A.F.M.T. Islam
SO
ASICT section, T&C Wing, BARI
P.K.Sarkar
PSO
IWM division, BARI
The groundwater recharge potentiality in PANASI project area was studied based on groundwater level (GWL) fluctuation and rainfall data during the year 2001 to 2010. There were variations in water table fluctuation and groundwater recharge from year to year which varied from 1.91 m to 7.07 m and from 210 mm to 525 mm respectively. The GWL is not declining continually i.e. the rise and fall of GWL do not follow any definite pattern. Results proved that the maximum ground water level goes beyond the suction limit of STWs, so the operation of manual and centrifugal pumps were in danger during the study period in case of Pabna and Natore district. On the other hand in case of Sirajgonj those pumps could lift water in the dry seasons. The average recharge based on GWL fluctuation was calculated 358 mm/ season where as the average maximum allowable abstraction, considering the groundwater level to lie within the suction limit of the STW, was 306 mm/season. These indicate that within suction limit the maximum abstracted water could be replenished by monsoon season rainfall recharge. Finally an equation was derived to get recharge from monsoon season rainfall where GWL data are unavailable.
PANSI project, STW, water table fluctuation, irrigation
Pabna-Natore-Sirajgonj (PANASI) minor irrigation project under BADC
Crop-Soil-Water Management
The specific objectives of this study were to generate spatial distribution specific yield and ground water level by using GIS over the study area, to estimate the amount of groundwater recharge based on GWL in the study area, to establish an emperiucal relationship to determine groundwatrer recharge from rainfall, and to estimate the maximum allowable abstraction of groundwater for STW irrigation in the study area.
This area is situated at 250 N latitude and 800 1’ E longitudes. The study period was 2001-2010 and based on secondary data especially GWL, Rainfall and specific yield. The specific yield and GWL data were collected from BADC where as rainfall data were collected from Bangladesh Meteorological Department (BMD). BADC installed a number of monitoring well in the project area. Seven monitoring wells have been considered as basic units for the ground water level monitoring in the study area (Table 1).
Year wise recharges for each upazilla were derived from careful analyses of the GW hydrographs and aquifer properties. The average maximum fluctuation “∆H” was worked out from the hydrograph. Groundwater recharge was estimated by using the following formula:
Recharge, R= ∆H×Sy................................... (1)
Where, R= Annual recharge, mm
∆H = average maximum fluctuation “∆H” (Diff between max GWL at August-
October and min GWL at the end of irrigation season i.e. April-May)
Sy= Specific yield of soil strata
From GWL and specific yield data, GIS map was generated over the study area. A relationship was derived by fitting the estimated values of rainfall recharge and the corresponding values of rainfall through the regression technique.
Finally the maximum allowable abstraction of groundwater for STW irrigation in the study area was estimated. Considering the STW suction lift of 7 m and groundwater irrigation to generally begin in January each year, maximum allowable abstraction at each observation well location, in depth unit, maximum allowable abstraction was calculated as:
Max allowable abstraction = Ds×Sy............. (2)
Saturated thickness, Ds=GWL01 Jan-(GL-7m)
GWL01 Jan= Ground Water level at 01 January, m
GL= Ground level, m
BARI Annual Research Report 2010-2011
Results indicated that the GWL is not declining continually i.e. the rise and fall of GWL do not follow any definite pattern in PANASI project area. Results also demonstrated that in peak irrigation period the STW would be dried out in Pabna and Natore district where as in Sirajgonj district the STWs would be workable during the peak irrigation period. In case of recharge, there were wide variations of calculated recharge which did not follow any definite pattern as well. It is clear that recharges are not declining continually like GWL fluctuation. Based on the estimated recharge and observed rainfall, an empirical relationship between recharge and rainfall was developed which could estimate recharge from rainfall. Finally the results showed that the maximum abstracted water could be replenished by monsoon season rainfall recharge within suction limit in the project area.
Report/Proceedings