274 



CONSERVATION 



from precipitation, but is gathered 

 from the surface in part only ; another 

 part appearing from seepages and 

 springs after a trip underground. The 

 former we wiU call "flood run-off," 

 the latter "seepage run-ofif." 



Flood run-off is that part of rain or 

 snow fall which remains on or very 

 near the surface, flows directly to 

 swamps, lakes or streams, and imme- 

 diately or in a short time runs away. 

 Following showers, flood run-off raises 

 streams ; following prolonged rains or 

 melting snow it occasions high water, 

 which quickly recedes when the rain or 

 melting ceases ; and following excess- 

 ive rains or melting, flood run-oif 

 produces great floods. 



Flood run-oif is thus the most tran- 

 sient, irregular, wasteful and danger- 

 ous part of precipitation. 



It damaged the people in the United 

 States in eight months, January i to 

 August 31, 1908, $237,000,000. In the 

 year 1907 it occasioned the loss of 

 $118,238,000. In the ten years prior to 

 December, 1906, it cost not less than 

 $1,500,000,000 in goods, buildings, 

 bridges, roads, railroads, and real es- 

 tate, washed away. 



These losses are net losses ; they do 

 not include deterioration of values not 

 actually destroyed, nor do they cover 

 the incalculable, irreparable loss of fer- 

 tile soil from our mountains, grazing 

 lands, and fields. This loss amounts 



to approximately 1,000,000,000 tons of 

 soil per annum. Nor does the financial 

 loss include the sum of human suffer- 

 ing or the loss to the Nation through 

 lowered efficiency and morale of the 

 citizens who sufifer from floods. 



Seepage run-ofif stands in direct con- 

 trast to flood run-ofif. It is slow and 

 gradual where the other is quick and 

 spasmodic ; it is regular where the 

 other is irregular ; it continues when the 

 other fails. The uses of surface waters 

 ( crop growing, city water supply, sani- 

 tation, water power, and navigation) 

 depend on reliability and regularity. 

 Hence it is obvious that the works of 

 man should be designed to increase that 

 part of rainfall and snowfall which, 

 sinking into the ground, contributes to 

 seepage run-oft' and to regulate the 

 flow of that considerable part which 

 cannot enter the ground. 



Rain falling on a well-tilled field or 

 grass or forest largely sinks in. Fall- 

 ing on bare, baked, incrusted ground, 

 it dashes off. Whichever in any place 

 occurs, some farmer or herdsman or 

 lumberman is responsible, for there is 

 now no considerable part of the United 

 States that man does not make or mar. 

 But at the best there will always re- 

 main a notable proportion of precipita- 

 tion that will form flood run-oft", and 

 this we must commit to the care of the 

 engineer as part of the surface flow 



w 



hich it is his dutv to control. 



( To be continued) 



