Drain Package (DRN)

Please Register

Last modified on Wednesday, January 31, 1996 - 5:33:54 PM

Skip forward to Input instructions for the Drain Package.

The original instructions for the Drain Package are on pages 9-77 to 9-8 of McDonald and Harbaugh (1988).

Introduction: The Drain Package is used to simulate discharge into agricultural drains. Unlike the River or Streamflow-Routing packages, no recharge of the aquifer can occur from the drain. Instead, if the head in a cell drops below the base of the drain, no flow occurs between the drain and the aquifer. If the head in the aquifer is higher than the base of the drain, discharge into the drain is a linear function of head.

Go back to Contents.

Input Instructions

• Line 1
  • Spaces 1-10, MXDRN, Integer, Maximum number of drain cells active at one time
  • Spaces 11-20, IDRNCB, Integer, (You must also set ICBCFL in the Output Control option to print or save cell-by-cell flow terms.)
    • if IDRNCB > 0, IDRNCB is the unit number for cell-by-cell flow terms;
    • if IDRNCB = 0, cell-by-cell flow terms will not be printed or saved;
    • if IDRNCB < 0, Drain leakage will be printed on the main output file.
• Lines 2+, One copy of Lines 2+ followed by 0 or ITMP copies of Lines 3+ are read for each stress period.
  • Spaces 1-10, ITMP, Integer
    • If < 0, Drain data from the last stress period will be reused
    • If >= 0, ITMP is the number of active drains during the current stress period.
• Lines 3+, The number of copies of Lines 3+ depends on ITMP in Lines 2+
  • Spaces 1-10, Layer, Integer, The layer number of the cell containing the drain
  • Spaces 11-20, Row, Integer, The row number of the cell containing the drain
  • Spaces 21-30, Column, Integer, The column number of the cell containing the drain
  • Spaces 31-40, Elevation, the elevation of the base of the drain
  • Spaces 41-50, Cond, hydraulic conductance of the drain (length^2/time)

Line 1, Spaces 1-10, Variable = MXDRN, Integer

Go back to Input instructions for the Drain Package

Line 1, Spaces 11-20, Variable = IDRNCB, Integer

• if IDRNCB > 0, unit number for cell-by-cell flow terms;
• if IDRNCB = 0, cell-by-cell flow terms will not be printed or saved;
• if IDRNCB < 0, Drain leakage will be printed in the main output file.

Lines 2+, Spaces 1-10, Variable = ITMP, Integer

• If ITMP < 0, Drain data from the last stress period will be used. There will be 0 copies of Lines 3+ immediately following this copy of Line 2.
• If ITMP >= 0, ITMP is the number of active drains during the current stress period. There will be ITMP copies of Lines 3+ immediately following this copy of Line 2.

Go back to Input instructions for the Drain Package

Lines 3+, Spaces 1-10, Variable = Layer, Integer

Go back to Input instructions for the Drain Package

Lines 3+, Spaces 11-20, Variable = Row, Integer

Go back to Input instructions for the Drain Package

Lines 3+, Spaces 21-30, Variable = Column, Integer

Go back to Input instructions for the Drain Package

Lines 3+, Spaces 31-40, Variable = Elevation

Go back to Input instructions for the Drain Package

Lines 3+, Spaces 41-50, Variable = Cond

1. Measure the discharge to the drain (discharge downstream - discharge upstream).
2. Measure the head in the drain.
3. Measure the head in the aquifer at a distance from the drain.
4. Compute the difference in head between the drain and the aquifer.
5. Repeat these measurements at a variety of drain discharges.
6. Correlate discharges (y) to head differences (x).
7. The conductance is the slope of the line relating y to x. The line should pass through the origin.

Go back to Input instructions for the Drain Package
Go back to Contents.