LAND DRAINAGE.

Hauraki Plains Gazette, Volume XXXIII, Issue 4425, 9 June 1922, Page 4

LAND DRAINAGE.

| NEW ZEALAND AND AMERICA ' MR,. J. B. THOMPSON’S REPORT. No. 4. EXCAVATION OF CHANNELS) The excavation of all ditches is performed—for at least 90 per cent--by machinery. The following machinery is standard practice : Floating dipper, dredge, % to 8 cubic yards capacity; floating grab or clani shell dredge, % to 6 ; dryland dipper excavator, % to 3; dryland grab excavator, % to 2 ; dragline scraper excavator, % to 3; hydraulic suction dredge, 10in to 24in suction and delivery. Dipper Dredges.—Floating dredges of dipper type are undoubtedly the best diggers of stiff clay seen, and are deservedly popular op account vf their performances as to output and economy. Fully 80 per .cent, of drainage channel excavation in the eastern States is done by dippers of various makes. The bucket capacity varies from % cubic yards to 8 cubic, yards, but in general ditch work the average would be about 2-cubic-yards capacity. Their performances were hotel under conditions such as exist in Ne v Zealand. The heaviest dredges were seen at work in the Everglades, Florida. hut they were engaged in excavating coralline limestone from large canals. Clam-shell Dredges.—ln the west' (California) the grab or claml shell floating dredge is .the favourite, and does remarkably good work. Machines fitted with booms 240 ft long and carrying 6-cubic-yard buckets were seen in operation in the Sacramento Valley They were engaged mainly on levee work. These machines cost about $190,000 in San Francisco, and are really for very large jobs. Walk’ng Dredges, Dipper Type.—

Laterals and sub-laterals are excavated by so-called walking dredges. Some of these straddle the ditches while others move back as the excavation progresses. They are of dipper, grab, clam-shell, and dragJine types. Fast work is done in favourable conditions, but it is somewhat ragged compared with hand labour, but good berms are left All types were observed in use, and it may be stated that they all have their weak points, and have frequent stoppages for repairs. However, .they are much favoured by many contractors, and should fulfil many of our requirements in New Zealand. Drag-line Scraper Excavators. — These are deservedly popular machines, and are in varied design, capacity, and power. They are extensively used for levee building and the enlargement of rivers, streams, and channels. They provide an excellent berm, and have generally a wide range of operation. They are alsp good for clean-out work. Some contractors are disciples of the “dragline,” just as others pin their f|aith on the “dippers’” Certainly,, these machines must appeal to anyone desiring efficiency and a wide range of operation.

Hydraulic Suction Dredges.—These are used for special jobs, such as building levees of large size along rivers, but are not by any means in general 'use on drainage of swamps. The cost of a lOin suction dredge in New Zealand would be about 18 000. Operating Costs of Various Machine?.—Operating costs vary very much, and it is not proposed to tra verse this question, with the exception of providing herein a schedule of costs-data provided me by the Department of Agriculture, Washington, D.C. These figures are representative of typical bids or tenders accepted in various States. General.—A close study was made bf the various machines in operation, and exhaustive inquiries made ofj the owners, operators, and supervising engineers as to efficiency, application, and economy of the various types anl makes. This was particularly necessary in view of the. purchases for New Zealand. Much assistance'was given in this respect by the various consulting drainage engineers, big contracting companies, and the Chief of Drainage Investigations. • Some ofthe contracting firms possess as many as forty machines of different, types. The conclusion arrived at is that dipper dredges, walking and drag-line excavators, are best suited to New Zealand drainage conditions.