THE INFLUENCE OF (x,y) UNCERTAINTY ON PREDICTION ERROR AND CONTOUR LINES FROM A THREE-DIMENSIONAL SURFACE1

ABSTRACT: In geohydrology, three-dimensional surfaces are typically represented as a series of contours. Water levels, saturated thickness, precipitation, and geological formation boundaries are a few examples of this practice. These surfaces start as point measurements that are then analyzed to interpolate between the known point measurements. This first step typically creates a raster or a set of grid points. In modeling, subsequent processing uses these to represent the shape of a surface. For display, they are usually converted to contour lines. Unfortunately, in many field applications, the (x, y) location on the earth's surface is much less confidently known than the data in the z dimension. To test the influence of (x, y) locational accuracy on z dimension point predictions and their resulting contours, a Monte Carlo study was performed on water level data from northwestern Kansas. Four levels of (x, y) uncertainty were tested ranging in accuracy from one arc degree-minute (± 2384 feet in the x dimension and ± 3036 feet in the y dimension) to Global Positioning Systems (GPS) accuracy (± 20 feet for relatively low cost systems). These span the range of common levels of locational uncertainty in data available to hydrologists in the United States. This work examines the influence that locational uncertainty can have on both point predictions and contour lines. Results indicate that overall mean error exhibits a small sensitivity to locational uncertainty. However, measures of spread and maximum errors in the z domain are greatly affected. In practical application, this implies that estimates over large regions should be asymptotically consistent. However, local errors in z can be quite large and increase with (x, y) uncertainty.     

Natural disaster mitigation: Environmental approaches in Tonga and Algeria

Summary The mitigation of natural disasters essentially depends upon the identification and adjustment of human ecological processes contributing to conditions of vulnerability. The analysis of vulnerability requires the local study of political, social, and economic processes which have contributed, and are contributing, to a vulnerable condition in a hazardous environment. One of the few similarities between Tonga and Algeria is a continuing experience of natural disaster after independence from previous colonial administrations. In two very different but complementary projects, ways are identified for the adjustment of assumed or inherited priorities for development, to take practical account of continuing hazards. The high vulnerability of rural areas is a factor common to both countries, as well as to many others. The analysis of conditions and systems in two dissimilar countries may have begun a process of implementation, one which must necessarily follow theoretical analysis for the realisation of practical value. The degree and nature of disaster impact is conditioned as much by normally prevailing conditions and systems as by the manifestation of natural hazard. Direct experience of hazardous environments, and of problems caused by disaster, must be made to result in the creation of multi-disciplinary environmental policies for disaster mitigation, inclusive of small scale development and education and training programmes for continued implementation. Comprehensive and simultaneous strategies for disaster avoidance, disaster resistance, and disaster accomodation must be made integral components of local development planning.     

COMPARING TWO MEASURES OF WATER BASED RECREATION PARTICIPATION1

ABSTRACT: Site specific studies of water based recreation participation are intended to describe use at a particular recreation area. Two common strategies employed in site specific studies are the on-site “entry” or “exit” survey and the off-site mailed questionnaire to known users of an area. Previous research has reported differences in psychological perceptions of a recreation engagement depending on whether a survey was administered during or after a trip. If such bias exists for behavioral reports, then managers and planners must be cautious in interpreting results of survey based use assessments for a particular site. Findings may be affected by the particular survey strategy employed. In this study, entry point and post-trip mailed questionnaire measures of water based recreation participation were compared for a sample of reservoir users. For most activities, a high degree of consistency in measures was found. Inconsistent reports were most likely to occur among participants in activities sharing significant common behaviors, such as power boating and water skiing. Inconsistency was also observed for those reporting very generalized behaviors, such as relaxing. In general, the use of either pre- or post-trip measures of water based recreation participation was supported.     

Secchi Disc Relationships1

ABSTRACT: The problem of estimating bulk light extinction coefficients in surface water impoundments is examined. It is shown that the bulk extinction coefficient can be accurately estimated from the Secchi disc depth. In addition, the equation derived is significantly different from that derived by Poole and Atkins in 1929. This empirical expression for the extinction coefficient is then used to develop a semiempirical expression for the euphotic depth as a function of the Secchi disc depth.     

MANAGING CRISIS: THE EFFECTIVENESS OF LOCAL DISTRICTS FOR CONTROL OF GROUND WATER MINING1

: This article examines the willingness and capacity of local districts to control ground water mining of the Ogallala Aquifer in the High Plains. The questions of willingness and capacity were approached through extensive field interviews and a survey of all district board members and managers. The analysis focuses on the policy alternatives board members and managers perceive and how they evaluate these alternatives. Methodologically, the study utilized factor analysis of responses rating the desirability of various policy alternatives to ascertain what alternatives were perceived by the sample. Then the sample's preferences for each of the identified factors were calculated. The results demonstrate that the sample of those who must regulate if ground water mining is to be controlled at the substate level are not oriented to regulatory policies and therefore lack the willingness to deal with ground water mining.     

Change,and vulnerability to natural hazard: Chiswell,dorset

Summary The occurrence of disastrous manifestations of hazard are not usually unique events. In analysis of the causes and effects of these occurrences there are problems for analysts, academics and policy-makers in the understanding of long-term perspectives as the context for recent events and future policies. Understanding will be made initially, but necessarily, more complex by the variety of standpoints of different interest groups in the affected community, and of the community at large. Physical permanence of a community cannot beassumed in a changing environmental condition. Vulnerability to the sea has increased during the thousand years of Chiswell's existence, and is continuing to do so. Understanding of this changing state by various groups in society, and their administrators, is the key to the selection and effectiveness of interacting social and technological measures whether undertaken specifically against hazard or not. The extent to which technology can be effectively mobilised and implemented to ensure prolonged community permanence may only be assessed by detailed analysis of environmental phenomena on the one hand, and by comparison with social adjustments on the other. Social adjustments cannot be compared until those options are made realistically available by the authorities elected for their administration. The condition of vulnerability is not static. Analysis and assessment of short- and longer-term issues is at once a multi-disciplinary process calling for a fusion of physical and earth sciences, social sciences, and political and administrative processes. That these sciences and processes are themselves evolving, and are not static, is as true as for vulnerability itself. That all are in short- and long-term processes of change must be understood if each is to be integrated with the other for maximum comprehensive and effective response to natural hazard.     

Forest management policies and elk summer carrying capacity in theAbies amabilis forest,western Washington

Effects of different forest management policies on long-term vegetation development are incorporated into a computer simulation of a western Washington watershed. The response of a Rocky Mountain elk(Cervus canadensis nelsoni) population to these vegetation changes is simulated using information on their differential use of vegetation types. Simulations include: 1) a cessation of timber harvesting leading to an immediate decline in elk members resulting from a reduction in summer habitats; 2) a stable elk population, similar to the present one, resulting from a constant timber harvesting rate, and 3) initial increases in herd size, followed within 50 years by a sharp decrease, resulting from cutting all old growth timber within the next decade and then a cessation of timber harvestings.