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Runoff Report 1999..... No Excessive Hot Periods

As described in the chapter about the snow melting process there are some factors that initiate or speed up the snow melting process. For details please review this section. In general, warm temperatures cause the snow to melt. The higher the temperature, the higher the altitude included in the snow melting process and the larger the produced water mass. This is important to forecast the flood danger along rivers and streams because it can lead to a temporary overload there. But a large water mass in the streams does not necessarily mean a fast raise of the lake. The Shuswap Lake is large enough to buffer a huge amount of water while draining a good portion of it, without significantly effecting the water level. And as shown in the last graph, the increase of the lake level causes the increase of the drainage.

Continuos hot temperatures for a period of time will change the balance. The result is a shortened time span for the runoff. And this is a very important point. In most cases the time span alone makes the difference between flooding and no flooding. Please click here for further information on the time span and my first attempt to put it into a formula.

A short time span will increase the flood danger around streams and the lake is ascending much faster. Especially close to the lake's peak this can lead very quick to flooding. On the other hand, short warm periods will stretch the time span and allow the lake to drain more water from the inflow. The difference between inflow and outflow is smaller, the lake level increase therefore smaller, too.

The 1999 runoff was not effected by long warm periods. Including May, the longest warm periods lasted only 3 days. June had one warm period with changing temperatures, sunny days not exceeding 2 continuous days. The July had 3 warm periods, which didn't effect the lake very much. The medium altitude snowpack was already gone lowering the overall melt water supply. The lake, at this point around its peak, couldn't simply increase any more. Most of the graphs in this report give a visual explanation in this matter.

The 1999 runoff time span therefore was very long. So long in fact that not all snow was able to melt before the winter. Some of the high altitude snowpack remained and will be added to the 2000 runoff.

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Copyright (C) 2003 Bernhard Kramer, Sicamous, BC - Canada