The operation of Glen Canyon Dam on the Colorado River affects several downstream resources and water uses including water supply for consumptive uses in Arizona, California, and Nevada, hydroelectric power production, endangered species of native fish, recreational angling for non-native fish, and recreational boating in the Grand Canyon. Decisions about the magnitude and timing of water releases through the dam involve trade-offs between these resources and uses. The numerous laws affecting dam operations create a hierarchy of legal priorities that should govern these decisions. At the top of the hierarchy are mandatory requirements for water storage and delivery and for conservation of endangered species. Other resources and water uses have lower legal priorities. The Glen Canyon Dam Adaptive Management Program ("AMP") has substituted collaborative decision making among stakeholders for the hierarchy of priorities created by law. The AMP has thereby facilitated non-compliance with the Endangered Species Act by the Bureau of Reclamation, which operates the dam, and has effectively given hydroelectric power production and non-native fisheries higher priorities than they are legally entitled to. Adaptive management is consistent with the laws governing operation of Glen Canyon Dam, but collaborative decision making is not. Nor is collaborative decision making an essential, or even logical, component of adaptive management. As implemented in the case of Glen Canyon Dam, collaborative decision making has actually stifled adaptive management by making agreement among stakeholders a prerequisite to changes in the operation of the dam. This Article proposes a program for adaptive, but not collaborative, management of Glen Canyon Dam that would better conform to the law and would be more amenable to adaptation and experimentation than would the current, stakeholder-centered program.

Hybrid system models - those devised from two or more disparate sub-system models - provide a number of benefits in terms of conceptualization, development, and assessment of dynamical systems. The decomposition approach helps to formulate complex interactions that are otherwise difficult or impractical to express. However, hybrid model development and usage can introduce complexity that emerges from the composition itself.

To improve assurance of model correctness, sub-systems using disparate modeling formalisms must be integrated above and beyond just the data and control level; their composition must have model specification and simulation execution aspects as well. Poly-formalism composition is one approach to composing models in this manner.

This dissertation describes a poly-formalism composition between a Discrete EVent System specification (DEVS) model and a Cellular Automata (CA) model types. These model specifications have been chosen for their broad applicability in important and emerging domains. An agent-environment domain exemplifies the composition approach. The inherent spatial relations within a CA make it well-suited for environmental representations. Similarly, the component-based nature of agents fits well within the hierarchical component structure of DEVS.

This composition employs the use of a third model, called an interaction model, that includes methods for integrating the two model types at a formalism level, at a systems architecture level, and at a model execution level. A prototype framework using DEVS for the agent model and GRASS for the environment has been developed and is described. Furthermore, this dissertation explains how the concepts of this composition approach are being applied to a real-world research project.

This dissertation expands the tool set modelers in computer science and other disciplines have in order to build hybrid system models, and provides an interaction model for an on-going research project. The concepts and models presented in this dissertation demonstrate the feasibility of composition between discrete-event agents and discrete-time cellular automata. Furthermore, it provides concepts and models that may be applied directly, or used by a modeler to devise compositions for other research efforts.

Dramatic changes in land use were associated with the rise of agriculture in the mid Holocene in the Mediterranean region. Both surface properties and drainage networks were changed along with direct modifications to surface properties (vegetation removal and change, sediment liberation and compaction); consequent drainage alteration (terracing, canals) and up and downstream responses in the watersheds communicated these changes throughout the landscape.

The magnitude, rate, and feedbacks with the growing human populations are critical questions in our effort to assess human-landscape interactions. To investigate these relationships, recent field work in the Penaguila Valley of southeast Spain included landform mapping, alluvial deposit description, and sample collection emphasizing areas of active erosion, remnant land surfaces and their relation to archaeological sites.

We have updated our geomorphic maps by refining the delineation of alluvial terraces, steep-walled (40m deep) drainages ("barrancos"), and hollows ("barrancos de fondo plano"). Hollows are curved, elongate, flat-bottomed gullies with steep walls (2-30m tall) and extend headward from the main barrancos. This work enables more accurate terrace correlations necessary for both landscape evolution modeling and interpretation of the development history of the basin.

Alluvial terraces are crucial to this research because they record periods of past stable topography. In the Penaguila, sites dating back to late Mesolithic and early Neolithic (around 6600 BP) and subsequent periods (Chalcolithic and Bronze Age) are exposed on a prominent terrace surface mapped as Terrace A. This broad low relief surface is scarred by deep barrancos and hollow formation that expose bedrock marls and overlying alluvial deposits. Stratigraphic profiles and texture analyses of Terrace A deposits reveal overland flow facies and channel networks in reworked and CaCO3-encrusted marls, and several organic-rich paleosols. Small remnant surfaces mapped as Terrace Z (below Terrace A) were observed within the main barrancos and indicate a later, brief accumulation period with subsequent incision to the modern channel.

Holocene landscape development in the Penaguila appears to have progressed from a period of stability to slope denudation with aggradation (stream infilling) followed by rapid incision which initiated sometime near the time of occupation. This change from a low relief alluvial surface to one cut by narrow channels may have been an important shift for local populations. Their response to that environmental modification may be associated with the horticulturalist to agricultural intensification noted in the archaeological record. Tighter chronology and better understanding of the driving processes for barranco incision and hollow formation will improve our ability to correlate the changing landscape with land use practices. Such an improved correlation leads to better understanding of human-landscape interactions.