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by Dan Hilliard
April 2023
 

To clarify understanding of the subject matter the following discussion may assist those unfamiliar with the progression of construction and related impacts to the Lower River.

 

The Cross Florida Barge Canal was a project promoted by the Johnson Administration in the mid-1960s.   The purpose was to reduce shipping time around the Florida peninsula.  With that said, construction on the Barge Canal and replacement of the Lake Rousseau Dam was completed on or about 1968.  One of the Army Corps of Engineer’s design features fully severed the river channel at the Barge Canal intersection and thus all flows to the Lower River.

 

The loss of flow to the Lower River did not mean the river went dry, but it did cause the fresh water flow to be replaced by sea water from the Gulf of Mexico.  As a result, a great deal of vegetation such as cypress trees and perhaps aquatic vegetation which are not tolerant of salt water perished.  Our understanding is that the Inglis Mayor, Mr. Dewey Allen, contested this very strongly and as a result the Inglis Bypass Spillway was constructed and became functional some time around 1970 or perhaps a short while after that.

 

For your reference, cypress trees heavily populated the river to a point west of Bennett Creek before the events described above occurred.  Cypress can tolerate up to 2 mg sodium chloride (salt) per liter of water for about 1 year.  Normal salt concentrations in sea water are in the neighborhood of 35 grams/liter. 

 

Normal flows in the river system average 1540 cubic feet per second (cfs) when examined from the perspective of total discharge through the period of one year.  The maximum flow capacity of the spillway is represented as 1450 cfs, and the balance is discharged over the Inglis Dam.  However, the river does not flow on an average basis.  While the spillway discharge rarely exceeds 1250 cfs, the dam discharge sometime exceeds 6,000 cfs. What we have lost as a result is the sporadic peak flows in the Lower River which scour sediments and hold sediment accumulation at bay.  The reason stems from the velocity of water flow through the river.  In short, the Lower River needs flow volume to increase 2-3 times which will increase flow velocity sufficiently to restore functional habitat for aquatic vegetation, freshwater fish, and other wildlife. Also, for your consideration, the relationship between flow volume and height of the water surface is not linear.  Put another way, if you double the flow volume you will not see the water surface elevation double.  What does increase is flow velocity and that is key to resolution of our problems.