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Anchoring a Benthic Chamber

Aquanoss Benthic Technologies offer two optional anchoring systems: the Screw-Type Anchoring System and the Grappling Anchor.  Anchoring a benthic chamber with a screw-type anchor and a grappling anchor is the best approach to set up a stable, secure platform to monitor benthic fluxes.

When To Use an Anchoring System

Except in very calm waters when the benthic chamber is to be deployed for a a very short period, we recommend using the Screw-type anchoring system with the Aquos™ BC-8 Benthic Chamber.  Rivers, coastal areas, estuaries and the sea are noted not only for strong currents, but the movement of sediment as well.  In marine environments, seagrasses and algal mats as well as benthic animals can make the secure deployment of a benthic flux chamber tricky.  The longer the deployment period, the greater the risk of the chamber toppling over or being knocked down.  The Screw-type anchoring system, in the 'Full Strength' deployment (i.e., 4 screw-type anchors deployed) is designed to hold the benthic chamber securely vertical in the sediment. 

In especially strong currents, e.g., near the sea shore where longshore currents may exist or where strong rip currents or strong coastal tidal currents are known to exist (see photograph below), we recommend deploying the 'Double Strength'  anchoring system, which involves deploying two sets of 4 Screw-type anchors for a single benthic chamber. 

Rocky beaches with strong currents demand secure anchoring of benthic flux chambers
Fig. A below shows the Full Strength Screw-Type Anchor deployment and Fig. B shows the Double Strength deployment.
Fig. A.  The Screw-type Anchor System in Full Strength deployment.  4 screw-type anchors are screwed into the sediment equidistant from each other.  Each downward-pointing arrow represents a screw-type anchor that is screwed into the sediment at that location.

Fig. B.  The Screw-type Anchor System in Double Strength deployment, as viewed from directly above the benthic chamber.  Each triangle represents a screw-type anchor screwed into the sediment.  Solid arrows represent user access to benthic chamber from all four directions after the benthic chamber is anchored.

Anchor Deployment

When deploying screw-type anchors, always ensure that the anchors are located equidistant from each other in the sediment.  This ensures that the benthic chamber is secure in all four directions.  Another advantage of equidistant spacing of the anchors is that you will then have unfettered access to the benthic chamber from all four directions.  This becomes very important when the Double Strength system is deployed, where there are now 8 cables joining anchors to the benthic chamber.  As shown in Fig. B above, as long as the anchor cables joined to a single headbolt are at a 90 degree angle, you will still have access to the chamber from all 4 directions, making tasks such as sampling from the benthic chamber very convenient.

Grappling Anchor deployment

The Grappling Anchor is an optional anchor that is offered with the Aquos™ BC-8 Benthic Chamber.  When deploying the benthic chamber in waters with strong currents, as described above, we recommend that one of the screw-type anchors be substituted with the grappling anchor as shown below in Fig. C.  In areas where longshore drift or longshore transport may occur, the sediment itself may undergo movement with the current, and the Double Strength anchor system used in conjunction with the Grappling Anchor, may well prevent the benthic chamber from being lost.

Fig. C.  The Grappling Anchor is used in place of one screw-type anchor.  The triangles represent screw-type anchors screwed into the sediment.  The grappling anchor is located upstream of the benthic chamber, in the direction of the water current.

Grappling anchors are routinely used to anchor small boats and dinghies.  However, this anchor is deployed differently with a benthic chamber than when it is used with boats.

When deployed with the benthic chamber, the folding flukes are fully opened, locked in place with the locking ring, and at least 2 flukes are firmly dug into the sediment upstream of the location that the chamber is deployed.  Ensure that the stainless steel cable between the grappling anchor (and all other anchors) and the chamber is taut.  In the unlikely event that all 7 screw-type anchors are pulled out of the sediment due to strong water currents or some other force, the grappling anchor is designed to prevent the benthic chamber from rolling away and being lost.

Screw-type anchor system
Anchoring secures benthic chambers in sandy sediment as well as from being bumped or moved by aquatic animals