POSTED BY ERIC SPRAGUE ON JULY 8, 2019
McPhee is currently releasing flows of approximately 400 CFS downstream as it follows its final ramp-down to base flows.
- Inflows are dropping daily, at a rate of up to a couple hundred CFS per day, until the snowpack runs out. Releases will fall accordingly, and are expected to reach base-flows later this week, ending the spill. Current weather forecasts show no indication that inflows will turn back up, even for a short time.
- Remain aware of the water level if on the river. For information on what types of craft are appropriate for different low flows, contact American Whitewater and Dolores River Boating Advocates (links below).
The following is more detailed information regarding how the spill is behaving, primarily repeated from previous posts.
McPhee is currently full and releases are varying as necessary to balance total reservoir outflows (including diversions) with total inflows in order to keep McPhee full, which is the first priority of reservoir operations during this period of the managed release. It is not known with certainty how releases will change through the end of the spill; however, they will vary regularly and trend downwards.
On a normal recession, daily average inflows can be expected to drop by a couple hundred CFS per day until the snowpack runs out.
Until the spill ends, releases will commonly fluctuate due to diurnal shifts and unpredictable weather patterns, similar to a more natural river hydrograph.
Earlier this year, releases from McPhee were managed to be as controlled and stable as possible, with standardized, measured changes following predictable ramping patterns. Because McPhee has reached full, releases are now following dropping reservoir inflows. Primarily, this means three things;
- First, that releases now follow a more natural hydrograph rather than extended periods at set flows. Instead, flows are behaving almost as if on an unmanaged river, reacting unpredictably to the combination of dynamic factors ranging from snow water content, coverage, and melt rates to solar radiation, temperature, precipitation, and transit loss. While reservoir operation moderates these rapid changes, releases will continue to follow inflows as much as possible and will be less steady than they have been. Releases will fluctuate to follow reservoir inflows less the current diversions.
- Second, that releases will fluctuate on a diurnal cycle, with larger releases at night in delayed response to snowmelt during the day, and lower releases during the day resulting from the reduced snowmelt at night.
- And third, that releases will not necessarily follow the standardized ramping rates experienced so far this year, or in previous years. Changes may come at any time of the day, and will change at roughly the same rate the upstream river is changing.
There is a possibility that releases may “hover” at some flows below 800 CFS (i.e. 200 – 799 CFS) for short periods of time as the seasonal recession in inflows progresses. At low flows in this range, there are small craft boating opportunities as represented on the American Whitewater website “Recommended minimum flows are 200 CFS for canoes/kayaks/inflatables” link below.
The primary goal of managing the releases this way is to fill McPhee and then keep it at full while ramping down. Because volume is intended to remain constant, there is a reasonable relationship which can be drawn between inflows and outflows in order to get an idea of what releases are about to do. In CFS,
“Dolores River Inflows” + “Other inflows” – “Irrigation Diversions” = “McPhee Releases”
“Dolores River Inflows” are forecasted by the Colorado Basin River Forecast Center (CBRFC) and can be viewed on the CBRFC website at https://www.cbrfc.noaa.gov/station/flowplot/flowplot.cgi?MPHC2. Please note that these flows are forecasts, and not at all guaranteed. They are updated daily and can vary substantially from day to day, especially if you’re looking more than about two days out.
“Other Inflows” is a catch-all value used to represent other sources of runoff into McPhee, e.g. House, Beaver, and Plateau creeks. This late in the season, this value is negligible, and can be treated as zero.
“Irrigation Diversions” is the total volume of water diverted from the reservoir to the project users. Currently, it is approximately 750 CFS, however there is some potential for it to increase during the next several days.
“Irrigation Diversions” and “Other Inflows” are running at approximately 750 CFS, so the releases will track at about 750 CFS less than the Dolores Gage (Real time Dolores Gage flows are at https://waterdata.usgs.gov/nwis/uv?09166500). Please note that these USGS readings do not look ahead like the forecasts mentioned above.
If you are watching the river inflows into McPhee to try and estimate what releases will be, please keep in mind; 1) that releases will not equal inflows – see the equation above, and 2) that it takes time for changes in releases to travel downstream. As a point of reference, in the past, it has taken approximately 20 hours at 800 CFS for changes in releases to be detected at the Slickrock gage, and it has taken even longer at lower flows.
If you have questions, the best way to address DWCD is through the “Contact” page of this website. Otherwise you can try calling 970-882-2164 extensions 5, 1 or 6.
Dolores Gage: https://waterdata.usgs.gov/nwis/uv?09166500
McPhee Elevation & Capacity: https://dwr.state.co.us/surfacewater/data/detail_tabular.aspx?ID=MCPRESCO&MTYPE=STORAGE
Dolores below McPhee: https://dwr.state.co.us/surfacewater/data/detail_graph.aspx?ID=DOLBMCCO&MTYPE=DISCHRG
Slickrock Gage: https://waterdata.usgs.gov/nwis/uv?09168730
Bedrock Gage: https://waterdata.usgs.gov/nwis/uv?09171100
Bureau of Land Management: https://www.blm.gov/visit/dolores-river-srma
The BLM has a detailed boating map of the Dolores river posted on their website. Link below.
BLM Avenza Map page for the Dolores: https://www.blm.gov/documents/colorado/public-room/map/colorado-dolores-river-100k-boating-map-17×40
The following are links to the American Whitewater River Inventory pages for the lower Dolores River: