19. Tile Drain

Tile drain improve the drainage of fields with poor drainage capacity. It uses underground perforated drain pipes to direct water to an outlet. It may work together with wascobs.

Required Inputs

Two shapefiles are required:

  1. Tile drain polygon shapefile to specify the location and attributes of the tile drain fields

  2. Optional tile drain outlet shapefile

The tile drain polygon shapefile must have eight data fields as shown below.

  1. id - unique ids

  2. Depth - drain pipe invert depth in mm

  3. Spacing - drain pipe spacing in mm

  4. Radius - drain pipe radius in mm

  5. Eleation - field elevation in m

  6. StartYear - the start year of operation

  7. StartMon - the start month of operation

  8. StartDay - the start day of operation

The tile drain outlet shapefile will be used as subbasin outlet. It must have an id column with unique ids.

Configuration Setup

In the model configuration file,

  • set tile_drain_boundary_shapefile to the name of the tile drain polygon shapefile.

  • set tile_drain_outlet_shapefile to the name of the tile drain outlet shapefile.

tile_drain_shapefile = tiledrain.shp tile_drain_outlet_shapefile = tiledrain_outlet.shp

Validation

Tile Drain Polygon Shapefile

  1. The shapefile is a poygon shapefile.

  2. id column is included in the shapefile and has unique values.

  3. all required columns are included in the shapefile and the values are not empty

Tile Drain Outlet Point Shapefile

  1. The shapefile has an id column with unique values.

Processing Steps

  1. Use tile drain outlet shapefile as pour point during watershed delineation if it’s defined.

  2. Generate tile drain parameter table. To determine the outlet reach id:

    1. If the tile drain outlet shapefile is defined, find the reach for each outlet and trace from each tile drain field from upstream to downstream. The first outlet is assigned to the tile drain field.

    2. Else find the lowest subbasin included in the tile drain polygon. If the drainage area is smaller than 10 ha, trace downstream until the drainage area is larger than 10 ha.

  3. Add tile drain polygon to parameter.h5