To make informed operation decisions, water managers need:

  • Current and potential future scenarios of precipitation.
  • Data that describes the current state of watersheds, channels, and water management facilities, including reservoirs, diversions, and other controllable features of the system.

An HEC-RTS watershed is a set of data, information, models, and images that represent watershed lands and the channels, gages, and water control features within the watershed.

  • Information about the likely future state (e.g., one hour to two weeks) of the watersheds, channels, and management facilities.
  • Information about the consequences of management actions that alter future states of the natural and managed systems.

Data that describes the current state of the system comes from a network of environmental sensors. These sensors, which are owned and operated by Federal, state, and local government agencies, utility companies, and commercial enterprises, measure:

  • Weather conditions, including air temperature, precipitation depths and rates, and evaporation depths and rates.
  • Watershed states, including snow accumulation.
  • Depth, velocity, and other conditions in streams, rivers, canals, and other waterways.
  • Lake or reservoir level (from which storage volume may be inferred), rates of release of water through outlets, settings of spillway gates, and other conditions of lakes, reservoirs, and diversions.

Data from sensors are transmitted by radio, satellite, telephone, the Internet, and other media to receiving sites, and then to water managers. There, the data are decoded, transformed, checked for quality (validated), and stored in databases. With this data, water managers have near-real-time reports on the current state of the watersheds, channels, and management features.
Using the environmental data from the databases, as well as forecasts, as inputs to models of watershed and channel processes, water managers can forecast future availability of water. A water manager can predict the runoff from a watershed, hours or even days into the future because of observed and forecasted precipitation values within the watershed. To do so, the water manager uses a mathematical model that simulates infiltration, overland flow, baseflow, channel flow, and other relevant watershed and channel processes.

A forecast is a simulation of watershed processes and consequences of flooding based on input data and information and hydrologic, reservoir operation, hydraulic, and impact analysis models. Forecast results include flow and stage in the channel from watershed runoff, reservoir release schedules, floodplain inundation maps, floodplain consequence reports, and reports listing actions for emergency responders to take. These results inform water management decision making.

With models of water control facilities, water managers can simulate and assess the impact of operation alternatives. For example, a water manager can determine which of two operation alternatives will more likely result in higher downstream water levels due to a large storm. The forecast of future inflow, combined with a mathematical model of the behavior of the reservoir and the downstream channel, makes this possible.

One operation alternative could be to release water now from a rapidly filling reservoir to accommodate future inflows. Another alternative could be to delay release in anticipation that inflows will diminish, and large releases will not be required. The manager has, with analysis software, the capability to compare these operation alternatives in a quantitative manner. Information from the simulation permits the manager to assess the economic, environmental, life safety, and other consequences of the operation alternatives. This information will lead to better-informed decisions.