Threshold response of small streams to surface coal mining,bituminous coal fields,central Pennsylvania

Stream response to surface coal mining and reclamation was studied in 29 small (0·13 to 5·72 km²) watersheds located in the bituminous coal fields of Central Pennsylvania. These basins, up to 82 per cent mined, were selected from 176 first-order tributaries of Beech Creek with similar vegetation, soil, lithology, and basin characteristics. Measurements were made at 262 cross-sections (an average of nine cross-sections per stream) of channel cross-section area, bankfull width, mean bankfull depth, dimensions of the largest moving blocks, stream slope, valley-side slope, basin area, and mined area. Observed differences in channel morphology were related to differences in extent of mining by means of scatter plots, correlation, cluster analysis, and bivariate regression. Stream response to increased peak discharge and channel shear stress produced by increased surface runoff from regraded mine spoil takes the form of enlarged channels and increases in the size of moving blocks. Large basin areas appear to dampen the effect of mining, resulting in limited channel enlargement with greater extent of mining. In contrast, where peak discharges and associated shear stresses exceed the combined erosional resistance of floodplain vegetation, colluvial blocks, and channel banks, streams adjust extensively to higher levels of mining, causing an abrupt increase in the size of transported blocks and eroded channels. In the first-order basins studied, this stepped response occurs at approximately 0·45 km² mined area and 50 per cent of the total basin area mined. For streams that have exceeded both threshold levels, disequilibrium is demonstrated by a strong, positive correlation between local stream slope and basin area. Where both threshold levels of mining are exceeded, steep channel slopes reinforce the tendency of stream cross-sections to increase with greater disturbance by mining, necessitating that these streams rapidly adjust their morphology in order to attain a new equilibrium which is compatible with the conditions imposed by mining and reclamation.     

River channel change: Problems of interpretation illustrated by the river derwent,north Yorkshire

Some inherent limitations of the spatial interpolation method of identifying and interpreting channel adjustment are illustrated by a study of the River Derwent in Yorkshire. Here, cross-sections downstream from a river diversion appear to have contracted in size when compared with predictions based on upstream relationships between channel form variables and basin area. However, these sections are slightly larger than expected for their diminished discharge, suggesting that they have not fully adjusted to altered environmental conditions and are still in a transient state.     

The Effect of Three Different Absorption Cross-Sections and their Temperature Dependence on Total Ozone Measured by a Mid-Latitude Brewer Spectrophotometer

Abstract

The influence of variations in atmospheric temperature and ozone profiles on the total ozone column (TOC) derived from a Brewer MKII spectrophotometer operating in Thessaloniki, Greece, is investigated using three different sets of ozone absorption cross-sections. The standard Brewer total ozone retrieval algorithm uses the Bass and Paur (1985) cross-sections without accounting for the temperature dependence of the ozone cross-sections which produces a seasonally dependent bias in the measured TOC. The magnitude of this temperature effect depends on the altitude where the bulk of the ozone absorption occurs. Radiosonde measurements for the period 2000 to 2010 combined with climatological ozone profiles were used to calculate the effective temperature of ozone absorption and investigate its effect on the retrieved ozone column. Three different ozone absorption cross-section spectra convolved with the instrument's slit function were used: those of Bass and Paur (hereafter BP), currently used in the standard Brewer retrieval algorithm; those of Brion, Daumont, and Malicet (Malicet et al., 1985; hereafter BDM); and the recently published set by Serdyuchenko et al. (2013 hereafter S13). The temperature dependence of the differential ozone absorption coefficient ranges between 0.09 and 0.13% per degree Celsius for BP, between ?0.11 and ?0.06% per degree Celsius for BDM, and between 0.018 to 0.022% per degree Celsius for S13, resulting in a seasonal bias in the derived TOC of up to 2%, 1.8%, and 0.4%, respectively. The temperature sensitivity of the differential ozone absorption coefficient for the Brewer spectrophotometer at Thessaloniki for the BP and BDM cross-sections is found to be within the range reported for other Brewer instruments in earlier studies, whereas the seasonal bias in TOC is minimized when using the new S13 cross-sections because of their small temperature dependence.     

Ozone UV spectroscopy I: Absorption cross-sections at room temperature

Because of the importance of the absorption cross-sections of ozone in the atmosphere, we give a new set of data at ambient temperature for the whole spectral region within the 195–345 nm range. Two new methods have been investigated for the experiments to measure the ozone pressures. Our results are compared with all of the previous data. The agreement between the more recent works is relatively good and can be improved by making some corrections in the WMO set. The new reference value at 254 nm proposed by Mauersberger et al. is confirmed and we suggest taking it as a new standard.