Dynamic Wave Overtopping Tests for Sandy Reservoir Embankments Exposed to Tropical Cyclones

The River-of-Grass, or the Everglades in south Florida, contains a unique ecosystem that is of national interest to the United States. Restoration and maintenance of this ecological marvel requires designing and building structures to withstand large storm events with budget/fiscal constraints, similar to that of shore protection projects in other nations. The US Army Corps of Engineers (USACE) began the restoration efforts centered on the construction of large impounding reservoirs to store storm runoff during the hurricane season for water supply during dry times. These reservoirs are exposed to tropical cyclones—high winds—that produce significant wind setup and wave generation that result in wave run-up and overtopping. Unfortunately, Florida’s embankment fill material is sandy (noncohesive, unlike New Orleans levees), but includes calcareous soils that demonstrate some cementitious characteristics. Because of the high potential for erosion, optimization of embankment heights is paramount to the realization of receiving public funds, while ensuring public safety as part of USACE’s shift to “risk informed” decision making in regards to dam-design criteria. However, optimization requires a more precise definition of the wave overtopping conditions and rates that will lead to embankment failure, which is not found in current literature. The USACE (with a sponsor) conducted multiple field tests on full-scale test cell embankments using a crest-located tank apparatus continuously spraying water down the slope. For dynamic overtopping conditions, prior research was primarily for cohesive soils. The USACE, in contract with Colorado State University (CSU), conducted prototype tests with CSU’s apparatus designed to simulate more dynamic waves on more cohesive embankment materials from the New Orleans region. Research performed in the Netherlands does incorporate wave dynamics and forms the basis of many other references, including that of the USACE, but does not appear to be fully applicable to shorter Florida storm conditions and a finite reservoir water supply. The USACE again contracted with CSU to utilize their equipment and expertise to run tests on soil and vegetation native to Florida. Tests included vegetated and bare soils trays with native Florida soils, as well as simulating the wave spectrum and wave characteristics expected under design storm conditions (i.e. using calculated significant wave heights and wave periods for planned reservoirs). This paper provides the methodology in which the USACE is contributing research efforts to fill knowledge gaps that were previously undefined for sandy embankments and their resistance to erosive wave overtopping events. Also, this research assists in making “risk informed” decisions that meets USACE shifting policy governing dam-design.