In Krishna delta, cultivation is gradually declining especially at the canal tail ends. The main reason being, sufficient quantity of water is not available for cultivation purposes, due to loss of canal water due to seepage, evaporation, and excess withdrawal of water by some errant farmers, etc. Seepage loss from the unlined canals is a major issue. The average loss due to seepage from the unlined canal is 0.415 cumecs. If canal lining is provided then the seepage could be reduced by about 88% (Uchdadiya & Patel, 2014) and the velocity of water in the canal will also increase as the surface of the canal will be smooth by providing a lining to the canal. This will increase the discharge carrying capacity of the existing canals. The canal lining can reduce the seepage, water logging, silting, and maintenance cost of canal considerably. So, the quantity of water saved from the lining can be used for irrigation. As the canal water is directly exposed to the sun, the loss due to evaporation is also noticeable. Evaporation losses range from 0.25% to 1% of the total canal discharge (Sahasrabudhe, 2011).

For this study, the Peddapatnam canal is selected as the study area. It is a branch or a distributary canal of Bantumilli canal. The required data for this study was collected and interviews are conducted, with the farmers and officials to know the reasons for the present problems. Land surveying has been done to determine the canal profile. The information gathered pointed to the following causes for the current issues, viz., (i) Canal is unlined, (ii) Canal section is highly distorted, (iii) Unequal water distribution, (iv) Excess withdrawal of water by errant farmers, (v) Unregulated animal movements, (vi) Evaporation losses, seepage, and water shortage.

In Panchnadi Minor Irrigation Project (Ratnagiri district, Maharashtra State, India), the unlined sections of the main canal were converted into lined sections, resulting in a 7 saving of 8.270 x 10 gallons of water, which may be used to irrigate about 43 hectares of additional area, thereby improving conveyance efficiency up to 75 percent from the present (Jadhav, Thokal, Mane, Bhange, & Kale, 2014). Another problem is evaporation. Using the 1MW canal-top solar plant, it is observed that about 9 million litres of water can be saved from evaporation. The efficiency of canaltop plant is 2%-5% higher than the ground-mounted solar plant (Patil, 2018).

The objectives of this study are,

• To effectively conserve the water to canal tail end for irrigation purposes to the Peddapatnam canal (Machilipatnam Mandal, Krishna District)
• To recommend cost-effective measures to improve the water distribution, thereby improve the economic value and habitation of Peddapatnam village farmers.

Availability of sufficient quantity of water for cultivation purposes has become a major challenge, due to loss of canal water due to seepage, evaporation, and excess withdrawal of water by some errant farmers, etc. Loss due to seepage from the unlined canals is a major issue and the average loss due to seepage from an unlined canal is about 0.415 cumecs. If a canal lining is provided then the seepage could be reduced by about 88% (Uchdadiya & Patel, 2014) and the velocity of water in the canal will also increase as the surface of the canal will be smooth due to the lining. This will increase the discharge carrying capacity of the existing canals. The canal lining can reduce the seepage, water logging, silting, and maintenance cost of canal considerably. So, the quantity of water saved from the lining can be used for irrigation.

As the canal water is directly exposed to the sun, the loss due to evaporation is also noticeable. Evaporation losses range from 0.25% to 1% of the total canal discharge (Sahasrabudhe, 2011).

In the Panchnadi Minor Irrigation Project (Ratnagiri district, Maharashtra State), the unlined sections of the main canal were converted into lined sections, resulting in a saving of 7 8.270 x 10 gallons of water, which may be used to irrigate about 43 hectares additional area, thereby improving conveyance efficiency up to 75 percent from the present (Jadhav et al., 2014).

The cost-effectiveness analysis of four water-saving irrigation techniques that are widely implemented in China were studied to understand the impacts of climate change, sprinkler irrigation, micro-irrigation, low-pressure pipe irrigation, and channel lining (Zou, Li, Cremades, Gao, Wan, & Qin, 2013).

Another problem is evaporation. Using the 1MW canal-top solar plant, it is observed that about 9 million litres of water can be saved from evaporation. The efficiency of canaltop plant is 2%-5% higher than the ground-mounted solar plant (Patil, 2018).

The socio-economic status of Bangladesh in terms of its current scenarios of growth of population, rice production and demand, methods of irrigation, energy and environmental conditions, and governmental renewable energy policy, which give a clear message that solar irrigation could be one of the vital options to create sustainable development in agriculture (Islam, Sarker, & Ghosh, 2017).

Figure 1 depicts the study area wherein the either ends of Peddapatnam canal are Bantumilli (16°21'35.89"N, 81°15'42.82"E) and Parvathipuram (16°19'24.92"N, 81°19'46.10"E) Krishna delta, Andhra Pradesh.

Figue 1. Study Area of Peddapatnam Canal

The flowchart shown in Figure 2 describes the sequence of activities carried out in the present study.

Figure 2. Flow Chart

4.1 Collection and Analysis of the Required Data

The hydraulic particulars of Bantumilli and Peddapatnam canals, groundwater details, and rainfall data are collected. After analysis, the following data is recorded. hich also resulted in the non-implementation of development activities proposed by the Government. Figure 4 depicts the stage of groundwater development, which also mentions the extent of development in percentage terms.

Figure 3. Details of Water Release (Source: Water Resources Department, Gudlavalleru, Andhra Pradesh State)

Figure 4. Stage of Groundwater Development (Source: Central Ground Water Board, Ministry of Water Resources, Government of India)

4.1.2 Water Release Data

• When compared with the water flows of year-2012, the water flows of year-2015 are 50% lower. This means the total area under cultivation is reduced to 50%.
• Inspite of this, cultivation is not possible in Peddapatnam village, as this 50% flow is not reaching Peddapatnam village.
• In the year-2013 and year-2014 flows were high when compared to previous years flows. Hence the aforementioned problem did not arise in these years, as shown in Figure 3.
• But, in 2015, the water flows reduced and hence no water reached the endpoints of the Peddapatnam canal as deepening of the canal was carried out, which led to variation in levels.

4.2 Surveying

A home interview survey was conducted to elicit information about the problems encountered by the farmers of the study area. Later, the survey was extended to gather opinions of various in-service and retired Government officials who are familiar with the study area, to know first-hand the reasons for these issues.

The respondents cited the following reasons : (a) seepage from canal (b) evaporation of a small quantity of canal water and distorted canal section (c) unequal water distribution (d) deposition of silt on the canal bed (e) reduction in Full Supply Level (FSL), and (f) reduction in Tail end water level attributed to the existing canal being unlined, excess water being withdrawn by farmers, animal movements and non-cooperation from influential farmers. The profile of the existing canal is shown in Figure 5.

Figure 5. Canal Profile

4.3 Design

4.3.1 Design of Canal Lining

Jadhav et al. (2014) suggested that canals be lined to reduce the seepage and improve the distribution efficiency.

4.3.1.1 The Design Details of the Lining for the Existing Unlined Canals.

• The lining is designed : as per IS: 10430 – 2000
• Duty : 5000 acres
• Longitudinal slope : 1 in 5000
• Full supply depth : 2 m
• Freeboard : 0.75 m
• Side slopes : 1.5: 1
• Bed width of the canal : 1.5 m

4.3.1.2 Safety Considerations for Slope Stability of Canal Lining

• Swedish method of slices is used to assess the slope stability and Fellenius method (Ramamurthy & Sitharam, 2005) is used for finding the center of the critical slip surface.
• Many trial slip surfaces were considered.
• After a detailed analysis:
•  The factor of safety is 1.09, for the cross-section shown in Figure 6 (when face failure is considered).
•  The factor of safety is 4.61, for the cross-section shown in Figure 6 (when toe failure is considered).

Figure 6. Canal Lining

4.3.2. Design of Retaining Wall

As per suggestions of Government officials, a retaining wall is designed (without changing the original cross-section of the canal), the cross section of which is shown in Figure 7.

Figure 7. Retaining Wall

4.3.2.1 Details of Retaining Wall

• Retaining wall is designed : as per IS :456 – 2000
• Duty : 5000 acres
• Longitudinal slope : 1 in 5000
• Full supply depth : 2 m
• Free board : 0.80 m
• Bed width of canal : 5 m
• Top width of canal : 5.20 m

4.3.2.2 Safety Considerations of Retaining Wall

• Safe against sliding (FOS = 1.75 > 1.5)
• Safe against overturning (FOS = 6.17 > 2.0)
• Pressure at toe is 73.82 kPa < 500 kPa
• Pressure at heel is 42.26 kPa < 500 kPa

4.4 Mix Design for M20 Grade Concrete

M20 grade of concrete is used for both canal lining and retaining wall and mix design has been prepared for the same. The particulars of the mix design are given below:

4.4.1 Mix Proportions

Cement : Fine aggregate : Coarse aggregate 1 : 1.45 : 2.96

4.4.2 Quantities of Materials to be used in the Field per Meter Length

• Cement = 475 kg
• Fine aggregate = 17 cft (0.17 units)
• Coarse aggregate = 34 cft (0.34 units)

4.5 Cost Estimation

Estimations were carried out using the procedure outlined by Chakraborty (2006).

4.5.1. Cost Estimation of Canal Lining

Total cost of lining and for the construction of a retaining wall are presented in Tables 1 and 2.

= 10000 x 5400

= 5,40,00,000 (5.4 crore Indian rupees)

4.5.2. Cost Estimation of Retaining Wall

The total cost of retaining wall per 10 km length = 10000 x 11,680 x 2 (retaining wall on both sides of the canal)= 23,36,00,000 (23.36 crore Indian rupees).

Table 1. Cost Estimate of Canal Lining

Table 2. Cost Estimate of Retaining Wall

4.6 Canal-top Solar Plant

An 8.5 MW canal-top solar plant, similar to the one shown in Figure 8, has been proposed to supplement the existing power generation facility of the study area and to cater to the needs of power requirements of surrounding villages. Canal-top panels also help to reduce evaporation of water by acting as a barriers between the sun's radiation and the canal water.

Figure 8. Canal-top Solar Panel System

Power generation and power cost details are considered based on the APSCSCL, MNRE, and NREDCAP recommendations.

4.6.1 Details of Peddapatnam Canal-top Solar Plant

•  Capacity : 8.5 MW ·
• Total solar area : 85,248 m²
• Solar energy per square meter : 4.61 kW
• Power Number of panels : 47,360
• Power generation per day : 38,250 kWh
• Government price per kWh : 2.50
• Market price per kWh : 4.00

4.6.2 Cost Estimate for Solar Panels

The following cost estimate has been prepared based on the information available from Chandrasan's 1MW solar plant (Patil, 2018).

• Benchmark cost for on grid system per watt: 60
• The total capacity of Peddapatnam solar plant: 8.5 MW
• As per the above details, the total cost of the solar plant: 51 crores
• Cost of Photovoltaic (PV) panels is 39.48% of total cost: 20.13 crores
• Civil, Electrical, engineering & construction cost is 30.62% of total cost: 15.61 crores.
• Module & Mounting structure cost is 24.81% of total cost: 12.65 crores
• Invertor cost is 5% of total cost: 2.55

4.7 Details of Return on Investment from the Alternatives Suggested

4.7.1 Income from Solar System

• Total power generation per day= 38,250 kWh
• As per government price income generation per day

     = 38250 x 2.5

     = 95,625 ≈ 1,00,000

• As per market price income generation per day

     = 38250 x 4

     = 1,53,000

4.7.2 Income from Paddy

• Average crop yield per Acre

         = 26.25 quintals

• Number of crops per year = 2
• Total yield of Peddapatnam canal paddy fields

         = 26.250 x 4735

        = 124293.75 quintals

• Investment cost per acre of paddy is = 51%
• As per MSP (Minimum Support Price) per quintal

         = 1500

• Income generated by this canal through paddy

         = 1500 x 124293.5 x 2

         = 37,28,81,250

• Investment cost for the paddy

             = 37,28,81,250 x (50/100)

             = 19,01, 69,450

• Total Income generated by this canal through paddy is

        = 37,28,81,250 - 19,01, 69,450

        = 18,27,11,800

4.8 Internal Rate of Return (IRR)

4.8.1 IRR for Canal Lining with Canal-top Solar Plant

Total project cost = 56.4 crores

Cash inflow per year = 21.27 crores

Factor = Project cost/ Annual cash inflows = 56.4/ 21.27 = 2.65

From cumulative tables of IRR (Aryasri, 2014), the value 2.65 lies in between that for 6% and 8%. The exact value is found by interpolation.

RI = Lowest rate of discount, assumed as 6%, the lower bound value

PVCFAT = Present value of cash inflow

PVC = Present value of cash outflow

△PV = Difference in calculated present values of inflows

△R = Difference in rate of interest

IRR = RI + [ (PV_CFAT – PVC) / △PV ] x △R

       = 6 + [ (56.85 – 56.4) / 2.04 ] x 2

      = 6.44%

By the trial and error discount rate percentage = 6% throughout.

The IRR of 6.44% is more than discount rate and hence, it is a viable project.

4.8.2 IRR for Retaining Wall with Canal-top Solar Plant

Total project cost = 73.06 crores

Cash inflow per year = 21.27 crores

Factor = Project cost/ Annual cash inflows

         = 73.06/ 21.27

        = 3.43

From cumulative tables of IRR (Aryasri, 2014), the value 3.43 lies in between that for 6% and 8%. The exact value is found by interpolation. The factor 3.43 in between that 6% - 8%. The exact percentage value is find out by a interpolation.

IRR = RI + [ (PV_CFAT – PVC) / △PV ] x △R

      = 6 + [ (73.70 – 73.06) / 3.26 ] x 2

     = 6.39%

The IRR of 6.39% is more than discount rate and hence, it is a viable project.

From the current study, after a detailed analysis and numerical calculations, the results are presented below.

• A detailed study of the groundwater data and the rainfall data of the Peddapatnam village region revealed very high salinity.
• From the water release particulars, it is noted that only 50% of the total expected flow is reaching the Peddapatnam village.
• Due to deepening of the canal, water did not reach the endpoints of the canal.
• The home interview survey revealed that insufficient water was available for irrigation, due to seepage, evaportation, siltation, excess withdrawal of water and movement of stray animals.
• The study revealed that lining of the canal, with a side slope of 1.5: 1 may be necessary to cut-off seepage considerably.
• For the cross-section of the canal provided, slip circle analysis yielded a factor of safety of 4.61 against toe failure.
• As per a suggestion of the government officials, regarding the consideration of the construction of a retaining wall, the study revealed that for the proposed cross-section of the retaining wall, the factors of safety against sliding and overturning are 1.75 and 6.17 respectively.
• The cost of lining for a 10 km stretch of the canal is  5.40 crores.
• Alternatively the cost of construction of a 10 km length of a retaining wall is  23.36 crores.
• The cost of installation of a 8.50 MW canal-top solar plant is  51 crores.
• The number of persons who will get benefited from any of the above alternatives is about 9000.
• The solar installation will generate 38250 units of power which is equivalent to  1,53,000 per day of income as per prevailing market rates.

The construction of the proposed canal lining or the retaining wall facilitates water distribution for 9,000 population and for irrigating 5000 acres of fertile land. The authors also recommend the installation of an 8.5 MW canal-top solar plant on Peddapatnam canal to save 75 million litres of water from evaporation.

The following recommendations are proposed,

• The estimated cost for lining and solar panel installation is  56.4 crores. This entire investment can be recovered in 2½ years as profit of  18.27 crores from the crop yield per year and  3 crores per year from solar power, respectively.
• The estimated cost of retaining wall and solar panel installation is  . 73.06 crores. This entire investment can be recovered in 3½ years as profit of  18.27 crores from the crop yield per year and  3 crores per year from solar power, respectively.
• The IRR calculations have confirmed that canal lining is a better viable option.

Acknowledgment

The authors wish to thank Er. B. Brahmanaiah, Fmr. Supdt. Engineer, I & CAD Department, Govt. of Andhra Pradesh State, Dr. ISN Raju, Fmr. CDO, Govt. of Andhra Pradesh State, Er. Mohan Rao, EE (Water Resources Department-Krishna Eastern Division), Govt. of Andhra Pradesh.