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Pit Inflow

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Pit Inflow

Calculations for open pits inflow are based on published analytical solutions for the following hydrogeological conceptual schemes:

Confined aquifer;

Unconfined aquifer;

Confined-unconfined aquifer; and

Leaky aquifer

Most schemes account for I-st or II-nd types of boundary impacts. The aquifer can be modelled as infinite, bounded, stripped or radial (circle-bounded).

The calculations are performed from the graphical window dialog "Pit Inflow". The dialog contains pit sketches in plan and profile as well as required fields for inflow calculations. The module will determine drawdown in a pit, when pit inflow is entered. When entering values in text box "Q, m^3/d" and "t, d"), inflow rate and time can be converted to other units using SHIFT (or CTRL) + MB.

To access this module, use "Hydrogeologist workbench > Pit inflow" or the button "Quick estimates of pit inflow" in the tab "In-Pit sumps" of the dialog window "Pit" (use button "Pit" on the dialog window AMWELLS).

 

a  b

 

c

Dialog window "Pit inflow"

 

"Q, m^3/d" text box

Information field showing the result of pit inflow calculations. If pit inflow is entered manually in this field, the calculations are conducted for drawdown

"so, m" text box

Drawdown in the pit (the same drawdown is assumed for the whole pit area)

"ε, m/d" text box

Recharge rate. This field is required for calculation of Radius of influence using the formula with recharge input

"Q', m^3/d" text box

Additional inflow. Use for circle aquifer for Neumann boundary

"s, m" text box

Drawdown in an observation well. This field is required for calculation of Radius of influence using the formula with drawdown in the observation well

"k, m/d" text box

Hydraulic conductivity

"B, m" text box

Leakage factor that is required for the "leaky aquifer scheme

"H, m" text box

Hydraulic head that is calculated in meters above the aquifer bottom. This field is required for calculations of confined-unconfined hydrodynamic conditions

"m, m" text box

Thickness of confined aquifer or initial saturated thickness of unconfined aquifer

"ro, m" text box

Effective radius of the pit. Can be entered manually or calculated (see frame "Pit radius")

"R, m" text box

Effective radius of the pit. Can be entered manually or calculated (see frame "Radius of influence"). This field is required for infinite aquifers. For an aquifer with circular boundary the entered value should correspond to the aquifer radius

"r, m" text box

Distance from the pit center to an observation well. This field is required for calculations of Radius of influence using the formula with drawdown in an observation well

"L1, m" text box

Distance from the pit center to the aquifer boundary (for aquifers with one boundary) or to the 1-st boundary (for aquifers with two boundaries)

"L" text box

Width of strip aquifer

"L2, m" text box

Distance from the pit center to the 2-nd aquifer boundary (for aquifers with two boundaries) or to the center of the aquifer (for aquifer with radial boundary)

"Conceptual scheme" list

Conceptual scheme for an aquifer (i.e. confined, unconfined, confined-unconfined or leaky aquifer)

"Boundaries" list

Hydrodynamic boundaries (infinite aquifer, stripped aquifer, square aquifer etc.) and boundary types (Neumann or Dirichlet)

"Pit radius (ro)" frame

Options to calculate pit radius using pit area, length and perimeter

"Area", "Perimeter" text box

Pit area (perimeter) that is required for calculations of Radius of influence for the non-elongated pits (ratio Width/Length > 0.5)

"Length", "W / L" text box

Pit length and its ratio to pit width. These fields are required for elongated pits with Width/Length ratio less than 0.5

"Radius of influence" list

Selects the method of calculation for Radius of influence: manually, using formula with recharge input, water level in observation well or storage properties

"Transient conditions" frame

This field is required when Radius of influence is changing with time and is calculated using hydraulic diffusivity (text box "a") or specific yield (text box "Sy") and time (text box "t"). Use this parameter for infinite aquifers and also for aquifers with boundaries that can not be modeled in steady state

Button "Heterogeneous stratified aquifer"

For unconfined aquifers. See section "Heterogeneous stratified aquifer"

Button "Report"

Creates report. This option is available in Russian language only

 

 

Analytical solutions for calculations of pit inflow (Q) and pit drawdown (so) for confined, unconfined and confined-unconfined aquifers

Boundaries

Confined aquifer

Unconfined aquifer

Confined-unconfined aquifer

Unlimited aquifer (radius of influence is required)

Radius of influence can be estimated outside of the module and entered manually. Other option is to use in-built formulas of the dialogue window:

1) general formula for transient groundwater flow:

2) general formula with recharge:

Unlimited aquifer(drawdown in observation well is required )

One boundary of the I-st type (Dirichlet)

One boundary of the II-nd type (Neumann)

Strip aquifer with two Dirichlet boundaries

Strip aquifer with two Neumann boundaries

Strip aquifer with one  Neumann boundary and one Dirichlet boundary

Square aquifer with Dirichlet boundaries

Square aquifer with Neumann boundaries

Square aquifer with Dirichlet and Neumann boundaries

Aquifer with radial boundary (Dirichlet)

Aquifer with radial boundary (Neumann)

 

Analytical solutions for calculations of pit inflow (Q) and pit drawdown (so) for leaky aquifers

 

The pit inflow is calculated using the formula for unlimited aquifer and drawdown formulas for each type of boundary

 

Boundaries

Leaky aquifer formula

Unlimited aquifer

 

One boundary of the I-st type (Dirichlet)

One boundary of the II-nd type (Neumann)

Strip aquifer with two Dirichlet boundaries

 

Strip aquifer with two Neumann boundaries

 

Strip aquifer with one  Neumann boundary and one Dirichlet boundary

 

Square aquifer with Dirichlet boundaries

Square aquifer with Neumann boundaries

Square aquifer with Dirichlet boundaries

Aquifer with radial boundary (Dirichlet)

Aquifer with radial boundary (Neumann)