120 



by the rains of the fall season (the replenishing period). If, now, there 

 is a deficiency of rain in the replenishing season also, a greater or less 

 Iiroportion of the rainfall of the winter and sitring months must go to 

 fill up the ground, and the run-off of this i:)eriod will be correspondingly 

 decreased. The most unfavorable condition, therefore, is a dry fall, 

 followed by a dry winter and spring. If, for example, such a fall as 

 that of 1908, with as low as 2.2 inches of rain at several of the stations, 

 for the three months, September, October and November, should be com- 

 bined with such a winter and spring as that of 1900-19(H (a not impos- 

 sible contingency), the probable catch of water, on the basis of 50 per 

 cent, of the rainfall of the stf)rage period, would be only 5 inches for 

 the entire yearV 



The available catch of water in a dry season, that is, one of 30 

 inches of rainfall, will be a considerably smaller proportion of the rain- 

 fall than the catch of a wet season. In the latter case the run-off may 

 be from 50 to CO per cent, of the rainfall, while in a dry season it is 

 likely to fall as low, in the region under consideration, as 25 per cent.. 

 ov even lower.- From these data it aip]iears that there will be years* 



' It is not doomed necossary to cutor licic into the technical discussion of the 

 relation of rainfall to run-oflf. A very full discussion of these points may be found 

 in the works of Vormeule and Rafter, cited above. Ordinarily, in this latitude the 

 runoff of the winter and spring months may vary from 50 to 75 per cent, of the 

 rainfall. For the remain ing months of the year it will vary from 0.0 to 20 per 

 cent, of the rainfall. rnfortunntoly there are no satisfactory run-off data for 

 the region. The gagings at Shoals from 100.'$ to 190C, inclusive, are the only ones 

 of a stream lying largely within the region under consideration. These indicate a 

 mean annual run-off of 12'>'.i inches, which is about .30 per cent, of the rainfall of 

 the region for the same interval. (The mean annual rainfall for the nearest sta- 

 tion, I'aoli, for this interval was 41i.7."> inches.) This interval includes two years 

 of less than 40 inches rainfall, namely, 100:'>, with ."55.18 inches, and 1904, with 

 39.09 inches. On the Muskingum I{iver in Ohio, a stream lying In a region of 

 similar topography and climatic conditions to the catchment of tlie east fork of 

 White River, and like the latter, mostly in the driftless area, the run-off has been 

 known to fall as low as 25 per cent, of the rainfall. 



- The run-off formula* of Vormeule are of interest in this connection. While 

 designed to cover the conditions in New .Jersey and southeastern New York, they 

 are based on certain general considerations, s-uch for cxanin!i> as mean annual tem- 

 perature, etc., which are applicable to other regions as well. Vermeule's general 

 formula is: E^dl -f 0.29 R i M. where E stands for annual evaporation, R for 

 rainfall, and M is a factor depending on mean annual temperature. The values 

 of M are as follows for the mean annual temperatures noted in the present region : 

 52°, 1.14; 53°, 1.18; 54°. 1.22; 55°, 1.26; 50°, 1.30; and 57°, 1.34. Thus for a 

 mean annual temperature of 52° the evaporation, with a rainfall of 30 inches, 

 should be 22.46 inches, and this subtracted from the total rainfall would leave a 

 run-off for the year of 7.54 inches. For the higher temperatures the run-off would 

 be correspondingly less, and might, according to the formula, fall as low as 2 

 inches. It is not probable, however, that it ever does fall as low as the latter 

 figure. 



