The Deep Tubewell drilling site is located at Bhanu-9, Turture Aalubari, Tanahu. The GPS coordinate of the project site is 28º02’11.6” N/ 84º27’22.9” E. The well site is easily accessible through the motorable road and is about 0.2 km to the west direction from Dumre- Besisahar-Chame Highway.
The main objective of the work was to construct the deep tube well and develop for the drinking purpose. The major scopes of works carried out were:
- Construction of deep tube well up to required depth
- Design of tube well and development of well assembly
- Lowering of casing pipe and well screen
- Well development
- Pumping Test
The present study area is physiologically characterized by mountains, hills and valleys, sloping land, and terraces. The area consists of sedimentary rocks such as sandstone and shale, as well as metamorphic rocks like slate and phyllite. Geologically, it lies in the Gyalung Formation. The area is influenced by numerous rivers, streams, and precipitation patterns including Seti Gandaki, Madi, and Marsyangdi rivers.
The well development by air compressor and pump test work was done after the installation of the Tube well. Development of the tube well was carried out immediately after installation of the pipe assembly. The well development has broad objectives:
- To repair the damage done to the formation (aquifer) by the drilling operation so that the natural hydraulic properties are restored.
- To alter the basic physical characteristics of the aquifer near the borehole so that the water will flow more freely to the well.
After the water well is developed, a pumping test of the well shall be conducted to determine the performance characteristics of the well and the hydraulic parameters of the aquifer. From the pumping test data, the principal factors of aquifer performance like transmissivity and storage coefficient can be calculated. Measurements taken in this pump test are:
- Static Water Level just before the start of the pump test
- time since the pump started
- pumping rate
- pumping or dynamic water level at various intervals during the pumping period
- time of any changes in discharge
- time at which pumping stopped
- water level after the pumping is stopped (recovery) at various intervals.
The pumping test was carried out by Constant-Rate Test. From the constant rate we obtain the value of Transmissivity and hydraulic conductivity using semi-log graphs (time-drawdown graphs) and the Cooper-Jacob method.
The well was tested at different discharge rates and the continuous pumping test was conducted at 14lit/sec discharge rates for the period of 24 hours.
The constant-rate test was conducted by using 15 HP electrical submersible pumps. In this test, the well is pumped at a constant rate for 24 hrs. The pumping test data and measurements taken during the pumping test are shown in Annex D. The static water level was 60 m. The dynamic water level after 24 hours was 70 m at 14 l/s discharge.
The Transmissivity and hydraulic conductivity are:
Transmissibility (T) = 22.90234m2/day
Hydraulic Conductivity (k) = 0.55m/day
After 1440 minutes of pump operation, the constant rate pumping test was stopped. A recovery test was conducted immediately after the pump had stopped. It took 12 minutes to recover the water level to the initial level (Annex D).
4. GROUNDWATER PRODUCTION
Static water level – 60 meters
Dynamic water level – 78meters
Discharge adapted for test – 14 lit/sec
5. CONCLUSION:
The well is 200/150mm in diameter. The screens are placed at different layers of the aquifer with a total thickness of 42 meters. The static and dynamic water levels of the well are 60 m and 78 meters respectively discharge of the well is about 14lit/sec. which indicates that the well is successful.
Depth(m) Lithology Thickness(m) Remarks
From To
List of Photographs:
Photograph of construction site and drilling work.