A Workable Solution for the Removal of Sediments From Storage Dams


Abstract
Storage type dams, regardless of weather they produce hydropower or are part of an irrigation scheme -- are subject to the significant and substantive buildup of sediments over decade and century long timeframes.

It must be noted that once river sediments fill in the upper levels of a dam (or completely fill in the basin behind the dam) the dam becomes structurally and functionally useless. This sedimentation process is part of the operation of all storage type dams, but in most cases is reversible.

The sedimentation process can be halted or reversed with most storage type dams, but special engineering processes are required. The abyssal water pressure inherently existant behind storage type dams can be used to flush out the accumulated sediments if the proper use of the dam's existing construction interfaces are used. However, most storage dams will be rendered non-functional during the sediment flusing process until it is redesiged to pass sediments.

Very few modern dams are designed to pass sediments without any structural impediments. The mixed "run of the river, storage type" dam that China commissioned on the Yellow River is capable of passing sediment -- and in many ways is the only one of its kind.

However, any storage type dam can be redesigned to pass sedimetns if it is shut down. 

 

Overview
The way storage dams (and almost all "run of the river" dams) are built requires that the river or stream be diverted. The result almost universally is that there are two penstock like tunnels on each side of the dam that divert the water around the dam construction area. These tunnels are sealed off with concrete (and often backed with stone or steel doors) while the dam is in normal operation.

These sealed off river tunnels are nominally accessible to dam personnel for structural inspection reasons. Most river access tunnels are often quite huge, some being up to 250m in radius and nearly universally at less than a 5 degree downward slope. There is plenty of room to pass plenty of sediment thru these tunnels.

The economic cost of filling these river access tunnels with concrete or conglomerate are high to extremely high. Hence, in normal operation the river access tunnels are never filled in and the cost of doing so is almost never factored into normal dam cost or normal operational running costs of the dam.

So, every storage dam has a free set of channels for flushing sediments. It can be used. 


General Procedure
The process for sediment removal can be broken down in a series of stages.

Stage 1

Stage 2

Stage 3

Stage 4

Stage 5


Repeating this procedure, for a completly clean sweep of sediments

Stage 1

Stage 2

Stage 3

Stage 4
















References

General dam design

The way storage dams are built

Penstock and like structure issues  

Fluid dynamics issues

Notable storage dams with this problem

Civil engineering issues downstream





Created by
Max Power

Created
11 June 2013

Last Updated
13 July 2013

Last Update
Created document

Revision State
Initial Draft 0.25a