Hydrodynamic and water quality 3D modelling of the Nam Theun 2 Reservoir (Lao PDR): predictions and results of scenarios related to reservoir management, hydrometeorology and nutrient input

Abstract

Hydrodynamic and water quality 3D modelling of the Nam Theun 2 Reservoir (Lao PDR): predictions and results of scenarios related to reservoir management, hydrometeorology and nutrient input Modélisation 3D de l'hydrodynamique et de la qualité d'eau du réservoir de Nam Theun 2 : prédictions et résultats de scénarios liés à la gestion du réservoir, à l'hydrométéorologie et à l'apport de nutrimentsV. Chanudet (1) , J. Smits (2) , J. Van Beek (2) , P. Boderie (3) , F. Guérin (4,5,6) , D. Serça (7) , C. Deshmukh (7 Abstract -A 3D water quality model has been applied to predict medium term evolution of the water quality in the Nam Theun 2 Reservoir and also to quantify the effect of various scenarios. 15-year simulations show that the oxygen concentration will continue to increase in the water column although the hypolimnion will remain anoxic in some areas of the Reservoir. In parallel, the concentration of reduced compounds will decrease with time. The significance of the hydrodynamics in water quality evolution is pointed out with two scenarios in which natural or human forcings have been modified. The comparison of simulations made for years with contrasted hydrometeorological conditions shows that and duration of major hydrometeorological related events (rainfall, flood and air temperature drop) have a major influence on the seasonal evolution of water quality in the whole Reservoir. Simulations also show that the physico-chemical quality of the water released downstream of the power house would have been different if the commissioning had been carried out immediately after the impoundment. Finally, the model has been used to quantify the impact of an increase of the NO 3 -and PO 4 3-incoming flux consecutive to potential changes in the watershed land use. The fluxes have been multiplied by a factor two separately (2 scenarios) and together. While the additional load of NO 3 -has almost no impact on physico-chemistry and phytoplankton activity, the INTRODUCTIONWater quality in reservoirs depends on many parameters and processes, including hydrodynamics. Interactions are so numerous (Stumm & Morgan, 1996) that it is difficult to predict or assess precisely the effect on water quality of a modification of forcing data (from change in the watershed to global change). A possible approach to overcome this difficulty is numerical modelling. Since the 1970s many water quality and ecological processbased models have been developed (Jorgensen et al., 1996) and the studies of water quality and ecosystem problems with numerical models are increasing rapidly (Cerco & Cole, 1993;Jorgensen, 1999;Gin et al., 2001;Arhonditsis & Brett, 2005;Chao et al., 2007). Some well-established threedimensional water quality models have been successfully applied to simulate water quality variables in rivers, lakes, estuaries and ocean environments (Cerco & Cole, 1995;Luyten et al., 1999;Antenucci et al., 2000;Wool et al., 2001;Hydroqual, 2004;Romero et al., 2004; Danish Hydraulic Institute, 2001;Deltares, 2013). This type of model has be...

First Assessment of Inorganic Nitrogen Deposition Budget Following the Impoundment of a Subtropical Hydroelectric Reservoir (Nam Theun 2, Lao PDR)

“…This is a transbasin hydroelectric reservoir that diverts water from the Nam Theun River (a Mekong tributary) to the Xe Bangfai River (another Mekong tributary). The reservoir was described in detail in Descloux et al (), and the carbon cycle and especially the greenhouse gas emissions were monitored since impoundment (Chanudet, Guédant, et al, ; Chanudet, Smits, et al, ; Deshmukh et al, , ; Guérin et al, ; Serça et al, ). The reservoir surface fluctuated from 140 km 2 (525.5 m above sea level) to around 490 km 2 at the full water level (538 m above sea level) between 2009 and 2013.…”

A Case Study of Fisheries Governance and Management in a Reservoir of Lao PDR: Perspectives for Improvement

“…The environment of the reservoir has been subject to multiple studies [20], starting with a hydrodynamic and water quality model based on the monitoring of 15 parameters [37]. A 3D model allows assessing the impact of watershed management on the primary productivity of the reservoir [38,39]. Plankton monitoring indicates the trophic status of the reservoir [20,40], but results have not been used to predict the evolution of fish stock.…”

Assessment of water quality variations due to operation of wastewater treatment plant in Ca Mau city

“…Several models have been applied in wastewater dispersion simulation, such as QUAL2K (or Q2K), DELFT 3D, and MIKE, all of which obtained favorable results in forecasting work in the early stages [1][2][3][4][5][6][7][8]. In this article, the MIKE model -software of the Danish Hydraulic Institute, has been selected to apply in the calculation of hydraulics and resources -environment, including rivers, estuaries, and coastal areas, and the sea.…”