Holmberg Technologies, Inc.
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Our Clients Success Stories
A Proven Alternative to Beach Nourishment
The issue of beach and bluff erosion of our coastlines continues to be a vexing and troublesome problem. Most attempts to protect these fragile landforms, such as walls and revetments of infinite variety, have protected bluffs temporarily, but are a documented cause of accelerated erosion rates upon adjacent properties.
Beach nourishment is a popular alternative to hardened shore protection systems. The width and height of the beach platform is enlarged by the application of dredged materials without adding structures to the beach. Since dredging of harbor inlets is a regular necessity, deposition of the dredged material on the beach (supplemented as needed by other deep water sources) has been seen by many as a win-win solution. Unfortunately, the gains from beach nourishment are documented to be very temporary, and the pre-existing ecosystem is smothered by large volumes of typically silty sediment.
A unique shore protection system has shown great promise in stabilizing previously eroding shorelines. Undercurrent Stabilizers (as patented and installed by Holmberg Technologies of Whitehall, Michigan) have been placed in a large number of locations over the last two decades. Monitoring surveys at these installations indicate that the traditional shortcomings of shore protection systems can be overcome. The survey data shows that gains in beach width and height are achievable, and that such gains are maintained over time.
Undercurrent Stabilizers are shore-perpendicular low-profile structures that are placed in configurations similar to that of traditional groins. However, the differences between stabilizers and groins are profound in both geometry and effect. Stabilizers consist of concrete filled, geotextile tubes. The rounded shape of stabilizers reduces the amount of wave reflection and turbulence created when significant waves reach the shore. Wave reflection and turbulence are primary reasons that structures such as walls, groins and revetments damage adjacent property and scour their own foundations.
The other unique geometric aspect of stabilizers is that they follow the bottom profile and taper down in size as they extend into the water. This is opposite of the geometry of groins that become larger in size and follow the water surface as they extend lakeward. The primary utility of tapering and hugging the bottom is that these structures are essentially permeable with respect the littoral (longshore) movement of sediments. Traditional groins are impermeable to littoral drift. The permeability of stabilizers is a reason that monitoring surveys have found no downdrift losses of beach or bluff.
A favorable effect of the low-profile geometry of Undercurrent Stabilizers is that they force additional shoaling of waves before reaching the beach. This, along with their less reflective nature, creates a low energy strand of beach. Since fast water picks up sand and slow water drops its load, the low energy beach will be the most likely place where deposition of suspended sediment load will occur.
Importantly, Undercurrent Stabilizers are successful at retaining the natural slope of the beach platform. Scouring at and adjacent to traditional structures creates an artificially deepened nearshore, which subjects those areas to greater wave energy. Scouring also occurs on natural and artificially nourished beaches. The material loss caused by wave action begins at the trough between shore and bar, progressing shoreward. If the storm duration is long enough for this deepening to reach the shore, losses of the beach platform and bluff occur. The orientation of stabilizers resists this deepening by helping retain the natural slope of the beach and nearshore. Professionals are finding in many fields that the more a man-made solution imitates natural forms, the more permanent and positive will be the results.
Because Undercurrent Stabilizers are often resisted by regulatory officials, monitoring surveys of permitted installations and demonstration projects have been performed. The most thorough investigation of this system is being performed by Western Michigan University. Included in two studies are surveys of control sections of similar beach for comparison. This is important for proper evaluation of effects, due to the plethora of other shore protection structures that are often found in the vicinity of any given installation.
At the Duck Lake outlet to Lake Michigan, severe and continued erosion has jeopardized an existing county road. After a number of failed attempts, a large-scale armoring of the road bank with a rock revetment was performed. As part of the plan to minimize the downdrift damage caused by this quarter-mile long revetment, an Undercurrent Stabilizer system was placed immediately to the south. In his interim report of the monitoring surveys at this location, Dr. David A. Barnes of WMU stated the following:
"The Undercurrent Stabilizer system has caused no negative impact at the installation site relative to an analogous control site. . . . Volume change analysis presented in this report suggests that the Duck Lake outlet revetment continues to influence near shore morphologic change in the area but that this negative impact is, at least, partially mitigated by the experimental erosion control structure. . . . At this time the Undercurrent Stabilizer system installation must be considered a nominal success in light of the proximity of the installation to an extensive rock revetment and the likely negative impact of this structure on the adjacent, down drift beach. Volume gain during the survey period along a profile line approximately 600 feet south (down drift) of the structure is noteworthy. . . . "
In his report of May 8, 1995 about an installation along Lake Michigan at Orchard Beach, Dr. Barnes stated: "Consistent profile volume gain measured in the vicinity of the experimental shore protection structure (relative to a regional trend of profile volume loss determined from an analogous control site) and significant foreshore/backshore ("beach") accretion with no apparent negative impact down drift must be viewed as "success" in almost any context."
An Undercurrent Stabilizer system was installed in 1995 at the Westgate residence on Lake Michigan (see photos).
This installation has been surveyed twice each year since then. The Michigan Department of Environmental Quality located survey transects at the installation and downdrift, in the zone most likely to be impacted. This beach is notable, as no other shore protection structures are in the vicinity of the project. In a report dated September 8, 1998, David L. Schultz, PE, a consulting hydrologist located in Montague, Michigan stated: "The growth in beach width from 1996 to 1998, as indicated by the location of the 581.5 elevation contour was significant throughout: 44’ lakeward at profile 1-1, 47’ lakeward at profile 2-2 and 19’ lakeward at profile 3-3, located 400’ downdrift of the most southerly end of the Undercurrent Stabilizer location. . . . The growth in beach elevation follows similar patterns. . . . . . The gain of 401,100 cubic feet of sand at and downdrift of the installation site is very significant. . . . . .If the results of the monitoring surveys continue to indicate such unqualified success at reversing the commonly accepted trend of beach and bluff retreat, and a method of gaining beach height and width does exist, attitudes at the academic, state and federal levels must be adjusted to account for this variance between present coastal theory and the documented facts of these monitoring surveys."
Other evidence is available. Sylvan Beach, Michigan was studied over a longer time span.
Changes from 1983, when an Undercurrent Stabilizer system was installed, and 1993, when the survey was replicated, showed long-term effectiveness of the technology (see photos). A net gain of 125,800 cubic feet was calculated at the study area. The average movement of the shoreline, set at the 579.5 elevation contour, was 7.8 feet lakeward. Zones where beach width and elevation increased were at and south (downdrift) of the stabilizers. It must be remembered that volume gains are even more significant in light of the commonly accepted "fact" of beach and bluff recession. At this location along Lake Michigan, the bluff recession as calculated by the State of Michigan is 12.6 feet over 10 years.
An Undercurrent Stabilizer system was installed for the Allegan County Road Commission, due to the undermining of a road along Lake Michigan. The WBDC Group, consultants located in Grand Rapids, Michigan, performed an evaluation for the road commission. Their 98 page study evaluated many alternatives, including revetments, stabilizers and even relocating the road. The consultant recommended, and the road commission installed, Undercurrent Stabilizers. To date, the road has not been re-eroded, and no downdrift portions of the county road have been eroded due to this installation.
The documented, positive performance of Undercurrent Stabilizers is a result of their geometry. Their low profile minimizes aggravation of the wave climate during storm events, especially when compared to other conventional shore protection options. The effect is to create a low energy beach which reduces sediment entrainment and encourages deposition. Also important is that stabilizers encourage retention of the natural beach slope, unlike walls and revetments, reducing the severity of scour during large storm events. Most importantly, Undercurrent Stabilizers indicate that beach and bluff protection can be achieved over the long-term, unlike beach nourishment. The fact that all studies to date have found no negative effects downdrift of Undercurrent Stabilizers makes this technology a superior alternative to all other shore protection systems available today.
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