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 Duchesne River Basin (Duchesne 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 Duchesne 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 Central Utah Water Conservancy District (CUWCD). 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 Duchesne River Basin, the Duchesne RW model includes the mainstem of the Duchesne River, Lake Fork River, and Uinta River. It also includes major tributaries and infrastructure from the Strawberry Aqueduct and Collection System (SACS). 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 solutions. 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 Duchesne 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 Duchesne 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 modeling dynamic outputs across different modes, while others, like the Duchesne Valley Water Treatment Plant, 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.

Observed data for the physical system are queried from the following sources:

USGS Stream Gages 

Reservoir Pool Elevation/Outflows, and Strawberry Aqueduct and Collection System

Canal Diversions

Backup Reservoir Data

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 Duchesne 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. Of the account types in the model that represent consumptive use, the Water Rights Solver allocates water in priority to each user. 

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 Duchesne Basin (particularly for agricultural users). The accounting system and Water Rights Solver are the key components 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 Duchesne 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, and a Losses account which estimates canal losses. Collectively, the diversion accounts represent the amount of water that each water user object diverts from the river representing water that accounts for Natural and Project diversions plus additional diverted flow to represent canal losses. 

The Duchesne 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 RiverWare Initialization Rules Set referred to as “UCRAF Initialization Rules”, a Rule Based Simulation ruleset referred to as the “UCRAF Ruleset”, and an Object Level Accounting Methods (OLAM) ruleset. The UCRAF Initialization Rules set known input data before the simulation starts to set initial conditions of the model. The UCRAF Ruleset 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 Duchesne 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 Duchesne 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 Duchesne RW model uses a RiverWare Initialization Rules Set referred to as “UCRAF Initialization Rules” to configure many model settings and parameters before simulation begins. This set initializes the model with historical data and operational inputs including USGS stream gages, observed diversions, SACS M&I diversions, and transbasin diversions. Appendix C describes the rules pertinent to the UCRAF Initialization Rules and also displays each of the initialization rules, descriptions, and notes.

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 Duchesne 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 Duchesne RW model. It also displays each of the methods, descriptions, and notes.