ABSTRACT
The design and construction of hydroelectric projects in regions containing soluble rocks necessarily involves the creation of water retention structures whose foundation conditions have a characteristically high permeability. The solution activity common to many limestones forms conduits of unpredictable dimensions and geometry whose permeability often is measured in centimeters or meters per second. If the works are located in soluble rocks, the design and bill of quantities must adequately reflect the probable scope of work to limit leakage. The recognition and treatment of these features is of prime importance during construction. Consideration must also be given to the erosion of solution related materials such as clays and other residual weathering products caused by the increased hydraulic gradients created by water impoundment. The formation of solution features in limestone requires a long time and the process is of no concern to most civil engineering works. However, the increase in permeability associated with the removal of already formed clays by internal erosion or the rapid solution of gypsum and anhydrite must be considered in the short term. Experience generally shows that, although construction methods do overcome most of these permeability related problems, monitoring is required to observe changes in flows over the longer term and to evaluate the desirability of performing remedial works in a timely fashion. Deferred action commonly leads to a volume of leakage whose velocity complicates generally available remedial measures.
