Use of Rock Revetments to Protect Industrial Facilities – Three Case Studies
WODCON XXIII - Dredging is changing - The Practice. The Science. The Business.
K. Badu-Tweneboah, R.G. Mijares
"Rock revetments are widely used in areas with important backshore assets subject to severe and ongoing erosion where it is not cost effective or environmentally acceptable to provide full protection using seawalls. The function of permeable revetments is to reduce the erosive power of the waves by means of wave energy dissipation in the interstices of the revetment. Revetments may not prevent on going shoreline recession unless they are maintained, and, if necessary, extended. If the shoreline continues to erode, the rock revetment may slump down, becoming less effective as a defense structure, but will not fail completely. Repairs and extensions may be necessary to provide continued backshore protection at the design standard. The authors have used rock revetments to protect three industrial facilities along the coastal areas located on the Savannah River and Atlantic Ocean in Savannah, Georgia, the Gulf Coast in Mississippi, and the St. Johns River and Atlantic Ocean in Jacksonville, Florida, all in the USA. These areas have been or were subjected to on-going or instant erosion from natural and man-made forces. Savannah River facility At the Savannah River facility, most of the severe erosion is caused by the frequency, travel speed, and resulting wave actions from ships passing through the river to the Savannah Harbor in addition to natural erosion from tidal effects from the river. Armor stones weighing as much as 1.8 tonnes (4,000 lbs.) are easily uplifted and thrown out by the wave action from ship traffic and then results to the shoreline being exposed to severe erosion. This, therefore, becomes expensive to the facility in its continual efforts to protect the shoreline. Since 2008, the authors have developed a long-range shoreline protection maintenance plan for maintenance of the shoreline from severe erosion. The plan consists of using a phased approach whereby the shoreline is broken down into four zones (A to D) with Zone A being areas of active erosion and areas of on-going loss of shoreline and Zone D being areas of limited erosion and areas of moderate potential for loss of shoreline. An implementation plan is then developed following annual site reconnaissance of the shoreline conditions. Stabilization consists of use of armored systems – armor stone, riprap underlayer stone, and gravel bedding layer – to repair areas that have experienced severe erosion (i.e., Zone A). Figure 1 shows a typical section illustrating one of the shoreline protection stabilization measures. The armor stone weight, size and gradation are generally designed or selected based on the studies performed by the U.S. Army Corps of Engineers (USACE 1984), Ahrens (1981), and the authors' experience. The underlayer stone and gravel bedding layer function as granular graded filter and are generally designed based on the guidelines established by the USACE (1955). Gulf Coast and St. Johns River facilities The experience gained from this facility were applied to the other two facilities. The Gulf Coast facility had a storm surge wall (i.e., seawall) that was susceptible to scour due to wave action under normal conditions and during a tropical storm/hurricane event. In 2012 it experienced significant scouring from Hurricane Isaac. The authors designed a seawall scour protection system consisting of rock revetments, as shown in Figure 2, and provided oversight during construction. The third facility located along the St. Johns River experienced severe erosion damage during Hurricane Irma in 2017. The design was broken down into three phases from severe and imminent to less severe, similar to the long-range plan for the Savannah River facility, to allow ..."
Keywords: rock revetments; shore protection; armored systems; shoreline erosion