# Tile Flow

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.

| Variable Name     | Definition                                                                             | File Name |
| ----------------- | -------------------------------------------------------------------------------------- | --------- |
| IPOT              | Number of HRU that is impounding water (that contains the pothole)                     | .hru      |
| MONTH/DAY or HUSC | Timing of release/impound operation.                                                   | .mgt      |
| MGT\_OP           | Operation code. MGT\_OP = 13 for release/impound operation                             | .mgt      |
| IMP\_TRIG         | Release/impound action code: 0: impound, 1: release                                    | .mgt      |
| SLOPE             | $$slp$$: Slope of the HRU (m/m)                                                        | .hru      |
| POT\_FR           | $$fr\_{pot}$$: Fraction of the HRU area draining into the pothole                      | .hru      |
| EVLAI             | $$LAI\_{evap}$$: Leaf area index at which no evaporation occurs from the water surface | .bsn      |
| POT\_VOLX         | $$V\_{pot,mx}$$: Maximum amount of water that can be stored in the pothole (mm)        | .hru      |
| POT\_TILE         | $$q\_{tile}$$: Average daily tile flow rate (mm)                                       | .hru      |