58 BULLETIN 300, U. S. DEPARTMENT OF AGRICULTURE. 
well, little trouble being experienced from the pump becoming 
choked. 
Manganese-steel impellers wear longer and withstand the abrasive 
action of sand and the shock of stones better than do cast-steel im- 
pellers. Manganese-steel impellers 34 inches in diameter fitted with 
shoes have handled as much as 60,000 cubic yards without showing 
serlous Wear. 
Hydraulic dredges have seldom been used on drainage ditches, but 
for large ditches their ability to excavate rapidly and at low cost 
would seem to warrant more extensive use. Hydraulic-fill levees 
have the following advantages: A wide foreshore can be left; there 
are no borrow pits to induce seepage; any side slope desired for the 
levee can be obtained; the fine material is deposited in the base of the 
levee, where it is most needed to prevent seepage; being composed 
mostly of sand, hydraulic-fill levees are not subject to damage by 
burrowing animals. By the hydraulic-fill method a levee can be built 
across an old bayou or lagoon with as little difficulty as on dry 
ground, and soggy, wet ground does not delay construction. 
MACHINES FOR CLEANING OLD DITCHES. 
The floating dredge, the dry-land dipper dredge, the nonrotating 
straddle scraper excavator, the rotary scraper excavator, the rotary 
excavator with orange-peel bucket, and the hydraulic dredge have 
all been used for cleaning out and enlarging old ditches. 
Where the amount of material to be removed is large the floating 
dredge has been found fairly satisfactory for such work, especially 
where sufficient water is available to float the dredge without requir- 
ing dams to raise the water level. The greatest objection to its use 
is the necessity of removing bridges or other obstructions spanning 
the ditch to allow the dredge to pass. 
The dry-land straddle dipper dredge has been found very satis- 
factory on small ditches that can be straddled by the machine. The 
maximum size of ditch that can be constructed by this type has a 
top width of 45 feet. It is not necessary to remove bridges, as it can 
pass around or over these. 
The rotary excavator, working on one bank of the ditch and 
equipped with either a scraper or an orange-peel bucket (PI. I, 
Fig. 1), is probably the most satisfactory machine for clean-out work. 
It can clean the material out of the bottom of the ditch without dis- 
turbing the slope of the ditch bank, or, if desired, can cut them to 
a different slope. It has a decided advantage over other types of 
machines in that bridges and other similar obstructions need not be 
removed and it can place the excavated material well back from the 
ditch. The principal objection to its use is that it is necessary to 
