What Are the Different Hydrology Jobs?

Hydrological elements are the main factors that make up the hydrological situation in a certain place or area at a certain time. They are the main physical quantities to describe the hydrological situation. They are the measurement methods used to describe the movement of the water. Hydrological elements can be obtained through hydrological surveys, observations and calculations.

Hydrological elements include hydrological phenomena of various hydrological variables. Precipitation, evaporation and runoff are basic elements of the hydrological cycle. At the same time, water level, velocity, flow rate, water temperature, sand content, ice and water quality are also listed as hydrological elements. ^[1]

The evaluation of water resources mainly includes the basic elements of hydrological cycle such as precipitation, evaporation, runoff, surface water resources, groundwater resources, total water resources, available water resources and other evaluation results, as well as their dynamic evolution and regional distribution.

The recurrence period has been widely used in engineering planning, design, operation and management. In the hydrological frequency analysis calculation, the calculation of the recurrence period has always been based on consistency. In the past century, climate change and human activities have caused very drastic changes in the global environment, and the evolution of the hydrological situation caused by such drastic changes has subverted the consistent premise of engineering hydrological frequency analysis and calculation. Milly et al. ^[3] also pointed out in the journal Science that under the influence of climate change and human activities, the theory and method of hydrological probability distribution estimation based on consensus assumptions have been unable to help people correctly reveal the evolution of water resources and floods in changing environments. It is a long-term rule that if we continue to use existing engineering hydrological analysis methods to formulate river basin development and utilization engineering schemes, flood control and drought resistance engineering operation scheduling schemes, etc., we will face risks brought by changing environments. Therefore, how to establish the calculation method of the recurrence period under the inconsistent conditions caused by the changing environment has very important theoretical and practical significance for assessing risk and engineering risk management. Based on the definition of the recurrence period, this paper summarizes the calculation method of the recurrence period under the consistent condition, and derives the formula for the calculation of the recurrence period under the non-consistent condition. The main problems faced. ^[4]

Definition of recurrence period of hydrological elements

There are usually two definitions of the recurrence period. The first definition is: in a randomized trial,

Figure 1 Explanatory diagram of the definition of the recurrence period

The average number of random trials before encountering a certain event of interest (DD ₀ , D ₀ is a critical value or design value); for example, if D ₀ is a certain design flood peak, if more than D ₀ flood event, and there are limited ( = 0, 1, ...) time periods from the time of operation, then after the project starts running, it will encounter the average number of time periods N greater than this design flood peak for the first time. (That is, the return period). The second definition is: the average number of periods W between successive occurrences of a certain event of interest (DD ₀ ). The above two definitions can be further explained with reference to FIG. 1. The second definition focuses on the average recurrence interval of a random event (DD ₀ ), that is, how often the average interval of the event occurs once, and how often is it encountered once, and in the first definition Emphasize the number of time periods required for the project to encounter this random event for the first time (DD ₀ ). If a random event (DD ₀ ) occurs at the beginning of the project, that is, = 0 (see Figure 1), at this time, the random variable N and the random variable W have the same value, then the first definition and the second definition The expressed recurrence period is the same size. Because the sampling method usually uses the maximum value in a certain period in the analysis of hydrological frequency, the sample independence is easier to meet. Therefore, this paper mainly studies the calculation of the recurrence period under the conditions of consistency and non-consistency.

Calculation method of recurrence period under the condition of consistency of hydrological elements

According to the first definition of the return period, the calculation of the return period can use the following formula:

Among them, P (T = n | n> ) = P ((D ₁ D ₀ , D ₂ D ₀ , ..., D _n-1 D ₀ , D _n > D ₀ ) | n> ), In the calculation of hydrological frequency, the hydrological series meets the requirements of independence.

Hydrological Elements Research Conclusions

Due to the strengthening of climate change and the impact of human activities, the consistency in traditional hydrological frequency analysis calculations has been destroyed, making the consistency-based calculation formula for the return period no longer applicable. The calculation of the recurrence period has not yet received enough attention. Under the premise of introducing two different definitions of the recurrence period, this paper summarizes and deduces the calculation method of the recurrence period under the conditions of consistency and non-consistency, and takes the year's largest flood peak series of Longchuan Station in Guangdong Province from 1956 to 2009. The data is taken as an example to compare and analyze the calculation of the recurrence period under different conditions.

(1) Due to the significant downward trend in the annual sample of the largest flood peak series at Longchuan Station, if the sequence is still assumed to be consistent, the calculated recurrence periods under different definitions are greater than those under non-consistent conditions that consider the downward trend. Return period.

(2) There are two different definitions of the recurrence period. The recurrence period under the first definition takes into account that a specific random event has not occurred within the period , so the calculation of the occurrence of the event in the remaining period is calculated. The probability increases and the recurrence period decreases; and because the Hongfeng series of Longchuan Station used in the example has a downward trend, the recurrence period under non-consistent conditions is much longer than that under consistent conditions.

(3) Although the hydro-frequency analysis method based on time-varying moments takes into account the inconsistency of the Hongfeng series and uses time as a variable, it is impossible to calculate a considerable period in the future because the Hongfeng series cannot maintain an indefinite downward trend indefinitely. The frequency of internal flood peak events, so the value of i in the formula for calculating the non-consistent recurrence period cannot approach infinity. This is also the main problem faced in the non-uniform hydrological frequency analysis method based on time-varying moment, that is, when using time as a variable to fit the trend of the mean and variance, delaying the time variable outside the time will not meet the actual situation For example, a downward trend can cause the parameter to be negative, while an upward trend can cause the parameter to go to infinity. Therefore, when this method is used to calculate the recurrence period under non-consistent conditions, the calculation result will be biased. Reasonable non-consistent hydrological frequency analysis and calculation methods are also the main challenges in the field of hydrological frequency analysis and calculation. ^[5]