| Jing River-Dongting Lake basin system is in the Yangtze River Basin with the characteristics of large spatial scale,large difference in topography and complicated hydrologic regime,which is an important research object of flood control and water resources security.Since the operation of the Three Gorges,the hydrological situation of the Jing River-Dongting Lake basin system and the eco-environment of the lake area have undergone drastic changes,and the complex relationship between rivers and lakes has become more and more intense.The Three Gorges Reservior has different operation modes in different periods,and has different influence on the downstream of the reservoir.Three Gorges Reservoir carries out flood control operation so as to control out-of-the-library flow,after the flood season,the reservoir begins to store water,storage to the highest water level,so as to ensure that the reservoir has enough water to generate electricity and maintain the benefit;when the dry season,Three Gorges Reservoir develop compensation operation to meet downstream navigation,ecology,drought resistance and other water demand.Therefore,a 1D-2D coupled hydrodynamic model is constructed in order to reveal the hydrological and hydrodynamic processes of the Jing River-Dongting Lake basin systemand the main characteristics of the main pollution load of the lake area after the operation of the Three Gorges.Based on the model,the hydrological processes of Jing River-Dongting Lake basin system,were simulated with and without the Three Gorges Reservior regulation in dry season,flood period and storage period respectively.At the same time,a water quality module is added to the hydrodynamic coupling model to study the spatio-temporal variation of TN,TP concentration in lake area.In order to reflect the the flow regulation of three Gorges Reservior in the dry seasons and TN,TP concentration variation in the lake area,the variation situation of TN,TP concentration in the lake area was simulated when the discharge increases by 1000 m~3/s and 3000 m~3/s respectively.The following conclusions are drawn:(1)Influences of the Three Gorges Reservior operation on the mainstream of Jing River and its branches:the effect of the three Gorges Reservoir on the hydrological processes during the dry period is obvious,raising the water level of the mainstream,increasing the diversion ratio of lake inlets and the discharge into the lake,in which the influence on the diversion of the Songzikou is the greatest,the Taipingkou is the second,and the Ouchikou is the smallest.The whole period of flood control is relatively balanced,and the flood control operation of the Three Gorges Reservior has a strong peak-cutting effect on the main flow,during the impoundment period,the deverted flow in the mainstream and the lake inlets are greatly reduced after the operation of the Three Gorges Reservior,and the most significant decrease in the volume is observed in October.(2)Operation influence of the Three Gorges Reservior on outflow of Chenglingji outlet:during the dry seasons,the outflow of Chenglingji outlet increases slightly,and the variation of water level is small.There was obvious water-level fluctuation during the flood period.The fluctuation of the water level in the flow regulation periods is smaller than that in the dry period and the storage periods,while the discharge change is larger than that in the dry period,especially from July to August.During the storage period,the water level of Chenglingji decreases greatly.Consequently,there was an obvious increase in the hydraulic gradient at the Chenglingji outlet,which lead to an flow increase within a short period.However,the total runoff during the impounding periods was still decreased due to the sharply decreased inflow to the Dongting Lake.(3)Hydrological effects of the Three Gorges Reservior on the Dongting Lake:after the operation of the Three Gorges Reservior,the water level and capacity of Dongting Lake increases slightly during the dry period.The spatial distribution of the stage variation in the lake area is quite different,especially The stage variation in the deep channels trough of the lake area is the largest.The flood control operation of the Three Gorges Reservior in flood seasons has greatly reduced the water level and capacity of Dongting Lake,and greatly reduced the flood control pressure of Dongting Lake.In addition,the water level decreased obviously during the storage period.During the dry season and May and June,the operation of the Three Gorges Reservior slowed down the intensity of the water exchange between the mainstream and Dongting Lake,which increased the proportion of the inflow from three Outlet.During the main flood and the storage periods,the operation of the Three Gorges Reservior slowed down the intensity of the water exchange between the mainstream and Dongting Lake,which increased the proportion of the outflow from Chenglingji.(4)The temporal and spatial variation regulation of TN,TP concentration in Dongting Lake after the operation of the three Gorges,which is listed as follows:the TN,TP concentration of Dongting Lake can be reduced by increasing the discharge of the Three Gorges Reservior in low water period,and the influence of Dongting Lake in the Middle East is the greatest,followed by South Dongting Lake and Muping Lake is the least;the predischarge period also reduces the concentration of TN,TP in the lake area.However,the decrease degree is smaller than that in the dry period.The variation of TN,TP concentration during the main flood seasons is opposite to that of May or June,that is,increasing the concentration of TN,TP in the lake area as a whole.The storage process of the Three Gorges Reservior deteriorates the water quality of Dongting Lake to a certain extent during the impounding period,which signigicantly affected the water quality of Wuping Lake,deteriorated the water quality to some extent in the East Dongting Lake and the South Dongting Lake.(5)The influence of water supplement from the Three Gorges Reservior on the concentration of TN,TP in the lake is summarized by the prediction simulation,which mainly includes the following aspects:the increase of the discharge of the reservoir is beneficial to to the improvement of water quality in the whole lake,in which the largest decrease is in the Middle East,the next is in the South Dongting Lake,and the least change in the Muping Lake.At the same time,with the increase of the discharge of the reservoir,the spatial distribution difference of TN and TP concentration in the whole lake area gradually decreases,and from 10d to 30d,TN and TP concentration in the east Dongting lake changes the most,followed by the south Dongting lake,and the smallest in the Muping Lake. |
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