Water may be removed from the pothole in three different types of outflow. When the volume of water in the pothole exceeds the maximum storage, the excess water is assumed to overflow and enter the main channel in the subbasin. When the retaining wall or berm is removed (this is done with a release/impound operation in the management file), all water stored in the pothole enters the main channel. The third type of flow from the pothole is via drainage tiles installed in the pothole.

Pothole outflow caused by overflow is calculated:

$V_{flowout}=V-V_{pot,mx}$ if $V >V_{pot,mx}$ 8:1.3.10

where $V_{flowout}$ is the volume of water flowing out of the water body during the day (m$^3$ H$_2$O), $V$ is the volume of water stored in the pothole (m$^3$ H$_2$O), and $V_{pot,mx}$ is the maximum amount of water that can be stored in the pothole (m$^3$ H$_2$O).

When drainage tiles are installed in a pothole, the pothole will contribute water to the main channel through tile flow. The pothole outflow originating from tile drainage is:

$V_{flowout}=q_{tile}*86400$ if $V>q_{tile}*86400$ 8:1.3.12

$V_{flowout}=V$ if $V \le q_{tile}*86400$ 8:1.3.13

where $V_{flowout}$ is the volume of water flowing out of the water body during the day (m$^3$ H$_2$O), $q_{tile}$ is the average daily tile flow rate (m$^3$/s), and $V$ is the volume of water stored in the pothole (m$^3$ H$_2$O).

Table 8:1-3: SWAT+ input variables that pertain to potholes.

When a release operation is scheduled, all water in the pothole becomes outflow:

$V_{flowout}=V$ 8:1.3.11

where $V_{flowout}$ is the volume of water flowing out of the water body during the day (m$^3$ H$_2$O), and $V$ is the volume of water stored in the pothole (m$^3$ H$_2$O).