John Petrie

Statistical approach to sediment sampling accuracy

A variety of hydraulic and ecological processes in rivers depend in part on the grain size distribution of the riverbed. For this reason it is important to accurately sample the bed to determine the grain size distribution. To describe the accuracy of riverbed sediment samples, techniques based on the multinomial distribution are presented. These techniques allow confidence intervals to be calculated for grid, areal, and volume samples. Additionally, sample sizes can be estimated to achieve a desired accuracy for the three sample types. A transformation is necessary when considering areal and volume samples. This is because neither of these two sample types is well conditioned for statistical analysis. The transformation is based on the results of a previously performed grid sample. The transformation then estimates either an areal or volume sample size that is necessary to match the accuracy of the grid sample. This procedure is useful when obtaining a hybrid distribution from grid and areal samples. Having areal and grid sample results of known accuracy allows confidence intervals to be placed on the final hybrid distribution. A series of laboratory experiments is used to illustrate the various techniques. Comparisons are also made with techniques presented in the literature.

Use of Snow Fences to Reduce the Impacts of Snowdrifts on Highways: Renewed Perspective

In northern climates, snow fences are usually established in or beyond the right-of-way to eliminate blowing and drifting snow on roadways and thus improve road safety. To make snow fences more effective on highways and provide guidelines for the departments of transportation siting the fences, this work reviews the literature as well as survey responses from practitioners in northern states. This review combines information obtained from the resources to detail several aspects of snow fence use, including history, design protocols, siting policies, benefits, challenges, and numerical modeling. Particular attention is paid to living snow fences as an alternative to traditional structural snow fences. The survey results show that almost all the responding agencies have launched snow fence programs, which have various design and siting protocols that depend on the specific conditions.

Sensitivity of Transient Seepage Analysis to Variation of the Input Parameters

Transient seepage analysis using numerical methods is characterized by an increase in the required number of input parameters when compared with a steady-state analysis. Among these additional parameters are those that represent unsaturated soil characteristics, and obtaining these unsaturated soil properties is generally more difficult, requires special testing apparatus, takes longer than conventional tests, and thus costs more. To obtain more reliable transient seepage results with reasonable effort, this study demonstrates which input parameters are more critical and sensitive to the modeling results. The soil water characteristic curve, volumetric water content, and saturated hydraulic conductivity are determined experimentally and varied within a reasonable range of each value in the numerical model; and the pore water pressure at a certain point in the model is compared to determine the influence of each parameter on the modeling results. Based on this analysis, the most sensitive and critical parameters are identified. These results will allow an assessment of the relative cost-benefit ratio so that the desired accuracy can be achieved at lowest cost.