In the technique of horizontal stone closures, stone is deployed from both sides into the closing gap. The stone must be heavy enough to counter the increased velocity that results from the reduced flow profile. An added complication is the creation of turbulent eddies, which lead to further scouring of the seabed. It is therefore critical to lay a foundation of stone prior to commencing the closure. The closure of the Zuiderzee in 1932, as depicted in the attached photograph, vividly illustrates the downstream turbulence at the closing gap. Notably, during the Afsluitdijk closure, boulder clay was utilised in a manner akin to stone, which circumvented the need for costly imports of armourstone.
In the Netherlands, horizontal stone closures have been relatively uncommon due to the high costs associated with armourstone and the prerequisite soil protection. Conversely, in countries where stone is more affordable and soils are less prone to erosion, horizontal stone closures are more frequently employed. A notable instance of this method was the closure of the Saemangeum estuary in South Korea, where a scarcity of heavy stone led to the innovative use of stone packed in steel nets as dumping material. The logistical challenges of transporting and deploying stone, especially within the constraints of a tight timeframe to prevent excessive bottom erosion, often pose significant challenges.