Outline for Final Report

Last week our team focused on finishing up our research on soil erosion so that we could get ready to write our final report. On Thursday we polished up our outline and began writing. Below see our outline:

Outline for Final Report:
I. Introduction
   a. Poilao
   b. The problem
II. Strategies (summary of each)
   a. Vegetation
   b. Rip-Rap
   c. Geotextiles
   d. Terracing
   e. Soil bioengineering
   f. Fertilizers & chemicals
III. Proposal (use this, this, not this [and explain why])
   a. Terracing
   b. Vegetation
   c. Geotextiles
   d. Rock riprap + joint planting
IV. Implementation & Methods
   a. Discussion of each solution
   b. Instructions
V. Appendices
   a. Pugh charts
   b. Works cited
   c. Vegetation recommendations
VI. Contacts & Additional Info
VII. Acknowledgements

We will give Amy a draft of our final report by the end of class on Monday, so that we will have plenty of time to edit it before the end of the semester.

Research Update

Happy Thursday evening! It's almost the weekend...yay!

Today in class we began solidifying our ideas on our final product for this project. We have decided to present many options to our partners in Cape Verde in a written report. In said final report, we are going to list all of the techniques we considered to combat soil erosion, and describe why or why not we recommend each one, in varying depth. We will focus on terracing and vegetation (including planting techniques such as a brush mattress and mats) for the majority of the slope, and rock riprap + joint planting for the toe of the slope. We find these methods to be the best solutions to the issue of soil erosion at the Poilao Dam.

Below see pictures of terracing and rock riprap:

For the section of the report on vegetation, we will focus on identifying a number of solid options for trees, shrubs, and ground-cover to plant on the slope. This section will also include the criteria (for example root depth and rapid growth) that we used for identifying effective plants. 

During our meeting with Amy we also decided on how to approach our discussion of the costs of each technique. Instead of making assumptions about the Cape Verdean government's budget for the Poilao Dam, we will provide the broad cost information for each technique we're suggesting for implementation. That way the appropriate people can decide on the best option based on a host of information we do not have access to.

Lastly, we are trying to make contact with some science professors at the University of Cape Verde to get some information about what kind of vegetation is present on the island of Santiago. 

Check back for more on our research!

Soil Erosion: Possible Solutions

In class on Monday we began the next faze of our project: actually trying to find a solution to soil erosion at the Poilao Dam. We've done a lot of research, so we decided to try and talk globally about all the techniques we've come up with so far.

Below see a picture of some of the techniques and some questions we generated during class:

The starred techniques are ones that we feel comfortable recommending for implementation. The question mark next to the rock riprap + joint planting option shows that we have a lot of questions regarding what to do with the toe of the slope. Depending on the angle of the slope (assumption from pictures: relatively gentle slope), we are thinking of putting a wall of rock and willow at the base of the slope. One reservation we have about this technique is that we have read that it harms the aquatic habitat. We want an effective way to fight soil erosion at the base of the incline, but also don't want to harm the surrounding environment. Another option is a snow fence, which is a wooden fence built in the water a bit beyond the toe of the slope that controls erosion.

As you can see, we still have a lot of questions to answer. Our next task is to work on identifying what kind of vegetation would be good to recommend for planting. Since willow is the best vegetation to use for many soil bioengineering techniques, we are hoping to find a species of willow, or a similarly fast-growing plant, that is native to Cape Verde. 

Stay tuned for our findings!

Design Review

At the beginning of Thursday's class, each team briefly presented their prototypes or research updates to the class and received some feedback. For this design review, each of the members of our team made a chart on the techniques they've been researching for combatting soil erosion at the dam. Fiona made a poster on the benefits of different soil bioengineering techniques, Zehra made a poster on the use of chemicals to combat soil erosion, Mackenzie made a poster on different aspects of using vegetation, and Kalyani made a poster on the different soil erosion products that can be used. 

Vegetation:

Soil Bioengineering:

Soil Erosion Products:

Chemicals:

And here is a chart that we made comparing all of the different broad techniques for combatting soil erosion surrounding the dam:

These posters will help us determine what techniques will work well in conjunction with others, and what techniques are most feasible given the context of Cape Verde.

Meeting with Elizabeth Pierce, Geosciences Department

To learn more about soil erosion and dam management, Zehra and Mackenzie met with Professor Elizabeth Pierce in the Geosciences Department.

Elizabeth emphasized the importance of having the right amount of moisture in your soil to prevent erosion and seconded our top solutions for avoiding soil erosion which are vegetation and terracing. On Wellesley's campus, terracing using wooden stakes and netting/metal mesh is present near Lake Waban, and has been effective in preventing soil erosion. It is key to terrace whole area around the dam, instead of only areas close to the bank, because of the risk of undercutting which affects slope stability. Any instability above or below on the slope can be a problem, so we can't just target the lower half of the slope. 

She also said the first thing that came to mind when we asked about strategies to prevent soil erosion was to introduce clay to the system to retain moisture. This is something we would like to research further. 

We asked some questions regarding check dams and walls or barriers that have been built in other locations to prevent soil erosion, but Elizabeth pointed out that the concrete used to build a wall would prevent sediment replenishment because it introduces a new sediment, so walls are not a good solution. We also could have scouring on the banks of the stream feeding into the dam.

Resources she recommended were the US Geological Survey and the DOD (Department of Defense) case studies. Dams in the Pacific Northwest might also might serve as useful models.

Meeting with Professor Kristina Jones

Planting vegetation can be an effective way to mitigate soil erosion because plant roots stabilize soil. To learn more about vegetation selection, Fiona and Mackenzie met with Professor Kristina Jones, Director of the Botanic Gardens.

Selecting the right vegetation for the slopes surrounding the Poilao Dam is challenging because we know so little about our site, as we have not been able to have a conversation with our community partner. But, given one photo of the dam, Kristina was able to give us some valuable insights:

We had been researching vegetation erosion control techniques on slopes, but Kristina advised us to research soil erosion management onroad cuts and other newly cut land features because the dam’s impoundment was cut out of hillsides. Thus, a lot of the topsoil has probably eroded away.

Soil

When choosing plants for a site, it is critical to know what the soil type of the site is. We need to do more research on the soil to learn if it’s sand, clay, or basalt, and if the soil is compacted. Since Cape Verde is a former site of volcanic activity, there is a good chance that our soil is partially basalt. We also want to know what the pH, moisture, and nutrient content of the soil is. Since the slopes have been eroding, much of the organic matter present in the topsoil has probably eroded. This means that organic matter will have to be added to the soil before planting so that the plants have the necessary nutrients. Hugelkultur is a cheap way to increase soil nutrient content: essentially you bury wood debris under the soil and it breaks down slowly over time and creates organic matter.

Vegetation Type

While doing research on vegetation types, we came across conflicting recommendations (ex. Plant grass! DON’T PLANT GRASS!). Kristina told us that we shouldn’t think about trees vs. grass but rather we should ask “do we want fast growing plants or not?” The answer to this depends on how dire the erosion is. Our best plan is probably to plant a fast-spreading groundcover that will quickly stabilize the topsoil. At the same time, we can plant tree and shrub seedlings, which will grow slowly and eventually shade out the groundcover (succession!) and provide deeper structural support against erosion. This approach provides short and long-term solutions to erosion.

Plant Species

Whatever plants we choose will have to be very drought tolerant. We are going to research drought-tolerant willows, which sucker underground to form thickets and grow really quickly. We could try a willow mat – a layering of willow branches that will sprout when the conditions are right. For a cheap groundcover, we can try to source a local plant and divide up and plant its rhizomes. Since a lot of Cape Verde’s plant life is exotic, we will want to be sure that we don’t introduce anything that could be invasive, even if it’s not a native plant. 

Research Updates

Our research has been coming along nicely, despite the hurdles we face in terms of access to information on the Poilao dam. We are forging ahead with research on soil erosion in general, and are hoping to be able to narrow our focus on each of the subtopics even further once we talk with Ms. Cortet.

From Kalyani:
My part of the initial research involves looking at the causes of and solutions for controlling erosion. I've been reading reports of studies which explore different options for planting, mulching, and erosion control products, as well as a book specifically about erosion in the tropics, Soil erosion in the tropics: priniciples and management, by Rattan Lal (1990). This has been a great resource in helping to learn specifically about erosion in warmer climates, and it also outlines some solutions with diagrams and graphs of the results. I've also been reading about the soil of Cape Verde, since the soil of the area is integral to how erosion occurs. 

What I've learned so far: the Cape Verdean islands formed as a result of volcanic activity, and there are frequent droughts, sometimes lasting upwards of fifteen years. The mountains receive about 8cm of rainfall yearly, and the coast is much drier, with 1.5 cm yearly. Many strategies for erosion control have already been integrated into the Cape Verdean landscape, such as rock terraces and planting acacia trees to hold the soil together.

Links:“UUSC aids cooperatives in Cape Verde,” Cape Verdean News, February 5, 1987 Soil & Tillage Research 55 (2000) 207-212

Rainfall erosivity in Cape Verde, C.M. Mannaerts and D Gabriels

From Zehra:

As initial research, I have been reading about major dams both domestic and abroad to collect information on the characteristics of an efficient dam. This is to help our team come up with various solutions, and eventually a model to prevent soil erosion around the Poilao Dam, as well as for when Cape Verde constructs new dams for crop irrigation and frequent droughts.

Abroad: The Aswan Dam in Cairo, Egypt along the Nile Delta, and the Hirakud Dam in India. Both dams are used for crop irrigation, hydroelectric power, and flood control. Both of these dams have led to the creation of artificial lake reservoirs that have been useful but face the challenge of soil erosion and deterioration, and as a result, various soil conservation methods have been proposed and employed that can be considered for the Poilao dam.

Domestic: The Lemon Dam in Colorado has faced issues with hillslope erosion and debris flowing into drainage basins, which has led several groups to come up with mitigation techniques. There will be more updates on these specific techniques as I continue investigate these dams.

Links:

Smith E., Scot. “Coastal Erosion along the Egyptian Delta,” Journal of Coastal Research, Vol. 4, No 2 (Springs, 1988), pp. 245-255.http://www.jstor.org/stable/4297400.

Kumar, Kanti. “Management of Water in Hirakud Dam Project.” Wordpress. February 1989. http://bitscape.files.wordpress.com/2012/12/management-of-water-in-hirakud-dam-project.pdf

Choudhary, Pranab. “Floods, Fields and Factories: Towards Resolving Conflicts around the Hirakud Dam.” Odisha State Resource Centre. Maharashtra: August 2012. http://www.academia.edu/1993991/Floods_Fields_and_Factories_Towards_Resolving_Conflicts_around_the_Hirakud_Dam

deWolfe, V. G.; Santi, P. M.; Ey, J.; Gartner, J. E “Effective mitigation of debris flows at Lemon Dam, La Plata County, Colorado.” 2008. Geomorphology, 96: 366 – 377. http://pubs.er.usgs.gov/publication/70032099.

Aswan Dam:

Hirakud Dam:

Lemon Dam:

From Mackenzie:

I have been researching vegetation strategies for soil erosion management. I have learned about the functional uses of vegetation in mitigating erosion, and the characteristics of different plant types and their suitability for various sites and applications. I have also developed some guidelines for maximizing the benefits of vegetation, such as criteria for choosing the appropriate species for a site, and vegetation management practices. I am beginning to look into specific drought-tolerant plant species native to West Africa. I also need to do more research on erosion control techniques on road cuts.

From Fiona:

My research has been focused on how soil bioengineering can stop erosion surrounding the Poilao dam. There are many techniques, ranging from adding a layer of willow stalks to the slope, to actually planting willows and other vegetation in a way that will combat soil erosion, to adding a wall of rock to the land-water contact point. At this point in my research I am trying to fully grasp each concept in order to determine the feasibility of each technique as it relates to this specific dam and the very unique environment of Cape Verde. My next steps will be to evaluate the cost of each technique and also to find out what kind of vegetation is already present on the slope (similar to Mack's goals). 

Pugh Chart #1: Determining our Project Focus

In order to quantify and visualize our reasons for narrowing our project focus to soil erosion, we made a Pugh chart! We identified the determining factors that would lead us to succeed with this project: research availability, feasibility, team interest, urgency, cost, and local resource availability. We compared soil erosion, drip irrigation, and concrete maintenance, and made drip irrigation our standard.

Below see our beautiful Pugh chart:

....and soil erosion won!

Stay tuned for updates on our research.