South Florida Reservoir Embankment Study

Abstract

As part of the Comprehensive Everglades Restoration Project (CERP), the Jacksonville District of the U.S. Army Corps of Engineers is designing an impoundment embankment cross-section. The structure is intended to comprise the perimeter of a water supply basin. The conceptual cross-sections feature interior step and berm embankment faces to armor the containment levee, reduce wave overtopping to acceptable levels, and control reflected wave energy. The goal of the study was to develop engineering guidance for optimizing the structure crosssection to provide the minimum structure that met both wave overtopping and wave pressure design criteria. A small-scale physical model study of waves impacting and overtopping the embankment was conducted. A parallel effort was also completed using the Cornell Breaking Waves and Structure (COBRAS) numerical model based on the Reynolds-averaged Navier Stokes (RANS) equations. The COBRAS model was shown to predict both wave overtopping and hydraulic pressures on the embankment well. An empirical equation was developed to predict wave overtopping as a function of structure configuration and wave and water level conditions. The study concluded that the stepped structure with no berm was optimal at reducing overtopping. The structure with continuous steps inhibits turtle egress from the basin. Therefore, guidance is provided for smooth slopes as well as for slopes employing separated blocks for overtopping reduction. The maximum pressures were shown to vary unpredictably with increasing berm width and depth. The maximum pressure was generally higher for the stepped structure without a berm than for the sections with berms. The highest pressures on the embankment appeared to be more a function of the details of the breaking wave interacting with the structure face than the structure geometry.

Wave Overtopping of Stepped Revetments

“…A data set of wave overtopping at stepped revetment (cotα = 3) with smaller dimensionless step heights (5 < H m0 /S h < 8) was provided by Melby et al (2009) [18]. Below the SWL (with the vertical coordinate z = 0) the stepped revetment continued up to a distance of 0.375 < z/H m0 < 0.6.…”

“…The work of Van Steeg et al (2018) [9] was based on an internal project report [15] and provided data for stepped revetments with cotα{2; 3}. Compared to the before described studies ( [6,18]) the analyzed dimensionless step heights were smaller (1.6 < H m0 /S h < 6.7) and plunging and surging wave breaking were covered (1.7 < ξ m−1,0 < 3.7). The provided roughness reduction coefficients were in a range of 0.8 < γ f < 0.9 for small steps (S h = 0.023 m) and reduced values in a range of 0.6 < γ f < 0.7 for steps with a doubled height (S h = 0.046 m).…”

Wave Impact Pressures on Stepped Revetments

“…Both studies lack a comprehensive discussion on the instantaneous pressure impact events with corresponding wave conditions. Hence, the systematic analysis of the wave impacts on stepped revetments conducted in the experiments in the present study includes a comparison with the data and evaluations provided by References [8,10].…”

“…Rather, it is recommended to consider the smaller surge pressures with a longer duration to determine the critical dynamic load. In addition, Reference [10] conducted hydraulic model tests in a Froude scale of 1:20 for stepped revetments (Sh = 0.015 m), focusing on wave run-up and wave overtopping. The vertical wave impact was measured on a single step with a sampling rate of only 100 Hz, which is considered as rather inappropriate for measuring rapid, i.e., almost instantaneous, wave impact pressures.…”

“…The vertical impact for the large steps is negligible as it represents only the hydrostatic pressure induced by the overflow of the incident wave. Additionally, data from Reference [10] are given. The relative step height of H m0 /S h = 7.5 is comparable to the data set provided by Reference [8] for horizontal wave impacts.…”