Graveline Bayou Navigation and Habitat Study

Geoscience Consultants worked with a local environmental firm for the City of Gautier, MS and the Jackson County Board of Supervisors who were seeking authorization to conduct routine maintenance dredging to restore navigation depths at the mouth of a local bayou. A preliminary sediment transport analysis study was undertaken in order to address questions relating to sediment transport into the bayou and the possible need for a jetty structure to protect the channel.

During this initial study, however, it became apparent (Figure 1) that the issue of channel maintenance was a secondary problem and was largely a result of the extreme shoreline erosion and habitat loss that had occurred here since Hurricane Katrina. The study area was expanded to examine the trends and it was determined that the coastal land-loss issues were likely the outcome of up-drift shoreline hardening following Katrina, which starved the existing barrier spit of sediment (Figure 2) and brought about the loss of habitat. As a result the bayou mouth had widened over 400 feet and the ability of the channel to self-scour had been reduced. If the existing trends continued the channel itself is likely to silt in and change course (Figure 3).

Figure 1. 2013 aerial image of the bayou mouth; the blue outline is the 1992 shoreline and the green outline is the inland extent of the 1992 sandy beach stabilizing the spit.

Figure 2. Lidar derived elevation changes between 2005 and 2009. Blue is a loss of elevation and red is an increase. This surface was used to generate volumetric changes during the period.

Figure 3. 2015 aerial image with potential new channel location

This example highlights an interesting and important relationship between healthy shorelines and the continued use of the existing/historical navigation channels. Changing/degrading coastal habitats can have more than just environmental consequences. Examination of the coastal system as a whole along with the long-term coastal trends were important in this case to highlight the causes and make recommendations for addressing both the environmental and navigational issues in this dynamic setting.