in very dry years, a period of some length in which the water is high from rains.
"There
is also a period of high-water in the spring, due to melting of the
snow which has accumulated during the winter on the higher altitudes of
the Sierra.
"The
mass of material thus put in motion in narrow and steep riverbeds is
carried along to the lower parts of the rivers, each tributary
contributing its share of flood-water and detritus, and uniting to
form at or near the edge of the foot-hills the rivers to which we have
given names. As the detritus reaches lower portions, the streams, less
concentrated and with constantly diminishing fall in the bed, find
themselves unable to carry to the lower course the load which they
transported in the upper. When these streams, as they were before
mining was begun, reached the plains of the Sacramento Valley, the fall
of the beds diminished to a very few feet per mile, perhaps 3 or 4, so
that, all along the whole lower course of the river, the bed first, and
afterwards the plains bordering the river where the banks were low,
became depository places for the material the river was no longer able
to carry. The river bed in the plains first becomes obliterated by
deposits, and then the alluvial lands adjoining become a waste of sand,
gravel, and 'slickens.' Instead of a river bed there is a wide plain
overflowed at high stage, through which, meandering in constantly
varying channels, the summer river pursues its devious course."*
The
topography of the country along the lines of the mountain streams,
though rugged, affords every facility for carrying out successfully a
plan for storing the tailings. The banks are generally of great
height, with slopes which vary from fifteen to fifty degrees. The
general slope is about thirty-five degrees, and " an elevation of fifty
feet adds one hundred and forty to the width, which extended width,"
says Col. Mendell, " reduces the height of floods, the cubes of the
heights being proportional to the squares of the widths. Doubling the
width reduces the height one third, which reduction in height reduces
the suspending power of the water and the exposure of the structure to
floods." f The storage capacity is consequently increased by this
additional width as the bed of the stream is elevated.
The chief obstacles to be encountered in the erection
* Annual Report of the Chief of Engineers U. S. Army for 18S1, Appendix MMT. t Col. Mendell's Report on Mining Debris in California Rivers, p. 41.
