Modelling Soil Erosion, Sediment Transport and Closely Related Hydrological Processes (Proceedings of A(\H a symposium held at Vienna, July 1998). IAHS Publ. no. 249, 1998. w / Transport characteristics of tile drain sediment in clay loam soils M. STONE Environmental Studies, University of Waterloo, Waterloo, Ontario, Canada NIL SGI B. G. KRISHNAPPAN Aquatic Ecosystems Protection Branch, National Water Research Institute, Burlington, Ontario, Canada L7R 4A6 Abstract Increasing use of subsurface tile drains in agricultural watersheds has created concern for sediment delivery to receiving waters and potential undesirable effects on surface and subsurface water quality. In this study, transport characteristics of sediment from tile drains in predominantly clay- loam soils of a southern Ontario watershed were tested in a rotating circular flume located at the National Water Research Institute, Burlington, Ontario. Tile drain sediments were collected and mixed with river water at different speeds in the flume to study transport processes such as deposition, erosion and flocculation as a function of bed shear stress. Empirical relationships are developed to describe erosion and deposition processes of tile drain sediment. The relationships are in a form suitable for use in the fine sedi- ment transport model developed by Krishnappan (1997) and can be used to predict transport characteristics of tile drain sediment in receiving streams. INTRODUCTION Areas of highest sediment yield in the Laurentian Great Lakes basin coincide with agricultural and industrial land use activities in basins with fine-grained glacio- lacustrine parent materials (Stone & Saunderson, 1996). There are management concerns about the effects of irrigation practices on the delivery of cohesive materials to receiving streams (Richards & Baker, 1993) and the role of these materials in the fluvial transport of contaminants (Ongley et al., 1992). While some information is available on transport properties of cohesive sediment in rivers (Krishnappan, 1997) and lakes (Lick, 1982), much less is known about transport characteristics of fine-grained tile drain sediment in relation to soil texture. Empirical relationships quantifying erosion and deposition processes are required to model the transport and fate of cohesive sediment and associated contaminants. In this paper, transport characteristics of tile drain sediment collected from a southern Ontario agricultural watershed with silt-clay soils are studied in the laboratory using a rotating annular flume. Empirical relationships required for a fine sediment transport model developed by Krishnappan (1997) are determined. METHODS The tile drains under investigation are located in a sub-catchment of the Sydenham River near St Thomas, Ontario. Soils at the study site are characterized as the Huron