Christopher W. Reed

MODELING SHORE-NORMAL LARGE-SCALE COASTAL EVOLUTION

Abstract We present a model for the evolution of the shelf surface in response to marine sedimentary processes. Following morphodynamical theory, the model presupposes a characteristic configuration of the shelf surface, that in profile is a concave-up exponential curve, whose steeper inner limb is the shoreface. The profile is seen as an equilibrium response to the variables of sedimentation. The profile translates landward or seaward as sea level rises or falls, but will do so in an state of dynamic equilibrium with the shape of the profile varying according to changes in: (1) the rate of sea level change, (2) the time-averaged wave and bottom current conditions, (3) the average allochthonous sediment supply rate, and (4) the sediment grain size distribution. The governing equations for the model include an equation for time-averaged cross-shore (diabathic) sediment flux and the sediment continuity equation. p ]Simulations of continental margin profiles show that profile adjustments affect mainly the coefficient of curvature of the profile. An increase in the rate of sea level rise straightens the profile; it decreases the slope of the shoreface, but increases the shelf slope. An increase in sediment input increases profile curvature; the shoreface steepens while the shelf floor flattens. An intensification of hydraulic climate straightens the profile in a manner similar to an increase in the sea level rise rate, while an increase in grain size increases profile curvature as does an increase in sediment input.

Contaminant dispersal on the Palos Verdes continental margin: III. Processes controlling transport, accumulation and re-emergence of DDT-contaminated sediment particles

Abstract A large mass of DDT-contaminated sediment lies buried beneath a thin cover on the Palos Verdes shelf and slope off Los Angeles, California. Analyses, including several types of numerical simulation, have been applied to an extensive data set to evaluate the biological and physical processes controlling the fate of the strongly particle-reactive pollutants. Sequential measurements of the p,p′ -DDE (an isomer of DDT) content in cores from monitoring locations indicate that contaminated sediment particles are being re-introduced into the marine environment from the buried historic deposits at a significant rate. There is considerable scatter in the data but the trends for ongoing release over the 8 years between 1983 and 1991 are statistically significant at the 90% level. A comprehensive mathematical model of shelf sediment dynamics (Resuspension Model) has been used to explore sediment erosion and deposition during major storms of the early 1980s and of 1988. This modeling shows that storms alone cannot explain the observed losses of contaminated sediment particles from the historical deposits of the Palos Verdes shelf. On the other hand, it also demonstrates that both severe and common storm events do re-entrain some of the bottom sediment at all water depths across the Palos Verdes shelf. A numerical model (Contaminant Release Model), which couples upward biodiffusion of DDT with storm removal, satisfactorily explains the observed losses. The infaunal activity that creates biodiffusion has been explored in two separate ways. In calibrating the Contaminant Release Model, the depth-dependent biodiffusion coefficient profile is estimated by comparing the predicted and measured depth concentration distributions. A separate analysis has been conducted using the measured vertical distribution of infaunal species (Stull et al. 1995; Swift et al., 1995). The agreement between these two methods is good. Both show that bioturbation extends to the level of the high contamination. Bioturbation is now playing a significant role in redistributing the buried historic contaminants. The Contaminant Release Model, in combination with evaluations of the total sedimentation rate and the natural background sedimentation rate, clearly shows that the flux of solids from the outfall enhances the rate of accumulation of natural sediment on the Palos Verdes shelf. A sharp reduction of the flux of solids, such as would accompany conversion from partial to full secondary treatment, will result in considerably prolonging the high rates with which DDT and other particle-reactive contaminants are re-entering the marine environment.

The Coastal Modeling System Flow Model (CMS-Flow): Past and Present

Abstract CMS-Flow is a coupled time-dependent circulation, sediment transport and morphodynamic model based on the numerical solution of the mass, momentum and transport equations on a Cartesian (quad-tree) grid network with both explicit and implicit solvers. It has been developed and is currently supported under the Coastal Inlets Research Program (CIRP) conducted at the U.S. Army Engineer Research and Development Center (ERDC), Coastal and Hydraulics Laboratory (CHL). The models primary function is to support multi-disciplinary research teams and conduct practical projects at coastal inlets. CMS-Flow has been designed with a relatively simple code structure which allows for rapid development and inclusion of new sediment transport algorithms, while always being accessible to the general modeling community, including both USACE and commercial users. Today, CMS-Flow is an integral component of the CIRP, providing technology for simulating hydrodynamics, waves, sediment transport and morphology for short and long timeframes in coastal inlets, adjacent beaches, navigation channels and bays.

Numerical Simulations of Coastal-Tract Morphodynamics

A finitv difference nttrnedcal model has been developed to represent the large-scale morphodynamics of complex coastal systems. The model is based on the Coastal System Tract (CST) concept. This model contains representations of coastal features such as tidal inlets, bays and rivers, beach systems (including littoral drift and profile migration), as well as the offshore zone comprised of the shoreface, shelf and upper continental slope. The purpose of the model is to diagnose the large-scale morphodynamical interactions between the components of the CST that have previously only been represented as separate or incompletely link dements. The results show that there are important forcing factors that result from different characteristic response times of the independent system components. This means that the system components are never properly tuned to respond in unison to perturbations in the large-scale forcing parameters. INTRODUCTION The need to plan and engineer coastal facilities, such as ports or offshore artificial islands that do not upset area-wide coastal processes, has focused attention on a need for long-term and large-scale quantitative representations of large coastal systems morphodynsmics, Over the past decade it has become increasingly apparent that representing the complex processes that shape open-ocean coastline with mathematical models provides for quantitative diagnosis of the relationship between environmental forcing and morphological response. Because coastal systems are complex assemblages of subeomponents and because many available models operate with time steps that resolve wave motions (i.e. seconds), it has been common practice to consider relatively short-term processes (less than a decade) and to isolate portions of overall coastal systems for study (e.g. the surf zone, inlets or the shoreface). More recently, models have been developed to represent large-scale and long-term processes and to link some of the components of overall open-ocean coastal systems. The time-, and length-scales of interest are decades to centuries and tens to hundreds of kilometers. This paper reports on the development and application of a large-scale numerical model representing an entire coastal system tract. It allows exploration of interactions between the shoreline sediment sources and sinks (e.g. river mouth, tidal inlet), the surf zone littoral sediment Vice-President, URS, 3676 Hartsfield Road, Tatlahassee. FL 32303 USA. Alan niedoroda@urscorp.com z Sefflor Project Scientist, URS, 3676 Hartsfield Road, Tallahassee, FL 32303 USA. Chris reed@urscorp.com Pro~ssor, Delf University of Technology, Faculty of Civil Engineering and Geosciences, Delf Hydraulics, (P.O. Box 177, 2600 MH) Delft, The Netherlands. Marcel.stive@wdelft.nl 4 Professor, Institute of Marine and Ocean Sciences, University of Sydney, NSW 2006, Australia. P.cowell@csu.usyd.edu.au

Doppler Radar-Derived Rainfall Data Monitoring to Support Surface Water Modeling of TMDL

Abstract A Calibrated High-Resolution Precipitation Database (CHPD) represents an enhanced tool for modelers developing Total Maximum Daily Loads (TMDL) or using water resource related surface water (SW), ground water (GW) or integrated SW-GW models. With software support from the National Oceanic and Atmospheric Administration (NOAA), funding support by the Florida Department of Environmental Protection (FDEP) and the Environmental Protection Agency, and academic support from Florida State University (FSU), Florida is the first State to have successfully completed the construction of a practical CHPD. Precipitation input for a watershed model typically has relied on weather data obtained from rain gauges that are sparsely distributed in a watershed. A popular method for computing precipitation is the Thiessen method. This method assigns an area called a Thiessen polygon around each gauge. The polygon is an area in which every interior point is closer to the particular gauge than to any other. In effect, the precipitation in the entire polygon is assumed to be uniform and equal to the gauge value. This method does not provide information about the rainfall distribution between gauges. In addition, the method cannot give the true rainfall distribution for isolated or fast moving storms that may cover one side of a street, but not the other, and change intensity and coverage along its passage. Hourly Doppler radar-derived rainfall (NEXRAD/WSR-88) estimates possess superior temporal and spatial resolution compared to gauges and can be applied to watershed modeling as part of TMDL projects. The Doppler-derived precipitation estimates are produced hourly on a 4-kilometer by 4-kilometer grid covering the nation. This paper introduces the eleven years of historical precipitation data in CHPD released through FDEPs computer world-wide-web server and the CHPD applications by using three watershed models – WAMView, Mike-SHE, and WASH. The WAMView application assesses the potential benefits of CHPD data in the Black Creek Basin, which is a small (1,253 Km2) watershed in North Florida. The Mike-SHE application investigates the comparative diagnostic advantages of using fully distributed CHPD- or Thiessen (gauge)-derived rainfall rates in the Black Creek Basin of modest topography during both convective and synoptic conditions. The WASH application is the FDEPs first TMDL modeling project using the CHPD data.

Developing Engineering Design Criteria for Mass Gravity Flows in Deep Ocean and Continental Slope Environments

A series of developments that led to both new understandings of mass gravity flows in the marine environment and in the techniques to quantitatively analyze them. Methods have been developed that exploit the newly emerging technical capabilities to perform very precise and detailed field investigations in deep continental slope settings that support numerical models which simulate the flows and their deposits. This combination of technologies provides a means to create engineering design criteria for mass gravity flows. In this paper, the methods that have been developed for these analyses are described and illustrated with examples.

Analysis of Packery Channel Public Access Boat Ramp Shoreline Failure

Abstract The shoreline stabilization adjacent to the public access boat ramp in the Packery Channel basin has been damaged in two separate events. For the shoreline damage at the boat ramp bulkhead, toe scour is the likely mechanism for failure. Typical sources of hydrodynamic forcing that can lead to toe erosion include storm currents, locally generated storm waves, and offshore storm waves propagating into the basin through Packery Channel. Quantitative analysis of storm induced wind generated waves and currents eliminated them as possible causes of the damage. However, photographic and movie evidence indicate the presence of low-frequency low-amplitude waves propagated into the basin and impacted the boat ramp. The Coastal System Model (CMS) was used to simulate a range of these low-frequency low-amplitude waves and the results demonstrated that these waves could produce sufficient flows in the vicinity of the boat ramp shoreline to cause the damage. Subsequent modeling was used to develop design criteria for additional shoreline stabilization.