Determine River Falls.This sub-indicator is calculated as the difference of altitudes terrain, where the source and the mouth of the river.For example, the Angara River flows out of Lake Baikal, the altitude at this point is 456 meters above sea level.Angara river flows into the Yenisei at the point where the height is 76 meters above sea level.Thus, the fall of the river is 456-76 = 380 meters.Remember that, in calculating this index for rivers flowing into the seas and oceans, with the altitude mouth should be taken 0.
Find out the length of the river bed, that is its length.This information can be found in the statistical reference books and encyclopedias.For example, the length of the Angara River is 1779 kilometers.As a rule, in the problem of geography for t
he eighth grade in the calculation of the slope of the river give information on the length of the channel, and the fall is necessary to define yourself.
Calculate the slope of the river by the formula:

Slope = Fall River / length of the river.

To express this and figure River Falls, and its length in the same units, for example in kilometers or alternatively, in meters.Translations into one unit will allow to calculate the slope of the river as a percentage or ppm.In the case of the Angara River, you get the following value slope of the river:

Angara River Slope = 0.38 km / 1779 km = 0.0002136 or 0.02136%, or 2,136 ‰.
Interpret the resulting slope value of the river and check yourself.Bias in 2,136 ‰ means that the section length of 1 kilometer height of the terrain through which the river flows, changes to 21.36 centimeters.If you get too great importance to the flat slope of the river, then an error has crept into the calculations.
Remember that the average slope of the river, ie, the ratio calculated for the entire length of the bed, not informative.It is better to calculate this indicator for shorter sections of the river.