Modeling water quality management alternatives for a nutrient impaired stream using system dynamics simulation

A system dynamics (SD) simulation model is developed using an object-oriented modeling environment to simulate and analyze water quality management strategies for a nutrient impaired stream. An object-oriented simulation environment, STELLA, conceived on the principles of system dynamics (SD) is used for the development of the model. The modeling process consists of developing stock-flow diagrams and carrying out computer simulations using difference equations to integrate stocks and flows. The model structure and behavior of the system is validated using dimensionality, replication and sensitivity tests; and calibration along with validation is carried out using an appropriate model performance measure. The model helps the user to separate policy questions from the data and provides the facility to generate ‘what-if’ scenarios while keeping the modeling process transparent. Case study application of this model is illustrated by developing a total maximum daily load (TMDL) allocation strategy for a nutrient impaired stream in the southeastern region of Kentucky, USA. Results suggest that the fate and transport process of total phosphorus in a river system can be simulated using a conceptually simple object-oriented simulation model.