Managing sedimentation to ensure hydro sustainability

One of the most important factors influencing the sustainability of hydro projects is the efficiency of the project concept related to the management of sedimentation of the storage reservoir and/or intrusion of sediment into the power discharge for run-of-river hydro projects. Unfortunately the project design criteria in the past often neglected the requirements of aspects related to sediment management consequently some of the major hydro projects in the world are facing the adverse impacts of sedimentation.

Sediment related problems affecting hydro projects are becoming more and more evident especially in areas where the rivers transport large quantities of sediment in suspension. The nature of problems encountered are:

•  Sediment load experienced by the projects are much in excess of rates estimated during the design stage.
• Loss of storage volume often much faster than predicted during the design stage resulting in sediment intrusion into the power discharge only after a few years of operation .
• Performance of various types of conventional sediment excluders like sedimentation chambers with continuous sediment flushing systems are often marginal and turbines and associated components are subjected to severe abrasion. As a result at times plant shutdown during high river discharges is necessary, causing significant loss of annual energy production.

Analyses of some of the existing projects enable us to conclude that experiences did not serve as lessons for future projects and some of the unsuccessful design concepts were repeated causing same type of problems.

In the design of future projects we should avoid proposing project concepts and structural arrangements which did not perform satisfactorily. Thorough investigations of the causes for which the projects did not perform should be made and the finding should be published so that others may benefit from these experiences.

Some of the design parameters and features that in our opinion should be carefully appraised so that improved sediment management may be achieved are the following:

1. Site selection and general layout
2. Sediment transport characteristics at the project site
3. Characteristics of sediment material
4. Project concept and structural arrangements
5. Settling basin concepts and their usefulness
6. Project operating procedures for sediment management in the reservoir itself
7. Importance of state-of-the-art physical modelling