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