Physical processes and hydrodynamic modeling in lakes and reservoirs

Transcription

1 Physical processes and hydrodynamic modeling in lakes and reservoirs

2 Surface Water Numerical Modeling Freshwater Saline Water Rivers Lakes and Reservoirs Coastal Ocean Estuaries introduction

3 A half of World Population (3 Billion) live in the coastal areas and estuaries Food, Life, Business, Industry everything depends on ocean and sea The Population in these areas will be doubled by 2025 Coastal ocean and Estuaries introduction

4 Pollution Control Is one of the most critical environmental concerns in the coastal areas Water quality and Ecosystem are mainly affected by the release of urban, industrial and agricultural waste and waste-water Coastal ocean and Estuaries introduction

5 Surface freshwater resources include only 0.88% of the whole usable water in the hydrosphere and beside the groundwater supply the needs for freshwater. Lakes and Reservoirs contain the 90% of reserved liquid surface freshwater. Lakes and Reservoirs introduction

6 Prediction of Water Quality in lakes and reservoirs is one of the most critical issues in the lake and reservoir environment and operations. Stratification and Eutrophication in the lakes and reservoirs lead to the degradation of water quality and the disability of the aquatic environment to supply in-lake and downstream ecosystem. Lakes and Reservoirs introduction

7 Water Resources Quality Management Observation Theoretical Analysis Numerical Modeling Hydrodynamic and Water Quality models are unavoidable to use in water resources management and studies now Complexity of natural aquatic environments Development in computational capabilities in temporal and spatial simulation of aquatic ecosystems Based on differential equations and numerical methods introduction

8 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

9 Unsteady Reynolds Averaged Navier-Stokes Equations (RANS) Transport of momentum Transport of scalars Governing Equations Vertical Mixing model

10 Fundamental Horizontal velocity evolution equations explicit implicit In semi-implicit schemes, a part of the equations is discretized explicitly the other part(s) is discretized implicitly L() operator: advective discretization B() baroclinic discretization D() horizontal turbulent diffusion discretization Semi-implicit Discretization

11 The model is unconditionally stable for purely barotropic flows. for stratified flows, the model uses explicit discretization of the baroclinic terms in the momentum equation leading to a time step constraint based on the internal wave Courant-Friedrichs-Lewy condition (CFL). Stability constraint for semiimplicit schemes with explicit horizontal diffusion: is the viscous stability condition, derived for homogenous flows TimestepLimitations

12 Named TRIM, by Kassuli 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 Method. (Semi-Implicit Finite difference) Numerical Method

13 Water Quality Models Contaminants Nutrients (N-P-C-Si) Biochemical model Air-Surface interactions Algae.Fish.Bacteria.Zooplankton Seagrass Sediment-Water Interactions Diagenesis

14 Physical L Processes in lakes and reservoirs introduction

15 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

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

17 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

18 Warm Water Cold Water By: Todd Carlson Sather Source: youtube Freshwater Saline Water Density currents By: Claudio Andres Iturra Ulloa University of Concepcion Chile Source: youtube

19 Tehran, Iran, 2014 Kuwait, 2011 Turbidity currents introduction

20 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

21 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

22 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

23 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

24 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

25 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

26 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

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

28 Bathymetry materials and methods

29 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

30 Conclusions

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

32 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

33 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

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

35 Conclusions A different response of the reservoir in the two connected basins. Despite of thermodynamics, the connecting canyon between two impoundments separates the hydrodynamic behaviour of two connected impoundments. The lacustrine zone before canyon enforces the turbidity currents to be entrapped mostly in the upstream impoundment and the downstream impoundment 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

36 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

37 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