Saturday, January 30, 2010

Vertical Migration of SWMM 5 Calibration Files

Note: It is often important to compare the results for your link flows, node heads and system variables between SWMM 5 versions to help you calibrate the new version based on the old version results. If you run a SWMM 5 model in an older version, save the .rpt and .out file and then open up the SWMM 5 input file in a newer version of SWMM 5 you should see a active graph symbol. The active symbol means that you can plot the results of the old model in the newer SWMM 5 GUI.

For example, you can plot one of the system variables and then save ALL of the system variables to either a clipboard or a system calibration file. You can then use the Calibration dialog of SWMM 5 to compare the older results with the simulation results of a new version of SWMM 5.

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Sunday, January 24, 2010

Water Analogies for Divergence, Curl and Gradient

Comment: A really nice water analogy for the field properties Divergence, Curl and Gradient from the Blog Starts With a Bang's pretty mathematically intensive, but what's missing from most textbooks and E&M courses are physical explanations of what the mathematics means. For instance, I've started teaching about fields, and pretty much every textbook out there goes on and on about the properties of fields. They say you can do three things to fields, take the gradient, divergence, or curl of them.
(Are you asleep yet? I'm sorry!)
What do these things mean? An easy way to picture it is in terms of water. If you placed a drop of water anywhere on, say,Earth, the magnitude and direction of how it rolls down is the gradient of the Earth's elevation.
If you let that drop of water flow, as it goes downhill, it can either spread out or converge to a narrower stream. When we quantify that, that's what the divergence of the field is.
And finally, when that water is flowing, sometimes it gets an internal rotational motion, like an eddy. A measure of that rotational motion is called thecurl of the field.
Well, one math geek statement is as follows: the curl of the gradient of a scalar field is always zero. What does this mean, in terms of our water? It means that I can take any topography I can find, invent, or even dream up.
I can drop a tiny droplet of water on it anywhere I like, and while the water may roll downhill (depending on the gradient), and while the water may spread out or narrow (depending on the divergence of the gradient), it will not start to rotate. For rotation to happen, you need something more than just a drop starting out on a hill, no matter how your hill is shaped! That's what it means when someone says, "The curl of the gradient is zero."

This passage uses the metaphor of water flowing over terrain to help explain some concepts from vector calculus and electromagnetic fields. Let's dig a little deeper into each of these mathematical operations and their physical implications.


The gradient is a vector operation that acts on a scalar field. It tells you the direction and rate at which the field changes most rapidly. In the water analogy, the gradient of the Earth's elevation is the direction and magnitude of the steepest downhill slope at a given point. It's the direction the water would naturally roll down.


Divergence measures the degree to which a vector field sources or sinks at a given point. In the context of water flow, the divergence of the field describes whether the water is spreading out or converging to a narrower stream as it moves downhill. A positive divergence indicates that the water is spreading out, like a water source, while a negative divergence implies it is converging, like a sink or drain.


The curl of a field measures its rotation or twisting. In the water flow example, the curl would represent the rotational motion of the water as it flows, such as the swirling of an eddy in a river.

The statement "the curl of the gradient of a scalar field is always zero" can be understood with our water analogy. When a droplet of water is placed on a landscape (which represents our scalar field), it can roll downhill (gradient) and it can spread out or converge (divergence), but it will not spontaneously start to rotate (curl). Any rotation (curl) in the water's motion requires an additional influence beyond just the shape of the landscape. It could be introduced by an external force like wind, or by irregularities in the terrain, but it's not a natural outcome of a droplet simply being placed on a slope. This is the physical interpretation of the mathematical statement "The curl of the gradient is zero."

This explanation aids in visualizing these abstract mathematical concepts, making them more tangible and understandable, especially for those who are new to these ideas or find them difficult to grasp. It also provides a more intuitive understanding of the mathematical operations involved in vector calculus and their significance in the study of fields, of both in physics and engineering.

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Saturday, January 23, 2010

Water Hits and Sticks: Findings Challenge a Century of Assumptions About Soil Hydrology

From Science Daily

ScienceDaily (Jan. 23, 2010) — Researchers have discovered that some of the most fundamental assumptions about how water moves through soil in a seasonally dry climate such as the Pacific Northwest are incorrect -- and that a century of research based on those assumptions will have to be reconsidered.

A new study by scientists from Oregon State University and the Environmental Protection Agency showed -- much to the surprise of the researchers -- that soil clings tenaciously to the first precipitation after a dry summer, and holds it so tightly that it almost never mixes with other water.

The finding is so significant, researchers said, that they aren't even sure yet what it may mean. But it could affect our understanding of how pollutants move through soils, how nutrients get transported from soils to streams, how streams function and even how vegetation might respond to climate change.

The research was just published online in Nature Geoscience, a professional journal.

"Water in mountains such as the Cascade Range of Oregon and Washington basically exists in two separate worlds," said Jeff McDonnell, an OSU distinguished professor and holder of the Richardson Chair in Watershed Science in the OSU College of Forestry. "We used to believe that when new precipitation entered the soil, it mixed well with other water and eventually moved to streams. We just found out that isn't true."

"This could have enormous implications for our understanding of watershed function," he said. "It challenges about 100 years of conventional thinking."

What actually happens, the study showed, is that the small pores around plant roots fill with water that gets held there until it's eventually used up in plant transpiration back to the atmosphere. Then new water becomes available with the return of fall rains, replenishes these small localized reservoirs near the plants and repeats the process. But all the other water moving through larger pores is essentially separate and almost never intermingles with that used by plants during the dry summer.

The study found in one test, for instance, that after the first large rainstorm in October, only 4 percent of the precipitation entering the soil ended up in the stream -- 96 percent was taken up and held tightly by soil around plants to recharge soil moisture. A month later when soil moisture was fully recharged, 55 percent of precipitation went directly into streams. And as winter rains continue to pour moisture into the ground, almost all of the water that originally recharged the soil around plants remains held tightly in the soil -- it never moves or mixes.

"This tells us that we have a less complete understanding of how water moves through soils, and is affected by them, than we thought we did," said Renee Brooks, a research plant physiologist with the EPA and courtesy faculty in the OSU Department of Forest Ecosystems and Society.

"Our mathematical models of ecosystem function are based on certain assumptions about biological processes," Brooks said. "This changes some of those assumptions. Among the implications is that we may have to reconsider how other things move through soils that we are interested in, such as nutrients or pollutants."

The new findings were made possible by advances in the speed and efficiency of stable isotope analyses of water, which allowed scientists to essentially "fingerprint" water and tell where it came from and where it moved to. Never before was it possible to make so many isotopic measurements and get a better view of water origin and movement, the researchers said.

The study also points out the incredible ability of plants to take up water that is so tightly bound to the soil, with forces nothing else in nature can match.

The research was conducted in the H.J. Andrews Experimental Forest near Blue River, Ore., a part of the nation's Long Term Ecological Research, or LTER Program. It was supported by the EPA.

Much to the surprise of the researchers, soil clings tenaciously to the first precipitation after a dry summer, and holds it so tightly that it almost never mixes with other water. (Credit: iStockphoto/Mats Lund)
Oregon State University (2010, January 23). Water hits and sticks: Findings challenge a century of assumptions about soil hydrology.ScienceDaily. Retrieved January 23, 2010, from

Sunday, January 17, 2010

Runoff Example Files for SWMM 4

These are 48 Runoff Example Files that I created based on PC-SWMM 3, SWMM 3 and new SWMM 4 features at UF between 1985 and 1981..

These files will work with any SWMM 4 version. If you look at page

we have a variety of SWMM 3 and SWMM 4 engine.

The File Runoff45.DOC is the text documentation for the SWMM 4 Runoff File.


AI Rivers of Wisdom about ICM SWMM

Here's the text "Rivers of Wisdom" formatted with one sentence per line: [Verse 1] 🌊 Beneath the ancient oak, where shadows p...