Flumes and pipes

Although pipes and flumes are not classified as a lining, they should be considered as an alternative to the remediation of a channel to reduce the seepage where supported by other advantages. A pipeline could possibly be described as the most effective lining option as it also prevents losses due to evaporation and allows pressurised delivery if required. However, pipelines are generally the most expensive option, especially for pipes over 1m in diameter.

A flume is an artificial channel of wood, metal, concrete or masonry, which is usually supported above the surface of the ground. Entire flume networks are commonly found in countries around the Mediterranean basin and other areas with similar conditions - hilly topography, limited water resources occurring in quite small streams, high returns per unit of water, well-developed infrastructure with intensive use of arable land, and local availability of suitable materials.

The use of pipelines is rapidly increasing in countries with highly developed irrigated agriculture. There are many materials that can be used but the most widespread type are PVC and concrete. In the United States, PVC pipes are used almost exclusively for pressure pipes up to about 450mm diameter; larger diameters are steel or reinforced concrete. However, this decision is purely one based on costs rather than performance. For non-pressure applications USBR uses corrugated PE pipe up to about 450mm; then concrete pipe.

The continued development and improved understanding of HDPE pipelines and their applications has meant they are increasingly being used to replace open channel systems. HDPE pipeline systems have benefited from the following developments:

Longer lengths, hence lower installation costs.
Light-weight materials, making installation easier.
Improved performance in handling pressure spikes from water hammer effects.
Field fusion providing a robust joint. The advantages of pipeline systems include:
Little loss of land, as practically all of the system is buried.
Labour-saving operation and maintenance.
Adaptability to topography. Pipe systems operate under water pressure, which can be laid uphill and downgrade, which can reduce the total length of the network.
Close control of water distribution.
Evaporation and seepage are minimal.
Weed seed contamination is reduced or eliminated.
Severances are eliminated.

The disadvantages of pipeline systems include:

The problem of detecting and sealing leaks.
High initial cost. The replacement of channels with pipelines should be considered in the following situations:
In urban and other areas with intensive cultivation of high-value crops.
Where right.-of-way costs are high and where full use of irrigable land is important.
Where the value of water is very high owing to the scarcity and/or high delivery cost, necessitating efficient use.
Where the water saved can be utilised for additional high-quality crop production.

Replacement of large channels by pipelines is not considered feasible on technical or economic grounds in the foreseeable future in many situations. Pipelining large channel sections involves large works of high capital costs (estimated at $1,000/m), and usually with high ongoing operation and maintenance costs, especially if pumping stations are required (Sinclair Knight Merz, 1998).

Hard surface lining techniques
Concrete
Shotcrete
Grouted fabric mats
Soil-cement lining
Tiles and bricks
Asphalt

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Page last reviewed on 8/3/04