Vol. 25, No.2

Extreme values and rising tendencies of sea levels along Vietnam coast

2009-01-01T00:00:00Z

Extreme values and rising tendencies of sea levels along Vietnam coast Hoang, Trung Thanh; Pham, Van Huan A review of the investigations on the sea level changes in South-china sea is presented. The full set of year1y sea level data at 25 tide gauges along Vietnam coast is used for extreme analysis and trend analysis. Based on the level data collection up to year 2007 the empirical extreme analysis yields new estimates of the design values of sea level with different rare frequencies. The results of extreme analysis are compared with the theoretical extreme heights of tide obtained by predicting hourly tide heights in a 20-year period. For stations with 11 harmonic constants of main tidal constituents the theoretical astronomical extreme tide levels were calculated by the Peresipkin iteration method. The comparison showed a good agreement between two methods. The analysis also showed that the tidal extremes and design level values of 20-year return period are of the same range. The level values of longer return period are affected mainly by floods and surges at a decreasingly extent. The rate of yearly changes of sea level due to global warming and other effects is evaluated to be about 1 mm per year.

Application of a Godunov type numerical scheme and a domain decomposition technique to the parallel computation of tidal propagation

2009-01-01T00:00:00Z

Application of a Godunov type numerical scheme and a domain decomposition technique to the parallel computation of tidal propagation Nguyen, Tat Thang; Nguyen, The Hung A parallel computing model for the numerical solution of the general 20 shallow water equations in conservative form has been developed, tested and implemented in the MPI parallel environment set up on a parallel computer with four 2.8 GHz CPUs in Institute of Mechanics, VAST. The model is based on a Godunov-type numerical scheme, which is devised for 20 unstructured computational meshes, and on a domain decomposition technique. That newly developed parallel computing model has been applied to a tidal wave propagation problem in the Gulf of Tonkin in the South China Sea. The computed results show good agreement with that of the TIDE20 model. !t is of high importance that computation time is significantly reduced.

Phytoremediation of Cadmium and Lead contaminated soil types by Vetiver grass

2009-01-01T00:00:00Z

Phytoremediation of Cadmium and Lead contaminated soil types by Vetiver grass Vo, Van Minh; Le, Van Khoa Phytoremediation is an alternative technology to remove heavy metals in contaminated soil. Vetiver grass (Vetiveria zizanioides (Linn.) Nash) was used for Cadmium (Cd) and Lead (Pb) removal experiments in 4 various soil types: {SI) sandy soil with abundant organic matter; (82) sandy soil with poor organic matter; (83) clay soil with abundant organic matter; (84) clay soil with poor organic matter. Plants were grown for 30 days before transferring to experimental pots. Pb(N03)2 solution was added to Ihe soil types in each experimental pot at O, 100, 300 and 700ppm; similarly CdC12 : O, l O, 30 and 60ppm. Plants were observed for their growth and harvested after 3 months. Cd aud Pb accumulation in roots and shoots was analyzed. The results sho'wed that Vetiver grass grew in 4 various soil types. The statistical analysis indicated that vetiver's uptake ability of Cd and Pb increase as the level of Pb, Cd in various soil types increase. Cd accumulation rates between shoots and roots of vetiver grass were fairly low (<13.32%); on the contrary, the accumulation rates ofPb shoot/ root is very high (9.72%-88.14%). Therefore, vetiver grass can use to phytoextration of Pb and phytostabilization of Cd.

Distribution of Arsenic, Copper, Lead, Zinc elements in water and soils of sulfur deposits in the North West of Hanoi

2009-01-01T00:00:00Z

Distribution of Arsenic, Copper, Lead, Zinc elements in water and soils of sulfur deposits in the North West of Hanoi Dang, Mai The quantitative distribution of As, Cu, Pb, Zn elements in water and soils around Giap Lai and Minh Quang sulfur deposits is presented in this work. The preliminary results delineate the following: i) The content of As in water is quite low and is below the polluted limit. The soils was symptomatic of pollution byAs at low level. ii) The contents of Cu and Zn are higher than that of Pb, especially in some localities, Cu and Zn contents are over the permissible threshold of the surface water quality and form high anomalies. iii) The content of As, Cu, Zn, Pb in the Red River's water is higher than that in the exploitation area. This reveals that the arsenic and other heavy metals presented in the Red River's water may come from other sources located in the upper course of the river.