Peak Flow Forecasts, April 1, 2009   www.cbrfc.noaa.gov


NOAA, National Weather Service
Colorado Basin River Forecast Center
Salt Lake City, Utah
www.cbrfc.noaa.gov

Contents


Introduction

NEW: Starting in May 2011, we now estimate, where possible, an instantaneous flow for each mean daily flow forecast. These instantaneous flows are estimated from a historical regression analysis at each point. For more information view the regression plots.

Streamflow varies dramatically over the course of the snowmelt season. To characterize the magnitude of a year with a single seasonal peak sometimes can be an oversimplification. Hydrographs (or graphs of mean daily flow versus time) for each site can be viewed by clicking on the site name. The hydrographs include an example high and low year alongside last year and this year.

River recreationists often ask what are the high and low years. Rankings of a sites peak flows can be viewed by clicking the site name below. Reservoir regulation plays a major role in determining observed peak flows. As would be expected, higher (but more short-lived) peaks are generally observed in the pre-regulatory era (before 1960).


Upper Colorado Peak Flow Forecasts (mean daily cfs)

Prepared by: Alcorn, Cox, Reed
2009 Forecast Exceedance Probability
Historic
Peak
Average
Peak
Flood*
Flow
2008
Peak
2008
Date
90% 75% 50% 25% 10% Normal time
of Peak
Issuance
Date
Observed
Peak
Observed
Date
Colorado
Kremmling, Nr 12,700 3,900 10,150 6,120 5/23 N/A N/A N/A N/A N/A 5/15 - 6/27 4/1
Eagle
Gypsum, Blo 6,580 3,600 6,600 4,500 6/03 3,000 3,400 3,900 5,000 6,000 6/1 - 6/21 4/1
Colorado
Dotsero, Nr 20,800 9,425 17,200 12,400 5/22 7,500 8,500 10,000 13,000 16,000 5/25 - 6/20 4/1
Crystal
Redstone, Nr, Avalanche Ck 3,500 1,965 3,100 2,330 6/19 1,600 1,800 2,100 2,300 2,600 5/29 - 6/22 4/1
Roaring Fork
Glenwood Springs 11,800 6,150 16,800 7,070 6/20 5,500 6,000 6,500 8,000 9,500 6/3 - 6/18 4/1
Colorado
Cameo, Nr 38,000 17,500 23,700 22,500 6/04 15,000 17,000 19,000 24,000 28,000 5/29 - 6/18 4/1
Plateau Ck
Cameo, Nr 4,100 1,460 4,370 2,010 6/03 700 900 1,200 1,700 2,300 5/9 - 6/11 4/1
East
Almont, Nr 5,000 2,080 2,970 2,710 5/22 1,700 2,000 2,250 2,500 2,900 5/28 - 6/17 4/1
Nf Gunnison
Somerset, Nr 7,080 3,310 8,305 4,120 5/21 2,700 3,100 3,600 4,200 4,800 5/11 - 6/2 4/1
Surface Ck
Cedaredge 640 210 1,540 304 5/21 100 140 190 270 350 5/3 - 6/8 4/1
Uncompahgre
Colona 1,900 1,390 3,765 1,220 5/21 N/A N/A N/A N/A N/A 5/20 - 6/27 4/1
Gunnison
Grand Junction, Nr 23,200 9,660 19,525 14,500 5/22 7,100 8,200 9,300 10,500 13,000 5/3 - 6/12 4/1
Colorado
Co-ut Stateline, Nr 68,300 26,150 47,600 38,900 6/04 21,000 24,000 28,000 34,000 42,000 5/22 - 6/16 4/1
Dolores
Dolores 6,950 2,980 7,905 4,040 5/21 2,200 2,400 2,800 3,300 3,900 5/9 - 6/4 4/1
San Miguel
Placerville, Nr 2,740 1,310 2,960 1,600 6/19 970 1,050 1,200 1,300 1,500 5/26 - 6/23 4/1
Dolores
Cisco, Nr (see Note1 Below) 12,900 6,050 N/A 4,610 5/22 N/A N/A N/A N/A NA 4/26 - 6/5 4/1
Colorado
Cisco, Nr 69,500 28,800 57,800 40,100 5/23 24,000 27,000 31,000 37,000 45,000 5/20 - 6/15 4/1
Green
Daniel, Nr, Warren Bridge, At 5,620 2,975 N/A 2,770 6/27 2,200 2,600 2,900 3,000 3,400 5/30 - 6/30 4/1
New Fork
Big Piney, Nr 9,110 5,285 9,870 3,530 6/21 3,300 3,700 4,300 5,000 5,500 5/31 - 6/24 4/1
Green
Labarge, Nr 18,800 9,270 13,950 6,800 6/27 N/A N/A N/A N/A N/A 5/30 - 6/24 -
Big Sandy
Farson, Nr 1,690 820 1,250 650 5/22 N/A N/A N/A N/A N/A 5/28 - 6/23 -
Green
Green Rvr Wy, Nr 15,400 7,110 15,500 4,400 7/12 N/A N/A N/A N/A N/A 5/23 - 7/11 -
Hams Fork
Frontier, Nr, Pole Ck, Blo 2,000 825 1,580 815 5/21 450 550 650 800 950 5/10 - 6/9 4/1
Blacks Fork
Little America, Nr 6,970 2,440 5,450 1,370 6/09 700 850 1,200 1,700 2,300 5/2 - 6/27 4/1
Yampa
Steamboat Springs 5,870 3,240 4,700 3,590 6/03 2,600 2,800 3,200 3,800 4,500 5/19 - 6/12 4/1
Maybell, Nr 24,400 10,475 21,000 16,700 5/23 9,000 9,700 10,800 12,600 15,000 5/13 - 6/10 4/1
Little Snake
Lily, Nr 13,400 4,745 24,000 7,660 5/23 4,600 5,100 6,000 7,300 9,400 5/5 - 6/12 4/1
Yampa
Deerlodge Park 32,300 13,955 17,200 21,800 5/23 13,400 15,000 16,300 18,400 22,000 5/11 - 6/6 4/1
Green
Jensen, Nr (see Note1 Below) 38,500 17,600 24,000 22,900 5/24 17,700 19,300 20,600 22,700 26,300 5/14 - 6/11 4/1
Rock Ck
Upr Stillwater Res 2,080 1,350 N/A 1,275 5/21 890 1,000 1,100 1,250 1,450 5/25 - 6/20 4/1
Uinta
Neola, Nr 4,640 1,640 5,670 790 5/20 650 750 1,000 1,150 1,400 5/25 - 6/15 4/1
White Rocks
Whiterocks, Nr 4,640 1,230 5,290 590 5/20 400 500 600 700 900 5/10 -6/10 4/1
Duchesne
Tabiona, Nr 2,320 765 4,090 815 6/17 350 550 750 950 1,100 5/15 - 6/15 4/1
Randlett, Nr 11,500 2,755 7,400 535 6/25 550 750 1,200 1,800 2,700 4/27 - 7/5 4/1
White
Meeker, Nr 6,320 3,200 5,930 3,380 5/21 2,500 2,800 3,200 3,700 4,500 5/21 - 6/14 4/1
Green
Green River, Ut (see Note1 Below) 47,200 22,560 46,600 26,200 6/09 21,000 23,000 25,200 28,500 34,100 5/18 - 6/16 4/1
Cataract Canyon (estimated)
116,700 51,350 N/A 61,600 6/06 45,000 50,000 56,000 65,000 79,000 5/20 - 6/16 4/1
San Rafael
Green River, Nr 3,600 910 N/A 420 6/25 300 350 450 550 950 5/17 - 7/16 4/1
Muddy Ck
Emery, Nr 515 205 N/A 160 5/21 100 110 120 140 200 5/19 - 6/18 4/1
Dirty Devil
Hanksville, Nr, Poison Spgs ** 1,310 445 N/A N/A N/A N/A N/A N/A N/A N/A 3/12 - 5/31 -
Escalante
Escalante, Nr *** 227 72 N/A 20 3/21 30 35 40 60 80 3/24 - 6/2 4/1
San Juan
Pagosa Springs 4,640 2,485 6,840 2,870 5/21 2,400 2,600 2,900 3,300 3,700 5/15 - 6/12 4/1
Animas
Durango 10,700 4,675 9,555 5,850 5/21 3,500 4,000 4,600 5,000 5,700 5/28 - 6/14 4/1
Farmington 11,000 4,900 8,810 6,080 5/21 3,700 4,100 4,800 5,500 6,000 5/31 - 6/15 4/1
San Juan
Bluff, Nr (see Note2 Below) 15,600 7,340 40,485 8,850 6/05 7,500 8,000 8,500 9,500 10,000 5/21 - 7/4 4/1

N/A = Not Available (Not a flood forecast point or no forecast procedure exists.)
* = Flood flow is for current year only and is an instantaneous value.
- = Exceedance value has already occurred during the current runoff season.
note1 - For releases below McPhee Reservoir call 970-565-7562, Peak flow forecasts on the Green River below Flaming Gorge Reservoir are based on USBR planned regulation.
note2 - Peak flow forecasts on the San Juan below Navajo Reservoir are based on USBR planned regulation.
** = Runoff period March - June.
*** = Runoff period March - June does not include contribution from Boulder Creek.


Great Salt Lake Peak Flow Forecasts (mean daily cfs)

Prepared by: Bernard
2009 Forecast Exceedance Probability
Historic
Peak
Average
Peak
Flood*
Flow
2008
Peak
2008
Date
90% 75% 50% 25% 10% Normal time
of Peak
Issuance
Date
Observed
Peak
Observed
Date
Bear
Utah-wyoming Stateline, Nr 2,680 1,610 4,275 1,850 5/21 890 990 1,170 1,420 1,690 5/22 - 6/14 4/1
Logan
Logan, Nr, State Dam, Abv 1,870 985 1,355 722 5/21 860 950 1,090 1,240 1,350 5/18 - 6/10 4/1
Blacksmith Fork
Hyrum, Nr, Up&l Dam 1,530 490 915 314 5/8 370 400 450 520 630 4/24 - 5/20 4/1
Weber
Oakley, Nr 4,170 1,625 2,790 1,880 6/19 1,100 1,250 1,450 1,650 1,850 5/24 - 6/16 4/1
Chalk Ck
Coalville 1,420 600 1,890 614 5/21 290 350 460 630 810 5/5 - 5/31 4/1
Provo
Woodland, Nr (regulated) 2,530 1,685 3,145 2,450 5/20 990 1,100 1,200 1,350 1,600 5/11 - 6/6 4/1
Little Cottonwood Ck
Salt Lake City, Nr 762 470 800 220 6/18 300 340 390 430 480 5/23 - 6/20 4/1
Big Cottonwood Ck
Salt Lake City, Nr 980 430 800 300 5/21 230 270 320 360 420 5/18 - 6/9 4/1
Mill Ck
Salt Lake City, Nr 153 65 180 40 5/21 40 45 55 65 75 5/18 - 6/10 4/1
Parleys Ck
Salt Lake City, Nr 605 180 350 50 7/01 120 130 160 200 250 4/23 - 5/22 4/1
Emigration Ck
Salt Lake City, Nr 164 55 130 20 5/08 25 30 35 45 50 4/11 - 5/19 4/1
City Ck
Salt Lake City, Nr 322 90 210 20 4/29 75 80 95 105 120 5/12 - 6/1 4/1
Sevier
Hatch 1,990 594 1,170 406 5/21 340 370 430 510 580 5/4 - 6/15 4/1

N/A = Not Available (Not a flood forecast point or no forecast procedure exists.)
* = Flood flow is for current year only and is an instantaneous value.
- = Exceedance value has already occurred during the current runoff season.


Lower Colorado Peak Flow Forecasts (mean daily cfs)

Prepared by: G. Smith
2009 Forecast Exceedance Probability
Historic
Peak
Average
Peak
Flood*
Flow
2008
Peak
2008
Date
90% 75% 50% 25% 10% Normal time
of Peak
Issuance
Date
Observed
Peak
Observed
Date
Virgin
Virgin 10,600 780 5,130 400 4/15 350 430 550 750 830 3/13 - 5/4 4/1
North Fork Virgin
Springdale, Nr 2,820 570 5,570 300 4/15 300 390 430 550 630 4/10 - 5/15 4/1
Santa Clara
Pine Valley, Nr 393 65 N/A 30 5/10 20 25 30 45 60 4/25 - 5/25 4/1

N/A = Not Available (Not a flood forecast point or no forecast procedure exists.)
* = Flood flow is for current year only and is an instantaneous value.
- = Exceedance value has already occurred during the current runoff season.


River Running Permits/Information



Definitions

Peak Flow
The peak flow forecast represents the maximum mean daily flow (the highest average flow for an entire day during the runoff season) at a point during the April through July period, unless otherwise noted. It does not represent the instantaneous peak (the maximum flow at a single moment). In the case of smooth snowmelt regimes (hydrographs), it may be acceptable to approximate one with the other. In Arizona, the normal snowmelt period is from February to May. Occasionally, heavy rainfall events can produce higher peak flows than the snowmelt peak flows. For verification and calibration purposes, the maximum mean daily flow during the February through May period was used regardless of the runoff source. The Average Peak and Normal Time of Peak (defined as the average date of peak plus/minus one standard deviation which should include approximately 70% of the peaks) for a given gage are all derived from 1971 through 2000 data whereas the Historic Peak is derived from the period of record, including the most recent years, after reservoir regulation began.

Forecast Probabilities
Peak flow forecasts are presented in terms of probabilities or, more specifically, exceedance probabilities. The forecast labeled "most probable" is actually the 50% exceedance level meaning there are equal chances of being below the value or above the value (i.e., 50 chances out of 100 of being exceeded). The other exceedance probabilities associate the likelihood of exceeding other levels. In general, a close bunching of the exceedance forecasts indicates low variability and that the user can have a high degree of confidence in the forecast information. Conversely, a large spread in the exceedance forecasts indicates high variability.

Modeling Techniques
The peak flow forecasts that follow have been derived using a combination of (1) physically-based conceptual models and (2) statistical regression models. The conceptual model is the National Weather Service River Forecasting System in the Ensemble Streamflow Prediction (ESP) mode. Since the conceptual model requires reservoir operation plans for up to five months into the future, ESP application is limited to basins where regulation is minimal (mostly in the headwater areas). The farther downstream a forecast point is, the more likely it is that a statistical regression was used between natural snowmelt runoff volume and the observed maximum mean daily flow to generate the forecast. Such an approach performs better when the correlation between regulated and unregulated flow is strong and is constant from year to year.


Additional Information

Flow extremes, Not Supply
Peak flow forecasts are fundamentally different than water supply volume forecasts. Although the watershed snowpack is a principal component in both analyses, peak flows are not a supply question at all. Rather, peak flows characterize runoff extremes by predicting maximum mean daily flow at a single point during the spring snowmelt season. This extreme is related to the water supply volume, but the relationship is not direct or constant from year to year. As such, peak flow forecasts contain much more uncertainty than water supply volume forecasts.

Regulated vs. Natural Flows
An even more fundamental limitation is that peak forecasts describe regulated (actual or observed) in-stream flow well into the future, something difficult to do considering the quantity and changing nature of diversions in the Colorado River and Great Basin watersheds. (Note: supply forecasts deal with hypothetical "natural" flow - that which would have resulted in the absence of regulation). The Colorado Basin River Forecast Center routinely forecasts regulated streamflow, but only for several days into the future. Further into the future the ability to forecast reservoir regulation becomes more limited.

Different Uses and Users
Peak flow forecasts are used for different purposes than water supply volume forecasts. Users of these forecasts would include river recreationists, flood control agencies, emergency service directors, wildlife managers and anyone interested in the combined effect of watershed yield and human regulation on the actual (observed) in-stream maximum mean daily flows at a site.

Flood Flows
The National Weather Service defines flood flow as the flow at which damage to structures begins to occur. Over-bank flow may occur but still be below the defined flood flow. Flood flows contained in this document change from year to year due to such channel processes as deposition and scouring. Therefore, the flood flows that follow should only be applied to the current runoff season. It should also be noted that they are instantaneous flows and not maximum mean daily flows.