Irving Stricklin

Every year, 35-50% of this attain is flooded in the course of the rainy season. The impression of street embankments and similar infrastructure developments on the motion of this flood water is an more and more vital consequence of improvement. Table 2 summarises the mean annual flows alongside the mainstream. The imply annual movement getting into the lower Mekong from China is equivalent to a relatively modest 450 mm (18 in) depth of runoff. Downstream of Vientiane this will increase to over 600 mm (24 in) because the principal left financial institution tributaries enter the mainstream, mainly the Nam Ngum and Nam Theun. The circulate stage falls once more, even with the precise financial institution entry of the Mun-Chi system from Thailand. Although the Mun-Chi basin drains 20% of the lower system, common annual runoff is only 250 mm (10 in). Runoff in the mainstream increases again with the entry from the left bank of the Se Kong from southern Laos and Se San and Sre Pok from Vietnam and Cambodia. Table 2: Lower Mekong Mainstream annual circulate (1960 to 2004) at selected websites. Flows at Chiang Saen getting into the decrease basin from Yunnan make up about 15% of the wet season flow at Kratie. This rises to 40% through the dry season, even this far downstream. Through the wet season, the proportion of average movement coming from Yunnan quickly decreases downstream of Chiang Saen, from 70% to lower than 20% at Kratie. The dry season contribution from Yunnan is rather more vital. The key portion of the balance comes from Laos, which factors to a serious distinction in the low-movement hydrology of the river. One fraction comes from melting snow in China and Tibet and the remaining from over-season catchment storage within the decrease basin. This has implications for the incidence of drought circumstances. For instance, if runoff from melting snow in any given 12 months could be very low, then flows upstream of Vientiane-Nong Khai can be lower. In a large river system like the Mekong, seasonal flows may be quite variable from yr to yr. Although the pattern of the annual hydrograph is fairly predictable, its magnitude is just not. The typical month-to-month flows alongside the mainstream are listed in Table 3, providing an indication of their vary and variability from yr to yr. At Pakse, for instance, flood season flows throughout August would exceed 20,000 m3/s (5,300,000 US gal/s) nine years out of ten, but exceed 34,000 m3/s (9,000,000 US gal/s) just one year in ten. Table 3: Mekong Mainstream month-to-month discharge, 1960-2004 (m3/s). There's little evidence from the last 45 years of information of any systematic adjustments within the hydrological regime of the Mekong. The internal drainage patterns of the Mekong are unusual amongst those of large rivers. Most giant river methods that drain the interiors of continents, such because the Amazon, Congo, and Mississippi, have comparatively easy dendritic tributary networks that resemble a branching tree. Typically, such patterns develop in basins with gentle slopes the place the underlying geological structure is fairly homogeneous and stable, exerting little or no management on river morphology. In marked contrast, the tributary networks of the Salween, Yangtze, and notably the Mekong, stretch mark cream pregnancy are advanced with totally different sub-basins usually exhibiting different, and distinct, drainage patterns. Reach 2 is dominated in both wet and stretch mark cream dry seasons by the Yunnan Component. Reach three is more and more influenced by contributions from the massive left financial institution tributaries in Laos, particularly the Nam Ngum, Nam Theun, Nam Hinboun, stretch mark cream bio oil Se Bang Fai, Se Bang Hieng and Se Done Rivers. The Mun-Chi river system from the correct bank in Thailand enters the mainstream within this attain. Reach 4: Pakse to Kratie. The primary hydrological contributions to the mainstream on this reach come from the Se Kong, Se San, and Sre Pok catchments. Together, these rivers make up the most important hydrological sub-part of the decrease basin. Over 25% of the imply annual circulation volume to the mainstream at Kratie comes from these three river basins. They are the important thing factor in the hydrology of this part of the system, especially to the Tonle Sap movement reversal. Reach 5: Kratie to Phnom Penh. This attain includes the hydraulic complexities of the Cambodian floodplain, the Tonle Sap and the great Lake. By this stage, over 95% of the overall flow has entered the Mekong system. The focus turns from hydrology and water discharge to the evaluation of water degree, over- financial institution storage and flooding and the hydrodynamics that decide the timing, duration and quantity of the seasonal circulate reversal into and out of the good Lake. Reach 6: Phnom Penh to the South China Sea. Here the mainstream divides into a fancy and increasingly controlled and synthetic system of branches and canals. Key options of circulate behaviour are tidal influences and salt water intrusion.