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urban watersheds

Mackenzie Osypian defends her thesis on stream restoration and transient storage

Woman in stream with PVC pipes (piezometers)

Mackenzie tending to piezometers in one of her streams.

Mackenzie Osypian is defending her MS research in Civil Engineering at UNC Charlotte, April 22nd at 4:00 pm in McEniry Hall 441 on the UNC Charlotte campus. Mackenzie is advised by Anne Jefferson and Sandra Clinton. John Daniels and Jim Bowen are on her committee.

Mackenzie’s research is titled: “Evaluating restoration effects on transient storage and hyporheic exchange in urban and forested streams.”  Her abstract is below:

Millions of dollars are spent each year on restoration projects designed to improve stream habitat, but few studies have investigated effects of restoration on groundwater- surface water interactions. Hyporheic exchange and transient storage in four second-order streams (urban/forest; restored/unrestored) were studied by measuring geomorphology, streambed vertical head gradients and water fluxes, and by using conservative, impulse-loaded tracer studies along with the OTIS model. Total storage exchange and percent hyporheic exchange were found by utilizing the OTIS P parameters and the sum of downwelling fluxes calculated in SURFER. The upwelling and downwelling varied between -1.783 m/m to 3.760 m/m in the restored urban stream, which contains large step structures, while the unrestored urban stream had no measured upwelling or downwelling (0 m/m) along the reach, which is incised to bedrock.  The forested restored stream had a smaller range of hydraulic gradients (-0.012 m/m to 1.99 m/m) compared to the forested unrestored stream, which ranged from -0.725 m/m to 0.610 m/m. The forested unrestored reach had the highest percent of hyporheic exchange, reaching 22% during the winter season. The urban restored has the smallest percent of hyporheic exchange of 0% across all seasons due to the exposure of bedrock in the streambed. The restored reaches were found to have between 0% and 6% of total transient storage exchange occurring in the hyporheic zones, with some seasonal variability.

The results indicate that restoration increases the hyporheic storage when the stream has incised to bedrock, but that large in-channel storage is also created. When the stream has an alluvial bed (as in the forested streams), the percent of hyporheic flow compared to total storage is reduced. The forested unrestored stream had the largest average hydraulic conductivity of 0.006 cm/s compared to the forested restored, 0.001 cm/s, and the urban restored, 0.001 cm/s.  The restored forested site had a maximum area to storage area ratio of 247 m2/m2 in the spring, which was higher than the forested unrestored site. That site had a maximum of 16.4 m2/m2, which occurred during the fall season.

We are currently preparing her thesis for publication.

Lost Rivers documentary showing in Kent!

I’m super-excited! Super super excited. I’ve just found out about a new documentary on Lost Urban Rivers! The trailer looks great (see below). And it’s showing in Kent! This week!

Lost Rivers is a new documentary by Montreal-based Catbird Films, and it tells the story of how cities built around water, then built over it “losing” the rivers, and how today we are starting to uncover those rivers again. The film was released earlier this year, and there’s only been two other screenings of it in the US so far. And totally unbeknownst to me, the third US screening is here in Kent, Ohio on Friday (April 19th) as part of the Who’s Your Mama? Environmental Film Festival. The film festival runs from 5 to 9 pm, with lots of great shorts, and Lost Rivers is the featured documentary, which will show at 7:30 pm. The film festival is in the Kiva on the Kent State Campus, and admission is $7, $5 for students and seniors, or free for kids under 12. There will also be local food tastings and booths by local environmental organizations, including Kent State’s student group CRICK.

Lost Rivers – OFFICIAL TRAILER from Catbird Productions on Vimeo.

Doesn’t it look great? I’ll definitely be at the screening on Friday, and I hope I’ll see some of my students there as well (though I know many will be on a field trip). In any case, I’ll report back, but I’m hopeful that by the next time I teach Urban Hydrology, I’ll have a copy on DVD and be able to show it to my class. Whee!

Rain garden resources

A compilation of some of the better resources available on line for rain garden design. If you find other good resources, please contact me or leave a comment.

In my mind, an adequate resource should help you figure out how to do the following things:

  1. Determine the needed size, depth, and location.
  2. Understand your soils and figure out how to build a soil for infiltration
  3. Provide recommendations for planting the garden (e.g., species lists, things to consider) that are appropriate for your climate, soil, and shade conditions.
A good resource will help you do those things and understand how and why the size, depth, soils, and plants work together to reduce runoff.

Urban Hydrology students: Please search the web for one good rain garden design resource to be added to the list above. When you have found one, leave a comment or email me with the link. I’ll update the list as we go along.

 

Combined sewer overflows: Solving a 19th century problem in the 21st century

Combined sewers are pipes that catch both sewage and stormwater and route it to a waste water treatment plant. In dry weather, it’s all sewage in the pipes. In small rain storms, the pipes carry sewage mixed with stormwater and it all goes to the wastewater treatment plant to get cleaned up and returned to a stream or lake. The origins of combined sewers predate waste water treatment, when there was little distinction between stormwater and sewage and stream and city dwellers just wanted the foul-smelling, disease-festering stuff out of their way as soon as possible. Later, engineers and public health folks added the crucial waste water treatment plant step to the system but the sewers remained combined. Combined sewers were common until the early 20th century, so over 772 communities in the US, mostly in the Northeast and Great Lakes regions have combined sewers, as shown on this map from the US EPA:

Pink US with black dots stretching from Iowa to Maine

US EPA map of Combined Sewers. Click for source.

Most of the time, combined sewers route all of the water to the waste water treatment plant, and all is relatively well. But in large storms, the volume of stormwater and sewage can overwhelm the waste water treatment capacity. If the volume of water was too much to treat, you can imagine the pipes starting to fill up with sewage. If there were no “pressure release valve” on the system, urban dwellers in combined sewer cities would see the sewage/stormwater cocktail start to back up into their basements, sinks, … and, you get the picture. Fortunately for those city residents, there is a “pressure release valve in the system,” but it’s a solution that creates more problems downstream, literally. When flows in the combined sewers are too great to be treated, the sewage/stormwater cocktail overflows out of the pipe network and into local streams. Then you’ve got raw sewage in your stream and that’s not pretty, or healthy, or environmentally friendly. This is the infamous combined sewer overflow or “CSO.”

Dry weather all water in pipe is sewage and goes away from the stream. Wet weather sewage and stormwater overflow in the stream

US EPA diagram of a combined sewer in dry and wet weather. From U.S. Environmental Protection Agency, Washington, D.C. “Report to Congress: Impacts and Control of CSOs and SSOs.” Document No. EPA 833-R-04-001 found on Wikimedia commons. Click for source.

Here’s a Northeast Ohio Regional Sewer District video explaining combined sewers and touting their treatment system:

Under the Clean Water Act, cities and sewer districts can be required to bring their raw sewage discharges down to acceptable levels by reducing the frequency and magnitude of combined sewer overflows (CSOs). Right now, Cleveland, the District of Columbia, Philadelphia, and other cities are under mandate to reduce their CSO discharges. This is a big, expensive undertaking because we’re talking about billions of gallons of overflows each year and thousands of miles of combined pipe network underneath the city. Big problems require big solutions, so how are the cities dealing with their CSO problem? It turns out that they are taking a range of different approaches.

In Cleveland, waste water treatment and stormwater are managed by the Northeast Ohio Regional Sewer District (NEORSD). Their “consent decree” with the EPA was filed in July 2011, and according to that decree, they have 25 years to reduce CSO volumes by 90%. That’s taking the CSOs from 4.5 billion gallons per year to the still non-trivial 494 million gallons per year. If they meet that goal, 98% of all wet weather flows will be treated before being released to a stream. The price tag for this ambitious project is $3 billion, and it has been termed “Project Clean Lake” in homage to Cleveland’s Lake Erie shoreline. a source of regional pride.

How is NEORSD planning to reduce CSOs? With a lot of digging. Most of the money and effort is being spent on “gray infrastructure” – big engineering projects. BIG engineering projects. NEORSD is boring 7 tunnels, each 2-5 miles long, up to 24 feet in diameter, and up to 300 feet below the ground or lake bottom. These tunnels will intercept the combine sewers before they overflow and store the water until the treatment plants have capacity to treat it.

Sewer pipes with human to scale.

The 7 future storage tunnels of Cleveland’s combined sewers. Image courtesy NEORSD. Click for larger.

This is a massive undertaking, and it’s just getting started. The videos below show the first tunnel boring machine arriving in Cleveland and a tour of the tunnel first tunnel to begin construction. You can follow the progress of the tunnel boring on the NEORSD blog.

But it’s not just tunnels, NEORSD is also enhancing their wastewater treatment capacity and spending $42 million on green infrastructure. Green infrastructure is defined as “a range of stormwater control measures that use plant/soil systems, permeable pavement, or stormwater harvest and reuse, to store, infiltrate, or evapotranspirate stormwater.” These can include things like green roofs, green streets, bioretention swales, and other projects. The goal is control 44 million gallons of would-be stormwater using green infrastructure, with projects completed in the next 8 years. Those numbers are nothing to sneer at it, but it’s 1% of the current combined sewer overflow volume and 1.5% of the budget. The fact that the budget % is bigger than the volume percent may hint at why green infrastructure isn’t being used more broadly in Cleveland.

Washington DC is taking a somewhat different approach than Cleveland. One-third of DC is served by combined sewers, and they are spending $2.6 billion over 25 years to reduce their overflow problem, which is currently about 2.5 billion gallons per year. DC Water has nicknamed their CSO program the “Clean Rivers Project.” Like Cleveland, they are also building large storage tunnels, improving their waste water treatment plants, and rehabilitating pumping stations. Unlike Cleveland, DC will actually be separating the sewers in some areas, sending sewage and stormwater down different pipes from each other. In DC, green infrastructure seems to get only a rhetorical nod, rather than a significant component of the budget. Their plan says they will “advocate implementation of Low Impact Development,” but they’ve only budgeted $3 million for it, a mere 0.1% of their overall project cost. However, they do have the world’s best explainer video.

Philadelphia is taking a radically different approach. Like Cleveland and DC, their price tag comes out to about $3 billion over 25 years. However, in Philadelphia it’s a “Green City, Clean Waters” program and green infrastructure steals the show. Philadelphia’s goal is to “reduce reliance on construction of additional underground infrastructure” by pushing extensive green infrastructure throughout the city. In other words, they don’t want to dig tunnels. Instead, they want to green acres:

Each Greened Acre represents an acre of impervious cover within the combined sewer service area that has at least the first inch of runoff managed by stormwater infrastructure. This includes the area of the stormwater management feature itself and the area that drains to it. One acre receives one million gallons of rainfall each year. Today, if the land is impervious, it all runs off into the sewer and becomes polluted. A Greened Acre will stop 80–90% of this pollution from occurring.

Philadelphia’s rationale for making green infrastructure their big push centers around social and economic benefits to come and their historic heritage as a park city. Their video is all about people, not all about pipes:

Philadelphia’s vision is the most radical departure from a traditional “grey infrastructure” approach like that pursued in Cleveland, DC and other cities. There’s certainly an aesthetic and emotional appeal behind greening a city and its stormwater. This is the way many people want to move urban hydrology in the 21st century, integrating the built and natural environment more closely than we’ve done in the past. But it will be interesting to watch where Philadelphia succeeds and if and where it fails, as the fully green infrastructure approach could be seen as much riskier than a traditional engineering-driven approach. Fortunately, EPA is devoting some funding to research on the effectiveness of Philadelphia’s project. I won’t be doing that work directly, but I will be following it closely and think it would be fascinating to put together a more rigorous multi-city analysis of approaches and outcomes.

More broadly, the combined sewer overflow problem is a fantastic example of how our environmental and societal choices are constrained by decisions made in the past. No one today would build a combined sewer, but yet millions of people live in cities served by them, thousands of engineers, scientists, and sewer district workers work with them, and billions of dollars are being spent trying to mitigate the problems they cause. We can’t just rebuild cities from the underground up, so we have to work with what we’ve inherited and try to make decisions that won’t cause consternation for future generations.

Note: This blog post is adapted from the lecture I gave today in Urban Hydrology. If I’ve gotten anything wrong or missed an important point, please let me know and I’ll try to make it better for current and future students.

Collecting Data on the Cuyahoga River in Kent

Next week my Urban Hydrology class embarks on their first project: exploring the potential water quality changes in the Cuyahoga River as it flows through the City of Kent, which is really the first good-sized town on its path to Lake Erie.

Here’s a summary of what we’ll be doing, and you can click through to the attached document to get more details.

Beginning February 5th, we’ll be collecting near-daily water quality measurements of Cuyahoga River water as it flows through Kent. Using the data we collect, we’ll attempt to answer the following questions:
• How does water quality change as the river flows through an urban area?
• How does water quality vary with respect to discharge in the Cuyahoga River?

Each student will sign up for one weekday on the class calendar. On the assigned day, that student will be responsible for taking a suite of measurements at 2-4 locations. The measurements we will take are (1) turbidity, (2) specific conductance, and (3) temperature and we will also collect water samples for later analysis on the Picarro water isotope analyzer. Each student will be required to take one set of measurements at the base of the steps just upstream of Main Street and one set of measurements at the beach just downstream of Summit Street. Students with access to cars are also encouraged to take measurements at the River Bend Road boat launch (at Kent’s upstream end) and at the Middlebury Road boat launch (at Kent’s downstream end). Details of each measurement technique and each site are [in the linked document].

Trail and stairs going down to river. Patches of snow and ice in the scene.

River access just upstream of the Main Street bridge in Kent. This is one of the spots we’ll be using to sample the river.

Reflecting on my cities and their water

This week’s mini-assignment for my urban hydrology class reads thus: “In 1-2 paragraphs, describe your hometown (or some other city you know well) in terms of its location, size, and form and why it is that way (i.e., historical context). Then write a paragraph describing your city’s relation to water. For example, what is the water supply and where is wastewater disposed? Are there local water bodies or water issues important to the community? You don’t need to include references with your assignment, but you should check your facts if you are unsure about anything.”

Because I’m a water geek, and I wanted to model a good response to these questions, I present not one, but two, reflections on cities I’ve known well and how those cities relate to water.

Winona, Minnesota

I grew up in Winona, Minnesota, a town of about 28,000 people in the southeastern corner of Minnesota. The main part of the city is situated in the middle of the Mississippi River floodplain, with the main channel on one side and a former channel (now lake) on the other. The Winona area was inhabited by Native Americans for millennia, prior to its establishment by white settlers in 1851. Winona’s location along the river made it an important link for railway and steamboat transportation, and Winona was the second place on the Mississippi to be crossed by a railroad bridge (opened in 1891). Winona grew rapidly, and by 1900 had almost 20,000 residents. Winona was a major sawmilling center (with logs floated down the river to the mills), and Winona is still a major port on the river for loading agricultural products onto barges. In southeastern Minnesota, the Mississippi River sits in a ~500 foot deep valley, so as the city has grown larger, it has spread outwards into tributary valleys and up onto the plateau. However, most of the population still lives on the floodplain, and most of the developed area (including pretty much all of the industrial and commercial areas) is in the valley bottom.

As is apparent by the paragraph above, Winona as a city is intricately tied to the Missisisippi River, physiographically and economically. River recreation (boating, fishing, duck hunting) is also a major past-time (and economic contributor) for Winonans. The river holds pride of place in town, but it was also a source of major and frequent flooding until 1985 when an 11-mile levee was built surrounding the town. Other than the occasional flood (now more a curiosity than a catastrophe), periodic public engagement with dredging of sand from the river bottom, and the enjoyment of boat trips on the river, I would say that Winonans’ aren’t particularly attentive to water issues, because it is abundant and out of their way. The city gets its water supply from a Cambrian sandstone aquifer several hundred feet below town, where water is abundant and good quality. It disposes its treated wastewater into the river at the downstream end of town. The big water issue I remember growing up, was about water quality in the Lake, which was quite degraded by the invasive exotic, Eurasian water milfoil. There is actually a water issue that has cropped up over the last several years in the region, which is getting local attention, and that is the mining of “frack sand” from the local sandstone formations. This is getting attention because of problems with heavy truck traffic in town, blowing sand from exposed storage piles, and from destruction of rural areas where the sandstone is being mined. However, to me, it is ultimately a water issue, because those sandstone formations are the regional aquifers. It’s not clear to me yet what effect the mining will have on local or regional water quality, but it seems like an issue to watch.

Charlotte, North Carolina

I spent five years living in Charlotte, which is the largest city in North Carolina, with a metropolitan population of 1.8 million people. Charlotte is a major financial center, and also the home of NASCAR. The city was founded around 1755 at the intersection of two Native American trading paths, and it was a “hornet’s nest of rebellion” during the American Revolution, being the first place that city leaders signed a declaration of independence from Great Britain. Charlotte’s history includes being close to the site of the first gold boom in the US, and becoming a major cotton processing center and railroad hub. Banking and NASCAR rose to prominence since the 1970’s, and the region has experienced explosive population growth (and urban sprawl) since then. The population of the city itself has gone from 241,000 in 1970 to over 730,000 in the 2010 census. There is a relatively small, high density city center surrounded by miles of low density residential, commercial, and industrial development. The gentle rolling topography of the Piedmont forms no barriers to the geographic expansion of the urban area. Several small towns have been agglomerated by the urban area, and many people commute from these communities into the city center or across the city.

The Catawba River, which has a watershed area of 3343 miles upstream of the South Carolina border (Charlotte’s southern boundary), flows through the urban area a few miles west of downtown Charlotte. The River is impounded in a series of reservoirs used for hydroelectric generation by Duke Energy, and was one of the first rivers in the country used for that purpose. Most of the land along the river is privately owned by relatively affluent people, and there are only a few public parks on the reservoirs. Power-boating recreation is popular with those along the river, but swimming is banned in the county in which Charlotte sits, because of concerns about liability. The river forms the water supply for the city, because the fractured crystalline rocks in the area don’t support pumping of large groundwater volumes. Wastewater is treated and disposed of back into the river (farther downstream) or into local streams. There are a number of small urban streams that flow through the city, and these streams are quite prone to flooding during heavy rainstorms. The city and county have undertaken a major stream restoration and stormwater management program to try to reduce flooding hazards, and a series of greenways have been established along the some of the streams. When I moved to Charlotte in 2007, we were in the middle of an intense drought, and subject to limitations on outdoor water use. However, as soon as the drought lifted, local water conservation mindfulness seemed to disappear too. There is an illusion of abundance of water in the southeastern US, even though as population grows water supplies are becoming stressed (Atlanta is a stark example of this). In a recent book, author Cynthia Barnett highlighted Charlotte as a prime example of a city that was “disconnected” from its water supply, meaning that the people of the area lacked a water culture or ethic that would encourage conservation and sustainable use.

I probably spent about 20 minutes writing each piece, but I’m fairly familiar with the water issues and setting in each area (see above: I’m a water geek). So it might take you a bit longer to do a similar amount of writing. One essay is 499 words, and the other is 528 words, but you could write less and still cover the relevant information. I haven’t included hyperlinks to lots of sources here, because I didn’t require that of my students, but I might go back later and add them, because it just seems like wasting the capabilities of the web to not do so.

My job as an urban hydrologist, only using the 1000 most common English words

Thanks to an incredible text editor and inspiration from the creator of XKCD, here’s how I summed up what I do, using only the 1000 most common words in the English language:

I study how water moves in cities and other places. Water is under the ground and on top of it, and when we build things we change where it can go and how fast it gets there. This can lead to problems like wet and broken roads and houses. Our roads, houses, and animals, can also add bad things to the water. My job is to figure out what we have done to the water and how to help make it better. I also help people learn how to care about water and land. This might seem like a sad job, because often the water is very bad and we are not going to make things perfect, but I like knowing that I’m helping make things better.