Flooding in the Valley

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Randy Cerveny from the School of Geographical Sciences at Arizona State University will talk about all of the flooding in the city yesterday. He will explain why it happened and how it can be prevented.

Ted Simons: Good evening, and welcome to "Arizona Horizon," I'm Ted Simons. Yesterday's monsoon storms made for massive flooding around the Valley with some areas mainly to the north getting as much as five inches of rain. It got so bad parts of I-17 near Dixiletta Road turned into a river of muddy water from a nearby wash. Joining us to talk about all this is Randy Cerveny from the ASU School of Geographical Sciences. This is amazing stuff.

Randy Cerveny: Good to see you.

Ted Simons: Where was the worst spot as far as flooding was concerned?

Randy Cerveny: Most of the storm yesterday was centered over the Northern part but there were parts in the southeast that hardly got a drop associated with this big mass of water that came up from Mexico.

Ted Simons: I-17 sounds like New River became a big river, Levine seemed to be hit again. Are those always the places that seem to be hit the worst when it comes to flooding?

Randy Cerveny: It depends on the movement of the storms. In this particular case the storms were coming up from the South, and what happens is the topography plays a really, really big role. When the moisture hits a slope that slopes up, it can drop out that moisture. In this particular case the moisture hit that upslope area and then sat there and kept running into it and dumping more and more water. It's very much topography based. It's where the Valley turns into an upland slope that you're going to get the most flooding.

Ted Simons: The previously same thing at South mountain, where it ran up the mountain and just sat there.

Randy Cerveny: During the monsoon we don't have very strong winds aloft that move these things really fast. In the Midwest, storms move really fast because the jet stream is pushing them along. Here during our monsoons there's nothing to basically push the thunderstorm once it gets started. When it finds a mountain, it keeps pushing the moisture up and up the mountain and sits there.

Ted Simons: We had an incident from Skunk Creek, water gets into the CAP canal -- how does that happen?

Randy Cerveny: The amount of water funneled in from Sun Creek through this particular storm was incredible. We were getting four and a half to five inches over a four-hour period. That is a return time that we would expect to see only once every to, years. So this is a pretty rare event that we were looking at.

Ted Simons: We heard once in a thousand year event when it was parked over South Mountain last week. What's going on over there?

Randy Cerveny: It's kind of like two winners of the lottery from the Valley. It can happen, it's rare, but in this particular case we had two thousand-year events. They were located in different areas, both associated with localized storms.

Ted Simons: Did areas not used to flooding get hit more this time around? Or again, are these the usual suspects?

Randy Cerveny: These are pretty much the usual suspects. We've had flooding around New River to Black Canyon City in the past. Where exactly it happens is a function of the localized thunderstorm itself. Where this terrain turns into more of an upslope position, it's going to be the areas where we have the greatest chance for the water to be funneled down into the rivers.

Ted Simons: With that in mind, are the flood control efforts out there, are they simply not used to this kind of rain? Are they not -- are our efforts not prepared for this kind of thing?

Randy Cerveny: I think we actually handled it pretty well. There was no loss of life, there were some pretty incredible rescues, but not any loss of life. The key is how many people are affected as to what we want to do. Back many decades ago there was a similar type of situation over Indian Bend in Scottsdale.

Randy Cerveny: What they decided to do was simply change the withhold MMM wash area into a greenbelt so it would not influence people. It would be trapped in golf courses that exist in that area. We could do something like that but it would cost money, and the amount of people affected would be less than Scottsdale.

Ted Simons: The Indian Bend wash was hit again, although people had to be rescued from El Dorado Park on McDowell and Miller because again, it got too high.

Randy Cerveny: And part of it, too, is just a lack of knowledge. A lot of people that have come to the valley and just -- in just say the last five to years don't realize how quickly the situation can change. That where places like maybe Tempe or Scottsdale only get a little bit of water, when that water gets funneled down into a stream system, it can rapidly turn a dry river bed into a raging torrent.

Ted Simons: With that in mind, can't we get -- something like yesterday, will that change the topography? Will that change the geography? Will it change the way the washes run in areas that were flooded? Are they carving out a new normal?

Randy Cerveny: They are definitely geologic scale events, so there have been changes in the actual landscape of the area, say around South mountain or around New River. Now, what happens, though, is the city will go in and actually re-channel things so that it doesn't start to form a new normal. They will try to get it back to a more normalized flow.

Ted Simons: The idea of flood control efforts after something like this, how far do you go? How far do you change things? Hay, it's once ever thousand years, good luck to our next generation?

Randy Cerveny: I think it's a cost-benefit situation. You have to look at how many are impacted and what the cost of doing those changes would actually be. Also I think we need to make sure people are aware of the logistics. You don't put a home down in a dry lake bed or dry river bed here in Arizona. It's just a silly thing to do.

Ted Simons: But they are doing it, aren't they?

Randy Cerveny: It's really nice to have those trees you find along these normally dry riverbeds, to build a house around. But those dry riverbeds can be --

Ted Simons: It's not so nice to watch your home float away while you're on the bank waving good-bye. Are there ordinances or should there be more in the way of making sure folks aren't building in floodplains?

Randy Cerveny: And that's a problem. There are a lot of places where developments have gone in and not really taken into account the local topography and the local drainage patterns. If you go up around Deer Valley there are dams built where you have housing on both sides of the dam. Obviously that doesn't work very well. I think what we have to do is make sure when these housing tracts are going in, that the planners take into account not only how many people they can jam into a given area, but also the underlying topography, the underlying landscape that exists, and try to work with it as much as possible.

Ted Simons: New River, Black Canyon City, those areas especially in the North. We saw I- and Dixiletta Road and the water coming out, when they -- will you get slow-moving wet monsoons, are they just always -- are we going see this kind of thing, maybe not alongside the freeway, I still don't know how it got alongside of the freeway, somebody has to do something about that. Basically that's the way it is?

Randy Cerveny: There are some places in the Valley that do tend to get more concentrated storms for some reason or another. Union hills commonly floods when we get a monsoon thunderstorm. The question is how much gets into these areas and how fast are the pumps that can pump it out. When the freeways for example, when they flood, they simply can't handle the amount of water going into the system.

Ted Simons: Last question I've asked this numerous times to you and others. I've been here a long time. Seems like in the past the west side never got the storms. It was always dry and the storms came around somewhere in the east side. Doesn't it seem to you in the last years or so the west side is getting hammered by storms more so than in the past?

Randy Cerveny: I think there are some cycles to this. Yes, it seemed like the east side was the place getting the buildup, you would watch it coming off the superstition mountains and coming into Mesa or Tempe. I think what happens, because the monsoon is such an individual beast, each year's is different from the last. Sometimes it'll come in from the west and the east but we haven't figured out why so we don't know.

Ted Simons: We really don't know. It's been a pretty good summer though, hasn't it?

Randy Cerveny: The actual temperatures have been great. We all know, parts of the Valley got their share of monsoon water.

Ted Simons: Good to see you again.

Randy Cerveny: My pleasure.

Randy Cerveny:Professor, School of Geographical Sciences at Arizona State University;

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