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Show System Definition The basis of system identification is the conceptual model of the real world developed through various kinds of data which are gathered about the system. System identification involves two important steps, both of which are dependent upon the objectives of the study, or the kinds of questions which might be asked of the model: 1. A demarkation of the boundaries or limits of the system to be modeled. 2. The establishment of model resolution in terms of the time and space dimensions and functional considerations ( both physical and social). In the case of the Great Salt Lake study, the long- range goal is to develop a comprehensive planning and management model with predictive and decision- making capabilities of the entire water resource system of the lake. This objective requires a model which is sufficiently broad in scope to consider the entire lake system, including its environs, and also which has adequate resolution in terms of both the time and space dimensions and functional considerations to realistically represent the system. A gross conceptual model of the Great Salt Lake system is shown by Figure 6, which is intended to represent the basic physical and sociological components. With reference to the hydrologic component, the lake itself is a residual quantity whose level, volume, and quality are influenced and determined by characteristics of its tributaries and surrounding areas. Thus, any alteration in the regimen or character of tributary inflows ( both surface and subsurface) will affect the lake. Further, this complex hydrologic system, of which the lake is an integral part, has an inextricable influence on the biological and quality components of the total system. Consequently, in order to assess the impacts of any management scheme, a clear identification of the entire system is needed, including the physiographic, hydrologic, salinity, biologic, lim- nologic, and societal aspects, and the complex and dynamic couplings which are inherent in a system of this nature. The development of a comprehensive model of a system such as that identified by Figure 6 is a difficult and lengthy process. For this reason, the problem is approached by decomposing the total system into a number of subsystems. For example, each of the boxes shown by Figure 6 might be considered to represent a subsystem. A close examination of any one of the subsystems depicted by this figure would reveal some of its internal processes, and thus lead to an improved conceptual understanding of the system as a whole. The usual approach is to consider the total system as being organized in terms of hierarchies or levels as shown by Figure 7. This procedure permits the separate identification and subsequent development of models for the various parts of the total system. In this process model resolutions might be varied from one component subsystem to another, depending upon the requirements of the overall model and the available knowledge of each particular subsystem. Eventually, submodels are linked to comprise an overall model of the entire system. Evaluation and Analysis of Available Studies and Data The review and evaluation of previous studies and available data for a water resource system is an important step in the simulation of the system. Previous studies involving the system provide insight into system components and allows, when appropriate, established procedures for describing certain components of the system to be included in the simulation model. Data from a particular system or subsystem provide an understanding of the real world, and thereby provide a basis for evaluating model performance. The accuracy of predictions from a particular model is governed to a large degree by the reliability of the information on which the model is based and the accuracy of the data which are input to the model to provide the predicted output functions. Past investigations of the Great Salt Lake system, which includes the watershed, nearshore, and lake, have been structured toward the investigation of individual components of the system. The result of this kind of uncoordinated research has been that not all components of the system have received attention and in many areas an adequate understanding of specific components of the system has not been attained. Additionally, little work has been done on investigating the interactions between components of the system and on how such interactions affect the entire lake system. The Great Salt Lake drainage area or watershed is composed of the Bear, Weber, and Jordan River basins, which, when combined, form the major inflow to Great Salt Lake, and a number of minor drainage basins. Components of the Great Salt Lake watershed have been the subject of various studies due to the importance of this watershed in Utah's water develop- iment. The Utah Water Research Laboratory and the Utah Division of Water Resources have performed a series of water budget studies of the Bear, Weber, and Upper Jordan drainage areas ( Hyatt et al., 1969; Haws et al., 1970; and Haws and Hughes, 1973). Simulation model studies of the hydrology and salinity within the Bear River basin were performed by Hill et al. ( 1970 26 |