PURPOSE: The following document provides a technical definition of thin layer placement (TLP) activities for U.S. Army Corps of Engineers (USACE) applications. A discussion of the development, history, and examples of TLP applications are also provided. BACKGROUND: Sediments are routinely intentionally placed into the environment to achieve beneficial outcomes, including beach nourishment, wetland creation, and other activities (Landin et al. 1989; USACE 2015; National Research Council 1995). Many publications and reports document the beneficial use of sediment, including dredged materials, to support infrastructure and enhance ecological outcomes (Yozzo et al. 2004; USEPA and USACE 2007; Faulkner and Poach 1996). Recently, increasing interest has focused on the placement of dredged sediments in thin layers; this provides opportunities for sediment management, beneficial use of dredged material, and ecological restoration or enhancement (Wilbur et al. 2007; Smith and Niles 2016; Berkowitz et al. 2017). Several terms associated with TLP appear in literature (Table 1), highlighting the need for further discussion of the topic and a definition specific to USACE applications. BENEFITS OF TLP: In the late 1970s, practitioners began investigating potential benefits of thin layer sediment applications (Reimold et al. 1978). The application of thin layers of sediment may have advantages over traditional, thicker sediment placement applications in a variety of environments where thicker layers of sediment pose potential challenges to natural resources, infrastructure, navigation, or other assets. For example, a number of reports document the benefits of thin layer sediment applications such as increased marsh elevation, improved soil stability, and enhancement of wetland functions while maintaining characteristic plant communities (Figure 1) (DeLaune et al. 1990; Mendelssohn and Kuhn 2003).
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