A NATIONAL PLAN FOR AMERICAN FORESTRY 435 



value for storage of flood water for use in extended drought periods 

 will be greatly impaired much sooner. Losses of investment in engi- 

 neering works from silting may be liquidated to the satisfaction of 

 financial interests and additional dams may be built to suffer a similar 

 fate, but the consequent decay of communities dependent upon 

 irrigation cannot be so liquidated. 



FLOODS 



Closely related to rapid run-off from slopes depleted of vegetation 

 and to abnormal erosion are destructive summer floods. In the 

 Colorado River Basin such floods occur, often in intermittent stream 

 courses, mainly as a result of heavy rains. High water results 

 normally each spring from snow melt, sometimes assuming destruc- 

 tive proportions in the lower reaches of the river and in its main 

 tributaries. Those spring flows seldom become destructive in the 

 smaller tributaries except in the occasional year when heavy warm 

 rains produce unusually rapid snow melt. The destructive flash 

 floods which follow semitorrential summer storms originate in greatest 

 number and greatest in tensity in the pinon-juniper and mountain- 

 brush types and on nonforested areas at lower and intermediate 

 elevations where the vegetation is thin. In 1921, for example, 

 severe floods largely from such types occurred in the Dolores River, 

 Henson Creek, Lake Fork, and East and West Rifle Creeks of Colorado 

 following a 4-day rainy period with a maximum precipitation at 

 Ashcroft, near Aspen, Colo., of 2.5 inches. -The Dolores River 

 washed out many miles of railroad track, and Henson Creek caused 

 considerable property loss at Lake City by cutting a new channel 

 through part of the town. 



Price River has had numerous floods originating on the higher 

 mountain forested areas. In 1927, for example, floods transporting 

 immense amounts of debris and silt damaged railroad and mine 

 property, highways, bridges, irrigation works, city water supply, and 

 farm crops to the extent of at least $500,000. The watersheds of 

 Gordon Creek and Willow Creek, the two tributaries which con- 

 tributed most of the flood waters, had suffered a heavy reduction 

 in plant cover on forested areas through extreme grazing use. In 

 contrast the drainage of Miller Creek, a nearby tributary comparable 

 to Gordon Creek, has been protected from excessive grazing use 

 since a time several years prior to the 1927 flood, and maintains a 

 relatively abundant ground cover even in the nonforested portions. 

 It shows almost no abnormal erosion or channel cutting, while 

 Gordon Creek is newly channeled to a depth of 50 feet and a width of 

 100 feet. 



Floods have been a source of great loss to the agricultural industry. 

 The valley bottom lands most suitable for irrigation have been 

 subjected to inundation and debris deposit or have been cut away by 

 flood waters. A number of small reservoirs have been rendered 

 useless by silting or the dams have been washed out. Silting of 

 irrigation ditches and loss of headgates and diversion dams have 

 occurred to some extent on every stream in the region. 



Conditions on the Paria River, in southern Utah, present an 

 outstanding example. Approximately two thirds of the Utah 

 portion of this watershed, i.e., 11 or 12 townships, is occupied by 

 forests, chiefly of the woodland and mountain-brush types, with 



