Impacts of tile drainage

Abstract

The objective of the research described in this report is to investigate the hydrology of the agricultural drainage process, and its impacts on the land phase of the hydrologic cycle. Work included the development of an annotated bibliography following an extensive literature review. Statistical tests were performed on flow data in an attempt to identify trends in the data which could be attributed to the drainage process. Finally, the impacts of both tile drainage at the field level and ditch drainage at the small basin level were considered and analysed through the use of a physically-based hydrologic model capable of simulating the drainage process continuously through the frost free period. Required input includes field and tile geometry (field length and slope, number and spacing of drain tiles, depth of tile) , soil characteristics (depression storage capacity, depth of ploughed layer and depth to impervious layer), groundwater parameters (saturated hydraulic conductivity and drainable porosity), and meteorological data (hourly rainfall and mean daily temperature).Output includes soil moisture storage, groundwater table height, subsurface hydrograph and contribution to surface runoff. The model has been tested on two fields in southeastern Ontario. The data collection program and the techniques for the practical measurement of physical parameters for the test fields are described. The model successfully replicates observed flows and water tables for two distinct soils and for a wide range of antecedent conditions and storm rainfall. Applications of the model to the evaluation of the hydrologic impacts of tile drainage are discussed.