construction and refurbishment of earthen irrigation channel banks

cation exchange capacity (CEC) a measure of the capacity to exchange cations and is equal tothe sum of all exchangeable cationschannel the open irrigation device which is used to convey irrigation water. Other terms usedinclude canals, ditches flumes and laterals. In this manual, open irrigation systems of all sizesare referred to collectively as channels.channel lining low permeability membrane of concrete, compacted clay, bituminous or plasticmaterial, placed on the inner face of earthen channel, or within the bank, to prevent water lossby seepage. Linings may be protected by earth cover.channel regulator a permanent structure constructed across a channel and fitted with means ofadjusting the waterway area so as to control the rate of water flow along the channel and theupstream water level. Most regulators are one of two general types which utilise differenthydraulic characteristics for specific applications, ie• overfall weir where water flows over a weir crest which can be varied in level forchanging flow rates• undershot gate having an adjustable sliding gate allowing flows to pass beneath the gate,the rate of flow being controlled by the size of the opening.channel tenure land which the irrigation authority has rights to; whether by freehold, easement,lease or agreementcirclip remover a hand tool rather like a rowel (a tool with a shaft about 2-4 mm dia which isground or tapered to a point) with a 90 bend near the end.clay primary soil particles with a diameter less than 0.002mm or 2µm. Also, a texture given tosoil in which the clay content is greater than about 40% by weight. Also used in an adjectivalsense to describe soils which have a moderate clay content, eg. clay loam or sandy clay loam.coagulation the aggregation of the particles of a clay sol as a result of the addition of anindifferent electrolytecobble substrate particles with a diameter of 64mm to 256mm.colloid particles less than 1 µm in diameter which form a stable sol when dispersed in acontinuous phasecompaction increasing the soil bulk density and decreasing the soil porosity, by the applicationof mechanical forces to the soil.compaction curve the curve which illustrates the relationship between the moisture content andthe dry density of a soil. Refer optimum moisture content.critical flow occurs at the unique depth where the specific energy of a given discharge is aminimum. For any other flow, two velocities are possible. Due to this unique velocity, depth,and slope which can occur for a given discharge and channel shape, critical flow is importantin the design of hydraulic structurescurls lumps of compacted soil material formed from the blade of a bulldozer of scraperdesign bank level the finished bank level which consists of the maximum water level or designdischarge level plus freeboard.design discharge level (DDL) the level at which a channel will flow at its maximum designedflow rate. For most open channels, the level is parallel to the bed of the channel. It issometimes found after construction that the channel is smoother than was assumed in designand so, at the design flow rate, the water level is below the designed discharge level. On theother hand, siltation can reduce the waterway area and weed growth can increase theConstruction and Refurbishment of Earthen Irrigation Channels August 2002 - Edition 1.0 24-2