Conocimiento de la dinámica del proceso y las formas de almacenamiento de los sedimentos en el río es importante para comprender los impactos del cambio climático y cambio en el uso del suelo en la producción de sedimentos, morfología longitudinal y transversal del canal del cauce, y los hábitat acuáticos y de ribera. Entre las formas importantes de almacenamiento de sedimentos están los bancos dentro de los canales: nivel, depósitos fluviales escalonados que ocurren a diferentes alturas sobre el fondo del canal pero por debajo de la superficie del llano de inundación principal. En este estudio, la presencia contemporánea de bancos dentro de los canales en cauces en el Piedmont fue examinada, y las características hidrológicas de las localidades de estudio fueron investigadas como potenciales causantes de la formación del banco. Nueve localidades en el canal del cauce, estudiadas originalmente en 1964, fueron reexaminadas para determinar cambios en el número de niveles en el banco dentro del canal y las características morfológicas actuales del banco. De uno a tres niveles de banco no documentados en 1964 se observaron en varios lugares que tienen áreas de drenaje a menos de 600 km 2 . Se encontró que generalmente los bancos de bajo y medio nivel son altamente discontinuos, dominados casi exclusivamente por vegetación herbácea, y con frecuencia bien estratificadas. A pesar de que instancias específicas de ocurrencia de bancos pueden ser controladas a nivel local, la correspondencia entre las elevaciones de los bancos dentro de los canales y etapas de flujos de periodos de sequía con intervalos de recurrencia similares a las del llano de inundación activo más alto y más grande bajo condiciones hidroclimáticas promedio, sugieren un vínculo entre la morfogénesis del banco y las sequías. El crecimiento reciente de los bancos en la última década de sequía en el Piedmont es demostrable en una localidad, utilizando restos culturales que pueden ser adjudicados a una fecha específica. Sin embargo, la asignación inequívoca de edades específicas a los depósitos del banco sigue siendo problemático.
For more information on the USGS-the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment, visit http://www.usgs.gov or call 1-888-ASK-USGS. For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprodTo order this and other USGS information products, visit http://store.usgs.gov Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. Elevation, as used in this report, refers to the distance above the vertical datum. Vertical coordinate information is referenced to the North American Vertical Datum of 1988 (NAVD 88).Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83), and projected in Universal Transverse Mercator (UTM). Erosion Monitoring along the Coosa River below Logan Martin Dam near Vincent, Alabama, Using Terrestrial Light Detection and Ranging (T-LiDAR) TechnologyBy Dustin R. Kimbrow and Kathryn G. Lee AbstractAlabama Power operates a series of dams on the Coosa River in east central Alabama. These dams form six reservoirs that provide power generation, flood control, recreation, economic opportunity, and fish and wildlife habitats to the region. The Logan Martin Reservoir is located approximately 45 kilometers east of Birmingham and borders Saint Clair and Talladega Counties. Discharges below the reservoir are controlled by power generation at Logan Martin Dam, and there has been an ongoing concern about the stability of the streambanks downstream of the dam. The U.S. Geological Survey, in cooperation with Alabama Power conducted a scientific investigation of the geomorphic conditions of a 115-meter length of streambank along the Coosa River by using tripod-mounted terrestrial light detection and ranging technology. Two surveys were conducted before and after the winter flood season of 2010 to determine the extent and magnitude of geomorphic change. A comparison of the terrestrial light detection and ranging datasets indicated that approximately 40 cubic meters of material had been eroded from the upstream section of the study area. The terrestrial light detection and ranging data included in this report consist of electronic point cloud files containing several million georeferenced data points, as well as a surface model measuring changes between scans.
The U.S. Geological Survey, in cooperation with the City of Tuscaloosa, conducted a bathymetric survey of Carroll Creek, on May 12-13, 2010. Carroll Creek is one of the major tributaries to Lake Tuscaloosa and contributes about 6 percent of the surface drainage area. A 3.5-mile reach of Carroll Creek was surveyed to prepare a current bathymetric map, determine storage capacities at specified water-surface elevations, and compare current conditions to historical cross sections. Bathymetric data were collected using a highresolution interferometric mapping system consisting of a phase-differencing bathymetric sonar, navigation and motion-sensing system, and a data acquisition computer. To assess the accuracy of the interferometric mapping system and document depths in shallow areas of the study reach, an electronic total station was used to survey 22 cross sections spaced 50 feet apart. The data were combined and processed and a Triangulated Irregular Network (TIN) and contour map were generated. Cross sections were extracted from the TIN and compared with historical cross sections. Between 2004 and 2010, the area (cross section 1) at the confluence of Carroll Creek and the main run of Lake Tuscaloosa showed little to no change in capacity area. Another area (cross section 2) showed a maximum change in elevation of 4 feet and an average change of 3 feet. At the water-surface elevation of 224 feet (National Geodetic Vertical Datum of 1929), the cross-sectional area has changed by 260 square feet for a total loss of 28 percent of cross-sectional storage area. The loss of area may be attributed to sedimentation in Carroll Creek and (or) the difference in accuracy between the two surveys.
Methods of practice and guidelines for using survey-grade global navigation satellite systems (GNSS) to establish vertical datum in the United States Geological Survey: U.S. Geological Survey Techniques and Methods, book 11, chap. D1, 102 p. with appendixes.
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