Channel Shoaling with Deepening of Houma Navigation Channel at Cat Island Pass, Louisiana

Abstract

ROSATI, J.D. and LAWTON, C., 2011. Channel Shoaling with Deepening of Houma Navigation Channel at Cat Island Pass, Louisiana. In: Roberts, T.M., Rosati, J.D., and Wang, P. (eds.), Proceedings, Symposium to Honor Dr. Nicholas C. Kraus, Journal of Coastal Research, Special Issue, No. 59, pp. 256-265. West Palm Beach (Florida), ISSN 0749-0208. This study evaluated the potential increase in shoaling and associated sources of sediment as a result of proposed channel improvements for the Houma Navigation Channel in the vicinity of Cat Island Pass, Louisiana. Using morphologic change data and historical maintenance dredging rates, historical and forecasted with-deepening sediment budgets were developed. Conclusions from this study were that deepening the channel from 5.5 m to 6.1 m relative to Mean Low Gulf, a local low water datum, would increase the shoaling rate from the present 191,000 m 3 /year to 220,000 m 3 /year, and the likely source of shoaling would be sediment that is presently bypassed naturally. It was recommended that all environmentally-acceptable sediment dredged from Cat Island Pass be placed on the downdrift barrier island, East Island, part of the Isle Dernieres barrier island system. Clays and silts should be placed on the bayside of the island and sand similar to or coarser than the existing beach sand should be placed downdrift of the nodal zone on the Gulf side of East Island. Historically, sediment dredged from Cat Island Pass has been placed in designated dredged material disposal sites located 760 m west of the channel. Based on morphologic change in the region from 1980 to 2006, it appears that sediment may be transported from this placement site to deposit back into the channel. It is recommended that, if sediment cannot be placed on either East Island or Timbalier Island, that the dredged material disposal site be moved further to the west, away from the channel. Finally, based on movement of Timbalier Island and Cat Island Pass over the past 100 years, it is recommended that the channel be moved further to the west to avoid future impingement by Timbalier Island. Based on the results of this and other studies of the Houma Navigation Channel, channel realignment was approved in 2009, and authorization of the deepened channel is being requested during 2010.