| The Pinglu Canal is an important part of the"New Western Land and Sea Corridor".After the implementation of the Pinglu Canal project,the increased saltwater intrusion in the Qinjiang River Estuary will be a key factor affecting the life of the proposed Qingnian Hub locks and the safety of upstream water intake.Therefore,it is of great significance to study the characteristics of salt water intrusion in the Qinjiang River estuary after the Pinglu Canal project and give some suggestions on the salt mitigation at the Qingnian Hub.The analytical model for predicting the saltwater intrusion length was used to derive a prediction model for the saltwater intrusion length of the Qinjiang River estuary considering the effects of topographic changes,runoff and tidal dynamics.Then the validity of the model and the Van der Burgh coefficients is verified based on the measured data of discharge,tide level and topography in recent years.And the calculated results show that estuarine topography,discharge and tides are important influencing factors for saltwater intrusion in the Qinjiang River estuary,which provides a reference for the numerical experimental design of salt reduction measures after the Pinglu Canal project construction.A three-dimensional numerical model of saltwater intrusion in the Qinjiang River estuary was established based on an unstructured triangular grid in Cartesian coordinates.The simulated tide level,flow velocity,and salinity of the model generally agree well with the measured data,indicating that the model can effectively reflect the hydrodynamic and saltwater intrusion processes in the Qinjiang River estuary.The established three-dimensional numerical model of salt water intrusion was used to simulate the change process of salt water upstream in the Qinjiang River estuary after the Pinglu Canal project operation,and the spatial and temporal characteristics of salt water upstream in the Pinglu Canal were analyzed.In terms of time distribution,the salinity of the salt water upstream during the dry period is serious,the salinity at the outlet of the approach channel under the Qingnian Locks gradually accumulates as the flow discharge decreases,the salinity of the Qinjiang River confluence section and the offshore section has the fastest growth rate along the way,and the salinity stratification phenomenon is mainly concentrated in the Qinjiang River section.During the mid-water period,the extent of saltwater upstream weakened and the salinity decreased compared with the dry-water period,and the salinity along the Qinjiang River confluence section had the fastest growth rate,and the salinity stratification phenomenon was mainly concentrated in the Qinjiang River confluence section.The saltwater intrusion degree is the weakest during the flooding period,and the saltwater intrusion fails to reach the outlet of the approach channel under the gate.The salinity gradually increases along the route from the offshore section,and the salinity stratification phenomenon is mainly concentrated in the confluence section of Qinjiang River.On the planar distribution,the salinity shows a trend of decreasing salinity along the range as it goes upstream.At the time of rising rest,the salt water is most severely upstream,and the isosaline is obviously convex upstream.At the time of falling rest,the salt water falls back downstream with the tide,and the isosaline is obviously convex downstream.Based on a series of three-dimensional salinity numerical tests,the downstream of Qingnian Lock salinity reduction effects of different excavation widths,youth lock releases and youth hub releases were analyzed.The width of excavation is directly proportional to the salinity of the outlet of the approach channel under the lock.Under the condition of ensuring navigation,the best effect of salt reduction is achieved when the width of excavation is reduced from 105m to 90m.Under different lock discharge conditions,the more frequently the lock is crossed,the lower the salinity at the exit of the approach channel.And under different hub discharge conditions,the larger the flow rate is,the faster the salinity at the exit of the approach channel is reduced,and the best effect of salt reduction is achieved when the flow rate is greater than 20 m~3/s.Based on the analysis of the effect of salt reduction proposed the Qingnian Hub downstream salt reduction measures:(1)in the premise of not affecting the navigation conditions,the appropriate use of reducing the width of the canal excavation to alleviate the intrusion of saltwater downstream;(2)the lock maintenance period should be arranged as far as possible in the small tide rest time;(3)the approach channel outlet salt reduction effect will be more significant when the Qingnian hub discharge is greater than 20m~3/s. |
