Canal components, borrow pit and spoil bank

Components of a canal section

    spoil bank          bank          bank   borrow pit
        __              ____          ____     ___
   ____/  \____ GL ____/    \__ FSL __/    \___/   \____
                       berm  \______/ berm
                              bed

• Bed and side slopes: the bottom and the inclined sides of the channel.
• Full supply level (FSL) and free board: the water level and the safety height above it.
• Banks: earth embankments on one or both sides; the top of the wider bank carries the service road.
• Berm: a horizontal strip between the canal and the toe of the bank; it gives stability, protects the bank from erosion and leaves room for silting.
• Dowel (dowla): a small bank on the outer side of the road for safety and protection.
• Borrow pit: a pit from which earth is taken to build the banks when the excavation of the canal is not enough (canal mainly in filling).
• Spoil bank: a heap of surplus excavated soil placed in layers along the canal when the excavated earth is more than that needed for the banks (canal in deep cutting).

Requirement of borrow pit and spoil bank

• If the canal depth is less than the balancing depth, the excavation is less than the filling needed, and earth must be taken from borrow pits. They are preferably dug within the canal section (in the bed), where they later fill with silt. If they are outside, they should be shallow, continuous strips at least about 5 m from the toe of the bank, so that they do not cause seepage problems or breaches.
• If the depth is greater than the balancing depth, there is surplus earth, which is dumped as a spoil bank at a safe distance from the canal edge so that it does not slide back or block drainage.
• Both are located so as to avoid damage to land, with the least possible lead and cost.