Table of Contents
SERVICE ROAD AND DOWLA
- A service road is provided usually on the left bank of the channel.
- In case of very small channel i.e. minor, it may or may not be provided.
- The top width of the bank carrying service road should not be less than 5 m.
- According to CWPC minimum road width should be 61 m.
- On large canals service roads may be provided on both the banks.
- Service road level should be 50 cm to 1 in above the F.S.L. depending upon the size of the canal.
- A Dowla is provided along the service road, separating service road from berms.
- This is provided as a measure of safety.
- Dowla is an earthen bond 50 cm high and 50 cm wise at the top.
- The side slope of Dowla is 1.5: 1. It also prevents erosion of the slope due to rain.
- The width of land, required to accommodate the canal cross-section.
- Its connected elements, is know land width for the canal.
- The distance between outer toes of canal banks plus a few metres on both sides for the construction of side.
- Rainwater drains or for growing tree rows is know the permanent land width of the canal.
- This land has to be acquired before canal construction is started.
- During construction of the canal, some additional land is required for borrow pits and for stacking the materials.
- Such additional width of land is know temporary land width.
- This land is acquired temporarily and returned to the owners after its use.
- Compensation is paid to the owners for their temporarily acquired lands.
Following are the recommendations of C.W.P.C. in regard width of the land.
(i) Width of land to be acquired clear of banks when canal is in less than balancing depth of cutting.
(a) For major canals.
- Width due to full height of bank + 5 m. (b) For minors and distributaries.
- Width due to full height of banks above ground + 1.5 m. In this case
(i) extra land is required for borrow pits.
(ii) Width of land to be acquired clear of banks when canal cutting is more than balancing depth.
(a) For major canals.
- As per actual drawing + 5 m.
(b) For minors and distributaries. As per actual requirements + 1.5 m.
- It is also known as back berm.
- It is provided on the outer slope of the banks.
- It is required only in case of high banks and very permeable soils.
- Its main purpose is not to allow the seepage line expose on the outer slope of the bank.
- It is a method of disposal of surplus excavated soil from very deep reaches of the canal.
- When quantity of surplus excavated soils is not much it is used either to widen.
- The banks or to raise the height of banks.
- If amount is large it is disposed of, by constructing spoil banks parallel.
- To canal banks, but slightly away from the banks.
- The area enclosed between canal banks and spoil banks is properly drained.
- When the amount of soil obtained from cutting is not enough to complete.
- The banks of the canal extra earth is required.
- This extra earth is obtained from the borrow pits.
- Borrow pits may be constructed out of canal section or within the bed of the canal.
- Outside borrow pits are not preferred as they may become mosquito breeding centres during rains.
- The outside borrow pits should not be deeper than 30 cm so
- that they may be easily reclaimed by the owners when land having borrow pits is returned to them.
- Outside borrow pits should be located at least 5 m away from the toe of the bank.
- In case of small canals, and 10 m in case of large canals.
- Inside borrow pits are preferred to outside ones.
- The reason being that inside borrow pits get silted up during course of time, automatically.
- Inside borrow pits should not cover area more than half the bed width.
- Suitable unexcavated bed should be left after each section.
- So that water remains held up in them during running of the canal for silting purposes.
- Depth of inside borrow pits should not exceed 1 m.