[1] Continuous estimates of streamflow are challenging in ephemeral channels. The extremely transient nature of ephemeral streamflows results in shifting channel geometry and degradation in the calibration of streamflow stations. Earlier work suggests that analysis of streambed temperature profiles is a promising technique for estimating streamflow patterns in ephemeral channels. The present work provides a detailed examination of the basis for using heat as a tracer of stream/groundwater exchanges, followed by a description of an appropriate heat and water transport simulation code for ephemeral channels, as well as discussion of several types of temperature analysis techniques to determine streambed percolation rates. Temperature-based percolation rates for three ephemeral stream sites are compared with available surface water estimates of channel loss for these sites. These results are combined with published results to develop conclusions regarding the accuracy of using vertical temperature profiles in estimating channel losses. Comparisons of temperature-based streambed percolation rates with surface water-based channel losses indicate that percolation rates represented 30% to 50% of the total channel loss. The difference is reasonable since channel losses include both vertical and nonvertical component of channel loss as well as potential evapotranspiration losses. The most significant advantage of the use of sediment-temperature profiles is their robust and continuous nature, leading to a long-term record of the timing and duration of channel losses and continuous estimates of streambed percolation. The primary disadvantage is that temperature profiles represent the continuous percolation rate at a single point in an ephemeral channel rather than an average seepage loss from the entire channel.

The gypsum-bassanite-anhydrite phase transition sequence was followed up to 550 K at ambient pressure in a naturally occurring gypsum using Raman spectroscopy. The spectral variations of the internal (CaSO 4 AE 2H 2 O) modes of sulphate tetrahedra and were used to probe the structural phase transitions. A new Raman mode (m 1 m 2 ) emerged at 1026 cm-1, in the mode region, at around 388 » 5 K, indicating the onset of the bassanite m 1 phase. This mode became weaker after showing an initial increase. The anhydrite (CaSO 4 AE 0.5H 2 O) (CaSO 4 ) phase, with an onset temperature of around 448 » 5 K, was also characterized by the appearance of the Raman mode at 1016 cm-1. From the Arrhenius-type changes in the reduced intensity, the activation energies associated with the gypsum to bassanite and bassanite to anhydrite transitions were estimated to be 92.25 and 32.94 kJ mol-1, respectively. The observed spectral anomalies in the mode clearly corroborate the transition sequence. m 2

Compressional and shear wave velocities and attenuation measurements have been carried out in some of the borehole samples of acidic, basic and intermediate granulites of Mahabalipuram, Tamil Nadu, India. The results have been obtained at ambient conditions using 'time-of-flight' pulse transmission technique at 1.0 MHz frequency. The results show linear relationships between velocity and density, and velocity and attenuation properties of the rocks. The acidic granulites show lower velocities and higher attenuation than the intermediate and basic granulites. The average values of the Poisson's ratio of acidic, intermediate and basic granulites have been found to be 0.210, 0.241 and 0.279 respectively.The variations in velocities and attenuation in these low porosity crystalline rocks are found to be strongly influenced by their mineral composition. The laboratory velocity data (extrapolated to high pressure) of the present study and the published field velocity data from deep seismic sounding studies indicate that these granulite facies rocks may belong to mid-crustal depths only.

No abstract

No abstract