Trend analysis is defined as a mathematical technique that uses the historical results to predict the future outcome. A number of parametric and non-parametric tests have been used for trend detection. Non-parametric tests are more suitable for non-normally distributed data, such as groundwater levels. The best non-parametric test is based on the Mann Kendall test and has been used by various researchers to understand the long-term trends in groundwater levels. The data collected by monitoring groundwater can be used to determine the amount of water that can be safely be withdraw before no more water can be pumped. In this way local water managers can prevent wells from going dry and prevent movement of poorer quality groundwater into aquifer.
Selection of method is one of the major tasks in trend analysis. Selection of method depends on nature of data. A test may be slightly more powerful in one instance but may be much less powerful in some other reasonable cases. The test selected should therefore be robust, it should have relatively high-power over-all situations and types of data that might reasonably be expected to occur. Some of the characteristics commonly found in water resources data are distribution (normal, skewed, symmetric, heavy tailed), outliers (but true measurement), cycles (seasonal, weekly, tidal, diurnal), missing values (a few isolated values or large gaps) and censored data (less-than values, historical floods). In Linear trend the model function is a linear combination of parameter such as y = mx + c i.e., the mode can be representing a straight line. In non-linear trend, the parameter appears as a non-linear combination of parameter such as y= 𝑥3 + 5𝑒3.
Study Area
The study area considered for assessment of groundwater resources in the Handri river basin, a tributary of Tungabadra river in Kurnool district, which is in Andhra Pradesh state (India) lies between a latitude of 140 35' 35" − 160 09' 36" N and longitude of 750 58' 42" − 780 56' 06" of E. Figure 1 shows the details of the study area. The origin of sub-basin between Pattikonda and Aspari and mingle in river Tungabhadra which is one of the major tributaries of river Krishna. The study area receives an average rainfall of 665 mm per annum. The geological formation consists of shales, limestones, granite, gneiss, and quartzites (Sudhakar P, M. et. al., 2017).
The watersheds in the present study are namely Adoni, Devanakonda, Kodumur, Kalluru, Dhone, Krishnagiri, Aluru, Aspari, Gonegandla, Pathikonda, Veldurthi. The groundwater levels for 17 years are used in this study from 1997 to 2012.