348 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 8 



measurements of rainfall and condition of the ground and by a rapid 

 system of collecting reports, he can compute in advance when and how 

 high the waters will rise. He can confine the rivers by levees, but he 

 must provide for temporary diversion of excess waters over capacious 

 lowlands. He can straighten the stream channels to hasten the water 

 on its way but, without great care, such relief upstream may mean 

 a greater flood downstream. The operation of control dams and 

 diversions could be more intelligently directed if great rains could be 

 foreseen more than a day or two in advance. This is not impossible, 

 and studies in long-range forecasting are already rather promising. 

 But whatever success may be attainable in weather and river-stage 

 forecasting the main point to bear in mind is that 10-inch rains do 

 fall, sometimes in a few hours, and that if man does not control the 

 speed with which the water reaches the streams and then whither it 

 goes floods will devastate the valleys. 



