Climate Sense

[

] 206

A Nordic perspective on

climate change and dam safety

Sten Bergström and Johan Andréasson, Swedish Meteorological and Hydrological Institute, Norrköping, Sweden

ne fundamental issue in dam safety work is proper

assessment of the design flood. If this flood is underes-

timated, there is a risk of failure of the dam, often with

disastrous consequences. There are also environmental concerns

related to dam safety. A major dam failure will, of course, have

huge environmental consequences when industrialized areas are

flooded. But smaller mine tailing dams can also be hazardous.

They are also likely to have a longer exposure period, as they are

often designed to remain as a deposit of waste after the mining

activities are finished. In Sweden alone, there are as many as

10,000 dams for various purposes. The most important ones are

components of the hydropower production system.

Design flood determination is one of the most important ques-

tions in scientific hydrology. Traditionally, the concepts Probable

Maximum Precipitation (PMP) and Probable Maximum

Flood (PMF) have been used by many countries. PMF

is a very extreme flood that cannot, in principle, be

exceeded. Unfortunately, the scientific foundations for

the concepts of PMP and PMF are somewhat shaky,

with the prospect of global warming further complicat-

ing the situation.

For the hydroelectric power industry, a new situ-

ation has arisen. Large investments have been made

to upgrade dams to comply with the latest safety

requirements. At the same time, the mining industry

has realised that the hazards of global warming cannot

be ignored, and has joined the hydropower industry

in studies on climate and dam safety. However, exist-

ing regional climate scenarios continue to vary greatly,

isk

overnance

and

anagement

Proper design of the capacity of the spillway is crucial for the safety of a dam. The spillway is activated at the Porjus dam in the River Luleälven in September 2007,

after a safety upgrade according to the new Swedish guidelines for design flood determinations

Image: Sten Bergström, SMHI