Himalayan River System Research Articles

Morphometric Analysis and Identification on Specific Metric Characters Pertaining Growth of the Osteobrama cotio of the Brahmaputra, Barak and Teesta River of North Eastern Himalayan River Systems

The variations of morphometric features and the identification of the characteristic features involved in growth variation of Osteobrama cotio were studied from three Eastern Himalayan River Systems: The Brahmaputra, Barak and Teesta River systems. Altogether 220 specimens of different sizes were analysed. Each morphometric character including total length of 220 individuals ranging from 47 to 86 mm and the standard length (SL) from 31 to 65 mm, were recorded. We tested the hypothesis that the body proportion changes gradually rather than abruptly by fitting the linear and quadratic regression curves against the SL of each metric character. The subpopulation from all the locations appeared to be relatively uniform in all of the characters examined. Out of the nine metric characters examined, all the eight characters (head length, snout length, eye diameter, body depth, pre dorsal length, post dorsal length, dorsal fin length and caudal fin length) demonstrated the allometric growth of the fish as described by quadratic regression, except anal fin character which is isometric in growth.

Detrital zircon evidence from Burma for reorganization of the eastern Himalayan river system

The first <i>in situ</i> Hf and U-Pb isotope analyses of detrital zircons from Upper Miocene sandstone in the Inner-Burma Tertiary Basin, together with data of igneous zircons from the eastern Transhimalayan batholith from southern Tibet to Burma, enable us to study the sedimentary source to sink relation and river evolution around the eastern Himalayas. Among 47 out of 62 dated zircons from the Miocene sandstone that exhibit Cretaceous and Paleogene ²⁰⁶Pb/²³⁸U ages, 24 grains have positive ε_Hf(T) isotope values up to +16. Whilst zircons of such ages are common in the Transhimalayan plutons, those showing high ε_Hf(T) values have been observed so far only in the Gangdese batholith. Our results, therefore, support the notion that by Late Miocene time the Yarlu Tsangpo, which flows past the Gangdese batholith in southeastern Tibet, drained into the Irrawaddy River. We attribute this river routing to not only regional topographic control but also the dextral movement of the Jiali-Gaoligong-Sagaing fault system that appears most active during the Middle Miocene. Subsequent reorganization of these mountain rivers was affiliated with headward erosion of the Brahmaputra River that eventually cut across the Namche Barwa Syntaxis and captured the Yarlu Tsangpo drainage to form the modern eastern Himalayan river system.

Reorganization of the western Himalayan river system after five million years ago

Uplift of mountains driven by tectonic forces can influence regional climate as well as regional drainage patterns, which in turn control the discharge of eroded sediment to the ocean. But the nature of the interactions between tectonic forces, climate and drainage evolution remains contested. Here we reconstruct the erosional discharge from the Indus river over the past 30 million years using seismic reflection data obtained from drill core samples from the Arabian Sea and neodymium isotope data. We find that the source of the Indus sediments was dominated by erosion within and north of the Indus suture zone until five million years ago; after that, the river began to receive more erosional products from Himalayan sources. We propose that this change in the erosional pattern is caused by a rerouting of the major rivers of the Punjab into the Indus, which flowed east into the Ganges river before that time. Seismic reflection profiles from the Indus fan suggest high mass accumulation rates during the Pleistocene epoch partly driven by increased drainage to the Indus river after five million years ago and partly by faster erosion linked to a stronger monsoon over the past four million years. Our isotope stratigraphy for the Indus fan provides strong evidence for a significant change in the geometry of western Himalayan river systems in the recent geologic past.

Relative contributions of silicate and carbonate rocks to riverine Sr fluxes in the headwaters of the Ganges

Exhumation of the Himalayan-Tibetan orogen is implicated in the marked rise in seawater 87Sr/ 86Sr ratios since 40 Ma. However both silicate and carbonate rocks in the Himalaya have elevated 87Sr/ 86Sr ratios and there is disagreement as to how much of the 87Sr flux is derived from silicate weathering. Most previous studies have used element ratios from bedrock to constrain the proportions of silicate- and carbonate-derived Sr in river waters. Here we use arrays of water compositions sampled from the head waters of the Ganges in the Indian and Nepalese Himalaya to constrain the end-member element ratios. The compositions of tributaries draining catchments restricted to a limited range of geological units can be described by two-component mixing of silicate and carbonate-derived components and lie on a plane in multicomponent composition space. Key elemental ratios of the carbonate and silicate components are determined by the intersection of the tributary mixing plane with the planes Na = 0 for carbonate and constant Ca/Na for silicate. The fractions of Sr derived from silicate and carbonate sources are then calculated by mass-balance in Sr-Ca-Mg-Na composition space. Comparison of end-member compositions with bedrock implies that secondary calcite deposition may be important in some catchments and that dissolution of low-Mg trace calcite in silicate rocks may explain discrepancies in Sr-Ca-Na-Mg covariation. Alternatively, composition-dependent precipitation or incongruent dissolution reactions may rotate mixing trends on cation-ratio diagrams. However the calculations are not sensitive to transformations of the compositions by incongruent dissolution or precipitation processes provided that the transformed silicate and carbonate component vectors are constrained. Silicates are calculated to provide ∼50% of the dissolved Sr flux from the head waters of the Ganges assuming that discrepancies between Ca-Mg-Na covariation and the silicate rock compositions arise from addition of trace calcite. If the Ca-Mg-Na mixing plane is rotated by composition-dependent secondary calcite deposition, this estimate would be increased. Moreover, when 87Sr/ 86Sr ratios of the Sr inputs are considered, silicate Sr is responsible for 70 ± 16% (1σ) of the 87Sr flux forcing changes in seawater Sr-isotopic composition. Since earlier studies predict that silicate weathering generates as little as 20% of the total Sr flux in Himalayan river systems, this study demonstrates that the significance of silicate weathering can be greatly underestimated if the processes that decouple the water cation ratios from those of the source rocks are not properly evaluated.

Derivation of unit hydrograph from GIUH analysis for a Himalayan river

Unit Hydrograph (UH) is the most popular and widely used method for predicting flood hydrograph resulting from a known storm in a basin area. However, the non-availability of UH due to poor network of raingauge stations in flood prone Indian river basins is a major concern. The computation of Horton's ratios and their application in generating the Geomorphological Instantaneous Unit Hydrograph (GIUH) can provide a solution for ungauged rivers. A detailed drainage network analysis was carried out for a 5th order flood- prone Himalayan river system in order to highlight its significance in flood management program. The equations for GIUH of 5th order stream were derived through Markov Chain analysis. The GIUH model for the 5th order stream was used to derive the first ever analytical UH of the river. Further, it was applied to determine the 50-yr return period flood. The 50-yr return period flood matches with the result of flood frequency analysis based on observed peak discharge data. This drainage network analysis and application of GIUH can provide a significant contribution towards flood management program.

Distribution of rare earth elements and heavy metals in the surficial sediments of the Himalayan river system.

Rare earth elements (REEs) are considered as useful tracers of various surface geological processes in the river system. REEs and heavy metals (V, Pb, Cr, Co, Ag, Zn, Cd, Ni) were analyzed from the suspended sediments of Ganges and surficial sediments of Yamuna, Brahmaputra, Jamuna, Padma and Meghna, using VG Thermal Ionization Mass Spectrometer. Physical weathering process seems to be a major controlling factor for the distribution of REE and trace metals in the sediments of the Himalayan rivers. Weathering of the surface crustal area in the drainage basin shows significant variations due to changes in lithology and influence of tributaries. The distribution of REE shows an almost uniform pattern due to factors such as river transportation processes and high level of terrigenous mixing in the bed sediments. The results show that finer grain size and high content of clay mineral (illite) in these sediments are possible traps for the accumulation of metals. Anthropogenic activities seem to have very little influence in controlling the elemental distribution in the Himalayan rivers.

The 187Os/188Os Record of Himalayan Palaeorivers: Himalayan Tectonics and Ocean Chemistry

Significant debate exists on the role of the uplift and unroofing of the Himalayan mountain range on the chemical evolution of seawater, atmospheric C02 consumption and climate change. Weathering of silicate minerals as the Himalayas were uplifted would consume significant quantities of atmospheric CQ, possibly sufficient to cool the earth's atmosphere (Raymo and Ruddiman, 1992). Variations in the S7Sr/S6Sr record of the oceans has thus been used as proxy for the extent of silicate weathering of the high Himalayas during uplift, due to the large volumes of sediment carried by Himalayan river systems (e.g. Edmond, 1992). However recently, Quade et al., (1997) has suggested that the source of Sr measured in Himalayan rivers are from carbonates (which do not consume CO2 during weathering) from the foothills and lesser Himalaya. Therefore, the marine Sr record may not be a proxy for greater Himalayan unroofing, silicate weathering, COs consumption or change in global climate. Seawater lSVOs/188Os ratios have undergone a rapid rise over the past 15 Ma (e.g. Ravizza, 1993). Currently debate exists as to whether this increase can be attributed in part to the increase in continental erosion due to Himalayan uplift, in analogy with the marine Sr isotopic record. The evolution of the osmium isotopic ratio of seawater provides another means of deciphering the relative contributions of continental weathering to the chemical evolution of seawater, aTsr and 187Os are radiogenic daughter products of aTRb and lS7Re, respectively. Changes in the isotopic ratios of Os and Sr are therefore dependent on time and the amount of the parent isotope present, however Re and Os are hosted by different minerals than Rb and Sr. Thus combining the Os and Sr isotopic records, which are distinct geochemical and mineralogic systems, we can constrain the geologic process(es) that affect ocean chemistry and atmospheric C Q consumption. Quade et al, (1997) focused on carbonates from palaeosoils of rivers draining the Himalayas and western Nepal. The palaeosoils form in floodplains