EFFECTS ON WATER TABLE ELEVATION DUE TO TILE DRAINAGE INTO A RIPARIAN BUFFER ZONE

Surface water quality is an issue for the agricultural Midwest. Runoff from fertilized crops introduces nutrients into water utilized for human consumption. Collaborating with the City of Bloomington, we have studied how much the water table increases due to redirected discharge from a tile drain into the riparian buffer zone, and whether this will reverse head gradient in this area. Head levels were monitored in six nests of wells, screened at 1.5m, 2.28m, 3m, and 4.57m, and four up gradient wells in a RBZ along a low-order stream. Pressure transducers installed in the wells and a diversion box that directed flow into a drainage tile within the RBZ, recorded head every 15 minutes. A rain gauge collected precipitation data. Using Decagon depth sensors rigged into wells perpendicular to the tile drain, we were able to analyze a transect of the water table in the affected tile drainage area. In July, tile water was redirected into the RBZ; this occurred during a period of drier conditions and lower tile flow. Following the diversion of tile water into the RBZ, head levels near the tile increased but slowly returned to the original water table. Head level increased 50mm at the depth of 3m and at 40mm for the screen depth of 2.28m. For comparison, the tile is at a depth of 1m. The redirection of tile water did not create a permanent water level increase. Although there is a direct correlation between tile drainage and an increase in water table elevation, the response is short lived, which may be a due to the dry conditions observed during the diversion of tile water. Although there is a direct correlation between tile drainage during precipitation events/tile drainage and an increase in water table elevation, crop runoff has minimal effects on surrounding land. Tile drainage has the greatest effect on land furthest downgradient from the tile and had progressively less of an effect on the water table as land elevation increases.