USMA Athena
USMA Athena is a secure digital service managed by the United States Military Academy Library to make the work of USMA scholars freely available, while also ensuring these resources are organized to preserve the legacy of USMA scholarship. The mission of USMA Athena is to showcase the academic impact and intellectual capital that has become synonymous with the celebrated heritage of educational prowess attributed to the Long Gray Line. Scholarship submitted to USMA Athena benefits from added visibility and discoverability via Google Scholar in addition to the use of persistent URLs that will provide enduring access to the work over time.
Communities
Select a community to browse its collections.
Recent Submissions
Estimating catchment‐scale sediment storage in a large River Basin, Colorado River, USA
(Wiley, 2024-05-05) Kemper, John T.; Knox, Richard L.; Raffae, Muhammad; Schulz, Evan; Bailey, Ryan; Morrison, Ryan R.; Wohl. Ellen
Catchment-scale sediment storage is conceptualized as increasing in magnitude downstream, although reach-scale controls may override this trend. We use empirical data from a literature review and two numerical models to quantitatively estimate sediment storage across the Colorado River Basin, USA. We use assumed alluvial thickness with floodplains delineated in the GFPLAIN model from 30 m digital elevation models. We use the SWAT+ model based on model-estimated (i) groundwater storage and (ii) sediment storage. Existing studies indicate that sediment stored in floodplains and on low terraces is ~0.3–6 m thick. A first-order approximation of volumetric storage capacity for natural floodplains is ~105 m3 per km. Sediment storage volumes of floodplains are ~108–1011 m3 over river lengths of 101–103 m. For the modeling estimates, we evaluated sediment storage by stream order and by elevation band within the Upper and Lower Colorado River Basins. Comparisons among the outputs cause us to place more confidence in the GFPLAIN and SWAT+ aquifer volume estimates. Each method includes substantial uncertainty and constitutes a first-order approximation. Results suggest using 21 and 130 billion cubic meters as approximate lower and upper bounds for total sediment storage in the Upper Basin and 314 and 482 billion cubic meters as approximate lower and upper bounds for the Lower Basin. The largest proportion of sediment is stored in the montane and steppe zones in the Upper Basin and in the Sonoran zone in the Lower Basin.
A first-order approximation of floodplain soil organic carbon stocks in a river network: The South Platte River, Colorado, USA as a case study
(Elsevier BV, 2022-12) Wohl, Ellen; Knox, Richard L.
The lack of watershed-scale estimates of floodplain carbon stocks limits recognition of the important role of floodplains and river corridor restoration in efforts to enhance carbon sequestration. We use the South Platte River watershed of Colorado, USA as a case study to illustrate spatial patterns of, and controls on, floodplain carbon stocks at the watershed scale. This case study illustrates the disproportionate importance of floodplains for soil carbon stocks relative to adjacent uplands and provides an example of how spatially explicit data can be used to prioritize floodplain restoration with regard to carbon sequestration. We use the hydrogeomorphic floodplain tool GFPLAIN to delineate the extent of 100-year floodplains in the South Platte River watershed. We distinguish elevation bands for the steppe, montane, subalpine, and alpine zones. We also differentiate bead (floodplain width/channel width ≥ 5) and string (floodplain width/channel width < 5) reaches within the montane and subalpine zones. Drawing on prior, field-based measurements of organic carbon stock in downed, dead wood and soil in these floodplain types, we estimate total floodplain organic carbon stock based on median values of stock in different floodplain types and the spatial extent of these floodplain types. This estimate includes organic carbon stocks in lake and reservoir sediments in the watershed. Soil constitutes the greatest reservoir of floodplain carbon. The total estimated area of floodplain is 2916 km2, which is 4.3 % of the total watershed area of the South Platte River. Our preferred estimate is 42.7 Tg C stock (likely range of 39.1–42.7 Tg). This equates to 11.1 % of a previously estimated overall carbon stock (above and belowground biomass and soil organic carbon) in the entire watershed of 384 Tg C. Floodplains are thus disproportionately important, relative to their surface area, in storing organic carbon in this semiarid watershed. Field measurements of floodplain soil organic carbon stocks from across the globe indicate that this finding is not unique to this watershed, with implications for prioritizing floodplain management and restoration as a means of enhancing carbon sequestration.
A river ran through it: Floodplains as America’s newest relict landform
(American Association for the Advancement of Science (AAAS), 2022-06-24) Knox, Richard L.; Morrison, Ryan R.; Wohl, Ellen E.
Artificial levees are a major human modification of river corridors, but we still do not have a clear understanding of how artificial levees affect floodplain extent at regional and larger scales. We estimated changes in river-floodplain connectivity due to artificial levees in the contiguous United States (CONUS) using a combination of artificial levee databases, delineations of floodplain areas, and deletion of artificial levees from topography. Our results indicate that artificial levees do not only decrease floodplain extent but also alter locations of floodplain connectivity. Anthropogenically connected and disconnected locations are similar in land cover and are predominantly, in decreasing order of extent, cultivated, wetland, forested, and developed land cover types, with more than 30% of the entire floodplain area in the CONUS cultivated or developed. This study indicates that artificial levees cause complex changes in river-floodplain connectivity and can increase flooded areas in some rivers.
Identification of Artificial Levees in the Contiguous United States
(American Geophysical Union (AGU), 2022-04) Knox, Richard L.; Morrison, R. R.; Wohl, E. E.
Artificial levees are anthropogenic structures designed to hydrologically disconnect rivers from floodplains. The extent of artificial levees in the contiguous United States (CONUS) is unknown. To better estimate the distribution of artificial levees, we tested several different geomorphic, land cover, and spatial variables developed from the National Elevation Dataset, the National Land Cover database, and the National Hydrology Dataset HR Plus. We used known levee locations from the National Levee Database as training data. We tested machine learning and general logistic models’ ability to detect artificial levees in a 100-year hydrogeomorphic floodplain of seven geographically diverse 8-digit HUC basins. Random forest models outperformed other models in predicting the location of levees using variables representing geomorphic attributes, land cover, and distance from streams ranging in size between stream order one through six. To demonstrate the ability of our approach to detect unknown levees, we conducted a leave-one-out cross-validation in the lower Mississippi Basin using approximately 1,100 artificial levees. This approach detected known levees constituting 94% of the total levee length in the basin. Scaling up to the CONUS, we applied a high performing (overall accuracy of 97%) random forest model using land cover and stream order variables. We detected 182,213 km of potential levees, mostly along streams of order 2–6 in the Mississippi and Missouri River Basins, indicating that the national levee database contains 20.4% of levee length. Potential levees and those documented in the national levee database modify 2% of the total length of streams in the contiguous United States.
A geomorphic approach to the analysis of bedload and bed morphology of the Lower Mississippi River near the Old River Control Structure
(Elsevier BV, 2016-09) Knox, Richard L.; Edgardo M. Latrubesse
The Mississippi River is the ultimate single-thread meandering river. Five hundred kilometers upstream from its mouth, about 25% of the river's discharge and sediment load is diverted into the Atchafalaya River. This diversion is controlled by the Old River Control Structure (ORCS), built by the U.S. Army Corps of Engineers (USACE) in stages since 1961, to stop the avulsion of the Mississippi River into the Atchafalaya. The effects of ORCS on sediment and water discharge and geomorphic change to the Lower Mississippi River (LMR) channel are not yet completely understood and require placing the river into a geomorphic context, first classifying the channel into similar categories before evaluating change. The objectives of this study are to estimate the LMR bedload, develop and apply a geomorphic classification of the LMR near the ORCS, and explore geomorphic change within the classified areas.
We studied a 115-km-long stretch between ORCS and Baton Rouge that is highly impacted by engineering. We used six sets of bathymetric multibeam echosounder surveys conducted by the USACE, multitemporal cartographies, and a field survey supported by multibeam echosounder bathymetry, acoustic Doppler current profiler (ADCP) measurements, sediment samples collection, and geomorphic observations. A three-dimensional method for estimating bedload from time-elapsed bathymetric surveys was developed and applied on seven sets of time-elapsed surveys downstream from ORCS from 2010, 2011, and 2012. We estimate that the fraction of bedload as a percentage of total sand load between 2003 and 2011 was 13.2%. A bedform classification scheme, based on bedform height, was developed. The bed was almost completely mantled by sandy bedforms above the − 24-m isoline.
The studied reach was divided into ten zones according to four geomorphic types based on channel planform, geologic controls, presence of islands, and other morphometric parameters. These zones were shown to be physically distinct in terms of bedform location, depth to bedform size, channel sinuosity, channel width-to-depth ratios, and adjustments in the thalweg and channel width from 1948 to 2012.
The 1948 to 1975 period displayed a relatively large amount of thalweg aggradation, with a spatial average of 1.8 m and an average channel narrowing of 80 m. The 1975 to 2012 period had much lower spatial aggradation of 0.5 m and a lower average channel narrowing of 35 m. Thalweg sinuosity did not adjust very much, with an average reduction of 0.02 from 1948 to 2012 and an average of zero adjustment between 1975 and 2012.
The shape and spatial extent of a very large, anomalous bar near ORCS varied at seasonal and decadal timescales and may be influenced by the ORCS. Bed morphology was specific to geomorphic zones, which were shown to be physically significant, and should be employed in future studies of large rivers.