Government of Bangladesh has undertaken several groundwater based irrigation projects in the North West region of Bangladesh. The successful implementation of these groundwater irrigation projects depend on the reliable quantitative and qualitative assessment of groundwater resources. In a study, it has been observed that there is groundwater resource constraint in some of Upazilas in high barind area as Godagari, Tanore, Dhamoirhat, Gomastapur, Patnitala, Mahadevpur, Niamatpur and Nachole Upazilas.
|Digital Elevation map for Barind Region|
Surface water model simulation has been carried out under Barind to assess the dry period water availability in major rivers of the study area. The following major rivers have been included in the model.
The Ganges River enters into Bangladesh in Chapai Nawabganj District at 18.0 km below Farrakha Barrage and then flows as common border for about 106 km. A major flow diversion of the Ganges takes place from Farakka Barrage. This diverts flows. Although the flow is diverted, this river can represent the major source of dry period irrigation water supply in high Barind areas.
The Atrai River enters into project area at Simulbari from India. This river flows from north to south. At Manda, Sib-barnai River has bifurcated from Atrai. The bifurcated point had been closed by embankment.
The river flows from north to south. The river almost dries up during summer, except in the depression area along the river. This River is flowing through the eastern side of Tanore Pourashava. Water is not available throughout the year. There is no significant natural Khal flowing through the Tanore Pourashava area. However there is a beel named ‘Beel Joania’ with an area of 0.62 sq. km.
In selecting design event, most weightage has been given for 80% dependable flow. Frequency analysis for monthly minimum flow data up to 2005 for some selected locations in the major rivers have been carried out. Table 1 shows the dry period 80% dependable flow in different rivers of the study area. It is observed from Table 1 that water resources available at Atrai and Sib-Barnai are very limited. For sustainability of a river, it is not feasible to conserve or utilize all available water resources. Useable resource has been considered as 70% of the available resources and 30% of the available resources have been taken into account as "in-stream flow requirement" in the river.
Due to Barind Irrigation scheme, mass GW abstraction is occurring in this region. In this situation, potential for all likely sources should be tapped. The north~eastern part of Tanore is comparatively low and surface runoff from Barind Tract is trapped initially at this depression. A retention pond in this region may be feasible to store the rainfall runoff from adjacent catchment. The catchment has the potential for RWH to conserve a huge amount of water. There are a number of Pourashavas in the vicinity, so water supply could be effective from this conserved water. Impact of climate change on the rainfall possesses may adversely affect the flow availability of Siva Barnai and in this situation conservation scheme may be quite effective.
Rainfall and Percolation
There are two low lands named ‘Beel Kumari’ and ‘Beel Joania’ located east of the Tanore Pourashava. The combined areas of these Beels are approximately 1 km2. This area contains water round the year. There are rainfall stations at Tanore, Manda, Nachole.
IWM and BUET conducted a study to carry out seepage and percolation in several locations in Barind region in 2005. This study has found following results. Thses findings will be used to calculate the infiltration loss.
After analyzing 30 year data of rainfall, Average yearly net rainfall (after percolation) has found 961 mm. It is observed that in dry season there is apparently no rainfall and percolation rate is higher. After forming a reservoir, some water will percolated into soil. In that case, percolation loss would be a little higher. An average monthly rainfall is presented graphically below:
After analyzing recently evaporation data of Rajshahi, it found that average dry season (November~ April) evaporation loss (39.58 mm) is greater than average wet season (May~ October) evaporation loss (34.19 mm). Assuming the same catchment area total dry season evaporation loss is 158,320 m3 and wet season evaporation loss is 136,760 m3.