What specific seabed characteristic must be meticulously mapped during a cable route survey to prevent long-term cable damage from abrasion?

The specific seabed characteristic that must be meticulously mapped during a cable route survey to prevent long-term cable damage from abrasion is the presence, distribution, and characteristics of rock outcrops and mobile seabed features, particularly areas with exposed bedrock and the presence of sand waves or migrating gravel beds. Subsea cables connecting tidal energy plants to the grid are susceptible to abrasion, which is the wearing away of the cable's outer layers due to friction against the seabed. Rock outcrops and exposed bedrock present hard, sharp surfaces that can cause significant abrasion damage over time, especially in areas with strong tidal currents. These currents can cause the cable to move and rub against the rock, gradually wearing away the protective layers and eventually exposing the conductors. Mobile seabed features, such as sand waves and migrating gravel beds, also pose a significant abrasion risk. These features are dynamic and can shift position over time due to tidal currents and wave action. If a cable is laid across or near these features, it can be subjected to continuous abrasion as the sand or gravel moves around it. Therefore, a cable route survey must accurately identify and map the location, size, and shape of rock outcrops, exposed bedrock, and mobile seabed features. This is typically done using a combination of sonar, multibeam echo sounders, and remotely operated vehicles (ROVs) with video cameras. The survey data is used to create detailed maps of the seabed, identifying areas that pose a high abrasion risk. These areas should be avoided when laying the cable. If it is unavoidable, protection measures, such as cable burial or the use of protective sleeves, should be implemented to minimize the risk of abrasion. For example, if the survey reveals the presence of a sharp rock outcrop along the planned cable route, the route should be adjusted to avoid the outcrop. If this is not possible, the cable can be buried beneath the seabed or protected with a rock mattress to prevent it from rubbing against the rock.