Water Quality Modeling
The Water Quality Modeling Research Group focuses on developing, verifying and validating numerical models for simulating environmental water quality and pollutant transport processes. Water quality modules for one, two and three-dimensional models (CCHE1D-WQ, CCHE2D-WQ, and CCHE3D-WQ) have been developed and can be coupled with hydrodynamic and sediment transport models of NCCHE. These modules can be applied to simulate transport, chemical, and bio-chemical processes of water quality variables in natural rivers, streams, lakes and coastal waters.
CCHE1D-WQ module is for simulating processes in channel networks. It can be interfaced with a watershed model and used as a tool for evaluating watershed management practices.
CCHE2D-WQ module is for simulating water quality processes in streams, river channels, lakes and coastal waters. It is used as a module of the CCHE2D hydrodynamic and sediment transport model and can be used as a tool for evaluating water quality in these free surface flows with a variety of boundary conditions of flow, sediment and water quality.
CCHE3D-WQ module is for simulating water quality processes in river channels, lakes and coastal waters with cases of strong three-dimensionality. It is used as a module of the CCHE3D hydrodynamic and sediment transport model. This model should produce more realistic results when vertical distributions of flow and water quality variables are of concerns: stratification of temperature and concentrations occurs in the flows of water, or recirculation induced by wind shear stress.
Deep Hollow Lake watershed
The Water Quality Modeling Group has the mission:
Develop the state-of-the-art computational water quality models for simulating transport of pollutants and water quality constituents with chemical and biochemical processes in natural free surface flows and analyzing their impacts on environment. The water quality models can be used as tools for evaluating environmental control measures conducted by Environmental Protection Agencies and in agriculture practices.
The current research interests are focused on the following areas:
1. Conservative/non-conservative mass transport
Based on the mass transport equation, transport modules have been developed to couple with CCHE1D, CCHE2D and CCHE3D models. These modules are used to simulate transport and distribution of conservative or non-conservative mass concentrations in free surface flows. Transport modules are verified using analytical approach: numerical solutions are compared with the associated linear analytical solutions. A few verification cases have been tested using the mass transport module. For more details please click here.
2. Temperature distribution
A three-dimensional numerical module has been developed for the CCHE3D hydrodynamic model to simulate heat transfer in turbulent buoyant flows in open channels. The density and temperature stratification induced buoyant force is included in the flow simulation model, and the influence of temperature stratification on turbulence closure schemes is also considered. This module has been validated with experiment data. Click here for some test cases.
3. Water quality modeling
The formulations of CCHE1D-WQ, CCHE2D-WQ and CCHE3D-WQ for simulating eutrophication are all based on physical, chemical and bio-chemical processes in water bodies at different levels of complexity. These processes are generally related to environmental factors such as temperature, salinity, pH and sediment size and concentration etc. These processes comprise of cycles of carbon, oxygen, nitrogen, phosphorus and phytoplankton as well. The modules solve the unsteady convection-diffusion-reaction equations to determine the time-history of spatial distribution of simulated substances. The modules can make predictions of long- and short-term effects of environmental control measures.
At present the water quality modules simulate the processes in the water column. The influences of the processes in and near bed surface due to benthos are given as boundary conditions. The simulation of benthic processes is under development.
A module to simulate the fate of toxic substances in waters is under development. Heavy metals, organic substances such as PCB, DDT, etc. would be included. The interaction and exchange processes between toxicants, suspended sediments and bed materials would be simulated based on theoretical and empirical relationships.
3.3 Effects of sediment on the water quality processes
Sediment has been identified as the leading nonpoint-source pollutant. Excessive sediment reduces light or solar energy penetration needed for the growth of phytoplanktons. Nutrients interact with suspended sediments through the processes of adsorption and desorption in the water. In addition, nutrients contained in the sediment (mud) layers may be released from stream or lakebeds. To study these complex processes, the effects of sediment on the phytoplankton, nutrients and dissolved oxygen are considered in the water quality model.
Listed are past and current Water Quality Modeling Group projects:
1. Numerical simulation of water quality in Deep Hollow Lake
The Deep-Hollow lake is one of the oxbow lakes in North Mississippi, which has water quality problems due to excessive nutrients and sediment loads carried by runoff from surrounding agriculture lands. Fine sediments can affect the light attenuation. They are thus playing an important role in the ecological cycles of lakes. Various best management practices (BMPs) have been employed to reduce sediment load on the farm lands, water quality improvement of the lake are expected to be related to these BMPs. Both water quality modules, CCHE2D-WQ and CCHE3D-WQ, have been applied to simulate the physical and bio-chemical processes with boundary conditions of runoff, sediment concentration and nutrients.
The models were calibrated first to determine parameters for the flow, mass transport and water quality using measured data. Phytoplankton (as total chlorophyll) was simulated with inputs of nutrients, suspended sediments and related weather information. The influence of fine sediment on phytoplankton concentrations was simulated by accounting for its effect on solar radiation reduction. Results from a series of numerical experiments showed that the water quality in the lake could be improved if the sediment load were reduced.
1.1 Dye test cases
Measurements, Numerical solution
(a) T= 90minutes, H=0.5m
Measurements, Numerical solution
(b) T=180 minutes, H=0.5m
Measurements, Numerical solution
(c) T=300minutes, H=0.5m
Measurements, Numerical solution
(d) T=1500 minutes, H=1.25m
Comparison of simulated and measure dye concentration distribution in Deep Hollow Lake under the influence of near Northward wind condition.
Transport process in Deep Hollow is dominated by wind driving flow circulation, which has been observed by sampling released dye distribution at different times. This data set has been used for validating the mass transport simulation capability under wind driven condition.
1.2 Numerical simulation of water quality (CCHE3D-WQ)
Numerical simulation of nutrient concentration in Deep Hollow Lake (8/28/99-12/26/99)
Numerical simulation of chlorophyll concentration in Deep Hollow Lake(8/28/99-12/26/99)
2. Numerical simulation of water quality in Tualatin River (CCHE2D-WQ)
Tualatin River in northwestern Oregon used to have water quality violations in summer time. Total maximum daily loads (TMDLs) for nitrogen and phosphorus have been established and proved to be effective. During the study of TMDLs of this river, discharges and water quality constituents were measured in the main stem and tributaries in the low-flow summer periods for years. The CCHE2D hydrodynamic model was calibrated with this measurement. Eutrophication process involving interaction between nitrogen and phytoplankton was simulated with CCHE2D-WQ.
Unsteady Flow Simulation (1991)
Simulated and measured concentration of ammonia, nitrate+nitrite, and phytoplankton at RM 8.7
3. Numerical simulation of temperature in open curved channel
The temperature model is validated in an experimental case of a curved open channel with dimensions of 11.5?0.4?0.29m. At the inlet of the channel the thermally stratified flow is created by discharging two streams of water with different velocities and temperatures. For the upper warm water layer, the thickness is 0.02m, the temperature is 32 o C, the discharge is 0.00075 m3/s and the density is 995.05kg/m3; For the lower cold water layer, the thickness is 0.27m, the temperature is 22 o C, the discharge is 0.004890 m3/s and the density is 997.80kg/m3.
180 degree Open curved channel
Temperature distribution at 90 degree section
The 3D grid for the flow simulation and the resultant temperature distribution at the apex section of the channel.
(a) Measured results (b) Numerical results
Comparison of the measured and simulated secondary flow vectors at 90 degree cross-section
4. Model verification cases
Case. 1 Salinity intrusion
This is a simple 1-D estuary case with constant depth and river flow. Given the boundary condition at upstream river inflow S equals 0, at the downstream seaward S equals S0. Fig shows the salinity distribution along the channel.
Case.2 Continuous source discharged into the channel for a finite duration
Research Associate Professor
Dr. Yafei Jia
Dr. Dalmo Vieira
Visiting Research Associate
Dr. Xiabo Chao
Ms. Ting Ting Zhu
The CCHE1D-WQ module is for simulating processes in channel networks. It can be interfaced with a watershed model and used as a tool for evaluating watershed management practices.
CCHE2D-WQ is a module of the CCHE2D model. It simulates transport and chemical and bio-chemical processes of pollutants and water quality constituents in natural environments, such as rivers, lakes, etc. This module shares all the capabilities of the CCHE2D model such as simulating unsteady turbulent flows and sediment transport in complex natural hydraulic, geometric and topographic conditions. The module simulates transport of and interactions between phytoplankton’s, nutrients (dissolved and particulate nitrogen, phosphorous) and suspended sediments under a variety of conditions of dissolved oxygen, solar radiation, and temperature. The pollutant exchange processes between the flow and deposited sediments are currently under development. The graphic user interface for this module will also be made available to the public.
CCHE3D-WQ is a module of the CCHE3D model, it simulates transport and chemical and bio-chemical processes of pollutants and water quality constituents in natural environments, such as rivers, lakes, etc. This module shares all the capabilities of the CCHE3D model such as simulating unsteady turbulent free surface flows and sediment transport in complex natural hydraulic, geometric and topographic conditions. The module simulates transport of and interactions between phytoplankton’s, nutrients (dissolved and particulate nitrogen, phosphorous) and suspended sediments under a variety of conditions of dissolved oxygen, solar radiation and temperature. Flow circulation and mixing due to wind shear can also be simulated. The influence of deposited sediment on the water quality, the exchange processes of water quality variables in the flow and deposited sediments are currently under development. The graphic user interface for this module will also be made available to the public.
(1) Chao, X.B., Shankar, N.J.and Cheong, H. F. (2001), 2-D and 3-D Oil Spill Model for Coastal Waters, Ocean Engineering, Vol. 28, 1557~1573.
(2) Shankar, N.J., Chao, X.B. , Cheong H.F and Li, Y.Q.(2001), Numerical Simulation of Oil Spills in the Singapore Coastal Waters, In Recent Advances in Marine Science and Technology 2000, N. Saxena, Ed., PACON International, 177-188.
(3) Pavlo Tkalich and Chao, X.B. (2001), Accurate simulation of oil slicks, The 17th International Oil Spill Conference, Florida, USA, March 26~29(CD-ROM).
(4) Chao, X.B., Shankar, N.J. and Wang, S.S.Y(2003), Development and Application of a Three-Dimensional Oil Spill Model for Singapore Coastal Waters, ASCE Journal of Hydraulic Engineering, Vol. 129, No.7, 495~503.
(5) Chao, X.B., Jia, Y.F. and Wang, S.S.Y.(2004), Three Dimensional Numerical Simulation of Buoyant Flow and Heat Transfer in a Curved Open Channel, The 6th International Conference on Hydroscience and Engineering, Brisbane, Australia, May 30~June 3(CD-ROM).
(6) Chao, X.B., Jia, Y.F. and Shields, D.(2004), Three Dimensional Numerical Simulation of Flow and Mass Transport in a Shallow Oxbow Lake, World Water & Environmental Resources Congress 2004, ASCE, Salt Lake City, USA, June 27-July 1(CD-ROM).
(7) Chao X.B., Jia, Y.F. and Shields, D., Three Dimensional Numerical Simulation of Water Quality in a Shallow Oxbow Lake (in press).
(8) Zhu, T., Jia, Y. and Shields, F.D. Jr. (2004), Water Quality Modeling of Lake Using CCHE2D, Protection and Restoration of Urban and Rural Streams, Proceedings of the Symposium of World Water & Environmental Resources Congress 2003, Philadelphia, 306-315.
(9) Zhu, T., Jia, Y. and Wang, Sam S.Y. (2004), Validation of Two-dimentional Water Quality Model, Proceedings of the International Conference of Hydroscience and Engineering Brisbane, Australia (CD-ROM).