On the Seddon speed formula

Abstract

The Seddon speed formula expressed mathematically as c = dQ/dA (or alternatively, as c = (1 + m)u_o; where Q is the discharge, A is the area of cross-section, c is the wave speed, u_o is the normal flow velocity, and m is a dimensionless parameter) is revisited in the context of elasticity and thermodynamics. Its link with the linearized solution of St Venant's equations for wave celerity, which does not appear to have been reported in the hydrological literature, is established. The rating exponent m is shown to be equivalent to the dimensionless relative celerity and is found to be the ratio of two specific heats, viz. c_p and c_v which are the specific heats at constant pressure and volume, respectively. The use of the parameter m as a complex variable helps describe shallow wave characteristics, the damping capacity of a wave, and the mechanism of occurrence of the hysteretic phenomenon. The damping capacity is found to describe the magnitude of wave subsidence, whereas the hysteresis also describes the speed of subsidence.     

Plant studies in the first Himalayan Biosphere Reserve: a review

Nanda Devi Biosphere Reserve(NDBR) was declared as the first Himalayan Biosphere Reserve owing to its unique biological and cultural wealth. Its core zones, Nanda Devi National Park and Valley of Flowers National Park, are a UNESCO World Natural Heritage Site. In spite of lying at a high altitude, interplay of factors such as unique geographical location, climate, topography and wide altitudinal variations have endowed NDBR with a rich and diverse flora. Proportionately high percentage of endemic and near endemic plants makes NDBR a very important protected area from conservation point of view. However, its floristic wealth is facing unprecedented threats in the form of climate change and growing anthropogenic pressure. Hence, a need was felt to assess the directionality, quality and sufficiency of past and ongoing research for the conservation of floral and ethnobotanical wealth of NDBR in the absence of any such previous attempt. Based on an extensive review of more than 150 plant studies on NDBR, this communication provides a detailed account of the current state of knowledge and information gaps on flora, vegetation ecology, rare, endangered, threatened(RET) and endemic plants and ethnobotany. Priority research areas and management measures are discussed for the conservation of its unique floral wealth. Incomplete floral inventorization, lack of biodiversity monitoring, meagre studies on lower plant groups, population status of medicinal plants, habitat assessment of threatened taxa and geo-spatial analysis of alpine vegetation were identified as areas of immediate concern.     

Modelling Chorabari Lake outburst flood,Kedarnath, India

In this study, the Glacier Lake Outburst Flood(GLOF) that occurred over Kedarnath in June 2013 was modeled using integrated observations from the field and Remote Sensing(RS). The lake breach parameters such as area, depth, breach, and height have been estimated from the field observations and Remote Sensing(RS) data. A number of modelling approaches, including Snow Melt Runoff Model(SRM), Modified Single Flow model(MSF), Watershed Management System(WMS), Simplified Dam Breach Model(SMPDBK) and BREACH were used to model the GLOF. Estimations from SRM produced a runoff of about 22.7 m3 during 16–17, June 2013 over Chorabari Lake. Bathymetry data reported that the lake got filled to its maximum capacity(3822.7 m3) due to excess discharge. Hydrograph obtained from the BREACH model revealed a peak discharge of about 1699 m3/s during an intense water flow episode that lasted for 10–15 minutes on 17 th June 2013. Excess discharge from heavy rainfall and snowmelt into the lake increased its hydrostatic pressure and the lake breached cataclysmically.     

Experimental real-time multi-model ensemble (MME) prediction of rainfall during monsoon 2008: Large-scale medium-range aspects

Realistic simulation/prediction of the Asian summer monsoon rainfall on various space–time scales is a challenging scientific task. Compared to mid-latitudes, a proportional skill improvement in the prediction of monsoon rainfall in the medium range has not happened in recent years. Global models and data assimilation techniques are being improved for monsoon/tropics. However, multi-model ensemble (MME) forecasting is gaining popularity, as it has the potential to provide more information for practical forecasting in terms of making a consensus forecast and handling model uncertainties. As major centers are exchanging model output in near real-time, MME is a viable inexpensive way of enhancing the forecasting skill and information content. During monsoon 2008, on an experimental basis, an MME forecasting of large-scale monsoon precipitation in the medium range was carried out in real-time at National Centre for Medium Range Weather Forecasting (NCMRWF), India. Simple ensemble mean (EMN) giving equal weight to member models, bias-corrected ensemble mean (BCEMn) and MME forecast, where different weights are given to member models, are the products of the algorithm tested here. In general, the aforementioned products from the multi-model ensemble forecast system have a higher skill than individual model forecasts. The skill score for the Indian domain and other sub-regions indicates that the BCEMn produces the best result, compared to EMN and MME. Giving weights to different models to obtain an MME product helps to improve individual member models only marginally. It is noted that for higher rainfall values, the skill of the global model rainfall forecast decreases rapidly beyond day-3, and hence for day-4 and day-5, the MME products could not bring much improvement over member models. However, up to day-3, the MME products were always better than individual member models.     

Chemical and sulphur isotope compositions of pyrite in the Jaduguda U (–Cu–Fe) deposit,Singhbhum shear zone,eastern India: Implications for sulphide mineralization

The Jaduguda U (–Cu–Fe) deposit in the Singhbhum shear zone has been the most productive uranium deposit in India. Pyrite occurs as disseminated grains or in sulphide stringers and veins in the ore zone. Veins, both concordant and discordant to the pervasive foliation, are mineralogically either simple comprising pyrite ± chalcopyrite or complex comprising pyrite + chalcopyrite + pentlandite + millerite. Nickel-sulphide minerals, though fairly common in concordant veins, are very rare in the discordant veins. Pyrite in Ni-sulphide association is commonly replaced by pentlandite at the grain boundary or along micro-cracks.     

HARMONIC INVERSION OF AN AEROMAGNETIC ANOMALY FROM A REMANENTLY MAGNETIZED PRECAMBRIAN SCHIST BELT (KARNATAKA,INDIA) *

The conventional methods of magnetic interpretation consider in general the induced magnetization only. However, in a computer oriented inverse method, the direction of magnetization can be taken as arbitrary. Following this procedure, this study aims to present a realistic interpretation of an aeromagnetic anomaly from Chitaldrug Schist belt (Mysore, India) assuming a three-dimensional configuration of the causative source possessing remanent magnetization. It further provides the direction of remanent magnetization of the source rock as obtained from the analysis of the magnetic anomaly. The total intensity map obtained delineates the surface and sub-surface structures in the region and provides informations regarding the characteristics of primordial crust.     

DEPTH ESTIMATION OF MAGNETIC SOURCES BY MEANS OF FOURIER AMPLITUDE SPECTRA*

The Fourier transform of a square-shaped section of a magnetic survey, digitized in a square grid, forms a rectangular matrix of coefficients which can be condensed to a series of average amplitudes dependent only on their frequency and no longer on the direction of the respective partial waves. These average amplitudes together represent a spectrum which–when plotted in a semilogarithmic coordinate system (log amplitude versus frequency)–often shows straight segments which decrease with increasing frequency. By continuing the given field downwards these straight segments become horizontal at a certain depth, the so-called “white depth”. This white depth may be used as a first estimate for the depth of magnetic sources producing the respective part of the field. It is shown that the sources which correspond to such use of the white depth can be expected to be “randomly distributed with some positive autocorrelation”. As an example for such a depth estimation the interpretation of the aeromagnetic survey of NW-Germany by a relief in 8–16 km depth is given. The relief divides the subsurface in an upper nonmagnetic layer and a lower layer with magnetization M= 2 Am^?1.     

TWO-DIMENSIONAL POWER SPECTRAL ANALYSIS OF AEROMAGNETIC FIELDS *

A study of probability distribution function and spectrum of the Airborne Total Intensity Map for an area of 3000 Squ. miles covered by the Bundelkhand granite in India has revealed a close correlation between the Gaussian or non-Gaussian nature of distribution and the shape of unite value contour on the spectrum plot. Further studies of radial spectrum plots suggest that the surface magnetic sources are mainly responsible for the non-Gaussian character of the distribution function and as well as for irregular spectrum shape. The histogram of depth values for magnetic sources obtained from radial spectrum plots show three horizons, namely (i) surface (ii) 410 m(1400′) and (iii) 1000 m (3400′). Based on these informations blocks with ferromagnetic composition at the surface can be identified from those which are non magnetic at the surface.