A lazyweb question for any of the Calfornia water geeks in the audience….
My old employer, the Pasadena Star-News, had an editorial over the weekend that raised the question of groundwater recharge in the following backhanded way:
During a recent dust-up over city of Pasadena water rates, two of the conservation skeptics wrote an essay for our Perspectives page with an entirely new twist on the anti-conservation point of view. When homeowners and businesses with large plots of landscaping don’t water very much, they argue, there’s a lot less water going back into the underground aquifers from which many cities and water companies still get plenty of well water. In other words, conserving could be counter-productive.
Is this right? I know that the answer to the question here in Albuquerque is a complex function of where the lawn is located, so there’s probably no easy answer to this. But in general, in Southern California, how much recharge from municipal watering occurs?
Easy answer: For a southern US climate, unless the soil is made of gravel or sand, expect almost all infiltrated water to be lost as evapotranpspiration, not g/w recharge.
I agree completely with Daniel, but let me elaborate a bit.
If the water being used to irrigate was pumped from local groundwater sources the argument is absolutely absurd because you are suggesting that water was pumped from the ground solely for the purpose of putting it back in the ground – a complete waste of energy. If you are irrigating with an imported water source, you might be able to make the argument with a straight face, but in order to induce significant recharge would require significant overwatering of turf areas, in which case the excess water is more likely to run off into nearby drainages and/or be lost to evapotranspiration. If there is extra water available from an imported source it makes far greater sense to intentionally recharge by using designed recharge facilities ensuring maximum benefit from that recharge. Of course if the goal is to maximize water utility revenues, maybe it does make more sense to just encourage wasteful use.
@Daniel
Do you have references?
Thanks.
Eric, in hydro circles, there’s really no question – as Chris’s comment suggests. But if you want some more meat, see the relevant refs in Collins and Bras 2007 (WRR) – sorry, that’s the fastest way of answering your question. (It even applies to Yucca Mtn 😉
Hey Folks,
I agree with the general tone here, but I’ll point out that people *frequently* claim some sort of public benefit from actions that are actually privately beneficial. It’s called the “baptists and bootleggers” paradigm.
(I’m gonna steal this example for my blog 🙂
Great answer from Chris.
Don’t forget the water quality issue. Should any inflitrating lawn water make it to the aquifer, it could be loaded with pesticides and fertilizer. Homeowners tend to overapply that stuff to their lawns.
Gentlemen:
Perhaps I need provide some additional information to all those making rash comments above about Mr. David Powell’s preliminary professional opinion that it is plausible that conservation activities could deplete the Raymond Basin in Pasadena, California beyond its safe yield level.
First, Mr. Powell’s qualifications: David Powell, P.E. is a Cal-Tech engineering grad, former head of the San Diego office of the California Department of Water Resources, former chief engineer for Bookman-Edmonston Engineering, qualified as an expert by a Special Master on Arizona vs. California Colorado River case, among many other eminent qualifications. He is presently retired and lives in Pasadena and is well-apprised on groundwater issues dealing with the Raymond Basin.
As I understand it, Powell is well versed with the mathematical and hydrological models previously conducted in the Raymond Basin by several water engineering firms. Those studies indicate the City of Pasadena has been overdrafting the basin beyond its safe yield level for quite some time. Moreover, the EIR for a proposed conjunctive use water storage program by the Metropolitan Water District of Southern California indicated that a significant percentage of landscape irrigation beyond evaporation losses was necessary to recharge the Raymond Basin to maintain its safe yield level.
Next a piece of anecdotal information: The neighboring City of La Canada is over a portion of the Raymond Basin. La Canada suffered a precipitous drop in its water table when it shifted from septic systems and leech fields to sewers. This is a possible historical indicator of what could happen to the Raymond Basin.
The Raymond Basin is not suffering due to what is somewhat euphemistically being called “California’s Wettest Drought.” Rather, the Pasadena Dept. of Water and Power Water Fund is suffering a revenue shortfall due to water conservation and a large number of unoccupied new downtown new housing units which are not generating water sales. Thus, water rates have to be increased due to conservation.
Doing something “green” is not necessarily good for the Raymond Basin and Pasadena’s Arroyo Seco watershed and ecology wherein the famed Rose Bowl is located. The Arroyo Seco is a large area of sand, gravel and silt which includes the Devil’s Gate Dam and Basin upstream from the Rose Bowl.
Actual water use in Pasadena over the last 10 years is flat in absolute measures – read here – “Downtown New Development Soaks Up Water from Others is an Urban Myth” – link:
http://pasadenanow.com/main/2009/06/10/opinion-downtown-new-development-soaks-up-water-from-others-is-an-urban-myth
It might actually be about the same cost for Pasadena to buy imported water than to enact new ordinances which criminalize over-watering – read here: “Would It Be Better to Buy Imported Water or Hike Water Rates?” link: http://pasadenasubrosa.typepad.com/pasadena_sub_rosa/2009/06/would-it-be-better-to-buy-imported-water-or-hike-water-rates.html
Now that you know a little more about the situation in Pasadena I hope that you can realize that Mr. Powell’s preliminary professional opinion is well founded. The situation with Pasadena’s Raymond Basin is probably paradigmatic to the other seven large water basins in Southern California and the rest of California. That the environmental professions have entirely missed the unintended consequences of water conservation on local ecologies and aquifers is yet another story.
I invite you to join Mr. Powell and I in educating the public about this paradoxical issue where doing something green (conservation) could likely harm the natural environment.
I’m sorry, maybe it’s just that I’m a dumb journalist, and not a hydrologist, but this makes no sense to me. Maybe Wayne or someone can correct me where my thinking has gone off of the rails.
Let’s say I pump up 100 gallons of water from the Raymond Basin and put it on my lawn. And let’s say 75 gallons of it ends up percolating back down into the aquifer. So the aquifer has been depleted by 25 gallons – the evapotranspiration of my lawn.
Would the aquifer not have been better if I’d left the whole 100 gallons down there? We can tweak the assumptions all we want, but the amount getting back down to the aquifer is always going to be less than the 100 gallons I pumped up.
What am I missing?
jfleck, what you need is a more efficient lawn irrigation system so that you only have to pump 60 gallons to water your lawn. the lawn still uses the 25 gallons to grow, but you’re now only recharging 15 gallons.
BUT, you can tell everyone that you’ve reduced your pumpage!! This is a good thing, yes? The really great news is that you can now add some more lawn, pump 70 gallons, consumptively use 30 gallons (25 for the original lawn and 5 for the new lawn), recharge nothing, and still claim to be a water conservationist because you’ve reduced your pumpage from 100 gallons to 70.
Water use efficiency improvements in a closed basin rarely effect the consumptive water use that drives groundwater depletions, but they sure look good!
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If the choice is between pouring a gallon of water on your lawn, and pouring a gallon of water down the toilet, then sure, you’ll get more recharge out of pouring it on your lawn (AFAIK Pasadena doesn’t do groundwater recharge with treated wastewater, as some cities do; everything from the sewers goes straight to the ocean – though it’s been 5 years since I’ve worked on the Raymond Basin groundwater model, so I could be misremembering). I just can’t imagine a scenario in which this is the actual tradeoff – seems much more likely that people would simply reduce their water use.
On a certain level the way it is characterized by Powell is true – if an imported water source is used to irrigate landscaping, some of that water will recharge the aquifer. And if that irrigation is stopped, that recharge will no longer occur. The La Canada example is instructive – most indoor water use is not consumptive, so when you are using a septic system typically 90-95% of your water use infiltrates to recharge the aquifer. But outdoor use is usually considered to be mostly consumptive, i.e. 70-80% is lost to evapotranspiration with inefficient irrigation, more if you are efficient. This makes recharge via lawn irrigation very inefficient hydrologically. Economically, I suppose it depends on the marginal cost of the extra water applied to induce recharge vs. the cost of recharging some other way (assuming an imported source, if the source is local groundwater it’s a loser from the get-go).
So if the choice is between importing water and having some of it recharge by way of irrigation vs. not importing the water in the first place – Powell’s argument has some merit. But you have to consider what other uses that water could be put to, such as recharging by some more efficient means or a different use entirely. His argument presents a false choice, in my opinion, where the correct answer must be to continue the status quo – but if all possible choices are considered the answer is different.
Chris – Thanks for the helpful elaboration.
So, to pursue my metaphor, if we take the 100 gallons of Colorado River water and water our lawn, we get 20 to 30 gallons of increase in the Raymond Basin. If we stop watering our lawn entirely, and instead use the extra Colorado River water to offset 100 gallons of Raymond Basin pumping, we get a 100 gallon increase in the Raymond Basin.
Am I doing this right?
Yes, John, it’s not rocket surgery.
And I think DZ has the right approach, though I might switch “politics” for “money”.
I seem to have become the subject of some controversy and discussion. Unfortunately, the dicussion seems to have gotten off-track from what I was attempting to point out, and to have attributed to me views which I have not expressed.
Let me first say that: I am not opposed to water conservation; I am not proposing that users deliberately overirrigate their landscaping; I do not consider that overwatering of landscaping creates new water supplies; I do recognize that withdrawal of ground water from return flow uses energy; and I do recognize that some portion of the applied landscape irrigation water represents irrecoverable losses in the form of evaporation losses and runoff to paved surfaces which do not result in ground water recharge..
In order to understand the point I was trying to make, we need to understand the setting. Water users overlying the Raymond Basin obtain their water from two sources: extractions from the ground water basin; and imported water supplies purchased from The Metropolitan Water District of Southern California. Those supplies are insufficient to meet demands at historical levels. So to get through the current period of water supply deficiency, it is necessary to reduce the net draft on the local and imported water sources.
I have no objection to irrigating more efficiently. It is probably a good idea. But let us not fall into the trap of thinking that we are thereby substantially reducing the net draft on available resources. The reduction in water applied to landscaping is in large part offset by a reduction in that portion of the groundwater basin recharge derived from return flow. What we are doing is transferring a portion of the water normally obtained from Importation to increased overdraft on the Raymond ground water basin .
The only real question is what portion of the over-irrigation appears as return flow to groundwater and what portion represents irrecoverable losses. It is my opinion that the vast majority returns to ground water and that irrecoverable losses are minor. There seem to be those who hold the opposite view. I should be most interested in learning the basis for their view.
One final note. I have found it beneficial to have some indication as to the qualifications of those who offer their opinion on technical subjects. I have done a lot of ground water studies. I was in charge of a ground water management program when I was the head of the engineering department of a Water District in the San Francisco Bay Area. Later, while in private practice, I acted as the Engineer for a water agency which was the manager of one of the largest ground water management programs in Southern California.
@Daniel
Thanks for the reference in Water Resources Research.
Is there ‘rocket surgery’? I have heard of rocket science but not surgery. 😉
Also the reference Collins and Bras. Collins does not turn up much in Google. Bras does. 😉
My qualifications in hydrology-few.
My qualifications in chemistry, math, biochemistry, engineering, and modeling-lots.
I am just trying to learn a bit here from the rest of the folks and construct a model in which all the pieces fit together, hence my questions about following each water molecule to see where they go.
Yeah, yeah Eric. I’m trying to catch up with Bras. Just give me a few decades.
Dave, since there are number of themes now going along here, which ones do you disagree with?
I know you don’t think much of my first comment, but in response to the question being asked at the top, it is widely accepted hydrological knowledge. Where evaporative demand is high (SoCal), hydraulic conductivity is low and porosity is high (pretty common; non-gravel/sand; lawns), and soil is permeated by plant roots (lawns; down 10-30 cms) you should expect very little drainage below the root zone unless you’re really crazy with the irrigation (but in that case you’ll have a whole lot more runoff).
That said, I don’t actually see how this conflicts with your specific assertion. It’s possible the PSN journalist thinks there’s a conflict. Do you?
@Daniel
Thanks for very clear explanations.
Daniel:
Let me try to answer what I think are your questions.
Regarding the Pasadena Star-News editorial, I would disagree with the characterization that I am anti-conservation and the suggestion that I say that conserving could be counter-productive. I think my view could be more properly expressed by saying that the illusion of conserving is not the equivalent of actually conserving. I thought this was brought out rather thoroughly in my earlier posting.
I would strongly disagree with the view that return flow from applied irrigation water is not a significant part of the replenishment of groundwater. I would suggest that you do a little research into the views held by technical people in California. Contact the California Department of Water Resources, or the U. S. Bureau of Reclamation. See what academics at UC Davis and UC Berkeley have to say on the subject. In that regard, I might specifically direct you to the paper “UC cooperative extension groundwater hydrology program”–it is available on line. Also, you might talk to those who actually operate major groundwater management programs, such as the Water Replenishment District of Southern California or the Orange County Water District. After you have done that, let us know if you are still willing to contend that your view is widely accepted in the hydrological community.
Let’s now direct our attention to the specifics of the area being eiscussed– the Raymond Basin. You indicate that my contention would not be valid unless the area is underlain by gravel or sand. Just what, pray tell, do you think makes up the upstream portion of alluvial fans? Also, I would expect that before expounding on the flaws in the opinions of others, one would try to ascertain what hydrologic studies have already been made. I would refer you to the EIR for the Pasadena Groundwater Storage Program. The hydrology appendix for that EIR was based on groundwater modeling done by Geoscience Support Services. I assume this is the Raymond Basin groundwater model mentioned in an earlier posting by Maria. The EIR can be found at:
http://www.ci.pasadena.ca.us/planning/environmental/PasadenaGroundWater/PasadenaGroundWaterStorage_Home.asp
If you study the hydrology appendix and the response to my comments on the EIR. you will find that the water balance includes a contribution to ground water of some 7,000 acre-feet per year of return flow from applied water. That is nearly 1/4 of the adjudicated safe yield of the Raymond Basin.
I look forward to hearing your response.
Reply to J.Fleck on “wouldn’t it be better to leave the whole 100 gallons in the basin in the first place?”
There are two portions of a water basin: the portion that is “unsafe” to pump without depleting it and the “safe yield” which is the portion that will naturally replenish itself each year. So the answer to your question is NO, it is not better to leave 100% of adjudicated safe yield in the basin. Mr. Powell could educate you, as he has me, that allowing the basin to replenish without pumping to its safe yield could lead to a condition called “mounding” which could put pressure on the outer edges of the basin and the basin would start losing water.
According to Mr. Powell’s post below, if about 25% of the safe yield or 7000 acre fee of water is recirculated back into the Raymond basin each year that would reflect about 20% of the City of Pasadena’s total water use per year. Pasadena is being asked to cut back at least 10% in water use this year with likely another 10% cutback at least looming the future.
The cost or producing groundwater in Pasadena is about $125/AF. The new Tier 4 & 5 water penalty rates by the Metro Water District, the regional water importer, are about $800 to $1000/AF. Do the math. Pasadena could save $675 to $875/AF by relying on groundwater, or $2.3 to $3 million per year. Pasadena’s reliance on groundwater in 1999 was 60%; today dropping to 30%.
You might want to read my article “The Real Green Paradox: Staying in City May Reduce C02 But Importing City Water is Unsustainable” here http://greeneconomics.blogspot.com/2009/02/interesting-e-mail-on-water-and.html
David –
How many acre feet of water need to be applied to Pasadena landscaping in order to create that 7,000 acre feet of return flow? My point is that it is, necessarily, greater than 7,000 acre feet.
John:
First, one small correction. The Raymond Basin underlies not only the City of Pasadena–it also underlies portions of the Cities of La Canada-Flintridge, Arcadia and Sierra Madre together with the community of Altadena and other unincorporated territory. The 7,00 acre foot figure is for the entire basin.
I can’t answer your question directly. The 7,000 acre foot figure is that used by Geoscience, and their hydrology as contained in the EIR does not permit a determination of the corresponding irrigation water used on landscape area. I have not tried to independently estimate it, but my educated guess would be somewhere around 12,000 to 15,000 acre feet.
Pasadena has recently relied on the Raymond Basin for about 40% of its total annual water demand of about 37,500 acre feet of water. So that amounts to about 15,000 acre feet of groundwater. This is almost the same figure that David Powell estimates in the above post is needed to generate 7,000 acre feet of recharge.
Perhaps a better question than “how much groundwater recharge occurs from watering laws” might be “should a municipal water department such as Pasadena’s intentionally deplete its groundwater basin to the point of destruction as a rational choice?”
William Blomquist in his 1992 book Dividing the Waters: Governing Groundwater in Southern California asked precisely this question. An excerpt from his book specifically on whether the Raymond Basin should be intentionally overdrafted can be found at the following link:
http://pasadenasubrosa.typepad.com/pasadena_sub_rosa/2009/05/would-city-water-rate-increase-effectively-destroy-the-raymond-basin.html
Wayne and David –
I went back and read the original op-ed, in light of the comments here, and now I have absolutely no clue what your point is, especially given Wayne’s most recent point that the long term depletion of the aquifer is the central issue.
You wrote:
“We believe that if residents seriously cut back on irrigation in their yards, there will be a profound effect on the Raymond Basin’s replenishment. Simply put, not enough water will seep down from our landscaping, and well-intentioned efforts to “conserve” will backfire.”
The water being used for irrigation isn’t free. It comes from one of two places.
Are you that imported MWD water, used for irrigation, is what’s recharging the aquifer? If “yes”, wouldn’t conserving yard water and using the city’s Aquifer Storage and Recharge wells instead be more efficient, that is, get more water underground and therefore leave the aquifer in better shape? (Though it is worth pointing out, Wayne, that you seem to be arguing that MWD’s rates do not make this an attractive option.)
You certainly can’t be arguing that pumping up groundwater and putting it back in the ground is the best approach to maintaining the aquifer in the long run.
Sorry, now I’m just completely lost. Perhaps if you could sketch out, with a simple set of water budget numbers (aquifer pumping plus imported MWD as source, consumptive use plus recharge on the other side of the balance sheet) for the approach the city took and the one you’d prefer, I’d have a clearer idea of what you’re getting at.
Wayne & David,
As to your original comment about the unintended consequences of reduced residential irrigation – let me see if I have the overall scenario correct. Because of reduced deliveries from MWD, Pasadena is requesting conservation from water customers to match those reductions so that it can adequately serve all customers. Your point is that reducing demand by conserving on landscape irrigation will have unintended negative consequences because it will reduce the amount of water that returns to the aquifer after application to landscaping. This in turn will reduce the amount of water the local utilities can pump from the aquifer in the future, leading to further reductions in water use.
Is it your point that conservation should occur elsewhere – i.e. in some 100% consumptive use sector – or that conservation might be a bad idea period?
Clearly over-watering of lawns is an easy target for conservation because it’s viewed as wasteful and therefore a low-value use of water. However, as you point out there may be unrecognized benefits to that over-watering. But the extent of those benefits depends on many factors that aren’t considered in your analysis.
Most importantly, there is probably no way of knowing where the water used for irrigating is originally coming from. I stick to my original point that if the water comes from the aquifer in the first place, this is not a sensible way of recharging the aquifer. If the water is imported it might make sense, but you need to know a bit more about how the water is applied, where it is applied, and a more accurate estimate of the amount of benefit to the aquifer before recommending it as a way to induce recharge. To say nothing of the fact that the only reason for lawns to be over-watered in the first place is because water is simply too cheap. This means that conservation efforts should be targeting much more than simply excess irrigation water.
I glanced through the EIR, which unfortunately doesn’t indicate how they came up with their return flow numbers, or what exactly they mean by return flow. My experience has been that often those numbers are estimated in such a way that they fit into a necessary parameter of the model, but aren’t necessarily based on truly empirical estimates. But I’ll stick with your assumption that it refers to return flow from irrigation. If the numbers you cite for total water demand are correct that 7,000 ac-ft value seems high. Do you know the percentage of residential water use that goes outdoor vs. indoor? It typically runs about 40-60% outdoor, which would mean approx. 18k used for irrigation, so about 40% return flow. That would be an average number, so some areas are above and some below that figure. Typically, when irrigation efficiencies are that low the excess is not simply infiltrating and possibly recharging the aquifer – some is also running off into streets, entering drainages or ponding and evaporating – so that could be a faulty assumption. But as I said, I don’t know for certain how the 7,000 ac-ft value was derived, so if there is some empirical basis for it I’d have to reevaluate this point.
BTW, if you’re concerned about my qualifications to comment on this, I have 16 years of experience as a consulting hydrogeologist, with extensive experience in both AZ and southern CA, a registered geologist, and a licensed attorney in AZ. I have some experience to inform my opinions.
Wayne,
I have been reading through some of the posts on the Sub Rosa blog (your blog?) on this issue and just wanted to quickly clarify a point related to recharge of the Raymond Aquifer. And you are correct to point out the enormous importance of the aquifer to the communities which obtain a portion of their water supply from it.
Using the numbers that have been mentioned here – if you are pumping 15,000 ac-ft from the aquifer for landscape irrigation, of which 7,000 returns to the aquifer as recharge, you do not have a net gain of 7,000 ac-ft to the aquifer. You have a net loss of 8,000 ac-ft from the aquifer – the amount of evapotranspiration or runoff resulting from that irrigation. So if Pasadena passed an ordinance banning outdoor watering that 7,000 ac-ft of recharge would no longer occur, as you note, but that is actually a good thing because that water is still in the aquifer along with the 8,000 ac-ft that would have been lost as a result of the irrigation. This is why the source of the water used for irrigation is so important.
I hope this helps and keep up your advocacy for sound management of your local aquifers.
Chris:
I am a layperson when it comes to hydrology. But do I need to tell a hydrologist what a Safe Yield is? The Raymond Basin has an adjudicated Safe Yield of about 30,000 AF/Year of which Pasadena has rights to extract about 15,000/AF/Year. IT IS NOT BETTER TO LEAVE A NET 8,000/AF/YEAR IN THE BASIN BECAUSE AS I UNDERSTAND IT AS A LAYPERSON, THAT COULD LEAD TO “MOUNDING” AND DOWNSTREAM LEAKAGE AT THE RIM OF THE BASIN ALONG THE RAYMOND FAULT. The Safe Yield is the sustainable yield. So it does not harm the basin to extract up to the Safe Yield each year. The total capacity of the Raymond Basin if I remember correctly is something like 700,000 AF of which only 30,000/AF is extractable each year.
The problem with the City of Pasadena’s water conservation ordinances is that they refused to complete an EIR which would likely have concluded that unless the loss to the Raymond Basin from conservation is mitigated it will eventually become a depleted basin. One mitigation measure that should have been required is rain basins in tandem with all the drought gardens being installed all across Pasadena. Read here:PASADENA’S NOT-SO-GREEN CITY (IN)ACTION PLAN ON GROUNDWATER REPLENISHMENT
http://pasadenasubrosa.typepad.com/pasadena_sub_rosa
/2009/06/pasadenas-notsogreen-city-inaction-plan-on-groundwater-replenishment.html
And here
SHOULD PASADENA REQUIRE RAIN GARDENS AS MITIGATION FOR DROUGHT LANDSCAPING?
http://pasadenasubrosa.typepad.com/pasadena_sub_rosa/2009/06/should-pasadena-require-rain-gardens-as-mitigation-for-drought-landscaping.html
Ah, the “safe yield” myth. That’s so last millennium. (And anticipating pesky requests for references from Eric ;-), see here, and references there-in [especially the prescient Theis]. Though Google would also be a good guide.)
Good call Daniel. I for one am beginning to see the futility of dragging this discussion out further.
Posted by John Fleck on Behalf of David Powell, though I seem to have no better luck than David did with the table.
John and Chris:
I think this will deal with questions raised by both of you.
As Chris points out, The Raymond basin EIR Hydrology Appendix is pretty short on details. However, if one looks at the first page that comes up, it makes reference to “additional comments to the final EIR”.
On page 3 of the aforesaid document appears the following statement:
However, GEOSCIENCE has indicated that the updated modeling for the project defined in the EIR (included in Appendix A) utilized a 7% recharge percentage for leaky pipes, and 10% recharge from applied water.
I apparently not have made it clear enough that I have merely tried to point out conceptually the effect of irrigating at a higher efficiency. I have not tried to make the detailed studies which would be required to quantify the effects in the case of the Raymond Basin: rather, I have relied on the results of studies made by others. I could make a rough cut at refining the figures with a few man-days of work; I could do a somewhat more complete job by spending a few man-weeks on it; or I could start from scratch by spending man-months or man-years. Unfortunately, none of those are things that I am willing to undertake.
So, lets look at a somewhat simplified water balance for a hypothetical basin. I make no claim that these specific numbers are in any way applicable to the Raymond Basin. The table presented subsequently in this posting will conceptually deal with the phenomenon I am trying to illustrate. In that hypothetical analysis, let’s make the following assumptions:
• The area is urban and fully built out and is served by a distribution system using 100,000 acre feet per year.
• 40% of that 100,000 acre feet per year is obtained by extraction of groundwater, and 60% by purchase of imported water.
• 40% of the use is for landscape irrigation and the other 60% is inside uses plus some minor outside uses (car washing, decorative ponds, swimming pools, etc.).
• The landscape irrigation takes place at an efficiency of 50%.
• The water delivered through the distribution system is a co-mingled mixture of water from the two sources.
A hypothetical summary of water supply and disposal under these conditions is shown in the table column headed “Stable Condition”.
Now let us assume that the supplier of ground water tells the water distribution agency “Sorry, we no longer have enough water to meet all demands, and we are going to have to cut our deliveries to you by 15,000 acre feet per year.” So the distribution agency implements a water conservation program, focusing primarily on landscape irrigation based on the view that there is where the savings could most readily be achieved. And they are successful. Irrigation efficiency is boosted to 68% and deliveries of water for irrigation use are cut by 30%.
A hypothetical summary of water supply and disposal under these new conditions is shown in the table column headed “Reduced Imported Supply”.
Reduced
Stable
Imported
Item
Condition
Supply
Water Supply
Groundwater
40,000
40,000
Imported Water
60,000
45,000
Total
100,000
85,000
Water Use
Non-Irrigation
Consumptive use + Irrecoverable Loss
1,000
500
Sewage Outflow
59,000
56,500
Subtotal
60,000
57,000
Landscape Irrigation
Consumptive use + Irrecoverable Loss
20,000
19,000
Return to Groundwater
20,000
9,000
Subtotal
40,000
28,000
Total Use
100,000
85,000
So there is great rejoicing, high fives and belly bumps and many gleeful shouts of “We did it” and “We have struck a blow against waste”. But then the joyful shouts die down, because the ground water levels, instead of recovering during wet years, keep going down. The joyful shouts of success are replaced by mournful cries of “What happened?”
The answer is that what happened is that most of the cutback in water deliveries showed up as a reduction in groundwater recharge from return flow of irrigation water, creating overdraft on the groundwater basin.
Is this conceptually what is happening in the Raymond Basin? Yes. Are the specific numbers representative of the Raymond Basin? No. To make a table like the above for the Raymond Basin would require a detailed study. Perhaps it is available from the many studies that have been made of the Raymond Basin. I used the hydrology appendix to the Raymond Basin conjunctive use program EIR as an example to demonstrate one consulting firm’s view of the situation. Unfortunately, the breakdown in the hydrology appendix is not sufficient to make a table like the above. Also, I find there are some areas that I don’t believe have been adequately addressed by Geoscience.
So let me go back to those opinions I originally expressed and which still stand by:
• The major portion of landscape irrigation water applied to lands overlying an unconfined groundwater basin consisting of coarse alluvium will appear as return flow making up a significant portion of the safe yield (measured in terms of gross extractions) of the basin.
• The reduction in water deliveries achieved by irrigating more efficiently is largely offset by reduced return flow to the groundwater basin with an accompanying decrease in basin safe yield.
• The resultant increase in overdraft on the basin is not sustainable, and on a long term basis will deplete the stored groundwater.
• The views I have expressed are representative of the views held by most technically trained water resource professionals I knew when I was actively engaged in the practice of water resource engineering prior to my retirement.
I have taken my best shots at trying to provide an understandable explanation of my views. From some of the comments, I have failed to express it in sufficiently clear terms. For that, I apologize.
There is one basic question which really divides us–what are the relative proportions of the landscape irrigation water applied in excess of consumptive use which return to ground water and which appears as irrecoverable loss (runoff to streets, evaporation to paved surfaces, etc. I consider that the majority of it is return flow. Others contend that the majority of it is irrecoverable loss. Unfortunately, I have seen no very convincing arguments in support of the latter view.
There is a legitimate question of what alternatives there are to overdrafting the Raymond Basin to meet the shortfall in imported water supplies. One possibility is the reduction of consumptive use by replacement of urban landscaping traditional to the area with drought tolerant landscaping. That has some disadvantages. It can be rather costly to the water user, and it produces an urban environment less pleasing to many.
Another solution is the development of additional water supplies. Again, there are major costs involved. But it needs to be addressed. To explain the program which needs to be undertaken in this regard is sort of going into another whole different area, and would require this tome be even further lengthened.
I rest my case.
Unfortunately, the table in my last posting got completely garbled
It should have looked something like the following:
Stable Reduced
Item Condition Import
Water Supply
Groundwater 40,000 40,000
Imported Water 60,000 45,000
Total 100,000 85,000
Water Use
Non-irrigation
Cons. Use+ Irrecov. Loss 1,000 500
Sewage Outflow 59,000 56,500
Subtotal 60,000 57,000
Landscape Irrigation
Cons. Use+ Irrecov. Loss 20,000 19,000
Return to groundwater 20,000 9,000
Subtotal 40,000 28,000
Total Use 100,000 85,000
Maybe this time it will work!!!!
———————————————–Stable ————–Reduced
Item—————————————–Condition———–Import
Water Supply
—Groundwater——————————40,000———— 40,000
—Imported Water—————————60,000———— 45,000
——Total————————————100,000————-85,000
Water Use
—Non-irrigation
——Cons. Use+ Irrecov. Loss————-1,000—————-500
——Sewage Outflow———————–59,000————56,500
———Subtotal——————————-60,000————57,000
Landscape Irrigation
—Cons. Use+ Irrecov. Loss————–20,000————19,000
—Return to groundwater—————– 20,000————–9,000
——Subtotal———————————-40,000————28,000
—Total Use———————————100,000————-85,000