Requiem for the Santa Cruz: An Environmental History of an Arizona River

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Requiem for the Santa Cruz

Malka Pattison: Good afternoon. I'm Malka Pattison, and I'd like to welcome you, Happy New Year, to the office of policy analysis first seminar of the year, our speaker Julio Betancourt has a new book.

It gives away the topic Requiem for the Santa Cruz. Rivers and cities have a way of rising together, but in this case the city made some decisions that meant the demise of the river, and what we have to learn from this, in the west and even in Arizona with one last free remaining river, The San Pedro.

Please welcome Julio Betancourt.

Julio Betancourt: Malka, thank you very much for inviting me to give this talk. Thanks for everybody coming. I hear that there is a fairly good audience that would be participating in the webinar.

I am not going try to spend too much time plugging the book. As you've heard Malka, it's not necessarily a feel good story. The title of the book is, in fact, the Requiem for the Santa Cruz. Basically, stick a four Kennett it's pretty much dead. It cannot be revived nor restored.

What I am trying to do is take you through some of the history of decisions and changes on the Santa Cruz river floodplain in the Tucson basin, and just take you through the timelines of what happened, what decisions were made, and what the impact was.

It turns out that the channel changes went hand-in-hand with water development, kind of an action, reaction along the Santa Cruz. Every time there was a water development, there was a channel change. Then there was a water development to address the channel change and the water change.

I am going to be talking about, primarily, central and southern Arizona. The Santa Cruz is right on the border with Mexico. It's the river that flows through Tucson. It starts on the Arizona border, then flows south deflected by a fault. It comes back north-east of Nogales, Mexico and Nogales, Arizona. A few miles down the stream, it enters the Tucson basin and eventually flows into the Gila River. It seldom gets to the Gila River. Even flood, falls seldom get to the Gila River.

Most of the water and sediments that come from the Santa Cruz end stranded somewhere north of Tucson. It's part of the Gila River basin. There are some other rivers that I'll allude to at the end of my talk including the Gila River, the upper Gila in particular, the San Pedro River, the Verde River which is also a tributary along the in central Arizona. These rivers are actually experiencing quite a bit of change, primarily due to urbanization in the region.

Most of those rivers do have some flow. Some rivers, like the upper San Pedro, have perennial flow throughout. Then others, like the San Pedro River and the Santa Cruz River, are intermittent. Meaning, there's perennial flow along some reach, but for the most part they're relatively dry, and in some cases there are more dry reaches than there are wet reaches. The wet reaches are actually supported by relatively high groundwater that intersects with the valley's surface.

You'll have an unconfined or a confined aquifer in the alluvium of the basin. Particularly during the plasticine the groundwater just accumulated during the last ice age. For the most part, these are groundwater tables that in places are brimming and springing to the surface, so there's an intersection of the groundwater with the surface of the valley that creates these so called oases of perennial flow.

They're usually relatively broad flood plains, and often times with areas that have a lot of riparian vegetation. They'll have marshes, they'll have mesquite forests, cotton wood forests, and they team with wildlife.

These places in southern Arizona, particularly the Santa Cruz River, and the San Pedro River, before the turn of the century were one of the hot spots of bird bile diversity in North America simply because they are oriented north south and they're along flyways of Neotropical tropical birds. They're usually just teaming with birds. That's no longer the case on the Santa Cruz. It's still the case on the San Pedro.

This is what these streams look like. This is an upper reach of the Santa Cruz River. We're not talking about rivers with a lot of water in them, with enough water to actually support a lot of vegetation and wildlife, but not much more. What I'm going to be talking about initially is actually the transformation of these perennial reaches of the Santa Cruz and the San Pedro.

They were subject to erosion before the turn of the century. Primarily, between about 1865 to about 1915. Most of these rivers actually down cut, or in size Aroyaz into the flood plain, where the surface flow run across the surface of the valley and did not occupy a trench, did not occupy a real discernable channel.

Before that time this flood flows would just come through the valleys and they didn't necessarily find a channel, they would spread across the valley in Tuscan, sometimes a mile or two miles wide. This is what happened from 1865 to 1915, that most of this alluvial of valleys in the desert south west ended up gulling or cutting an Aroyaz.

The history of this is fascinating, because even in the geologic record it seems like it's happening all at once, like within a 30, 40, 50 year period, all of this streams in the dry south west are down cutting more or less at the same time.

The way they down cut it is, you would have a nib point in the valley along the longitudinal profile of the valley, and then much like Niagara Falls except in soft settlement, they would develop a head cut which then would migrate very quickly up the valley.

It turns out that long Santa Cruse River, because it was an area that was urbanized over a long period of time, and you had the evolution of a Mud will village wall of village in to a modern metropolis, there is a lot of information. We could track this in some cases, we can track this by hour, and not just days.

I already mentioned this, but this is a quote from a report by the super intendancy of irrigation for the office of Indian affairs, Bergen and Shank. It's accompanied by a letter from the secretary of the interior who was then I believe, Franklin Lein.

This was a report that had to do with hearings, about the use of water in the Indian reservations. Particularly the Indian reservation that's directly south of Tuscan. The sun have a year Indian reservation , Indian reservation.

This report is fascinating to read, it's December ninth 1913, and this guys were really, really good and they anticipated just about everything that happened, and described what it happened before that lead to it. The quote is the two subjects of water development, flood action are so intimately associated that it's necessarily to consider them in conjunction.

In other word you cannot separate water development in geomorphology along these South Western rivers. They are dynamic enough and sensitive enough that anything you do on the flood plane would translate in to some isomorphic process kicking in.

This is an old map that I drafted of the two sound base in the Santa Cruse Rivers. The river ruins from as South to North, so Phoenix is above you and Nogales and the international boarder are to the South.

For the most part through the two sound base and historically part of the turn of the century, there were relatively short plenty of ridges, and that were feed by ground water out cropping at the surface of the valley. Those are in the black here.

The more notorious ones were the one by historic Tuscan, and then the one in the sun have your reservation over here, here's the san xavier mission. They were notorious, simply because they were the focus of a lot of initial development. Both in terms of Spanish colonization and urban growth. Those are the perennial riches.

Here is the san xavier mission, which was actually founded in fairly earlier at the end of the 17th century. This particular building was actually built at the end of the 18th century. There was a lot of irrigation, Tuscan basing was actually the locus of prehistoric agricultural populations in Arizona.

There were probably more people in the Tuscan basing than there were anywhere else in Arizona. In fact as early as 3000 years ago, they were practicing early irrigation agriculture, the earliest irrigation agriculture anywhere in the South West. This is pretty early on.

This is a complicated place, and right from the very beginning you can imagine a lot of prehistoric settlement. People doing agriculture, people growing all sorts of crops, and then having marshes and riparian forest, with lots of with lots of poaching areas.

This is a place where human ecology and natural resources kind of play off from the very beginning. There are a lot of resources there that birds and other wildlife can pilfer, for example agricultural fields. There's a lot of water and poaching areas as well, for wildlife, like birds.

This is what Tucson looks like, right around 1890. You're looking to the West, there's a little, kind of long hill on the right hand side here. This was the locus of the desert laboratory, where I worked for about 30 years, in a something that belonged to the Carnegie Institute, the Carnegie Institution of Washington. It was set up to study ecological or ecophysiological adaptations of plants to heredity.

Tucson basically grew up on the banks of the Santa Cruz River, as most urban cities that got started early do. As a consequence, it was only less than a mile to the offices of the Arizona Daily Star, the Tucson citizens. Everything was recorded in great detail.

This is what it looks like from the hill, and I just mentioned to him Michael, looking West, up what is currently known as Broadway or Congress Street. Into the downtown area, the University of Arizona is already established and it's right here. It's now completely engulfed by the city.

You can't really pick up a channel of the Santa Cruz River. In fact, there was no channel of the Santa Cruz River in this sector, because it'd been completely sub planted by acacias or canals, that fed the irrigation through the flood plain.

This is prime agricultural land that that are growing on falfa, weed and barley. Once a railroad arrived and Chinese immigrants arrived in Tucson along with building of the railroad. They started watering vegetables, which require a lot more irrigation. That played out in a Water Rights Court case in 1884-1885.

That ended up creating big changes in the Santa Cruz Valley. This is a picture taken by Ed Ranstand, who is Linda Ranstand's uncle, in the 1930s, in 1981 and then again in 2007. I just put this in here to give you an idea of how much the flood plain of the Santa Cruz River has actually changed over that time.

This is actually become an urban metropolis where there was agricultural land right in front of the city. That agricultural land was lost to a royal cutting, to incision. As soon as it was lost to incision, it became urbanized.

The incision of the flood plain, right around 1890, was bad for some people and actually good for others, because it provided drainage and allowed for the urbanization of the flood plain. That's in Tucson and then further South, near the San Javier Mission. This is actually looking South, as recently as 1942, when the ground water table was still near the surface.

In fact, there are places where the ground water was actually out-cropping along the bottom of the stream in 1942. What you're looking at is the remnants of this big mesquite, bosket or forest, that had trees as tall as 60 to 80 feet, and two or three feet in diameter. We hardly ever see that now in Southern Arizona.

There was also a system of marshlands, that were fed by a perennial branch of the Santa Cruz, called "Aqua de la mission," or the spring branch that actually brought water to the San Javier Mission.

Just as it heads up, I wanted you to see what actually happened on the spot. This is 1942. The Aroyaz is already cut, and it's in the foreground. This is 1981 and you can see the whitening of that channel. This is 1989 and this is 2002. Very quickly from 1942 to around 2000 this whole landscape has been transformed.

By 1980, the water table, because of ground water pumping, had dropped from the surface of the valley about 140 feet. There's no way that current recharge rates, that you can bring that water table back up again, and one of the casualties of the dropping ground water was actually the depth of these marshes in the mesquite bosket.

In part, this story is actually about the loss of that habitat. Basically, migratory birds stop over a habitat in other habitat for wild life because of not just the incision that happened, but also because of ground water overdraft.

We know a lot about the Santa Cruz River Valley. This is one of those places that we probably know the most about, in terms of rivers in Southern Arizona. In the two different reaches of Tucson and San Javier, we've done a lot of alluvial stratigraphy and figured out the history of, both the height of the ground water table, and also the history of cutting and filling, in the flood plain.

We know it with tremendous detail. We also know it in the San Javier reach, to the same degree. We know that a royal cutting and filling has been part of a landscape throughout the Holocene of the last 10,000 years.

We also know the rate at which these aroyals, or these incisions, that sometimes can be as big as the current channel. We know how long it takes for them to fill back up.

In general, what happens is that they fill back up because the water table is so high to the surface, that you end up with a lot of vegetation that slows down the flood flows. So you get a lot of sedimentation that occurs in these areas with perennial reaches and the channel basically heals itself fairly quickly.

In a matter of a couple of centuries the channel can fill right back up again. It's this resilience that high ground water tables and these perennial reaches bring to these areas, that is actually key.

Without the ground water table being that high and that much vegetation being able to slow down the flood flows, you would end up with serious geomorphic change. In fact, that's what happened along the Santa Cruz River.

We know the details from lots of different information, both in terms of field evidence and historical evidence. Many years ago I sat in front of a microfiche machine, looking at newspapers and looking at general land office notes, the Cadastral surveys that started in 1871 and ran right through the 1930's, so we know where everything was.

We knew exactly what the width of the channel was, we knew how much water there was in it. We know a lot of detail. This is the San Javier reach, and basically you have these surveyors that are surveying section lines in the township and range system, and they're telling you exactly what is happening, beginning in 1871 along the river.

In the San Javier area you have a very interesting habitat. You have the San Javier Mission, you have all of this agricultural land, and then you've got this waterlogged soil just upstream of a natural geologic dam, that set apart the upper part of the Santa Cruz from the Tucson Basin. In that area there were springs that out-cropped the surface on both sides of the valley, and then they flowed through and were diverted all across this cultivated field.

This is a map from 1880. Marshlands, mesquite forest, the analogs. The picture of the analogs are on your left. That's the kind of habitat that was there, with a large Native American population, that was there continuously for at least 3,000 years and more likely more, but doing irrigation agriculture.

This story was about people, and sometimes we forget that most of these are about people, and they're people that actually make decisions. At some point they get blamed for the decisions, or they get rewarded by history for the decisions that they've made. These are all characters that I squint my eyes and I know fairly well, down to their personalities.

Solomon Warner came into the area in the 1870s and basically built a damn, later on built a lake, was involved in the water rights cases. Leopoldo Carrillo was a slumlord; he developed springs, ended up building a bunch of houses and renting them out. Sam Hughes was a Welsh immigrant, he decides to build a canal, an irrigation canal after the water rights case and 1884 and 1885, didn't protect the heading, and that actually became the Santa Cruz River Arroyo.

Robert Leatherwood was the mayor of Tucson, and he's actually the guy who started the Tucson water company. You get what I'm saying here, these are all people that were making decisions all through the history of Tucson.

Imagine today, the people that are making decisions, for example in the neighboring river on the San Pedro, they're characters just like this that are actually making decisions or not making them, that will be ultimately be responsible for what happens on the San Pedro.

I don't want to go into a lot of detail, but like any history there are timelines. These timelines here have to do with a bunch of things that happened along the Santa Cruz River, in terms of water development.

But also some natural happenings, things that you wouldn't normally think of. For example, in 1887, in May of 1887 there was a 7.2 earthquake called the Bavispe earthquake which actually changed the locust of many of the springs.

Water would appear in flood plains where there was no water before, and water would disappear in flood plains where it was there before, so this earthquake had tremendous hydrologic effects. We don't know the extent to which the earthquake actually helped cause Arroyo cutting along the Santa Cruz. The Santa Cruz River channel started eroding during some big floods in July and August of 1890, and I'll show you some pictures of that pretty soon.

Once the Arroyo cuts through, there is all this scrambling around to react to it, and create new irrigation water supply projects. And at the time, in the early 1900s, they were like a dime a dozen. From 1890 to 1920, they're just all of these efforts to increase the water supply to irrigation fields that had been left high and dry on the floodplain by the Arroyo initiation.

That kind of plays out. Then the vertical turbine pump, which was invented in 1902, is introduced into the area in the twenties and the thirties and Tucson starts pumping. First they start pumping from the San Javier Indian Reservation, and I'll speak to that in a second. In 1931, Tucson mayor George Smith, in a congressional field hearing argues that Tucson needs to water from the San Javier Indian Reservation, otherwise it's just not going to be able to grow.

The decision is made and ultimately the ground water upstream of the San Javier mission is depleted. Then you have the 1950s drought, this is the worst drought in the southwest over the last couple of hundred years.

They're in the middle of the drought, they're trying to all sorts of water development to react not just to the incision of the Arroyo, but also to this major drought. Then the water table is depleted about 140 feet in the San Javier District, and at least a couple hundred feet in the area through Tucson.

Then all of a suddenly we get into an era of big floods, including the 1983 flood, a tropical storm in an El Nino year, that ended up doubling the hundred year flood. At that point the only thing that they could do, the only reaction was to basically soil cement the river as it runs through Tucson.

Then after that channel stabilization, people are having to make some decisions about water for a variety of reasons, including the fact that they've depleted it, but also the fact that there are contaminant plumes running through the groundwater that's left.

This ultimately results in the decision to actually bring Central Arizona Water Project to Tucson, and now it's about 75 percent, 25 percent mix CAP in groundwater that people see when they turn on their tap.

What ends up happening is the river incises from what was called then the Hospital Lane, right here, Saint Mary's Road, and it incises from a point of incision or a nick point right here, and it runs right through the valley all the way past Martinez Hill between 1890, and roughly about 1912. Here's another photograph taken from a hill...Yes?

Audience Member: I'm sorry, what was the approximate cause that started of the head cutting?

Julio: It's complicated. I'll talk about it a little bit more in a second but it's very complicated. There's a word called equifinality, which is, it's kind of a strange word but it basically means multiple causes and you can't figure out which.

I worked on this many years ago, I was extremely frustrated that you couldn't pinpoint the cause. There were so many things going on, it was such a complicated landscape, from climate all the way to land use, and that it's hard to sort out. A lot of the explanations have to do with your profession, so climatologist will point to the skies for an explanation, and range ecologists will point to cattle.

It's never been resolved. It hasn't been resolved for the Tucson Basin, much less for the whole Southwest. Mind you that these are things that are happening synchronously over large areas, so there's got to be some common thread there, and the most common signal is probably climate, but there was also a lot of land use. A lot of these lands were being developed simultaneously, so it's really hard to sort out. Does that answer your question?

Audience Member: Yeah.

Julio: You're looking at the floodplain in the 1890s. At the lower left hand corner is Solomon Warner's mill, so they actually had lakes just upstream of this point in a mill race that was actually turning a water wheel, and the water would go back towards Tucson, and there was an ice house there so they were actually producing ice, by having the water flow through this ice house.

Then Tucson is not very big, it's just there on the western outskirts. Hard to pick out where the Santa Cruz River is, right in the middle of it is a mission that was actually started in, again, in the late 1700s.

Here's Solomon Warner's mill, and at some point after the 1884, 1885 water rights case, basically he has to go in and dam a branch of the Santa Cruz River to get another lake that he could run his mill race on. Every time there was some sort of change on the floodplain, or there was litigation, just about anything happened, somebody did something on the floodplain that ended up spelling problems for the Santa Cruz River.

At the bottom right picture, this is one of the few pictures that I actually have in the late 1800's of the unincised channel. The lake is damming up the west side of the Santa Cruz, and the Santa Cruz is the one at the extreme left, and it's just running on the surface of the valley.

There was another lake called Silver Lake, in fact it was a resort and there was horse races up behind it and a house of prostitution in that hotel. This is what it looks like in 1981 and 2001, this place has changed a lot.

After the 1884, 1885 water rights case, Sam Hughes, this Welsh immigrant that came into Tucson 1850s, and his son-in-law, a guy named Robert Treat, they decide that there's not enough water. The stream goes underneath the ground; it goes subterranean right at St. Mary's Road or the hospital lane.

They decide to build an artificial ditch, something called an intercept ditch, that would intercept the groundwater and then the water would collect in that ditch and then they could, a few miles down the stream, bring it on to the floodplain to irrigate.

They didn't have a lot of money, they did this primarily with Mexican labor, and they didn't have enough money to protect the heading. Imagine the longitudinal profile of the stream with a certain drop to the river, and then at the hospital Lane, the drop to the river got really steep, because you had this little artificial nick point, or head cut, or intercept ditch, and this is where the Arroyo started.

This is during a minor flood in October of 1889, and the water is running across the floodplain during even minor flood flows. There is no channel, and then it dumps into this channel. A few months later, in 1890, in July and August, you end up with amazing rainfall, six inches in July and six inches in August. Maybe here that doesn't mean very much, but that's basically in two months doubled the annual rainfall in Tucson.

You have these big floods spaced just a few days apart. They're just eroding that headcut in a very rapid rate. I mean, to the point where the newspapers are following what's happening to this headcut.

I want to go back one picture to remind you what this looks like. This is exactly the same place in July of 1890. Four major floods spaced three to ten days apart. It took Sam Hughes Ditch and basically turned it into this erosional headcut that's migrating through the valley really, really rapidly. This is not a matter of happening in days. This is happening in hours.

Audience Member: That's three kilometers in 10 days?

Julio: Yeah.

Audience Member: Wow.

Malka: Repeat the question. That's something we have to have a few more lines.

Julio: Well, I'll repeat the statement. The headcut itself from Sam Hughes Ditch and in fact, there was a guy that referred to it as Sam Hughes Ditch taken a walk to Silver Lake, because that's exactly what's happening.

This monstrous headcut is eroding and it forks right where you see that little island. That little island is gone in a matter of days. In a few hours, it's already reached to almost Silver Lake. The newspapers are reporting on this thing.

This is an environmental disaster. Imagine all your agricultural land and you now have this gouging channel that's moving up the valley, and you have no way of predicting what exactly it's going to do. It moves really, really fast. I think it was three kilometers upstream within the span of about 72 hours.

This is looking downstream. Again, you see these little erosional remnants downstream that this huge flood is leading as it cuts through. This is a floodplain that was an incise only the year before. It cuts upstream. This is at the bottom of a mountain. It keeps cutting upstream. It goes through Waters Lake. It completely destroys Waters Lake. In fact, this is the run of some of the waters dam, which run across here.

It completely took it out as the headcut migrated upstream on the west branch, and then up the Santa Cruz River and continued on upstream. This is what it looks like now. The reason that you can't pick out that channel on the foreground is that, this is all been completely modified as a consequence of the water project called the Tucson Farms Company in the cross-cut.

Then, you end up with big floods in 1914 and 1915. The Tucson decides that it's going to do something different, so they build in a system of wells, about 17 wells across the valley. It completely failed. All of these water projects that are being put in as it roils cutting through completely failed.

In 1931, now, you've got this big channel. 1931, Mayor George Smith in testimony before the US Senate writes, "The City of Tucson has been scanning for some time to get a larger more available water supply for the city. We are growing community. We have an adequate supply for the present, but we must look forward to the future."

He sees the San Xavier Reservation upstream as the most available place for water in the entire river course. He suggests, "Let's go pump the groundwater from the San Xavier Indian Reservation."

This results in a tremendous drop in the water table. The San Xavier reached of about 140 feet and about 200 to 300 feet in the central valley across from Tucson as Tucson's population keeps growing. They need more, more water.

Starting in the 1930's and the 40's, the pumping results in this tremendous groundwater overdraft, basically taking the groundwater table far from the eroding depth for the most hits.

In diagram form, this is what it looked like. At the top during initial conditions when the water table was at the surface and you had all these marshes and this skip bust is, you have the down-cutting occurring from 1889 to 1914. You disconnected the groundwater from the surface water.

Now, it's completely different system that you can't revive or restore. You actually need groundwater in order to do that to be able to fill that channel back up again by slowing the flood flows with vegetation.

South of Martina's Hill, South of San Xavier Reservation, this is what it looked like in 1913 that the headcut is right here. This is what it looks like now. This whole area was destroyed. Along with it, the great moss forced in the marshlands that were the focus of early ornithologist in the early 20th Century.

There were about a hundred species of resident water and neo tropical birds. Many of these no longer occur in the US, or threatened or endangered. Beautiful birds, by the way that you've never seen in Tucson, except in some places where they're trying to do some restoration using sewer jet filling. This is the soil-cement along the Santa Cruz. Just to remind you, this is where the headcut was in exactly the same place.

Now, we're still pumping groundwater but we brought central areas on a project water that via aqueducts and tunnels in pumping stations from Lake Havasu on Arizona, California border to San Xavier.

This is the largest single resource of renewable water supplies in Arizona. Some of these CAP waters actually being its recovered water. Meaning, it's being recharged in the upper valley next door, and then transported over the Tucson Mountains to Tucson. This is how it's being restored with sewer jet flowing downstream of the Ina Road Sewage Plant. It has some of the highest chemical loads of any river in the United States in this area.

I think this is the point that Malka wanted me to make is that, we have a bunch of rivers that are just on the coast. We'll experience what the Santa Cruz River experienced in the next couple of decades. This is happening really fast

The upper hill of the Verde and, of course, to San Pedro and the Gila, the Arizona Water Solomon Act in 2004, now has a whole list of diversion in other water projects in the upper hill on the New Mexico side, that is going to profoundly change the upper Gila river.

Groundwater pumping in the Chino Valley along the Verde to support population growth is also having a lot of impact. Of course, the development of Siera Mist and the Fort Huachuca, the decision by the Arizona Department Water Resources to basically approve a hundred-year water supply for that development.

Well, in fact, congressmen doubts the availability of water for the Riparian for this BLM San Pedro National Riparian Area.

This is going to get really, really complicated because everybody has their straw in the San Pedro. There are a lot of wells on the San Pedro. It is very likely that the San Pedro River large riches of the San Pedro River that are now plenty are going to be again disconnected from the groundwater.

It's not just going to be about the lost of the Riparian Area. It's also going to be about the fact that we're going to see a new geomorphic regime, because of this disconnection of the groundwater and the surface water.

Drying the upper San Pedro could initiate a new erosional regime with a lot slower recovery times. It's not just that we're going to lose the Riparian Area; it's also that there's going to be an erosional regime that actually threatens all the infrastructure in the upper San Pedro.

I wanted to end with a quote by Stewart Udall, the building's named after Secretary Udall, "Over the long haul of life on this planet is ecologist, and not the bookkeepers of business, who are the ultimate accountants."

I think if you actually did an autopsy on the Santa Cruz River, many of the things that are lost or ecological things that they'll never be regained that are probably the indicators of healthy river systems in the southwest. Thanks.

Malka: Questions from the room?

Julio: Yes?

Audience Member: The interesting thing is that many of the changes that set all these motion could have been, apparently a population versus few tens of thousands?

Julio: In some of those pictures that you see about Tucson, there are no more than two or three thousand people.

Audience Member: I'm not sure that anybody at that time would have been able to foresee what could have been, and what could have occurred.

Julio: That's an interesting comment and we cover it in the book, but there were a number of instances when in fact there were hydrologists or engineers that pretty much saw where we were, and forecasted where we were going to be. Even at that time, people were aware that things were happening on the Santa Cruz that we were causing them, and that there was going to be a time of reckoning.

In fact, there's a guy named G.E.P. Smith, a hydrologist from the University of Arizona that actually predicted pretty much what was going to happen with groundwater overdraft. There were people around. They were compelling voices, but they weren't listened to.

Malka: Questions from the Internet.

Julio: None yet.

Malka: Another from the room. I get to ask a question. What have we learned from the most recent floods in the Santa Cruz in 2014? You almost need to amend that new book.

Julio: I don't think so. The reason floods were a series of tropical storms that happened this past summer, and they were not any bigger than some of the other floods that we've seen particularly in the '80s and the 1990s.

We've been in a period of drought. People have been lulled by the fact that the Santa Cruz has been dominated pretty much by low flood flows. There hasn't been anything major happening since about 1993. There were some nice flood flows, but they weren't what was initially predicted. This is an issue though because the Santa Cruz River nowadays, for the City of Tucson, Eastern Pima County, it's pretty much about flood control. I mean that's all it is.

It could end up being the decisions that were made to soil cement. The banks may end up coming back to buy the the soil cemented channels actually being filled in with natural sedimentation, reducing the cross-section. There's a lot of development along the flood plains.

It could very well be that confining the channel, allowing sedimentation to occur in the channel reducing the cross-section may reduce the capacity of the channel. You could end up seeing something like 1993 or 1983 creating huge floods along the Santa Cruz.

This has gone from people had to deal with floods in the 1880s and the 1890s and it was a big deal, but they also got a lot of ecological services out of the river, including water, to a point now where all we have is basically a storm drain running through the city. Everything that gets done is trying to keep people safe.

This is very much about managing the flood plain, lowering the risk. Not so much about conservation or even water at this point. I'm guessing that the same thing could happen on the San Pedro fairly quickly. These flood plains are capable of carrying very large flood flows particularly during tropical storms that come from south of Baja, California and then get pulled inland where it just rains for days.

We have to decide what it is that we want. Do we want to reduce flood risk in these urbanized areas and conserve infrastructure? Do we want a handful of ecological services at best? Do we want water out of these systems?

I think it's that schizophrenia that is problematic now. We're making decisions mostly as individuals rather than as a society.

Malka: Questions from the Internet.

Audience Member: I'm not sure if you answered this already, but we have an online question. How will this affect the river in the Yuma area?

Julio: The Colorado River, very little. In terms of the changes on the Santa Cruz, very little. Not much water from the Santa Cruz ever reached the Gila River which then flows into the Colorado near Yuma.

Where it does affect matters is once you start talking about the Central Arizona Project. If Southern Arizona is now bringing in water through the Central Arizona Project from the Colorado River, that means there's less ecological or bio-available water in the lower Colorado River. That's how it affects it.

Malka: Questions from the room.

Julio: Lauren.

Lauren: How does the current drought compare with the historic drought? Like in your show, and I can't remember the period of time, but you referenced about longest drought period. I was just kind of curious how this current drought compares with that historic drought.

Julio: I think it's comparable. The current drought had a different geography than the 1950s drought. It's kind of hard to compare them because the bull's-eye, the epicenter of those droughts are different.

The 2002-2003 drought which was extreme, no matter where you talk about it, that particular year is as dry as any year we see in the record of the past several hundred years. This current drought is not over yet.

I know climate variability over the long-term fairly well, year-by-year, almost like vintage wines. My guess is that there's so much decadal to multidecadal variability in precipitation in the Southwest that's associated with the oceans, that it's very likely that we're going to see a return to wet conditions in the next few years. Primarily, due to warming in the Tropical Pacific.

The problem is everybody's running around, yelling about drought and the fact that it's going to continue because of global warming, but there's another issue. That is that there is so much decadal to multidecadal variability that's likely we're going to get into another wet period.

We were in a really wet period from the 1960s to the 1990s, and then got into a dry period after that. It's likely we're going to return to a wet period. People are just not paying enough attention to realize that those are moments of opportunity, of great opportunity.

When you can bank water, you can do all sorts of treatment projects when it's wetter than when it's dryer. You should poised to take advantage of having all of these additional water that in fact you can recharge.

In the Southwest, we're not equipped to take advantage and be nimble of those opportunities, even though we know about decadal to multidecadal variability in the Southwest.

Malka: We have two questions from the Internet.

Audience Member: First question. Is groundwater being recharged from lawn watering?

Julio: Can you repeat the question? I'm sorry.

Audience Member: Is groundwater being recharged from lawn watering?

Julio: No. The answer, very simply, is no. The most recharge that's occurring along the Santa Cruz River now is it's either CAP water, that's actually being recharged into the Avra Valley to give you this sort of recoverable water from CAP, or it's happening with big flood flows along channel beds wherever you don't have soil cement, you actually have a raw channel.

When you have flood flows, you get recharged. The most recharge that occurs is actually along the channel bottoms and banks. Another thing to think about it is that if you soil cement the banks, you're basically eliminating recharge.

Audience Member: Another question. How has the development and pumping by Nogales on the Mexico side impacted the Santa Cruz River?

Julio: I don't have all of the details. We don't really have very good information on that, simply because the stretch near Nogales is still perennial. It actually hasn't lowered the river flow at Nogales. Also, the river at Nogales has been supplemented by sewage effluent that is the subject of another conservation having to do with contamination of groundwater.

Audience Member: We have another question. How are the lessons learned from the Santa Cruz being shared with the decision makers on the San Pedro, Gila and other rivers?

Julio: It's primarily through conversations like the one that we're having. There's been a lot of promotion of the book. The book has passed many, many hands allowing people to read what could happen on the San Pedro, and what could happen on the or the Gila. Whether or not conversations like this have an impact is another story.

There are lots of different studies going on all over the Southwest on these rivers that are barely perennial and are endangered by groundwater overdraft, but there are a lot of unanswered questions.

Scientifically, it's very, very hard to answer some of the questions having to do with "OK, so if I have this many wells in the floodplain pumping and this is the amount they're pumping." How does that affect the groundwater precisely? USGS, for example, has groundwater models you can use to address the question but there are always a lot of uncertainties. People use those uncertainties to keep from acting.

This is always problematic, if you have to prove up on a hundred years of water supply for a development like this development, about 20,000 people, about 7,000 acres in Sierra Vista along the San Pedro, if all you do as a developer is hire a hydrologist who basically looks at the numbers, and argues whether or not you can prove up on a hundred years of water supply.

The mayor of Tucson in 1931 was actually predicting than the San Javier Indian reservation provided a 50-year supply for Tucson, and also for the Tohono O'odham Nation, and it was exactly 50 years when the water table dropped below. It was very, very accurate. The problem is you can get a little bit hung up on the ground water modeling, in the end in making no decision whatever.

When it's fairly clear from history and what happened along the Santa Cruz and along other Southwestern rivers, that they are going to dry up with ground water pumping. It's just a matter of cooking the numbers and figuring out what's actually sustainable. What's actually sustainable, this question of sustainability, is a key question in our society. Frankly, it's not an easy one to answer.

Mike: We got one more question. What is the long-term recharge goal with cap infiltration, and is wastewater recharge polishing ponds a key during wet and dry seasons?

Julio: I'm sorry, Mike. Can you repeat it? I'm hard of hearing.

Mike: Sure. It says, "What is the long-term recharge goal with cap infiltration, and is wastewater recharge polishing ponds a key during wet and dry seasons?"

Julio: Those are two separate questions. The CAP recharge, part of it, is politically driven. It's not like you're going to recharge the Tucson basin with central Arizona project water. There's just not enough water to actually do that over the long term.

Using CAP water allows you to use your annual allotment, put it into long-term storage, but then you're pumping it out at about the same rate. The other question about using sewage effluent, there's some gain for that but again, the recharge rates along the Santa Cruz downstream of the sewage plant is not enough to bring up the water table.

Actually, the best thing to hope for is that we get more of these late summer/ fall tropical storms that actually are extremely efficient at recharging the river. Leaving as much of the channel raw, and not soil cemented is going to be fairly critical.

We can't continue like Los Angeles. We can't continue to channelize the river. We'll just eliminate recharge all together.

Thanks very much.

Transcription by CastingWords