Rendering of Proposed Erosion Management Plan

Below see a beautiful rendering of our proposed erosion management plan drawn by Kalyani! Features include rock riprap, vegetation, geotextiles, and terracing.

The drawing is intended to be one year after implementation, and is not to scale.

Paper, paper, paper....poster!

Hello!

Our project is wrapping up. We've been working hard on our final paper, and are currently on our second draft. We got some valuable feedback from Amy on the first draft. We will have it done by next Monday.

We are also in the process of creating a comprehensive poster of our project! There will be a public exhibition of all the final projects from Making a Difference Through Engineering, and also from Amy's other engineering class on Tuesday, December 10th at 4:15pm.

Be there! It will be joyful and there will be food.

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.