TMDLs: Tall Tale of Fishes and Silt

June 10th, 2005 by Leave a Comment

By Harold Brown

The king of Clearwater liked to fish, but he was distraught that he could catch only a few, or none, in the streams near the castle and sent his Knights of Fisheries to investigate.

The Knights of Fisheries learned that a witch from the neighboring kingdom of Sweetwater had cast a spell to warn all fish away from the streams near the castle. The witch was dead, but apparently her spell lived on. Concerned, the king ordered the fishery knights to draw up an “anti-witchery plan” for the fish-poor streams of his kingdom.

It turns out, however, that the fish knew nothing of the witch’s works; in fact, they just didn’t like the streams of Clearwater. When the king found out that the streams of Clearwater and Sweetwater were really no different, he declared that the “anti-witchery” plan would be applied to his kingdom’s streams anyway; he was a cautious man.

There’s a parallel in the fiction of Clearwater and the cleaning of Georgia’s streams. The document entitled, “Total Maximum Daily Load Evaluation for Thirty-One Stream Segments in the Chattahoochee River Basin For Sediment (Biota Impacted),” from the Georgia Department of Natural Resources tells the story. (Actually, the same tale is told in similar documents for other river basins in the state, but the Chattahoochee is a typical example.)

The 31 stream segments were found to have too few fish or not enough diversity of fish, or biota. (They could have just as well have said “fish,” because that’s all that was measured). The streams were listed as “impaired,” or not fully supporting the intended use, which in this case was fishing. Sediment – silt – was cited as the reason.

If streams are found to be “impaired,” federal law requires that a Total Maximum Daily Load of pollutant – sediment in this case – be calculated and applied to restore the stream to its intended use. So the job here is to calculate a load of sediment (TMDL) going into the stream that is small enough to restore the stream and make the fish come back.

An updated erosion model was used to estimate sediment delivery to the streams; land use in the watersheds was catalogued and an erosion factor assigned to each land use. The approach was to compare the impaired streams to those in the basin that had plenty of fish, rated as unimpaired.

When sediment delivery for the 31 impaired and 42 unimpaired streams was compared, however, there was no difference.

Impaired stream watersheds in the Piedmont part of the Chattahoochee basin delivered 0.74 tons of sediment per acre per year; unimpaired streams delivered 0.77 tons per acre. In the Coastal Plain, the corresponding figures were 0.63 tons for impaired streams and 0.88 tons for unimpaired streams. A measure of sediment suspended in the water, turbidity, also did not differ in the two classes of streams.

If as much sediment is going into unimpaired streams as into impaired ones, how can sediment be the cause of impairment, and how can setting of a TMDL for sediment on impaired streams correct the situation?

The document reaches a surprising conclusion: “Based on the findings of the source assessment, it was determined that most of the sediment found in the Chattahoochee River Basin streams is due to past land use practices and is referred to as “legacy” sediment. Therefore, it is recommended that there be no net increase in sediment delivered to the impaired stream segments, in order that these streams recover over time.”

The conclusion is surprising both for its assessment of cause and for its recommendation. “Legacy” sediment is that sediment washed into streams decades ago by careless cultivation of cotton and other crops. All the TMDLs in the bureaucratic bluebook won’t erase “legacy” sediment, besides, the remedy is already in place.

The recommendation that “there be no net increase in sediment delivered to the impaired stream segments, in order that these streams recover over time” is both vacuous and misplaced. It is the equivalent of a social recommendation that we “have no increase in the growth of crime.”

It is misplaced because it appears that both the impaired and unimpaired streams have the same sediment “problem” and should be treated the same. Are the unimpaired streams allowed to continue to receive sediment? They are now receiving the same load as the impaired streams.

It may be of comfort to some that the report found that urban sediment currently entering streams in the Chattahoochee basin is less than 1 percent of the total; roads contribute six times as much; grasses and wetlands twice. Perhaps the most useful part of this exercise to produce unnecessary TDMLs is the hidden good news. It reminds us that the “legacy” sediment is a problem of our profligate past, not a vital current concern.


University of Georgia Professor Emeritus R. Harold Brown is an Adjunct Scholar with the Georgia Public Policy Foundation and author of “The Greening of Georgia: The Improvement of the Environment in the Twentieth Century.” The Georgia Public Policy Foundation is an independent think tank that proposes practical, market-oriented approaches to public policy to improve the lives of Georgians. Nothing written here is to be construed as necessarily reflecting the views of the Georgia Public Policy Foundation or as an attempt to aid or hinder the passage of any bill before the U.S. Congress or the Georgia Legislature.

© Georgia Public Policy Foundation (June 10, 2005). Permission to reprint in whole or in part is hereby granted, provided the author and his affiliations are cited.

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