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I've always been happy with the Alden team. Their technical skills, quality of work, and willingness to adapt is what makes them industry leaders.

Nat Sekhar

Environmental Services Professional

Recent Projects

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Alden was retained by the Northern Water Conservancy District (Northern Water) for the Hansen Supply Canal Poudre River Drop Structure Replacement Project. Alden was the prime consultant for the Project and provided complete structural and hydraulic engineering services, including hydraulic modeling for the design of the replacement drop structure and overall site improvements. The new structure included a stepped spillway, stilling basin, and retaining walls.

Alden performed Computational Fluid Dynamics (CFD) modeling of the existing structure and the proposed structure. The new structure is designed for a peak discharge of 1,500 cfs. Alden also performed 3D finite element modeling for the structural design. Alden collaborated with Northern Water staff to identify maintenance needs and preferences for the new structure. The stilling basin includes an access bridge, jib cranes, and stoplogs to isolate the structure for future maintenance and inspections. The existing site featured extremely steep slopes at 1V:1H with poor surface drainage. The final grading established stable slopes and improved surface drainage to keep water away from the new structure.

Details of the project included:

  • Concrete structure demolition, removal, and repair
  • New concrete stepped spillway, concrete stilling basin, and concrete retaining walls
  • Foot bridge with access stairs
  • Subsurface drain system and surface drainage improvements
  • Temporary construction cofferdam and dewatering
  • Site grading and access road
  • Trapezoidal channel restoration and riprap sizing

The project also required coordination regarding the environmental impacts to the Preble's mouse habitat and an adjacent eagle's nest. Design was completed in July 2019. Construction was completed in March 2020 with the first water flowing through the structure on April 1, 2020. 

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2020 H2O Project Award

The Poudre River Drop Structure Project was the recipient of The Colorado Contractors Association's 4th Annual H2O Awards. The Project won in the category of Open Concrete Flow Structures under $6 million. 

The overall Project Team included: 

  • Design Team – Alden and geotechnical subconsultant, Lithos Engineering
  • Client – Northern Water 
  • Contractor - Zak Dirt
 
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The newly constructed Poudre River Drop Structure along the Hansen Supply Canal
Civil Infrastructure
Poudre River Drop Structure Replacement

Alden provided structural and hydraulic engineering and CFD modeling to replace the Poudre River drop structure with a stepped spillway and stilling basin.

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Dam Remediation Using High and Low Mobility Pressure Grouting

Logan Martin Dam, owned and operated by Alabama Power Company, is a hydroelectric generation site located on the Coosa River in Vincent, Alabama. Since construction in the late 1960’s, ongoing remedial pressure grouting projects have targeted significant seepage flow reduction beneath the embankment dam which is founded on karst, a limestone geology characterized by underground aquifers, caverns, and the potential for sinkholes, particularly as seepage flow erodes the underlying limestone and continually changes its distribution. Alden and Alabama Power have partnered to design and construct a large scale enclosed pressure grouting test chamber (3’ wide by 3’ tall by 30’ long) and an associated test protocol to evaluate and optimize grout mix design performance in geo-materials that simulate the fractured, cavernous geology at Logan Martin Dam.

This first-of-a-kind test approach uses a small production scale grout plant to prepare and inject the high mobility grout mixtures into the test chamber. The test chamber is designed with discharge ports along its length to allow water initially occupying the test chamber—and subsequently grout—to be displaced as newly batched grout is injected. Throughout the grout injection process, pressure and temperature measurements within the test chamber, as well as discharge flow rate and discharge flow specific gravity measurements out of the test chamber, are used to monitor and evaluate grout dispersion characteristics within the chamber.  

Grout injection criteria used to govern test advancement and later termination includes displaced grout quality (i.e., displaced grout specific gravity relative to that of the freshly batched grout) and the internal test chamber pressure. After grout injection, various performance metrics are evaluated to quantify mix effectiveness. The normalized grout take, for example, evaluates the overall mix efficiency by relating the injected grout volume to the volume available within the geo-material for grout to occupy.

Since conception, updates to the test facility and protocol have been made to facilitate low mobility grout testing, as well as grout performance testing in the presence of water cross flow. Results from this ongoing research program are being used to reduce grouting cost through grout mix design and bore hole spacing optimization, while also improving dam safety by increasing knowledge on how grout penetrates rock fractures without in-situ excavation.

Contact us if you would like to learn more.

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Alden and Alabama Power have partnered to design and construct a first-of-its-kind grout performance testing chamber
Civil Infrastructure
Grout Performance Testing – Logan Martin Dam

An innovative large scale enclosed pressure grouting test chamber is being used to evaluate and optimize grout mix design performance at Logan Martin Dam

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Through funding made available by the U.S. Department of Energy, Alden conducted a series of studies to evaluate and optimize the design and operation of two modular and scalable fish bypass systems developed specifically to provide safe downstream passage of silver American Eels at hydropower projects. The goal of the studies was to address the need for biologically effective and less expensive downstream fish passage technologies for silver eels. The studies were developed specifically for this fish species and life stage due to population declines in many areas of its range and the potential for mortality to occur if eels migrating to the marine environment to spawn are entrained through hydro turbines during their journey to the sea. The large size and unique behaviors of silver eels have made it difficult for dam owners to implement downstream passage measures that are both biologically and cost effective, resulting in a need for new innovative technologies.

The studies conducted by Alden included a laboratory evaluation of the biological performance of the two bypass systems, a field evaluation of biological performance conducted with full-scale bypass systems installed at the intake of a small hydro project in New Hampshire, CFD modeling of the laboratory flume and field evaluation site, and a desktop assessment of the potential for application of each technology at hydro projects within the known range of American Eel and the expected benefits (i.e., biological and economic). Few organizations have the capabilities to conduct this array of technical studies, but Alden’s scientists and engineers have been using various combinations of these approaches and methods to develop and evaluate state-of-the-art fish passage and protection systems for nearly 50 years.

Assistance with the performance and completion of these studies was provided by Lakeside Engineering (bypass design and installation) and Blue Leaf Environmental (DIDSON acoustic camera and 3D acoustic telemetry services).

 

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The laboratory evaluation was conducted in a large re-circulating flume using the Klawa horizontal zig-zag eel bypass system and a vertical eel bypass system developed by Lakeside Engineering
Natural Resources & Environmental Planning
Modular and Scalable Downstream Passage for Silver American Eel

Read how Alden tested the effects of innovative downstream fish passage technologies with lab, CFD, and field analysis. Funded by the Department of Energy

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Dive in to learn more about the Alden advantage

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Technical Paper
Air Ingestion and Transport Testing in a Rotating Drum Raw Water Strainer
Download
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Technical Paper
Hydraulic Modeling of Air-Entraining Vortex Formation During Flow Withdrawal from Water Storage Tanks
Download