Comparing earthen channels with plastic piping for efficient and cost-effective irrigation

In the Eastern Gangetic Plains, many farmers have made many positive changes to irrigation practices. For example, farmers have started using diesel pumps and have adopted better water application practices such as using furrows. But, water conveyance to fields is often still through the use of earthen channels. For large plots of land, farmers have constructed permanent channels that connect different plots. Farmers working with small plots of land, often marginal and tenant farmers, use temporary earthen channels (mostly based on seasonal requirements).

Earthen channels, however, have some disadvantages. Earthen channels incur huge water losses and  lead to a reduction in the effective area available for crop cultivation. To convey water from water source to the fields, a flexible plastic pipe can be a better alternative to these earthen channels.

While working in the project villages for DSI4MTF, scientists and field staff have found that farmers cite the cost of conveyance plastic pipes as the major reason for not adopting plastic pipes for conveyance. To demonstrate the effectiveness and economic benefit of plastic pipes to farmers, DSI4MTF conducted a field experiment and economic comparison that assessed the benefits and costs of earthen channels and plastic piping.

Flow-rate at the end of the 100 m channel is taken with a V-notch weir.

Water loss assessment

During a recent field visit, engineers from the University of South Queensland (USQ), Australia and the International Water Management Institute (IWMI) measured the loss of irrigation of water through earthen channels. In Bhagwatipur, a project site of the DSI4MTF project, a straight 100m permanent earthen channel that begins at a water source was selected for the assessment. Scientists used a portable V-notch weir for measuring the flow of irrigation water in the earthen channel.

For this experiment, scientists and field staff first cleaned the 100m permanent earthen channel and properly sealed any leaks so that no loss of irrigation water could occur from rat and crab holes. After, scientists and staff inserted the calibrated V-notch at the end of 100-meter-long channel and properly sealed it from all sides. The earthen channel was filled up with water and was left for one hour until a steady state of flow was achieved. At this point, the flow rate of the solar pump water source was taken by using a 60 litre bucket and stopwatch and compared with the mechanical inline flowmeter reading. Simultaneously, the reading of the flow rate at the V-notch was taken. The difference in flow rate between the source and the V-notch weir at the 100 m point of the channel revealed the loss in irrigation water through the earthen channel.

The irrigation water loss through an earthen channel was finally compared with that of plastic conveyance pipe used by farmers. The result of conveyance losses through earthen channel as well as plastic conveyance piping is given in table-1.

Table-1: Percent loss of irrigation water through earthen channel and plastic pipe

Total loss through 100m of the earthen channel is 2.7 litre per second. Conveyance efficiency of water irrigation method is calculated by dividing the flowrate at the V-notch at the end of the 100 meter pipe by the flow rate of the water source. Thus, farmers lose 47% of total irrigation water through earthen channel.

Field staff seal the bottom and sides of the channel with plastic.

Economic comparison

To understand the cost difference between using earthen channels and plastic pipes, a cost comparison was carried out. Construction of earthen channels involves sacrificing productive land because land must be allocated for the channel itself. Irrigation pipes require no special land allocation. To carry out the economic comparison, labour required, area lost, and the life of the systems were compared. Earthen channels last for 5-10 years while plastic pipes last for 2 years (Table 2). For the sake of analysis, a 7 year life-span was assumed for permanent earthen channels.

Table 2: Costs associated with earthen channels and plastic pipes

Conclusion

After an analysis of experiment results, carrying out a cost comparison, and discussing with farmers about conveyance systems,  DSI4MTF staff have concluded that the water loss from earthen open channels is significant and the cost of the earthen open channel is higher than that of plastic pipes. Farmers must consider these costs and loss of water when choosing a water conveyance system for irrigation.

Further development of smart apps for data collection and decision support

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Mobile technology is becoming commonplace in all industries and agriculture is no exception. While the number of farmers with smartphones in the project intervention villages is still very low, this will not always be the case.

The DSI4MTF project team are continuing to develop a suite of mobile friendly applets. The applets are still in development phase but have been designed with three (somewhat overlapping) audiences in mind. Some applets are designed to be used by farmers, some are designed to be used by engineers undertaking technical assessments, and others are designed for the DSI4MTF project staff team to help them accurately collect and report data.

Each week the DSI4MTF staff are collecting data on the groundwater level, pond levels and water quality, as well as key meteorological data (rainfall and pan evaporation). This data is then entered directly into the mobile phone app which sends the data for each site to a cloud based server. The apps are cached on the mobile phone which means that they can still be used even if the phone has no data connection. The next time the phone has a connection (or connected to a WiFi network), the data stored on the phone will be synchronised to the server. This allows for near real-time reporting of field data which is critical when the data is being used to help provide irrigation scheduling advice to farmers.

The attached Technical Note provide an overview of the applets that have been developed for the project. If you would like further information on the applets. Please contact  Michael Scobie

1005628 – Technical Note 1 – DSI4MTF Applets (PDF 3 MB)

Irrigation Infrastructure Assessments

In November the DSI4MTF team were involved in a number of irrigation infrastructure assessments. The assessments included solar pump efficiency, diesel and electric pump tests, drip and micro-irrigation uniformity and soil moisture assessments. This data collection is an important part of Project Activity 1.2 (to assess the efficiency of infrastructure), but was also used as a training and demonstration event for farmers, project staff and government representatives.

It is important to develop a data set of evaluations to show the true cost of pumping water over the range of duties (pressures and flows). The farmers can then compare the cost of pump rental with the true cost of pumping to help make decisions about capital investments in pumps. Similarly for irrigation systems (drip kits, micro sprinkler, ridge and furrow), assessing the performance of the system against the crop requirement is important for the farmer to make decision on how and when to schedule irrigations to best meet the crop demand.

At each of the study areas (Madhubani, Cooch Behar/Alipurduar, and Saptari, the DSI4MTF team spent time in the field collecting some simple measurements to build a data set.

The level of farmer interaction varied from site to site, but was encouraging to see the interest and the improvement in understanding. A key term (litres water pumped per litre of diesel used – Lwater/Ldiesel ) was introduced to help farmers visualise what they are paying for. It is well understood that a bigger pump will move more water (and will also use more diesel), but if we are to compare one pump with another, we cannot just talk about how many litres of diesel are burned per hour.

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Farmers and field staff measuring the discharge from electric and diesel pumps

Drip irrigation assessments were undertaken in Saptari on a number of 10m x 10m drum kits systems. There were two different styles assessed with two very different results. The new style of preformed drip tape seemed to outperform the older style of drip tube in terms of uniformity of application, which is a key parameter in making sure that each plant is getting enough (but not too much) water.

Setting our ‘catch cans’ to measure the uniformity from drip and micro sprinkler irrigation systems

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Setting out ‘catch cans’ to measure the uniformity from drip and micro sprinkler irrigation systems

 

The field staff will continue to undertake assessments and collect data. These will be written up as field case studies and will be shared here in the next month.

 

 

What is the Depth to Groundwater?

Tubewell testing in the dry season

Tubewell testing in the dry season

As the team were visiting villages in the site selection phase of the project, they were asking the local community “What is the depth to ground water?” Many people were quick with a response, but the numbers seemed too high. The measurements that they were providing were in fact the total depth of the tubewells in the area.

The reason for the question was to see if end suction centrifugal pumps (commonly called surface pumps) would work throughout the dry season when the water table is lowest. The maximum theoretical depth that this type of pump can draw from is 9.8m below the centreline of the pump, and in reality this may be significantly reduced when we take into account the head (pressure) loss that takes place through friction in the suction line, the minor losses in the bends and constrictions, as well as the specific constraints of the pump set. Therefore, if the water table drops below say 7m or 8m, a surface pump won’t work, and a submersible pump will be required. Submersible pumps are often more expensive and more difficult to repair and maintain.

When the project team was in Madhubani District of Bihar in May this year, the question was asked “Do we need to use submersible pumps, or is a surface pump adequate?” To answer this question, the team undertook a simple experiment to measure the standing water level in a tubewell, and then pumped the tubewell for 6 hours to measure how far the water draws down and how quickly the tubewell can recover. The results for the experiment will be written up soon, so watch this space.

 

Site selection well under way

Now that project agreements are getting signed off we are progressing into the important phase of final site selection

The Process being followed has been:

Part 1 village shortlisting. This was undertaken by IWMI and USQ as trial during September visits and is continuing through Regional Partners and IWMI. Short listing is based on local knowledge, a brief visit and understanding of project requirements.  We are targeting SRFSI sites where possible.

Part 2 Data collection and assessment: To be completed Nov/Dec. Site selection Questionnaires are being distributed and will be completed for each site by Partners and IWMI staff. After completion of questionnaire this is run through a ranking tool to help guide selection.

Part 3 Report compilation and Finalization of Sites : Finally a brief report is prepared from the questionnaire response. The report and outcome of the ranking will determine final village selection. IWMI and project partner satff will visit all proposed sites to finalise site selection by end January and commence engagement for planning interventions.

 

Site slelection visit September 2014 in West Bengal