Category: Wave Attenuator
Location: Payette Lake – McCall, Idaho USA
Type of Project: Wave Attenuator
Products Used: Hazelett Elastic Mooring Systems
Details of Installation: Reduced loads and anchor count.
Challenges Overcome: Large structural loads.
Collaborators: Kropf Industrial

The Mile High Marina project is a high-load wave attenuator installation on Payette Lake in McCall, Idaho, where the challenge was not simply to add more floating infrastructure but to stabilize a long, heavily loaded protective edge in a basin exposed to long fetch, seasonal water-level change, winter ice, and large structural loading. Public planning records for the Mile High Marina expansion show that the marina sought to replace its existing log breakwater with wave attenuator infrastructure as part of a broader expansion that would add approximately 90 boat slips and more than 1,000 feet of public boardwalk. That matters because the wave attenuator at Mile High Marina is not just a protective accessory. It is also a functional marina edge carrying public access, side-tie use, and the loads that come with a commercial dock system.

The engineering context is unusually well documented in the public design package. The attenuator design sheet for the Mile High Marina Wave Attenuator System identifies a proposed 10-foot-wide by 450-foot-long wave attenuator walkway dock, tied into existing and new dock walks, with an 80-foot ADA aluminum gangway rated for a 75 pounds-per-square-foot minimum live load. The same design package shows seasonally varying water depths ranging from roughly 40 to 70 feet in the outer portions of the marina, which helps explain why a high-load mooring approach matters here. Deep water, fluctuating lake levels, and a long floating structure combine to make anchoring geometry, line behavior, and shock-load control central design issues rather than secondary details.

The exposure conditions at Mile High Marina are also much harsher than a casual inland-lake project description might suggest. The public design criteria state that the marina basin is exposed to more than 2 miles of open-water fetch from the north, 1.5 miles from the northwest, and 1.2 miles from the west. Predominant daily winds are listed in the 8 to 20 mph range with gusts of 30 to 40 mph, while occasional high wind events from the north-northwest have reportedly reached 60 to 70 mph. On top of that, Payette Lake water levels vary seasonally by about 8 to 10 feet, and winter conditions can include 8 to 12 inches of ice plus 36 to 48 inches of snow accumulation on the lake surface. In other words, the Mile High Marina installation had to be engineered for a floating structure that would see both significant environmental forcing and large changes in geometry over the course of the year.

That is where Hazelett Elastic Mooring Systems and expertise become technically important. Hazelett’s elastic rode system maintains constant tension, reduces point loads, and allows the structure to move more gently instead of surging until a rigid chain or cable system snaps tight. A Hazelett manufatured single Elastic Rode is tested to withstand more than 20 kN of force and can repeatedly elongate more than 200 percent before returning to its original length. In a wave attenuator application, that type of controlled elongation is valuable because it changes the way energy is transferred into the structure and its anchors. Rather than concentrating short-duration shock loads at a few connection points, the mooring system can absorb and redistribute energy over time. That dynamic response aligns directly with the project brief, which notes reduced loads and a reduction in anchor count as key outcomes of the Mile High Marina system.

Kropf Industrial was a project partner, and Kropf’s public marine materials show that the company manufactures steel-tube floating breakwaters designed for harsh environments, heavy ice conditions, long service life, and low maintenance. Public reporting on the Mile High Marina expansion likewise notes that the wave attenuator would use steel plates hanging below the dock structure, reinforcing that this was a heavy floating protection system rather than a lightweight recreational float. In a hybrid setup like this, the floating attenuator structure and the mooring system have to be treated as one engineered system. The structural mass and hydrodynamic behavior of the attenuator determine the mooring demand, while the mooring system determines how those structural loads are moderated before they reach anchors, gangway connections, and dock hardware.

The public performance criteria make the technical demands even clearer. The design package demands the attenuator  be engineered to withstand a 4-foot long-fetch wind wave and to mitigate a typical wakeboard-boat wake generating a 2-foot wave at a 2.2-second period, with an exposed dock-face force of 300 pounds per linear foot and a maximum 20 percent coefficient of transmission to the wave beyond. That is the kind of language found in a true performance-driven marina project, not a generic dock installation. For the Mile High Marina project, Hazelett’s role was to help stabilize a large floating attenuator in a setting where environmental exposure, large structural loading, and varying water levels would otherwise drive-up anchor demand, maintenance burden, and fatigue on the system over time.