Lance D. Yarbrough

The Effects of Riparian Vegetation on Bank Stability

In northern Mississippi, roots in riparian zones were studied in an attempt to quantify the effects of root reinforcement of the soil matrix. The roots of trees can be treated as elastic-reinforced elements, and a function of the tensile strength of the roots can be added directly to the Mohr-Coulomb equation for failure criteria. Estimating root reinforcement and root-soil matrix interactions allows for the determination of whether bank vegetation is beneficial or detrimental. The research was conducted at the Goodwin Creek Experimental Watershed, located near Batesville, MS. This investigation quantifies root tensile strength of the sweet gum ( Liquidamar syraciflua ) in a cohesive, fine-grained, primarily loess-derived fluvial material. During the field research, trenches were excavated to gain access to the roots being studied. These trenches allowed mapping of the roots, as well as direct tensile testing of the roots. Increased tensile strength due to root reinforcement was found to be between 0.0 and 245 kPa, depending on depth. For a given depth of 40 cm, the increased tension due to root reinforcement averaged 148 kPa, depending on lateral distance from tree. A modified root reinforcement model was developed to explain the root-soil interaction observed at the research site. Itascas Fast Lagrangian Analysis of Continua model was employed in determining the role of root reinforcement. The modeling results showed a contrast between root-reinforced and unreinforced soil. When no root reinforcement existed, the slope failed marginally. When simulated root reinforcement of 20 kPa was applied, the slope was shown to be completely stable.

Using at-sensor radiance and reflectance tasseled cap transforms applied to change detection for the ASTER sensor

The Tasseled Cap Transform (TCT) was originally created for agricultural land investigations. It is a vegetative index commonly used as an indicator of vegetation health and assessing vegetation and land cover change. The nature of the TCT requires linear combinations specific to each sensor. Additionally, the varying units of the reported digital number (DN) require supplementary eigenvectors. TCTs were derived for the at-sensor radiance and at-sensor reflectance and compared using differing change detection application in Mississippi. The Tasseled Cap Soil Brightness Index (SBI) and the Greenness Vegetative Index (GVI) were conducted and evaluated. It was found that the at-sensor radiance based TCT was most useful in a change detection analysis. The desired spectral characteristics were well contrasted while the at-sensor reflectance based TCT tended to be less effective.

Investigating Spatial Downscaling of Satellite Rainfall Data for Streamflow Simulation in a Medium-Sized Basin

Abstract The objective of this study was to investigate spatial downscaling of satellite rainfall data for streamflow prediction in a medium-sized (970 km2) river basin prone to flooding. The spatial downscaling scheme used in the study was based on the principle of scale invariance. It reproduced the rainfall variability at finer scales while being conditioned on the large-scale rainfall. Two Tropical Rainfall Measuring Mission (TRMM)-based real-time global satellite rainfall products were analyzed: 1) the infrared (IR)-based 3B41RT product available at 1 hourly and 0.25° scales and 2) the combined passive microwave (PMW) and IR-based 3B42RT product available at 3 hourly and 0.25° scales. The conceptual Hydrologic Engineering Center-Hydrologic Modeling System (HEC-HMS) was used for the simulation of streamflow. It was found that propagation of spatially downscaled satellite rainfall in the hydrologic model increased simulation uncertainty in streamflow as rainfall grid scales became smaller than 0.25°. T...

Presentation of the Kauth–Thomas transform for WorldView-2 reflectance data

We present the Kauth–Thomas (K-T) transform coefficients for the reflectance data of the WorldView-2 (WV-2) sensor. The K-T transform is a widely used spectral enhancement, which employs a set of eigenvectors that transforms the given spectral space into a defined feature space. This feature space offers the user a physically based coordinate that helps to describe the spectral signature of the individual pixels. The two most prevalent of the alignments in feature space are the brightness and greenness coordinate axes. These coordinate axes of the first K-T transform have become well known and form the first plan of the defined feature space known as the tasselled cap.

Use of Revised Universal Soil Loss Equation (RUSLE) and Historical Imagery for Claims of Sedimentation of Lakes and Streams

The consequences of erosion and subsequent sedimentation of lakes and streams are many and widespread. The natural process of erosion can be accelerated by land cover changes with an increase in areas of impervious surfaces. Sediment is continually being transported along all streams in nature and can come from anywhere in the watershed. Lakes slow the rate of velocity of the water and allow the entrained sediment to settle and accumulate. When sediment impacts water impoundments, legal actions may result. Even with evidence of specific sediment release, the forensic analysis may not be an open-and-shut case. The author presents a method to investigate the validity of a legal claim of a sediment-impacted lake at the outfall of a mixed rural/urban watershed. By combining land use change, soils, elevation and precipitation data, a maximum possible annual sediment loss was approximately 154 tonne per hectare (15.4 kg/m2). Lacking evidence of specific historic events of erosion and subsequent sedimentation, this method provides an equitable means of determining compensatory damages. Using aerial and satellite imagery provided historical evidence of land cover change and examples of significant erosion in the watershed and not named in the lawsuit. The focus of the litigation started with the property adjoining the effected lake. The analysis provides a method to investigate erosion and subsequent sedimentation claims at a watershed-scale.

Rating the Shrink/Swell Behavior of the Porters Creek Formation

The Porters Creek Formation, a Tertiary age formation found in the Gulf Coastal Plain region, is known to exhibit shrink/swell behavior. This formation consists of mixed-layer clays composed mostly of montmorillonite. However, to date, the Porters Creek Formation has been ranked as only moderately expansive compared with other expansive geologic materials. During this investigation, surface and subsurface samples of the Porters Creek Formation were subjected to a variety of geotechnical tests to determine their shrink/swell potential. The tests included Atterberg limits, percentage of clay, activity, and volumetric change of samples using a potential volume change meter. The results were used to rank the shrink/swell behavior of the samples in six commonly used classification systems that are based on empirical relationships between the engineering properties of the clay mineral constituents. The same classification systems were then used to classify other geologic formations known to exhibit shrink/swell behavior; then, these results were compared with the results of analyses of the Porters Creek Formation. The samples from the Porters Creek Formation generally ranked in the highest or second highest category of shrink/swell potential, higher than generally expected. This indicates that the Porters Creek Formation has the same high potential for damaging shrink/swell behavior as other formations known to cause damage to roads and other engineered construction, and the current ranking of the Porters Creek Formation by the Federal Highway Administration is too low.