Development And Improvement Of WAS Model And Application Of Water Resources Allocation In Beijing-Tianjin-Hebei Region

Water resources allocation plays an important role in scientifically and rationally development and utilization of water resources.With the construction of water conservancy proj ects such as reservoirs and the increased scale of social water use,river runoff and ecological environment have changed,and natural social water resources system presents significant complexity,dynamics and linkages,and the traditional water resource allocation models are difficult to meet the needs of this situation.Therefore,according to the characteristics of natural society water resources system,new models and methods need to be developed to achieve refined water resources management.Based on the improved WAS model(Water Allocation and Simulation Model),this paper selects the Beijing-Tianjin-Hebei region with strong water competition and severe human activities as the study area,and constructs the water allocation and simulation model in Beijing-Tianjin-Hebei region,and the status quo and future water resources allocation,natural social water balance and mutual relations of Beijing-Tianjin-Hebei are studied.The main results are as follows:(1)Based on the WAS model,a total-partial nested convergence method with versatility and generalization is proposed.This method is a convergent topology calculation method for calculation unit with a natural-social binary attribute formed by the superposition administrative division and basin,and it is divided into three parts:calculation unit division,unit confluence in sub-basin and unit confluence between different sub-basins.This method can perform convergence topology and generalize the river network generation on the calculation unit with multi-element attribute at different scales by using the DEM and river network data with the resolution matching the scale,realize the water collection and water balance calculation based on the calculation unit in the natural-social water resources systerm,and reflect the convergence nature of the calculation unit.(2)The water allocation and simulation model in the Beijing-Tianjin-Hebei region is constructed and verified.The NSE of the model hydrological station is basically higher than 0.65 in validation period,and the R2 is basically above 0.80;The relative error rate between the simulated and actual values of the surface water resources for multi-years average is 6.2%,and the relative error rates at the 25%,50%,and 75%frequency years are 4.4%,5.2%,and 5.9%,respectively;The total resource allocation error is 1.2%.The results show that the model has a good simulation effect on regional water resources and water resources allocation,and can meet the requirements of water resources evaluation and management,and has strong applicability.(3)Natural social binary water cycle in the Beijing-Tianjin-Hebei region in the current year of 2016 is analyzed.The current inbound water of the Beijing-Tianj in-Hebei region is 3.14 billion m3,the interbasin water transfer is 2.43 billion m3,the regional precipitation is 125.53 billion m3,the soil evaporation is 96.19 billion m3,and the phreatic evaporation is 2.74 billion m3,thus forming surface water resources is 13.73 billion m3.The total water supply in the region is 24.56 billion m3,total water consumption is 17.47 billion m3,the water discharged into the river is 2.45 billion m3,the recycled water reuse is 1.96 billion m3,the irrigation infiltration is 2.68 billion m3,and the water entering into the sea is 4.9 billion m3.(4)Based on the assumption that the groundwater in the Beijing-Tianjin-Hebei region has reached the balance between exploitation and replenishment in 2035,and the interbasin water transfer water supply gradually reaches the engineering water supply capacity,the balance of water supply and demand in the Beijing-Tianjin-Hebei region is analyzed.The results show that under the scenario that the groundwater reaches the balance between exploitation and replenishment and the interbasin water transfer water supply reaches its supply capacity,the total water shortage rate in the Beijing-Tianjin-Hebei region is 3.6%,and the Gini coefficient of the water shortage rate is 3.8%.Although after interbasin water transfer is fully effective,it effectively reduces the overall water shortage rate and the spatial heterogeneity of the water shortage distribution.The water shortage rate has increased to 7.9%in consideration of the dry year scenario,and more water supply is needed for ecological improvement and restoration in the Beijing-Tianjin-Hebei region.To ensure the safety of water resources in the Beijing-Tianjin-Hebei region,on the one hand,it is necessary to reduce the demand for water and further improve local water saving;on the other hand,it is necessary to add new water supply,such as seawater desalination and the east route of South-to-North Water Diversion Project.(5)After the interbasin water transfer is fully effective,the natural social water cycle transformation in the Beijing-Tianjin-Hebei region is analyzed.The precipitation in the region produces surface water of 14.1 billion m3,inbound water is 4.45 billion m3,interbasin water transfer is 5.79 billion m3,total incoming water is 24.34 billion m3;reservoirs and channel water storage increased by 1.64 billion m3,and reservoirs and channel evaporation is 1.09 billion m3,river and reservoirs water supply is 11.36 billion m3,treated sewage drainage is 1.88 billion m3,total water storage,consumption and drainage is 12.21 billion m3;total outbound water is 12.14 billion m3.After considering the natural social water cycle,due to the internal social water intake and drainage in Hebei Province and the regulation and storage of the reservoirs,the inbound water of Beijing decreased by 26%compared with the natural water cycle;the corresponding total inbound water of Tianjin decreased by 32%compared with the natural water cycle.While inbound water is reduced,and internal social water intake,storage and drainage and interbasin water transfer in Beijing,the total outbound water decreased by 25%compared with the natural water cycle,which social drainage accounts for 21%of outbound water;the corresponding total outbound water of Tianjin decreased by 34%compared with the natural water cycle,which social drainage accounts for 4%of outbound water.It shows that the WAS model has a strong function for dynamic mutual feedback simulation of each unit inside the system.