While polluted coastal bays have often been studied observationally, less effort has focused on developing computer models that simulate the processes that disperse, depositand resuspend pollution and contaminants on the seabed. Such models would not only help interpret observational data but would also benefit resource managers charged with upholding state and federal clean water laws.

We propose to establish, maintain, and augment the sensors for UCLA's oceanographic mooring near the edge of the continental shelf in Santa Monica Bay; extensively sample the water quality within the surrounding region, and interpret the measurements in combination with satellite sensing and three-dimensional, fine-scale numerical simulations of the local region. This will be done in coordination with other proposed measurements in the Southern California Bight that collectively are establishing a long-term, multi-purpose observing system for the regional environment. The research issues to be addressed with the measurements include water quality and pollution, ecosystem productivity, biogeochemical cycling, zooplankton and forage species distributions, mesoscale circulation patterns, and climate variability.

We propose to establish, maintain, and augment the sensors for UCLA's oceanographic mooring near the edge of the continental shelf in Santa Monica Bay; extensively sample the water quality within the surrounding region; and interpret the measurements in combination with satellite sensing and three-dimensional, fine-scale numerical simulations of the local region. This will be done in coordination with other proposed measurements in the Southern California Bight that collectively are establishing a long-term, multi-purpose observing system for the regional environment. The research issues to be addressed with the measurements include water quality and pollution, ecosystem productivity, biogeochemical cycling, zooplankton and forage species distributions, mesoscale circulation patterns, and climate variability.

This dissertation mainly addresses the generic types of ageostrophic instability in general continuously differentiable, interior, horizontal and vertical shear flows without special "edges" (vertical, side or equatorial boundaries or frontal outcropping). In contrast to the classic barotropic and baroclinic instabilities, whose nonlinear dynamics (geostrophic turbulence) have an ''inverse cascade" characteristic, the ageostrophic instabilities serve as a local route for the breakdown of balance in the interior ocean or atmosphere, leading to an efficient energy cascade towards small scales. For the first part of this dissertation, the linear instabilities, both momentum-balanced and unbalanced, in several different U(y) shear profiles are investigated in the rotating shallow water equations. The unbalanced instabilities are strongly ageostrophic and involve inertia-gravity wave motions, occurring only for finite Rossby (Ro) and Froude (Fr) numbers. Aside from the classic shear instability among balanced shear wave modes (i.e., B-B type), two types of ageostrophic instability (B-G and G-G) are found. Here B represents balanced shear wave mode, and G represents inertia-gravity wave mode. The B-G instability has attributes of both a balanced shear wave mode and an inertia-gravity wave mode. The G-G instability occurs as a sharp resonance between two inertia-gravity wave modes. The criterion for the occurrence of the ageostrophic instability is associated with the second stability condition of Ripa 1983, which requires a sufficiently large local Froude number. When Ro and especially Fr increase, the balanced instability is suppressed, while the ageostrophic instabilities are enhanced. The profile of the mean flow also affects the strength of the balanced and ageostrophic instabilities. For the second part of this dissertation, the linear instabilities of several rotating, stably stratified, interior vertical shear flows U(z) are solved in Boussinesq equations. Two types of baroclinic, ageostrophic instability, AI1 and AI2, are found in antisymmetric U(z) for intermediate Rossby number (Ro). AI1 is a stationary (zero frequency) instability, which appears in a continuous transformation of the unstable mode properties between classic baroclinic instability (BCI) and centrifugal instability (CI). It begins to occur at intermediate Ro values and horizontal wave numbers (k, l) that are far from l = 0 or k = 0. AI1 grows by drawing energy from the kinetic energy of the mean flow. The instability AI2 always has inertial critical layers at certain heights; and hence it is associated with an inertia-gravity wave. For an unstable AI2 mode, the coupling is either between an interior balanced shear wave and an inertia-gravity wave (B-G), or between two inertia-gravity waves (G-G). The main energy source for an unstable B-G mode is the mean kinetic energy, while the main energy source for an unstable G-G mode is the mean available potential energy. AI1 and AI2 of the B-G type occur in the neighborhood of A-S = 0 (McWilliams et al. 1998), while AI2 of the G-G type arises beyond this condition (A-S denotes absolute vertical vorticity minus strain rate in isentropic coordinates). Both AI1 and AI2 are unbalanced instabilities, which lead to a loss of balance in 3D interior flows.

The Southern California Coastal Ocean (SCCO), defined as the region inclusive of the Southern California Bight and the Santa Barbara Channel, from the shoreline to beyond the continental shelf, has significant anthropogenic injections of many materials through the air, rivers, runoff, outfalls, sediments, and marine spills. These inputs are superposed on a dynamic system of internal processes including water motions, biological production in the surface layers, particle sinking, dissolution, and scavenging. In spite of lengthy and continuing sequences of SCCO measurements at various scales, a synthetical understanding and an ability to make skillful predictions and comprehensive assessments of the fate and transport of these materials in the SCCO remains illusive. In many cases the interpretation of localized measurements lacks a regional context. Conversely, there is little information on the regional impacts of localized sources. It is clear that an integrated computational model of the most relevant processes is needed before these goals can be achieved. An integrated model will be of great value to environmental managers responsible for sewage discharges, storm water discharges, and coastal fisheries. The overall project objective is to develop, test, and use for practical purposes an integrated computational model of the physical, chemical, and biological processes relevant to the distributions of natural and anthropogenically injected materials in the Southern California.

The overall goal of the research project is to develop a model of water and sediment quality capable of forecasting environmental events occurring over small space and time scales in the coastal zone, including embayments, harbors, and shoreline regions.

The purpose of this document is to present in a compact form the capabilities of the UCLA version of the Regional Ocean Modeling System (ROMS), incorporating sediment transport algorithms developed in collaboration with the U.S. Geological Survey, to address water and sediment quality issues in the coastal ocean with particular reference to the Southern California Bight and the coastal region near Los Angeles and Orange County. In the following sections the components of the ROMS model are discussed, including examples of applications. The document concludes with a summary of needs for future model development and potential new applications.