|Mapping your next Trip|
MAPPING OUT YOUR NEXT TRIP
Many of you will soon start actively planning next year's trips. If you are considering a river up north, that planning will include studying a number of maps and river guides - and may be some trip descriptions. In spite of all your research efforts, you may run into surprises. But studying the maps can tell you a lot about what those surprises might be.
A few years ago a group of our friends went on two of the major northern rivers - the Nahanni and the Coppermine. In both cases they encountered severe flood conditions. On the Nahanni the flooding came on suddenly after heavy rains and they had to wait for the water to recede before they could continue. On the Coppermine the flood was there when they arrived, and after a few days of lake paddling and running a couple of rapids on the upper part of the river, they decided to turn back.
Even the most careful study of maps could not have predicted the flood on the Nahanni. You could determine that the water level in the Nahanni will respond quickly to heavy rain and drop quickly when the rain stops. This may not be important when you are deciding which river to run, but it can be important information when you are on the trip. If the water level is high it is nice to have some idea how long you may have to wait for the level to drop.
In the Coppermine case there was a way to predict that the water level was likely to be high. The big difference between the two rivers in terms of how their flow rates behave is that the Nahanni drainage area does not have significant lakes or other terrain that can hold back a lot of water. When it rains, the water is quickly flushed downstream. The Coppermine flows out of very large lakes, and its water level is largely determined by the last winter's snowfall. In a heavy snow year the lakes fill up, and it will take weeks to drain the lakes down to a normal level. The lakes also reduce the effect of a few days of heavy rain because the water level in the river is directly controlled by the level of the lake, and it takes a lot of rain to have much effect on a large lake. As you go down the river, the effect of the lake's water level on the river's flow diminishes because more and more of the river's flow will come out of tributaries that probably are not controlled by big lakes. But if the upper part is flooded, you will most likely have a flood all the way down.
The above observations offer one opportunity for trip planning: If the river you are planning to run flows out of large lakes that would take a long time to drain down to a normal level, you could look into the winter's snow conditions and change your plans to a different river if the area is experiencing a heavy snow year. The information you need to determine a river's likely flow behavior is readily apparent on a small-scale map (1:1,000,000 or similar).
A more detailed evaluation of a river requires a large scale map like 1:50,000. It is an exercise that is well worth doing, but a good description of the process requires more space than we have here. A very good source is Chapter 2 "Researching a River" in Cliff Jacobson's book "Expedition Canoeing".
|Last Updated on Thursday, 25 June 2009 18:17|