Research Into Seawater Intrusion In Typical Areas Of Quanzhou Through Experiment And Numerical Simulation

Nowadays natural hazardous, say seawater intrusion, seawater in welling, surface subsidence and so forth happened to coastal areas and became increasingly serious. With respect to research into seawater intrusion, developed countries had commenced from19th century, while China from1970s. In fact, China focuses on very narrow fields and the total research level is very low. However, situation of groundwater exploit is aggravating, coastal provinces like Guangdong, Fujian etc, have faced different seawater intrusion problems with different degrees. But reports and researches basing on Fujian on this issue are rare and concentrating on in-site detection. Hardly, researches into developing law and prevention measures of seawater intrusion are exposed to public.Regarding typical areas of Quanzhou as project background, incurring reasons, developing laws, and prevention measures of seawater intrusion in Quanzhou are discussed through in-site detection, indoor experiments, finite numerical simulations. Main research fruits are displayed as follows:1、Two main reasons contribute to seawater intrusion. One is related to human, because of blindly exploiting groundwater, water table has been greatly decreased which means the equilibrium of fresh water and seawater is disturbed. Consequently, seawater intrusion happened. The other is due to nature, tide is a common practice of Quanzhou bay, the average value of lowest tide table and highest one is approximately4meter, such a high distinction lead to seawater intrusion. On top of that, typhoon, storm composed other inducing factors of seawater intrusion.2、A upper bound(2/Δρ+1Lmax salt), critical value(Hcr) and lower limit(2/Δρ+1Lmin salt) of fresh water table can be found on condition that seawater level varies in period. If Lfre≤2/Δρ+1Lmin salt, seawater intrusion would be consecutively developed; If2/Δρ+1Lmin salt<Lfre≤Hcr, seawater intrusion would be developed accumulatively; If Hcr<Lfre≤2/Δρ+1Lmax salt, seawater intrusion would appear during the varying period, eventually, however, total intrusion was avoided; If Lfre>2/Δρ+1Lmax salt,no intrusion can be found;3、Existence of silty clay can make a great difference on intrusion velocity. The thicker the silty clay layer is, the greater the intrusion velocity would be. Basically, silty clay play a role as aquiclude which separates sand into two independent developing areas of seawater intrusion, upper layer and lower layer. Generally, intrusion velocity in upper layer is slower than lower one.4、By analyzing concentration curve of sample points, greater distinction between fresh water table and saltwater level means greater amplitude of seawater intrusion and retreat, as a result of it, magnitude of cumulative intrusion is higher. But the magnitude will decline with the distance becoming increasingly far away from the fresh-salt boundary.5、Counting on current hydrogeological condition,2out of3typical sections will be threatened posed by seawater, To be more exact,5years and6years later, section Ⅱ-Ⅱ and Ⅲ-Ⅲ will face the threat, respectively, due to groundwater level is lower than that of seawater because of tide.6、Basing on current situation of seawater intrusion and local hydrogeological condition in Quanzhou, a method, combining ASR technique and surface reservoir was put forwarded to prevent seawater intrusion, and ways to implement are simply proposed as well.