The Atchafalaya River in south-central Louisiana is of geomorphic interest because of the large v... more The Atchafalaya River in south-central Louisiana is of geomorphic interest because of the large volumes of flow and sediment transported and its role as a major floodway for the lower Mississippi River, notwithstanding its potential to become an avulsion pathway at Old River. Since its origin in the sixteenth century, it has undergone many transformations and currently receives flow from the Red River and partial flow of the Mississippi River through multiple pathways. Flow increased progressively beginning in the mid-1800s and continued until concerns of diversion spurred placement of engineering structures to regulate flows at the juncture between the Mississippi and Atchafalaya rivers in 1963. Prior studies, that looked at reaches or six to seven rangelines or cross sections on hydrographic surveys document areal, width, and depth increases in the uppermost 80 km (50 mi) of the Atchafalaya River from 1880 to 1974. This study assesses how channel geometry of the Atchafalaya River has changed with flow variations since the 1880s by evaluating instantaneous dischargemeasurements that document change at superior temporal resolution and differences in thalweg values from coupled modern hydrographic surveys which document change at better spatial resolution than prior works.While structures have regulated and limited flow into the Atchafalaya since 1963, the highest values of discharge, cross-sectional area, and width at Simmesport (upstream) follow river regulation. Associated geometry data at Simmesport and Morgan City (downstream) document that mean bed and thalweg elevations have risen. Comparison of thalweg elevations on hydrographic surveys from 1963 and 2006 show pronounced local variability in bed elevation change but also reaches dominated by degradation (including the Red River and uppermost section of the Atchafalaya) near the Old River diversion. Aggradation occurs in the lower Atchafalaya, a zone where along-channel lakes are filling, flow and sediment quantities are changing in part caused by the constructed Wax Lake Outlet, and deltas have been growing in Atchafalaya Bay. Findings are relevant to river engineering and flood management, especially navigation, and help in better understanding the evolution of large distributaries and the role of human impacts.
Change in fluvial systems has interested geomorphologists for several decades, but awareness of c... more Change in fluvial systems has interested geomorphologists for several decades, but awareness of change dates back much further to the ancient Greeks. This paper introduces seven articles that focus on aspects of temporal and/or spatial change in rivers in the central and southeastern United States of America. Timescales examined span from the late Pleistocene through historical and into modern times. Spatial scales investigated range from small watersheds to the juncture between two of the larger rivers in North America. Natural drivers of change discussed include sea-level rise which followed the last glacial maxima and influenced drainage connections, avulsions, and lateral migration which influenced channel position and caused stream capture; and transitions across geomorphic provinces with differing bedrock and structure. Human-induced drivers of change include land use alterations such as settlement and logging which influenced sediment input and channel form, artificial cut-offs, removal of log rafts, dredging, and artificial channels and floodways which changed flow, sedimentation, and geometry, and the introduction of contaminants which influenced sediment quality. Collectively, these papers fill voids in the literature on topics and places where there has been little prior investigation.
Change in fluvial systems has interested geomorphologists for several decades, but awareness of c... more Change in fluvial systems has interested geomorphologists for several decades, but awareness of change dates back much further to the ancient Greeks. This paper introduces seven articles that focus on aspects of temporal and/or spatial change in rivers in the central and southeastern United States of America. Timescales examined span from the late Pleistocene through historical and into modern times. Spatial scales investigated range from small watersheds to the juncture between two of the larger rivers in North America. Natural drivers of change discussed include sea-level rise which followed the last glacial maxima and influenced drainage connections, avulsions, and lateral migration which influenced channel position and caused stream capture; and transitions across geomorphic provinces with differing bedrock and structure. Human-induced drivers of change include land use alterations such as settlement and logging which influenced sediment input and channel form, artificial cut-offs, removal of log rafts, dredging, and artificial channels and floodways which changed flow, sedimentation, and geometry, and the introduction of contaminants which influenced sediment quality. Collectively, these papers fill voids in the literature on topics and places where there has been little prior investigation.
Floodplain and instream mining are activities that generally increase channel change or instabili... more Floodplain and instream mining are activities that generally increase channel change or instability. To quantify this effect, it is necessary to have some idea of natural or baseline rates of change in rivers in the same region where stream have similar topography, climate, geologic units and vegetation. The Pascagoula River and its tributaries traverse a number of geologic units and the basin shows a diverse set of land cover and land uses, including two streams with considerable historical and recent mining activity. This study quantifies the rates of change in the Pascagoula and some of its tributaries, suggesting at which point planform changes are clearly modified, directly or indirectly, more so by human action. This is done by digitizing the larger and mined tributaries of this system in a GIS using varied sources of data (aerial photographs, topographic maps and digital ortho quarter quadrangles). Polygon areas derived from overlays characterizing changes (areas of erosion, deposition, no change, and areas between channels) in channel position and planform were extracted from the GIS and normalized for scale, so that larger rivers could be compared with the headwaters, as well as smaller rivers and creeks. This study provides insights into the natural factors and anthropogenic activities that influence channel changes in this basin, and thus where future change might be expected to occur. Those insights, in turn, can be applied to management and engineering in the basin.
Change in fluvial systems has interested geomorphologists for several decades, but awareness of c... more Change in fluvial systems has interested geomorphologists for several decades, but awareness of change dates back much further to the ancient Greeks. This paper introduces seven articles that focus on aspects of temporal and/or spatial change in rivers in the central and southeastern United States of America. Timescales examined span from the late Pleistocene through historical and into modern times. Spatial scales investigated range from small watersheds to the juncture between two of the larger rivers in North America. Natural drivers of change discussed include sea-level rise which followed the last glacial maxima and influenced drainage connections, avulsions, and lateral migration which influenced channel position and caused stream capture; and transitions across geomorphic provinces with differing bedrock and structure. Human-induced drivers of change include land use alterations such as settlement and logging which influenced sediment input and channel form, artificial cut-offs, removal of log rafts, dredging, and artificial channels and floodways which changed flow, sedimentation, and geometry, and the introduction of contaminants which influenced sediment quality. Collectively, these papers fill voids in the literature on topics and places where there has been little prior investigation.
... Living with the Louisiana Shore Joseph T. Kelley et al. Living with the Alabama-Mississippi S... more ... Living with the Louisiana Shore Joseph T. Kelley et al. Living with the Alabama-Mississippi Shore Living with the Coast of Maine Wayne F. Canis et al. Living with the Coast of Alaska Owen Mason et al. Joseph T. Kelley et al. ... The Alabama-Mississippi book was a different story. ...
The Atchafalaya River in south-central Louisiana is of geomorphic interest because of the large v... more The Atchafalaya River in south-central Louisiana is of geomorphic interest because of the large volumes of flow and sediment transported and its role as a major floodway for the lower Mississippi River, notwithstanding its potential to become an avulsion pathway at Old River. Since its origin in the sixteenth century, it has undergone many transformations and currently receives flow from the Red River and partial flow of the Mississippi River through multiple pathways. Flow increased progressively beginning in the mid-1800s and continued until concerns of diversion spurred placement of engineering structures to regulate flows at the juncture between the Mississippi and Atchafalaya rivers in 1963. Prior studies, that looked at reaches or six to seven rangelines or cross sections on hydrographic surveys document areal, width, and depth increases in the uppermost 80 km (50 mi) of the Atchafalaya River from 1880 to 1974. This study assesses how channel geometry of the Atchafalaya River has changed with flow variations since the 1880s by evaluating instantaneous dischargemeasurements that document change at superior temporal resolution and differences in thalweg values from coupled modern hydrographic surveys which document change at better spatial resolution than prior works.While structures have regulated and limited flow into the Atchafalaya since 1963, the highest values of discharge, cross-sectional area, and width at Simmesport (upstream) follow river regulation. Associated geometry data at Simmesport and Morgan City (downstream) document that mean bed and thalweg elevations have risen. Comparison of thalweg elevations on hydrographic surveys from 1963 and 2006 show pronounced local variability in bed elevation change but also reaches dominated by degradation (including the Red River and uppermost section of the Atchafalaya) near the Old River diversion. Aggradation occurs in the lower Atchafalaya, a zone where along-channel lakes are filling, flow and sediment quantities are changing in part caused by the constructed Wax Lake Outlet, and deltas have been growing in Atchafalaya Bay. Findings are relevant to river engineering and flood management, especially navigation, and help in better understanding the evolution of large distributaries and the role of human impacts.
Change in fluvial systems has interested geomorphologists for several decades, but awareness of c... more Change in fluvial systems has interested geomorphologists for several decades, but awareness of change dates back much further to the ancient Greeks. This paper introduces seven articles that focus on aspects of temporal and/or spatial change in rivers in the central and southeastern United States of America. Timescales examined span from the late Pleistocene through historical and into modern times. Spatial scales investigated range from small watersheds to the juncture between two of the larger rivers in North America. Natural drivers of change discussed include sea-level rise which followed the last glacial maxima and influenced drainage connections, avulsions, and lateral migration which influenced channel position and caused stream capture; and transitions across geomorphic provinces with differing bedrock and structure. Human-induced drivers of change include land use alterations such as settlement and logging which influenced sediment input and channel form, artificial cut-offs, removal of log rafts, dredging, and artificial channels and floodways which changed flow, sedimentation, and geometry, and the introduction of contaminants which influenced sediment quality. Collectively, these papers fill voids in the literature on topics and places where there has been little prior investigation.
Change in fluvial systems has interested geomorphologists for several decades, but awareness of c... more Change in fluvial systems has interested geomorphologists for several decades, but awareness of change dates back much further to the ancient Greeks. This paper introduces seven articles that focus on aspects of temporal and/or spatial change in rivers in the central and southeastern United States of America. Timescales examined span from the late Pleistocene through historical and into modern times. Spatial scales investigated range from small watersheds to the juncture between two of the larger rivers in North America. Natural drivers of change discussed include sea-level rise which followed the last glacial maxima and influenced drainage connections, avulsions, and lateral migration which influenced channel position and caused stream capture; and transitions across geomorphic provinces with differing bedrock and structure. Human-induced drivers of change include land use alterations such as settlement and logging which influenced sediment input and channel form, artificial cut-offs, removal of log rafts, dredging, and artificial channels and floodways which changed flow, sedimentation, and geometry, and the introduction of contaminants which influenced sediment quality. Collectively, these papers fill voids in the literature on topics and places where there has been little prior investigation.
Floodplain and instream mining are activities that generally increase channel change or instabili... more Floodplain and instream mining are activities that generally increase channel change or instability. To quantify this effect, it is necessary to have some idea of natural or baseline rates of change in rivers in the same region where stream have similar topography, climate, geologic units and vegetation. The Pascagoula River and its tributaries traverse a number of geologic units and the basin shows a diverse set of land cover and land uses, including two streams with considerable historical and recent mining activity. This study quantifies the rates of change in the Pascagoula and some of its tributaries, suggesting at which point planform changes are clearly modified, directly or indirectly, more so by human action. This is done by digitizing the larger and mined tributaries of this system in a GIS using varied sources of data (aerial photographs, topographic maps and digital ortho quarter quadrangles). Polygon areas derived from overlays characterizing changes (areas of erosion, deposition, no change, and areas between channels) in channel position and planform were extracted from the GIS and normalized for scale, so that larger rivers could be compared with the headwaters, as well as smaller rivers and creeks. This study provides insights into the natural factors and anthropogenic activities that influence channel changes in this basin, and thus where future change might be expected to occur. Those insights, in turn, can be applied to management and engineering in the basin.
Change in fluvial systems has interested geomorphologists for several decades, but awareness of c... more Change in fluvial systems has interested geomorphologists for several decades, but awareness of change dates back much further to the ancient Greeks. This paper introduces seven articles that focus on aspects of temporal and/or spatial change in rivers in the central and southeastern United States of America. Timescales examined span from the late Pleistocene through historical and into modern times. Spatial scales investigated range from small watersheds to the juncture between two of the larger rivers in North America. Natural drivers of change discussed include sea-level rise which followed the last glacial maxima and influenced drainage connections, avulsions, and lateral migration which influenced channel position and caused stream capture; and transitions across geomorphic provinces with differing bedrock and structure. Human-induced drivers of change include land use alterations such as settlement and logging which influenced sediment input and channel form, artificial cut-offs, removal of log rafts, dredging, and artificial channels and floodways which changed flow, sedimentation, and geometry, and the introduction of contaminants which influenced sediment quality. Collectively, these papers fill voids in the literature on topics and places where there has been little prior investigation.
... Living with the Louisiana Shore Joseph T. Kelley et al. Living with the Alabama-Mississippi S... more ... Living with the Louisiana Shore Joseph T. Kelley et al. Living with the Alabama-Mississippi Shore Living with the Coast of Maine Wayne F. Canis et al. Living with the Coast of Alaska Owen Mason et al. Joseph T. Kelley et al. ... The Alabama-Mississippi book was a different story. ...
Uploads
Papers by Joann Mossa
and sediment transported and its role as a major floodway for the lower Mississippi River, notwithstanding its
potential to become an avulsion pathway at Old River. Since its origin in the sixteenth century, it has undergone
many transformations and currently receives flow from the Red River and partial flow of the Mississippi River
through multiple pathways. Flow increased progressively beginning in the mid-1800s and continued until
concerns of diversion spurred placement of engineering structures to regulate flows at the juncture between
the Mississippi and Atchafalaya rivers in 1963. Prior studies, that looked at reaches or six to seven rangelines
or cross sections on hydrographic surveys document areal, width, and depth increases in the uppermost 80 km
(50 mi) of the Atchafalaya River from 1880 to 1974.
This study assesses how channel geometry of the Atchafalaya River has changed with flow variations since the
1880s by evaluating instantaneous dischargemeasurements that document change at superior temporal resolution
and differences in thalweg values from coupled modern hydrographic surveys which document change at
better spatial resolution than prior works.While structures have regulated and limited flow into the Atchafalaya
since 1963, the highest values of discharge, cross-sectional area, and width at Simmesport (upstream) follow
river regulation. Associated geometry data at Simmesport and Morgan City (downstream) document that
mean bed and thalweg elevations have risen. Comparison of thalweg elevations on hydrographic surveys from
1963 and 2006 show pronounced local variability in bed elevation change but also reaches dominated by degradation
(including the Red River and uppermost section of the Atchafalaya) near the Old River diversion. Aggradation
occurs in the lower Atchafalaya, a zone where along-channel lakes are filling, flow and sediment
quantities are changing in part caused by the constructed Wax Lake Outlet, and deltas have been growing in
Atchafalaya Bay. Findings are relevant to river engineering and flood management, especially navigation, and
help in better understanding the evolution of large distributaries and the role of human impacts.
and sediment transported and its role as a major floodway for the lower Mississippi River, notwithstanding its
potential to become an avulsion pathway at Old River. Since its origin in the sixteenth century, it has undergone
many transformations and currently receives flow from the Red River and partial flow of the Mississippi River
through multiple pathways. Flow increased progressively beginning in the mid-1800s and continued until
concerns of diversion spurred placement of engineering structures to regulate flows at the juncture between
the Mississippi and Atchafalaya rivers in 1963. Prior studies, that looked at reaches or six to seven rangelines
or cross sections on hydrographic surveys document areal, width, and depth increases in the uppermost 80 km
(50 mi) of the Atchafalaya River from 1880 to 1974.
This study assesses how channel geometry of the Atchafalaya River has changed with flow variations since the
1880s by evaluating instantaneous dischargemeasurements that document change at superior temporal resolution
and differences in thalweg values from coupled modern hydrographic surveys which document change at
better spatial resolution than prior works.While structures have regulated and limited flow into the Atchafalaya
since 1963, the highest values of discharge, cross-sectional area, and width at Simmesport (upstream) follow
river regulation. Associated geometry data at Simmesport and Morgan City (downstream) document that
mean bed and thalweg elevations have risen. Comparison of thalweg elevations on hydrographic surveys from
1963 and 2006 show pronounced local variability in bed elevation change but also reaches dominated by degradation
(including the Red River and uppermost section of the Atchafalaya) near the Old River diversion. Aggradation
occurs in the lower Atchafalaya, a zone where along-channel lakes are filling, flow and sediment
quantities are changing in part caused by the constructed Wax Lake Outlet, and deltas have been growing in
Atchafalaya Bay. Findings are relevant to river engineering and flood management, especially navigation, and
help in better understanding the evolution of large distributaries and the role of human impacts.