Surface Water Supply Index / Definitions
The following tems are used in this documentation.
| Term | Definition |
|---|---|
| AWDB | The NRCS Air and Water Database makes data available to the public through web services. |
| CIM | Colorado Information Marketplace, where the State of Colorado publishes SWSI results |
| Colorado’s Decision Support Systems (CDSS) | A system of databases and software tools used to help the State of Colorado make decisions about water resources. |
| ColoradoWaterHBGuest | HydroBase data are made available to the public from web services. ColoradoWaterHBGuest is the public account that is allowed accessed to the HydroBase web services. |
| ColoradoWaterSMS | The State of Colorado’s Satellite Monitoring System transmits real-time hydro-meteorological data to a central storage database. While these data are made available, they are typically considered provisional and have not been quality-controlled. |
| Command file | A text file with a .tstool extension that is used by TSTool software and contains commands for data acquisition, analysis, and visualization. |
| Control file | The Excel workbook named CO-SWSI-Control.xlsx that is used to define all configuration properties and input data needed to run the Colorado SWSI analysis. |
| Current Period | The water year that includes the current month for which the SWSI analysis is being computed. |
| CWCB | Colorado Water Conservation Board |
| Data Composite | The sum of the SWSI component volumes (reservoir storage, previous month’s streamflow, and forecasted runoff) for a HUC8 or river basin. |
| DWR | Colorado Division of Water Resources |
| Forecast SWSI Value | A SWSI value that was computed using forecasted natural flows for the forecasted runoff component. |
| Forecasts | Future runoff volumes predicted by the NRCS using regression equations and observed hydro-meteorological data as predictor variables. The NRCS issues these forecasts on the 1st of the month from January to June at locations throughout the West dominated by snowmelt-runoff. In Colorado, the forecasts represent future runoff volumes for a specified forecast period. The forecasts are presented as probabilistic ranges. For the purposes of the Colorado SWSI analysis, the 50th percent exceedance (expected value) forecast is used. |
| Historical Period | The period used to establish the distribution of SWSI and NEP values, currently defined as WY 1971-2010. In this period, historical natural flows are used for the forecasted runoff component. |
| Historical SWSI Value | A SWSI value that was computed using historical natural flows for the forecasted runoff component. |
| HUC | Hydrologic unit codes are basin boundaries established by the US Geological Survey. The length of the code indicates the relative spatial scale. For example, HUC2 represents major river basins, while HUC8 represents watersheds. In the Colorado SWSI analysis, all references to HUC refer to the 8-digit HUC. |
| HydroBase | The State of Colorado’s official database that stores water administration data and hydro-meteorological data. These data are accessible in TSTool using HydroBase web services. |
| Native flow | For the purposes of the Colorado SWSI analysis, native flows are approximate estimates of the streamflows that would occur at a given location in the absence of human influences and that result from natural hydrologic processes such as rainfall-runoff and snowmelt-runoff: Q_native=Q_observed+∆ReservoirStorage+∆Irrigation+∆Transbasin where: Qnative = the native streamflow calculated at a given location for a given time interval Qobserved = the streamflow observed at a given location for a given time interval ∆ReservoirStorage = ∑(∆reservoir storage) for all reservoirs upstream of the given location for the given time interval ∆Irrigation = ∑(diversions – return flows) for significant demands upstream of the given location for the given time interval. This term is often omitted unless observed data are available. ∆Transbasin = ∑(transbasin exports – transbasin imports) upstream of the given location for the given time interval. |
| Natural flow | For the purposes of the Colorado SWSI analysis, the terms "native flow" and "natural flow" are used interchangeably and represent an approximation of the streamflows that would be in the river at a given location if not for human influences. See definition for native flow. |
| NEP | Non-exceedance probability, or the probability of not exceeding a given value. |
| NRCS | Natural Resources Conservation Service |
| Observed flow | Streamflows in a river channel measured using a stream gage and rating curve. These flows reflect human influences to the river. |
| OIT | Colorado Governor's Office of Information Technology |
| OpenCDSS | The open source software initiative for Colorado's Decision Support Systems. See the OpenCDSS website for software documentation and downloads, such as for TSTool. |
| Override | An override is a value specified by the user that is manually entered and will be used even if data for that time interval already exist in a time series. |
| OWF | Open Water Foundation, developer of the TSTool software and SWSI tool. |
| Recent Period | The period between the historical period and the current period. In the monthly Colorado SWSI analysis, data for the recent period are not required but are helpful for comparison against current results. The recent period results are calculated the same way as the current month’s SWSI: the composite volume is assessed using the historical dataset. However, the forecasted runoff component in the recent period is calculated using historical natural flows. This means that in the monthly analysis, the SWSI results for the recent period represent “historical SWSI” values. When generating historical forecasts of the Colorado SWSI (for example, because the station assignments for a HUC have been changed), the forecasted runoff component in the recent period is calculated using forecasted natural flows, same as that used in the current period. This means that in the re-forecast analysis, the SWSI results for the recent period represent “forecast SWSI” values. |
| RESC | A data type used by the NRCS AWDB web services to represent historical reservoir storage contents. For a monthly time step, the data values represent end-of-month storage. |
| SRVO | A data type used by the NRCS AWDB web services to represent historical natural flow volumes. |
| SRVOO | A data type used by the NRCS AWDB web services to represent historical observed flow volumes. |
| SWSI | The Surface Water Supply Index was developed by the NRCS and Colorado DWR for Western States that rely on snowmelt-runoff and reservoir storage for water supply (Garen, 1993). |
| Time series product | Text file with a .tsp extension that is used by TSTool as a template for plotting data and placing annotations on one or more graphs. |
| TSTool | A data acquisition, analysis, and visualization tool developed by the State of Colorado as part of the Colorado’s Decision Support Systems (CDSS). TSTool processes are used to promote transparency, repeatability, and automation for complex water resources analyses. See the TSTool software page on the OpenCDSS website. |
| Water Year | A water year runs from October of the previous calendar year to September of the current calendar year. For example, water year 1971 begins October 1970 and ends September 1971. |
| WATF | The State of Colorado’s Water Availability Task Force (WATF) interprets available hydrologic information from across the State and takes action to mitigate drought effects when appropriate. |