Object Based Modelling for the Irrigation Suitability using Hydrogeochemical Parameters and Land use Dynamics in the Lower Ganga

The north Indian Ganga basin is one of the densely populated basins of the world. Most agricultural and industrial contaminants drained throughout the river length are likely to be accumulated in the lower part of the Ganga basin. We used ten derived irrigation suitability parameters, which are obtained from 495 sampling points locations, besides using long term climate data (GLDAS_NOAH025_M) using “Technique for Order of Preference by Similarity to Ideal Solution” (TOPSIS) model to get the irrigation suitability map. Multi-Criteria Decision Making (MCDM) using TOPSIS helps make the best choices from the available finite number of alternatives based on their ranking. The obtained entropy weight for irrigation suitability parameters such as Electrical Conductivity (Ec), Sodium Adsorption Ratio (SAR), Magnesium Hardness (MH), Sodium Percent (Na%), Total Hardness (TH), Kelly’s ratio (KR), Permeability Index (PI), Chloride concentration (Cl−), Groundwater Level Fluctuation (GWLF), and lang factor (Df) are found to be 0.08, 0.14, 0.02, 0.02, 0.04, 0.08, 0.01, 0.32, 0.29 and 0.01 respectively. We find that SAR, Cl−, and GWLF controls the water quality for irrigation in the Lower Ganga basin since these parameters have relatively higher entropy weights (more than 0.10). The results obtained from the computed performance index or the closeness coefficient show that the area percent having very good, good, and very poor groundwater quality in the Lower Ganga basin is 34.67%,42.36%, and 22.97%, respectively. The LULC change pattern indicates that the percentage change of water and agricultural land was -11.96 and -0.86%, whereas an increase in the settlement area of 131.42% for the period between 2000 and 2015.

Hydrochemical Characteristics and Irrigation Suitability Evaluation of Groundwater with Different Degrees of Seawater Intrusion

Groundwater in coastal aquifers is often affected by seawater intrusion, resulting in water quality deterioration. Using groundwater influenced by seawater intrusion for irrigation can lead to crop failure, erosion of machinery and pipes, and adverse effects on farming. In this study, the results of water testing, methods of statistical analysis, ion ratios, a Piper diagram, and a variety of groundwater irrigation suitability models were used to analyze the chemical composition of groundwater and the influence of seawater intrusion. The result shows that the content of Na+, K+, Ca2+, Mg2+, Cl−, and SO42− in groundwater would increase due to seawater intrusion, and the increasing trend was consistent with the freshwater–seawater mixing line. With the deepening of seawater intrusion, the hydrochemical type gradually changes from Ca-HCO3·Cl to Na·Mg-Cl·SO4 and then to Na-Cl type, and the source of hydrochemical composition changes from “Rock Weathering Dominance” to “Evaporation Dominance”. When the Cl− concentration is greater than 7.1 meq/L, groundwater will corrode pipelines and instruments; when greater than 28.2 meq/L, excessively high salinity of groundwater will have adverse effects on planting; and when greater than 14.1 meq/L, the groundwater hardness is too high, which may make the groundwater unsuitable for cultivation.