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The Fragile Fringe - Wetland Loss: Digging of Canals


Objective: To illustrate the destruction of wetlands that resulted from the digging of canals for oil and gas exploration in the coastal wetlands and cypress logging in the swamps.

The small canals and channels naturally occurring in the marsh were perfect for small boats and canoes used by hunters, trappers, and fishermen. With the advent of oil and gas explorations in the marshes and cypress logging in the swamps around the Lake Maurepas/Lake Pontchartrain area, deeper and wider channels were needed for larger boats. The channels did not meander like many of the natural ones; they were dug straight and deep. The spoil was piled on the banks which smothered and destroyed any vegetation that would stabilize the bank structure. The spoil also set up barriers to the natural flow of water across the wetland, resulting in the flooding of many areas.

The increased boat traffic produced greater wave action against the banks. The faster velocity of the water moving in a deeper, wider channel, and the decreased quantity of plant roots along the banks resulted in the widening of the channels and the loss of wetlands. Currently, the use of existing channels is encouraged rather than the construction of new channels to access areas of the marshes or swamps. This practice cannot return the lost acres, but it can prevent further destruction of the fragile areas that remain.

Activity: (for elementary - middle school students)

1. Have 2 groups of students fill a large pan or dishpan half full of soil. Each group will create a canal, piling the spoil on each side of the canal as it is dug -one group will dig the canal horizontal to the direction of flow of the water and the other group will dig the canal vertical to the flow of water (Fig. 6).

Have the students observe and record the results of water flow representing rainfall, flooding, and high tides using a watering can, water hose or bottle of water to simulate different phenomena. What are the effects of excess water pooling in the wetland? Would it have been possible to dig the canals in such a way as to avoid the destruction of the wetlands?

View Figure 6.

Extension: (for middle - high school students)

  1. Have the students examine topographic maps of the area in which they live to identify natural and constructed canals in the wetlands. If possible, find older maps and compare the area of wetlands before and after major canals were built.
  2. Have the students research the relationship between channel building, subsidence and salt-water intrusion, and wetland loss in both fresh and saltwater wetlands across the United States.