National Park Service
Date of this Version
7-2004
Citation
U.S. Department of Interior, Archeological Assistance Program Technical Brief No. 18, July 2004.
Abstract
Introduction
Federal laws and regulations encourage preserving archeological sites in place when they are threatened by roadbuilding, reservoir construction, and the like.1 However, proactive managers favor the idea even when sites are not immediately at risk. Excavation is costly, with the curation of artifacts adding appreciably to the expense. A resource-specific conservation plan, carefully designed and implemented, substantially reduces management costs. At the same time, the plan can be aesthetically pleasing while serving to enhance other aspects of the surroundings.
There are many alternatives one can employ to stabilize sites and shorelines (Thorne 1991). A modeled approach to developing a stabilization strategy has been devised that can be applied to any setting (Thorne et al. 1987; Thorne 1988a, 1989, 1990, 1991). In many cases, however, funds are severely restricted, and factors such as environmental compatibility and aesthetic appeal come into play.
An experimental program, described here, addressed these and other issues in reversing the severe erosion at South Dakota’s Lake Sharpe, which was caused primarily by wind-blown waves and the annual freeze-thaw cycle. The lack of stabilizing vegetation in the unconsolidated glacially deposited soil also contributed to the erosion.
The approach, devised by the U.S. Army Corps of Engineers, uses hay bales in concert with revegetation to abate erosional forces. While not suited to every situation, this cost-effective alternative may be a low-cost solution for conservation planning.
The Plan–A Case Study at Lake Sharpe
Lake Sharpe was created by Big Bend Dam, constructed in 1963 to generate electricity. Over the course of a year, the water level fluctuates less than two feet, creating a near-constant ring of erosion around the lake. Lake Sharpe is shallow, which contributes to the severity of the waves. Ice reaches a thickness of almost three feet, and during thaw the wind drives large floes into the bank.
As might be expected, the setting dramatically tests any stabilization technique other than riprap, which would be inappropriate and too expensive for the entire lakeshore. The violent combination of wind, waves, and ice undercuts the entire shore. Given the area to be protected and the almost constant loss, a cost-effective approach is essential.
To armor the bank and its 200 archeological sites, the Corps instituted a stabilization program, ongoing since 1987. Though the overall program is still experimental, the efficacy of its hay bales/revegetation component has been amply demonstrated.
Acquiring the Bales
Placing the Bales
Revegetation
The Technique in Action
Acknowledgments
Endnote
References