Practice versus policy-led coastal defence management     

M.C. O&#x;Connor  G. Lymbery  J.A.G. Cooper  J. Gault  J. McKenna 《Marine Policy》2009,33(6):923

Throughout northwest European coastal countries risks associated with coastal erosion are significant but spatially and temporally variable. The level of this risk is largely dependent on the extent of development within the coastal zones and a variety of approaches have been adopted for its management. The decision-making process for responding to erosion risk depends to a large extent on national policy. Coastal protection policy in northwest European countries varies in terms of the level of centralisation and formality of arrangements. In this paper the practical outworking of the informal practice-based system of Ireland, where there is no national policy framework, is compared with the policy-led system of England and Wales where formal national guidelines exist. Using case studies, the strengths and weaknesses of both the bottom-up and top-down approaches are assessed. The findings reveal strengths and weaknesses in both existing types of approach.  相似文献   

Wind tunnel evaluation of a wedge-shaped aeolian sediment trap   总被引：4，自引：0，他引：4  

W. G. Nickling  C. McKenna Neuman   《Geomorphology》1997,18(3-4)

A detailed set of tests in a wind tunnel investigated the characteristics of flow and sampling efficiency of a low cost sediment trap that can be used in wind tunnels and field applications. The trap is constructed of thin sheet aluminum and has a wedge shape (32° internal inlet angle with a 20 × 500 mm rectangular inlet orifice that extends 40 mm beyond the wedge form. Relatively unimpeded airflow through the trap is achieved by the large exit area (130 × 500 mm) which is covered with fine, stainless steel mesh (62.5 μm openings, 60% porosity), and collected all but the finer (silt) sediment sizes. Despite its angular shape, the trap has good characteristics of flow and a very high sampling efficiency (> 90%) over a wide range of wind velocities because of its near isokinetic characteristics of flow. Results also indicate that this trap, and others that have wide side profiles, are very sensitive to incident wind angle. Incident angles > 5° significantly reduce the sampling efficiency and promote scour around the trap inlet.  相似文献   

Response to John Hall's Discussion (EQE‐16‐0008) to Chopra and McKenna's paper, ‘Modeling viscous damping in nonlinear response history analysis of buildings for earthquake excitation’          下载免费PDF全文

Anil K. Chopra  F. McKenna 《地震工程与结构动力学》2016,45(13):2235-2238

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UXO target area identification with hidden Markov models     

Sean A. McKenna 《Stochastic Environmental Research and Risk Assessment (SERRA)》2009,23(2):193-202

Site characterization activities at potential unexploded ordnance (UXO) sites rely on sparse sampling collected as geophysical surveys along strip transects. From these samples, the locations of target areas, those regions on the site where the geophysical anomaly density is significantly above the background density, must be identified. A target area detection approach using a hidden Markov model (HMM) is developed here. HMM’s use stationary transition probabilities from one state to another for steps between adjacent locations as well as the probability of any particular observation occurring given each possible underlying state. The approach developed here identifies the transition probabilities directly from the conceptual site model (CSM) created as part of the UXO site characterization process. A series of simulations examine the ability of the HMM approach to simultaneously determine the target area locations within each transect and to estimate the unknown anomaly intensity within the identified target area. The HMM results are compared to those obtained using a simpler target detection approach that considers the background anomaly density to be defined by a Poisson distribution and each location to be independent of any adjacent location. Results show that the HMM approach is capable of accurately identifying the target locations with limited false positive identifications when both the background and target are intensities are known. The HMM approach is relatively robust to changes in the initial estimate of the target anomaly intensity and is capable of identifying target locations and the corresponding target anomaly intensity when this intensity is approximately 60% higher than the background intensity at intensities that are representative of actual field sites. Application to data collected from a wide area assessment field site show that the HMM approach identifies the area of the site with elevated anomaly intensity with few false positives. This field site application also shows that the HMM results are relatively robust to changes in the transect width.  相似文献   

Quantifying and reducing uncertainty in UXO site characterization     

Sean A. McKenna  Brent Pulsipher 《Stochastic Environmental Research and Risk Assessment (SERRA)》2009,23(2):153-154

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Emplacement age of the Markagunt gravity slide in southwestern Utah,USA     

McKenna E. Holliday  Tiffany Rivera  Brian Jicha  Robin B. Trayler  Robert F. Biek  Michael J. Braunagel  W. Ashley Griffith  David B. Hacker  David H. Malone  Danika F. Mayback 《地学学报》2023,35(1):66-72

The Markagunt gravity slide (MGS) is a large-volume landslide in southwestern Utah that originated within the Oligocene-Miocene Marysvale volcanic field. Gravity slides are single emplacement events with long runout distances and are now recognized as a new class of volcanic hazard. Accumulation of volcanic material on a structurally weak substrate along with voluminous shallow intrusive events led to collapse. Here, ⁴⁰Ar/³⁹Ar data for landslide-generated pseudotachylyte, the landslide-capping Haycock Mountain Tuff and the deformed Osiris Tuff are combined with a Bayesian age model to determine an emplacement age of 23.05 + 0.22/−0.20 Ma for the MGS. The results suggest a lag time of <200 kyr between the caldera-forming eruption of the Osiris Tuff, additional buildup of the unstable volcanic pile and subsequent mass movement.  相似文献