Watershed Hydrological Simulation

I. Concepts

Basin hydrological simulation is a simulation of the hydrological process occurring on the basin, and a mathematical model is built and implemented on a computer. Consider a river basin as a system, know its input, and require its output. During calculation, the state of the system, that is, the hydrological process occurring on the watershed, should be simulated and calculated. The input is a rainfall process, excluding snow melting, water quality, sediment, etc. Therefore, a rainfall runoff basin model is established, and the output of the system is the flow process of the exit section of the watershed. Another input is the steam emission capacity of the watershed, and its corresponding output is the actual steam emission of the watershed, which forms a complete watershed water balance computing system. The state of this system is soil humidity, storage of river slots and groundwater, and so on.

There are multiple types of hydrological models, including deterministic models and uncertainty models. The deterministic model is divided into the Black Box Model and the conceptual model. We need to use a conceptual model to simulate the hydrological process occurring on the watershed. It is a physical concept model, it can also be called a white box model.

Ii. Overview of hydrological methods before the conceptual model, several types of methods were used in the application of hydrology: 1) mathematical and physical methods; 2) Unit Line Method; 3) Experience-related; 4) generalized reasoning; 2) for the unit line method, see: the Unit line method is used to calculate the flood process at the exit of the watershed. 3. The hydrological simulation technology is used to combine the above four methods. The so-called simulation is to simplify the objective conditions, remove secondary and occasional factors, and retain the primary and basic rules, based on this condition, a physical equation or logical formula is established for calculation. A conceptual model must be a mathematical model that can be implemented on a computer. The concept of the model is exactly the same as that of a computer. The calculation steps and methods of the model are called structures.It is equivalent to a computer program, which can be expressed in a block diagram or a flowchart. In the model structure, Certain parameters are required to specify the hydrological characteristics of the watershed.This is equivalent to the constant to be read in a computer program. With the structure domain parameters, the hydrological laws and characteristics of the watershed are completely described. As long as there is input, the corresponding output can be calculated. As for the model status, it is a variable, which can be completely calculated by the model, not a real measurement. The model is the structure plus parameters. The purpose of Hydrological Simulation is to determine the structure and parameters of the model. The structure is constructed based on our understanding of the hydrological laws. The parameters are the hydrological characteristics of the watershed and are hydrological data that can be measured in principle. Therefore, to determine the structure and parameters of the model, we do not have to have the hydrological data of the actual measurement, as long as there are topographic and geological data. However, we usually use the tested hydrological data to test the structure and parameters and use the preferred method to evaluate the parameters of the model. This is a method to identify the nature of the model and make up for the shortcomings of other materials. The model's computing scheme is not only completely objective, but also completely agreed without internal conflicts. The model needs to simulate the process, so it uses the recurrence format of time periods. One year is added by day, and one time is the sum of time periods, during which there is no conflict in process division. The calculation method applies to all time periods without any conflicts in reasoning. Only by doing so can the model be of universal significance. Its structure can be used in a wide range of regions, and its parameters have Regional Regularity. The model is not only a tool, but also a hydrological rule and scientific. Only the two ends of rainfall and runoff are known, and there is no actual measurement data in the intermediate process. Therefore, whether it is a black box model, experience-related model, or a conceptual model, the application accuracy is similar, only when the intermediate process is measured and strictly calculated by mathematical and physical methods can the level be improved. The physical concepts in the conceptual model are virtual and have not been proved by actual tests. Therefore, any method with high accuracy does not need to be investigated for its objective regularity and scientific nature.

Watershed Hydrological Simulation