with a significant role in flood
ED
Research presented at two meetings ably demonstrated the growth in technique and scope experienced by the field of paleoflood hydrology and served as the impetus for this special issue.
PT
In September of 2016, the 5th International Paleoflood Conference convened in Rapid City,
CE
South Dakota. This four-day workshop brought 60 researchers together from five continents. Presentations, field trips (Fig. 1), and discussions spanned all aspects of paleoflood hydrology. A
AC
point of emphasis was increased recognition by managers and regulators of the importance of paleoflood information for evaluating flood hazards for critical infrastructure, such as dams, bridges, and energy facilities. The second meeting was a technical paper session held during the 2016 Annual Meeting of the Geological Society of America (GSA) in Denver, Colorado, titled ‘Paleofloods and Related Fluvial Processes during the Late Quaternary: Reconstructions and Causes.’ This session attracted 10 presentations of paleoflood studies from all corners of North
2
ACCEPTED MANUSCRIPT America and was sponsored by the American Quaternary Science Society, the Quaternary Geology and Geomorphology Division of the GSA, the Society for Sedimentary Geology, and the Past Global Changes (PAGES)-Floods Working Group. Common themes across the papers presented included processes that can affect flood deposit preservation, such as sediment
T
exhaustion from prior storm events, and the increasing use of multimethod approaches to
IP
paleoflood reconstructions, such as combining traditional sedimentological approaches with
CR
hydraulic modeling and dendrochronology, to yield the most robust analyses possible. The papers in this special issue originate from both meetings convened in 2016 and
US
demonstrate a diverse array of flood science questions addressed with current techniques and
AN
principles of paleoflood hydrology, including hydrologic hazard and risk assessments, the examination of prehistoric human migration patterns, understanding relationships between large
M
floods and climate, and the investigation of cataclysmic flood processes. The geographic
ED
locations and applications of paleoflood hydrology continue to expand, creating ever more
PT
potential for new regional syntheses of paleoflood records to be accomplished. 1.1 Overview of papers in this issue
CE
Remo et al. (pages xx-xx) is the first of three papers in this special issue that uses a
AC
retrodictive modeling approach to evaluate human impacts on hydrologic processes and to improve flood hazard assessments. Their study examines the combined impacts of dams and levees on the hydrology of the middle and lower Mississippi River by reconstructing the magnitude, timing, and frequency of floods over the last 130 years by piecing together available historical records for multiple river segments and integrating them into a hydraulic model. The longer-term perspective offered by this approach shows that artificial levees have acted to increase peak flood discharges by reducing flood water storage but that this effect has been
3
ACCEPTED MANUSCRIPT partially offset by tributary reservoirs that reduce peak flood magnitudes. Their work provides insight into the hydrology of the Mississippi River before widespread establishment of navigational and flood mitigation infrastructure and quantifies the effects of river regulation on
AC
CE
PT
ED
M
AN
US
CR
IP
T
flood hazard for the largest river in North America.
Fig. 1. Conference attendees examining slackwater deposits trapped within shallow caves and rock alcoves in a canyon located in the Blackhills of South Dakota during the 5th International Paleoflood Conference convened in Rapid City, South Dakota, 12-15 September 2016.
4
ACCEPTED MANUSCRIPT On the Manawatu River basin in New Zealand, Fuller et al. (pages xx-xx) reconstruct 3000 years of floods and associated magnitudes by integrating geochemical analyses of sedimentary records with documentary evidence. Their paleoflood record implies that the largest floods of the last 3,000 years correspond with European settlement and land clearance beginning
T
in the mid-nineteenth century A.D. Sedimentary evidence of floods that occurred during the
IP
nineteenth century was well preserved, providing a high-resolution record of flood magnitude
CR
and frequency; sedimentary signatures of floods that occurred prior to this time and were more distally deposited from the main channel, in contrast, were best preserved in cases of extreme
US
floods only. Their findings demonstrate the sensitivity of hydrologic processes to land use and
AN
land cover change and provide more evidence that geochemical indices derived from X-ray fluorescence scanning (e.g., Zr/Rb ratios) can help identify flood layers, while also
M
demonstrating spatial variability of flood preservation related to hydrgeomorphic complexities.
ED
Cloete et al. (pages xx-xx) demonstrate the utility of paleoflood hydrology for infrastructure planning and resilience, while also providing new insights into hydrologic
PT
variability in Africa in response to centennial- and decadal-scale climatic variability. They
CE
combined paleoflood data with historical and instrumented hydrologic data into a flood frequency analysis to determine the discharges and recurrence intervals of the most extreme
AC
floods that occurred in the Fish River Basin of Namibia over the last 400 years. Their flood frequency analysis demonstrated that the largest discharges in their paleoflood record had recurrence intervals of just 300 and 100 years and exceeded the design flood and safety check floods for a large dam planned for the Fish River basin as determined by conventional frequency analysis. Beyond its applicability to infrastructure planning, their paleoflood chronology revealed
5
ACCEPTED MANUSCRIPT significant variability in flood frequency and magnitude associated with the Maunder Minimum and the Little Ice Age. All environmental reconstructions— including paleoflood records —depend on geochronologic techniques. Knight et al. (pages xx-xx) evaluate the accuracy of optically
T
stimulated luminescence (OSL) for dating relatively modern alluvial sediments. Their study
IP
examines alluvial sediments on a reach of the Sabie River (South Africa) to evaluate how fluvial
CR
processes and geomorphic setting influence the ability of OSL dating to accurately represent the age of the uppermost alluvium. They found that variations in sediment transport processes
US
between channel and floodplain environments affected the degree of grain bleaching. This effect
AN
resulted in a wide range of ages for channel sediments transported during peak discharges but more constrained age ranges for sediments deposited in floodplains during the falling limb of
M
flood events. These findings will be critical as OSL is more widely applied to interpret
ED
depositional histories of fluvial systems (Chamberlain et al., 2018; Munoz et al., 2018). Hazelwood and Stetler (pages xx-xx) make a compelling case for how two fluvial
PT
incision events (both likely initiated in the last ca. 5 Ma) created differences in topographic relief
CE
and hydrologic networks across the Black Hills of South Dakota. These incision events made this location prone to extreme flood events, which in turn made it suited to the preservation of
AC
paleoflood deposits. The study presents a new method — ‘watershed decomposition’ — to identify relict landscapes based on digital elevation models and longitudinal profiles implemented in a GIS and applies this method to understand the evolution of the Black Hills and its drainages to their modern states. Finally, a special issue on paleofloods would be remiss to not provide some consideration of the Missoula Floods — a series of cataclysmic floods that occurred at the end of the
6
ACCEPTED MANUSCRIPT Pleistocene in the Pacific Northwestern U.S. and have been a cornerstone of geomorphology and paleoflood hydrology since they were first studied in the early twentieth century. In this issue, Stetler et al. (pages xx-xx) examine the provenance of materials comprising active and inactive sand dunes located in vicinity of the Hanford Site (an active nuclear waste repository) within the
T
Pasco Basin in south-central Washington. Surficially, this environment appears entirely aeolian;
IP
but a combination of stratigraphic interpretations, particle size, and sedimentary petrographic
CR
analyses suggests basal units of the dunes are of a glaciofluvial provenance likely associated with the Missoula Floods between about 21,000 and 12,000 years ago.
US
This edited volume represents not only the breadth of paleoflood hydrology, but
AN
importantly, several recent advances in paleoflood hydrology, including the integration of multiple types of evidence to develop a more comprehensive reconstruction of hydrologic
M
history, an ability to develop paleoflood records across a variety of landscapes, a focus on
ED
quantifying the effects of human activities on fluvial systems, and the use of advanced statistical and computational modeling. These advances represent a field that is growing in its applicability
PT
to critical questions around water resource management and hazard mitigation and maturing in
CE
its suite of available tools and techniques. In light of these advances, the paleoflood community should continue to advocate for its routine application to applied problems in science and
AC
engineering. At the same time, we must continue to reflect on the remaining challenges in the field and consider additional prospects for the future. Reducing uncertainties in reconstructions of flood timing and magnitude remains an important challenge, though several of the papers in this special issue point to ways forward by integrating multiple types of evidence in reconstructions and systematically assessing chronological techniques. Sediment characteristics — particularly grain size and geochemical proxies — have emerged as a common tool to build
7
ACCEPTED MANUSCRIPT and quantify paleoflood chronologies, but important questions remain about how depositional and post-depositional processes affect these interpretations. The development of paleoflood records is a costly endeavor — though these costs pale in comparison to the costs associated with operating a gauging station for centuries or millennia — but basin-wide and regional
T
perspectives will be critical to reduce uncertainties in our reconstructions and to evaluate the
IP
controls on flood occurrence. This special issue encapsulates an exciting moment in paleoflood
CR
hydrology as the field matures in its approaches and applicability. We look forward to the field’s continued growth in light of the daunting environmental challenges societies face in the coming
AN
US
decades.
References
ED
M
Benito, G., Thorndycraft, V.R., Rico, M., Sánchez-Moya, Y., Sopeña, A., 2008. Palaeoflood and floodplain records from Spain: Evidence for long-term climate variability and environmental changes. Geomorphology 101, 68-7
PT
Chamberlain, E.L., Törnqvist, T.E., Shen, Z., Mauz, B., Wallinga, J., 2018. Anatomy of Mississippi Delta growth and its implications for coastal restoration. Science Advances 4(4), eaar4740.
CE
England, J.F., Jr., Cohn, T.A., Faber, B.A., Stedinger, J.R., Thomas, W.O., Jr., Veilleux, A.G., Kiang, J.E., and Mason, R.R., Jr., 2018. Guidelines for Determining Flood Flow Frequency—Bulletin 17C: U.S. Geological Survey Techniques and Methods, Book 4, Chap. B5. U.S. Geological Survey, Reston, VA,148 pp.
AC
Gregory, K.J., Benito, G., Dikau, R., Golosov, V., Jones, A.J.J., Macklin, M.G., Parsons, A.J., Passmore, D.G., Poesen, J., Starkel, L., Walling, D.E., 2006. Past hydrological events related to understanding global change: an ICSU research project. Catena 66, 2–13. Harden, T.M., O'Connor, J.E., Driscoll, D.G., 2015. Late Holocene flood probabilities in the Black Hills, South Dakota with emphasis on the Medieval Climate Anomaly. Catena 130, 62-68. Johnstone, E., Macklin, M.G., Lewin, J., 2006. Holocene river dynamics and flooding in Great Britain: Evaluating regional responses to climate and land-use change. Catena 66, 14–23.
8
ACCEPTED MANUSCRIPT Macklin, M.G., Benito, G., Gregory, K.J., Johnstone, E., Lewin, J., Soja, R., Starkel, L., Thorndycraft, V.R., 2006. Past hydrological events reflected in the Holocene fluvial history of Europe. Catena 66, 145–154. Munoz, S.E., Giosan, L., Therrell, M.D., Remo, J.W., Shen, Z., Sullivan, R.M., Wiman, C., O’Donnell, M., Donnelly, J.P., 2018. Climatic control of Mississippi River flood hazard amplified by river engineering. Nature 556(7699), 95-98.
CR
IP
T
Lisa Davis, Tessa M. Harden, Samuel E. Munoz, Jeanne Godaire, Jim E. O’Connor
List of figures:
AN
US
Fig. 1. Conference attendees examining slackwater deposits trapped within shallow caves and rock alcoves in a canyon located in the Blackhills of South Dakota during the 5th International Paleoflood Conference convened in Rapid City, South Dakota, 12-15 September 2016.
CE
PT
ED
6885: Remo et al. 7084: Fuller et al. 7056: Cloete et al. 7088: Jasper Knight et al. 6857: Kyle Hazelwood and Larry Stetler 6956: Larry Stetler
AC
(1) (2) (3) (4) (5) (6)
M
Suggested paper order:
9
Lisa Davis, Tessa M. Harden, Samuel E. Munoz, Jeanne Godaire, Jim E. O'Connor PII: DOI: Reference:
S0169-555X(18)30435-5 https://doi.org/10.1016/j.geomorph.2018.10.021 GEOMOR 6559
To appear in:
Geomorphology
Received date: Revised date: Accepted date:
12 October 2018 24 October 2018 24 October 2018
Please cite this article as: Lisa Davis, Tessa M. Harden, Samuel E. Munoz, Jeanne Godaire, Jim E. O'Connor , Preface to historic and paleoflood analyses: New perspectives on climate, extreme flood risk, and the geomorphic effects of large floods. Geomor (2018), https://doi.org/10.1016/j.geomorph.2018.10.021
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Editorial Preface to Historic and paleoflood analyses: New perspectives on climate, extreme flood risk, and the geomorphic effects of large floods
Abstract
T
Paleofloods are flood events that occurred prior to instrumented records that are discerned from
IP
sedimentary evidence. Historic floods are flood events that predate the instrumented record that have been
CR
reconstructed based on evidence provided by historical sources. This special issue presents papers on historic and paleoflood analyses that stemmed from the 5th International Paleoflood Symposium held in
US
2016 and a technical paper session convened during the 2016 Annual Meeting of the Geological Society
AN
of America (GSA) in Denver, Colorado, titled ‘Paleofloods and Related Fluvial Processes during the Late Quaternary: Reconstructions and Causes.’ The papers included in this special issue address a wide variety
M
of flood science questions, including hydrologic hazard and risk assessments, the examination of
ED
prehistoric human migration patterns, understanding relationships between large floods and climate, and the investigation of cataclysmic flood processes.
1. Introduction
CE
PT
Keywords: paleofloods; paleoflood hydrology; floods
AC
Paleoflood hydrology is the study of undocumented floods, or paleofloods, based on underlying principles drawn from the disciplines of geology, biology, hydrology, geomorphology, and engineering. Once a drawing room pastime for debating the origin of boulder erratics and inexplicable sand deposits, paleoflood hydrology has grown to be a highly quantitative and technologically sophisticated field capable of providing new insights into flood processes on Earth, as well as on other planets. Paleoflood analyses produce centennial- and millennial-scale flood data, and these longer flood records have been used to explain how 1
ACCEPTED MANUSCRIPT climate affects flood frequency (Gregory et al., 2006; Benito et al., 2008; Harden et al., 2015), including the identification of specific synoptic climatological mechanisms responsible for flood clustering (North Atlantic Oscillation, for example) (Benito et al., 2008), and how human activities change flood frequency (Johnstone et al., 2006; Macklin et al., 2006). These insights
T
required a long-term perspective that shorter, systematic flood records alone cannot provide.
IP
Furthermore, paleoflood hydrology has become an important resource for managing flood risk,
CR
particularly with regard to quantifying the frequency of extreme floods. As a case in point, newly revised guidelines developed by the U.S. federal government for flood frequency analysis
US
include new methods for incorporating paleoflood data to improve estimates of extreme flood
AN
risk (see England et al., 2018). Thus, what began as an effort focused on geological curiosities in
science and risk analyses worldwide.
M
the nineteenth century is now a mature, quantitative science with a significant role in flood
ED
Research presented at two meetings ably demonstrated the growth in technique and scope experienced by the field of paleoflood hydrology and served as the impetus for this special issue.
PT
In September of 2016, the 5th International Paleoflood Conference convened in Rapid City,
CE
South Dakota. This four-day workshop brought 60 researchers together from five continents. Presentations, field trips (Fig. 1), and discussions spanned all aspects of paleoflood hydrology. A
AC
point of emphasis was increased recognition by managers and regulators of the importance of paleoflood information for evaluating flood hazards for critical infrastructure, such as dams, bridges, and energy facilities. The second meeting was a technical paper session held during the 2016 Annual Meeting of the Geological Society of America (GSA) in Denver, Colorado, titled ‘Paleofloods and Related Fluvial Processes during the Late Quaternary: Reconstructions and Causes.’ This session attracted 10 presentations of paleoflood studies from all corners of North
2
ACCEPTED MANUSCRIPT America and was sponsored by the American Quaternary Science Society, the Quaternary Geology and Geomorphology Division of the GSA, the Society for Sedimentary Geology, and the Past Global Changes (PAGES)-Floods Working Group. Common themes across the papers presented included processes that can affect flood deposit preservation, such as sediment
T
exhaustion from prior storm events, and the increasing use of multimethod approaches to
IP
paleoflood reconstructions, such as combining traditional sedimentological approaches with
CR
hydraulic modeling and dendrochronology, to yield the most robust analyses possible. The papers in this special issue originate from both meetings convened in 2016 and
US
demonstrate a diverse array of flood science questions addressed with current techniques and
AN
principles of paleoflood hydrology, including hydrologic hazard and risk assessments, the examination of prehistoric human migration patterns, understanding relationships between large
M
floods and climate, and the investigation of cataclysmic flood processes. The geographic
ED
locations and applications of paleoflood hydrology continue to expand, creating ever more
PT
potential for new regional syntheses of paleoflood records to be accomplished. 1.1 Overview of papers in this issue
CE
Remo et al. (pages xx-xx) is the first of three papers in this special issue that uses a
AC
retrodictive modeling approach to evaluate human impacts on hydrologic processes and to improve flood hazard assessments. Their study examines the combined impacts of dams and levees on the hydrology of the middle and lower Mississippi River by reconstructing the magnitude, timing, and frequency of floods over the last 130 years by piecing together available historical records for multiple river segments and integrating them into a hydraulic model. The longer-term perspective offered by this approach shows that artificial levees have acted to increase peak flood discharges by reducing flood water storage but that this effect has been
3
ACCEPTED MANUSCRIPT partially offset by tributary reservoirs that reduce peak flood magnitudes. Their work provides insight into the hydrology of the Mississippi River before widespread establishment of navigational and flood mitigation infrastructure and quantifies the effects of river regulation on
AC
CE
PT
ED
M
AN
US
CR
IP
T
flood hazard for the largest river in North America.
Fig. 1. Conference attendees examining slackwater deposits trapped within shallow caves and rock alcoves in a canyon located in the Blackhills of South Dakota during the 5th International Paleoflood Conference convened in Rapid City, South Dakota, 12-15 September 2016.
4
ACCEPTED MANUSCRIPT On the Manawatu River basin in New Zealand, Fuller et al. (pages xx-xx) reconstruct 3000 years of floods and associated magnitudes by integrating geochemical analyses of sedimentary records with documentary evidence. Their paleoflood record implies that the largest floods of the last 3,000 years correspond with European settlement and land clearance beginning
T
in the mid-nineteenth century A.D. Sedimentary evidence of floods that occurred during the
IP
nineteenth century was well preserved, providing a high-resolution record of flood magnitude
CR
and frequency; sedimentary signatures of floods that occurred prior to this time and were more distally deposited from the main channel, in contrast, were best preserved in cases of extreme
US
floods only. Their findings demonstrate the sensitivity of hydrologic processes to land use and
AN
land cover change and provide more evidence that geochemical indices derived from X-ray fluorescence scanning (e.g., Zr/Rb ratios) can help identify flood layers, while also
M
demonstrating spatial variability of flood preservation related to hydrgeomorphic complexities.
ED
Cloete et al. (pages xx-xx) demonstrate the utility of paleoflood hydrology for infrastructure planning and resilience, while also providing new insights into hydrologic
PT
variability in Africa in response to centennial- and decadal-scale climatic variability. They
CE
combined paleoflood data with historical and instrumented hydrologic data into a flood frequency analysis to determine the discharges and recurrence intervals of the most extreme
AC
floods that occurred in the Fish River Basin of Namibia over the last 400 years. Their flood frequency analysis demonstrated that the largest discharges in their paleoflood record had recurrence intervals of just 300 and 100 years and exceeded the design flood and safety check floods for a large dam planned for the Fish River basin as determined by conventional frequency analysis. Beyond its applicability to infrastructure planning, their paleoflood chronology revealed
5
ACCEPTED MANUSCRIPT significant variability in flood frequency and magnitude associated with the Maunder Minimum and the Little Ice Age. All environmental reconstructions— including paleoflood records —depend on geochronologic techniques. Knight et al. (pages xx-xx) evaluate the accuracy of optically
T
stimulated luminescence (OSL) for dating relatively modern alluvial sediments. Their study
IP
examines alluvial sediments on a reach of the Sabie River (South Africa) to evaluate how fluvial
CR
processes and geomorphic setting influence the ability of OSL dating to accurately represent the age of the uppermost alluvium. They found that variations in sediment transport processes
US
between channel and floodplain environments affected the degree of grain bleaching. This effect
AN
resulted in a wide range of ages for channel sediments transported during peak discharges but more constrained age ranges for sediments deposited in floodplains during the falling limb of
M
flood events. These findings will be critical as OSL is more widely applied to interpret
ED
depositional histories of fluvial systems (Chamberlain et al., 2018; Munoz et al., 2018). Hazelwood and Stetler (pages xx-xx) make a compelling case for how two fluvial
PT
incision events (both likely initiated in the last ca. 5 Ma) created differences in topographic relief
CE
and hydrologic networks across the Black Hills of South Dakota. These incision events made this location prone to extreme flood events, which in turn made it suited to the preservation of
AC
paleoflood deposits. The study presents a new method — ‘watershed decomposition’ — to identify relict landscapes based on digital elevation models and longitudinal profiles implemented in a GIS and applies this method to understand the evolution of the Black Hills and its drainages to their modern states. Finally, a special issue on paleofloods would be remiss to not provide some consideration of the Missoula Floods — a series of cataclysmic floods that occurred at the end of the
6
ACCEPTED MANUSCRIPT Pleistocene in the Pacific Northwestern U.S. and have been a cornerstone of geomorphology and paleoflood hydrology since they were first studied in the early twentieth century. In this issue, Stetler et al. (pages xx-xx) examine the provenance of materials comprising active and inactive sand dunes located in vicinity of the Hanford Site (an active nuclear waste repository) within the
T
Pasco Basin in south-central Washington. Surficially, this environment appears entirely aeolian;
IP
but a combination of stratigraphic interpretations, particle size, and sedimentary petrographic
CR
analyses suggests basal units of the dunes are of a glaciofluvial provenance likely associated with the Missoula Floods between about 21,000 and 12,000 years ago.
US
This edited volume represents not only the breadth of paleoflood hydrology, but
AN
importantly, several recent advances in paleoflood hydrology, including the integration of multiple types of evidence to develop a more comprehensive reconstruction of hydrologic
M
history, an ability to develop paleoflood records across a variety of landscapes, a focus on
ED
quantifying the effects of human activities on fluvial systems, and the use of advanced statistical and computational modeling. These advances represent a field that is growing in its applicability
PT
to critical questions around water resource management and hazard mitigation and maturing in
CE
its suite of available tools and techniques. In light of these advances, the paleoflood community should continue to advocate for its routine application to applied problems in science and
AC
engineering. At the same time, we must continue to reflect on the remaining challenges in the field and consider additional prospects for the future. Reducing uncertainties in reconstructions of flood timing and magnitude remains an important challenge, though several of the papers in this special issue point to ways forward by integrating multiple types of evidence in reconstructions and systematically assessing chronological techniques. Sediment characteristics — particularly grain size and geochemical proxies — have emerged as a common tool to build
7
ACCEPTED MANUSCRIPT and quantify paleoflood chronologies, but important questions remain about how depositional and post-depositional processes affect these interpretations. The development of paleoflood records is a costly endeavor — though these costs pale in comparison to the costs associated with operating a gauging station for centuries or millennia — but basin-wide and regional
T
perspectives will be critical to reduce uncertainties in our reconstructions and to evaluate the
IP
controls on flood occurrence. This special issue encapsulates an exciting moment in paleoflood
CR
hydrology as the field matures in its approaches and applicability. We look forward to the field’s continued growth in light of the daunting environmental challenges societies face in the coming
AN
US
decades.
References
ED
M
Benito, G., Thorndycraft, V.R., Rico, M., Sánchez-Moya, Y., Sopeña, A., 2008. Palaeoflood and floodplain records from Spain: Evidence for long-term climate variability and environmental changes. Geomorphology 101, 68-7
PT
Chamberlain, E.L., Törnqvist, T.E., Shen, Z., Mauz, B., Wallinga, J., 2018. Anatomy of Mississippi Delta growth and its implications for coastal restoration. Science Advances 4(4), eaar4740.
CE
England, J.F., Jr., Cohn, T.A., Faber, B.A., Stedinger, J.R., Thomas, W.O., Jr., Veilleux, A.G., Kiang, J.E., and Mason, R.R., Jr., 2018. Guidelines for Determining Flood Flow Frequency—Bulletin 17C: U.S. Geological Survey Techniques and Methods, Book 4, Chap. B5. U.S. Geological Survey, Reston, VA,148 pp.
AC
Gregory, K.J., Benito, G., Dikau, R., Golosov, V., Jones, A.J.J., Macklin, M.G., Parsons, A.J., Passmore, D.G., Poesen, J., Starkel, L., Walling, D.E., 2006. Past hydrological events related to understanding global change: an ICSU research project. Catena 66, 2–13. Harden, T.M., O'Connor, J.E., Driscoll, D.G., 2015. Late Holocene flood probabilities in the Black Hills, South Dakota with emphasis on the Medieval Climate Anomaly. Catena 130, 62-68. Johnstone, E., Macklin, M.G., Lewin, J., 2006. Holocene river dynamics and flooding in Great Britain: Evaluating regional responses to climate and land-use change. Catena 66, 14–23.
8
ACCEPTED MANUSCRIPT Macklin, M.G., Benito, G., Gregory, K.J., Johnstone, E., Lewin, J., Soja, R., Starkel, L., Thorndycraft, V.R., 2006. Past hydrological events reflected in the Holocene fluvial history of Europe. Catena 66, 145–154. Munoz, S.E., Giosan, L., Therrell, M.D., Remo, J.W., Shen, Z., Sullivan, R.M., Wiman, C., O’Donnell, M., Donnelly, J.P., 2018. Climatic control of Mississippi River flood hazard amplified by river engineering. Nature 556(7699), 95-98.
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Lisa Davis, Tessa M. Harden, Samuel E. Munoz, Jeanne Godaire, Jim E. O’Connor
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Fig. 1. Conference attendees examining slackwater deposits trapped within shallow caves and rock alcoves in a canyon located in the Blackhills of South Dakota during the 5th International Paleoflood Conference convened in Rapid City, South Dakota, 12-15 September 2016.
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6885: Remo et al. 7084: Fuller et al. 7056: Cloete et al. 7088: Jasper Knight et al. 6857: Kyle Hazelwood and Larry Stetler 6956: Larry Stetler
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