20 BULLETIN 115, U. S. DEPARTMENT OF AGRICULTURE. 



riprap, effectually preventing scouring of the bottom above and be- 

 low the structure, which eventually would cause the failure of the 

 gate through undermining but for these cobbles. On this particular 

 structure, as shown in figure 2, the cut-off walls extend but 12 

 inches below the bottom of the floor. The ditch headed by this gate 

 is 14 feet wide on the bottom and has a maximum carrying capacity 

 of 400 second-feet, to be diverted from St. Vrain Creek, which has a 

 normal flood flow of about 1,100 second-feet. 



In order to raise the crest of the diversion dam in times of very 

 low water, a set of flashboard guides is loosely placed in tin-lined 

 holes in the concrete dam proper, the tin acting as the form for the 

 holes when cast. The original plans called for a concrete footwalk 

 over the weir, from which it was possible to pull the flashboards 

 and also the guides in times of very high water, so that the obstruc- 

 tion offered by the weir could be reduced to a minimum. These plans 

 were afterwards changed and a plank walk loosely bolted to the piers 

 was substituted. A flood of sufficient size to cause damage to the 

 structure would break these boards, and there would be no obstruc- 

 tion to the passage of trees and heavy debris, with the exception 

 of the piers, which are placed so that a net opening width of 16 

 feet remains between them. 



This structure was built in 1911. Including the bridge in connec- 

 tion, it contains 90 yards of concrete, reinforced with five-eighths 

 inch twisted bars. The concrete was machine mixed in a ratio of 

 1:3:5 cement, sand, and river gravel. The construction was carried 

 on by force account, and the total cost of the structure, excepting 

 the iron work of the gates proper, was $450. Cement cost $1.75 per 

 barrel at Hygiene, on the Burlington Railroad, 4 miles distant. The 

 foreman was paid $100 per month, and common labor cost $2.25 per 

 day. The total engineering charge against the structure was $40. 

 The iron gates cost $75, in addition to the $450. 



HEADWORKS. SOUTH BOULDER AND COAL CREEK DITCH, COLORADO. 



A short distance above the town of Eldorado Springs, on South 

 Boulder Creek, Colorado, the South Boulder and Coal Creek Ditch 

 diverts 53.55 second-feet of water. m As shown in Plate VI, figure 1, 

 the creek at this point has a very rapid fall in a canyon. The bottom 

 is strewn with bowlders from the size of a cobblestone to that of a 

 small house. 



The diversion dam is a makeshift of boards spiked to a heavy cross 

 timber which is braced against the bowlders of the creek, the whole 

 structure being weighted with a sloping pile of loose cobblestones. 



The gate structure has 8-inch concrete side walls 10 feet lorg 

 which bond with the bowlders of the canyon, in effect merely squar- 

 ing up the face of the bowlders. Two vents are formed by a central 



