Revetment protects delicate Louisiana shoreline
Wave-induced erosion has long plagued Lake Borgne in eastern Louisiana, wearing away sections of the shoreline at a rate of nearly 8 feet per year. The brackish lake’s shoreline forms part of the southern boundary of the East Orleans Land Bridge and separates Lake Borgne from Lake Pontchartrain, making it important for storm surge and wetlands protection.
To prevent Lake Borgne from breaching the Land Bridge and merging with the Intercoastal Waterway, a 7.8-mile revetment is being built as part of the Orleans Land Bridge Shoreline Protection project. The project will also re-establish the lake’s perimeter and stop marsh loss and further erosion of the shoreline.
This shoreline protection is being constructed using geogrid marine mattresses filled with approximately 84,000 cubic yards of concrete debris recycled from demolition of the I-10 Twin Span Bridge that was damaged during Hurricane Katrina. Because of the size of the recycled concrete materials that were available, project engineers ruled out an offshore breakwater at the onset of the project, opting instead for a revetment placed directly on the shoreline.
Armoring the shoreline against wave-induced erosion is projected to stop the loss of as much as 110 acres of marsh in the area.
Soft marsh soils and lack of access created several obstacles for project engineers. A geogrid marine mattress revetment had never been used on soft marsh soils such as the soils present on Lake Borgne’s shoreline. While other products are used in similar soil conditions, engineers determined the other products could not withstand the waves found along the shoreline.
With this in mind, project engineers turned to Tensar International and the company’s Triton Marine Mattress System to complete the project. An 18-inch mattress was chosen based on the maximum wave height, anticipated storm surge, tidal range, density, and porosity of the crushed concrete as well as foundation properties.
The revetment was constructed in 18 sections, creating gaps at bayous, tidal channels, and ponds that occur along the shoreline to maintain some flow with the marsh interior and allow access to the marsh by marine organisms. Each section will terminate with riprap to prevent failure from scouring. Anticipated settlement of the revetment during the 20-year life of the project is expected to bring the top elevation of the revetment flush with the existing marsh.
Aside from the soil challenges, access to the site also was an issue. Because no construction equipment was allowed on the shoreline, all of the mattresses were filled offsite and placed onto a barge that brought them to the shoreline.
As the project nears completion, engineers are hopeful for the future of the shoreline. The bearing capacity of the soil and the elevation of the breakwater will be key to the long-term success of the project. Based on geotechnical analysis, the revetment structure should be supported by the soils and the height will protect the landward marshes for the entirety of the 20-year project life.
By Jeff Fiske, Coastal & Waterways Industry manager, Tensar International Corporation
Surveying 1,824 manholes for GIS database
KS Associates, a civil engineering and surveying firm based in Elyria, Ohio, has completed the Interceptor Surveying and Mapping (ISM) Project for the Northeast Ohio Regional Sewer District (NEORSD). The project involved surveying 1,824 manholes throughout NEORSD’s expansive sewer network to collect and document current data regarding the locations and physical characteristics of sewer interceptor manholes for inclusion into NEORSD’s GIS database. KS Associates performed the services as a subconsultant to lead design firm AECOM.
NEORSD owns and maintains a network of sewer interceptors comprised of 127 miles of pipe, many of which were constructed prior to the district’s formation. The interceptors convey sewage to three wastewater treatment plants and minimize the amount of pollution entering Lake Erie and the Cuyahoga River. The ISM project is part of NEORSD’s initiative to develop and maintain an extensive GIS database containing the physical characteristics of the district’s entire sewer system. The ISM project aims to ensure that manhole coordinates and system connectivity of the interceptors are represented consistently and accurately, providing reliable information for the district’s GIS, Operations and Maintenance, and other departments.
KS Associates’ role on the project was to determine locations and elevations of manholes that provide above-ground access to the interceptors. This included obtaining attribute data such as pipe sizes, inverts, and other physical features. Quality control procedures were implemented to provide manhole location and casting elevation data to achieve 0.2-foot accuracy. The assignment required deployment of multiple survey crews over seven months and specialized services of confined-space entry for approximately 420 manholes.
Information provided by KS Associates
Mississippi utility enters P3 for wastewater treatment
The Desoto County Regional Utility Association (DCRUA) based in Hernando, Miss., entered a public-private partnership (P3) with Severn Trent Services. In late 2012, Severn Trent took responsibility for the complete operation, maintenance, and management of the association’s system of nine wastewater treatment plants in the northwestern part of the state. DCRUA plants serve approximately 20,000 residential, commercial, and industrial customers in Hernando, Horn Lake, Olive Branch, Southaven, and Walls, Miss.
The plants’ design treatment capacity is 8.4 million gallons per day (mgd) with an average capacity of 6.9 mgd. When a new treatment plant in Johnson Creek, Miss., is brought online in April 2013, replacing four older, existing plants that will be decommissioned, the combined design capacity of the DCRUA plants will total 10.2 mgd.
Award-winning retaining walls
Redi-Rock International announced the winners of its annual Rocky Awards for projects completed in 2012. The awards honor the best Redi-Rock walls built in the categories of Residential, Freestanding, Water Application, and the People’s Choice Award, which was chosen by the public in an online vote. More than 120 Redi-Rock manufacturers across North America and Europe competed for the awards.
Signature Stone, Greeley, Colo., received "Residential Wall of the Year" for the Ledgestone texture gravity walls installed at a 21,000-square-foot home. In early 2012, the homeowners needed to replace several failed, small-block mechanically stabilized earth (MSE) walls along the driveway that provided primary access to the house. The owner and engineer chose Redi-Rock to minimize the required excavation work.
Grand Rapids Gravel, Grand Rapids, Mich., received the "Freestanding Wall of the Year" award for the Lubbers Stadium Renovation at Grand Valley State University. The renovation included dropping the elevation of the football field by 6 feet, which required 9,200 square feet of retaining and freestanding walls.
Redi-Wall, based in Brighton, Mich., was awarded "Water Application Wall of the Year" for the Caseville Resort & Marina project, which included replacing a failing dry-cast retaining wall with a 26.5-foot-tall Redi-Rock Cobblestone gravity wall. Construction of this project was complicated by houses located directly above the failing wall and the fact that the new wall had to be constructed from an 8-foot-wide boardwalk below the new wall. The ability to build the new wall without geogrid made this project possible.
Paxton Precast, Dalmatia, Pa., was awarded the "People’s Choice Rocky Award" for a series of walls at the Sunbury Riverfront. This project included 17,000 square feet of walls to help stabilize the banks of the Susquehanna River, halt further erosion, and prevent flooding in the nearby downtown area (see CE News, January 2013, page 52). The walls also helped create a riverfront park.
Information provided by Redi-Rock International
Enterprise asset management
Four times a year, the City of Surrey, B.C., Canada, conducts "sector checks" during which field crews inspect assets along the city’s road network, recording any issues along the way. To better manage this time-intensive task, Surrey deployed Cityworks in 2006 to manage its day-to-day infrastructure maintenance and operations. Even though recording and tracking citizen requests and work orders was a primary driver, interfacing the application with the city’s finance, human resource, and warehousing systems was equally important to improving asset life cycle management.
Leveraging data from Surrey’s GIS (Esri ArcGIS), Cityworks provided the tools necessary for better maintenance management of critical assets and to a broad range of employees throughout the city. With the ability to see their world in an accurate and consistent map view, Surrey employees were able to better understand the characteristics and relationships shared by various assets. Clicking on an asset, field staff now have instant access to detailed information such as manufacturer, material, and condition of an object, as well as the ability to view the entire maintenance history of any object, interact with current work orders, or respond to service requests.
A significant part of the city’s maintenance management strategy was to provide state-of-the-art asset management capabilities across the enterprise – in the office and in the field. Field crews were equipped with Cityworks on lightweight Panasonic Toughbook computers with real-time access to the city’s GIS asset and land information. Detailed asset information, service requests, and work orders are all visible in real time on accurate digital maps. Up-to-date information flows seamlessly among field crews, supervisors, dispatchers, and management.
Pick lists built into user-defined templates reduce typing requirements so that field workers can record information easily on the spot. The map-based interface has replaced costly, printed map-books. With the city’s rapid growth rate, paper maps quickly become outdated.
"With Esri’s GIS capabilities built-in, Cityworks gives our crews instant access to satellite and aerial imagery, helping them locate the infrastructure they are after a lot faster and a lot easier," said Gord Simmonds, project supervisor and computer applications, City of Surrey. "This has been especially useful for inspections in the rural areas of the city."
Information provided by Azteca Systems Inc.
Surrey launches service request app
The City of Surrey launched a new mobile phone app designed to make it easier for residents and businesses to submit service requests and report issues. The app allows people to take photos and report concerns such as potholes, illegal dumping, localized flooding, graffiti, and other issues. The location of the problem is pinpointed through the smartphone’s built-in GPS, the service request is automatically entered into the city’s workflow system, and the user can easily check for updates on the status of the request.
Blending green and grey infrastructure
The San Francisco Public Utilities Commission (SFPUC) selected MWH to provide planning, design, and construction management services for the Central Bayside System Improvement project. The contract was awarded as a joint venture with URS, and is a key component of SFPUC’s $6.9 billion Sewer System Improvement Plan (SSIP). The SFPUC has identified three primary goals for the project: provide reliability and redundancy; upgrade the aging infrastructure for seismic protection; and stormwater management by incorporating green infrastructure for community benefits.
Of San Francisco’s 49 square-miles, approximately two-thirds of the total drainage area drains into San Francisco Bay while the remainder flows into the Pacific Ocean. MWH/URS will identify a combination of "green" and "grey" solutions to manage combined sewage discharges and minimize flooding within these urban watersheds. Green infrastructure may include permeable pavement, bio-retention planters, rain-gardens, green roofs and other options as warranted in different areas of the city. Combining these green measures with traditional grey solutions such as pumping, storage, and conveyance offers improved environmental solutions at lower costs.
"It’s only fitting that San Francisco Public Utilities Commission, which serves a city known for its environmental leadership, should take the state’s first steps toward blending green and grey solutions to manage stormwater," said Bruce Howard, Americas president of government and infrastructure for MWH. "A deep experience and knowledge of tunneling and sewer systems will help MWH update the city’s infrastructure in a way that minimizes its environmental impact while preparing for the climate of the future."
The project will address alignment of a conveyance tunnel to carry wet and dry weather flows from the north and central part of the city to the Southeast Treatment Plant. The project will be planned, designed, and constructed to meet six major goals set by SFPUC:
- Provide a reliable, resilient, and flexible system that can respond to catastrophic events such as earthquakes and severe rainstorms.
- Integrate green and grey infrastructure to manage stormwater and minimize flooding.
- Provide benefits to impacted communities.
- Prepare the system for the effects of climate change.
- Achieve a balance between economic and environmental stability.
- Minimize rate impacts on area residents.
San Francisco also is planning eight "Early Implementation Projects" (EIPs) located in eight urban watersheds in the city to evaluate the effectiveness of green infrastructure in managing stormwater during the wet season. Results will be used in planning and design of similar facilities as part of SFPUC’s SSIP.
Information provided by MWH
San Diego Water Authority Board approves seawater desalination project
The San Diego County Water Authority’s Board of Directors voted to approve a landmark agreement to purchase as much as 56,000 acre-feet of water annually from what will be the nation’s largest seawater desalination plant in Carlsbad, Calif. The plant is expected to start producing as many as 50 million gallons a day (mgd) in 2016. The board approved a 30-year Water Purchase Agreement with project developer Poseidon Resources. The reverse-osmosis facility will make local water supplies more reliable by reducing the region’s dependence on water from the Colorado River and the Bay-Delta that is vulnerable to droughts, natural disasters, and regulatory restrictions.
After securing financing, Poseidon and the Water Authority will commence construction of the desalination plant next to the Encina Power Station and a 10-mile pipeline that connects it to the Water Authority’s aqueduct in San Marcos. By late 2015, the Carlsbad facility is scheduled to begin start-up testing. Commercial operations are expected early the following year. Poseidon’s plant will produce 48,000 to 56,000 acre-feet of desalinated seawater annually, roughly one-third of all water generated in San Diego County. Two Water Authority member agencies, Vallecitos Water District and Carlsbad Municipal Water District, will purchase a combined total of 6,000 acre-feet of the desalinated water as their own local supply under separate agreements with the Water Authority.
The Water Authority will not have to make payments to Poseidon until the company produces water that meets predetermined quantity and quality standards. In addition, Poseidon is responsible for all cost overruns during construction. After 30 years of plant operation, the Water Authority has the option – but not the obligation – to purchase the plant for $1. The agency also has the right to buy the facility after 10 years, though it isn’t required to do so.
Under the Water Purchase Agreement, the total price for the desalinated water – including related upgrades to the Water Authority’s pipelines and treatment plant – is projected to start between $2,041 and $2,290 per acre-foot (in 2012 dollars), depending on how much is purchased annually. The purchase agreement says the price of water from Poseidon can only be adjusted for inflation and certain predefined circumstances.
Information provided by San Diego County Water Authority
Submit news and photos of planned, ongoing, or recently completed projects and research to Bob Drake at firstname.lastname@example.org.
In June, "Project Notes" will focus on stormwater and site planning; the July section will highlight water/wastewater and transportation projects.