Study On The Influence Of Runoff Variation And Sea Level Rise On Saltwater Intrusion In Nandu River Estuary

Estuary area is an important place for human survival and development,estuary water resources are rich,fertile soil,which makes this area an important agricultural base.In addition,many rivers from the upper reaches of the river into the ocean through the mouth,the mouth also brings a wealth of nutrients,making the estuary offshore become an important fishing ground.Around two thirds of the world population lives in coastal and estuarine areas,where there are many large cities that have developed into important economic,trade and cultural centres.However,under the influence of climate change and human activities,salty tide disasters occur frequently.Saltwater invasion is a major hydrological problem in estuarine areas,not only will affect the local farming,but also directly affect changes in migratory routes and spawning site location of fish,causing a huge threat to the human living environment,the urgent need to study the response to changes in the law of estuarine Water Resources Environment.The Nandu River is the largest river in Hainan Island.In recent years,saltwater intrusion has been increasing year by year due to climate change and human activities.By establishing a one-dimensional model of water flow and salinity in the Nandu River under sea level rise and upstream runoff changes,this paper attempts to reveal the difference in the distance of salty tidal invasion in the Nandu River estuary after environmental change and the difference in the time-space of salinity over time.The main findings are as follows:(1)Based on MIKE11 hydrodynamic(HD)module,the one-dimensional model of the Nandu river channel was established by the cross-section data of the Nandu river channel,and the flood rate of the Nandu River was determined and verified.Salinity simulation using MIKE11 AD(convection diffusion)module to calculate the magnitude and phase of the water level and salinity simulation and the measured value changes are basically the same,the model for calculating the size of the flood and tide water level salinity CC values are above 0.9,indicating that the calculated value and the measured value correlation;The SS values are also above 0.9,indicating that the calculated values and the measured values match excellent,better simulation.It is proved that the model has good reliability when simulating the tidal level and salinity of Nandu River.(2)Set seven kinds of runoff and sea level scenarios to simulate seawater intrusion,the flow rate is set to Nandu river dry season average flow,a total of three scenarios were set 46 m3/s,105 m3/s and 210 m3/s.The sea level datum was initially 0m,and the sea level rise scenario was simulated by adding 0.2m and 0.4m respectively.Conclusion:(1)Sea intrusion distance decreases with the increase of runoff,the smaller the runoff,the more intense saltwater intrusion,saltwater intrusion process salinity decreased slower;the greater the runoff,the weaker saltwater intrusion,salinity along the way decreased faster.The relationship between runoff and saltwater intrusion distance is:L(28)2333649.Q^0-.577(2)Sea intrusion distance and sea level was a positive correlation,when the flow rate is set to 46 m3/s,when the sea level rise 0.2m,0.45 salinity line basically did not change,when the sea level rise 0.4m,and other salinity line moved 800m.(3)The size of the upstream water intake tidal salinity changes:the impact of runoff on salinity changes:(1)when the dry season flow of 46 m3/s the salinity of the five monitoring points are more than the standard value,the time range of 25h salinity statistics for the longest and cumulative excess time is 25h.When the flow rate increases to 210 m3/s:Station3 size tidal salinity for the longest time exceeded 13h,the cumulative time exceeded18 and 16h,respectively.Station4 monitoring point salinity is not exceeded.The longest time and cumulative time exceeded the size of the tide exceeded are 0h.When the salty tide traceability is more serious,you can increase the displacement of the upstream saltwater intrusion to alleviate the situation,so that the water salinity can reach the qualified state.(2)The effect of sea level rise on salinity changes:sea level rise on the whole will increase saltwater intrusion,salty tide traceable distance farther,the salinity of the tide is slightly smaller than the salinity of the low tide.Sea-level rise will enhance saline irrigation,but will facilitate access to upstream suitable water intake.