nature Archives - Reduce Flooding

After Year of Isolation, The Gift of Nature

After three years of investigating flooding problems and a year of isolating during COVID, it’s time to rejuvenate. What better way to clear your head than with nature? So let me share some pictures with you. In August 2016, shortly after I retired, I spent five weeks driving my Chevy 10,562 miles to the Arctic Circle and back.

Road Trip of a Lifetime

It’s a trip I will never forget thanks to Nikon. And, or course, the U.S. Army Corps of Engineers, which built the 1,500 mile Alaska Highway through northern Canada in 1942 as part of the World War II effort.

When I left Texas, the temperature was 106. When I got to the Yukon, it was 46. The aspens were already turning color in mid-August and birds had already started migrating south from Alaska.

To put this nature trip in perspective:

When you get to Calgary from Houston, you’re not even halfway to Fairbanks.
Canada’s land mass equals that of the U.S., but the U.S. population is 9X greater.
75% of Canadians live within 100 miles of the U.S. border.
Yukon, Northwest Territory and Nunavit (the northern tier of provinces) contain 40% of Canada’s land and only 4% of its people.
The Yukon is larger than California, but has a population less than 40% of Kingwood’s.
At one point, I saw just three grocery stores in 1,000 miles, none larger than a convenience store.

So if you ever want to really clear your head, consider this nature trip. Just bring along plenty of granola bars. Below are some pics and links to more.

What You See Between Houston and the Arctic

*Glacial Valley near Stewart, British Columbia*

*Folded Moutain, in northern Alberta (if I remember correctly).*

*Great Sand Dunes National Park in Colorado. Note the man at the crest of the dune in the foreground.*

To See More

Here are 60 more of my favorite pics from this trip. I hope you enjoy viewing them as much as I did taking them. To see more of my nature photography, visit BobRehak.com, another of my websites. Click on Portfolios and then Landscapes.

If You Decide to Go Yourself

If you decide to take this trip yourself, make sure you go in mid summer. By September, many of the northern roads and accommodations are closing. Snow chains were required in many places after mid-September. No joking. I actually ran into a heavy snowstorm near Edmonton in August. Buy new tires before you go. And fill up at every gas station you see once you get into the Yukon. They can be very far apart.

Posted by Bob Rehak on 12/21/2020

1210 Days since Hurricane Harvey

Study Suggests Large Cities Like Houston Can Intensify Rainfall and Runoff From Hurricanes

A November 2018 article appearing in the peer-reviewed scientific journal Nature found that urban growth can intensify both rainfall and runoff from hurricanes. Further, urban growth can increase the risk of flooding and shift the location of flooding. The article specifically studied the effects of Hurricane Harvey on Houston and found that urban growth increased the probability of such an extreme flood across the basin by 21X.

A sister publication, Scientific American, reviewed the article the same month and helped explain the findings in Nature.

The Nature study looks at two distinct effects of urbanization. The first is the impact of impervious surface on RUNOFF. The second is the impact of the urban landscape’s surface roughness on RAINFALL.

The Runoff Component

Numerous studies have looked at the relationship between percentage of impervious cover, runoff, and flooding – a well documented phenomenon. Impervious cover accelerates transport of rainfall from neighborhoods to rivers. That raises peak flows rather than spreading them out over time. Dr. William Dupre, professor emeritus from the University of Houston visualized the relationship this way.

*Effect of Urbanization on Peak Stream Flows” by Dr. William Dupre, professor emeritus from the University of Houston.*

Rainfall Component Much Less Studied

However, the effect of urban growth and a city’s surface topography on RAINFALL from hurricanes is much less studied. The authors say in Nature that, “Urbanization led to an amplification of the total rainfall along with a shift in the location of the maximum rainfall.” (Page 386).

“Much less is known regarding the urban effects on the organized tropical rainfall of a hurricane, in particular during one like hurricane Harvey, which stalled for several days.” They continue, “…experiments (with computer models) clearly show a large increase in rainfall arising from urbanization over the eastern part of the Houston area.”

The authors compared present and past urban landscapes and also modeled a scenario in which the entire region was cropland.

Mechanisms Responsible for Increase Rainfall

To understand the physical mechanisms responsible for the heavier rainfall, they analyzed the vertical convergence of winds and wind fields.

Kingwood Greens Evacuation During Harvey by Jay Muscat — *Evacuation During Harvey. Photo courtesy of Jay Muscat*.

“The enhanced rainfall … and the shift of rainfall … are tied to the storm system’s drag induced by large surface roughness,” say the authors.

Scientific American explains in more detail. Kerry Emanuel, an atmospheric scientist at Massachusetts Institute of Technology, who did not work on the study said, “We know cyclones are sensitive to characteristics of the surface—mountains, streams, marshland. This new twist is that cities have become big enough to tangibly alter the storm.” Said Gabriele Villarini, an environmental engineer at The University of Iowa and an author on the study, “We removed the urban areas from Houston and replaced them with cropland.”

“The presence of urban areas enhanced all the things you need to get heavy precipitation,” Villarini, one of the study’s authors says. “A stronger drag on the storm winds, associated with a larger surface roughness length” contributed to the increased rainfall.

Emanuel explained, “First, the artificial ruggedness of an urban area slows air down. Whenever air slows in a hurricane, he says, it gets shunted toward the center of the storm and up into the sky. That increases rainfall everywhere [in a metropolitan area].” He added, “A storm moves particularly slowly over downtown areas where buildings are tallest, but the winds bearing down from outside the city are still moving quickly. So, [the storm] is piling up on the city.”

Impact on and Implications for Houston

This increase in urban growth in flat terrain creates problems from a flood perspective, despite mitigation measures already in place.

Urbanization has increased the probability of an event like the flooding associated with Hurricane Harvey by about 21 times, say the authors in Nature on page 388.

The authors make several high-level recommendations.

Urban planning must take into account the compounded nature of the risk now recognized.
Flood mitigation strategies must recognize the effect of urbanization on hurricanes.
Weather and climate models must incorporate the effects of urbanization to increase forecast accuracy on local and regional levels.

“It is critical for the next generations of global climate models to be able to resolve the urban areas and their associated processes,” conclude the authors.

About the Authors and Models

The authors are:

Wei Zhang and Gabriele Villarini from the Department of Hydroscience & Engineering, The University of Iowa, Iowa City, IA
Gabriel A. Vecchi from the Department of Geosciences, Princeton University and the Princeton Environmental Institute, of Princeton, NJ
James A. Smith from the Department of Civil and Environmental Engineering, Princeton University, Princeton, NJ.

This presentation explains the Noah Model that the authors used to calculate air/ground interactions.

Local Questions Raised by Study

To date, the role of a city in altering rainfall during tropical cyclones has received very little attention. Houston has had the largest urban growth and the fifth-largest population growth in the United States in the period from 2001–2011. Much of that growth is now on the periphery of the city. The two fastest growing parts of the region are Fort Bend and Montgomery Counties.

As the city grows, we need mitigation measures that can offset the impact of that growth. That’s why the meeting of the Montgomery County Commissions on August 27th is so important. They will vote on whether to close a loophole that allows developers to avoid building onsite detention ponds. Closing that loophole is important. It will help protect hundreds of thousands of downstream residents as well as those in Montgomery County.

Also, the new NOAA Atlas-14 (rainfall measurements updated after Harvey) does not consider forward-looking urban growth effects. The precipitation frequency data in NOAA Atlas 14 was determined by a statistical analysis of historical rainfall, a key input for FEMA Flood Insurance Rate Map (FIRM) modeling. With all that uncertainty, we need to err on the side of caution in flood planning.

For more about Atlas 14, see this link.

Posted by Bob Rehak on 8/18/2019

618 Days after Hurricane Harvey

Is Time Running Out for Sand?

Given the amount of sand we’re currently trying to remove from the mouth bar of the West Fork, this post may seem counter-intuitive to many. However…

Worldwide, sand is becoming scarce according to a number of recent reports and articles from respected sources. And as the scarcity transforms economies, it also transforms our environment.

*Sand mine complex on the west fork of the San Jacinto adjacent to Kingwood.*

Many now question the sustainability of an economy built on sand extraction from rivers and are exploring ways to reduce our dependence on that source … or import sand from places that are still producing it faster than they are using it.

Sand from Greenland?

An article in the New York Times points to people who are actually researching the feasibility of exporting sand produced by Greenland glaciers to Europe where river mining is outlawed in many countries. Such an endeavor would raise the cost of sand.

The article quotes Jason C. Willett, a minerals commodity specialist with the United States Geological Survey. “Currently almost all sand is mined within 50 miles of where it is used,” he said. “Once you move it any distance, it then costs too much.”

Regardless, the world makes so much concrete (more than 10 billion tons a year), that producers are investigating new ways to supply demand. Population is forecast to grow by more than 25 percent by 2050. “That makes sand, which is about 40 percent of concrete by weight, one of the most-used commodities in the world, and one that is becoming harder to come by in some regions,” says the Times.

Sand Extracted Faster than Nature Replacing It

Another article in the July 2019 international journal of science called Nature claims, “Sand and gravel are being extracted faster than they can be replaced.”

The article goes on to say:

Sand and gravel make up the most extracted group of materials, even exceeding fossil fuels¹.
Urbanization and global population growth are fuelling an explosion in demand, especially in China, India and Africa².
Roughly 32 billion to 50 billion tonnes are used globally each year, mainly for making concrete, glass and electronics³. (Note: this number is higher than the one quoted above but also includes additional uses.)
This exceeds the pace of natural renewal⁴ such that by mid-century, demand might outstrip supply².
Desert sand grains are too smooth to be useful, and most of the angular sand that is suitable for industry comes from rivers (less than 1% of the world’s land)⁵.
This extraction of sand and gravel has far-reaching impacts on ecology, infrastructure and the livelihoods of the 3 billion people who live along rivers^3,6,7

For example, the Nature article says, “In the Mekong delta, the Vietnamese government estimates that nearly 500,000 people will need to be moved away from river banks that are collapsing as a result of sand mining in the channel.”

Likewise, in Bangladesh, the Umngi River expanded when people started mining sand from the river bid.

UNEP Questions Sustainability

Another recent report by the United Nations Environment Program (UNEP) says, “Shifting consumption patterns, growing populations, increasing urbanization and infrastructure development have increased demand for sand three-fold over the last two decades,” claims the UN Report. “Further to this, damming and extraction have reduced sediment delivery from rivers to many coastal areas, leading to reduced deposits in river deltas and accelerated beach erosion.”

The report also called for reducing demand for sand and gravel through improved designs that cut the amount of concrete in buildings and infrastructure. (Lighter designs would also help address carbon dioxide emissions: Manufacturing cement, the reactive ingredient in concrete, creatives about 5 percent of global carbon dioxide emissions.

UNEP also warns that, “To meet demand in a world of 10 billion people without harming the environment, effective policy, planning, regulation and management will be needed. Currently, sand extraction and use is defined by its local geography and governance context and does not have the same rules, practices and ethics worldwide.” The report aims to start a productive global conversation on sand extraction.

“To curb irresponsible and illegal extraction, ” the report suggests a customization of existing standards and best practices to national circumstances.”

To read or download the full report on sand and sustainability, click here.

Difficulty of Change

Like all large scale transformations, this one will not be smooth or simple. The problem with all such reports is that they apply global observations to local conditions. And local conditions always govern actions and economics. As long as it’s cheaper to mine local sand than import it from Greenland, someone will mine it locally.

Those transportation costs can be a killer. In commodity businesses, every penny saved represents a competitive advantage. When you track that penny through the supply chain to the cost of finished goods ( i.e., to a house, a building, or a street, for example), it can have a substantial impact on affordability.

In a highly competitive, free-market economy like ours, producers will always fight to lower their cost of production. Getting them to voluntarily adopt practices that could benefit society is tough.

We can’t even get sand miners to push back 100 feet from the river. 4,000 miles to Greenland is a bit of a stretch!

That tiny problem aside, the value of reports such as these is that they let us develop alternatives before time runs out.

Posted by Bob Rehak on 7/16/2019

686 Days since Hurricane Harvey

San Jacinto River at Its Finest: Nature the Way It Was Meant to Be

Today, I took a much needed rest from floods, sand mines, sedimentation and tax appraisals. A friend took me and two others out on his boat for a day long encounter with nature. We explored the West Fork, East Fork, Taylor Gulley, Caney Creek, Peach Creek and Luce Bayou. It was a cool, overcast day…the kind that’s perfect for nature photography. Diffused light. Saturated colors. Quiet moments. An intense feeling of beauty and oneness with nature. Restful and rejuvenating. It taught me that there are still places on the San Jacinto that haven’t been screwed up yet. Places worth fighting for. Today reminded me of something Ansel Adams once said, “If you want to preserve nature, inspire people with its beauty.” Here’s my humble attempt. I hope you enjoy these moments as much as I did. Most were taken far up the East Fork.