It's difficult to explain the Great Lakes fully to those who have not spent time near the shore of twenty percent of the fresh water on earth.
The system consists of five lakes which drain into each other from highest to lowest. The uppermost is Lake Superior, because it is the highest, not because of an attitude problem.
The next are Lake Michigan and Lake Huron which are one lake divided by the lower portion of the state of Michigan. This means that the Lakes share the same water level since they are connected without restriction.
Lake Erie is next and then Lake Ontario.
These lakes were formed by glaciation which excavated the lakes only about 20,000 - 30,000 years ago which by geological standards is very recent.
The area of the Great Lakes was once an ancient sea and has varied geology that can be anything from Precambrian basement rock to pockets of loose marine sand. Clay is often found on the southern end of the lakes.
The problem is that the lakes are young and still settling.
This is not a problem in times of high water, but now as we have reached a new record low in January of 2013 the problems are stacking up for vessel and facility operators.
This is affecting every aspect of maritime business, from recreational providers to visiting seagoing ships.
The problem is that the fairly loose and mobile shoreline is breaking down and settling into working ares. The lack of snow cover throughout the winter increases sedimentation by wind erosion in addition to exposing the parched soil to the first heavy rains of the year.
For reasons mostly based on finances and apathy we have neglected our maritime infrastructure for the past fifty years and many of these structures are failing. Often this failure is below the surface so the frightening sight of failing pilings and walls is now coming into view.
No significant dredging projects have been underway in the past several years because of budget cuts.
Now many, many small operators are faced with the loss of income or a six figure dredging bill, or both.
Fuel docks on Lakes Michigan and Huron are already warning that the docks will be inaccessible because of very limited draft.
A small operator who removes and disposes of the 30,000 cubic yards that is the limit of small scale projects is faced with a bill from $100,000 to one million USD or more.
The huge range of price is reflected in the type of dredging which is determined by the bottom structure. Much of the shoreline work can be done with a dipper bucket on an excavator. Spoil is loaded onto a barge or truck for disposal. Disposal of some highly polluted sediments is particularly expensive.
Sandy sediments and gravel are removed with a suction dredge while the clay in the southern half of the lakes requires a bucket or dipper dredge. The eastern lakes have rock embedded in silt and clay which causes a dredging operations in these areas to run very slowly.
Then there is rock, not loose rock, but bedrock. The majority of the shore of Lake Superior is bare rock or covered with a thin layer of sandy soil. This geology continues to the northern half of Lake Michigan.
The worst kind of dredging includes blasting as well as digging. It is slow and dangerous and very, very expensive costing thousands of dollars a yard in the worst situations.
Saint Claire River Dredging
The drainage for the upper lakes is the St. Claire River near Detroit. Over the past fifty years the U.S. Army Corps of Engineers has modified the bottom of the channel to increase draft for large ships. Left untouched for a few decades, the river has scoured down to a soft layer which was washed away lowering the level of the upper lakes.
The restoration of the St. Claire River is being considered for study while Great Lakes shippers see tighter and tighter limits put on their drafts which are currently reduced by as much as twenty five percent.