Impact of Hurricane-Induced Mudslides on Pipelines
Authors: Nodine Mary C. , Gilbert Robert B. , Kiureghian Stephen G. Wright , Cheon Jeong Yeon , Wrzyszczynski Mark , Coyne Michael , Ward E.G. 
Published: March 2009

Large hurricane waves in the Gulf of Mexico can trigger mudslides on the seafloor offshore in the Mississippi River Delta. Both Hurricanes Ivan in 2004 and Katrina in 2005 produced mudslides in this area that damaged pipelines. In this paper, the mechanism of mudslides is examined concerning its practical implications on pipeline design and operations. One major conclusion is that significant waveinduced mudslides only occur when relatively large waves pass over the Delta. There have been three major hurricanes that produced significant mudslide activity in the past 40 years: Hurricanes Camille, Ivan and Katrina. A second major conclusion is that mudslides are generally localized features, on the order of several thousand feet long by hundreds of feet across by 50 to 100 feet deep, and they do not likely lead to large-scale regional mudflows. A third major conclusion is that the most effective means for minimizing the impact of mudslides to pipelines are to minimize the length of pipeline traversing the mudslide prone area of the Delta and to locate pipelines in the mudslide prone area in the deepest waters. Orienting pipelines within the area to minimize the impact of mudslides is difficult. Field data and modeling from Hurricanes Andrew, Lili, Ivan, Katrina and Rita are included to support and illustrate the major conclusions.

Introduction

Large waves caused by hurricanes in the Gulf of Mexico can trigger submarine slope failures, commonly referred to as "mudslides." In the wake of Hurricane Camille in 1969 where platforms were destroyed by a mudslide in South Pass Block 70 (Sterling and Strobeck1), Coleman et al.2 examined sediment instabilities in the offshore Mississippi River Delta region of the Gulf of Mexico and identified a large area of instabilities and mudslide activity. Facilities in this area have generally required special attention in design. We will refer to this area as the mudslide prone area in this paper.

Recently, both Hurricanes Ivan in 2004 and Katrina in 2005 produced mudslides in the mudslide prone area. Mudslides in Hurricane Ivan caused significant damage to pipelines, as described by Nodine et al.3 Using data from Hurricane Ivan, Nodine et al.3 studied the mechanism of mudslides and compared predicted performance with observations from the field. They concluded that relatively simple models are capable of predicting the occurrence of mudslides in terms of the wave characteristics and the properties of the seafloor. They also concluded that mudslides are not likely outside the mudslide prone area in the Delta.

In this paper, the mechanism of mudslides is examined concerning its practical implications on pipeline design and operations. Field data and modeling from Hurricanes Andrew, Lili, Ivan, Katrina and Rita are included to support and illustrate the major conclusions.

Mechanism for Mudslides

A schematic of the forces imposed by a wave on the seafloor is shown in Figure 1. The forces driving a shear failure in the seafloor are the weight of the soil on a slope with angle ß and the maximum bottom pressure induced by the wave, pmax, which is related to the height and length of the wave. The force resisting a shear failure is the shear strength of the soil, s, which acts over a slip surface that passes through the soil.