Physical processes and hydrodynamic modeling in lakes and reservoirs

Transcription

1 Physical processes and hydrodynamic modeling in lakes and reservoirs Thesis: Comparison of the 3D hydrodynamic models and predicting the response of reservoirs to climate change effects Behnam Zamani * Supervisor: Prof. Manfred Koch * Co-supervisor: Prof. Ben R. Hodges ** * University of Kassel, Germany ** The University of Texas at Austin, USA

2 Physical Limnological Processes introduction

3 Global warming and lakes: Increased nutrient loading is leading to increased water column stability Lower oxygen concentrations at depth of deep lakes and reservoirs around the world Many reservoirs are being drawn down due to decreases in runoff Surface heat flux and buoyancy fluxes are being affected Global Warming global warming impacts are adversely effecting the ecosystem health of all deep standing waters introduction

4 Heat transfer. Stratification and mixing. Scalar mixing and transport. Wind energy and wind induced momentum. Solution of Free surface evolution and velocity equation. Horizontal diffusion of momentum and scalars. Advection of scalars Hydrodynamic Models introduction

5 Lake Opeongo South Canada Maroon Reservoir Southwest Iran My cases to be studied introduction

6 4th European Large Lakes Symposium ELLS2015 August Joensuu, Finland Simulation of the movement of a turbid density current during a flood event in a large reservoir with complex morphology (Maroon reservoir, southwest Iran) * University of Kassel, Germany ** The University of Texas at Austin, USA by: Behnam Zamani * Manfred Koch * Ben R. Hodges ** Photo: Lake Pyhäselkä, Joensuu, Finland

7 When a flood enters a reservoir, it entrains suspended solids as a turbid density current which then plunges along the thalweg Depending on the magnitude and characteristics of the density variations, density currents can enter the epilimnion, metalimnion, or hypolimnion. In arid and semiarid regions, rivers entrain large amounts of sediments with high fraction of fine silt and clay. Density currents introduction

8 The fine portion of the current may remain suspended for several months. Turbidity caused by density currents directly affects the entire ecosystem in reservoirs. Effects: Changing the light penetration in vertical water column over a long period which: alters adversely the primary production and the distribution of biotic organisms and fish there. introduction

9 Maroon reservoir: Rockfill dam with clay core Volume: 1200 mcm Area: 24.6 km2 Thalweg length: 30 km Max. depth: 115 m Upstream watershed: 3840 km2 Operating since: 2000 Limnological Class. : Warm-monomictic introduction

10 our Questions and Objectives How turbidity currents propagate and move in the deep narrow reservoir? Reservoir stratification and mixing processes How different are the two connected basins in responding to the turbidity currents? How the very narrow connection between two basins affects the currents? Revising the management strategies Maroon reservoir in southwest Iran Simulating Turbid density currents What are the benefits and limitations of the hydrodynamic models in simulating deep-narrow water bodies? Assessment of the withdrawal and outlets operations predicting the effect on reservoir & downstream ecosystem introduction

11 ELCOM (Estuary, Lake and Costal Ocean Model) A 3D- hydrodynamic flow and transport model Simulating, temporal variations of flow temperatures and densities in stratified lakes and reservoirs with environmental forcing Numerically solving the Reynolds-averaged Navier-Stokes (RANS) equation for flow by a Finite Difference scheme. CAEDYM (Computational Aquatic Ecosystem Dynamics Model) Comprehensive process representation of the C, N, P, Si and DO cycles Several size classes of inorganic suspended solids Phytoplankton dynamics and numerous optional biota MIKE-3 by DHI Solves the equations for the conservation of mass and momentum, salinity and temperature in response to a variety of forcing functions. Includes several modules to be coupled to simulate ecosystem (Ecolab), sediment transport (Mud transport), Oil spill etc. Density variations can be treated in different manners and radiation stresses from wave simulations can be readily included. materials and methods

12 Named TRIM-3D, by Cassuli and Cheng (1992), this method numerically solves the governing differential equations C-grid by Arakawa (1997), is the method to create the grid for Finite Difference scheme (Semi-Implicit Finite difference) Numerical Method materials and methods

13 Bathymetry and dam structure info. Inflow Sed. and Temp. data Hydrological data Meteorological data of the site Water Column turbidity data Water Column temperature data Used data and Boundary conditions materials and methods

14 Model discretization: Horizontal: 200X200 m Vertical: 1m Bathymetry and ELCOM model mesh materials and methods

15 Bathymetry materials and methods

16 Maroon River measured suspended sediment data Soil Average density Perecentage class (kg/m3) D50 (mm) Clay 35 % E-03 Silt 58 % E-03 Sand 7 % E+00 Suspended sediment settings of CAEDYM model SS class Soil class Precentage Average density (kg/m3) D50 (mm) Critical Shear Stress (N/m2) SSOL1 Clay E E-02 SSOL2 Silt+Sand E E-02 Suspended Sediment information materials and methods

17 Results

18 Height above lakebed (m) Height above lakebed (m) Height above lakebed (m) Turbidity and water level 5 4 Station E 3 Feb 18:00 Water level TSS (mg/l) 11 Feb 09:00 11 Feb 18: TSS (mg/l) TSS (mg/l) Exp Model Results

19 Depth (m) Depth (m) Measured Temperature C Depth (m) R² = RMSE= 0.31 C Simulated Temperature C Feb 15 Water Temperature ( C) Water temperature results Feb 8 Water Temperature ( C) Feb 25 Water Temperature ( C) Measured Model Results

20 Canyon Elevation (m above sea level) Simulation Period: JAN 25 MAR 8 Inflow Inflow water temp. ( C) Water temp. ( C) Outflow Air temp. ( C) Fine Portion SS (mg/l) Inflow rate (cms) Coarse Portion SS (mg/l) Results

21 Surface layer -50 m (below N.O.L.*) -80 m (below N.O.L.) * N.O.L.: Normal Operating Level Results

22 Conclusions A different response of the reservoir in the two connected basins. Despite of thermodynamics, the connecting canyon between two basins separates the hydrodynamic behaviour of two connected basins. The lacustrine zone before the canyon enforces the turbidity currents to be entrapped mostly within the upstream basin and the downstream basin is affected less by the density currents with a relatively long lag. Pro and Cons 3D hydrodynamic models can capture the boundary mixing and internal-wave-driven pumping of the benthic boundary layer very well in sloping boundaries which are very important in simulating the turbidity current underflows. In ELCOM-CAEDYM, Having no possibility to define buttom slopes, limits the accuracy of predictions in the benthic boundaries Conclusions

23 Simulating the further scenarios with other set up configurations in order to investigate the effects of: Multi-Inflows from ungauged tributaries (by a tracer analysis) Summer stratification on the movement patterns of the currents Different reservoir management strategies in controlling the turbidity currents Simulating the effects of the turbidity originated from density-currents on the ecosystem of Maroon reservoir To be continued Conclusions

24 Thank You! Behnam Zamani University of Kassel Dept. of Geohydraulics and Eng. Hydrology Kurt-Wolters-Str Kassel, Germany behnam.zamani@uni-kassel.de Ministry of Natural Resources and Forestry