Evaluation of Groundwater Potentiality and Exploitation in Barind Area and Its Impact on Environment

Abstract

The study aimed to understand overexploitation, potentiality of groundwater for irrigation in Barind area and its probable impact on environmental. The study area was Chapai Nawabganj district in Barind area located in North-western part of Bangladesh. The study area consisted of five Upazilas in the district, namely Nawabganj, Shibganj, Nachole, Gomastapur and Bholahat. The study has considered secondary data collected from different organizations and five boring log samples were collected from five Upazilas of Chapai Nawabganj district in Barind area. A total of 50 representatives deep tubewells (DTWs) water samples were collected from 5 selected locations of each Upazila during the month of March (pre-monsoon) and October (post-monsoon), 2014. The experimental data were statistically analyzed using various software and the results were discussed to interpret the geochemical characteristics, water type, and water quality. The study results illustrate that the highest groundwater depletion was about 29 m found at Nawabganj Upazila in 2010 and the lowest was about 5 m at Shibganj in 2003. A 10-year rainfall data of the district showed that the maximum annual rainfall recorded was 1804 mm in 2007. Since then, rainfall was gradually decreasing for consecutive three years, but it was again increased 439 mm in 2011 from 1015 mm recorded in the previous year. The highest annual rainfall received in the area was 1793 mm in 2007 and the lowest was 1025 mm in 2010 in the district. The average rainfall received in Chapai Nawabganj district was 1372 mm during 2002-2011. The estimated run-off and infiltration results of Chapai Nawabganj district in Barind area illustrate that decreasing trends in run-off and infiltration were observed for consecutive three years since 2007, but they were increased in 2011 in all Upazilas due to higher rainfall received. The analysis results show a good relation among rainfall, infiltration and run-off indicating that the higher amount was the rainfall, the higher amounts was the estimated runoff and infiltration. A good trend of water table fluctuations of Chapai Nawabganj district was found during 2002 to 2011. The minimum groundwater level was recorded in 2004 and maximum was in 2011. The study results reveale that a good relation between rainfall and water table fluctuations was observed where the groundwater table was recharged through the rainfall. The overall yearly water table declining trend indicate that the unsustainable withdrawal of groundwater for irrigation purposes played a vital role in groundwater table depletion in the study area. Moreover, groundwater level fluctuation depended on the extraction and recharge of the area. Specific yield of the five Upazilas were determined and the values were found around 10 (%) which indicate good permeability of the areas, except Bholahat Upazila, where the value was 8.4 (%) indicating low permeability. The results illustrate that Nachole Upazila has a large storage volume, i.e., 49,305 Hec-m, but the other Upazilas have a storage capacity between 8000 to 18000 Hec-m. The storage capacity of the five Upazilas was followed the order: Nachole>Nawabganj>Shibganj>Gomastapur> Bholahat. The highest number of DTWs was installed at Nachole Upazila in the district and the extracted amount was 8848 Hec-m and the amount for the district was 26822 Hec-m . The study results indicate that the over withdrawal of groundwater for irrigation has threaten sustainable water resource management. The analysis results of the hydro-chemical composition of the DTWs water in Chapai Nawabganj district show that the groundwater of the study area was neutral to slightly alkaline pH and fresh category. Ca2+ was the dominant ionic species among the cations of the DTWs water samples, with an average of 50.37 mg/L (range 35.24-69.9 mg/L). The catonic order of the groundwater was: Ca2+> Mg2+> Na+> K+> Fe3+> As(total). Among the anions, HCO3 - was the dominant species with an average of 245.301 mg/L (range 60-510 mg/L). The major anions of the DTWs water were followed the order of HCO3 -> Cl-> SO4 2-. The Piper tri-linear diagram relating to HCO3 -, SO4 2- and Cl- showed the most of the groundwater samples contain a high amount of HCO3 - and the cation diagram showed the majority of groundwater samples contained higher amount of Ca2++ Mg2+ than Na++K+. The diagram showed that HCO3 - and Ca2+ were the dominant ions in groundwater samples. Therefore, most of the analyzed DTWs water samples fall in the field of Ca2+-HCO3 - type in the quadrilateral diagram during the pre and post-monsoon.

As the Mg2+ concentration in water samples was lower compared to the Ca2+ concentration, thus the results suggest that the water type of this area was considered to be Ca2+- HCO3 -. The analysis results suggest that the concentration of TH, HCO3, Ca, Na, K, Mg, and Fe, ions in water were the cause of weathering of aquifer materials. So, groundwater of Chapai Nawabganj district in the Barind area shows a wide range of characteristics in terms of physical, chemical and microbial parameters during two seasons. The study observed that the quality of groundwater was very much suitable for irrigation and domestic purposes. The study results illustrate the overexploitation of groundwater in Nachole Upazila has led to highest depletion (10 m) of water table in 10 years during study period. The scenario of water level depletion of the Upazila forcast the drought and water scarcity in the area will prevail if the unplanned groundwater extraction is continued in the long run. Despite a slow depletion of groundwater level in other Upazilas during the study period, a holistic approach in water resource management is very much needed for sustainable environment. The study results identified the groundwater extraction of Chapai Nawabganj district for irrigation as a critical environmental concerned. The study observe that the below average rainfall has another cause of groundwater depletion and thus further aggravated the situation in the study area. The key impediments to potentiality of groundwater have been identified as over exploitation of groundwater use in Boro rice cultivation in the Barind area. Fortunately, arsenic was not detected in any DTW water samples collected in the study despite the overdraft of groundwater in some parts of the study area. The groundwater management for sustainable irrigation and crop production in the region is imperative. A well planned water resource management would be taken to achieve sustainable use of groundwater for irrigation aiming to achieve food security as well as ecological friendly environment.