Sediment entrainment in rivers caused by pipeline watercourse crossing construction may represent a constraint on pipeline route selection and construction methods as designers attempt to develop a sediment and erosion control plan which meets regulatory approval without risk of costly delays. To avoid the risk of significant sediment entrainment, conventional open-cut crossing techniques may be replaced by more costly directional drilling methods. However, the concern over suspended sediment is greatest in high velocity rivers where the bed material includes a large fraction of fine sand, and in rivers with a large fraction of fine grained bed material which becomes suspended upon disturbance by construction activities. According to the current understanding of aquatic impacts due to elevated suspended sediment levels, the occurrence of suspended sediment may not be excessive at open-cut excavation in certain types of streams depending on the material consistency, fine sand content and river flow velocity (Anderson et al, 1996). Control of sand entrainment can normally be achieved by low cost sediment control systems during construction. Methods of prediction, impact assessment, and control of sediment entrainment have been developed so that high risk crossings can be identified and impacts minimized. The application of the study findings and best management practices (BMPs) for sediment control will allow developers to choose the most appropriate crossing method while avoiding potentially adverse impacts, based on a sound understanding of river sediment transport, bed material conditions and downstream aquatic resources.

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