Cover Image
close this bookIrrigation Reference Manual (Peace Corps, 1994)
View the document(introduction...)
Open this folder and view contentsChapter 1 - Introduction
Open this folder and view contentsChapter 2 - Physical and biological resource base
Open this folder and view contentsChapter 3 - Developing water sources
Open this folder and view contentsChapter 4 - Estimating irrigation requirements
Open this folder and view contentsChapter 5 - Farm water delivery systems
Open this folder and view contentsChapter 6 - Farm water management
Open this folder and view contentsChapter 7 - Waterlogging and salinity
Open this folder and view contentsAppendix A - Math skills and tool use
Open this folder and view contentsAppendix B - Community organization and development
View the documentAppendix C - Summary of international irrigation center (IIC) training modules
View the documentAppendix D - Case studies
View the documentAppendix E - Annotated bibliography
View the documentAppendix F - Glossary of terms

Appendix D - Case studies

CASE STUDY

Pipe Size and Accessories

A farmer in Honduras grows cabbage during the dry season using a gravity flow sprinkler system. He uses two rolls of 3/4" polyethylene (100 m/roll) in his main line piping. He wants to increase the flow capacity to his field, so he buys two rolls of 1" polyethylene tubing. The water source is about 200 m from a small tank. The farmer uses the main line to fill the tank and from there the water is distributed to the field.

In the installation of the new system, the farmer decides to have two mainlines because he did not buy unions and because the 3/4" tube fit snugly into the 1" tube. Each main line consists of one roll of 3/4" and one roll of 1", and the two lines are used to fill the tank.

Is this efficient use of tubing? Could a main line of two rolls of 1" tubing with a union have a higher flow rate into the tank than the present system? Is the tank necessary?

CASE STUDY

Pump Sizing and Installation

A farmer in Bolivia buys a small centrifugal pump with the assistance of a special credit program offered by an international agency. The farmer installs the pump without any technical assistance, plants a hectare of potatoes, and begins irrigating the crop by surface irrigation in furrows.

Midway through the growing season, the farmer finds that he is spending too much money on fuel for the pump, so he lengthens the irrigation frequency from every 10 days to 3 weeks. After going through only one cycle of this schedule, it is obvious to the farmer that the potato plants are in need of more water and will soon die if nothing is done. He goes into town to look for technical assistance at the local agricultural extension office.

The extensionist accompanies the farmer to his field. They first go to the location of the pump, and the extensionist finds that the pump has been installed 5 m above the stream. She checks the pump and observes that it has a 3" inlet and outlet and also finds that both the suction line and main line are 2" pipe.

What recommendations would you give the farmer to save his crop this year? What recommendations would you give the farmer for future plantings?

CASE STUDY

Inlet Flows into Furrows

An international agency donates an 18 hp centrifugal pump with aluminum coupled piping to an orphanage in southern Bolivia. The orphanage is irrigating vegetables by furrows for its own consumption on small 20 m


20 m plots that total less than 1/2 hectare.

The water is pumped into a head ditch at a very high flow and is channeled past each plot so that it can supply water to them. There is no control structure, so the entire flow is diverted towards a plot when irrigation begins and then into a single furrow. The water rushes down the furrow and, because there is no tail ditch, overflows the furrow and floods the end of the plot. It is repeated for each furrow.

At the midpoint of the growing season, it is apparent that something is wrong with the crop. Plants at the beginning of the furrows are small and unhealthy, while the plants at the end look healthy and are of normal size.

What has occurred in this irrigated field? What can be changed to improve the water distribution? Is this the appropriate method of irrigation under these circumstances?

CASE STUDY

Community Organization

This project started when the Committee for Community Development approached the Volunteer with an interest in constructing an irrigation project.

The water source was measured and, although small, was adequate for the project. The village was tucked into a valley, and the water source was well above the fields, resulting in a good gravity-fed, pressurized system. The soils were well-drained sandy loams and loams. Some of the village members were starting to experiment with growing alternate crops with surface irrigation during the dry season by utilizing small springs below the village. Because of the topography of the area, water from the larger spring above was to be piped in.

The next village had a successful pressurized pipe hose drag irrigation system, which motivated the Committee to approach the Volunteer. The spring was on the community common land, so there was no problem with water rights.

The topographical study was done, and the system was designed. Community meetings were held regularly during this period. These meetings were tumultuous. There were disagreements but, as long as it was clear that everyone could participate, the project planning process continued. A funding source was obtained, and everything looked good.

One afternoon the Committee president approached the Volunteer to tell him the community had decided not to go through with the project. Another village meeting was held, but no agreement could be reached. The project was never completed.

Late in the Volunteer's service, he attended a big social event in the community. None of the Committee members were to be found at the celebration - they were at their own private celebration. The Volunteer then learned there were two religious sects in the village, and the Committee for Community Development was made up of only one of these religions. Ignoring one sect had doomed the project from the beginning. A blended committee of both sects may have been able to complete the system, but it was too late for that Volunteer.

CASE STUDY

Estimating Community Need

The Community Development Committee approached a Volunteer about a potable water project. The community had some limited small, private water systems, but no community wide system. The village was spread out, and most village members had to go a long way to collect water.

The Committee members showed the Volunteer the potential water source, which was 15 liters/sec. This is much more than a village of 45 families requires from a potable water system.

A meeting was called to discuss the water system and possible irrigation with overflow. The Committee, some women, and children attended the meeting. This discouraged the Volunteer, but she described the project, and the Committee said they'd drum up support. The next week the Committee presented the Volunteer with a list of families committed to the project. This list included 42 names. Since there was now a large amount of support, plans were drawn up for a community water system with potable water and a surface system with overflow, to be directed to the plots belonging to the 42 interested people.

Community meetings were sparsely attended, with most families being represented by old women and children. The men were too busy to attend.

The municipal government was funding similar projects and agreed to fund this one if the community paid 25% of the costs and supplied local labor and supplies. In this wet/dry climate, dry season vegetables and potatoes got a good price and paying off this 25% could be done within the first year. The Committee took this news back to the community and, after a week, they responded that they would do the project only if all the costs were paid by the municipality. They also wanted food as payment for their labor, as this was how similar projects had been done in their area. The project failed, and there was no interest in pursuing other sources.

CASE STUDY

Community Participation

Using small springs and surface irrigation, a mountain village in a wet/dry climate had been working with a Volunteer on alternate crop projects during the dry season. A large water source was located 6 km from the village. The Volunteer and village members did a topographical study and waterflow test and found the water source to be high enough and large enough for a good pressurized pipe irrigation system. The water source was close to another village and on its common land. There were numerous water sources in this area, but some were too low to be useful in this irrigation project.

When the paperwork for the water rights was being done, other village members came to the government offices and testified that they would be left without water if this project were completed. The water rights petition was denied. Not knowing what to do, the Volunteer met with the community and told them they would have to solve this problem. The community then decided to pay the water authority's fact-finding committee to visit the spring site. Both communities met, with almost every member of both communities in attendance. An agreement was reached regarding where some of the springs would go for the system. The topography, along with a 600 m drop along the system, made the design of the project difficult.

A government loan was secured, and the project began. The work crews were organized by the community, and the Volunteer visited the site weekly. The Irrigation System Committee and the Volunteer drew up the following rules and regulations:

1. Funds for repairs and maintenance would be taken from annual donations.

2. A list of the system's supplies and who would be responsible for them was composed, along with a statement of group ownership.

3. Volunteers to serve on the committee, along with a tools/repair supervisor, would be elected annually.

4. A process for changing members was created.

5. Fines would be imposed on those who wasted water or did not maintain their individual branches.

6. If no water was used by a member within a 2-year period, it could be sold to a new member by the group.

When the project was almost finished, the community took some of the extra cement and PVC tubes to a spring at the neighboring community. They captured one of the smaller springs with a simple spring box, and laid out a stand pipe potable water system as a gift to their neighbors in this community. The reason for this was that there had been tension between the communities, and the committee wanted to prevent possible future sabotage.

Five years later, the system is still functioning well. During the dry season slash and burn, one fire got away but, because the plastic tubes were buried 60-80 cm below the surface, the tubes were not damaged. Two members have moved away, and one member was removed forcibly by the irrigation group. This caused some tension, but this member had not used his water, refused to pay his dues, and had not replaced broken lines.

CASE STUDY

Project Description

A pressurized pipe hose drag system irrigating 25 equal parcels, totaling 2 ha.

Project Costs

Materials:


PVC tubes

$4,031.15


PVC accessories

629.00


Cement

831.00


Reinforcing bar

1,250.00


Sprinkler heads

350.00


Total for materials

$7,091.15

Labor - mason:


26 days @ $8.00/day

$ 208.00

Transport:


2 trips


$90.00/trip

$ 180.00

Total Project Investment

$7,479.15

The government Agricultural Development Bank will finance the project with a 5-year loan at 10% interest. Loan repayment = $7,479.15


0.2638 (amortization factor) = $1,973/year.

Scenario #1

Project is being used to irrigate dry-season crops.

5-Year Projection

VARIABLE COSTS

Year 1

Year 2

Year 3

Year 4

Year 5

Loan payments

$1,973

$1,973

$1,973

$1,973

$1,973

Maintenance fund pmts.

125

125

125

125

125

Extra seed, fertilizer, agro chemicals

100

140

160

200

240

BENEFITS

Year 1

Year 2

Year 3

Year 4

Year 5

Production on dry-season plots (kg/ha)

200.00

250.00

300.00

310.00

320.00

Dry-season price (kg)

9.20

9.30

9.40

9.50

9.60

Return ($)

1840.00

2325.00

2820.00

2945.00

3072.00

Scenario #2

Project is being used to supplement insufficient rainfall.

5-Year Projection

VARIABLE COSTS

Year 1

Year 2

Year 3

Year 4

Year 5

Loan payments

$1,973

$1,973

$1,973

$1,973

$1,973

Maintenance fund pmts.

125

125

125

125

125

Extra fertilizer with irrigation

45

50

55

60

65

BENEFITS

Year 1

Year 2

Year 3

Year 4

Year 5

Yields under irrigation (kg/ha)

200.00

250.00

300.00

310.00

320.00

Price (kg)

3.00

3.10

3.20

3.30

3.40

Irrigated return

600.00

775.00

960.00

1023.00

1088.00

Yields without irrigation (kg/ha)

50.00

55.00

60.00

65.00

70.00

Price (kg)

3.00

3.10

3.20

3.30

3.40

Return w/o irrig.

($)150.00

170.50

192.00

214.50

238.00

CASE STUDY

Users Associations

In the Azua Region of the Dominican Republic, water is scarce. Irrigation projects built in the mid-1900s had resulted in dismal failures. Areas near to the supply canals received excess water whereas areas farther away received no water. Excess irrigation in some places had resulted in waterlogging and salinity problems. Less than half of the land that could be irrigated actually was. Canals and drains were choked with weeds, and maintenance was a shambles. Large farms received water while small farms received none. The lack of discipline in the system did not permit irrigation schedules to be observed, maintenance to be undertaken, or water charges to be collected.

The diagnostic analysis of the system in the early 1980s showed a number of problems, which were then addressed with success. Water users associations were formed so that farmers could cooperatively address water issues. Through the water users associations, and with the assistance of the on-farm water management program, a number of positive changes resulted. For example:

1. Discipline was greatly improved so that water supplies could be more equitably distributed.

2. Small parcels of land were consolidated so that they could be irrigated efficiently.

3. On-farm irrigation works were developed that allowed farmers to irrigate efficiently, and farmers were trained to manage these systems.

4. Waterlogging and salinity problems were addressed through better water management and construction of a few drains.

5. Technical assistance allowed farmers to address other problems, such as pest management and soil fertility.

6. Maintenance was taken over by the water users, and it greatly improved. The water users organization was able to collect water charges much more effectively than had been done previously.

CASE STUDY

Inappropriate Technology

In the mid-1900s, the government of Peru attempted to help small-scale farmers in the mountain regions to improve their agriculture through irrigation. In a project near the mountain village of Chicche, a hastily implemented irrigation program brought water down to the area that was to be irrigated in open canals. Some canals were lined, and some were not. The area to be irrigated had slopes up to, and sometimes in excess of, 20%. No means for getting water to the farms from the main system were implemented.

Tremendous erosion problems developed quickly, and the expensive water system was not used. Finally, in the late 1970s, another program to improve irrigation in the mountains was developed. This included social formation and technical assistance. The costs of putting in delivery works and on-farm improvements on steep hillsides, however, were excessive, and the financial support to small-scale farmers that would allow them to improve their farms was non-existent. Thus, progress in developing the area for irrigation was very slow. This and many other similar projects failed because the farmers were not provided the means of financing improvements at the farm level. Projects often fail because planners and implementers do not account for some of the physical, financial, social, institutional, and other constraints faced by the farmer him or herself.