Study On Hydrological Situation Simulation Of Zhalong Wetland Based On Hydrodynamic Model

As one of the important environmental factors in wetland ecosystem,the changing of hydrological regime can directly affect the structure pattern and ecological function of wetland ecosystem.Under the influences of human activities and climate changes,increasingly severe shortage of wetland water resources has seriously affected and damaged the structure and function of wetland ecosystem.In order to protect the increasingly scarce of wetland resources and provide the suitable habitats for wildlife,the work of manual water replenishment was developed in the wetland reserve area.However,both the quantity and time of water replenishment are at present lack of quantificational basis,and this is mainly due to the fact that the dynamic change data of wetland depth often difficult to obtain which unable to effectively simulate the flooding process of downstream wetlands and its impact on habitats under the different incoming conditions in the upstream watershed.Therefore,in order to quantitatively simulate the change of wetland hydrological situation in the lower reaches of the lower reaches of river basin under different recharge conditions and formulate a scientific and effective strategy of wetland recharge,in this paper,the hydrodynamic model of MIKE21 is constructed to simulate the change of water level in Zhalong wetland by using the field measured data?measured water level data from Longan Bridge,Teller,Tumuke and Keertai hydrological stations?,climatic and meteorological data?precipitation,evaporation and wind speed?,land use data,DEM elevation data and radar images.Furthermore,In order to scientifically evaluate the practicability of hydrodynamic model in the simulation of wetland hydrological process,the hydrodynamic model was calibrated and validated by water level gauge and depth data measured by hydrological station in different time periods.The results show that the certainty coefficient R² is between 0.95-0.97 and the Nash efficiency coefficient E_ns varies from 0.86-0.96 when the rate of the model is set as May 2014.Moreover,the certainty coefficient R² is between 0.85 and 0.96,the Nash efficiency coefficient E_nss varies from 0.81 to 0.95,and the relative error RE is less than+3%,when the validation period of the model is set as July-August and September-October.Satisfactory verification results show that hydrodynamic model of MIKE21 can effectively simulate the changing of water level in marsh wetlands.Compared with the wetland flooding range extracted from radar remote sensing images,the simulation results of Zhalong wetland inundated areas are basically in accordance with that extracted from Radarsat-2 image,which shows that the simulation results of the model has a satisfactory performance.The sensitivity analysis of the model was used to verify the influence of hydrological parameters on the simulation results of wetland water level by comparing the simulation of water level under different hydrological parameters with the measured data when the period was choose from July 15 to August 15,2014.The results show that the Manning coefficient related to land cover type has an enormous effect on the accuracy of model,and the slight changing of Manning coefficient also have a significant impact on the simulation results of wetland water level.Therefore,the spatial differences of Manning coefficient should be considered and more accurate results can be obtained by parameter calibration.The simulation results of water level of Zhalong wetland show that the average water level of Zhalong wetland is the highest in August and inundated areas is the largest,while April and May are the low water level period of Zhalong wetland and the breeding period of rare waterfowl,so it is more reasonable to replenish water in this reason.In summary,wetland recharge should take into account both recharge time and the changing of wetland hydrological conditions after recharge.The results of this paper can not only provide a scientific basis for wetland water replenishment strategy,but also provide a data basis for the study of wetland eco-hydrological processes under the influence of climate change and human disturbance.