20 BULLETIN 115, U. S. DEPABTMENT OF AGBICULTUBE. 
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 j)ossible 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 Eailroacl. 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. As shown in Plate YI, 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 
