Hi Niam

The construction of an earth fill dam is a simple balance of the anticipated flow of the river and the speed that the dam can be constructed.

The biggest risk is overtopping which is where a flood will flow over the partly completed dam and wash it away.

There are two ways around this:

1. Complete river diversion through a relief chanel - best way but expensive.

2. Part river diversion through the turbine tunnel.

So stage 1 is the completion of the diversion and construction of the haul roads.

You may need a grout curtain through the river bed cracks so this will need a temporary coffer dam.

Stage 2 is getting enough haul units to carry both the clay infill and the earth embankments to build up the dam ahead of the rise in the river. Also make sure you have enough consolidation units at the dam to handle the incoming fill. You will need a colts foot roller for the clay core and vibrating rollers to compact the granular fill in the specified layers.

This is a crucial calculation and needs expert engineering input.

The higher up the dam the less earthfill is needed so it goes up quicker.

Start at the beginninbg of the dry season and consider using conveyor belts from the borrow sites.

Most contracts allow for the possibility of a 50 year flood as the employers risk.

When the dam has reached its top level then you place the riprap and construct the spillway.

The trubine hall can be started downstream when the dam is about halfway up when the risk of overtopping is reduced.

Installation of the turbines should coincide with the topping of the dam.

BTW a concrete dam will withstand an overtopping.

I trust that helps.

Best regards

Mike Testro