River Crossings: Lessons Learned From Lowering Pipelines by Natural Flexion

When a buried pipeline is exposed in the middle of a river, the need of a mitigation action immediately arises. Lowering the pipeline by natural flexion is sometimes chosen after competing in magnitude, complexity and cost with other alternatives such as river bank and bed erosion control protections. Although simple in its conceptual design, its implementation requires taking into consideration several factors that can affect its successful outcome in terms of the final position of the pipeline and the remediation measures needed to restore the terrain and environment to its original situation. Five different field cases are presented: Río Colorado, Río Santa María, Río Negro and Río Suquía, all of them located at northern Argentina, and a fifth one placed at the Patagonian desert. For each of them references are made regarding the following issues: reasons for the selection of this option, in or out of service movement operation, depth of burial, design of the lowering curve based on pipe allowable tensions, topographic reference system, ditch design, drainage and stabilization, need for river diversion, lowering equipment, ditch interceptors design, ditch filling and soil compaction procedure, and ROW remediation. Finally, a set of recommendations are included as a way to share this experience and provide a guideline for future works.