Wyniki wyszukiwania - BazTech

1

Riverbed armoring and sediment exchange process in a sand–gravel bed reach after the Three Gorges Project operation

Li Linlin, Xia Junqiang, Zhou Meirong, Deng Shanshan

Acta Geophysica

|

2020

|

Vol. 68, no. 1

243--252

EN

Upstream damming greatly altered the fow and sediment regime entering downstream reaches in the Middle Yangtze River, and the bed material in a sand–gravel bed reach coarsened continuously, which had a signifcant infuence on the sediment transport and bed evolution. In order to study the riverbed armoring, the sediment exchange process (SEP) among bed material, bed load and suspended load in a sand–gravel bed river is frstly clarifed, and then, the three-state transition probability model (Markov chain) is proposed in this study, with the hiding-exposure efect of non-uniform sediment being considered. Finally, the equilibrium equation of sediment quantity in an active layer is presented to calculate the grain size distribution of bed material. In this model, the infuences of fow and sediment conditions, riverbed erosion and deposition on the SEP are discussed. The results show that the composition of surface bed material at the Zhicheng station became obviously coarse, and the median grain size (d50) of surface bed material increased from 0.230 to 0.424 mm in 2003–2017, with an upward increasing trend. The proposed probabilistic model was validated against feld measurements of bed material, and calculated results show reasonable agreement with the measured data at Zhicheng. Accordingly, the probabilistic model can be used to predict the riverbed armoring and to investigate the non-equilibrium transport of non-uniform sediment in a sand–gravel bed river.

2

Influence of the Three Gorges Reservoir on the vegetation of its drawdown area: effects of water submersion and temperature on seed germination of Xanthium sibiricum(Compositae)

Wang Q., Yuan X., Liu H.

Polish Journal of Ecology

|

2014

|

Vol. 62, nr 1

25--36

EN

Xanthium sibiricum, an annual weed, unexpectedly and dramatically occupied the exposed drawdown area after water had been impounded for the first time in the newly created Three Gorges Reservoir in China. In order to explain this phenomenon and establish an appropriate management strategy, the effects of constant submersion on seed viability and germination of X. sibiricum were investigated at two constant temperature regimes (25°C and 30°C) under artificial laboratory conditions. The results indicated that the seeds of X. sibiricum exhibited a high level of tolerance of submersion and up to 99% of seeds were viable in each treatment regime. The effect of submersion on germination was not obvious at 25°C until the submersion was prolonged for 180 days, while at 30°C the eventual germination rate of X. sibiricum, even after submergence for only one day, was significantly improved. The speed of germination was also consistently accelerated by prolonged periods of submersion. The proportion of seeds that germinated in all treatments combined was less that 56% due to seed dimorphism, thereby providing a seed bank. We conclude that the interaction between long-term winter flooding and high temperature in summer is the major reason that X. sibiricum was able to occupy the newly exposed drawdown area in the absence of competition. These findings provided further insight into how germination strategy and reservoir water-management regime contributed to this dramatic species outbreak.

3

Effect of long-term winter flooding on the vascular flora in the drawdown area of the Three Georges Reservoir, China

Wang Q., Yuan X., Liu H., Zhang Y., Cheng Z., Li B.

Polish Journal of Ecology

|

2012

|

Vol. 60, nr 1

95-106

EN

The dam construction and water impoundment have extensively altered flow regime and riparian ecosystems. However, the effect of long-term winter flooding of reservoir on plants of drawdown area is poorly known. The Three Gorges Dam in China, the largest dam in the world, created a drawdown area of 348.93 km2 between 145 m and 175 m above sea level around its reservoir. The drawdown area was submerged for more than half year in winter and exposed in summer. In the summer of 2009, the vegetation of fourteen sites in the drawdown area was investigated to determine the impact of winter flooding on vascular flora and to explore flood-tolerant species for vegetation reconstruction. One hundred and seventy five species of 58 families were recorded in present work, which indicated that 55% of vascular flora species disappear or became rare. The number of perennial species decreased to 50%. Therophytes, with 87 taxa, were the dominant life form. Strictly aquatic species were rather scarce for summer drought. Mean vegetation cover in the drawdown area was more than 70%. Species richness and vegetation cover along the elevation gradient exhibited a negative pattern correlated with flooding duration. The remarkable reduction of plant richness, variation of life form composition and alternation of dominant species indicated the strong influence of long-term winter flooding on vascular flora. Cynodon dactylon and Cyperus rotundus was highly resistant to long-term winter flooding and summer drought. Eight hardwoods (Vitex negundo, Morus alba, Sapium sebiferum, Glochidion puberum, Rhus chinensis, Melia azedarach, Pterocarya stenoptera and Trema levigata) exhibited high tolerance to winter flooding and may be potential candidates for vegetation restoration.

4

Chiny Trzech Przełomów

Warcholak P., Winter J.

Gospodarka Wodna

|

2007

|

Nr 1

43-48

PL

W polskich i światowych mediach pojawiły się wiadomości o budowie wielkich chińskich obiektów energetyki wodnej. Ponieważ mieliśmy okazję wraz z grupą polskich hydrotechników zwiedzić Zaporę Trzech Przełomów na rzece Jangcy w czasie jej budowy, chcielibyśmy podzielić się informacjami zdobytymi na jej temat oraz osobistymi spostrzeżeniami.

EN

The Polish and world media published information about the construction of large Chinese water power industry constructions. As we, together with a group of Polish hydrotechnicians, had the occasion to visit the Three Gorges Darn on the Yangtze River at the time it was under construction, we would like to share the information we got, as well as personal observations.