Statistical analysis of groundwater level variability across KwaZulu-Natal Province,South Africa |
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| Authors: | M S Ndlovu M Demlie |
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| Institution: | 1.School of Agricultural, Earth and Environmental Sciences,University of KwaZulu-Natal,Durban,South Africa |
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| Abstract: | This paper reports the results of analysis of groundwater level changes and its relationship with rainfall across KwaZulu-Natal (KZN) Province of South Africa. The study used 32 groundwater level monitoring sites and 15 selected rainfall stations located across the province. The Mann–Kendall test was used to explore the presence of trends in groundwater level and rainfall data at 10% significance level. The slope of the trend was estimated using Sen’s slope estimator. To understand the cause–effect relationship between rainfall and groundwater level changes, the cumulative rainfall departure (CRD) was computed at the respective rainfall stations influencing the groundwater monitoring site. The results show variable but a general decreasing trend. The variability of the groundwater level trends was analyzed based on water management areas (WMA): (1) both groundwater level and rainfall have a decreasing trend for the entire record period in the Usuthu–Mhlathuzi WMA. Groundwater level around Tembe and Mbazwana areas declined by 0.7 and 2.7 m, respectively. Areas around Richards Bay experienced a reduction between 0.7 and 6.3 m from 2004 to 2015. During the same period, the rainfall within the WMA decreased by 26, 6 and 18% from the mean around Tembe, Mbazwana and Richards Bay, respectively; (2) The northern sector of the uThukela WMA, around Dundee and Newcastle exhibited groundwater level increase by about 1.5 m between 2004 and 2010 but later declined by 1.2 m from 2014 to 2015. The rainfall increased by 8% from 2004 to 2010, and decreased by 22% at the end of 2015. The central part of the uThukela WMA, around Tugela Ferry and Greytown, experienced groundwater level and rainfall reductions of 3.2 m and 15%, respectively, during the entire record period; (3) Within the Mvoti–uMzimkulu WMA in the vicinity of Maphumulo, groundwater level decline by 11 m from 2005 to 2011. However, it recovered by 8 m between 2012 and 2013 following an increase in rainfall by 21%. Areas around Durban exhibited increasing trend from 2005 to 2008 in response to an increasing rainfall amount by about 13% for the same period. The reduction in rainfall by 21% from 2012 to 2015 resulted in a decline of groundwater level by 0.4 m. The steady decline in groundwater levels across the province appears to be a response to prolonged reduction in rainfall, which consequently reduced the amount of groundwater recharge reaching the aquifer. The general response of groundwater levels to changes in rainfall across the province has a lag time from 1 to 4 months. |
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