Water quality model, also known as water quality mathematical model, is a mathematical description of water quality change law. It can be used to predict water quality, study water pollution and self-purification, and control pollution discharge. Its types can be divided into single water quality index, coupled water quality index and aquatic ecological model, time-invariant steady-state model and time-varying unsteady-state model, zero-dimensional, one-dimensional, two-dimensional and three-dimensional models, etc. Its mathematical expression can be divided into differential equation, integral equation, algebraic equation, difference equation, differential difference equation and so on. According to the different water objects that describe the water body, it can be divided into river water quality model, estuary water quality model, lake (reservoir) water quality model, bay water quality model and underground water quality model.

Establishment of model

Take the river water quality model as an example. The mathematical model of river water quality is to describe the internal laws and relationships of physics, chemistry, biology and ecology in the process of river water pollution with mathematical language and methods, that is, to transform a complex river system into a set of suitable mathematical equations for mathematical simulation. Basic equation of river water quality model

Steps of establishing water quality model:

(1) Collect and analyze data and information related to modeling, and make preparations for modeling.

(2) According to the obtained information and data, select appropriate model variables, determine the mutual influence and change law between variables, write the best structural form of mathematical equations describing these relationships, and reflect the basic characteristics of describing phenomena.

(3) Some parameters in the model equation need to be determined in some way, such as empirical formula, indoor experiment or mathematical method. However, when determining the parameters, it is necessary to make the obtained values pay more attention to the observation data after being substituted into the model.

(4) After the water quality model is established, it is necessary to test whether the model structure is effective and predictive.

Classification method

There are many classification methods of water quality models, which can be divided into dissolved oxygen (DO) model, biochemical oxygen demand (BOD) model, heavy metal model and radioactive model. Biochemical oxygen demand (BOD) and dissolved oxygen (DO) are the two most important water quality indicators, which are often used as the basis for establishing organic water quality models.