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HYDROGRAPHY.
■i 23
may be indicated the Emun, the Hel’gean, the Lagan, the Nissan, the
Ätran, and the Viskan, etc. Finally, a third category within this group
embraces a number of larger lowland rivers, such as the Tämnanin and
the Nyköpingsån — wliirh drain parts of the Central Swedish Lowlands
— and the Käviingeån and the Rönneän, which drain a considerable
part of the Skåne Lowlands.
Small littoral- and boundary-ritiirs drain 15 c/e of the country. Of
these. 70 have drainage areas varying between 1 000 and 200 square
kilometers.
Ths general geographical character of the Swedish water-systems is
intimately connected with the geological development of the country.
In consequence of the great changes brought about by the ice-period,
the rivers have all been impressed with the characteristics of —
geographically speaking — young rivers. One result of this is the great
number of lakes the country possesses; only such areas — Finland, for
example, or Canada — as, like Sweden, have had an ice-period, being
able to compete with the latter country in this respect. Another result
is an undeveloped longitudinal profile, with numerous waterfalls and
>upids, which, from the point of view of water-power, makes Sweden
one of the most important countries of the globe. (See the section dealing
with the waterfalls of Sweden. Part II.) A third consequence is, that
the different river-basins are generally but indefinitely separated from
each other, so that ventral areas and bifurcations are of frequent
occurrence. This is especially so in those districts where the divides are
disposed over extensive bog-lands which are of very låte geological
origin.
A series of investigations has been carried out for the purpose of
determining the character of the soluble and other alluvial matter in the waters of the
rivers. As regards the percentage of soluble matter, these examinations have
shown to what a very great degree this depends on the rocky soil and the
character of the looser strata. For example, the chemical denudation, estimated
in grammes per square meter, in the rivers of Upper Sweden and the Småland
Highlands, whose basins are characterized by primary formations, is estimated at 10
grammes per square meter, but in those tracts where Silurian röck occurs to any
very great extent — in that drained by the Indalsälven, for example — this figure
rises to 19 grammes. In the rivers of the Central Swedish Lowlands, the figures
are much higher, being, for example, in the Nyköpingsån 12, in the Mjölnaån
— by which the waters of Lake Tåkern escape — 24, and in the Tidan, 26.
The percentage is highest in the rivers of Skåne, as in the Rönneån, where it
amounts to 28 and in the Kävlingeån, 44 grammes per square meter.
Apart from the area of the basin drained, the varying levels or
gauge-lieightg and the discharge-fofawies of the waters of the rivers and lakes
depend, in the first place, on the extent and distribution of the precipitation;
secondly, and in a very great degree, on the extent to which the water is
stored up, in the form of snow, or in lakes, or as subterranean water, and.
lastly, on the character of the röck formations, of the looser upper strata,
and of the vegetation.
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