oa Research in Irrigation Canal Lining: An Experience from Sudan

The amount of water below 1000 m³ per capita per annum is considered as the water poverty zone. With business as usual scenario it is estimated that by the year 2025 half the world's people will live in countries with high water stress. Based on Global averages irrigation water demands accounts for about 70% of all water uses. Meanwhile water use efficiencies of irrigated projects are generally very low particularly those under traditional surface methods. On the other hand conveyance losses vary within a range of 25–50% of the total diversion. Generally canal lining can save about 75% of the conveyance losses. However, high quality linings were found to practically eliminate such losses. The paper reviews the benefits of canal lining, which include hydraulic, economic and environmental benefits. Since seepage from irrigation canals is the most important factor in lining considerations the paper presents some review on the phenomenon. Canal lining is usually classified into four main types: hard surface linings, membrane linings, earth linings and soil sealants. The paper critically discusses the different types and highlights the criteria for selecting the appropriate lining technique. The paper also reviews the recent technical developments and research at the global level in this field; these include the development of new materials and techniques. Finally the paper presents a review of the canal lining related research executed by the National Centre for Research, Sudan during the last 20 years. These include development of low cost lining (building) materials using locally available aggregates (sand and gravel), lining irrigation canals on expansive soils and development of low cost concrete pipes and production of precast canal-lets. Canal lining was found conserve irrigation water, reduce fuel consumption, reduce irrigation time and reduce labour requirements. Development of Low Cost Building Materials for Canal Lining:: Four low cost building materials have been studied, these are namely khafgi, ferrocement, kenaf sheets and concrete made of small-sized gravel available near RDRC. Kenaf sheets were rejected because of the low durability expected. The other three materials were found to be feasible based on strength, permeability and durability. Water transported sand near RRS was found to be suitable for building works including lining whereas wind transported sand can hardly be recommended for such works.

Hand placement cast in-situ was adopted using the semicircular configuration, as besides improving structural integrity of the canal, it is the most hydraulically efficient section particularly for small canals. A semi circular cast-in situ form was made to construct channel sections that accommodate maximum discharges at RDRC. The work is done in alternate sections and the lap-joint technique was used. Pipe Casting:: It have been noticed that some desert farms the canalization system is liable to be buried by wind-blown sand. To avoid this problem the system should adopt pipes instead of open channels; however, traditional farmers cannot afford to cover such expenses since such pipes are relatively expensive in the local market. To overcome such problems the study was extended to develop intermediate technologies for pipe casting. A form was designed and constructed in a local workshop. The form is made of PVC pipe equipped with a handle as an internal unit the external unit is made of sheet metal also a wooden base is used. The external unit is composed of two semi-cylinders; a steel channel is welded to each end of each semi-cylinder to facilitate fastening meanwhile a rubber strip used to prevent water leakage. Again locally available aggregates were used. Laboratory tests (Impact Value and Crushing Value) showed that locally available gravel is suitable for pipe casting. The internal unit of the form is removed about an hour after the end of the casting process and the external one after a day. The pipes were then cured for 7 days. Compressive Strength and permeability tests proved that the produced pipes comply with the Known International Standards. Additionally the pipes were tested in the field by passing a tractor, which represent the maximum expected load in such farms without being damaged. Lining Irrigation Canals on Expansive Soils:: Um Jawaseer Desert Farm Project, which is located in Wadi El Magadam, the Northern State was established in the year 1989 for the settlement of the nomads of El Hawaweer Tribe. The project harnesses water from an aquifer of about 40 m below ground surface for irrigation and other purposes. Evaluation studies showed that the project is successful in creating better livelihood for the people of the area.

Huge water losses were encountered in the first two phases. In the third phase the project adopted stone lining, which is estimated to conserve about 1/3 of the irrigation water. However, stone lining is known to be one of the least effective lining techniques. Identification tests were carried out in accordance with the British Standards and showed that Um Jawaseer soil possesses swelling properties.

To reduce (mitigate) the expansive potential of Um Jawaseer soil some additives (cement, lime, bituminous emulsion and refuse oil) were tested, these additives were added to the soil at a rate of 6% by weight as recommended by some authors.

To avoid damage the linings a combination of soil treatment and construction technique was used for the lining of Um Jawaseer irrigation system. The soil was first excavated to a depth of 60 cm and mixed with the additive (cement). Water is added to the soil/ cement mixture till the optimum moisture content (plastic limit) was reached. Finally the mixture was compacted into two layers (30 cm each). As for the construction technique the semi-circular channel cross section was used since it produces integrity in structure and the channels so constructed can resist external forces. This combination gave very encouraging results since it is found to mitigate upheaval damage and produce strong and efficient conduits. Precast concrete canal-lets:: The merits of precasting are attributed to the high quality control coupled with the technique. Precasting was advised by some authors for mass production of tertiary canals. The J- Section was selected for ease of casting the form is made of metal sheets.

The form was filled of concrete, while being compacted with steel rod, left for an hour to allow for setting of concrete and then released. The finished section is allowed to dry for 24 hours and then cured for 7 days by wetted kenaf sacks. Keyword: Seepage, Irrigation, Canal lining, Pre-casting, efficiency