Great Plains Region

As manager of Green Mountain Reservoir, Reclamation’s Eastern Colorado Area Office (ECAO) facilitates coordination meetings with stakeholders responsible for the management and operations of storage reservoirs and irrigation diversions in the Upper Colorado River basin from the Colorado River headwaters to the confluence with the Gunnison River in Grand Junction, Colorado. These coordination meetings occur at least weekly during the irrigation season and are called the Historic User Pool (HUP) coordination call. A key aspect of these meetings is to share information regarding quantity and timing of reservoir releases, diversions, and return flows that impact flows in the 15-Mile Reach of the Colorado River. The 15-Mile Reach lies immediately upstream of the confluence with the Gunnison River and is identified as a critical stream reach for the recovery of Colorado River endangered fish. The U.S. Fish and Wildlife Service has defined a suite of recommended flows for this reach that are tiered to the hydrologic condition. Additionally, the HUP meetings identify and coordinate storage releases necessary for irrigation and replacement for out-of-priority diversions.

The Upper Colorado Basins Decision Support System (DSS) simulates expected streamflow along the river from the Colorado River near Kremmling gage to the Colorado River below Grand Valley Canal near Palisade gage due to changes in reservoir releases in the basin. This tool allows the user to assess and visualize the aggregate effect to downstream gaging sites the proposed operational changes at each reservoir during the HUP coordination meetings.

The system displays three different flow traces. The Native flow trace corresponds to the expected streamflow due to releases of reservoir inflow and any other water (replacement, augmentation, etc) that can be diverted by senior water rights in the Grand Valley. The Total-1 and Total-2 traces, correspond to the resulting streamflow produced by total reservoir releases under two different scenarios. The Total-1 and Total-2 traces include fish water delivered to the 15-mile reach or water for the Grand Valley Powerplant in addition to the native flow.

The DSS is updated prior to the HUP meeting using anticipated reservoir releases. This first update of the system simulates three flow traces (Native, Total-1 and Total-2). The Total-1 and Total-2 traces are the same initially. During the HUP meeting, if changes to projected releases are proposed, the DSS is updated using the proposed releases. The Native and Total-2 flow traces are updated. This allows for the comparison of the effect of different reservoir operational scenarios against target flows in the 15-mile reach.

The online tool shows a map of the Upper Colorado River from the headwaters in the Rocky Mountain National Park to Grand Junction. The map includes red icons at the locations of the streamflow gages and blue icons at the location of the main reservoirs in the system. Each icon includes the name of the site and links to observed and simulated data. By clicking one of the icons a callout is displayed with an option to Query DSS Data and other options to display observed data from different sources such as the US Geological Survey (USGS), Denver Water, Colorado River District, etc. The Query DSS Data option shows projected release data for each reservoir and modeled streamflow traces for the gages (Figure 1).

The user can select to display the modeled data in Daily or Hourly time step by choosing the time step in the radial bottoms above the map (Figure 1). If the time step is changed, the user needs to query the DSS again to update the results. The results of the query are displayed below the map in graphical and tabular formats as show in Figure 2.

Above the main map, there are three links to access summary tables of daily reservoir releases use to generate the the Native, Total-1 and Total-2 scenarios (Figure 1).

ECAO partnered with the Colorado Basin River Forecast Center (CBRFC) to develop a simplified hydrologic model for the DSS. The modeling tool for the DSS consists of two main components: 1) CBRFC’s computation of adjusted local flow time series; and 2) ECAO’s computation of adjusted total flow time series.

1) CBRFC’s adjusted local flow time series: The DSS hydrologic model relies on CBRFC’s deterministic streamflow forecasts. CBRFC’s hydrologic model of the Upper Colorado River above Palisade is complex and accounts for snow accumulation and ablation and rainfall-runoff models, multiple reservoir releases and depletions and return flows models. Stick diagrams of CBRFC’s forecasting system implementation are available at: https://www.cbrfc.noaa.gov/wsup/guide/stickdiagrams/uc_abvkrem.pdf, https://www.cbrfc.noaa.gov/wsup/guide/stickdiagrams/uc_kremtoglen.pdf, https://www.cbrfc.noaa.gov/wsup/guide/stickdiagrams/uc_glentopowell.pdf. For this project, CBRFC developed a simplified hydrologic model that removes the effect of reservoir releases from the total flow simulations at each of the gages. These time series that do not account for the effect of reservoir releases are called adjusted local flow time series.

2) ECAO adjusted total flow time series: ECAO implemented a simplified hydrologic model consistent with CBRFC’s simplified model. ECAO is using the open source software TSTool, a time series manager developed for the State of Colorado (https://sites.google.com/site/cdssstaging/tstool/). TSTool includes a built-in routing model equal to the model used in CBRFC’s forecasting system (https://www.nws.noaa.gov/ohd/hrl/nwsrfs/users_manual/part2/_pdf/24lagk.pdf). ECAO setup a TSTool command file to compute adjusted total flow time series at each gage by aggregating CBRFC’s adjusted local flow times series with routed reservoir releases. The aggregate time series are called adjusted total flow time series and correspond to the Native, Total-1 and Total-2 flow traces displayed by the Online Tool. The adjusted total flow time series are computed as follows:

Kremmling (KRMC2):

KRMC2 adjusted total = KRMC2 adjusted local + MBWC2 (Wolford) routed + BGMC2 (Green Mountain) routed + WFRC2 (Williams Fk) routed + CBGC2 (Granby) routed + WCKC2 (Willow Ck) routed – CAWC2D (Windy Gap pump) routed

Dotsero (EGLC2):

EGLC2 adjusted total = EGLC2 adjusted local + KRMC2 total adjusted routed

Cameo (CAMC2):

CAMC2 adjusted total = CAMC2 adjusted local + EGLC2 total adjusted routed + RUDC2 (Ruedi) routed

Palisade (CGYC2):

CGYC2 adjusted total = CGYC2 adjusted local + CAMC2 total adjusted routed

Routing Parameters

The following tables summarize the routing parameters for all modeled routing reaches. The Lag parameter represents the flow delay in hours. The K parameter attenuates the lagged flow and is also measured in hours. Routing parameters have been determined from historical records by CBRFC. For routing reaches in the DSS that coincide with routing reaches in the CBRFC forecasting system, the CBRFC’s routing parameters were adopted. For routing reaches in the DSS that do not coincide with the reaches in the CBRFC’s system, a subset of the CBRFC’s routing parameters was developed and adapted to the new DSS routing reaches.

In some cases, a constant Lag value is sufficient to route all possible flows (e.g. Granby to Kremmling, Willow Ck to Kremmling, Ruedi to Cameo, Dotsero to Cameo). In other cases, a variable Lag is used. The variable lag is a function of flow. The first Lag value (Lag1) is used for all flows less or equal than the first flow value (Q1). The last Lag value (Lagn) is used for all flow greater or equal than the last flow value (Qn). Linear interpolation is used to determine Lag values for flows that fall in between points in the Lag-Q curve. For all reaches, a single K parameter is used and applies for all possible flows.

Major Model Assumptions

Primary Use: To expedite the assessment of operational reservoir changes in projected river flow and to disseminate results to stakeholders in real time. Results from this system do not replace CBRFC's official forecast.

Routing Parameters: Routing parameters are subsets of the routing parameters used in the official CBRFC's operational forecast system (OFS). This DSS includes different routing reaches that are consistent with the simplifications in the hydrologic model. For example, CBRFC's OFS routes Granby release up to the confluence of the Colorado River with the Fraser and adds the routed release to the flow generated up to that point in the basin above the confluence. In this DSS, Granby release is routed up to the Kremmling gage and then added to the runoff generated above Kremmling.

Timing of flow changes: The time of change of reservoir releases is always at mid-night.

Simulation Period: Simulation Period 10 days into the future from the day the model is updated. The model is not updated automatically every day. Therefore, the future/projected data display in the Online Tool will always start at the current time and end 10 days after the date the system was last updated.

Adjusted Local Flow: All assumptions included in the CBRFC's operational streamflow forecast model are included in the DSS. Streamflow forecast uses 7 days of forecast precipitation and 10 days of forecast temperatures. Diversions are assumed to either stay at current levels or change to keep bypass flows constant or above minimum flow requirements. Unmeasured diversions are simulated using a consumptive use model calibrated to historical data from 1981 to 2015. For the Colorado near Palisade model simulation, the Grand Valley and Government Highline canal diversions are accounted for explicitly; future values are held at the last observed value. The model of return flows has been calibrated using historical data from 1981 to 2015. Return flows are estimated based on the time of year. Also, the model assumes water will be 'checked' as needed to allow the Grand Valley to take its full allotment. Return flows through the Palisade Pipeline are not accounted for.

Accounting – River Losses: The DSS does not include an accounting model. River losses as accounted by the State of Colorado are not currently included in the results. Physical losses in the river are accounted for by the simulation of hydrologic processes in the basin. The DSS hydrologic model uses CBRFC’s forecast. This forecast relies in the simulation of basin runoff from snow and rainfall events using the Sacramento Soils Moisture Accounting Model (SAC-SMA). The runoff model simulates the movement of water through the soil by characterizing two different soil zones: 1) a shallow zone with fast response to runoff and; 2) a deeper zone that produces a slower runoff response (e.g. baseflow). In addition to the rainfall-runoff models, the routing model simulates the translation and attenuation of the flow wave in the river. Diversion and return flows are also simulated using consumptive use models and other routines. CBRFC’s hydrologic models are calibrated to historical data. Model parameters are developed to match flow simulation to historical records as close as possible.

Time zone: All data are displayed in Mountain Standard Time (MST)