According to the present invention there is provided a liquid retention device comprising: a braced frame mountable on foundations in a plurality of locations, in which said device comprises a base section and at least one upstanding support, and in which said brace further comprises height-adjusting means for adjusting the height of said frame, and in which said device further comprises a face supported by said frame, in which said face is inclined at an angle to the at least one upstanding support, wherein said face is covered by a least one detachable mat.
