<p>Groundwater is an important source for water supply in Maputo City, Mozambique. A groundwater monitoring network has been established for systematically monitoring of groundwater level and salinity changes. Automatic data loggers were installed to register groundwater levels and EC values every hour. Three observation wells were installed in the coast to detect seawater intrusion. The measured groundwater levels show clearly tidal effects. In this study, time series analysis methods were used to identify dominant periodic changes in groundwater levels (GWLs), effects of tide, and estimation of aquifer diffusivity using tidal effect parameters. Autocorrelation and cross-correlation analysis were used to estimate the periodic components and lag time between the tide and GWLs, respectively. Spectral analysis was used to ascertain the dominant periodic components in the tide and GWLs by means of estimating amplitude spectrum and power spectrum density. Cross-spectral analysis was used to determine the lag time between the tide and GWLs by means of estimating cross-power spectrum density. Furthermore, wavelet analysis was used to investigate changes of periodic components over the measured period. The estimated amplitudes and lag times were used to estimate aquifer diffusivity. The results identified dominant periodic component with a 12hour period both in the tide and GWLs. However, groundwater level is lag behind the tide with 2-4 hours depending on the distance of the observation wells to the costal line. The wavelet analysis results show no changes of dominant periodic components over the time. Therefore, the estimated amplitude and lag time were used to estimate aquifer diffusivity. The estimated parameter values are 2.72595E-05 h/m<sup>2</sup>, 6.97843E-05 h/m<sup>2</sup>, and 6.14906E-05 h/m<sup>2</sup> from observation wells. These correspond values of transmissivity as 440 m<sup>2</sup>/d, 172 m<sup>2</sup>/d, and 195 m<sup>2</sup>/d, respectively. The estimated transmissivity values are useful for constructing saltwater intrusion models.</p>

Land reclamation not only provides valuable space for urban development, but also creates an upper aquifer in fill materials. Analysis of groundwater level (GWL) fluctuations in coastal aquifer formed due to land reclamation can provide important insight into the groundwater system (GWS) evolution, including the connectivity between the GWL and influencing variables (ocean tide and rainfall). This study presents wavelet analysis, multichannel SSA-wavelet analysis (MSSA-WA), and lag correlations to analyze the response of GWL to ocean tide and rainfall in the reclamation area of Zhoushan Island, China. The MSSA-WA results and the lag correlations show that the MSSA-WA provides better analysis results, specifically, clay layer and rainfall filtered information. The influence of the influencing variables on the upper GWL is relatively greater than the clay layer, and rainfall has a relatively stronger impact on GWLs than tides. The GWLs of the upper layer, SW18 and SW21, which are heavily influenced by influencing variables, can be predicted through variations in influencing variables. Finally, the analysis of the results shows that the lithology of different aquifers, offshore distance, preferential flow path, and pressure load can be factors between tides and GWLs. For rainfall and GWLs, different lithology of aquifers, properties of vadose zone, and topography can be influential factors. The combination method provides an optimization method for GWL fluctuations in coastal reclamation area with combined MSSA and wavelet analysis for correlation analysis between GWL and influencing variables (ocean tide and rainfall) and analysis of corresponding causes and influencing factors.