42 
BULLETIN 1017, U. S. DEPARTMENT OF AGRICULTURE. 
tions seem to indicate, however, that in the Keel River valley open 
drains do not materially increase run-off caused by melting snows in 
the spring, because a large majority of drains are completely filled 
or badly obstructed by snow and ice and do not begin to function 
until several days after the snow on the watershed has melted. Un- 
der such conditions run-off collects and flows in natural depressions 
or channels without being affected to any considerable extent by 
artificial drainage. 
EVAPORATION AND TRANSPIRATION. 
By far the greater part (between 85 and 98 per cent) of precipi- 
tation on the Red River watershed is disposed of by evaporation and 
plant translocation. As run-off comprises only the remainder of the 
precipitation those processes largely govern total run-off. Large 
quantities of water evaporate from the soil and from water and snow 
surfaces. Annual evaporation from the soil has not been determined 
definitely but under ordinary conditions this alone is probably as 
great as annual run-off. The process, however, goes on at a much 
slower — although more uniform — rate than does run-off, so its rela- 
tive effect is small when the run-off rate is high. 
The rate of evaporation from shallow water near Grand Forks 
has been measured and recorded by Prof. E. F. Chandler for the 
period 1905 to 1914. The results have been used in computing the 
probable evaporation from lakes and reservoirs. Table 10 shows the 
mean monthly evaporation and the mean monthly temperature for 
the period 1905-1914. 
Table 10. Mean monthly temperature and evaporation at University (near 
Grand Forks), N. Dak, 
Month. 
Mean 
tempera- 
ture. 
Mean evaporation. 
F. 
4.0 
7.3 
22.8 
44.5 
52.1 
65.0 
67.5 
65. 5 
57.7 
45.9 
27.6 
11.3 
Inches. 
0.40 
.60 
1.20 
3.22 
4.12 
4.94 
5.78 
4.60 
3.63 
2.11 
.63 
.40 
Billions of 
cu.ft. -per 
sq. mi. 
0.0009 
.0014 
.0028 
.0075 
May. . 
.0095 
.0114 
Julv 
.0134 
.0107 
• 00S4 
.0049 
.0015 
.0009 
The evaporation figures for April to November, inclusive, are results of observations by Prof. E. F. 
Chandler, 1905 to 1914; those for December to March are estimates made from available data relating to 
evaporation during winter months. 
The figures deduced by Meyer, 5 as to evaporation from snow and 
ice, agree very closely with the results of observations made by 
5 The Elements of Hydrology, Adolph F. Meyer. 
