Flooding in the Mekong Delta: the impact of dyke  systems on downstream hydrodynamics

Abstract. Building high dykes is a common measure of coping with floods and plays an important role in agricultural management in the Vietnamese Mekong Delta. However, the construction of high dykes causes considerable changes in hydrodynamics of the Mekong River. This paper aims to assess the impact of the high-dyke system on water level fluctuations and tidal propagation in the Mekong River branches. We developed a coupled 1-D to 2-D unstructured grid using Delft3D Flexible Mesh software. The model domain covered the Mekong Delta extending to the East (South China Sea) and West (Gulf of Thailand) seas, while the scenarios included the presence of high dykes in the Long Xuyen Quadrangle (LXQ), the Plain of Reeds (PoR) and the Trans-Bassac regions. The model was calibrated for the year 2000 high-flow season. Results show that the inclusion of high dykes changes the percentages of seaward outflow through the different Mekong branches and slightly redistributes flow over the low-flow and high-flow seasons. The LXQ and PoR high dykes result in an increase in the daily mean water levels and a decrease in the tidal amplitudes in their adjacent river branches. Moreover, the different high-dyke systems not only have an influence on the hydrodynamics in their own branch, but also influence other branches due to the Vam Nao connecting channel. These conclusions also hold for the extreme flood scenarios of 1981 and 1991 that had larger peak flows but smaller flood volumes. Peak flood water levels in the Mekong Delta in 1981 and 1991 are comparable to the 2000 flood as peak floods decrease and elongate due to upstream flooding in Cambodia. Future studies will focus on sediment pathways and distribution as well as climate change impact assessment.

Download Full-text

Flooding in the Mekong Delta: Impact of dyke systems on downstream hydrodynamics

10.5194/hess-2019-64 ◽

2019 ◽

Author(s):

Vo Quoc Thanh ◽

Dano Roelvink ◽

Mick van der Wegen ◽

Johan Reyns ◽

Herman Kernkamp ◽

...

Keyword(s):

Mekong Delta ◽

River System ◽

Dry Season ◽

Water Levels ◽

Mekong River ◽

Flood Season ◽

Tidal Propagation ◽

River Outflow ◽

Year 2000

Abstract. Building high dykes is a common measure to cope with floods and plays an important role in agricultural management in the Vietnamese Mekong Delta. However, the construction of high dykes cause considerable changes in hydrodynamics of the Mekong River. Therefore, this paper aims to assess the impacts of the high dyke system on water level fluctuation and tidal propagation on the Mekong River branches using a modelling approach. In order to consider interaction between rivers and seas, an unstructured modelling grid was generated, with 1D–2D coupling, covering the Mekong Delta and extending to the East (South China Sea) and West (Gulf of Thailand) seas. The model was manually calibrated for the flood season of the year 2000. To assess the role of floodplains, scenarios consisting of high dykes built in different regions of the Long Xuyen Quadrangle (LXQ), Plains of Reeds (PoR) and TransBassac were carried out. Results show that the percentage of river outflow at Dinh An sharply increases in the dry season in comparison to the flood season while the other Mekong estuarine outflows rise slightly. In contrast, the lateral river flows of the Mekong River system to the seas by the Soai Rap mouth and the LXQ decrease somewhat in the dry season compared to the flood season due to overflow reduction at the Cambodia–Vietnam border. Additionally, the high dykes in the regions that are directly connected to a branch of the Mekong River, not only have an influence on the hydrodynamics in their own branch, but also on other branches because of the connecting channel of Vam Nao. Moreover, the high dykes built in the PoR, LXQ and TransBassac regions are the most important factor for changing water levels at Tan Chau, Chau Doc and Can Tho, respectively. The LXQ high dykes result in an increase of daily mean water levels and a decrease of tidal amplitudes on the Song Tien (downstream of the connecting channel of Vam Nao). A similar interaction is also found for the the PoR high dykes and the Song Hau.

Download Full-text

The Impact of Hydropeaking on Juvenile Brown Trout (Salmo trutta) in a Norwegian Regulated River

Sustainability ◽

10.3390/su12208670 ◽

2020 ◽

Vol 12 (20) ◽

pp. 8670

Author(s):

Svein Jakob Saltveit ◽

Åge Brabrand ◽

Ana Juárez ◽

Morten Stickler ◽

Bjørn Otto Dønnum

Keyword(s):

Power Plant ◽

Brown Trout ◽

Salmo Trutta ◽

Water Levels ◽

Regulated River ◽

Low Flow ◽

High Survival ◽

Power Station ◽

Brown Trout Salmo Trutta ◽

The Impact

The Norwegian electrical energy supply system is based on hydropower. The now deregulated energy market has led to increased use of hydropeaking production, leading to greater fluctuations in discharge and water levels below hydropower stations. The power station HOL 1, with an outlet to the Storåne River, is a large hydropeaking facility. With over 300 rapid flow increases and decreases per year since 2012, it is a river subjected to frequent hydropeaking. To quantify the stranding risk downstream of the power plant, the effect of a series of different turbine shutdown scenarios was simulated in an earlier study. The residual flow of 6 m3·s−1 and a full production of 66 m3·s−1 were considered as the baselines for the calculation of dewatered areas. A three-year study of juvenile fish density both upstream as a reference and downstream of the power plant was undertaken. There were very low densities or even an absence of brown trout (Salmo trutta) older than young-of-the-year (YoY) below the outlet of the power station, despite high densities of YoY in previous years. This is probably due to the large and rapid changes in flow below the power station. Hydropeaking has less impact on the earliest life stages of brown trout during spring and summer, as well as on spawning and egg development during winter. This is attributed spawning in late autumn occurring at a low flow seldom reached during hydropeaking. The high survival of YoY during the first summer and early autumn is likely due to a lower frequency of hydropeaking and higher residual flows, leaving a larger wetted area.

Download Full-text

The Impact of Blade-to-Blade Flow Variability on Turbine Blade Cooling Performance

Journal of Turbomachinery ◽

10.1115/1.2019247 ◽

2005 ◽

Vol 127 (4) ◽

pp. 763-770 ◽

Cited By ~ 1

Author(s):

Vince Sidwell ◽

David Darmofal

Keyword(s):

Turbine Blade ◽

High Flow ◽

Low Flow ◽

Simplified Model ◽

Selective Assembly ◽

Turbine Blade Cooling ◽

Cooling Flow ◽

Blade Cooling ◽

Blade Row ◽

The Impact

The focus of this paper is the impact of manufacturing variability on turbine blade cooling flow and, subsequently, its impact on oxidation life. A simplified flow network model of the cooling air supply system and a row of blades is proposed. Using this simplified model, the controlling parameters which affect the distribution of cooling flow in a blade row are identified. Small changes in the blade flow tolerances (prior to assembly of the blades into a row) are shown to have a significant impact on the minimum flow observed in a row of blades resulting in substantial increases in the life of a blade row. A selective assembly method is described in which blades are classified into a low-flow and a high-flow group based on passage flow capability (effective areas) in life-limiting regions and assembled into rows from within the groups. Since assembling rows from only high-flow blades is equivalent to raising the low-flow tolerance limit, high-flow blade rows will have the same improvements in minimum flow and life that would result from more stringent tolerances. Furthermore, low-flow blade rows are shown to have minimum blade flows which are the same or somewhat better than a low-flow blade that is isolated in a row of otherwise higher-flowing blades. As a result, low-flow blade rows are shown to have lives that are no worse than random assembly from the full population. Using a higher fidelity model for the auxiliary air system of an existing jet engine, the impact of selective assembly on minimum blade flow and life of a row is estimated and shown to be in qualitative and quantitative agreement with the simplified model analysis.

Download Full-text

Exploitation of Documented Historical Floods for Achieving Better Flood Defense

Advances in Meteorology ◽

10.1155/2016/2317252 ◽

2016 ◽

Vol 2016 ◽

pp. 1-9 ◽

Cited By ~ 1

Author(s):

Slobodan Kolaković ◽

Julius Fabian ◽

Sándor Kovács ◽

Ljubomir Budinski ◽

Matija Stipić

Keyword(s):

Numerical Model ◽

Interdisciplinary Approach ◽

Water Levels ◽

Flood Mitigation ◽

Stream Network ◽

Detention Ponds ◽

Extreme Flood ◽

Tisza River ◽

Flood Elevation ◽

The Impact

Establishing Base Flood Elevation for a stream network corresponding to a big catchment is feasible by interdisciplinary approach, involving stochastic hydrology, river hydraulics, and computer aided simulations. A numerical model calibrated by historical floods has been exploited in this study. The short presentation of the catchment of the Tisza River in this paper is followed by the overview of historical floods which hit the region in the documented period of 130 years. Several well documented historical floods provided opportunity for the calibration of the chosen numerical model. Once established, the model could be used for investigation of different extreme flood scenarios and to establish the Base Flood Elevation. The calibration has shown that the coefficient of friction in case of the Tisza River is dependent both on the actual water level and on the preceding flood events. The effect of flood plain maintenance as well as the activation of six potential detention ponds on flood mitigation has been examined. Furthermore, the expected maximum water levels have also been determined for the case if the ever observed biggest 1888 flood hit the region again. The investigated cases of flood superposition highlighted the impact of tributary Maros on flood mitigation along the Tisza River.

Download Full-text

Water Level Fluctuations in the Turawa Reservoir in Relation to the Tourist Use of the Water Body

Miscellanea Geographica ◽

10.2478/mgrsd-2008-0013 ◽

2008 ◽

Vol 13 (1) ◽

pp. 133-144

Author(s):

Andrzej T. Jankowski ◽

Marek Ruman

Keyword(s):

Water Level ◽

Water Body ◽

High Water ◽

Ecological Condition ◽

Water Levels ◽

Water Level Fluctuations ◽

Natural Factors ◽

Odra River ◽

The Impact ◽

First Time

Abstract The aim of the paper is to assess the fluctuations of water levels in the Turawa Reservoir (50° 43’ N, 18° 08’ E) in relation to the tourist use of the water body. The reservoir is situated within the macroregion of the Silesian Lowland in the mesoregion of the Opole Plain. In administrative terms, the reservoir is situated in the pole Province within the borough of Turawa. In hydrological terms, in turn, it is situated in the catchment area of the Mała Panew river, which belongs to the basin of the Odra river. The Turawa Reservoir was opened for use in 1938, and in 1948 it was filled with water to its maximum for the first time. At present, the surface area of the reservoir, when it is filled with water to its maximum, is about 20.8 km2, its volume 99.5 mln m3, and its depth exceeds 13 meters. In the period of hydrological years 1976-2000 water levels in this reservoir were characterized by high, unnoticed in natural conditions, amplitudes of changes reaching 6.99 m. Anthropogenically stimulated fluctuations in the water level result in conflicts in terms of tasks and functions that the Turawa Reservoir was designed for. Changes in the level of the water surface in the Turawa Reservoir resulted from the impact of the natural factors (thaw and rainfall related high water levels), as well as anthropogenic ones (the need to improve sailing conditions, water supply for industrial and municipal needs). Decreasing the fluctuations of water levels in the Turawa Reservoir is necessary in order to maintain its tourist-recreational functions and keep the ecological condition of its waters at the appropriate level.

Download Full-text

A Selective Assembly Method to Reduce the Impact of Blade Flow Variability on Turbine Life

Volume 5: Turbo Expo 2004, Parts A and B ◽

10.1115/gt2004-53930 ◽

2004 ◽

Cited By ~ 2

Author(s):

Vince Sidwell ◽

David Darmofal

Keyword(s):

Turbine Blades ◽

High Flow ◽

Metal Temperature ◽

Low Flow ◽

Inlet Temperature ◽

Selective Assembly ◽

Turbine Inlet Temperature ◽

Assembly Method ◽

Turbine Inlet ◽

The Impact

A selective assembly method is proposed that decreases the impact of blade passage manufacturing variability on the life of a row of cooled turbine blades. The method classifies turbine blades into groups based on the effective flow areas of the blade passages, then a row of blades is assembled exclusively from blades of a single group. A simplified classification is considered in which blades are divided into low-flow, nominal-flow, and high-flow groups. For rows assembled from the low-flow class, the blade plenum pressure will tend to rise and the individual blade flows will be closer to the design intent than for a single low-flow blade in a randomly-assembled row. Since the blade metal temperature is strongly dependent on the blade flow, selective assembly can lower the metal temperature of the lowest-flowing blades and increase the life of a turbine row beyond what is possible from a randomly-assembled row. Furthermore, the life of a nominal-flow or high-flow row will be significantly increased (relative to a randomly-assembled row) since the life-limiting low-flow blades would not be included in these higher-flowing rows. The impact of selective assembly is estimated using a model of the first turbine rotor of an existing high-bypass turbofan. The oxidation lives of the nominal-flow and high-flow blade rows are estimated to increase approximately 50% and 100% compared to randomly-assembled rows, while the life of the low-flow rows are the same as the randomly-assembled rows. Alternatively, selective assembly can be used to increase turbine inlet temperature while maintaining the maximum blade metal temperatures at random-assembly levels. For the nominal-flow and high-flow classes, turbine inlet temperature increases are estimated to be equivalent to the turbine inlet temperature increases observed over several years of gas turbine technology development.

Download Full-text

Mekong River flow and hydrological extremes under climate change

Hydrology and Earth System Sciences ◽

10.5194/hess-20-3027-2016 ◽

2016 ◽

Vol 20 (7) ◽

pp. 3027-3041 ◽

Cited By ~ 69

Author(s):

Long Phi Hoang ◽

Hannu Lauri ◽

Matti Kummu ◽

Jorma Koponen ◽

Michelle T. H. van Vliet ◽

...

Keyword(s):

Climate Change ◽

River Flow ◽

High Flow ◽

Mekong River ◽

Low Flow ◽

Future Climate Change ◽

Climate Projections ◽

Low Flows ◽

Hydrological Extremes ◽

Hydrological Impact

Abstract. Climate change poses critical threats to water-related safety and sustainability in the Mekong River basin. Hydrological impact signals from earlier Coupled Model Intercomparison Project phase 3 (CMIP3)-based assessments, however, are highly uncertain and largely ignore hydrological extremes. This paper provides one of the first hydrological impact assessments using the CMIP5 climate projections. Furthermore, we model and analyse changes in river flow regimes and hydrological extremes (i.e. high-flow and low-flow conditions). In general, the Mekong's hydrological cycle intensifies under future climate change. The scenario's ensemble mean shows increases in both seasonal and annual river discharges (annual change between +5 and +16 %, depending on location). Despite the overall increasing trend, the individual scenarios show differences in the magnitude of discharge changes and, to a lesser extent, contrasting directional changes. The scenario's ensemble, however, shows reduced uncertainties in climate projection and hydrological impacts compared to earlier CMIP3-based assessments. We further found that extremely high-flow events increase in both magnitude and frequency. Extremely low flows, on the other hand, are projected to occur less often under climate change. Higher low flows can help reducing dry season water shortage and controlling salinization in the downstream Mekong Delta. However, higher and more frequent peak discharges will exacerbate flood risks in the basin. Climate-change-induced hydrological changes will have important implications for safety, economic development, and ecosystem dynamics and thus require special attention in climate change adaptation and water management.

Download Full-text

Flood Inundation Mapping of Low-, Medium-, and High-Flow Events Using the AutoRoute Model

10.5194/nhess-2019-180 ◽

2019 ◽

Author(s):

Michael L. Follum ◽

Ahmad A. Tavakoly ◽

Joseph L. Gutenson ◽

Ricardo Vera

Keyword(s):

Computational Efficiency ◽

Regional Scale ◽

High Flow ◽

Low Flow ◽

Flood Inundation ◽

Post Processing ◽

Hydrologic Modelling ◽

Continental Scale ◽

Modelling Framework ◽

Extreme Flood

Abstract. This article presents improvements and development of a post-processing module for the regional scale flood mapping tool, AutoRoute. The accuracy of this model to simulate low, medium, and high flow rate scenarios is demonstrated at seven test sites within the U.S. AutoRoute is one of the tools used to create high-resolution flood inundation maps at regional- to continental-scales. The model has previously only been tested using extreme flood events. In this article flood inundation results for low-flow events are shown to be accurate (average F value of 63.3 %) but tend to be overestimated, especially in flatter terrain. Higher-flow scenarios tend to be more accurately simulated (average F value of 77.5 %). Additionally, modifications to the AutoRoute model and post-processing scripts are shown to improve computational efficiency (i.e. simulation time) by over 40 % when compared to previous versions. With improved computational efficiency and the ability to accurately simulate both low and high flow scenarios the AutoRoute model may be well suited to provide first-order estimates of flooding within an operational, regional- to continental-scale hydrologic modelling framework.

Download Full-text

Water discharge and sediment flux changes in the Lower Mekong River

Hydrology and Earth System Sciences Discussions ◽

10.5194/hessd-2-2287-2005 ◽

2005 ◽

Vol 2 (6) ◽

pp. 2287-2325 ◽

Cited By ~ 15

Author(s):

X. X. Lu ◽

R. Y. Siew

Keyword(s):

Water Discharge ◽

Sediment Concentration ◽

Dry Season ◽

Water Levels ◽

Sediment Flux ◽

Mekong River ◽

Water Level Fluctuations ◽

Main Stream ◽

Discharge Water ◽

Ecological Changes

Abstract. The Lower Mekong River has witnessed extremely low water levels over the past few years. There is speculation that the changes are a consequence of the construction and operation of the Chinese cascade dams in the upper part of the Mekong main stream, the Lancang River. Dam construction on upper streams can produce a series of induced effects downstream, particularly in terms of water, sediment, channel and ecological changes. The infilling of the Manwan reservoir in 1992 caused water levels to fall to record lows in various parts of the Mekong River, and sediment concentration values decreased similarly. Analyses of discharge and sediment flux at various gauging stations on the Lower Mekong River have indicated a disruption in water discharge, water fluctuations and sediment transport downstream of the Manwan Dam, after its reservoir was infilled in 1992. Dry season flows showed a declining trend, and water level fluctuations in the dry season increased considerably in the post-dam (1993–2000) period. Monthly suspended sediment concentration (SSC) has also decreased significantly in several gauging stations in the post-dam period. The estimation of sediment flux is challenging since the measurements of SSC were sporadic. Our estimation based on the available data indicated that the areas along the upper-middle and lowermost reaches of the Mekong River have experienced a decline in sediment flux, possibly due to sedimentation in the Manwan Dam. However, the decrease is only statistically significant at Chiang Saen. Areas located in the mid-length of the river show less sensitivity to the operation of the Manwan Dam, as sediment fluxes have remained stable or even increased in the post-dam period.

Download Full-text

Water discharge and sediment flux changes over the past decades in the Lower Mekong River: possible impacts of the Chinese dams

Hydrology and Earth System Sciences ◽

10.5194/hess-10-181-2006 ◽

2006 ◽

Vol 10 (2) ◽

pp. 181-195 ◽

Cited By ~ 182

Author(s):

X. X. Lu ◽

R. Y. Siew

Keyword(s):

Water Discharge ◽

Sediment Concentration ◽

Dry Season ◽

Water Levels ◽

Sediment Flux ◽

Mekong River ◽

Water Level Fluctuations ◽

Main Stream ◽

The Past ◽

Ecological Changes

Abstract. The Lower Mekong River has witnessed extremely low water levels over the past few years. There is speculation that the changes are a consequence of the construction and operation of the Chinese cascade dams in the upper part of the Mekong main stream, the Lancang River. Dam construction on upper streams can produce a series of induced effects downstream, particularly in terms of water, sediment, channel and ecological changes. Analyses of discharge and sediment flux at various gauging stations on the Lower Mekong River have indicated a disruption in water discharge, water fluctuations and sediment transport downstream of the first Chinese dam among the 8 cascades (i.e. the Manwan Dam), after its reservoir was infilled in 1992. Dry season flows showed a declining trend, and water level fluctuations in the dry season increased considerably in the post-dam (1993–2000) period. Monthly suspended sediment concentration (SSC) has also decreased significantly in several gauging stations in the post-dam period. The estimation of sediment flux is challenging since the measurements of SSC were sporadic. Our estimation based on the available data indicated that the areas along the upper-middle and lowermost reaches of the Mekong River have experienced a decline in sediment flux, possibly due to sedimentation in the Manwan Dam. However, the decrease is only statistically significant at the nearest gauging station below the Dam (i.e. Chiang Saen). Areas located in the mid-length of the river show less sensitivity to the operation of the Manwan Dam, as sediment fluxes have remained stable or even increased in the post-dam period.

Download Full-text