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 San Rafael River Basin (San Rafael 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 six-year period (2018–2023). The San Rafael RW model implements observed, simulated, and perturbed datasets to generate a historical characterization of the San Rafael Basin. In the future, the model will use those 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), Emery Water Conservancy District (EWCD), 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 San Rafael River Basin, the San Rafael RW model encompasses flows of the three tributaries of the San Rafael River starting at headwater reservoirs. Those include Ferron Creek with Millsite Reservoir, Cottonwood Creek with Joe's Valley Reservoir, and Huntington Creek with five headwater reservoirs of Electric Lake, Huntington Reservoir, Cleveland Reservoir, Rolfson Reservoir, and Miller Flat Reservoir. The model also simulates two regulating reservoirs: one in the Cottonwood Creek Basin called Adobe Reservoir and one in the Huntington Creek Basin called Huntington North Reservoir. The model operates in two simulation modes: Natural Inflow and Baseline. Future model development will expand its capability to simulate in Change Case mode. If an update to observed data is implemented, these modes must run sequentially. Otherwise, the Change Case mode will solve 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 San Rafael 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 current version of the San Rafael RW model is simulating with observed demand data, and rules written in RiverWare Policy Language (RPL) to operate all nine reservoirs in the basin. Future work will expand these operations with accounting, and use these operations to extend the period of record for a more advanced planning model. 

Observed Data Limitations and Hurdles

The San Rafael model was uniquely challenging due to issues with data availability, consistency, and quality throughout the system. As part of the data compilation required for this project, PWRE compared all available historical data available from both Utah Division of Water Rights (DWRi) and Emery Water Conservancy District (EWCD). 

A separate document has been provided to CRAU which extensively details several of the data issues which resulted in setbacks to the modeling effort. These issues are generally categorized as:

1. Challenges in Data Availability and Acquisition

   1. Several key reservoirs and diversions in the basin have no historical data publicly available prior to 2018. When data was available, there were discrepancies between different sources of data for several of the same reservoirs, diversions, and gages. 

2. Mass Balance Issues for Reservoirs, Diversions, and Stream Gages

   1. The level of scrutiny historically applied to daily data in this basin has likely been lower than that which is required for model development, where water balance needs to be maintained throughout the entire system. This placed some responsibility for data quality-checking and development on the modeling team. 

3. Operational Understanding and Institutional Knowledge Transfer

   1. The Huntingon and Cottonwood Creek systems are operationally complex, and have undergone significant changes in recent years. In conjunction with limited access to local knowledge, this made model development challenging. 

The RiverWare workspace visually represents the San Rafael Basin's physical system using interconnected simulation objects with each containing relevant data such as inflows, diversions, and reservoir characteristics. The UCRAF-DST Documentation will divide 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 remain consistent and serve more supportive roles. Each object type—such as gages, reservoirs, and canals—will have 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 

Emery Water Conservancy District Stream Gages, Reservoir Pool Elevation/Storage and Outflow, and Canal and Pipeline Diversions

Utah Division of Water Rights Historical Daily Data for the Cottonwood Creek System

Utah Division of Water Rights Historical Daily Data for the Huntington Creek System

Utah Division of Water Rights Historical Daily Data for the Ferron Creek System

While the San Rafael model does not currently have an Accounting infrastructure, future work will develop this model capacity informed by conversations with EWCD and DWRi. 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. These accounts represent a legal right with an operational purpose. The San Rafael model will make use of the Accounting system by simulating Natural water, water in the system that would naturally be there, and Project water, the water that is supplemented by reservoir storage. All water is by nature, Natural; however, Natural can become Project water by exercising storage when there is no natural demand downstream by water users. 

The model will solve 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 natural water demand in the San Rafael Basin (particularly for agricultural users). The accounting system will be a key component of the San Rafael 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 San Rafael RW model will simulate through water user objects with each containing diversion accounts that represent water rights linked to specific agricultural fields. These rights will be grouped geographically and by priority date based on DWRi’s water rights network. Each water user object will also include 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 will 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 San Rafael 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 Initialization 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 values based on operational policy informed by DWRi and EWCD. Currently, the model has fourteen rules which operate the reservoirs throughout the system to meet demands, forecast inflows and spill when hydrologically necessary, and release for minimum flows when dictated by basin policy. 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 San Rafael RW model will operate 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.

The model verification process includes Root Mean Standard Deviation Ratio (RSR), Percent Bias (PBIAS), Nash Sutcliffe Efficiency (NSE), and Log-NSE statistical methods. These metrics help evaluate the model’s performance by comparing simulated (modeled operations) to historical record of operations. These model verification statistics have not yet been developed for the San Rafael model and will be made available when the Baseline mode is complete. 

Appendix A: Data Development

The development of data for the San Rafael 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 will be used alongside simulated demands to solve mainstem stream gages as outputs. Note that due to the complexity in gathering and processing data in the San Rafael Basin for the development of Natural Inflow, the model currently simulates the 2018 to 2023 period. Further model development will add a period of inflow for the basin to expand the simulation period to 1991 through 2023. 

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

Appendix B: Water Rights Accounts and Canal Mapping

Future work will include development of this section, which will map all Water Rights accounts throughout the system. 

Appendix C: UCRAF Initialization Rules

The San Rafael model utilizes several Initialization Rules to occasionally pre-process historical input data (e.g., remove known errant data in winter flows for some diversions and gages in the system), identify and populate all simulation objects with the correct input data (e.g., diversions with historical data or DRC data depending on the Model Phase), and initialize several simulation objects in a RiverWare calculation nuance that allow the rules to more accurately calculate required reservoir inflows and outflows. 

Appendix D: UCRAF Ruleset

This appendix will describe RiverWare Rule Based Simulation ruleset referred to as the “UCRAF Ruleset” that contains RPL logic used to simulate operations in the San Rafael 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. Currently, the model has fourteen rules which operate the reservoirs throughout the system to meet demands, forecast inflows and spill when hydrologically necessary, and release for minimum flows when dictated by basin policy. Appendix D will describe in more detail the rules pertinent to the UCRAF Ruleset and also display each of the rules, descriptions, and notes.

Appendix E: Object Level Accounting Methods Set

The Object Level Accounting Methods Set Appendix will describe each of the OLAM rules, known as methods, pertinent to the San Rafael RW model. It will also display each of the methods, descriptions, and notes.