29 January 2009

How Much Water Do Farmers Use?

In my post yesterday, I questioned the meaning of "use" when farmers do not receive all of the benefits of the water they divert.

Today, I want to question the accounting for water diversions.

Say that a farmer applies 10AF of water to his fields. If 2AF are consumed and offgassed by the plants, 3AF run off the property and 5AF sink into the soil, recharging groundwater, then how much water did the farmer use?

Put differently, if farmers "use" 80 percent of developed water supplies, how much double multiple counting is involved? If other farmers apply the 3AF of tailwater and still others pump the 5AF onto their lands, does that mean that farmers as a group are using 20AF or 10F?

I genuinely do not know the answer to this question. If the total is 20AF, then we need to think again about the meaning of "use". If the total is 10AF, then we need to be careful when discussing water rights. I'll let Ray's comment from yesterday illustrate:
Consumptive Use (CU) for your carrot patch is the amount consumed by growing the carrot. It will take a great deal more water to grow the carrot with flood irrigation methods, but much of the water will help recharge the groundwater. Sprikler irrigation of the crop is "more efficient", but the evaporation losses can be high and there is little if any recharge.

In dry regions, one man's use is the next man's water right. With flood irrigation, the secondary use would be from groundwater.


Converting from flood irrigation to sprinkler &/or drip irrigation (best management practices) is why groundwater aquifers are eventually depleted...too many straws and not nearly enough historic recharge.
Water accounting is a topic dear to my heart (one reason I want California to adopt comprehensive groundwater monitoring), and I came to the topic by accident. As I discuss in Section 6.3.4 of my dissertation, the Metropolitan Water District (importer of Delta and Colorado river water to SoCal) "forgot" to record its groundwater recharge deliveries. Why does this matter? Because it makes it look like local water supplies (which now include the recharged groundwater) are bigger than they really are, which makes it harder for activists to claim that imported water is encouraging sprawl.

Well, here's the news -- imported water (and the way it's priced) does encourage sprawl in SoCal.

Anyway -- back to farmers and agricultural water. Make the accounting clear so that everyone can track individual water diversions but also net out "reused" water when accounting for total sector use.

Bottom Line: If we mess up the accounting, we'll mess up other things.


Ray Walker said...

“Water Accounting” should be viewed from different angles. From a water rights perspective it needs to be accepted that water rights date back, some to the 1850’s and Indian water rights can predate even these. A water right is a right only to use. Generally speaking, the state still “owns” the water. Water rights were established by actual USE of a specified amount of water for specific uses from a specific source at a specific location on a specific date ( appropriation date). Water rights were put into a priority system ( line at the drinking fountain) by proper notice ( adjudications) to all so that objections could be heard and resolved by the Courts and/or State Engineers. Users already had water rights BEFORE they entered into these proceedings, but unless they went through the proper notice process and had their rights confirmed by the proper authorities, their unnoticed (unadjudicated) water rights would always be last in the line. Conditional water rights were given their place in line on the condition that they be perfected with diligence. Once a water right was diverted and put to its claimed beneficial use, it was absolute and further diligence and proceedings were not generally required. Both conditional and absolute water rights could be declared abandoned if it could be shown by others there was an intent to abandon, but again this had to be done by proper notice and by the proper authorities, usually the Courts.

A great deal of protection was afforded to those who had their water rights properly confirmed which often included actual ownership of the right to use the exact described water right. Late comers were not allowed by law to interfere with what the early settlers had achieved and established with difficult undertakings. Generally speaking, a water right is entitled to “the conditions that existed when the appropriation was made”. Changes in upstream drainage patterns, new storage, and/or anything that affected a downstream early (senior) water right owner to receive his established water right was supposed to be curtailed unless the new situation went before the proper authorities, provided proper notice and withstood all challenges that the new situation would not damage the vested senior water rights of others. Many times all that was necessary was for the new (junior) water right to cease diversions when there was not enough water available for the senior water right ie the Priority System of “First in Time, First in Right”.

Realize that a water right is a two edged sword … A senior water right was generally very specifically defined and held to its specific historic actual use. For example, a water right to irrigate 40 acres cannot just arbitrarily changed to accommodate a new subdivision with 40 houses, a pond and golf course. This would constitute a “change of water right” and requires the proper filing with the appropriate authorities so that proper notice can be given to ALL potentially damaged water rights in the drainage basin and now numerous agencies to evaluate the requested change as it may affect water rights for the environment, etc.

Now we are ready to enter “Water Accounting” as it pertains historic use to see who may be entitled to what from a consumptive USE standpoint. This procedure can be extremely complicated ! Let’s keep it somewhat simple and use the same example. First, we need to know something about the water right(s) that were utilized to irrigate the 40 acres, such a chain of title to the ownership of the water rights, how often were they in priority to irrigate, and do the water rights claimed match the description of the water rights awarded as to place of use, point of diversion, quantity and proper source. If any of these awarded aspects do not match, it may be contended that the 40 acres were irrigated with an unadjudicated water right and the change may very well be denied.

Assuming all is well … The crops irrigated on the 40 acres will establish an average consumptive use of __ AF/A (acre feet per acre). Each month is usually different because the crop(s) consumed different amounts of water each month. It usually does not matter how much water was actually applied to the 40 acres. Excess application rates will not be credited, only the actual consumptive use.

Our change case now has a credit of __ AF/A with monthly totals. What needs to be proven now is the depletions for domestic use (houses), lawn irrigation, pond evaporation and landscaping (golf course). Each geographical area will have different numbers for these uses. It is interesting to note that the domestic consumptive use will be a much different number than the one generally mentioned when describing an acre foot of water in the news. The average family (3 ½ ) DIVERTS on average 100 gallons per day per person which equates to 0.4 acre feet per year. However depending upon the type of sewer system, the consumptive use (CU) can be from 5% to 15% . A 10% C.U. factor means that domestic use is 0.04 AF/YR. An acre foot of water is therefore on average enough for the in-house use in 20 single family dwellings, not the 2 that are usually shown.
Hopefully it can now be appreciated that a million acre feet of non-tributary fresh water when introduced into the “line at the drinking fountain” (priority system) was never there before, so the established water rights have no claim to it because it “DID NOT exist at the time they made their appropriations”. The entire 325,900,000,000 gallons each year would all be a consumptive use credit ! By exchange, much of NV, AZ, CO, UT and CA could directly benefit and solve many of their water shortage dilemmas.

Let me know where I need to clarify matters,

Ray Walker (Retired Water Rights Analyst) waterrdw@yahoo.com

Philip said...

David, puzzling this out is an important part of getting water markets functioning more freely. We know the crop coefficients pretty well, so we can say that if a water district has a crop mix that historically consumes X acre feet, and switches to a mix (either through fallowing or planting something else) that consumes .75X , they should have .25X to sell. Measuring the amounts of water freed up by installing canal liners or drip systems is a bit more complicated, because you have to consider how much of the water "lost" in leaky ditches or in flood irrigation is truly "lost". Clearly water that picks up toxic levels of salts, or is left to evaporate, should be deemed to have been consumed (not wisely, but consumed nonetheless) by the irrigator, and steps taken to control that loss should be credited to his account. In fact, a good argument cold be made that failing to take such measures is a violation of the "beneficial use" doctrine. (The beauty of a market based solution is that the farmer can get money to do these things, instead of just being punished for taking measures that would otherwise be uneconomic.) Water that is used for carriage, recovered in tile lines or low lift pumps, or which can be shown to recharge groundwater supplies, is, I suppose, borrowed for a while, and I'm not sure how it should be handled. Right now, that, along with ground water, is considered "developed" water, and may be sold without threat to the seller's existing water right.
As a point of information, drip systems, except in very good rain years, do not completely eliminate the need for surface water application. In most places, about once a year you have to sprinkle or flood the field for leaching purposes.

Spreck Rosekrans said...

This issue is addressed in the State Water Plan, which inlcudes separate tables for "Applied Water Use", "Net Water Use", and "Depletion". See the regional water use tables, for example, in volume 3 of the 2005 update at http://www.waterplan.water.ca.gov/previous/cwpu2005/index.cfm.

There are different views of how these values are calculated and thus what degree of benefit is due to changing from flooding furrows to drip irrigation (for example). The Pacific Institute wrote a report on this subject - called something like "Separating the E from the T" (in evapotranspiration). Some who have switched to drip have also noted increased yields as well as reduced use of pesticides and herbicides.

Philip said...

There are a great many advantages to drip, but it is not necessarily the solution for all crops in all places. Lots of plastic must be purchased and eventually disposed of. Animals burrow and gnaw at the tubing, and must be poisoned or shot. The systems require a lot of electricity. On some soil types, the water savings are surprisingly small. Herbicide savings and increased yields are certainly a benefit, as are labor savings; but the latter means lost farmworker jobs. Still, it's a good technology, but the installation cost of $1,250 per acre (roughly) has to be recovered, and the banker lending the money for the system has to be convinced the farmer will have water to put through it, not just for one year but for many years. That is one of the sad ironies of efforts to hold up renewal of water contracts. Nobody can risk investing forward.