Frequently Asked Questions
Is the BRNS considered a Groyne?
To the uninformed, the initial impression may be “it looks like an underwater groyne”. It isn’t. Groynes generally work like a sea wall to stop the force of the wave energy with equal or greater force (weight of the rocks). If you have large waves, you will need to counter the force with a large groyne—the larger the groyne, the greater disturbance to that area’s equalization, and the more disruption to upstream and downstream beaches.
The primary difference between the BRNS and traditional hard structures is that a BRNS is engineered to absorb energy, similar to a healthy beach, not “reflect it” back offshore like a traditional hard structure would. This is why immediately after installation; the initial disruption in the “erosion process” will equalize in a few days and reverse creating a stabile, accreting beach and healthier environment.
Why is the Beach Recovery Nourishment System (BRNS) the long-term solution?
Most engineers and geologists generally agree that dredged and jettied channels cause widespread beach erosion. However, the reason why channels do this may be defined differently by the two disciplines. Engineers assume that jettied inlets interrupt the "river of sand," presumably the only source of sand for other beaches down the line. They consequently design sand bypass plants (fixed dredges) which are intended to transfer sand across the channelized interruption. For several reasons, such plants have seen little success in solving unnatural erosion. A primary reason for the ineffectiveness is incorrect modeling of natural sedimentary behavior.
From certain geological perspectives, jettied navigation channels do not interrupt a "river of sand," per se, rather they disrupt large onshore / offshore circulation cells. The resulting erosion causes a steepening of nearshore beach profiles in the vicinity of the channel. As profiles steepen with erosion, nearshore turbulence increases. Eventually this turbulence creates a kind of barrier, preventing the beach from accepting the onshore movement of sand from historic offshore reserves. More sand leaves than enters the beach system because of both channelized diversions and, of equal or greater significance, profile anomalies (channel-induced) that lose rather than gain sand from available sources. Geologists call this condition a "profile of deficit."
Beach profiles are sensitive to distribution of sediment sizes (the location of specific grain sizes on the profile). Sediments of varying size "find" a location on the profile where it is most stable. This is called a particle's "equilibrium position." Where the profile is relatively steep, generally nearest shore, larger sediments are more stable. As the profile shape becomes less steep (offshore, in deeper water) finer sediments become stable. Dredged beaches wash away in part because grain size distribution across the man-made profile is random and improperly sequenced. Waves and currents "work" the artificial fill. In the reordering process, most of the fill is lost offshore, unable to return naturally because of turbulence on the re-steepening profile.
An alternate approach to neutralizing the effects of dredged channels is to plant special (beach nourishment tube) structures in the nearshore which mimic the type of geology which causes natural beach profile elevation. Sand accretion on this type of "induced" profile is correctly sequenced with respect to grain size distribution (because natural processes rather than dredges guide the resedimentation process). Though inlets in the vicinity of treated beaches still jet sand offshore, less and less sand travels to the inlet "loss point" as the beach grows and becomes progressively more efficient at holding sand arriving from historic sources.
Beach Recovery’s BNS Technology has proven to neutralize the effects dredged channels have on shorelines. The system has caused natural beach growth in many locations, including severely eroded areas immediately downdrift of large navigation channels, without relying on continuous beach dredging programs or sand bypass plants.
How does sand move and where does “natural” sand come from?
Beach formation begins as eroded continental material--sand, gravel, and cobble fragments are washed to sea by streams and rivers. Two separate processes result in the deposit of this sand and sediment on the shore. Most sediment is suspended in sea water and transported along the coast by the longshore current, a stream of water flowing parallel to the beach that is created by the action of waves breaking at an angle to shore.
Longshore transport can deliver up to a million cubic yards of sediment annually to a single beach. In the second process, sand deposited onshore by the longshore current is then oscillated by waves breaking onto and receding from the beach. This continual onshore-offshore movement gradually pushes the sand along the beach edge. Both the longshore transport of sediment along the coast and the movement of sand by waves along the foreshore are a part of the process called littoral drift.