Sand Supply


There is a natural movement of sand along the shores of all the Great Lakes called the littoral drift. Sometimes called the river of sand, it flows under water slightly off shore. However, the direction varies depending on the location of the reach of shoreline. It is always inboard of the depth of closure which is the depth of water, beyond which wave energy can not reach the bottom to deliver the sand toward the water's edge.

The GLC targets sand supply because the natural littoral drift is vulnerable to human decisions such as structures perpendicular to the shore. It is often interrupted, and when it is, sand accretes on the up drift side. On the down drift side, the beach is reduced or destroyed. If obstructions are large enough, the river of sand is also diverted out beyond the depth of closure.

Navigation structures such as harbor piers that are invariably constructed and owned by the Federal Governments are large enough to cause permanent damage. Sometimes these structures are commercially owned by power companies.

Only a small portion of the interrupted sand accretes on the beach up drift of piers, but huge quantities have been diverted out into the lake beyond the depth of closure and thus lost to the beach forever.

These piers date back to the 1860's when most were constructed of wooden cribbing that offered navigational protection at the mouth of the harbor but still allowed the natural littoral drift Of sand. Yes, the Government knew early on that solid piers would cause erosion problems down drift, they just did not know how long the process would take. It was not until the later part of the last century that sheet piling was added to these piers so that the harbor entrance would not fill up with sand. That is when the interruption really started big time.

The United States Government recognizes their responsibility through section 111 of the Rivers and Harbors Act of 1968 in which Congress required the Army Corps of Engineers [ACOE] to quantify the degree of interruption in terms of cubic yards of sand interrupted per year. Congress then authorizes but does not require the ACOE to replenish the amount of sand thus removed from the littoral drift. In all it's goodness, the ACOE does sometimes replenish threatened reaches, but only after the annual budget override has been assured and appropriated funds are available. This always happens at the end of the fiscal year in the fall, and with almost no warning to even the affected municipality. It is impossible though GLC has not tried under FOIA, to obtain any timely information about ACOE replenishment plans.

Another fear of the GLC targets a new philosophy that is emerging from a current study of damage potential that uses Lake Michigan as a model. This theory holds that bluff erosion is a major source of sand supply to the beaches. If a property is protected by a retaining wall, as many are, this source of sand is blocked.

Under this theory, the ACOE is considering a penalty of 2 cubic yards of sand per year per lineal foot of wall to replace the quantity that would have occurred through natural erosion, had the wall not been built. The GLC successfully held off a proposal to this effect in the year 2000 with legislative pressure and many letters from members, but the delay is probably only temporary. GLC frustration is fueled by the hypocrisy of the Government in ignoring the enormous quantity of sand diverted and lost which has the same effect as the elimination of erosion.

The lake Michigan Potential Damages study [LMPD] conducted by the ACOE produced this map of the coast of Ottawa and Allegan Counties in Michigan. It concludes that 73% of erosion damage is due to the diversion of sand supplies by harbor piers.

sandsediment image

Using technology now available, the GLC calculations suggest that 89% of erosion damage is caused by interruption of the natural drift by government harbor piers. In either case, the effects of shore protection are minimal compared to dramatic starvation by navigation structures.

The ACOE thus far seems enmeshed in the process of predicting potential damage rather than developing methods to prevent losses while the GLC believes that 100% mitigation is more economical than the cost of erosion damage.



Erosion Facts!

Researchers such as Prof. Edward Hansen of Hope College and Dr. Alan Arbogast of Michigan State, have investigated dune history and found that after over 1000 years of stability the dunes have again become active within the last 500 years.

The activity is described as resulting from dune undercutting by wave action and 14 of the sites have a time frame established by carbon 14 dating that is consistent with the building of the navigation structures along the west coast of Michigan.

The photographs to the right (Holland, Frankenmuth, and two of St. Joseph) show evidence that river sediments and beach sediments are being diverted to deep water where they are lost from the shoreline sediment supply. Note that at St. Joseph the first picture in color show sediments coming from the north being diverted while the second photograph in black and white show sediments coming from the south also being diverted to deep water.

Calculations following the procedures described in the Coastal Engineering Manual, developed by the U.S. Army Corps of Engineers, determined that expected bluff erosion rates should be far less than the observed erosion rates.

We have now come to the point where the preponderance of evidence supports the hypothesis that the principal cause of erosion is due to the harbor structures.

erosion pic 1
erosion pic 2
erosion pic 3
erosion pic 5