River system models

Overview

Water system models, also called operations models, planning models, and policy models, are computer-based representations of water distribution and supply systems that allow analysis of historical and future scenarios involving different hydrologic inputs, and different operational, policy, and/or infrastructure assumptions. They simulate the movement of water through the network of inflows, diversions, uses, storage, and outflows, meeting physical water-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.

Reclamation maintains primary three system models for the basin, currently implemented in the RiverWater modeling framework:

• 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

Figure 1. CBRFC forecast evolution plot showing the multiple probabilistic forecasts of April-July Lake Powell inflows that were made at each stage of the 2020 forecast season as the snowpack evolved. Image: CBRFC; Annotations: Jeff Lukas.

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.

Additional Resources

State of the Science Report

Chapter 8 of the State of the Science report covers many aspects of Streamflow Forecasting in greater detail; Section 8.4 is specific to mid-range forecasts (seasonal and longer). Chapter 6, on Hydrologic Modeling, has a detailed description of the CBRFC forecast model framework in Section 6.3, under National Weather Service Models.

New and Notable Research (2020-present)

[<URL FOR PAPER>]

Summary