The Discharge Adjustment tab on the MNW2 pane contains controls relating to the parameters required for the selected well loss model. The Discharge Adjustment tab will be visible if the PUMPCAP checkbox on the Basic tab is checked.
Reference head (Hlift) is the reference head (or elevation) corresponding to the discharge point for the well. This is typically at or above the land surface, and can be increased to account for additional head loss due to friction in pipes.
Maximum lift (LIFTq0) is the value of lift (total dynamic head) that exceeds the capacity of the pump. If the calculated lift equals or exceeds this value, then the pump is shut off and discharge from the well ceases.
Lift at maximum pumping rate (LIFTqmax) is the value of lift (total dynamic head) corresponding to the maximum pumping (discharge) rate for the pump. If the calculated lift is less than or equal to LIFTqmax, then the pump will operate at its design capacity, assumed to equal the user-specified value of Qdes (in dataset 4a). LIFTqmax will be associated with the value of Qdes in the first stress period in which Qdes for the well is less than 0.0.
Well tolerance (HWtol) is a minimum absolute value of change in the computed water level in the well allowed between successive iterations; if the value of hWELL changes from one iteration to the next by a value smaller than this tolerance, then the value of discharge computed from the head capacity curves will be locked for the remainder of that time step. It is recommended that HWtol be set equal to a value approximately one or two orders of magnitude larger than the value of HCLOSE, but if the solution fails to converge, then this may have to be adjusted.
LIFTq0 and LIFTqmax define the two end points of the performance curve (head-capacity curve) for the pump installed in the well. One or more additional intermediate points on the curve must be defined in dataset 2h. The model will use linear interpolation to estimate values between defined data points. The number of additional data points on the curve (and lines in dataset 2h) must correspond to the value of PUMPCAP for this well (where PUMPCAP = 25). The data entered are typically provided by the pump manufacturer. The performance curves will only be applied for stress periods in which Qdes < 0.0 and CapMult > 0. Qdes and CapMult are specified on the Pumping Rate tab.
Number of rows (PUMPCAP) Number of rows in the head-capacity table
Lift is a value of lift (total dynamic head) that corresponds to a known value of discharge (Qn) for the given pump, specified as the second value in this line.
Q is the value of discharge corresponding to the height of lift (total dynamic head) specified on the same row of the head-capacity table. Sign (positive or negative) is ignored.
