The maximum velocity that does not cause excessive erosion depends on the erodibility of the soil or lining material. Normally flow velocity in excess of 0.6 m/s is non silting (Schwab et al., 1993). The velocity of flow in a canal or ditch should be non erosive and non silting that prevent the deposition of suspended substances. HPD = hours per day that water is deliveredĮ i = irrigation efficiency including conveyance efficiency of canal or ditch (percent). This is provided between 15.25% of normal depth of flow.Ĭhannel capacity can be estimated by equation given as:ĭDIR = design daily irrigation requirement (mm/day)Ī = irrigated area supplied by canal or ditch (ha) This is provided to prevent over topping of channel embankments or damage due to trampling. V) Freeboard: It is the vertical distance between the highest water level anticipated in channel flow and the top of the retaining banks. Iv) Hydraulic Slope (S): It is the ratio of vertical drop in longitudinal channel section (h) to the channel length (l). Iii) Hydraulic Radius (R): It is the ration of area of wetted cross section to wetted perimeter.

Ii) Wetted Perimeter (p): It is the sum of the lengths of that part of the channel sides and bottom which are in contact with water.

For a rectangular cross section, if b = width of channel and y = depth of water, the area of wetted section of channel (a) = b.y. I) Area of Cross Section (a): Area of cross section of for a rectangular cross section, of wetted section.

The terminologies used in the design of open channels of different geometry are given below:

Civil engineering formulas figure 12.2