River system models

Overview

River system models, also called water system models, operations models, planning models, and policy models, are computer-based representations of river basins, and associated water supply and distribution systems, that can simulate historical, current, and future conditions under scenarios involving different hydrologic assumptions, and even different operational, policy, and infrastructure assumptions. They simulate the movement of water through the network of inflows, diversions, uses, storage, and outflows, meeting physical water mass-balance constraints while also following all of the rules for water allocation and reservoir operations to the extent that they are represented in the model.

Many generalized modeling tools and frameworks have been developed over the past several decades, with different advantages and disadvantages relative to specific applications. Most larger municipal utilities and water districts, and state water agencies, in the basin use one of these tools, though some may employ simpler spreadsheet models.

Figure 1. The Mid-term Probabilistic Operations Model (MTOM) in object view superimposed on a basin map, showing how the features of the Colorado River Basin are represented in the model. (Source: Reclamation)

NOTE: In August 2021, Reclamation's Colorado River Modeling Group combined the 24-Month Study Model (24MS) and the Mid-term Probabilistic Operations Model (MTOM)--itself an offshoot of 24MS--into a single modeling platform: the Colorado River Mid-term Modeling System (CRMMS). CRMMS is run in two modes: 24-Month Study Mode and Ensemble Mode, which replicate the functions of 24MS and MTOM, respectively.

Reclamation maintains two primary system models for the basin, implemented in the RiverWare modeling framework:

• Colorado River Mid-term Modeling System (CRMMS) - system projections at 1-5 year timescales
  • 24-Month Study Model (24MS) - short-term (1-2 years) projections for operational decision-making
  • Mid-term Probabilistic Operations Model (MTOM) - mid-term (1-5 years) projections for risk-based operational planning
• Colorado River Simulation System (CRSS) - long-term (5-50 years) projections for planning studies and policy analysis

Relevance

Water system models translate inflow scenarios--which are themselves informed by a complex chain of research, data, and tools--into water supply outcomes that are meaningful to water managers, water users, and other interests in the basin. These simulated outcomes may directly determine near-term operational decisions (such as Reclamation's Annual Operating Plan) or indirectly guide discussions and policy-making over longer time spans. The three Reclamation models, in particular, are hugely influential in both operational decision-making and longer-term planning in the basin.

Methods

RiverWare is an object-oriented modeling platform in which the objects may be inflow points, river reaches, diversions, reservoirs, canals, pipelines, and other water-resource features. Rule-based simulation with adjustable logic statements (e.g., if X then Y) are applied on a regular time-step (monthly for the three Reclamation models) to track water through the network of objects according to the rules.

Data and Tools

Data and tools for the primary Reclamation models are listed on their respective pages:

• Colorado River Mid-term Modeling System (CRMMS)
• Colorado River Simulation System (CRSS)

Additional Resources

State of the Science Report

Chapter 3 of the State of the Science report, Primary Planning Tools, describes the three primary Reclamation system models in detail.