Balancing Canal depth

Balancing Canal depth:

Balancing canal depth comes when the canal is in partially embankment and partially in cutting.It is the depth of the canal(H) which gives equal amount of filling(i.e earth required for formation of Banks) and cutting(i.e earth from digging). For a given cross-section of a canal, it has only one balancing depth. For this depth the canal sectional will be economical.
B= Bed width.

b1,b2= width of embankment of left and right side respectively.

d= excavation depth.

h= embankment height.
H=height of embankment from the bed of the canal.

    X- sectional area in cutting =Bd+sd²

     ^{X- sectional area in embankment =} (b1+b2)h+2s1 h²

^{For balancing depth,}

^{Area in cutting= Area in embankment.}

^or,  Bd+sd^{2  =} (b1+b2)h+2s1 h²

or, Bd+sd^2=(b1+b2)(H-d)+2s1(H-d)^2.

From this equation 'd' can be calculated.

Appropriateness and sustainability of Micro- irrigation system in the hills of Nepal.

Micro-irrigations(i.e.Sprinkler and Drip) are the alternative method specially in the hilly areas. Sprinkler and Drip are appropriate and sustainable in the hills of Nepal due to the following reasons:

• Micro- irrigation system requires relatively high pressure which can be easily provided through gravity in the hills.
• It needs clean sediment free water, to avoid clogging of its component, which can be obtained from springs.
• The hill slopes are steep and can be eroded with other method of water application such as: canal irrigation.
• Micro irrigation systems require relatively less amount of water and in the hills, at the higher altitude water shortage may occur but by pumping of water from rivers this irrigation system can be enhanced for better crop yield. This means it suitable even in the area of water shortage.
• Crops in the hills can be sown in rows having appropriate lateral spacing(rows spacing) and spacing between them itself and they can be irrigated by Sprinkler and Drip with less amount of water for better yield. 
• Light soils in the hills are poorly suited to growing rice hence trying to provide irrigation system for growing rice may be proved uneconomic. Hence promoting for growing vegetables or other high value crops can be done with micro- irrigation system.
• Portable micro-irrigation systems are preferable to the farmers in the hills of Nepal because they live in uphills which is several hours walking distance away from the cultivated land. So portable irrigation system is appropriate and sustainable as it can be taken to the any desired place by the farmers.

Delta of a crop and Duty of water and their relation

Delta:

Some quantity of water is required for any crop to come to its maturity. The total quantity of water required for any crop during its base period(B) for its full fledged nourishment when expressed in depth of water(i.e. in 'cm' or in 'inches') is called its Delta. The total quantity of water(i.e. volume of water) is divided by the total irrigated area to obtain Delta of crop of the irrigated area.

     We have talked about base period(B), it is the time period between the first watering of the crop during its sowing to last watering before its harvesting. It is generally expressed in 'days'. 

   The another related term is Crop period. For practical purpose Base period and Crop period are taken as same but they have a little difference. Crop period is the time period between sowing of a crop to its harvesting. In this manner, Crop period is slightly greater than the Base period. 

Duty:

 Duty of a water simply expresses the number of hectare of land that can be irrigated for the full growth of the given crop by supplying 1 cumec water continuously during the entire base period of that crop. It is generally represented by 'D'. Its unit is hectare/cumec. For example, if water flowing at the rate of 1 cumec, runs continuously for B days of the crop matures 100 hectares then Duty of that crop is 100 hectare/cumec to the base of B days.

  Duty varies from point to point. It increases as one moves to downstream from the head of main canal to the head of branches. It is due to the transmission losses in the channels.

Relation between Delta and Duty:

Let a crop of Base period B for which 1 cumec water is supplied continuously for its full growth.

Then the total volume of water supplied during B days for that Crop = (1*B*24*60*60) cubic meter.

By the definition of duty, it is clear that it matures D hectares of land.

Then the total depth of water supplied during base period B = (1*B*24*60*60)/(D*10000)

                                                                                           =8.64B/D meters

We know total depth of water supplied during base period of a crop is Delta.

Then, Delta= 8.64B/D meters.

Crop water requirement, Operational water requirement and Irrigation water requirement.

 Crop water requirement is the water used by the crop for its survival. Plants use water for photosynthesis by which it produces carbohydrates which serves as food for the plants. Water is transfered into the leaves through roots of the plants, after utilization of some amount of water for photosynthesis the rest of the water comes at the surface of the leaves and finally it gets vaporized into the atmosphere which is known as transpiration. While transpiration occurs at the same time Evaporation from the surrounding surfaces such as: open water surfaces, bare soil or vegetative cover occurs. These two contributes for the crop water requirement which is generally measured under the name called 'Evapotranspiration' or 'Consumptive use'.

Operational water requirement is the water used for land preparation, percolation losses in flooded paddy fields. For irrigation water requirement, it must be supplied in addition to the crop water requirement.

Field water requirement:  It is the sum of crop water requirement and the Operational water requirement.

Net irrigation water requirement(NIR): It is the amount of water obtained after deducting the Effective rainfall from the Field water requirement. Effective rainfall is the portion of reliable rainfall that contributes to meeting the water requirement of the crop. It is generally taken as the 80% reliable rainfall multiplied by suitable factor.
          P-eff = f* P(80%)
f=0.70 for upland crops
f=0 if p(80%)<5 mm
f = .85 if 5mm < p(80%) < 100mm
f = .70 if p(80%) > 100mm

Gross irrigation water requirement, commonly said as irrigation water requirement, is the amount of water needed at the diversion intake.
 Irrigation system while conveying water losses water in the form of seepage, spillage and evaporation.
From the intake to the field application, water irrigation system has different efficiencies in its different component. It has field applicaton efficiency (E- field), on- farm distribution channel efficiency(E-farm), and the main canal efficiency(E-main).
Gross irrigation water requirement( I-gross)= NIR/ (E-field*E-farm*E-main).