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Chapter I
Introduction

The actual allocation of surface water resources is a complex task, one that involves determining the flow in a river and distributing that water to the appropriate users. The distribution of this water must be performed according to Wyoming State Water Law (WSWL), which is based on the prior appropriation doctrine ("first in time, first in right"). In addition, the WSEO determines how water is stored in reservoirs and how water is released from these reservoirs to the river system. Besides the uses listed by Brosz and Jacobs (1980), the WSEO must also consider water consumed by conveyance losses and evaporation.

Furthermore, since all water diverted from a stream is not consumed and some of the water returns to the river system, the return flow must be restored to the river system. Through the coordination of all water uses, an accounting of the available water in the river system is made. It is then possible for the WSEO to evaluate and adjudicate additional demands for this water.

The WSEO must consider an intricate array of variables and a large amount of stream data when allocating water resources. This complexity creates a favorable environment for a computer model capable of simulating river basin operations. The Wyoming Integrated River System Operation Study (WIRSOS) planning model was developed to simulate river basin operations. In addition to simulating river basin operations, the model does a water accounting (water balance) of the water in the river system.

WIRSOS models a stream system corresponding to WSWL. However, many nuances to river system operation exist that cannot be modeled according to WSWL, and hence do not allow WIRSOS to predict the water available in the river more precisely.

The purpose of this thesis was to develop a WIRSOS model that would conform to WSWL. One that could improve the precision of river system simulation in situations where WSWL is not strictly enforced.

To accomplish this purpose, the following tasks were established:

1. Develop a modular subroutine based program that would be easier for a user to understand and modify.
2. Examine previous versions of WIRSOS and the United States Bureau of Reclamation Program HYDROSS (Hydrologic River Operation Study System) and incorporate those features into the modularized version of WIRSOS which would improve its capabilities to simulate a river system in Wyoming.
3. Develop subroutines in WIRSOS which improve reservoir operations and improve the ability of WIRSOS to more precisely simulate true river system management in Wyoming.

Before any alterations were made to WIRSOS, the model was used in Wyoming to model the Wind River and the Green River. After calibration, the Wind River model was able to produce river flow that were within plus or minus 5% of actual river flows for the period of record (Wind 1991). The Green River produced flow that were within plus or minus 8% of actual river flows (Meena 1993). The objective of the current model is to improve this accuracy and to make it easier to model a river system.

A literature search was conducted to determine what previous work had been done in the area of water planning models. This information is discussed in Chapter II. WIRSOS modifications are discussed in Chapter III, and a description of WIRSOS5 is given in Chapter IV. The testing of the model is discussed in Chapter V; finally, the summary and recommendations are presented in Chapter VI.

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