The Yellow River Delta Wetland Water Cycle Simulation Model Research

Yellow River Delta wetland is located in the warm temperate zone, which belongs to the typical open coastal wetlands. Because of its unique geographical position, the relationship between the hydrological status indicators and wetland inflow plays an important role for flood controlling, water cleaning, biodiversity protecting and so on. However, in recent years, affected by the change of regional climate and the impact of human activities, the eco-hydrological situation of the Yellow River Delta wetland changed significantly, and the wetlands degraded seriously. Based on the characteristics of the water cycle of the Yellow River Delta wetland, a wetland water cycle model is established in this paper to study the response relationship between the wetland hydrological status indicators and the changes of the wetland upper runoff. It has a very important and practical significance to both the study of the ecology water requirement and the sustainable development of the Yellow River Delta wetland. The main research contents and results are as follows:(1) The characteristic analysis of water cycle elements for Yellow River Delta wetland. The changing characteristics of hydrometeorological elements such as precipitation, runoff, and so on were discussed and it is the foundation of the water cycle model establishment. Researches have shown that the wetland water cycle factors mainly contain the wetlands water source element and the water consumption element. The wetland water source is mainly formed by upper stream inflow, rainfall and artificial fill water (in summer), each of them has the characteristic of concentrated in the summer (June to October). The upper stream inflow is uneven within a year and it varies greatly between years. Artificial fill water for the wetland was started from2008, and a certain influence on the water surface area of the wetland was noticed. The water consumption is mainly formed by evapotranspiration amount, infiltration amount and the water dumped into the sea. The evapotranspiration amount of a day, a month and a year vary greatly with the time and space, and its distribution is a single peak within a year which is focused on from May to September. Relevant data shows that exception of introducing water to the wetland interior artificially,80%of the Yellow River water flow into the sea through the main stream.(2) The establishment of the Yellow River Delta wetland water cycle model. Based on the wetland hydrological cycle and water balance equation, a water cycle model for the Yellow River Delta wetland was established, which combines with the characteristics of the Yellow River Delta wetland. By curve fitting the parameters in the water cycle model were calibrated, and then the functional relationship between the surface area and the inflow of the wetland was got. The wetland water cycle model in this paper has taken into full account the open coastal wetlands characteristics, and also taken surface area as a typical wetland hydrology status indicator, and it was proved efficient through testing the wetland surface area from the year of2005to2009.(3) The response relationship between the indicators of the wetland hydrological status and the changes of the wetland upper runoff. Taken surface area as the typical wetland hydrology status indicator, the response relationship between the indicators of the wetland hydrological status and the changes of the wetland upper runoff under the natural frequency of coming water was analysed and the relationship between the water and the water area was discussed. The natural frequency of coming water was chosen as5%、10%、25%、50%、75%、90%and95%of the wetland upper runoff, and then the surface area of the wetland under different frequencies was calculated through the water cycle model separately. Results have shown that the changing trend between the annual inflow and the annual average surface area of the Yellow River Delta wetland is consistent, in other words, when the annual inflow is large, the annual average surface area is also big and vice versa. That is to say, with the increase of runoff in the frequency, the water area of the wetland shows a decreasing trend.(4) The forecast of water demand based on the water cycle simulation, that is, to calculate the artificial recharge of water at different levels under different natural runoff frequencies. Based on wetland ecosystem health evaluation criteria and objective management of the Yellow River Delta wetland ecosystem water requirement, the wetland surface area at different levels and the artificial wetland water under different runoff frequencies can be calculated by using the wetland water cycle model. The study has shown that wetland ecosystem health evaluation criteria including structural integrity, functional coordination, system stability, system openness and landscape aesthetic nature; the three objective levels for the Yellow River Delta wetland are the basic goal, the intermediate goal and the ideals goal, and the according water surface area of the wetland are128.62km2,205.88km2and332.57km2respectively; Under the natural runoff frequencies of50%、75%、90%and95%, auxiliary artificial recharge is needed to reach the water surface area of the wetlands at different levels.