Holmberg Technologies, Inc.
7161 Brookhaven Terrace
Englewood, FL 34224
Phone: 941-468-8802
dholmbrg@aol.com
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Coastal Restoration Technology

photo photo
Prior to treatment with Undercurrent Stabilizers. The beach had been destroyed by nearby navigational channels. Seven years after treatment, the beach continues to expand naturally.

It is surprising for many to learn that coastal engineers (the Army Corp., etc.) and coastal geologists fundamentally disagree about how beach systems actually work. A recent article in Smithsonian, for example, reports that "whenever coastal geologists and coastal engineers talk about the shore, they seem to be describing different places." The disagreements are basic, especially concerning the natural pathways sand takes to and from the beach. Geologists have demonstrated, for example, that offshore/onshore circulation cells are central to beach sedimentation in many areas. Coastal engineers, however, do not acknowledge these well-established findings.
(see Geological Evaluation of Coastal Engineering Theory.)

Undercurrent Stabilizer Technology is the only beach restoration system whose operand principles coincide with geological findings about natural beach sedimentation. The system has been developed and patented by D.L. Holmberg, who has successfully treated approximately 100 sites along Great Lakes and ocean shorelines.

In describing system performance, it is helpful to understand that beaches around the world have been generally elevating and expanding seaward in recent geologic history. Most coastal erosion today is consequently unnatural - largely the result of a multitude of navigational channels (artificial submarine canyons) which have been cut into modern shorelines. Navigation channels are bracketed with jetties, so called because they compress flows and make water "jet". Unfortunately, this self flushing channel design also flushes adjacent beaches to sea. A single navigational inlet progressively impacts many miles of shoreline.

Natural, undisturbed shoreline functioning is now best discerned by looking back in time. Scientists have determined that barrier islands, for example, germinated and grew out of the sea about 4000 years ago. At that time the rate of sea level rise was about what it is today. Despite consistent sea level rise over the past few millennia, most beaches and barrier islands steadily expanded seaward until recent times. Clearly defined beach ridges are left behind as beaches grow seaward. Through carbon dating and other means, the succession of beach ridges are studied much like growth rings in trees.

Infrared photo of a typical barrier island displays more than 180 beach ridges, representing the island's "growth rings."

Geological studies demonstrate that for a majority of sandy shorelines, offshore sand has been the primary source of beach growth. It is also clear that storms are at the heart of historic beach formation in most areas. The succession of beach ridges parallel to the water line are the result of onshore flow of storm driven sand. Most barrier islands are little more than a series of beach ridges which have prograded seaward to form what is called a beach ridge plain.

Intensive channel dredging and, secondarily, the damming and/or mining of river sediment, has reversed natural patterns of beach growth along many coasts over the past century or more. As unnaturally-induced erosion steepens beach geometry, nearshore turbulence progressively increases over a widening area (deeper nearshore water supports greater wave and current energies - which further deepens the nearshore, allowing still greater waves and currents into the nearshore, etc. etc). In-coming sand now meets turbulent nearshore barriers. This prevents offshore material from moving into subaerial (dry) beach formation.

The geometry of the nearshore beach profile (the degree of downward slope) largely determines whether storms cause net accretion or net erosion in many areas. On unnaturally steepened beach profiles, storms have generally become destructive where once they fostered beach growth. Because net yearly erosion has been widespread for decades, the coastal engineering community commonly defines the trend as natural and inevitable.

Undercurrent Stabilizer Technology neutralizes the impacts dredged channels have on sandy beaches. This has proven to routinely reverse unnatural erosion. The technology consists of modular, hydrodynamically shaped forms which are cast in place on the nearshore seabed, generally at right angles to the shoreline. Problems normally associated with erosion control structures are avoided through tapered, low-relief shaping, special landward tie-backs and patented filter fabric foundations.

The low-profile, flow-through array (sometimes simply called "speed bumps") progressively baffles unnatural nearshore turbulence, allowing sand to fall out of suspension in quieted waters within and adjacent to the treated area. Local shoaling progressively decreases remaining nearshore turbulence (beyond decreases induced by the system itself). As the nearshore progressively shallows out in response to the accretion template, less and less wave and current energy is supported to drive arriving sand from the treated area.

Upon treatment, unnatural erosion ceases and resedimentation begins, often with surprising speed. The accretion template itself is generally buried by rising sand levels as the nearshore beach profile becomes inherently accretional. Adjacent shorelines benefit because an unbounded feeder beach is established. A long-term university study of numerous installations concludes: "Consistent profile volume gain measured in the vicinity of the Undercurrent Stabilizer system (relative to a regional trend of profile volume loss) plus significant foreshore/backshore beach accretion with no apparent negative impact down drift must be viewed as success in almost any context."
(see Independent Monitoring)

Florida beach prior to treatment
The beach 6 years post treatment

Since beach systems are largely governed by non-linear processes, another way of viewing Undercurrent Stabilizer performance is in the language of non-linear dynamics. Self-reinforcing feedback loops are a central element of non-linear systems. Small changes in such systems may "snowball" into counter-intuitively large changes. The weather is a well-known non-linear system. A squall in Africa, for example, can amplify into an Atlantic hurricane through positive feedback mechanisms in the atmosphere.

Where coastal systems are concerned, the more a beach profile erodes, the more prone it becomes to further erosion. Deeper water supports greater wave and current energy - which increases erosion, further deepening the nearshore, etc. (a positive feedback loop with negative consequences). This is the condition of most shorelines today. On the other hand, the more the beach profile accretes, the more efficient it becomes at fostering further accretion (a positive feedback loop with desirable consequences).

The technology is also designed to supply immediate protection to threatened buildings upon installation but prior to beach profile elevation, which may take a year or more depending on available storm energy and the size and proximity of local sand sources. In general, ocean shorelines respond more quickly to treatment than do those on the Great Lakes. There is more sand in the ocean system and more of the kind of (long period) waves to move sand into the beach zone.

The California Coast, El Niño, and Sand Management

The North American continent has been slowly drifting westward for millennia. The Eastern Seaboard trails behind the land mass with a wide continental shelf in its wake - increasing opportunities for eastern beaches to source sand from offshore areas.

Along the leading edge Western Seaboard, the offshore shelf is narrow with relatively limited sand supply, not unlike beach systems in the Great Lakes.

In the Eastern U.S., studies show that offshore sand has been the primary source of beach sedimentation. In the West, beach sand is sourced largely from longshore areas, though onshore/offshore exchange can be significant.

On the energetic, relatively sand-poor western coastline, studies have shown that the very existence of sandy beaches is possible only because the actual rate of longshore sand transport is but a fraction of the potentially high rate of transport. The potential transport rate is reduced by resistant geology of all kinds - bottom piercing substrate, outcroppings, headlands, submerged rocks, etc., which slow the transport of sand to loss points (submarine canyons which intersect the shoreline).

Undercurrent Stabilizer Technology is a sediment management system designed to mimic beneficial geology for different types of eroding coastlines. The system has performed effectively and without undesirable side-effects both on shorelines with wide offshore shelves, as in Florida, and where the offshore shelf is narrow and beach sand is sourced predominantly from longshore areas.


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