Abstract:
The study was undertaken in the Teesta Barrage Project (TBP) area. Eight out of total 12 Upazilas under 3 Districts: Nilphamari, Rangpur and Dinajpur are considered for the current study to compare the pre and the post project groundwater conditions, to develop a statistical prediction model for groundwater storage change, to analyze the design surface water availability and to evaluate the prospect of groundwater irrigation in conjunction with the surface water during different cropping seasons. The Teesta Barrage Project went into operation in 1993. Since its implementation the irrigated area of the project has been increasing and the maximum irrigated area of 76000 hectare during Kharif 11 season was achieved in 2005. With the increase in irrigation area the recharge area from irrigated surface water in the project area has increased. It is found that the supplementary irrigation during Kharif II has a significant impact in increasing the groundwater recharge. An analysis was done with the weekly and the yearly maximum and minimum groundwater data within the project area. Similar analysis was done for outside the project area to evaluate the impact of the project on the groundwater system in the project area. It is observed that groundwater level in the project area has been increasing after the project implementation but this has been decreasing outside the project area. Again after project implementation groundwater withdrawal rate is increasing with time for dry season irrigation. This increased rate of withdrawal and the rise of groundwater level is the contribution of the surface water supplied through groundwater recharge. It is further observed that groundwater level has been increased not only through recharging from supplementary irrigation but also direct recharge from the rivers and the local rainfall. In respect of Teesta River flow at the project site it is observed that in the Teesta River at the project area the maximum water is being flowed on August (Kharif -11 season ) and minimum water is being flowed on February (Rabi season). It is observed that the design required quantity surface water flow is available during Kharif-11 season but is very small during Rabi (Boro) season. Historical discharge analysis shows that the Teesta River discharge is decreasing significantly all through the year. From 1990 to 2005 the discharge has decreased by 40% both in Karif II and Rabi seasons and this figure is lower during the Kharif I season. Thus, the decrease in flow of Teesta River has would cause non-availability of water for surface water irrigation and no recharge to the groundwater affecting the groundwater irrigation most importantly during the dry season. Therefore, there is potential to increase the groundwater irrigation in conjunction with the surface water during the different cropping seasons provided the flows of Teesta River would be maintained to supply design surface water during Kharif II season and the river water level is always above the groundwater.
