Abstract:
Over-reliance on groundwater in the northwest region (NW) of Bangladesh is causing a drawdown of the water table and creating tremendous pressure on food security. In many parts of the region, this drawdown has raised serious concern about the sustainability of groundwater use. It is now crucial to identify sustainable groundwater options that will help decide where more pumpage can be allowed or restrict it. Therefore, the study has delineated groundwater potential zones of the NW region for sustainable utilization and management so that proper monitoring and conservation can be accurately done.
In this regard, the thesis work used two different multi-criteria analysis (MCA) techniques (viz., Analytical Hierarchy Process and Multi-influencing Factor) and validated the assessment with an actual net recharge map. At first, literature reviews and experts' opinions were considered in selecting eight indicators, namely lithology, lineament density, geomorphology, slope, rainfall, soil, drainage density, and Land use/cover as the influencing factors. Secondly, the said two MCA techniques were used to assign weights to each indicator. Subsequently, all indicators were integrated using the weighted linear combination (WLC) method to delineate potential groundwater zones.
To determine the accuracy of the groundwater potential maps the receiver operating characteristics (ROC) and area under the curve (AUC) were used as a performance indicator. As it seems, both MCA techniques present similar results in terms of the areal extent but significant differences in the spatial distribution of the groundwater prospect. MIF method is found to perform better results on validation. Further, the lithology indicator shows more sensitivity in both the MCA techniques, hence, it is assigned with the highest weight and plays a dominant role in mapping potential zones for groundwater in the NW region.
In summary, the study shows that the northern part (Thakurgaon, Panchagarh, and Dinajpur) of the NW region is associated with ‘high’ to ‘very high’ potentiality. Remarkably, these northern three districts exhibit a low trend in groundwater level changes and have the least amount of dry season crop cultivation area among the rest of the NW districts. Further, their dominant lithology, i.e., coarse sand with gravel, has a high permeability level, which may be partly responsible for replenishing the depleted groundwater table. However, this formation has a big development constraint in drilling, hence, groundwater abstraction.
On the other hand, the southeastern part exhibits very low to low groundwater potentiality. Strangely, the dry season crop coverage is the lowest in Joypurhat, Naogaon, Natore, Chapai Nawabganj, Bogra districts but the groundwater table here has been declining alarmingly. Note that clay loam, which has a poor permeability, is the dominant lithology type in Joypurhat, Naogaon, Natore, Chapai Nawabganj, and Bogra district. Hence the potential of groundwater recharge from rainfall and surface water sources is less in this southern region. So, the paper suggests that the groundwater development program should be restricted in this area or the agriculture department should motivate farmers to cultivate alternative crops that require less water. Thus, these research findings may effectively help decision-makers formulate better planning in future water management programs with location specific information on effective production and protection of groundwater supplies.
