OurDam02_ConceptGullyWallDam

To seal the dam wall, a so-called Core Trench is excavated down to the impermeable clay layer along the centre of the dam wall, and filled with high-quality clay. To improve the impermeability of this core, it is additionally compacted.
The next step is to smoothen both sides of the dam. The lower flank is then covered with top soil, and the core is covered with a layer of gravel so it can be used by vehicles.
Furthermore, to control the maximal water level, and to guarantee a controlled water overflow during periods of heavy rain fall, a so-called Spill Way is built across the dam wall, usually either on one end of the wall, or in its middle.

The geological Treeton formation, where our property is located, is characterised by a clay layer at 5-10 m depth, which is water impermeable. The soil above this clay layer is water permeable. It normally consist of gravel and sand, with some occasional sheets of coffee rock. Hence, a dam wall, in order to hold the water, must be sealed down to the impermeable clay layer. - Building a Gully Wall Dam includes several steps:

After the top soil has been removed, the dam wall is pushed up by bulldozers to its rough shape. Mainly the gravelly to sandy material is use. Material with higher clay content is preferably used for the upper side of the dam wall, whereas the "poorer", less clayey stuff is used for the lower side.