# Study of the Dynamic Adaptive Calculation Method for River Water Environmental Capacity
## 3 Methodology
### Dynamic Adaptive Calculation Method for Water Environmental Capacity
#### 3.2.2 Calculation Model and Method
The normal period is from March to June, the wet period is from July to October, and the dry period is November and December, and January and February of the following year. In each hydrological year, the average flow for each water period is used as the empirical point data, and the P-III curve is selected to obtain the theoretical frequency curve. Then, the flow values at different design frequencies (such as 90%, 75%, and 50%) are obtained from the curve. The idea of calculating the design flow for a water period according to a typical year method is to select the monthly flow data from a long series of a hydrological station. The typical year should be selected according to the conventional method. The step is to select a series of monthly flow data from a hydrological station, taking the annual average flow of the hydrological year as the empirical point data, and using the P-III curve to obtain the theoretical frequency curve. From this curve, typical years at different design frequencies (such as 90%, 75%, and 50%) are obtained. The average flow of the wet, normal, and dry periods corresponding to the 90% typical year is the design flow value of each water period at 90% frequency, and the design flow of the other design frequencies in each water period is calculated in turn. 3. Monthly scale design flow determination is divided into monthly frequency calculation design flow and typical year frequency calculation design flow. The basic idea of calculating the monthly design flow based on monthly frequency is to select the monthly flow data from a long series of hydrological stations, classify the monthly average flows for each hydrological year (from January to December), and use these as empirical point data. The P-III curve is used for wiring, and the theoretical frequency curve is selected. The monthly design flow at different design frequencies (such as 90%, 75%, and 50%) can be obtained. The idea of calculating the design flow at the monthly scale according to the typical year method is to select the monthly flow data from a long series of hydrological stations, use the annual average flow as empirical point data, use the P-III curve for wiring, and obtain the theoretical frequency curve. The typical years at different design frequencies (such as 90%, 75%, and 50%) can be obtained. The average flow of each month corresponding to a 90% typical year is the design flow of each month at a 90% frequency, and the design flow for each month at other design frequencies is calculated in turn. In this study, the fitting calculation process of P-III frequency curve is programmed by Java language. Users only need to provide the average flow, design frequency, and time scale to obtain the design flow. 1. Design flow velocity  
According to the measured flow velocity data provided in the hydrological yearbook, a flow velocity relationship curve is fitted and a flow velocity relationship equation is obtained. Then, the design flow velocity is calculated according to the design flow. (3) Water quality target concentration C\({}_{0}\), Cs  
Cs is the upper limit of the water environmental quality standard. The initial pollutant mass concentration C\({}_{0}\) was the target concentration of water quality in the previous functional zoning. (4) Comprehensive attenuation coefficient  
The comprehensive attenuation coefficient is used to describe the natural degradation rate of pollutants in water, reflecting the natural attenuation process of pollutants in the water environment without any artificial treatment. At present, the main methods for calculating the comprehensive attenuation coefficient include laboratory simulations, measured data inversion, the least squares method, and the steepest descent method.