202 WATER-rOWEES OF SOUTH CAROLINA. 



autumn and winter rainfall on each drainacre basin. Here, again, the 

 number of years during wliich observations have been recorded, at least 

 so far as South Carolina is concerned, leave much to be desired, espocially 

 in the regions remote from the sea coast. Then comes the consideration 

 of the very complex factors affecting the disposition of this rainfall, the 

 proportion dissipated hy evaporation under the various and varying in- 

 fluences of temperature, the humidity of the atmosphere, the prevalence 

 of winds, the permeability of the soil, and its protection by forests, and, 

 lastly, the residue remaining to be discharged by the streams. Now, it 

 would seem that in these regards, the item of temperature only excepted, 

 the discharge of streams in the South should be greater than those of the 

 North. The force of the wind is less. No large lakes present broad sur- 

 faces for evaporation There is no loss by evaporation from snow and 

 ice during months of the year. The soil is deeper and more permeable, 

 and its protection by forests must be as great or greater. For the streams 

 of the sand hill region Mr. Swain seems to allow some force to such con- 

 siderations in placing the minimum flow at one-third to one cubic 

 foot per second for each square mile of drainage area. For the 

 other streams of South Carolina he allows a less discharge, placing 

 the minimum flow at 0.13 to 0.23 cubic feet per square mile of 

 drainage area, notwithstanding that the average minimum flow in 

 ten New England rivers which he gives, is 0.26 cubic feet. Whenever 

 Mr. Swain's estimates of fall or flow differ from those made by others, it 

 will be found that Mr. Swain's is much below theirs. As an instance of 

 how much such under-estimates may amount to, Mr. Swain himself points 

 out that while his estimate of the minimum flow on the Portman shoal, 

 of Seneca river, is one hundred and eiglity-nine cubic feet per second, 

 " it must be speciall}' mentioned here that Maj. Lee, who is an engineer 

 of eminence, long experience and well acquainted with the country, 

 writes that ' one thousand cubic feet of water per second all the year 

 round — two-thirds of the year double this flow — is to be had.' " But, 

 however far short of the aggregate Mr. Swain's estimates of the water- 

 power may be, there can be no question that, under the circumstances, 

 he has accomplished a great deal, and, as a preliminary reconnoisance, his 

 treatise is invaluable. 



Mr. Swain makes four estimates of the horse-power at each locality he 

 mentions : 



I. The minimum, being the minimum flow during a period not exceed- 

 ing a few days at intervals of several years. 



II. The minimum low seasons. This occurs for a period of three to 

 six weeks, when the stream is at its lowest. In most years the average 

 flow during: the season of least flow will exceed this amount, and a small 



