Modelling Tile Drains Under Present and Future Climate Conditions

by O'Neill, Patrick

Modelling the impact of climate change on the water from agricultural areas on a regional scale over a 40 year time period is the subject of this thesis. The Grand River watershed spans approximately 290 km with an area of approximately 6,800 km². Approximately 90% of the watershed is agricultural land some of which is tile drained. These tile drains, which cover approximately 15% of the total land of the watershed, are installed to augment field drainage. The tile drains usually outlet somewhere along the perimeter of a property; the discharge then typically moves along the surface until it discharges into a surface water body such as a river, pond, or lake.

Investigating the impact of climate change on agricultural tile drainage at a watershed scale can be achieved using modelling. The tile drains can affect both the water quality and the water quantity of a watershed. With the potential climatic changes, the storm intensity, and growing season also could change.

Spatial data for the Grand River watershed was gathered to allow for further simulation. The data for tile drained areas was added to land use/land class and soil data for the watershed to produce a map of tile drained agricultural areas.

Climate change scenarios were then simulated for each cell. Three climate change scenarios were investigated to determine the impact on tile drain discharge and the hydrological process for the watershed. The climate change

scenarios that were chosen were the A2, A1B, and the B1 scenario of the Intergovernmental Panel on Climate Change.

After the simulations were completed for the tiled areas and the results collected, the simulations showed the greatest impact of tile drain discharge in the spring season as well as the fall season.

For the tiled cells the annual average discharge was approximately 0.22 m3/ha for 1999. The average discharge was approximately 0.15 m3/ha for April of 1999. April accounted for approximately 65% of the annual tile drainage for 1999.

The climate change scenarios were simulated and the average annual discharge increased approximately 0.023 m3/ha and 0.021 m3/ha for the A2 and A1B scenarios respectively. The B1 scenario had an average annual decrease of approximately 0.022 m3/ha.