Every year, natural disasters such as storm, flood, drought, landslide, river erosion had cause great damage to life and property. The Huong river is the largest river in Thua Thien Hue province with length of 128 km and its area cover 2/3 of the province. It is particularly important role in the development of economy, the province's social . In recent years, the issue of the Huong riverside slide occurs more frequently and more serious each time, particularly from the Tuan confluence to Sinh confluence (the section of Huong river flows through Hue city). According to statistics in the period of (1999 – 2009), the Huong river bank of Thien Mu Pagoda are having the most serious erosion about an average of over 10m/year; section of river runs through Huong Long village (Long Ho Thuong, Xuoc Du, Bao Vinh, Tran Non) with an average speed erosion of 2-10m/year, landslides in some places of 10m deep into the coast and lasted nearly 1600m. Besides, due to global climate changes, as well as the impact of economic - social development in the basin, Huong riverside slide more and more, causing serious damage to economic- social development in the basin.
Acknowledging its urgent and important issues change the river bed, in recent years the State has invested in projects which aimed erosion mitigation, helped people in the region to have a stable life, shake off poverty and ensuring environmental sustainability.
That is why we required equipment and strategies to help the local management to prevent damage cause by river bank erosion. At present, the world is using four main methods for studying the river bed morphology: Field measurement methods; Physical model method; Mathematical model methods; Remote sensing and GIS methods. All four methods are indispensable and complement to each other in order to give more accurate and optimal results. The field methods may requires many years of field observation in a systematic way. Methods of physical models as a basis for building the empirical formula, capable of accurately simulation the river but required much effort and money.
In our country today, mathematical model and field measurement methods which armed to calibrate and test, are appropriate and very effective. Research institutes had also applied this method and got extensive results. In particular, in recent years, the Institute of Geography – Vietnam, Academy of Science and Technology had successfully applied the MIKE model (including Mike-Nam, Mike 11-HD, Mike 21C) to determine the changes in the Huong river (concentrated in the mainstream river begins from the Tuan confluence to Sinh confluence).
MIKE model which was created and developed by Danish Hydraulic Institute (DHI) has been applied successfully in some basins in Vietnam: Hong river, Ma river, Ben Hai river, Vu Gia – Thu Bon river ... with contents such as simulation of hydraulic, calculations flooding, construction runoff from rain or water balance calculations for the basin. With studying the changes in river bank erosion, MIKE 21C module is considered a powerful simulation tools and its high accuracy. MIKE 21C can simulate the hydraulic regime of flow, accretion, bed erosion, bank erosion and long-term forecasts of these events (after 10 years, 20 years or 30 years).
Map of application of MIKE model to calculated the bed morphology in Huong river
Mike models tested with the typical flood in 1983, from 0h on the 29th day of the October in 1983 to 7h on the 5th day of the November in 1983. The testing of hydraulic factors was carried out on several different locations on the river to ensure representation and accuracy for the calibration process and model testing.
Calibration and test results of Mike-NAM model
Calibration and test process show, Mike-NAM can be applied for good results in Huong river basins. Data of flow chain of Mike – Nam model is used in inputting data of Mike 11-HD.
Observation and calculation values of flood on 29/X-1/XI/1983 - Observation and calculation values of flood on 18 - 20/X/2000
Calibration and test results of Mike 11-HD model
Calibration and test process of model also shows that the calculated result is quite consistent with field document. Efficiency of the model reaches up 96% at Kim Long station and 92% at the Phu Oc station. Calculated results can be used in inputting data of Mike 21C model.
Observation and calculation values of flood at Kim Long in 1983 - Observation and calculation values of flood at Phu Oc in 1983
Calibration and test results of Mike 21C model
From confluence Tuan to that is 4413m - From confluence Tuan to that is 9449m
From confluence Tuan to that is 17464m - From confluence Tuan to that is 25737m
The water level is tested that Mike 21 C simulated in accordance with Huong river (from the Tuan confluence to Thao Long). Parameters are used in forecasting and warning process of erosion and deposition of Huong River – section of river runs through Hue city.
Based on the built parameters, the scientists simulated river bed erosion when the reservoir in upstream activities from which compare changing before and after regulation of the reservoir.
Terrain before the flood - Reservoir hasn’t been operating - Reservoir has been operating
Comparing the changes of the river bed before and after the flood reservoir – section of river run through Hue city
Comparison between simulated results show that after having the reservoir, river bed doesn’t change more intense, the rivers tend to shift toward the right bank.
Map of erosion status and map of the calculated erosion model
Researched results will contribute to further research to mitigate the damage caused by river erosion and deposition, to clarify the mechanism of river bed from the Tuan confluence to Thao Long to service planning sustainable development of Hue city.
Translated by Thu Lan
Link to Vietnamese Version