Final Thoughts

I started the semester wanting to know more about the effects of flooding and erosion, and what can be done to prevent them. The current flood in Colorado and the Missouri River Flood of 2011 provided great examples of two very different types of floods and their impact. The Colorado Flood was a "flash" flood and preventive measures were nil; while the Missouri River Flood was predicted a few months out so many preventive measures were used to protect lives and property. I found a great piece by the Missouri River Institute that explained how the Missouri River's channel changed due to the flood and the effects on flow and species habitat. It also gave some great pros and cons of flooding; noting most think of the negatives but many good things come from flooding. Erosion control was more difficult to research but the conservation methods used along the Bad River provided examples of the many small things that can be done to significantly reduce erosion. Also, a scientific article proved that some types of vegetation provide better erosion control then others. The most fascinating topic of my blogging experience was School of Mines seminar "A History of Especially Large Floods for the Black Hills Area" by Dan Driscoll. Not only was it exciting to understand much of the seminar due to what was covered in Hydrology class but the techniques that were used to estimate historic floods before there were records was very interesting.

I personally enjoyed blogging. It was a little bit more time consuming then I originally thought but much better then writing a paper. In writing a paper there tends to be a single topic but in blogging I was able to cover many subtopics under one broad topic making for a more diverse experience. It was also interesting to read the other blogs. I felt I received a broader range of knowledge this way. The most difficult things was finding a scientific article and getting it to post, which really isn't related to the actual blogging. I think blogging is a good media for students to learn, as not only do you learn about your own topic but the topics of the others as well. For example, I would have never given much thought about the laws over water rights but I found the "Politics in Water" blogs very intriguing. Blogging would be a great tool to use in future classes.

Missouri River Flood of 2011

In our hydrology class we have talked about a few methods fir predicting and modeling flood events. The Missouri River Flood of 2011 proved that it is not always a perfect system and that nature has its own set of rules. My family is from Fort Pierre, so I was able to see the affects of the flood firsthand. This flood was due to excessive snow pack in Montana and an unusually wet spring, so there was time to take precautions to reduce the effects of the flood. Both Pierre and Fort Pierre built a levee system to protect many of the structures within the cities. Storm drains were plugged by divers so the water would not back up into the streets. Pumps were brought in to pump rainwater out of the streets and back over the levees. Below are a few newspaper articles from the Capital Journal (Pierre, SD) that my Dad saved. Also there are some pictures showing the affects of the flood waters.

Photograph by South Dakota Highway Patrol

 This picture is just below the Oahe Dam on the west side of the Missouri River. The river typically flows several feet below the yards of these houses, the trees help mark where the yards once were. The water spread out to Highway 1806, which can be seen near the trees in the background.

Photograph by South Dakota Highway Patrol

 The causeway, indicated by the waves, typically is quite a few feet above the water level. The road connects Pierre (in background) and La Framboise Island (indicated by trees at right). Later in the summer the force of the water washed away part of the causeway.

Photograph by South Dakota Highway Patrol

 The stilling basin is located at the foot of the Oahe Dam and is used to release excess water. All tunnels were opened during the flood, a first in the Dam's history. When standing near this area you could feel the power of the water by vibrations in the ground. The waves reminded me of something you would see on the open ocean, not a river.

Photograph by the Capital Journal, Chris Mangan

A vortex appeared above the dam due to the turbulence of the water flowing from the stilling basin. The pontoon boat on the right can be used as a scale to determine the size of the vortex.

Vegetation and Soil Erosion

I found a peer-reviewed article about a study completed in Spain on vegetation cover and soil erosion. Three plots were planted on a hillside with an approximate slope of 35.5%. Each plot contained a different vegetation type, which included natural vegetation, rosemary, and wheat. The area of study tends to have large amounts of runoff and soil erosion, and the study was completed to verify the assumption that farming was increasing this problem. Over a four year period precipitation was recorded for this area and collectors were used to identify sediment and runoff. Soil losses and runoff were collected after each rainfall event. It was found that the Rosemary and natural vegetation reduced erosion by 99% and 98% respectively when compared to the wheat. It was found this reduction was due to the thick canopies of the Rosemary and natural vegetation intercepting much of the rainfall and reducing splash. Splash causes compaction of the soil which causes sealing and crusting. Less splash allows for infiltration of rainfall into the soil, reducing soil loss. Thick leaves from the Rosemary accumulated below the plant also reducing soil erosion. The wheat had scattered canopies and accumulation below the plant was easily removed by wind. So it was concluded that agriculture was increasing soil erosion and runoff.

So to reduce erosion, land use practices could be put into place on steeper slopes, different types of crops could be planted or other farming techniques could be used. What are your thoughts?

See article below.

Taking Flooding Back in Time

I attended the South Dakota School of Mines seminar "A History of Especially Large Floods for the Black Hills Area" by Dan Driscoll from the USGS (United States Geological Survey). I found it very interesting and thought it would fit nicely into my blog topic. I was also very excited when Mr. Driscoll spoke about hydrographs, flow velocities, gage stations, statistical analysis, and a few other concepts we learned about in our hydrology class because I understood to what he was referring.

Mr. Driscoll started the presentation with some hydrographs, pictures, and other data on the recent large flash flooding events in the area for which we have recorded data, including the 2007 Flood in Hermosa, the 1972 Flood in Rapid City, and a few other floods throughout the Black Hills from the early 1900s. As with any dangerous and destructive event minimization of structure damage and elimination of loss of life is the goal. This task becomes difficult due to recorded data only dating back just over 100 years and the infrequent nature of these floods. This is where geology and mathematics come into play. Currently large floods leave behind evidence, such as deposits of plant debris, boulders, gravels, sands, and fine-grain silts. Typically the fine-grain silts and sands settle out at lower velocities (slack-waters). Flood events should behave in a similar manner in the past. So, these "slack-water" deposits can aid in detailing flooding events within the last few thousand years, but only if they have not been eroded away by wind and water. Rock overhangs or "alcoves" and small caves protect these deposits from erosion and are the focus of study for the USGS and other local, state and federal agencies.

Holes were dug in a number of alcoves and caves within the canyons draining toward the eastern edge of the Black Hills. The different layers of sediment, including organic matter, were documented and a schematic diagram was created to detail the deposits. Samples of the deposits and organic matter were used to date the ages of the deposits going back a few thousand years. The geology of these canyons are known to erode very slowly; thus the height of the deposits from the canyon floor allow for a close estimation of water height. This can then be used to estimate water velocities. Many of the canyons studied showed evidence of much larger floods then the gage records. Mr. Driscoll stated the largest gage record was the 1972 flood at 50,000 cfs but some of the paleofloods showed flows of at least 75,000 cfs with evidence of at least five floods over 50,000 cfs in the Black Hills area. This indicates we haven't experienced the largest possible flood.

This information can assist in more accurately determining the 100-year and 500-year flood magnitudes. This in turn can help governing bodies to create policies to reduce the damage and eliminate loss of life for future flood events. The entire study can be read at the link below which includes some great images to further understand the information provided.

http://www.sddot.com/business/research/projects/docs/SD2008-01_Fact_Sheet_06-11-12.pdf

Bad River Turned Good

In my blogging experience I not only wanted to address flooding issues but also wanted to explore soil erosion by water and prevention methods. A great example of this in South Dakota is the Bad River in the west central part of the state. The United States Environmental Protection Agency outlined the project on its site at the following link: http://water.epa.gov/polwaste/nps/success319/SD.cfm
Note, there was also another interesting study on riparian improvement on the East River in which I will not be addressing this but feel free to read about it.

In the 1990s it was decided that the sediment load carried by the Bad River was excessive and accumulating in the river itself and the Missouri River in which it drains. The watershed is comprised mainly of dense clays that are easily erodible which causes many issues. These issues include filling the channel which in turn causes flooding, this can effect the turbidity and both of these effect sport fishing. Sport fishing is a large income for the Pierre/Fort Pierre area which is where the Bad River meets the Missouri River. Also the Oahe Dam creates power for many communities and needs the ability to flow adequately, which channel fill can hamper.

A committee was started to document where the largest sediment loads were originating. While it was proposed that most came from the upper watershed in the badlands area, the study showed that the lower watershed produced about two-thirds of the sediment due to gully erosion on grazing lands and streambank scour. So, what could be done to reduce the amount of sediment reaching the river? Many solutions were recommended including planned grazing and proper grazing use, structures to control erosion, riparian revegetation, seeding of range areas, water spreader systems, and alternative stock watering areas. The majority of these solution involved plant growth to hold the soil with their root systems. The alternative stock watering areas allowed for cattle and other stock to drink away from the river so as to not disturb the sensitive riparian areas. This also allows stock to graze other parts of pastures that are not near the river to prevent overgrazing, as they tend to stay near water sources. Water spreader systems divert water from continuing to flow in narrow channels and "spread" the water runoff across a broader area thus reducing gullies and rills (see image at bottom of blog). The structures more then likely included such things as dams and rock placement to reduce water flow; and fencing to keep livestock from entering sensitive and fragile areas.

Most of these solutions could not be completed without the willingness of farmers and ranchers within the watershed. The farmers and ranchers also understood the benefits to their land in actively participating. The results were higher then expected and there was a decrease in erosion and sediment load.

Image from the Pennsylvania Department of the EPA showing an example of a water spreader system.

An example of erosion control with rock placement, typically known as riprap.

Image from www.ccma.vic.gov.au

 

Notice the vegetation loss due to cattle continually watering at this location.

Image from www.omafra.gov.on.ca

 

The Mighty Mo!

One of our blogs was to be based on a popular science magazine, but because I would like to focus on the South Dakota Missouri River flooding in 2011, I was unsuccessful in finding such an article. I did however find an article written by Tim Cowman of the Missouri River Institute at the University of South Dakota. This article was excellent in describing many effects of the flooding and answered several of my questions. While this article detailed mainly the section of the river between Fort Randall and Gavins Point Dams, much of it can be applied elsewhere.

First, I wanted to understand how the channel was changed during the floods, as sandbars grew and changed shape or location. The river bed is generally unconsolidated silt, sand, and clay, which is easily moved at slower (or regular) velocities. So the high velocities during the flood eroded, carried, and deposited much larger volumes of sediment. According to the article typically dunes will build up to within two or three feet of the river level, and the levels rose to about 10 feet above normal levels. As the levels dropped and velocities slowed, the larger sediment load was deposited leaving larger dunes at several feet above normal river levels. So where did the larger sediment load come from? It seems the river channel is reportedly deeper then before in some areas leading to the conclusion of riverbed erosion. Also bank erosion was observed but to a lesser extent. The channel location moved in several reported areas, changing the flow rates, channel patterns, and surrounding landscape.

I was also curious about how flooding effected the surrounding ecology, which was addressed in the article as well. It was stated that changing flow rates can effect fisheries and wildlife patterns, changing established habitats and possible river crossing points for wildlife. The deeper channels drain surrounding wetlands that provide habitat for many species and helps control future flooding. Deposition has covered some wetlands and cropland hindering their original purpose. Cottonwood trees are an important factor in riparian forests and can withstand short periods of water inundation but longer periods observed during the flood can damage root systems. Undercutting of banks by floodwaters also knock over cottonwoods. On the positive side, downed cottonwoods can create an ideal habitat for certain fish and insects species, and the new sandbars and floodplain deposits can provided area for new cottonwood growth. Undesirable species such as Eastern red cedar and Russian olive trees cannot tolerate standing water, thus removing them from the area. Invasive species can fortunately also be wiped out of riparian areas, such as the mentioned purple loosestrife. This species will take over an area, not allowing other native species to grow. Unfortunately its seed can be carried by floodwaters and deposited to create new colonies.

Since a flood of this magnitude has not been recorded since the dams were built in the 1950s, many of the long term effects are unknown. Many of the above mentioned impacts will need to be monitored and it may be many years before the total effects will be known.

The article in its entirety can be found at the following link.

http://www.usd.edu/missouri-river-institute/upload/Impactsof2011Flood.pdf

The Colorado Flood 2013

While I was hoping to focus more on flooding and erosion in South Dakota, I feel the flooding in Colorado deserves some attention. Colorado is also special to me as I lived there for six years and many of my grade school friends currently live in or close to the effected areas.

So why did this flood happen? Well there have been several previous floods recorded in these same areas. This would be due mainly to the climate, underlying geology, topography, and vegetation. The climate this time of year is general dry but according to Martin Hoerling from Earth System Research Laboratory in Boulder, the moisture-laden air, moving up from Mexico, was drawn up by the mountains thus turning into rain. This event lasted unusually long in the affected area. Now as we all know the topography in the Rocky Mountains is very steep with narrow canyons. The Geology tends to be solid rock, while the vegetation is mainly coniferous trees and alpine plants. Also due to the recent wildfires in some of the effected areas, the newly growing vegetation would be sparse. All of these factors would lead to very small amounts of rainwater being absorbed creating large amounts of surface overflow. The surface flow would quickly drain to the bottoms of the canyons, picking up intensity as it went. This fast-moving water would wash away most anything in its path, creating the damage and devastation in the mountain towns. The water then reached the point where the canyons opened up to the plains. Many cities are located at these points, so while the water slowed somewhat and spread out, it still caused much damage due to the volume and already saturated ground. (Below are a few pictures from The Denver Post showing the damage.)

This flood reminded me of the Rapid City Flood of 1972. So, I wonder what provisions, if any, will Boulder, Longmont, Loveland, and the other affected cities take to keep this kind of damage, destruction, and death from happening again. I felt Rapid City's decision to create the green space along Rapid Creek was instrumental in saving lives and decreasing property damage from future flood events. Below is a flood map of Boulder. Notice the colored areas showing the 100-year and 500-year floodplains. I find it unsettling that the University of Colorado has student housing within the floodplain. So, hopefully better protection against future events will be put into place.

Photo by Joe Amon/The Denver Post

(Floodwater flowing through a housing area and over a road.)

Photo by Tim Rasmussen/The Denver Post

(Notice how the road was no match for the force of the water.)

Photo by Andy Cross/The Denver Post

(The floodwater easily eroded the soft fertile soil.)

Photo by Andy Cross/The Denver Post

(Notice the amount of debris left by flowing water and mudflows, the house is damaged on the left side. US 34 along the Big Thompson River)

Photo by Andy Cross/The Denver Post

(The fast flowing creek washed away the road but was contained by the rock canyon wall. Swollen Big Thompson River damaging US 34.)

Photo by Andy Cross/The Denver Post

(The shear force of the Big Thompson River. This is at Chasteen's Grove waterfall. Loveland's water treatment plant is on the right side of the picture)

 

Floodplain Map by Oakleafcontracts.com

(Notice where the high school and student housing are located.)

The theme for my first blog in my hydrology class is erosion and flooding effects. Both of these topics cover the force of water. In the summer of 2011 I had several of my family members affected by the flooding on the Missouri River. I was able to watch the process of preparing for the flood, the activity during the flood, and the aftermath after the water receded. I then became curious about learning more about how flooding changes the landscape both good and bad. My family also has a ranch in central South Dakota along the Cheyenne River. Much erosion can be seen along the Cheyenne and on the ranch land draining into the river. Once the topsoil is washed away, it is very difficult for grass to regrow. Water drainage also creates deep washouts that can be difficult for cattle or horses to cross. I am very interested in learning more about good practices to slow the erosion in these critical areas.

I feel a good blog is one that is interesting to read, while providing accurate and useful information. Blogs should not bore you with all the intricate details but summarize the important points. It should be fun and pleasing to the eye. A good blog will keep to it's topic so that followers know what to expect.