22 BULLETi:tT 193^ U. S. DEPAETMENT OF AGEICULTXTKE. 
bottom widths of the ditches by 8 feet for 14 to 25 foot widths, by \\ 
9 feet for 30-foot widths, and by 10 feet for 35 to 50 foot widths. All ' 
bridges should be placed on concrete abutments. 
RAILWAY CROSSINGS. 
Culverts of 36-inch and 48-inch pipe are recommended. where rail- 
ways cross drainage ditches that will need to carry not more than 
about one-fourth or one-third, respectively, of the computed capacities 
of ditches with 2-foot bottom widths, as planned for highway cross- 
ings. All other railway crossings are estimated as haK-through plate I 
girder bridges on concrete abutments, with spans about equal to I 
one-half the sum of the top and bottom widths of the drainage ditch. 
IRRIGATION CANAL CROSSINGS. 
As all irrigation canals consist of two levees between which the 
water flows over the natural ground surface, these must be carried 
over the drainage ditches at the crossings. It is impossible to deter- 
mine the exact number of such crossings there wiU be, as many of the 
present irrigation canals may not be in use w^hen the drainage ditches 
are constructed, and the data are not at hand to show where the i 
proposed ditches cross all the irrigation laterals. The cost has been 
estimated for each crossing of a drainage ditch with a main irrigation 
canal in use at the time of the survey, and the total for each district ] 
has been included in the total cost estimates given on later pages. 
Culverts of 36-inch and 48-inch pipe should be used for the small 
ditches under the same conditions as explained for highway crossings. 
Where it is expected that the drainage ditch wiU carry one-haH the 
computed capacity of the smallest ditch recommended, or more, the 
irrigation canal is to cross the drainage ditch in a wood flume sup- 
ported on timber bents or piles. Each flume should be about 10 feet 
longer than the top width of the drainage ditch, thus allowing about 
5 feet at each end for a firm bond with the bottom of the irrigation 
canal to prevent leakage. 
PINE ISLAND BAYOU IMPROVEMENT. 
All trees and brush should be cleared from the old channel of Pine 
Island Bayou for a strip 100 feet wide, which wiE give the present 
channel a capacity of 1,600 cubic feet per second, equivalent to about 
0.6 inch run-off per 24 hours from the drainage area above the 
Jefferson-Liberty County Hne. From the county line to Voth, such 
a strip would contain 270 acres; clearing this would cost, at $40 per 
acre, $10,800. Divided along districts Nos. 1, 2, and 4 in proportion 
to their areas, this cost would amount to $1,605, $3,870, and $5,325, 
respectively, or 27.7 cents per acre. 
TAYLORS BAYOU IMPROVEMENT. 
The drainage areas and computed maximum run-off for Taylors 
Bayou at several points have been determined as foUow^s: 
