Spatio-Temporal Analysis on Groundwater-Case Study for Thiruvallur District

. Thiruvallur District in Tamil Nadu is one such district, with groundwater levels reaching depths of 50m to 60m below the surface. Growing populations, variations in land use patterns, reduction in rainfall depth, and other factors all contributed to an increase in water demand and a decrease in water potential. This affects the quality of groundwater as well. In this study, the variation of both Groundwater potential and Groundwater Quality is analyzed. The collected data has undergone thorough processing to ensure its accuracy and relevance for the area to be studied. (Thiruvallur District). The base map for the place to be analyzed and the well-map are created in the QGIS software with the data. The processed data is imported into the QGIS to create a database. With the database, the spatial variation between the stations is mapped. The temporal variation of the stations is carried out. The spatial map is done for the groundwater level and Groundwater quality parameters like pH, TDS, Cl, etc. The temporal variation is shown in the graph for the GW level and GW quality parameters with respect to the well-points.


Introduction
Agriculture is the major contributor to the country's economy and it depends on irrigation.In most places, irrigation is dependent on groundwater.Agriculture is the backbone of our Country and almost 90 percent of groundwater is utilized for agriculture.Confined aquifers are bounded by two impervious layers which have good discharge and recharge capacity [10].The water balance in the ground water table should be ensured at all times for a good specific yield.However, in the present scenario due to urbanization, over-exploitation, and population growth, there is an acute shortage of groundwater sources.Several parameters including drainage, lithology, elevation, faults, and land use/cover affect the spatial characteristics of groundwater [11].
As oil, gold, or gas groundwater is extracted from the ground.Even though water resources are richly present on the Earth, the availability of the useful quantity of water is limited.
The major sources of groundwater contamination are divided into direct and indirect sources.Industrial wastewater dumping is a direct source of contamination.Overpopulation and urbanization are indirect sources [13].In order to understand the characteristic of aquifers, the various parameters like pH, Total Dissolved Solids, Chlorides, etc. are taken as the input parameters and analyzed in QGIS software.In recent years ground-penetrating radar (GPR) is commonly used for locating the groundwater potential zones.It can be done easily without digging the land.It helps locate the zones where the groundwater is available very deeper.GPR works by sending electromagnetic waves into the ground and measuring the reflection of these waves from subsurface layers.By analyzing these reflections, geologists and hydrologists can determine the location and characteristics of subsurface aquifers, which are zones of permeable rock or sediment that can store and transmit groundwater.GPR is particularly useful in very low rainfall areas called as arid regions, where water is scarce and access to groundwater is critical [6,8].The contamination of water becomes common nowadays due to overpopulation and lack of awareness.Due to the contamination of water bodies, agriculture in the specific place will get affected and the quality of the water will be affected [5].

Literature Survey
Astha Bista [1] did the spatial-temporal analysis on the river beds of the Platte River, United States.The analysis provided data that confirm the depletion of groundwater is due to urbanization.Groundwater management has been put under strain due to rapid population increase and climatic unpredictability.Using data mining approaches, researchers investigated explanatory elements (such as precipitation, pumping, and stream flow) that may be related to the dynamics of the groundwater table in the Platte River Basin in Nebraska.Weston Dripps et.al [15] suggested for effective groundwater modeling, the basic knowledge of the temporal and spatial distribution of groundwater recharge is important.A simulation study was carried out in the Trout Lake basin, a small forested watershed in northern Wisconsin.Park et al. [12] studied the water-table fluctuation (WTF) method is a simple and direct approach to estimating groundwater recharge.The apparent recharge rate (Ra) was calculated at four sites with the National Groundwater Monitoring Wells and the automatic weather stations in Korea.Considering the sites are under Monsoon climate conditions, all data were grouped separately for seasonal variations.He studied the time scale of precipitation, and the water-table rises were changed into the event base and the summation of total rises corresponding to the event, respectively.Elmahdy et al. [7] confirmed that the depletion of groundwater is happening in irrigationdependent agriculture places by uncontrolled population and variable climate change.Conservation and management of groundwater need a deep knowledge of the area, climate conditions, rainfall, soil type, and the bond between surface water and groundwater.Analyzing and collecting the above details is still a difficult job, as it is more expensive and inaccurate.Vijayalakshmi [4][5] used water quality sensors to measure the lake parameters.The author choose a small lake in the Gummidipoondi village and experimented with the change in the parameters like pH, and climate changes and displayed on the Internet.Qianqian Zhang [14] Groundwater quality deterioration is a growing concern in many parts of the world, including China.His study highlights the impact of pollution on the river bed region of Hutuo river groundwater quality.By using a water quality index (WQI) and multivariate statistical techniques, the study found that a significant portion of the groundwater samples in the region exceeded the very low grade of III for groundwater quality in China for nitrate (53.09%), sulfate (18.52%), and total hardness (83.95%).Irfan Muhammad [9] used the spatiotemporal analysis for Peat Hydrology Unit in South Sumatera.
Sumatera is a village town rich in plantations and wetlands.The author located 4 different places in the study area.The analysis provided the result of low GWL during summer and high GWL during the rainy seasons.
3 Materials and Methods of data collecting

Study Area
Thiruvallur district is a coastal district with the ocean surrounded on one side and the other side with land and population.The ocean's name is the Bay of Bengal to the east and several other districts of Tamil Nadu and Andhra Pradesh to the west, north, and south.With an area of 3550 square kilometers, Thiruvallur district has a total of 14 blocks, 526 villages, and 3842 habitations.

Proposed Methodology
The site is selected and the required data are collected.The required data are base map, well location, groundwater quality, groundwater level, and the average rainfall.The spatialtemporal analysis is done with the groundwater levels and the graphs are plotted for groundwater quantity and groundwater quality during pre-monsoon and post-monsoon seasons.

Preparation of Base map
Digitizing in GIS refers to the process of converting geographic data from a hardcopy map, scanned image, or other analog sources into vector data that can be processed and analyzed in a GIS.During the digitizing process, the features on the map or image, such as points, lines, or polygons, are traced and captured as coordinates in a vector format.The base map is prepared by digitizing the raster file of the Thiruvallur district.With the coordinates in the raster file the map is digitized.The base map of India is collected and the required study area is extracted for the study area map preparation.The boundary map is prepared with the data in the same way the block map is also prepared for the Thiruvallur district.The well-map is prepared by adding the points to the respective well locations in the base map of the Thiruvallur district.The data is converted to CSV format and imported as a layer in the QGIS.By the coordinates, the points are plotted.This prepares a well-map of the Thiruvallur district.The well-points are considered as monitoring stations or observation wells.The study area contains around 29 well locations.The Saidapet and Ponneri locations contain more well locations.Gathering the well locations will help to identify the water level and water quality in the predefined areas.

Temporal analysis
Temporal data is time-series data, which means that the data is collected over time, and the changes in the data can be tracked over time.Temporal analysis is the study of time-series data, which involves analyzing the patterns, trends, and relationships within the data over time.The groundwater level data is analyzed with respective to the time period of 2008-2021 based on the station points i.e. is well locations.In the same way, the groundwater quality parameters like pH, TDS, Cl, Turbidity and Conductivity are also analyzed based on the time.The pre-monsoon assessments cannot be predicted easily using the previous calculations, as the rainfall is not the same in all years.In all the pre-monsoon years, some of the monitoring wells in the study area have a band of 6m.The pH levels in the study area are constant and it is maintained at 7.5 to 8.0 from 2008 to 2020.This indicates the water quality of the study area is neutral and it is suitable for domestic purposes.

Conclusion and future scope
This conclusion is possible based on the findings of a tempo-spatial analysis of the availability level of groundwater level and quality of the water in terms of pH and total hardness, as well as the presentation of rainfall data.By analyzing the changes in groundwater levels and quality over time and in relation to spatial patterns, as well as considering the influence of rainfall, the conclusion that even a small amount of rainfall can lead to improved shallow groundwater quality makes sense.The results of such an analysis can help inform water management decisions and guide the development of sustainable groundwater management strategies.Groundwater quality is a critical factor that influences the usability of groundwater as a source of water for various purposes.Hence, monitoring and managing groundwater quality is a critical aspect of sustainable water management.Groundwater mapping or aquifer mapping is the process of delineating the presence of groundwater in aquifers, followed by the analysis of its quantity, movement, and sustainability.Thus both the spatial and temporal variations are analyzed for the Thiruvallur district of Tamil Nadu, India.The heavy precipitation increases both the groundwater potential and also the quality of the water in many aspects.It also reduces the hardness of the groundwater.

Funding
The authors declare that they have not received any funding for the current study.

Ethical Conduct
This current study does not involve any human and animal violations.

Fig. 2 .
Fig. 2. Overall methodology of the study area

Fig. 3 .
Fig. 3. a. Base map of the Thiruvallur district b.Well map of the Thiruvallur district

Fig. 5 .
Fig. 5. Pre-monsoon a. 2008 b.2012During the pre-monsoon period of 2008, the monitoring wells near Tirutani received good rain, and the wells are maintained at 6m.The other areas of the district received only less rain and the well have an average fill of 3m.In 2012, in the monitoring wells near Thiruvallur, the band was increased to 6m.

Fig. 10 .
Fig. 10.Temporal analysis of hardnessThe hardness level of the areas Ambattur, Arani, and Gummidipoondi are constant and there is no rapid change from 2008 to 2021.In recent years, Alinjivakkam also started having a constant hardness level as other areas.

Fig. 13 .
Fig. 13.Water quality Total hardness a. 2008 b.2012From 2008 to 2022, the total hardness of the study area is maintained uniformly at the heavier rate of 1000ppm to 1500ppm.The distribution is uniform throughout the area, and the hardness of the paper made it not suitable of all domestic purposes.