One of the advantages of marinas as compared to stationary bridges is that they are capable of following the water up and down. However, the bridges must be properly fastened in the horizontal direction. For the anchoring of a bridge concrete anchor, fastening balks or fastening struts may be used. 

Concrete anchors

The fastening of bridges and anchoring buoys by means of concrete anchors and chains is the most commonly used way of anchoring. Proper installation of concrete anchors with self-anchoring capacity is easy and safe and ensures sufficient movement for the bridge. If concrete anchors are used, they require sufficient depth (at least 1m). 
The armoured concrete of the anchors and the mooring rings are seawater and heavy impact resistant. The size and amount of anchors is chosen depending on the size of the bridge and the type of earth. The anchoring power can be increased, by adding intermediate weights. The length of the fastening chain of the anchor is five times as deep as the water. Intermediate weight is placed in the middle of the chain.