Nai River Basin Research Articles

Response of streamflow and sediment variability to cascade dam development and climate change in the Sai Gon Dong Nai River basin

Response of streamflow and sediment variability to cascade dam development and climate change in the Sai Gon Dong Nai River basin

Identifying the impact of land use land cover change on streamflow and nitrate load following modeling approach: a case study in the upstream Dong Nai River basin, Vietnam.

Tri An Reservoir is a vital source of water for agriculture, industry, hydropower, and public usage in Southern Vietnam. Due to human activities, water eutrophication has become a serious problem in recent decades. This study investigated for the first time the impact of land use and land cover (LULC) change on streamflow and nitrate load from the upstream Dong Nai River basin, which is the largest watershed of the reservoir. The study utilized several LULC scenarios, including LULC 2000, 2010, and 2020. The SWAT model was applied to model the watershed during the period 1997-2009. Results showed that the hydrological model performed satisfactorily based on the Nash-Sutcliffe efficiency (NSE) coefficient, the root mean square error observations standard deviation ratio (RSR), and the percent bias (PBIAS). The average simulated values of monthly streamflow and nitrate load were 453.7, 450.0, 446.7 m3/s and 17,699.43, 17,869.13, 17,590.81 tonnes for the LULC 2000, 2010, and 2020 scenarios, respectively. There were no significant differences in streamflow and nitrate load at the basin level under the different LULC scenarios. However, when looking at the subbasin level, there were differences in nitrate load among the scenarios. This suggests that the impacts of LULC on nitrate load may be more pronounced at smaller scales. Overall, our finding underscores the importance of modeling techniques in predicting the impacts of LULC change on streamflow and water quality, which can ultimately aid in the sustainable management of water resources.

Determination of the Pore Water Velocity Using a Salt Tracer Combined with Self-Potential Measurements

The tracer technique is recommended as an effective tool in surveying abnormal seepage through lakes and dams. By injecting a tracer into a known upstream location and monitoring the appearance of the tracer in the downstream leak point, it is possible to determine the direction and the average water velocity of the preferential flow through the dam. The detailed result achieved depends on the number of samples and the sampling locations to analyze tracer concentration over time in the field. This study proposes to use noninvasive self-potential measurements to determine the location and time the salt tracer moves through the seepage zone. The connection between the potential signal according to the propagation of the NaCl salt tracer and the water velocity was demonstrated through an experiment on a sandbox model. Experimental results express a good agreement between the time to reach the maximum value of the potential variation and the salt concentration variation with the time that water comes to monitoring locations. The result indicates an ability to determine the pore water velocity of the seepage zone based on the recording of potential signals produced by a salt tracer movement. The salt tracer test using NaCl combined with self-potential measurements was then applied to survey a leaking earth dam in the Dong Nai river basin (Vietnam).

Microplastics and solutions to remove microplastics in wastewater from wastewater treatment plants in the Saigon–Dong Nai river basin, Vietnam

Microplastics and solutions to remove microplastics in wastewater from wastewater treatment plants in the Saigon–Dong Nai river basin, Vietnam

Impact of Forest Conversion to Agriculture on Hydrologic Regime in the Large Basin in Vietnam

Deforestation due to agricultural land expansion occurred greatly during 1994 to 2005 with a high proportion of forests being converted into agriculture in the upstream Dong Nai river basin in Vietnam. Most of these conversions included expansions of coffee plantations in Dak Lak and Lam Dong provinces, which are in the world’s Robusta coffee production area. The aim of this study is to quantify the impact on the water cycle due to the conversion of forest to coffee plantations in a tropical humid climate region by the application of a hydrological model: soil and water assessment tool (SWAT). The model was calibrated with climate data from 1980–1994, validated with climate data from 1995–2010, and verified with statistical indicators such as Nash–Sutcliffe efficiency (NSE), percent bias (PBIAS), and ratio of the root mean square error (RSR). The simulations indicated that forest conversions into agriculture (expansion of coffee plantations) had significantly increased surface runoff (SUR) while actual evapotranspiration (ET), soil water content (SW), and groundwater discharge (GW) decreased. These changes are mainly related to the decrease in infiltration and leaf area index (LAI) post land cover changes. However, the soil was not thoroughly destroyed after deforestation due to the replacement of the lost forest with crops and vegetation. Therefore, changes in infiltration were marginal and not sufficient to bring large changes in the annual flow. Higher reductions in ET and SW were proposed, resulting in reduced streamflow in the dry season at the basin where the proportion of agricultural land was higher than the forest cover. Besides the plantation expansion, which resulted in streamflow reductions in the dry season, an existing problem was over-irrigation of coffee plantations that could likely deplete groundwater resources. Hence, balancing economic benefits by coffee production and mitigating groundwater depletion issues should be prioritized for land use management in the study area.

Civil society action: Another formation of civil society in Vietnam (The case studies of environmental protection in Dong Nai River Basin, Vietnam)

Most research on civil society in Vietnam tends to equate civil society with registered civil society organizations. This seems to provide an inadequate understanding of the civil society in Vietnam. To fill this gap, this research adopts the action-based approach that underlines civil society action-another formation of civil society in Vietnam. This approach is examined via the contrast cases between a foreign-invested company and a state-owned enterprise that were a better understanding about the formation and contribution of civil society action on Vietnam’s environmental issue. My findings confirmed that civil society in Vietnam is not only in the form of organizations but also the action via utilizing the chain of activities based on the voluntariness in public space toward common interest and it exists in the Vietnamese color. At the end of this article, I will discuss the implications of this study for the effective contributions of civil society in Vietnam.

Measuring water resource use efficiency of the Dong Nai River Basin (Vietnam): an application of the two-stage data envelopment analysis (DEA)

Measuring water resource use efficiency of the Dong Nai River Basin (Vietnam): an application of the two-stage data envelopment analysis (DEA)

Assessment of climate change impact on water availability in the upper Dong Nai River Basin, Vietnam

Abstract On a global scale, climate change is projected to have detrimental impacts on water availability. This situation will become more severe owing to accumulated impacts of climate change and anthropogenic activities. This study aims to investigate climate change impact on water availability in the upper Dong Nai River Basin using the Soil and Water Assessment Tool (SWAT) and Water Evaluation and Planning (WEAP) models. Future rainfall scenarios were downscaled from five different general circulation models under RCP4.5 and RCP8.5 using the Long Ashton Research Station Weather Generator (LARS-WG) tool. Under the climate change impact, annual river discharge in the study region is generally projected to have upward trends in the future, except for the near-future period of the 2030s under RCP4.5. In addition, dry-seasonal river discharge is expected to be increased in the future. Considering the baseline condition of water use, there was an annual water shortage of approximately 32.9 × 103 m3, which mostly occurred in the dry season from January to March. Climate change may reduce the water shortage in the study region ranging from 7.0 to 30.1% in the future. Under the combined impacts of climate change and increasing water demand, the water shortage will vary from −18.6 to 6.0% in the future. The results can provide valuable insights to implement appropriate future water resources planning and management in the study region.

Study on the isotopic compositionof rainwater in Long Khanh city,Southeast of the Mekong Delta region

The 2H/1H and 18O/16O isotope ratios in rainwater bring a lot of information about the fractionation of water molecules in the hydrosphere. The relationship between the isotope ratios of rainwater in an area characterised by the local meteoric water line, which is known as a reliable reference value for studies related to the identification of the recharge source of groundwater and climate change investigations. This study aims to establish a local meteoric water line in Long Khanh city (LK LMWL) in the period of 2020-2021, which is considered as a basis for research on the origin of groundwater in the area of Long Khanh city and subsequent studies on the origin of groundwater in the Southeast of the Mekong Delta region and the Dong Nai river basin. Results show that δ2H in rainwater ranges from -73.64 to 0.36 (‰ VSMOW) with an average value of -49.74‰ (n=19) and that figure of δ18O ranges from -10.91 to -1.59 (‰ VSMOW) with a mean of -7.68‰ (n=19). Due to the amount and specific meteorological conditions of the region, δ2H and δ18O in rainwater are enriched in the dry season but deplete in the rainy season. The LK LMWL follows a model of δ2H=(7.89±0.38)xδ18O + (10.28±2.93) (R2=0.96, n=19), which shows that the isotopic composition of δ18O in rainwater is more enriched than the isotopic composition of δ2H. The deuterium excess (d-excess) of rainwater in the region is found to be 10.28±2.93‰, which is comparable to those for the global scale of 10‰.

Meteorological and Hydrological Drought Assessment for Dong Nai River Basin, Vietnam under Climate Change

The main goal of this study is to examine future changes in meteorological, hydrological drought under the impact of climate change in Dong Nai River Basin, using Standardized Precipitation Index (SPI) and Stream flow Drought Index (SDI). The Soil and Water Assessment Tool (SWAT) is used as a simulated tool to estimate the streamflow in baseline (1980–2005) and climate change (RCP 4.5, 2016–2035) scenarios for meteorological, hydrological calculation. The results show that both types of drought tend to occur in the dry season. The area affected by meteorological and hydrological drought expand in both baseline and RCP 4.5 scenarios. In addition, meteorological drought duration is also significantly increased, especially severely drought months. Although it was detected slightly decreasing in the duration of hydrological drought, the number of months which is occurred moderately drought in sub-basins still goes up in the climate change scenario. These findings could be useful for water shortage assessment and allocation planning in this area in the climate change context in the Dong Nai River Basin.

Vulnerability assessment of water resources using GIS, remote sensing and SWAT model – a case study: the upper part of Dong Nai river basin, Vietnam

ABSTRACT Water resources vulnerability assessment provides the basis for the policymakers and the stakeholders regarding the state of the river basin to be focused for its better management. This research aims to assess the vulnerability index (VI) of the upper part of the Dong Nai (UPDN) river basin, which plays a crucial role for the socio-economic development of Ho Chi Minh City and 10 other provinces in the Southeast Vietnam, as well as its sub-basins. This study accounts from the year 1994 to 2030 (36 years) by using an integrated solution between the GIS, remote sensing (RS) and SWAT model in collaboration with guidelines prepared by United Nations Environment Programme (UNEP) and Peking University. Results from the land cover classification of Landsat images in the period of 1994–2020 revealed that the forest area decreased by 324,586 ha (approximately 29.4% of the basin area) and greatly influenced the VI. The UPDN basin’s water vulnerability was a moderate level of which VI was 0.276, 0.303 and 0.310 in 1994, 2004 and 2014, respectively. By 2030, the projected VI value could expect to be 0.318 under the climate change scenarios of the representative concentration pathway (RCP4.5). At the sub-basins, Dak Nong and Dak R‘Keh were two of the most vulnerable sub-basins of which VIs have could reach approximately 0.4 categorized as highly vulnerable areas. The results evidenced that the integrated techniques could be an efficient approach to provide useful information on the status of water resources to stakeholders in evaluating comprehensive options in terms of sustainable water resources management.

Evaluating two conceptual hydrological models: LST and NAM

Rainfall-runoff models are essential applications for water resources researches. A large number of models have been proposed and developed. Comparisons among models are helpful for researchers to have better choices for their studies of catchment water researches. This study focused on performance evaluations, and comparisons between the LST and NAM lumped conceptual rainfall-runoff models. Two models were applied to simulate runoffs of three catchments in the upper Dong Nai river basin: Phuoc Hoa, Ta Pao, and Phu Hiep. We used the data from 1984-1988 and 1989-1991 to calibrate and validate the Phuoc Hoa catchment, respectively. Those for Ta Pao and Phu Hiep catchments were 1988-1996 and 1997-1999. The results showed that both models performed well in the catchment monthly runoff simulation with NSE and R2 values greater than 0.90 for Phuoc Hoa and Phu Hiep stations and greater than 0.87 for Ta Pao station. The NSE and R2 by daily runoff simulations for Phuoc Hoa and Phu Hiep were approximate 0.90 except for the Phu Hiep runoff by the NAM model. That for Ta Pao was approximate 0.80. The obtained RSR and PBIAS are respectively lower than 0.50 and 10.00% in almost all simulations. Significantly, the LST model resulted in relatively better statistical performances than the NAM model in almost all statistical fitness values. The study would provide a noteworthy introduction of a good runoff simulation tool to hydrological studies in the future.

Vulnerability assessment of surface water resource of Dong Nai River basin in Lam Dong province

Vulnerability assessment of surface water resource of Dong Nai River basin in Lam Dong province

Water balance changes in the upper part of Dong Nai River basin

In recent decades, changes in land use and land cover (LULC) arising from socio-economic development, coupled with climate change, have severely undermined and compromised the environmental sustainability of the upper part of Dong Nai (UPDN) river basin. Assessing the long-term impacts of climate change and changes in LULC on hydrological conditions and water balance in the UPDN river basin is essential for sustainable watershed management. In the present study, Landsat images and SWAT (Soil and Water Assessment Tool) model were used to assess water balance changes due to changes of climate and LULC at three different intervals: 1994, 2004, and 2014. The results of Landsat images classification indicated that forest land was the main LULC type in the basin. In 1994 the forest cover was 706,803 ha (72.68% of the total landmass). In 2004 the forest area dropped to 520,359 ha (53.51%). In 2014 the forest area dropped further to 485,908 ha (49.97%). The change in LULC has caused changes in the annual and peak water flows. The analysis of the results revealed that the effect of historical climate variations on water yield was greater than the LULC change. With the scenario of LULC 2014, the consumption of irrigation water was the highest and mainly in the dry season. The findings can provide useful information for decision-makers in planning and formulating policies for sustainable watershed management and climate change adaptation.
 Trong những thập niên gần đây, sự thay đổi về sử dụng đất và thực phủ (LULC) do những hoạt động phát triển kinh tế - xã hội cùng với biến đổi khí hậu đã đặt ra những thách thức cho sự bền vững về môi trường ở lưu vực thượng nguồn sông Đồng Nai (UPDN). Đánh giá các tác động lâu dài của biến đổi khí hậu và những thay đổi trong LULC đến điều kiện thủy văn và cân bằng nước là việc cần thiết cho quản lý bền vững nguồn nước. Trong nghiên cứu này, các ảnh vệ tinh Landsat, công cụ đánh giá đất và nước (SWAT) được sử dụng để đánh giá sự thay đổi cân bằng nước do sự thay đổi khí hậu và LULC tại ba thời điểm khác nhau 1994, 2004 và 2014. Kết quả phân loại các ảnh Landsat cho thấy rừng là loại thực phủ chính trong lưu vực. Diện tích rừng của năm 1994 là 706.803 ha (72,68%). Diện tích rừng của năm 2004 đã giảm xuống còn 520.359 ha (53,1%) và đến năm 2014 chỉ còn 485.908ha (49,97%). Thay đổi sử dụng đất và thực phủ đã làm thay đổi chế độ thủy văn và dòng chảy đỉnh. Phân tích kết quả đã xác định rằng những sự thay đổi về điều kiện khí hậu trong quá khứ có ảnh hưởng đến lượng nước lớn hơn so với thay đổi về thực phủ. Với kịch bản LULC năm 2014, nhu cầu sử dụng nước tưới cho cây trồng là lớn nhất và chủ yếu trong mùa khô. Những kết quả đạt được trong nghiên cứu này sẽ cung cấp thông tin hữu ích cho các nhà hoạch định trong lập kế hoạch và ban hành chính sách cho quản lý lưu vực bền vững, thích ứng với biến đổi khí hậu.

Spatio-temporal pattern of water quality in the Saigon-Dong Nai river system due to waste water pollution sources

ABSTRACT This paper studies the current status of water quality, using both statistical and modelling approaches, in the waterways of the Saigon-Dong Nai river basin in relation to the nature of its environment and the effect of point and diffuse pollution sources. These sources are located mainly in the urban and industrial areas of Ho Chi Minh City (HCMC) and Dong Nai province. The statistical analysis of monitoring data allows us to determine the state of water quality while the modelling approach provides the means to manage the pollution sources. Both approaches are used in this work. Our statistical analysis of the water quality data collected at many stations from the upper reach of the Saigon and Dong Nai rivers to the urban waterways and the lower end of the rivers near the sea shows a contrast of water quality in different basin areas. These differences are consistent in both dry and rainy seasons and during the high tide and low tide. The results show that several hot spots of some water quality variables require management focus, such as organic waste water pollution at Binh Dien and Thay Cai in HCMC mainly due to local sources. Moderately and highly degraded water quality occurs at Binh Phuoc, Phu An and Cat Lai which are downstream from the industrial areas of Binh Duong (Binh Duong province) and Bien Hoa (Dong Nai province) before entering HCMC. Modelling of some important water quality variables also confirms the spatial extent of the areas where water quality is different as analysed from the statistical analysis of monitoring data. The MIKE-11 modelling system is shown to be a valuable tool for predicting the effect of different sources in HCMC metropolitan area on the waterway areas where water quality is important to protect the ecosystem and people health.

A possible solution for flood risk mitigation in Ho Chi Minh City and the lower Sai Gon-Dong Nai River Basin

The Sai Gon-Dong Nai Basin plays a very important role in the socio-economic development of Vietnam. The area of Ho Chi Minh (HCM) City is about 2095 km2, 60% of which lying under 2 m above MSL. Its population is about 8.136 million. Economic development has led to flood-related problems. The causes of floods are monsoon rainfalls, high tides, and outflows from the Dau Tieng Reservoir, upstream of HCM City. This paper proposed a plausible solution for flood mitigation in HCM City by uplifting the Dau Tieng dam crest. This solution can be recommended based on the results of an extensive simulation study which used: (i) a statistical downscaling procedure for evaluating the climate change (CC) impacts on precipitations; (ii) the MARINE model for simulating the rainfall-runoff process; (iii) the Telemac2D model for simulating the inundation; and (iv) the GIS tool for representing the inundated areas under different CC scenarios. It was found that under the A2 scenario an increase of rainfall by 2050s and added 40% of this rainfall (assuming due to tropical depression), the maximum regulated discharges released from the Dau Tieng dam could reach 1650, 500 and 300 m3s−1 without any enhancement then with the dam enhancement of 1.0 and 1.5 m, respectively. As comparing to event occurred on July 21, 2009 due to the combined effect of a heavy rainfall and a high tide condition, the inner city flooding area increases by 1.2, 1.3 and 8.2% with the dam enhancement of 1.5, 1.0 m and without dam enhancement, respectively. Results of this study have therefore provided critical information for making a logical decision concerning the possibility of uplifting the height of the crest of the Dau Tieng dam to mitigate the urban flooding in HCM City under the threat of CC and sea level rise.

Remote sensing applications for analysing the impacts of land cover changes on the upper part of the Dong Nai river basin

In recent years, activities related to socio-economic development have led to land cover (LC) changes in the upper part of the Dong Nai river basin. The use of remote sensing applications to analyse the impacts of these changes plays an important role in the managing the sustainability of theriver basin. This paper introduces a solution for analysing the impacts of LC changes on the water balancein the upstream catchment of the Dong Nai river in Lam Dong province. Landsat images were used for mapping and monitoring major changes over the last 20 years. Rainfall and water discharge data was collected from the local hydrometeorological stations to identify the impacts of the LC changes on the runoff in the catchment area. The results show that the forest area was reduced by more than 223,576 ha (23%). The main changes were an increase in the agricultural area from 18.2 to 31.3% and in water bodies from 0.9 to 2.2%. The latter was due to hydropower development projects in the catchment area. The LC changes caused by the changes in the hydrological conditions of the river basin have had a significant impact on water resources. The identification of the main LC changes in the catchment area could be useful for establishing a policy to protect the headwater forests and mitigate against future impacts.

Taxonomic notes on Indolestes Fraser, 1922 (Lestidae, Zygoptera). 3. Male and clarified type locality of Indolestes anomalus Fraser, 1946.

The male of Indolestes anomalus Fraser, 1946 is described and the holotype female is depicted. Its occurrence in Vietnam, Thailand and Malaysia is discussed, and the type locality is clarified (South Vietnam, Đồng Nai River basin).

Application of ensemble Kalman filter in WRF model to forecast rainfall on monsoon onset period in South Vietnam

Application of ensemble Kalman filter in WRF model to forecast rainfall on monsoon onset period in South Vietnam

Land Use and Land Cover Changes and Their Effect on the Flow Regime in the Upstream Dong Nai River Basin, Vietnam

The upstream Dong Nai River Basin is located in the country’s key economic development region and its water resources are a key component of sustainable regional development. The objective of this study was to assess the impact of land use and land cover changes (LULCC) on the flow regime in this tropical forest basin using a flow–duration curve analysis that has been widely used in Japan. This study combined two different temporal and spatial scales of satellite data, Landsat and Global Inventory Modeling, and Mapping Studies (GIMMS) normalized difference vegetation index (NDVI) to analyze LUCC. Results from the land cover classification of five Landsat images between 1973 and 2014 indicated that the forest area decreased significantly in the period of 1994 to 2005 due to population growth, leading to land conversion for agriculture. Furthermore, secular changes in the annual GIMMS-NDVI data revealed that land cover changes occurred from 1996 and a large amount of forest was lost in 1999; however, due to the rapid regrowth of secondary forest of tropical forests and the development of the crop, the vegetation recovered shortly afterwards in 2000 before decreasing again after 2004. Following large-scale deforestation, the total discharge, maximum flow, and the plentiful, ordinary, low, and small-scale runoff increased sharply and decreased thereafter because of vegetation regrowth.