Photo By Andrew Stamer | Inspectors perform a site visit to Nacala Dam in Mozambique to provide technical...... read more read more
NACALA, Mozambique - In the United States clean, reliable water is something we take for granted. It’s everywhere – public bubblers in schools and parks – anyone who wants a drink of water has access to it.
In Nacala, Mozambique, and surrounding villages, clean, reliable water is scarce. The Nacala Dam, the major source of their drinking water, is in serious disrepair.
The dam was overtopped due to lack of maintenance during the civil war in the 1990s, resulting in erosion, and there is also major leakage through rusted gates.
Halfway around the world, a team of New England District employees are working towards assisting the people of Nacala. They are working towards rehabilitation of the Nacala Dam and restoring a consistent, reliable water source.
In 2008, the Millennium Challenge Corporation asked the New England District to provide technical expertise related to dam rehabilitation and repair to support the ongoing water supply improvements in Mozambique. MCC is an innovative United States established foreign assistance program designed to reduce poverty by promoting sustainable economic growth. The MCC operates on the principle that aid is most effective in countries that promote good governance, economic freedom and invests in people.
“MCC is an agency that provides grant money to developing countries,” said New England District Project Manager Scott Acone. “There’s a grant with Mozambique that’s primarily centered around infrastructure improvements, most of it is related to road repair and drinking water.”
New England is a long way away from Africa, but the reputation of its engineers is world renown. "MCC has a nationwide agreement with the Corps of Engineers to provide technical support,” said Acone. “We were asked to do the project because of our expertise in dam rehabilitation and construction. New England District is a good fit because of the expertise of our engineers with design and construction of dams, as well as with rehabilitation of dams, for example at Hodges Village and West Hill, and we’re looking at our other projects. We are providing engineering and technical guidance and are reviewing designs as they come in.
“The Nacala Dam is located on the Muecula River, about 30 kilometers upstream from Nacala. It serves as the primary water source for the town. Construction on the dam was completed in 1975. Problems with the dam started in 1982 when the dam embankment was overtopped for 10 hours due to a spillway gate failure. Some repairs were attempted in 1983, 1995, and 2002. A preliminary study was completed by Michael Baker, Jr., Inc., in 2006. An MCC contractor, Jeffares and Greene, performed a geotechnical inspection program to assess the dam and reservoir for rehabilitation and augmentation. “Based on the reports, the dam is inherently unsafe and needs to be rehabilitated,” said Acone.
The rehabilitation project will not only provide drinking water for its people, but it will also help commercially develop that part of the country.
“Nacala Bay is the deepest naturally occurring harbor on the eastern coast of Africa,” said Acone. “So there’s a lot of potential there as a commercial center. One of the things that are limiting the development so far is a consistent reliable supply of clean water. Both the dam and all of the related infrastructure of piping and everything else is intended to provide that water so that the city can grow and develop as a commercial hub and provide income for the country of Mozambique.”
Patrick Blumeris is the project’s hydraulic engineer and has been to the project on two occasions and says it has some things in common with the New England District dams. “The dams here are earth fill dams and so is the Nacala Dam,” he said. The New England Dams, like Nacala, have a spillway at the end of the structure with a bridge structure that can take an inspector from the dam crest to the control tower.”
Essentially, that’s where the similarities stop. “The project is not a flood damage reduction dam as many New England dams are,” said Blumeris. “We don’t typically worry about touching water in our reservoirs, but the Nacala Dam is home to a few crocodiles. Even without crocodiles, it would be important not to touch any standing water. It might harbor mosquitoes (think malaria) or snails (schistosomiasis).”
Rehabilitating the dam is going to be about a $27 million project. “The preferred option is to move the existing National Road N12 off the embankment crest and move it onto a new embankment downstream of the dam wall,” said Acone. “By removing the national road from the dam crest, the crest width can be narrowed by about 5.5 meters (18 feet). The dam embankment can then be raised by 4 meters (12 feet) by making the slopes of the dam faces steeper (about 1:2) and not significantly increasing the footprint of the dam on the ground.”
According to the Nacala Dam Feasibility Study – Main Report, the impervious dam core will also be raised to within one meter of the crest level. The downstream face will be widened by the addition of a gravel aggregate layer, and by the inclusion of a mid slope berm. “Internal sand filters will be installed on the downstream face which will connect into a gravel drain that will link into a surface drain running along the berm to allow for any seepage through the dam to be safely collected,” said Acone. “A new rock toe will be incorporated into the downstream face, which will connect into seepage detection weirs at specified intervals so the dam’s performance can be monitored. Since the goal of this dam is to hold a permanent pool of water, we want to be sure we can monitor how much seeps through the dam and is lost to future consumption.”
The design work for the project was finished in fall of 2010. At the time of this article, Blumeris was overseeing the bid evaluations for the construction contractors that called for proposals on the design. The team hopes to award a construction contract this spring.
Other members of the team include Thomas Davidson (Geologist); Siamac Vaghar (Geotechnical Engineer); Ben Piteo (Civil Engineer) and Dave Descoteaux (Structural review along with Europe District). If all goes well, the project will be completed in the fall of 2012 and everyone in Nacala will be able to count on a glass of water anytime they want it.
| Date Taken: | 05.27.2011 |
| Date Posted: | 05.27.2011 12:15 |
| Story ID: | 71200 |
| Location: | NACALA, MZ |
| Web Views: | 110 |
| Downloads: | 0 |
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