Once a subsea cable leaves the cable-laying vessel and reaches the seabed, the job is often not finished.
To reduce the risk of damage from fishing gear, anchors, and other external threats, subsea cables are often lowered below the seabed. This process is generally known as Cable Burial. 

Terminology Note: In this article, Cable Burial refers to the overall process of lowering and protecting a cable below the seabed, while Trenching refers more specifically to creating or working a trench in the seabed. The terms are sometimes used interchangeably in industry documents, but they do not always describe exactly the same engineering activity. 

Deeper Is Not Always Better
There is no single burial depth suitable for every offshore wind farm.
Engineers consider seabed conditions, fishing activity, vessel traffic, anchoring risks, and installation feasibility to determine an appropriate Depth of Lowering (DoL).
The goal is therefore not simply to bury the cable as deeply as possible, but to achieve an appropriate level of protection while balancing installation risks and costs.  

How Do We Dig into the Seabed?
The seabed can consist of sand, clay, or harder materials, so different burial tools may be required. Three common approaches are jetting, ploughing, and mechanical trenching.
 • Jetting uses high-pressure water to disturb or fluidize suitable seabed sediments, allowing the cable to lower into the seabed.
 • Ploughing works much like a giant underwater plough. The tool is pulled along the seabed to create a path while guiding the cable downward.
 • For harder ground, a mechanical trencher may use cutting equipment to excavate the seabed and create a suitable cable trench.

Lay and Bury at Once - or Bury Later?
Both approaches are possible.
With simultaneous lay and burial, the cable is buried as part of the cable-laying operation. Alternatively, the cable can first be laid on the seabed and subsequently buried using dedicated equipment, known as Post-Lay Burial (PLB). 
The most suitable method depends on seabed geology, target burial depth, cable characteristics, equipment capability, and project conditions.

So, reaching the seabed does not necessarily mark the end of a cable's installation journey. From seabed surveys and burial risk assessments to jetting, ploughing, and mechanical trenching, these operations help protect the offshore wind farm's hidden “electrical arteries” throughout their service life.


References
 • Guide to an offshore wind farm | An informative resource for offshore wind (Image source)
 • IMCA code of practice for offshore cable laying in the renewable energy industry
 • Microsoft Word - OWA_S4_CPT_Clarification-Questions_v1
 • Cables | The Carbon Trust
 • Cable Burial Risk Assessment (CBRA) guidance | The Carbon Trust