Reservoir Sedimentation Along the Upper Washita River in Western Oklahoma and Northern Texas

In response to Dust Bowl flooding of the 1930's, numerous flood control dams were built in Oklahoma and Texas to slow discharge of tributaries into the main stem of the Washita River, effectively reducing peak flows and downstream flooding. The dams in this region have a projected sediment storage lifetime of 50 years, and some are approaching the end of their projected lifetime. Field measurements where made to estimate the volume of sediment impounded behind flood control structures by first determining thickness of sediment at the dam. Next, volume of sediment was estimated by calculating it as a geometric wedge shape, thickest at the dam and tapering to zero upstream. Calculated sediment volume for each site was then compared to predictions by the WEPP (Water Erosion Prediction Project) model for each reservoir. The WEPP model was found to severely underestimate sediment in each reservoir, with no statistical significance between observed and predicted values. Further investigation indicated that 77.5% of residual could be explained by considering length of section line roads in each watershed. In addition, all flood control dams measured were found to be filled to only a fraction of their sediment storage capacity, or to contain immeasurably small amounts.Department of Geograph

The effect of axial load on the sagittal plane curvature of the upright human spine in vivo

Copyright © 2008 Elsevier. NOTICE: this is the author’s version of a work that was accepted for publication in Pattern Recognition . Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of Biomechanics, Vol. 41 Issue 13 (2008), DOI: 10.1016/j.jbiomech.2008.06.035Determining the effect of load carriage on the human spine in vivo is important for determining spinal forces and establishing potential mechanisms of back injury. Previous studies have suggested that the natural curvature of the spine straightens under load, but are based on modelling and external measurements from the surface of the back. In the current study, an upright positional MRI scanner was used to acquire sagittal images of the lumbar and lower thoracic spine of 24 subjects. The subjects were imaged in standing whilst supporting 0, 8 and 16 kg of load which was applied axially across the shoulders using an apron. An active shape model of the vertebral bodies from T10 to S1 was created and used to characterise the effect of load. The results from the shape model showed that the behaviour of the average-shaped spine was to straighten slightly. However, the shape model also showed that the effect of load exhibited systematic variation between individuals. Those who had a smaller than average curvature before loading straightened under load, whereas those who had a greater than average curvature before loading showed an increase in curvature under load. The variation in behaviour of differently shaped spines may have further implications for the effects of load in lifting manoeuvres and in understanding the aetiology of back pain