The Utah Colorado River Accounting and Forecasting - Decision Support Tool (UCRAF-DST) is a drought mitigation planning tool developed for the Colorado River Authority of Utah (CRAU) by Precision Water Resources Engineering (PWRE) and Follum Hydrologic Solutions (FHS). The UCRAF-DST Documentation file describes the UCRAF RiverWare model of the Price River Basin (Price RW model). It outlines the model’s purpose, structure, data development, key processes, and usage, and is designed to be updated as changes are made to the model.

The RiverWare component of the UCRAF-DST is a planning model implemented with a daily timestep over a 32-year period (1991–2022). The Price RW model implements observed, simulated, and perturbed datasets to assess the impact of different drought mitigation planning scenarios on the overall mass-balance of water in the basin. Historic datasets of stream gages, canal diversions, reservoir elevations and releases, and more were gathered from resources such as United States Geologic Survey (USGS), Utah Division of Water Rights (DWRi) and The Bureau of Reclamation (USBR). Additional demand datasets were collected from OpenET and simulated by the Diversion Runoff Calculator (DRC). Changes to the simulated demands are the primary driver of changes in the RiverWare model.

Covering much of the Price River Basin, the Price RW model encompasses inflows to Scofield Reservoir down to the Price River at Woodside USGS gage. The model operates in three simulation modes: Natural Inflow, Baseline, and Change Case. If an update to observed data is implemented, these modes must run sequentially. Otherwise, The Change Case mode solves both the Baseline and Change Case solution. As part of each Baseline or Change Case simulation, the model simulates physical and accounting systems to analyze water use, ownership, and consumptive use where changes in consumptive use under different drought mitigation scenarios represent the possible conserved water.

The Price RW model uses three types of data—observed, computed, and simulated—to simulate water flow and usage across different operational modes. Observed data, such as streamflow, diversions, and reservoir levels, are used in the Natural Inflow mode to calculate unmeasured quantities. These calculated values, referred to as computed data, typically include quantities like local inflows and hydrologic inflows, each of which are calculated through mass balance equations. Simulated data, generated by the DRC, represents consumptive use in the basin and can either include the baseline demands, used in Baseline mode, or altered demands used in Change Case modes. Additionally, the baseline simulated demands supplement the observed demands where the observed demands are missing. This integrated approach ensures accurate modeling of water use and conservation scenarios, especially for drought mitigation planning, by maintaining consistency across simulations and data types.

The RiverWare workspace visually represents the Price Basin's physical system using interconnected simulation objects with each containing relevant data such as inflows, diversions, and reservoir characteristics. The UCRAF-DST Documentation divides the model's objects into two groups: those directly influencing consumptive use and conserved water estimates and those that support the model but do not directly affect drought mitigation outcomes. Some objects, like stream gages and water users, play a critical role in modelling dynamic outputs across different modes, while others, like the Price River Water Improvement District, remain consistent and serve more supportive roles. Each object type—such as gages, reservoirs, and canals—has its own section in the documentation including both physical and accounting details.

RiverWare's accounting system enables detailed water tracking by assigning physical water volumes to specific account types used in RiverWare, Passthrough, Diversion, and Storage, using model logic and RiverWare’s built in Water Rights Solver. These accounts represent a legal right with an operational purpose. Additionally, the Price RW model uses these account types to simulate different types of water including Natural (in-stream), Project (reservoir storage), and Drought Mitigation, among others, and ensures consistency between the accounting and physical water systems. The Price RW model utilizes water classes which determines the amount of Natural and Project water each user diverts on a given day. These classes represent collections of water rights.

The model solves the mass balance in the accounting system by associating all physical system changes to those in the accounting system to determine values like diversion, return flow, storage, and others, accurately representing water rights in the Price Basin (particularly for agricultural users). The accounting system is the key component of the Duchesne RW model that enables simulating drought mitigation scenarios to understand potential volumes of conserved water.

Consumptive Use Accounting at a Diversion

Consumptive use in the Price RW model is simulated through water user objects with each containing diversion accounts that represent water rights linked to specific agricultural fields. These rights are grouped geographically and by priority date based on DWRi’s water rights network. Each water user object also includes a Project account where Project water is allocated to estimate and aggregate distributed project water. Collectively, the diversion accounts represent the amount of water that each water user object diverts from the river representing water that accounts for Natural diversions and Project diversions. 

The Price RW model simulates physical and accounting processes using sets of logic, called rules and functions, written in RiverWare Policy Language (RPL) organized into different rulesets including: a Rule Based Simulation ruleset referred to as the “UCRAF Ruleset” and an Object Level Accounting Methods (OLAM) ruleset. The UCRAF Ruleset sets known input data before each timestep for initial conditions of the model. It then computes values at each timestep to set physical and accounting values based on operational policies. OLAMs apply general rules, known as methods, to accounts on specific objects enabling consistent method application across similar objects. Model operations vary by mode—Natural Inflow, Baseline, or Change Case—each triggering different subsets of rules to accurately represent basin policies and criteria.

The Price RW model operates in one of three modes—Natural Inflow, Baseline, or Change Case—determined by specific model inputs. Natural Inflow mode uses historical demand and hydrology patterns to calculate computed data including local and hydrologic inflows. The computed data is then fed into the Baseline and Change Case modes to enable running the model in a planning mode to assess potential drought mitigation scenarios. While the model can run from the RiverWare GUI, it is recommended to use ArcPro’s DRC/Mapping Tool interface for running the model in the Change Case mode more efficiently. When switching modes, certain setup scripts and input adjustments are required to ensure correct simulation operation.

Appendix A: Data Development

The development of data for the Price RW model involves a step-by-step process where observed data including streamflow, diversions, reservoir elevation, reservoir outflow, and others are set as input to Natural Inflow mode to compute local or hydrologic inflows collectively called "natural inflows." These natural inflows, once calculated, serve as inputs for the subsequent Baseline and Change Case modes after the basin's mass balance is established. In the Baseline and Change Case modes, observed data and computed local inflows are used alongside simulated demands to solve mainstem stream gages as outputs.

This section also discusses the calculation of local inflows, calculation of gage flows given local inflows, and data requirements.

Appendix B: Water Rights Accounts and Canal Mapping

This section conveys all water rights information that is produced by the DRC including a table of water rights accounts developed for the model and the canal mapping which describes the coding system utilized to numerically map canals in the model domain. 

Appendix C: UCRAF Initialization Rules

The Price RW model does not use an Initialization Rules Set but rather initializes data on each timestep to optimize runtime. 

Appendix D: UCRAF Ruleset

This appendix describes the RiverWare Rule Based Simulation ruleset referred to as the “UCRAF Ruleset” that contains RPL logic used to simulate operations in the Price RW model. Generally, the RPL rules invoke logic to set data to slots, perform drought mitigation logic, or write data to output slots for visualization. Appendix D describes the rules pertinent to the UCRAF Ruleset and also displays each of the rules, descriptions, and notes.

Appendix E: Object Level Accounting Methods Set

The Object Level Accounting Methods Set Appendix describes each of the OLAM rules, known as methods, pertinent to the Price RW model. It also displays each of the methods, descriptions, and notes.