Backdam

Two side dams are likewise thrown up, and extend as far as the cultivation, where they join a back dam; so that an estate is a complete island within itself, and dammed on all sides.

Source: wiktionary

[...] I, by these presents, sell, alienate, and in feu-farm dispone from me, my heirs and successors, to and in favour of James Boog, [...] that small piece of ground at Canonmills, on which eight lime pits are built, lying betwixt the foredam and the backdam, on a narrow point, [...]

Source: wiktionary

Back[-]dams had been built to allow of the utmost time being spent by the men in the foundations. When the sea receded from the dams the water was pumped out by steam power from a floating engine lying 120ft. from the rock, and the men were then able to work inside the dams until the water again overflowed.

Source: wiktionary

During the excessively heavy rainy season of 1907 the Saramacca River rose so high that in many places it overflowed its banks and flooded the cacaofields, so that the trees were standing in water. On the estate Johanna Catharina on the right bank of the river, the backdam broke, so that bushwater came in; at „De Morgenster“ it oozed through the backdam.

Source: wiktionary