Measuring In-situ Vertical Hydraulic Conductivity In Tidal Environments And The Corresponding Calculation Method

The hydraulic conductivity of intertidal sediments plays an important role inquantifying seawater-groundwater interactions. However, its accurate and economicalin situ evaluation is difficult since existing in situ methods do not apply in intertidalzones due to periodic tidal fluctuations. Here we present a new apparatus formeasuring the sediments’ vertical hydraulic conductivity in tidal environments andpropose a simple, finite-difference data analysis method to estimate this key parameter.The new apparatus is easy to operate, and is able to measure in-situ vertical hydraulicconductivity ranging from10-7m/s to10-2m/s in tidal environments with a testduration shorter than one hour.Laizhou bay, as a typical area influenced by seawater intrusion in China and evenall over the world, attracted much attention from coastal hydrologists. In thequantitative study and simulation of seawater intrusion, the hydraulic conductivity ofintertidal sediments is an important parameter. The new apparatus andfinite-difference method were verified by many in situ experiments in several coastalcase study sites of Laizhou Bay. The finite-difference method has adequate accuracyin estimating the hydraulic conductivity compared with the traditional least-squaresfitting method. The relative error between the estimates by the two methods wasless than10.52%and averages-2.09%for all experiments in location2(xinzhuang).The new apparatus and the finite-difference method have many advantages such aseconomy, efficiency, reliability, and simplicity. We recommend them tohydrogeologists for in situ applications.Space variation of the hydraulic conductivity can affect theseawater-groundwater exchange processes. For the seawater intrusion and marinepollutant migration it is the basis for high accuracy simulations. with Geostatistics andstatistics analyses of the hydraulic conductivity of18measuring points in Xin Zhuangshow the followings. Both K and log(K) approximately obeys normal distribution.The value of K ranges from4.49×10-4m/s to2.16×10-3m/s，the average equals1.063×10-3m/s, the mid-value equals1.06×10-3m/s, the mode equals1.06×10-3m/s,and the standard deviation equals3.44×10-4m/s. The K-value increases from inland to seaward in the cross-shore direction. In the along-shore direction, K-value fluctuatessignificantly. The along-shore distance of the adjacent K-measurement points is35m,and the cross-shore distance3m. The geostatistic results indicated that the correlationlength is40.75m on a section and is smaller than3m in the other section. Thecorrelation length is not able to be determined since the spatial measurement pointsare too sparse.