The Washington herald., 1922-02-05
SCIENCE WOULD
AVERT DRYING UP
OF ROCK CREEK
Experiments in Swiss
Forests Show Needs,
Says P.S.Ridsdale.

Plans outlined by. Lieut.. Col, c.
y. Sherrill,, =, of the department. OF
public buildings and grounds look
Ing to prevent Rock Creek from
drying up were highly praised yes
terday by y. s. Ridsdale. secretary
OF the American Forestry Associa-
ition. Mr.. Ridsdale points TO the
experiments. made by. Switzerland
rs TO the influence Of forests on the.
run-of in mountains.
. What a calamity" says secre-
tary Ridsdale. III we do not pro-
tect the headquarters of the creek
In the most famous 'rightrtn-a-city'
park in. the world. We should alt
wake up to Col Sherrill's sugges-
tion. Beneficial influence OF for
ests upon strcamfiow in hilly and
mountainous regions has long been
recognized. This recognition Is 30
Widespread many European coun-
tries have enacted Legislation for
the preservation of their mountain
forests. and the United States is
wen embarked on a program for
the acquisition by the Federal gov
eminent of forest lands on the
watersheds of navigable streams
The best example Is furnished by
the streamfiow Investigation that
has been under way at the Swiss
forest experiment. station since
1900.
Data on Streamhow.
Watersheds Of 1877 and ia
acres. the first Of which was al
most wholly forestcd and the other
slightly less than one-third for
ested. were selected. With the
single exception OF the forest cover,
the two watersheds were strictly
comparable In other respects, such
as form. topography. geology and
climate. For eighteen years com
plete meteorogical observations
have been made and acurate rec
ords OF run-ofr maintained In the
two basins. These have yielded
the most complete and convincing
data yet available as TO the pre-
else part played by u, for,NI in
the regulation OF streamfiow.
The proportion OF the yearly
run-ff to the total precipitation
averaged practically the same, ap-
proximately so per cent in the two
watersheds. The distribution of
the run-on was. however, very diff
ferent. In general the discharge OF
the stream from the well-forested
watershed was much more uniform
than that from the poorly-forested
one. with high minima and low
maxima. This difference is due to
the greater absorptiye capacity of
the forest soil. resulting from its
porosity and permesbility and not.
as wa sformerly thought. from it's
humus cover. The latter can. IT Is
true. retain a very large quantity
Of water. but 1t does not give this
up readily to the underlying soil.
In, fact, a thick cover of raw humus
and moss may. after II once be-
comes saturated. actually promote
surface run-off and thus prevent
the water from soaking into the
soil.
Absorption Of Rain.
"Downpours OF rain were alb
sorbed far more effectively by the
soil of the well-forested area than
by that of the poorly forested one.
Indeed the maximum discharge
from the former after such rains
was seldom more than one-third to
one-half as much as from the lat
ter. After prolonged rains the ef-
feet of the forest cover upon
SITedU1IlO" 0cpeDuCo OH IHt
ure content OF the soil at the be-
ginning of the rain.
"If the soil was comparatively
dry at that time its effect in pre-
venting surface run-off was quite
noticeable. while was already
thoroughly soaked there was little
difference in the discharge of the
two streams. Although the forest
cover was thus unable to prevent
all floods. equally heavy discharges
from the ll-forested watershed
did less damage than those from
the other because their velocity was
lower and they carried a smaller
amount of eroded material. All OF
the differences noted. would have
been more pronounced had the WELL
forested watershed not had sleeper
slopes than the other, and had the
latter been completely deforested.
Comparison In Colorado.
Soon We will compare these re-
suits with those obtained from the
very. similar study now under way
at Wagon Wheel Gap. Colo. The
clearing of the area took place a
year ago. so that 1t will soon be
possible to draw tentative con-
clusions.
Results of the Swiss investiga-
tion will greatly strengthen the
hands of those who are urging the
protection of our mountain forests
as a means of safeguarding our
water supplies. While the precise
relations determined to exist, there
are strictly applicable only to other
areas with the Same physical condi-
tions. careful analysis of the fac
tors concerned leaves no doubt that
the demonstrated tendency Of a
forest cover in hilly countries to
check surface run-off and to equal
izc stream flow is universal. Added
strength is thus given to the policy
of federal acquisition Of mountain
forests. inaugurated nearly ten
years ago hY the nassara af +ha