The drainage tab shows any wetlands, artificial drainage systems and grass filter strips.
You can add mole/tile or other drainage systems to blocks, add unfenced wetlands, add catchment details to fenced wetland blocks and/or add riparian strips to pasture blocks on this screen.
Mole/Tile and other drainage
Productive blocks can have artificial drainage specified. Only one type of drainage (either "mole/tile" or other") can be specified for each block.
If there is no artificial drainage on a block do not specify any drainage for the block.
Once drainage is specified for a block the drainage method will be displayed against the block on this screen. Drainage details can also be edited from this screen.
To delete an entire drainage system from your analyses you have to edit the drainage system by selecting the "Edit mole/tile drainage" or "Edit other drainage" button at the top of the screen, then there is a delete button at the bottom of the screen.
A fenced wetland block can be created in the block tab. Once the block is created the wetland catchment details will be required to be entered. Once a fenced wetland is created on the blocks screen there will be an error on the drainage screen on the fenced wetland block to ensure the wetland catchment details are to be entered.
Fenced wetlands cannot be deleted on this screen. They are required to be deleted on the blocks screen
An unfenced wetland can be created, edited and deleted from this screen.
If a riparian block was created on the block screen, then riparian model inputs can be specified in the Drainage tab. Select the "Specify riparian model inputs" button on the block. If these are not entered for the block the model defaults will be used.
A riparian strip/block is defined as a fenced area through which runoff water must pass before reaching a watercourse or water body. The fenced-off region is the area defined as the riparian block. Not all water captured by the catchment is intercepted by the riparian strip/block and water movement across a catchment is complex.
The riparian model within Overseer asks some detailed questions to provide a best estimate of likely efficacy of the riparian area, e.g. dimensions and amount of the catchment runoff that is intercepted. It is always of benefit to make some on-farm observations before trying to set up the riparian block.
Grass Filter Strips
A grass filter strips can be added to pastoral blocks in the Drainage tab. Select "Add Grass Filter Strip" and enter the details.
A grass filter strip is an area fenced off containing dense grass such that runoff water passes through it before reaching a water body such as a stream. Defining the effectiveness of a grass filter strip requires observation of how the strip operates during a runoff event. After making these observations, complete the fields provided on this page. Note that a grass filter strip near a stream could be a source of P. In this case P removal by the grass filter strip may be over-estimated due to no recycling of accumulated P and P bypassing the filter strip as re-emergent saturated flow.