Risks to Navigation at the Matagorda Ship Channel Entrance, Texas, Phase 2: Evaluation of Significant Risk Factors

Abstract : The Phase 1 Matagorda study (Maynord et al. 2007) examined eight factors to identify which pose a significant risk of disrupting navigation at the Matagorda Ship Channel (MSC) entrance. Three factors were identified that warranted further study of the risk of disrupting navigation. These three factors were flanking of the jetty and slope protection, strong and asymmetric currents on the bay side of the peninsula and in the bottleneck (constricted portion of the entrance channel), and slope failures that constrict the channel, create adverse currents for navigation, or lead to shoaling of the channel. The risk factor of flanking and breaching of the jetty and slope protection was found to have a minimal risk of disrupting navigation because the cross current through the breach is weak compared to the longitudinal current in the navigation channel. The risk factor of slope failure from the continuing scour of the channel bottom will have a minimal risk of disrupting navigation because the size of the slope failures are not large enough to disrupt currents or cause shoaling problems. However, slope failures will increase in frequency and severity due to the continuing scour of the bottleneck. The risk factor of strong and asymmetric currents poses a significant risk of grounding in the existing navigation channel. In the bottleneck, surface currents at the center of the channel equal or exceed 3 knots more than 60 percent of the time and equal or exceed 5 knots 20 percent of the time. Based on expert elicitation of the pilots, the reach between the bottleneck and Sundown Island (B SI) is the reach most likely to experience a powered grounding. A ship simulator was used to evaluate the effects of removal of the bottleneck.

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