Applying Short-Time Fourier Transform on Groundwater Fluctuation for the Estimation of Regional Groundwater Pumping

Abstract:

For sustainable management of groundwater resource, precise records of regional groundwater pumping is crucial. However, the fact that number of private pumping wells is too huge makes obtaining precise pumping records of each wells become difficult. Because the most significant response of pumping is drawdown and the influence radius of pumping might over several hundred meters, a network of observation wells can be used to sense the regional pumping. Groundwater fluctuations are the synthetic effect of different physical mechanisms include pumping, recharge, tidal effect and others and an analysis of short-time Fourier transform is applied to identified the temporal effects of each mechanisms. Because pumping is a kind of human activity and the most significant frequency of human activity is daily, the temporal amplitude with daily frequency (TADF) is the response of regional pumping in the neighborhood of the observation well and TADF can be a linear indicator of regional groundwater pumping. The proposed method was applied in the Pingtung Plain and the horizontal of analysis period is from 2008 to 2011. The TADF of each observation well can reflect the temporal variation of regional groundwater pumping around the observation well. For the well in coast area, the shape of TADF looks like a sinusoid line with a half year cycle and the peaks of large pumping respectively are during January and July. The peaks of large pumping are mainly caused by fish farms.