David L. Kriebel

Bio: David L. Kriebel is an academic researcher from United States Naval Academy. The author has contributed to research in topics: Breaking wave & Wind wave. The author has an hindex of 20, co-authored 61 publications receiving 1518 citations. Previous affiliations of David L. Kriebel include University of Delaware & University of Florida.

Numerical simulation of time-dependent beach and dune erosion

Abstract: A computational procedure is developed for predicting the time-dependent, two-dimensional beach and dune erosion during severe storms due to elevated water levels and waves. The model employs the equation of sediment continuity and a dynamic equation governing the cross-shore sediment transport due to a disequilibrium of wave energy dissipation levels. These equations are solved numerically by an implicit, double-sweep procedure to determine the change in position of elevation contours in the profile. Given sufficient time, the profile will evolve to a form where the depth, h, in the surf zone is related to the distance seaward of the waterline by the relationship: h = Ax23, which is consistent with many natural profiles and in which A depends on sediment characteristics. The model is verified qualitatively and quantitatively through application to several idealized cases and through a preliminary simulation of erosion during Hurricane Eloise. In general, the time scales for shoreline response were found to be quite long relative to natural storm systems and erosion in the early response stages was found to be sensitive to storm surge height, but much less sensitive to wave height. The model response characteristics for simulation of erosion due to time-varying storm conditions show a lag between the maximum storm surge elevation and maximum erosion with the maximum erosion rate occurring at the time of the peak surge. For the simulated erosion due to Hurricane Eloise, reasonable agreement was found between the post-hurricane dune profiles and those calculated. However, the eroded volumes were in better agreement than the profile forms as the steepening of the natural dune profiles was not reproduced in the model.

Convolution Method for Time-Dependent Beach-Profile Response

Abstract: A simple analytical solution is presented for approximating the time-dependent beach-profile response to severe storms. This solution is in the form of a convolution integral involving a time-varying erosion-forcing function and an exponential erosion-response function. The erosion-forcing function reflects changes in the nearshore water level and breaking wave height. In this paper, an idealized storm-surge hydrograph is considered from which an analytic solution is obtained for beach and dune erosion associated with severe storms such as hurricanes or northeasters. It is shown that for a given initial beach geometry and sediment size, the peak water level and the incipient breaking wave height determine the maximum erosion potential that would be achieved if the beach were allowed to respond to equilibrium. Because of the assumed exponential erosion rate, beach response obtained from the convolution method is found to lag the erosion forcing in time, and is damped relative to the maximum erosion potential such that only a fraction of the equilibrium response actually occurs.

Evaluation of Beach Erosion and Accretion Predictors

Abstract: This paper examines the capability of simple criteria to predict whether a beach will erode or accrete by wave-induced cross-shore sand transport. Emphasis is on beach change of engineering interest such as associated with storm erosion, poststorm recovery, and seasonal wave conditions. The criteria, originally developed based on data from small and large tanks and monochromatic waves, correctly predict most erosion and accretion events in a newly compiled field data set encompassing beaches around the world. Previous studies that found such criteria unsuccessful are reviewed and found to be questionable. Correspondence between events in the field with random waves and in large wave tanks with monochromatic waves is obtained if mean wave height is used in field applications; however, any statistical wave height can be used by adjustment of one empirical coefficient in each criterion. Two dimensionless parameters (fall speed parameter and a newly introduced Froude number) used in some criteria are shown to be related to a critical wave energy dissipation needed to suspend sediment.

Nonlinear wave interaction with a vertical circular cylinder - part ii: wave run-up

Abstract: Theoretical results for second-order wave run-up around a large diameter vertical circular cylinder are compared to results of 22 laboratory experiments conducted in regular nonlinear waves. In general, the second-order theory explains a significant portion of the nonlinear wave run-up distribution measured at all angles around the cylinder. At the front of the cylinder, for example, measured maximum run-up exceeds linear theory by 44% on average but exceeds the nonlinear theory by only 11% on average. In some cases, both measured run-up and the second-order theory exceed the linear prediction by more than 50%. Similar results are found at the rear of the cylinder where the second-order theory predicts a large increase in wave amplitude for cases where the linear diffraction theory predicts little or no increase. Overall, the nonlinear diffraction theory is found to be valid for the same relative depth and wave steepness conditions applicable to Stokes second-order plane-wave theory. In the last section of the paper, design curves are presented for estimating the maximum second-order wave run-up for a wide range of conditions in terms of the relative depth, relative cylinder size, and wave steepness.

Engineering Methods for Predicting Beach Profile Response

Abstract: This papers contains a review of so-called 'engineering methods' for predicting beach profile change based on equilibrium profile concepts. In the first part of the paper, three equilibrium profile forms are discussed, including two that account for realistic beach-face slopes. In the second part of the paper, these profile forms are used to obtain analytical solutions for the maximum erosion potential in response to a water level rise. These solutions assume that the water level is maintained steady until the profile reaches its full equilibrium response which is not realistic. Therefore, the final part of the paper presents a new method for incorporating time-dependent erosion effects based on a convolution integral.

Equilibrium Beach Profiles: Characteristics and Applications

Abstract: An understanding of equilibrium beach profiles can be useful in a number of types of coastal engineering projects. Empirical correlations between a scale parameter and the sediment size or fall velocity allow computation of equilibrium beach profiles. The most often used form is h(y) = Ay 2/3 in which h is the water depth at a distance y from the shoreline and A is the sediment-dependent scale parameter. Expressions for shoreline position change are presented for arbitrary water levels and wave heights. Application of equilibrium beach profile concepts to profile changes seaward of a seawall include effects of sea level change and arbitrary wave heights. For fixed wave heights and increasing water level, the additional depth adjacent to the seawall first increases, then decreases to zero for a wave height just breaking at the seawall. Shoreline recession and implications due to increased sea level and wave heights are examined. It is shown, for the equilibrium profile form examined, that the effect of wave set-up on recession is small compared to expected storm tides during storms. Profile evolution from a uniform slope is shown to result in five different profile types, depending on initial slope, sediment characteristics, berm height and depth of active sediment redistribution. The reduction in required sand volumes through perching of a nourished beach by an offshore sill is examined for arbitrary sediment and sill combinations. When beaches are nourished with a sediment of arbitrary but uniform size, it is found that three types of profiles can result: (1) submerged profiles in which the placed sediment is of smaller diameter than the native and all of the sediment equilibrates underwater with no widening of the dry beach, (2) non-intersecting profiles in which the sea- ward portion of the placed material lies above the original profile at that location, and (3) intersecting profiles with the placed sand coarser than the native and resulting in the placed profile intersecting with the original profile. Equations and graphs are presented portraying the additional dry beach width for differing volumes of sand of varying sizes relative to the native. The offshore volumetric redistribution of material due to sea level rise as a function of water depth is of interest in interpreting the cause of shoreline recession. If only offshore transport occurs and the surveys extend over the active profile, the net volumetric change is zero. It is shown that the maximum volume change due to cross-shore sediment redistribution is only a fraction of the product of the active vertical profile dimension and shoreline recession. The paper presents several other applications of equilibrium beach profiles to problems of coastal engineering interest.

Observations of sand bar evolution on a natural beach

Abstract: Waves, currents, and the location of the seafloor were measured on a barred beach for about 2 months at nine locations along a cross-shore transect extending 255 m from 1 to 4 m water depth The seafloor location was measured nearly continuously, even in the surf zone during storms, with sonar altimeters mounted on fixed frames The crest of a sand bar initially located about 60 m from the shoreline moved 130 m offshore (primarily when the offshore significant wave height exceeded about 2 m), with 15 m of erosion near the initial location and 1 m of accretion at the final location An energetics-type sediment transport model driven by locally measured near-bottom currents predicts the observed offshore bar migration, but not the slow onshore migration observed during low-energy wave conditions The predicted offshore bar migration is driven primarily by cross-shore gradients in predicted suspended sediment transport associated with quasi-steady, near-bottom, offshore flows These strong (>50 cm/s) currents, intensified near the bar crest by wave breaking, are predicted to cause erosion on the shoreward slope of the bar and deposition on the seaward side The feedback amoung morphology, waves, circulation, and sediment transport thus forces offshore bar migration during storms

Wave Crest Distributions: Observations and Second-Order Theory

Abstract: Many empirical and heuristic distribution functions for wave crest heights have been proposed, but their predictions differ considerably. Part of the lack of agreement is due to the difficulty of making measurements that accurately record the true height of the wave crests. Surface following buoys effectively cancel out the second-order nonlinearity by making a Lagrangian measurement. Pressure transducers filter the nonlinear components of the signal in complicated ways. Wave staffs have varying degrees of sensitivity to spray. The location of the instruments also plays an important role. There is clear evidence from measurements in the North Sea that spurious crests due to spray are a problem downwind even from mounting supports that appear transparent. Much of the theoretical nonlinearity can be captured by calculations correct to second order. Explicit calculation of the interactions of each pair of components in a directional spectrum is straightforward although computationally intensive. This technique has the advantage that the effects of wave steepness, water depth, and directional spreading are included with no approximation other than the truncation of the expansion at second order. Comparisons with measurements that are believed to be of the best quality show good agreement with these second-order calculations. Simulations for a set of JONSWAP spectra then lead to parametric crest distributions, which can be used easily in applications.

Embedding ecosystem services in coastal planning leads to better outcomes for people and nature

Abstract: Recent calls for ocean planning envision informed management of social and ecological systems to sustain delivery of ecosystem services to people. However, until now, no coastal and marine planning process has applied an ecosystem-services framework to understand how human activities affect the flow of benefits, to create scenarios, and to design a management plan. We developed models that quantify services provided by corals, mangroves, and seagrasses. We used these models within an extensive engagement process to design a national spatial plan for Belize’s coastal zone. Through iteration of modeling and stakeholder engagement, we developed a preferred plan, currently under formal consideration by the Belizean government. Our results suggest that the preferred plan will lead to greater returns from coastal protection and tourism than outcomes from scenarios oriented toward achieving either conservation or development goals. The plan will also reduce impacts to coastal habitat and increase revenues from lobster fishing relative to current management. By accounting for spatial variation in the impacts of coastal and ocean activities on benefits that ecosystems provide to people, our models allowed stakeholders and policymakers to refine zones of human use. The final version of the preferred plan improved expected coastal protection by >25% and more than doubled the revenue from fishing, compared with earlier versions based on stakeholder preferences alone. Including outcomes in terms of ecosystem-service supply and value allowed for explicit consideration of multiple benefits from oceans and coasts that typically are evaluated separately in management decisions.