Economic Analysis of Selected Offshore Petroleum Arrangements

As a result of the current decline of oil prices, exploration decisions are more carefully analysed than ever before. At the same time various governments have introduced incentives to reinvest in exploration and development in order to maintain or increase activity. As a result, most exploration decisions are now being analysed as "incremental investments". This has the effect of "trapping" investments in areas where profits are currently being made. This in turn creates serious problems for those developing countries which would like to attract exploration. The paper analyses issues related to sliding scale formulae based on the ROR, and the economic impact of the size of the area to which fiscal terms apply.     

SHORT-TERM FORECASTING OF SNOWMELT RUNOFF USING ARMAX MODELS1

ABSTRACT: Time series models of the ARMAX class were investigated for use in forecasting daily riverflow resulting from combined snowmelt/rainfall. The Snowmelt Runoff Model (Martinec-Rango Model) is shown to have a form similar to the ARMAX model. The advantage of the ARMAX approach is that analytical model identification and parameter estimation techniques are available. In addition, previous forecast errors can be included to improve forecasts and confidence limits can be estimated for the forecasts. Diagnostic checks are available to determine if the model is performing properly. Finally, Kalman filtering can be used to allow the model parameters to vary continuously to reflect changing basin runoff conditions. The above advantages result in improved flow forecasts with fewer model parameters.     

RELATIONSHIP BETWEEN ANNUAL RUNOFF AND WATERSHED AREA FOR THE EASTERN UNITED STATES1

ABSTRACT: As part of the U.S. Environmental Protection Agency's effort to determine the long-term effects of acidic deposition on surface water chemistry, annual runoff was estimated for about 1000 ungaged sites in the eastern U.S. using runoff contour maps. One concern in using contour maps was that a bias may be introduced in the runoff estimates due to the size of the 1000 ungaged sites relative to the size of the watersheds used in developing the maps. To determine if a bias was present the relationship between the annual runoff (expressed as depth) and the watershed area for the Northeast (NE) and Southern Blue Ridge Province (SBRP) was tested using five regional data bases. One short-term data base (1984 Water Year, n = 531) and two long-term data bases (1940–57, n = 134 and 1951–80, n = 342) were used in the NE. In the SBRP one short-term database (1984 Water Year, n = 531) and one long-term data base (1951–80, n = 60) were used. For the NE and the SBRP, runoff was not directly correlated with watershed area using the five regional databases. Also, runoff normalized by precipitation was not related to watershed area.     

A TAU-LIKE TEST FOR TREND IN THE PRESENCE OF MULTIPLE CENSORING POINTS1

ABSTRACT: A common problem arises in testing for trends in water quality when observations are reported as “less than detection limit.” If a single detection limit is used for the entire study, existing non-parametric statistical methods, modified for ties, are applicable. If, however, the detection limit varies during the course of the study, resulting in multiple detection limits, then the commonly used trend detection methods are not appropriate. A statistic similar to Kendall's tau, but based on expected ranks, is proposed. Monte Carlo simulations show that the normal approximation to the distribution of this statistic is quite good, even for small samples and a large proportion of censored observations. The statistic is also shown to have greater power than the ad-hoc method of treating all observations less than the target censored observation as tied.     

Structure-biodegradation relationships of polymeric materials. 1. Effect of degree of oxidation on biodegradability of carbohydrate polymers

The biodegradability of oxidized starch and inulin has been studied in relation to the degree of periodate oxidation to dialdehyde derivatives, by measuring oxygen consumption and mineralization to carbon dioxide. A higher degree of oxidation of dialdehyde starch and dialdchyde inulin results in a lower rate at which the polymers are biodegraded. It is demonstrated that the biodegradation rate of dialdehyde inulin derivatives decreases more than that of equivalent starch derivatives. The differences in biodegradation behavior between dialdehyde starch and dialdehyde inulin, resulting from comparable modifications, are discussed in terms of conformational structure.     

Nautical safety and efficiency: simulation and reality

The paper deals with training and research using maritime simulation techniques to provide cost-effective and safe solutions to maritime transportation problems. In order to reduce the probability of accidents, training and research is required in which the human factors are fully taken into account.     

The new regime for managing US—Mexican water resources

United States-Mexican transboundary water resources management is presently experiencing significant reform resulting from long-term demographic processes in the border region and greater economic integration. The recently concluded North American Free Trade Agreement and supplementary environmental accord modify existing agreements and provide old institution with new mandates. Particularly affected is the International Boundary and Water Commission (IBWC), long the lead agency in binational water management. This essay reviews the development of the new water management regime against the two preceding phases of management reform and considers its implications for improved water management in the border region.     

Restoration ecology of riverine wetlands: II. An example in a former channel of the Rhône River

Riverine wetlands, which provide numerous valuable functions, are disappearing in floodplains of a channelized European river. A restoration project has been proposed by scientists to restore a former braided channel of the Rhône River by the removal of fine organic sediments in order to enhance groundwater supply. A precise and intensive prerestoration monitoring program during one year (including comparison with a reference channel) has taken into account several variables and ecological performance indicators measured at various spatial and temporal scales. Three restoration techniques were then suggested, taking into account two characteristics of ecosystem functions for increasing restoration success and self-sustainability: (1) the riparian forest as well as the shores must be preserved or disturbed as little as possible; and (2) the upstream alluvial plug must be preserved to prevent direct supply of nutrientrich water from the Rhône River. Among the three restoration options proposed, it was not possible to carry out the less ecologically disturbing one as it was considered too expensive, time consuming, and difficult to realize. A precise and intensive postrestoration monitoring program, conducted over two years, demonstrated restoration success but also unpredicted problems, such as a locally thick layer of fine organic sediment. As long as a self-sustainable state is not achieved, this monitoring should be continued. Afterwards, a less precise and less intensive long-term monitoring should enable the detection of future events that may influence ecosystem changes.     

Insecticide pollution of Indian rivers

Summary Rivers are the main source of water in India, and are particularly used for agricultural irrigation and drinking water supply. As most of the rivers pass through agricultural fields, they are subject to contamination with the different insecticides used for crop protection. Residues of persistent organochlorines, which are still used in large quantities in India, are found in water from many Indian rivers. In certain rivers, the concentrations of DDT, aldrin and heptachlor are often present in excess of their guideline limits. Although the concentration level of gamma-HCH is well below the guideline limit, the accumulation of the carcinogenic beta isomer is a matter of great concern. A few organophosphorus insecticides have also been detected in river water. Recently, some organochlorine insecticides have been banned from use in India. The use of new, readily biodegradable insecticides and biocides in agriculture and public health programmes offers some optimism.Drs Satya P. Mohapatia, Vijay T. Gajbhiye and Narendra R. Agnihotri all work within the Division of Agricultural Chemicals at the above address. Dr Manju Raina is employed by the Ganga Project Directorate of the Ministry of Environment and Forests, New Delhi 11003, India.