| By the end of 2021,after 22 ecological water transfers in the lower reaches of the Tarim River,the groundwater level has risen significantly,the natural vegetation has been significantly improved,and the ecological water transfer effect has been significant;There are a series of new problems such as unbalanced spatial distribution of ecological water consumption,limited vegetation expansion,increased ineffective dissipation,and decreased conversion of river water to groundwater.In order to explore the effective spatial allocation of river water volume under the current water delivery pattern,this paper analyzes the transformation and dissipation of water volume under different water delivery methods by establishing a numerical model between ecological water delivery and groundwater,and accordingly proposes an optimal solution.The main research results of the water delivery scheme are as follows:(1)The downstream water delivery mode of the Tarim River has changed from single-channel water delivery to double-channel water delivery,then from the channel water delivery and the branched river to the combined water delivery method of the river,eventually evolved into a combined water conveyance mode of river channel.Long-term intermittent ecological water transfer leads to sedimentation on the surface of the river bed,and the rate of conversion of river water into groundwater gradually decreases.Continuous water transfer will reduce the conversion efficiency of river water.The water consumption of the river reaches is mainly regulated by means of ecological sluices,and the water conveyance and overflow of the branch river are carried out in a near-natural way.The current water delivery method causes the groundwater level to rise too high in some areas,the water surface is higher than the surface,the phreatic evaporation increases,and the water resource utilization efficiency decreases.(2)Under the action of the current water delivery,the downstream ecological environment has been effectively improved,resulting in the transformation between different land use types.The forest and grassland are mainly distributed along the main river and the overflow area,with an area of 124.03 km~2 and380.16 km~2,respectively.The growth rate is 4.18%/5a and 2.67%/5a respectively,showing a significant growth trend,while the growth rate of desert area is relatively low,only 0.19%/5a.Through the superposition analysis method,in view of the change of water delivery mode and the concentrated discharge of upstream water,from 2011 to 2021,the spatial characteristics of downstream water distribution are as follows:the change of water area is stable at about 19.88 km2,and the average burial depth is 1～2 m.The normalization of the current water delivery mode makes the river network water system gradually solidified,and relatively more waters have formed in the areas from Daxihaizi Reservoir to Kumutuge Ecological Gate,after Kumutuge Ecological Gate,Qiwenkule and Bozikule Wetland.The large overflowing water surface leads to the continuous increase of invalid evaporation,which is a new problem under the current water delivery pattern.(3)According to the ecological water consumption in the overflow area under the current water delivery pattern and the phreatic evaporation intensity at different burial depths,combined with the numerical simulation method of groundwater flow,it is concluded that the recharge in 2020 is 18135×10~4 m~3/a,and the discharge amount is 19697×10~4 m~3/a a.Among them,natural river infiltration recharge accounts for more than 70%of the total recharge,which is the main source of groundwater recharge in the study area;phreatic evaporation accounts for more than 80%of the total excretion,which is one of the main ways of water dissipation.Based on the verified hydrogeological parameters and the simulation curve of groundwater observation holes,the model can better reflect the groundwater movement characteristics and dynamic change trends in the study area,and can be used for groundwater flow field change prediction and water balance analysis under different water delivery schemes.(4)Based on the existing water distribution characteristics of the current water conveyance,the water conveyance modes of split flow and winter water conveyance are proposed,and the water quantity transformation trend under the improved water conveyance mode is predicted after 10 years.The groundwater level in the areas where the water was conveyed by the Cha River and in winter was significantly uplifted,and the range of the groundwater depth less than 7 m increased by 54.68 km~2 and 138.91 km~2compared with the horizontal year,and the water conveyance effect was more significant.The water transfer by branch and winter can not only rapidly expand the water level of the newly added water receiving area,but also increase the groundwater storage compared with the current water transfer method.Water delivery in winter is more conducive to the regulation of water volume during the year,avoids ineffective evaporation of water volume,improves water resource utilization efficiency,and provides theoretical support for future water volume scheduling management in the lower reaches of the Tarim River. |
