Irrigation event evaluations are a recognized “best” or “efficient” water management practice in either general water conservation programs or nonpoint source pollution programs. The general techniques have been developed over the last century by NRCS (the old SCS), universities, and private industry. Formal Irrigation Evaluation Services (IES) have been active in California since early 1980's. They are generally known as Mobile Irrigation Laboratories.
IES and nonpoint source pollution programs. Although IES can stand alone in a water conservation program, they are a natural, and probably essential, part of any nonpoint source pollution (NPS) program aimed at irrigated agriculture. You may want to refer to the full Advisory on Nonpoint Source Pollution (which includes a summary of common components of NPS control programs).
To review, NPS generally occurs in a 3-step process. These are:
- Availability – a potential contaminant is put in the environment
- Transformation/detachment – it is detached or transformed into a mobile entity
- Transport – it is moved to where it is becomes a contaminant IES and NPS programs
Transport mechanisms include wind, machine, and water. As related to irrigation, surface runoff can carry sediments, along with adsorbed chemicals and fertilizers to surface water bodies. Deep percolation can carry soluble chemicals and fertilizers into ground water.
Note that the general relationship defining Irrigation Efficiency (IE) is:
IE = beneficial use / total applied water
What isn't beneficial use (for each irrigation)? Surface runoff and deep percolation beyond leaching requirements. Thus, if irrigation efficiency is increased then there will be less surface runoff and/or less deep percolation, thus reducing transport.
An IES evaluates the following:
- System hardware – including the condition and the basic design
- System management
- Specific situation – how hardware/management works in that situation
- Usually evaluates Distribution Uniformity (DU)
- Includes evaluations of factors affecting overall Irrigation Efficiency (IE), such as leakage, irrigation scheduling techniques, and runoff
Please refer to the Advisory concerning Irrigation Performance Measurements . To review, there are two measures of performance:
- Distribution Uniformity (DU) – a measure of how evenly water is applied/infiltrated across a field
- Irrigation Efficiency (IE) – a measure of how much of the applied irrigation water is used beneficially (crop water use, leaching for salt control, frost control, and certain cultural practices)
There are two important relationships between DU and IE:
You need good DU before good IE, if the entire crop is to be watered sufficiently
Good DU is no guarantee of good IE
Thus, to improve irrigation efficiency first look to distribution uniformity (usually), then, look to aspects of overall efficiency such as:
- knowing “how much” to irrigate
- the ability to control the total application
- restrictions on flexibility at the farm level and the water supply level.
Note that in certain situations, maybe it will be best to look to timing, control, scheduling first.
An IES can evaluate irrigation efficiency (and they have been used to do so), but the calculation of IE depends on the physical boundaries (field, farm, district, basin) and the time boundary (single event, seasonal) of the measure. Calculation of IE also depends on accurate measurements of water volumes applied and drained from the field, and soil moisture depletions before and after the irrigation. Estimates of irrigation efficiency are open to misinterpretation. Concentrating on the calculation of a number for DU or IE misses what should be the point of the IES program, EDUCATION!
IES results will include an estimate of event distribution uniformity and identification of possible improvements. Note that the DU is “ESTIMATED”. The calculated number is not the absolute, accurate, cast-in-stone, constant DU. The following factors must be kept in mind:
- There is usually a questionable (if any) statistical basis for sampling during the evaluation.
- The evaluation occurs under specific environmental conditions.
- The accuracy of measurements taken during the evaluation may be +/- 5 – 15%.
MOST important is (should be) the educational value of IES. This includes identification of where improvements may be made in the system hardware and management, as well as teaching the basic science of the irrigation system type used. EDUCATION should be the goal, not calculation of a number.
IMPORTANT! - It is NOT recommended that you use the results of an IES program for important macro-level water allocation decisions. At farm level use them for guiding improvements. At policy level use the results for deciding where further programmatic efforts are needed, or to indicate that indeed, improvements are being made.
There may be extensions to standard IES programs. These might include efforts to improve fertilizer program management, energy efficiency programs (such as pump testing or energy audits), aides to on-farm irrigation scheduling, demonstrations of soil/plant moisture monitoring, etc.
It is actually fairly simple to develop an IES as far as the hard logistics are concerned. Standard lists of the required evaluation equipment are available and these can be filled for in the $1,000-5,000 range. Some type of vehicle will be needed to move the equipment to the field. Most often this has been a pick-up truck with a service body. However, in at least one situation, the sponsors decided on using a trailer. The concept was that private consultants or other government agencies would borrow the trailer and equipment.
The actual evaluation procedures have been standardized and in some cases computerized. There are some options here:
- One set of methods has been standardized and computerized by California State Polytechnic University at San Luis Obispo. They have also developed training courses.
- The NRCS has developed an evaluation method.
- Different Australian groups have developed their own methods.
Generally you will need a computer. But most important, you need experienced personnel, trained in the specific techniques.
Annual costs will include vehicle insurance, maintenance, and fuel, office, supplies, and replacement equipment. There will probably be a certain cost allocated for on-going training.
Most often IES has been a service provided by a local/state/ federal agency. In several cases these groups have become quasi-consulting groups for areas without an IES. Contracts at $800-1200/evaluation have been seen. An option is to hire private contractors. They will be responsible for their own equipment, vehicle, and training and will be on call as needed. This is a very flexible alternative and may result in lower evaluation costs. $650/evaluation is a starting point for one group in California. Consultants have been used in a major programmatic situation. They are also being used as an on-going service through a Resource Conservation District.
The question for either is quality control. Are the numbers being generated correctly? Is the education effort effective? An important component of an IES program is oversight. This may come from a technical committee, an outside consultant, or possibly a government agency charged with encouraging the use of IES.
IES are fairly simple to start. The question is keeping one going. Will the initial financing be from a Government grant or is there significant local support? Assuming that it is a grant, what happens when the grant “goes away”? Will the evaluation be offered as a free service or will a farmer contribution be required? Where will the equipment and vehicle be housed? Who supplies the office, insurance, and maintenance? Who will be responsible for overall program design and oversight.
To reiterate one important point, do not key on the numbers, key on the EDUCATION. An irrigation evaluation is a prime opportunity for one-on-one EDUCATION. It is admittedly a rather expensive contact, but with EDUCATION this cost can be leveraged.
Contact the Center for Irrigation Technology (559 278-2066) for more information and guidance if you are contemplating starting an Irrigation Evaluation Service as part of your Water Management Plan.