Tubewell Design

The tubewell design includes following factors

Upper Well Casing

The length of the upper casing is controlled by the requirements of the pump. The pump usually needs to remain submerged, with the minimum submergence recommended by the manufacturer.
The “operating” water level in the well can be calculated as the distance below ground level of the static piezometric level “static water level” (H) less the anticipated drawdown at the well (sw) less a safety margin(SF). The anticipated well drawdown (sw) is usually calculated for steady state conditions, as a function of the well design discharge and the aquifer transmissivity (or the product of the screen length and the aquifer permeability).
The Safety margin (SF) should include allowance for:
  • The variation in aquifer transmissivity due to aquifer heterogeneity;
  • Well deterioration;
  • Well energy losses (arising from flow through the screen and gravel pack);
  •  Future contingencies for well interference, seasonal or over-year decline in static water levels etc.;
So, the length of the upper casing becomes;
L = H+ Sw + SF + PR (5.1)
Where,
L length of the upper casing (m)
H depth to static water level (m bgl)
Sw anticipated drawdown (m)
SF Safety margin (safety factor)
PR Pump requirements that includes:
        • Pump submergence to the impeller inlet; plus
        • Length of pump below this point; plus
        • Manufacturer’s recommended clearance below this point;