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Assessing the dyke-system's impacts in An Giang province on the main stream flow regimes in the lower Mekong delta
Abstract
The objective of this study is to assess the impact of the full-dyke system in An Giang province on the main river flow regime. Statistical method of the development of full-dyke system was used in order to assess the impact of dyke system on the flow regime using hydrological indicators (IHA - Indicators of Hydrologic Alteration) for the period 1 - under construction (1997-2010) and period 2 - after the dyke system construction relatively completed (2011-2019). The results show that An Giang province has fast increasesdthe area protected by full-dyke systemin the two periods 1997-2004 and 2007-2010. By 2011, the area protected by dyke system accounts for more than 69% natural area of the whole province (the full-dyke is 54%, and the semi-dyke(August dyke)is 15%). The results of flow regime (discharge) change assessment show that both Chau Doc and Tan Chau stations, for theperiod 1 and 2, are found to be very high (over 67%); at Vam Nao station, the alteration in theperiod 1 and 2are 49.8% and 60.7% respectively. In general, during the construction of the dyke system (1997-2010), Chau Doc station was found to be most affected (71.2%), followed by Tan Chau (68.2%) and Vam Nao with slight changes (49.8%). However, when considering the period 2 (2011-2019) after the dyke system construction is relatively complete, the change in flow regime at Tan Chau and Vam Nao stations still increases significantly, 76.6% respectively 76.6% and 60.7%. Among the five groups considered, group 5 (rate and frequency of water condition changes) is found to have the largest changes at all three stations. In which, indicator 31 (flow increase) changes at a very high level in Chau Doc and Tan Chau stations. Meanwhile, indicators 32 and 33 at Vam Nao station have significant changes in both considered periods. The changes in flow regimes at Tan Chau and Chau Doc stations may be attributed by the changes from the upper Mekong flow. Therefore, it would consider comprehensively all causes leading to flow regime changes.
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