Este vorba de construcția unor diguri în porturi, termenul sud vine de la locația unde se construiește în portul respectiv. Iată niște exemple cu definiții și linkuri la situri legate de subiect:

https://www.portofconstantza.com/apmc/portal/vizstire.do?bif...
“Compania Nationala Administratia Porturilor Maritime SA Constanta, anunta publicul interesat asupra depunerii solicitarii de emitere a acordului de mediu pentru proiectul "Reparatii Dig de Larg - Port Constanta - Organizare de santier"”
“Compania Nationala Administratia Porturilor Maritime SA Constanta, anunta publicul interesat asupra depunerii solicitarii de emitere a acordului de mediu pentru proiectul "Reparatii Dig de Sud - Port Midia - Organizare de santier", propus a fi amplasat in judetul Constanta, Dig Sud Port Midia - Navodari.”
https://www.portofconstantza.com/apmc/portal/static.do?packa...
“NAVIGATIE Limitele portului: Portul este delimitat de Digurile de Nord si Sud”
https://www.agendaconstructiilor.ro/files/infrastructura/con...
“TRADE CONSAL make repairs to 61 million lei dams Constanta and Midia”
“As informs the contracting authority, this project involves the completion of repairs to the breakwater "Constanta Port" in the Km 0 + 000 - km 1 + 140, respectively repair works at the SOUTH PIER "Midia Port".”


https://www.slideshare.net/MAamerRaza/breakwaters-and-types
“BRAKEWATERS are structures constructed on coasts as part of coastal defense or to protect an anchorage from the effects of both weather and long shore drift.”
“A structure protecting a shore area, harbor, anchorage or basin from wave disturbance”
https://www.deme-group.com/expertises/breakwaters-harbour-da...
“DEME’s marine engineering experts have decades of experience carrying out coastal protection and improvement works by constructing breakwaters and dams. Projects range from those for the protection of coastal communities to others, where breakwaters, quay walls and harbour dams are used in port construction and expansion projects.”


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Note added at 1 day 16 hrs (2020-01-31 00:29:57 GMT)
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"DIGUL DE LARG" este "BREAKWATER"

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Note added at 2 days 5 hrs (2020-01-31 13:22:48 GMT)
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I would go with "south pier" where the item description is, then the "breakwater" for the other, but when talking generally about all of them, I'd use "dams"