Development and Application of a Distributed Conceptual Hydrological Model to Simulate Runoff in the Be River Basin and the Water Transfer Capacity to the Saigon River Basin,Vietnam

A distributed conceptual model(FRASC(Flow Routed Accumulation Simulation in a Catchment))has been developed,in which a rainfall-runoff module is modified from an original lumped conceptual model(Xinanjiang)via a GIS(Geographic Information System)-aided approach and a water allocation module contains reservoirs,water users and hydropower plants.The model is relatively easy to use and can easily obtain input data,but still has the ability to generate hydrological information at many points within a catchment.The model application to the Be River basin is evaluated and shows to be reliable in terms of close agreements between simulated and observed series.Daily natural flow rates for 36 years are simulated at 7,981 grid cells within a studied area of 7,650 km^2.Based on this simulated database,design discharges are predicted in various probabilities.Finally,the research determines that the water transfer capacity from the Be River basin to the Saigon River basin reaches 14%,18% and 23% of a planned value of 75 m^3/s during the dry period in a wet year(P10%),average year(P50%)and dry year(P90%),respectively.

Assessing and Forecasting Saline Intrusion in theVietnamese Mekong Delta Under the Impact of Upstreamflow and Sea Level Rise

Saline intrusion is a hot issue and has always been of concern in the VMD(Vietnamese Mekong Delta),especially in the context of many changes of impact factors such as upstream flows and SLR(Sea Levels Rise).Vulnerability to changes in the upstream flows and SLR ismust-have reasons for updated and interpreted information.This information is used for exploiting of soil and water resources.MIKE 11 model was successfully applied to assess the saline intrusion.The study provided the picture of the saline intrusion in the dry season from January to May in the VMD in the existing situation(2015 and 2016)and the future(2030 and 2050)under the impact of flow at Kratie in various frequencies of 18%,50%and 85%based on the time series of 2001-2016,and SLR according to RCP(Representative Concentration Pathway)4.5 scenario of MONRE(Ministry of Natural Resources and Environment)of Vietnam issued in 2016.The results show that in the year 2015 the ASI(Saline Intrusion Area)in the VMD was relatively low due to moderate tidal level and high Kratie discharge(P=18%).The scenario like the situation in 2016 and in the future ASI increased significantly compared to the 2015 baseline scenario which shows that the VMD is very vulnerable to saline intrusion.Based on multivariate regression analysis,the study also presented the formulas for the relationship between the ASI of 0.25 g/L,2.5 g/L and 4.0 g/L thresholds and the impact factors such as the average discharge at Kratie and the maximum daily tidal level in East Coast during the dry season from January to May.With an adjusted R2 at 0.913-0.974,these formulas are believed to be reliable for predicting ASIs based on the Kratie flow and the East Coast tidal level.

Simulation of Flood in the Thach Han-Ben Hai River Basin(Vietnam)under the Influence of the Upstream Reservoir System

The central provinces in Vietnam always suffer from the negative impacts of floods every year,especially in the downstream areas.Quang Tri province in the TBRB(Thach Han-Ben Hai River Basin)is one of the provinces suffering heavy damage caused by floods.A 1-dimensional hydrodynamic model was researched and applied connecting 2 dimensions in the MIKE model set(MIKE FLOOD)to simulate inundation level,inundation time,flood flow velocity for communes in TBRB.Simulation results for 111 communes in Quang Tri province show that:39 communes(35%)are not flooded;3 communes are flooded below 0.5 m;15 communes are flooded from 0.5-1.0 m,flooding time is about 1 day;30 communes are flooded from 1.0-2.0 m,inundation time is about 2 days;30 communes are flooded over 2.0 m,flooded for about 3 days,especially 3 communes are flooded over 4.0 m.This result helps to develop flood prevention plans for localities in the province.

Research to Establish a Set of Combinatorial Indicators to Calculate Flood Vulnerability Index in Thach Han-Ben Hai River Basin, Quang Tri Province, Vietnam

In recent times,approaches to flood prevention and mitigation have changed a lot.These changes are to shift the focus from flood control to flood risk management,in which the assessment of vulnerability to floods caused by each sector and field corresponding to each flood magnitude is typical.Current flood vulnerability assessment studies are basically holistic based on factors affected by floods or in aspects:economy,society and ecological environment,and aspects that are mentioned in all areas of social life.The content of the flood vulnerability assessment method usually considers 3 components:E(Exposure),S(Susceptibility),A(Adaptability-Recovery).Each component will contain many different variables belonging to different objects and different natural-economic-social characteristics in each area.Therefore,for each research area,the evaluation method needs to establish an appropriate set of indicators.A set of indicators used to assess flood vulnerability must:be scientific;be practical;simplify the investigation,collection and synthesis of data.This study has established a set of combinatorial indicators including 27 indicators for the T-BRB(Thach Han-Ben Hai River Basin)on the basis of analysis and synthesis from case studies.

Research and Experimental Application of Empirical Formulas to Calculate Riverbank Erosion in Tien River in the Mekong Delta

In recent years,the problem of riverbank and coastal erosion in the MD(Mekong Delta)is very complicated;landslides occur in most of the inland and coastal provinces.Most riverbank landslides occur gradually,but in contrast to sudden landslides that cause great damage,occur with increasing frequency.This shows that the trend of riverbank erosion will be more complicated and more frequent,especially in the context of extreme weather changes and changes in hydrological regime in the next time.Statistics from the authorities show that,if in 2010 the whole region had nearly 100 landslide points;by 2020 it had increased to more than 680 points;in which Dong Thap in the Tien River is one of the two localities with the most serious riverbank erosion.Currently,there are many methods used to assess and forecast the level of riverbank erosion in specific areas,such as:method of document analysis,measurement data;physical model;mathematical models and empirical formulas.In this study,the empirical formula is used to calculate the landslide level for the Tien River section in Cao Lanh,Dong Thap province.The calculation results according to the empirical formula have a certain agreement with the actual data,the correlation coefficient is 0.90 and the Nash coefficient is 0.78,the relative error of less than 15%is 80%of the cross-section.Such results have shown the possibility of applying empirical formulas to establish and calculate for other landslide areas along the banks of Hau River and MD.