COIR LOGS
COIR LOGS
This method involves the installment of logs used to combat erosion caused by wave energy and to trap sediment on the shoreward side of the log . This method is useful when conditions for oyster-based methods are not appropriate and accretion of marsh sediments is desired . In addition to coir logs stabilizing shorelines through the accretion of sediment , marsh plants can gradually colonize the portion of the bank on the shoreward side of the log . This results in the indirect creation of marsh habitat .
Site Selection
Coir logs can be placed in a range of positions along the intertidal bank , extending from directly bordering the marsh edge , to halfway between the marsh edge and the MLW line if a larger area of sediment accretions or marsh grass growth is desired . These logs perform best in low energy environments , where the likelihood of being dislodged and rapid degradation of the materials is minimized . Saline environments also facilitate the breakdown of organic materials , such as coir logs . Areas of open water with low salinity can extend the life of the coir fibers and reduce the number of times they need to be replaced . Below is a general overview of preferred conditions for the placement of coir logs and similar sediment entrapment devices :
›››› Lower salinity aquatic environments
›››› Low wave energy
Preparation and Materials
Coir logs are biodegradable cylinders of compressed coconut husk fiber , also known as coir . They are wrapped in a coir or jute netting that contains the compressed coir . They are available in a variety of lengths and widths but are typically sold in 10-foot lengths ( SCDNR , 2019 ). SCDNR has found it useful to “ wrap the coir log in an additional layer of coir netting with smaller openings to better contain the compressed coir fibers and lengthen the life span of the coir logs in the estuarine environment ” ( SCDNR , 2019 ). According to SCDNR , a folded underlayment of coir fabric is also beneficial at sites with soft or very soft sediment (> 10cm sink depth ). This underlayment reduces the amount that the coir log sinks into the soft sediment .
Coir logs are expected to degrade over time and will need to be replaced on a periodic basis if the stabilization of the marsh has not been achieved . It is important to note that coir logs are not expected to last beyond 5 years ; a 2-3-year lifespan is said to be more realistic , due to vulnerability to environmental conditions like dislodgement due to wave energy and material deterioration from salt .
Installation
Coir logs should be deployed in a gentle “ U ” configuration , with the inside bend of the U facing shoreward , and can be arranged in single or double rows . Double-row structures are ideal for trapping more sediment between the rows of logs . With this structure , the shoreward log can be placed at the marsh edge or pressed against an escarpment to protect an eroding area from wave energy , while the waterward log can run parallel downslope to facilitate sediment accretion . SCDNR recommends placing the waterward coir log at approximately 6 feet downslope from the shoreward log .
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