25 years of salt marsh erosion in Essex: Implications for coastal defence and nature conservation

This paper presents the results from a study which was undertaken to monitor, map and quantify salt marsh change along 440 km of shoreline within the county of Essex, south-east England, between 1973 and 1998. Results indicate that during this 25-yr period, 1000 ha of salt marsh has been lost in Essex, primarily due to coastal erosion. This figure represents ca. 25% of the total salt-marsh area originally present in Essex in 1973. The salt marshes of Essex are important nature conservation areas, with many sites designated as Special Protection Areas under the EC Birds Directive (79/409/EEC) and as Special Areas of Conservation under the EC Habitats Directive (92/43/EEC). Salt marshes are also natural features which significantly dissipate wave and tidal energy, thereby playing an important role in contributing to effective coastal defence. The large-scale loss of salt marsh in Essex has, therefore, implications for both nature conservation and flood defence. Potential hypotheses for, and implications of such losses are discussed in this paper, together with the identification of potential management approaches to alleviate the losses.     

CHANGING NEAR‐STREAM LAND USE AND RWER CHANNEL MORPHOLOGY IN THE VENEZUELAN ANDES1

ABSTRACT: The shape of a river channel is linked to surrounding land use through interacting hydrologic and geologic processes. This study analyzes the relationship between the change in near‐stream land use and the shape of the adjacent river channel over time. Three watersheds in the foothills of the Venezuelan Andes that have experienced differing degrees of development were studied to determine river channel width, sinuosity, and position relative to surrounding land use. Change in land use over time was obtained from multiple‐date aerial photographs (1946 and 1980) referenced to 1996 Landsat Thematic Mapper (TM) satellite imagery, and verified by field inspection. Measurements of land‐use type and amount and river channel morphology from the two dates were made using geographic information system (GIS) methods. The three watersheds differed in the extent of deforestation, the location of remaining forested land, and how much land‐use change had already occurred by 1946. Change in river channel morphology was greatest at the most deforested sites. Valley shape and channel constraint also had a discernible effect on change in channel morphology. This study introduces a method for analyzing change in coupled terrestrial‐aquatic systems based on multiple‐date, remotely sensed data and GIS analysis of spatial properties. The results document human impacts on river channels through a comparison of multiple watersheds over a 35‐year time interval.     

CHANNEL STABILITY DOWNSTREAM FROM A DAM ASSESSED USING AERIAL PHOTOGRAPHS AND STREAM‐GAGE INFORMATION1

ABSTRACT: The stability of the Neosho River channel downstream from John Redmond Dam, in southeast Kansas, was investigated using multiple‐date aerial photographs and stream‐gage information. Bankfull channel width was used as the primary indicator variable to assess pre‐ and post‐dam channel change. Five sin‐mile river reaches and four stream gages were used in the analysis. Results indicated that, aside from some localized channel widening, the overall channel change has been minor with little post‐dam change in bankfull channel width. The lack of a pronounced post‐dam channel change may be attributed to a substantial reduction in the magnitude of the post‐dam annual peak discharges in combination with the resistance to erosion of the bed and bank materials. Also, the channel may have been overwidened by a series of large floods that predated construction of the dam, including one with an estimated 500‐year recurrence interval.     

Regression analysis of forest damage by marginal models for correlated ordinal responses

Studies on forest damage generally cannot be carried out by common regression models, for two main reasons: Firstly, the response variable, damage state of trees, is usually observed in ordered categories. Secondly, responses are often correlated, either serially, as in a longitudinal study, or spatially, as in the application of this paper, where neighbourhood interactions exist between damage states of spruces determined from aerial pictures. Thus so-called marginal regression models for ordinal responses, taking into account dependence among observations, are appropriate for correct inference. To this end we extend the binary models of Liang and Zeger (1986) and develop an ordinal GEEI model, based on parametrizing association by global cross-ratios. The methods are applied to data from a survey conducted in Southern Germany. Due to the survey design, responses must be assumed to be spatially correlated. The results show that the proposed ordinal marginal regression models provide appropriate tools for analysing the influence of covariates, that characterize the stand, on the damage state of spruce.     

航空放射性测量

介绍了国内外航空放射性测量和评价系统（ＡＲＳＡＳ）的概况及其组成的功能。当今核能发电已在民办能源生产中占据重要地位，放射性航空测量作为辐射剂量监测的一种方法，比起起面环境介质的测量具有能快速圈定污染边界和确定污染水平的优点。但是，正确的航测结果的获得，还需有正确的估算方法，并且需用地面指定点上的测量证实。