Closing methods can be categorized into two principal groups: gradual closures and sudden closures. Within gradual closures, four distinct methods are identified: horizontal closure without a significant sill (a), vertical closure (b), horizontal closure with a sill (c), and sand closures. Sand closures further differentiate into horizontal and vertical types. Sudden closures are typically achieved through the deployment of (sluice) caissons, often positioned on a sill (d).