Sediment Transport and Channel Morphology Dynamics of Highly Regulated Alluvial Rivers - A Case Study of the Lowermost Mississippi River.

The Mississippi River delta is facing severe land loss. An urgent need exists to examine sediment transport and channel morphology dynamics along this highly engineered alluvial river that has shaped and will continue to shape its delta. This dissertation research focuses on investigating channel morphology dynamics and sediment transport in the recent three decades along a 327-km reach (from about 492 to 167 km upstream from the river’s outlet in the Gulf of Mexico) of the Lowermost Mississippi River (LmMR). The specific objectives of this research were to: 1) analyze riverbed adjustment, i.e., channel-bed aggradation or channel erosion at seven locations along the 327-km LmMR reach over the last three/four decades; 2) determine suspended sand availability under various discharge regimes at Tarbert Landing (the uppermost location of LmMR) during the period between 1973 and 2013; and 3) quantify bedload at Tarbert Landing, St Francisville and Baton Rouge (three uppermost locations of LmMR) and suspended load at St Francisville and Baton Rouge over the last one to four decades. This research found that the first 20–25 km LmMR reach below its diversion to the Atchafalaya River and the reach from ~ 80 to 140 km experienced significant riverbed aggradation, while the reach in between (i.e. from ~ 25 to 80 km) experienced riverbed degradation over the last three/four decades. The lower 187-km reach (i.e. from 140 to 327 km) showed higher sediment outflow and negligible sediment trapping. Furthermore, the LmMR discharged an average annual sand load (SLs) of 27 million tons (MT) during 1973 and 2013, at Tarbert Landing, varying largely from 3.4 to 52.3 MT. Also, during the four decades, the LmMR at Tarbert Landing carried about 71% of the total annual sand load in about 120 days each year, when the discharge was ≥ 18000 cubic meters per second (cms). The bedload transport rates along the LmMR gradually increased from Tarbert Landing [83 million tons (MT) during 2004-2015 for grain size of 0.125 mm] to Baton Rouge (at 367.5 rk) (96 MT during 2004-2014 for the same grain size). However, the total sediment supply (bedload + suspended sediment load) was substantially higher at Tarbert Landing (931 MT) and lower and nearly equal at the other downstream locations (550 MT at St Francisville and 544 MT at Baton Rouge) during 2004-2010 (the matching period of availability for both bedload and suspended load). These findings have relevant implications for the management of river-sediment diversions along the LmMR and other large alluvial rivers in the world. They could help determine specific sediment trapping sites and the development of land building schemes

Evaluation of growth rates and establishment patterns of water-elm (Planera aquatica) and baldcypress (Taxodium distichum) in response to hydrologic and climatic conditions at Catahoula Lake, Louisiana

Hydrologic alterations frequently lead to vegetation changes in floodplain ecosystems. In Louisiana, there has been an expansion of water-elm (Planera aquatica) and to a lesser extent baldcypress (Taxodium distichum) at Catahoula Lake, a Ramsar Wetland of International Importance. Water-elm and baldcypress both are flood tolerant species; baldcypress growth is known to be influenced by hydrologic conditions more than climate. The expansion of these woody trees has reduced herbaceous vegetation valuable for waterfowl. In this study, I tested two hypotheses that establishment of water-elm trees into the lake increased after the construction of water control structures in the nearby Black River and a diversion canal and water-control structure on the lake in 1971; and that growth rates of water-elm and baldcypress are more correlated with hydrologic regimes than with local climate. Water-elm trees have been found in the lake for at least 140 years, but most (171 of 219) sampled trees were established in the period following the construction of water-control. In addition, 48 of 67 plots consisted of trees established entirely in the post-control period. Hydrologic conditions in the lake changed with the modifications, including reduced variability in June and August lake levels and reduced fall flooding. These changes coincided with apparently increased establishment of water-elm trees during the post-control period. Finally, there are several sources of uncertainty that prevent clear interpretation of the effects of water control on water-elm establishment including prevailing climatic conditions, control measures by Louisiana Department of Wildlife and Fisheries and cattle grazing. My second hypothesis that growth of water-elm and baldcypress would be more correlated with hydrologic regimes than with climate was partially supported. Growth of water-elm was more related to climatic variables than with lake levels, whereas baldcypress radial growth was more correlated with lake levels than with climatic variables. The response of water-elm radial growth to lake hydrology was limited to a negative relationship with late spring lake levels in the pre-control period; baldcypress had a consistent positive response with lake levels during several seasons in both the pre-and post-control periods

Networks of Collaboration in Oligopoly

In an oligopoly, prior to competing in the market, firms have an opportunity to form pair-wise collaborative links with other firms. These pair-wise links involve a commitment of resources and lead to lower costs of production of the collaborating firms. The collection of pair-wise links defines a collaboration network. We study the architecture of strategically stable networks. Our analysis reveals that in a setting where firms are ex-ante identical, strategically stable networks are often asymmetric, with some firms having a large number of links while others have few links or no links at all. We characterize such asymmetric networks; the dominant group architecture, stars, and inter-linked stars are found to be stable. In asymmetric networks, the firms with many links have lower costs of production as compared to firms with few links. Thus collaboration links can have a major influence on the functioning of the market

Bilateralism and free trade

In recent years, there has been a great deal of research on the relative merits of multilateralism and bilateralism and their implications for the nature of the trading regime between countries. In this paper we explore the scope of bilateral free-trade agreements as a foundation for free trade, using recent developments in the theory of strategic network formation. We study a setting with many contries; in each country there are firms, which can sell in the domestic market as well as sell in the foreign markets. The possibility of selling in foreign markets depends on the nature of import tariffs faced by firms. Countries can sign bilateral free-trade agreements which lower import tariffs and thereby facilitate trade. We allow a country to sign any number of bilateral trade agreements. A profile of trade agreements defines the trading regime. We study the nature of trading regimes that are consistent with the incentives of individual countries. Our principal finding is that bilateralism is consistent with global free trade

A giant post auricular cutaneous horn: A rare case report

A cutaneous (cornu cutaneum) horn is a rare lesion which usually appears in sun-exposed areas and is very uncommon. It is a conical projection of hyperkeratotic epidermis and can be from a few millimeters to several centimeters in length. Here, we present the case of a large “horn” of long duration, arising in the right postauricular region in a 32-years-old male. The lesion was carefully examined, evaluated, complete excision was done with adequate margins and the defect was closed with primary closure after mobilizing the skin flaps adequately. Histopathologic examination showed the skin with underlying epidermis and extensive hyperkeratosis with no malignant cells seen at the base of the horn. It is important to mention that horn itself, is not the most important issue, but rather the underlying condition, which may be malignant also, needs to be ruled out and addressed

Effect of Nanographite on Electrical Mechanical and Wear Characteristics of Graphite Epoxy Composites

Effect of weight fraction (WF) of nanographite (NG, 400 nm) on electrical, mechanical and wear and characteristics of graphite epoxy composites (GECs) were investigated. For this purpose, a series of GECs was prepared through dispersion of various WF of NG into epoxy resin, followed by curing with polyamine. Dispersion of NG into epoxy matrix and onward formation of GECs and was revealed through UV, Fourier transformed spectra and atomic force microscopy (AFM). Photoelastic analysis in combination with AFM reveals the presence of uniformly dispersed domain of NG into stress free GECs with fringe order ranging 0.23 - 0.61 under compression of 8 - 20 kgf. GECs have rendered a rising trend in DC conductance ranging 98.32 - 0.54 μS/cm with electrical percolation threshold at 175 WF of NG. GECs have shown enhanced compressive, impact, tensile, strength, Rockwell hardness and wear resistance at 200 WF of NG. In general, GECs has shown a marginal modification in their compressive strength by 5.30 % over cured epoxy. However, their impact and tensile strengths were largely improved to 31.78% and 43.98% over cured epoxy. The present manuscript provides a novel method of modification in electrical, mechanical and wear behaviour epoxy through introducing NG as a novel alternative to traditionally used graphite as filler for development of GECs

Unusual histological presentation in neurofibromas: Two case reports

Various histological variants of neurofibroma have been described. The objective of this paper is to discuss the unusual histological findings seen in two cases of neurofibromas associated with neurofibromatosis type 1 Both cases presented with multiple subcutaneous nodules. Surgical excision of the largest nodule was done in both the cases. Histological examination of case no.1 revealed a benign tumor of the peripheral nerve sheath, of neurofibroma type with presence of mucus producing glands. The epithelial component was benign in this case. The second case showed presence of rosettes in between areas of typical neurofibroma

A multi-decadal analysis of river discharge and suspended sediment load in three Texas coastal rivers in relation to hurricanes, seasonal rainfall, and ENSO

Coastal river discharge and sediment load exert major influence on the sustainability of coastal systems. Controlled by various hydroclimatic/hydrometeorological agents, they exhibit distinct trend/variability at different time scales. Coastal Texas, while being a major target for tropical cyclones over the past 6 decades, has been experiencing drought and flood cycles associated with ENSO in the long term. However, it is still unclear the temporal variability of river discharge and the associated sediment delivery over this area at different time scales, and the controlling factors behind it. In this study, a 58-years (1960–2017) dataset is compiled to analyze the influence of ENSO, seasonal rainfall distribution and hurricanes event on the river discharge and suspended sediment load of three Texas coastal rivers-the San Bernard River, the Brazos River, and the Trinity River, at annual, seasonal and event scales, respectively. In the short-term, all three rivers attained the highest average daily discharge and sediment load during Hurricane Harvey. On a seasonal scale, the precipitation regime exerts more influence on the Texas watersheds than tropical storms and hurricanes. Over a multi-decadal scale, amplified rainstorms during the El Niño phases likely play an important role in the overall discharge and sediment transport in large rivers along the northern Gulf coast. Overall, it is reasonable to conclude that the magnitude of hurricane impacts on the overall discharge and suspended sediment load is regulated by the duration and intensity of the rainfall, as well as the coupled drought-flood cycle in relation to the intensity of ENSO